16

All inputs such as transducer signals
and control set points from the XT are
converted to digital values and stored in
selected memory cells called holding reg-
isters. During operation, the PC
achieves process control by comparing the

actual values in the holding registers
with those of their corresponding set
points. Based on the difference between

the actual and set point values, the PC
program writes digital values to its out-
put registers, which in turn activate the
valves, valve drivers, or
counters onthe drill test rig. Also
contained in the holding registers are
values that control the rates at which
the output registers are changed; this
allows smoother operation of the drills

and drilling rig.

appropriate

Drill Rig Positioning Control
The control elements for carriage and
boom movement are shown in figure ll.
During initial startup, the PC moves the
carriage and boom to the zero position,
where the limit switches on the drilling
rig are closed mechanically. Closure of
the limit switches resets the PC's high-

XT. Based on the PC's comparison between
the information provided by the position

transducer (100 counts per inch input to
the high-speed counter) and the count
corresponding to the set point, the car-

riage smoothly accelerates to its maximo
speed, then decelerates as it approaches
the set point position. After this posi-
tion is reached, the PC nulls the Ledex
driver card (input to Ledex of 4 V), thus
closing the hydraulic control valve, and
locks out the high-speed counter to make
sure it does not change during the test.
The above sequence is then repeated for
the boom. After a test is completed and
a new hole location is selected, the car-
riage and boom move to the new position
without moving to the zero position.

Carriage Lock Control

The carriage lock-unlock system, shown
in figure 12, is somewhat simpler than
the positioning system in that the PC is-
sues only an on-off command to the hy-
draulic control valve. The two horizon-
tal locking cylinders in the carriage
guide rail and the vertical foot jack
(fig. 7) are connected in parallel to ex-

speed counters with actual values of zero tend and retract simltaneously. Prior
and reference values corresponding to the to a carriage move, the PC sets the ap-
set points previously entered into the propriate bits in the discrete output
Analog
Digital signal 0-24 v-
. Total signal out ou’
Position] 100 counts/in fl counts - 818 fl o-8Vv
trans- ; = =
ducer High-speed| | pc | 4!5* null | J4venun Forward! Carriage
counter Valve position
Analog driver Back motor
output card
Status of -
limit area -
switch Hydraulic
control
Limit switch Discrete vowve
~ input card
Oor 24 V
Input from boom valve driver, _ Down Boom lift
similar to that of carriage cylinder
valve driver _ Up

FIGURE 11.—Drill rig carriage and boom positioning system.


33

110 T T T T T — T
1O6/- 4
@io2r 4
gd 98
S 4
4
& 94Fr 4
oO
a 9OF 4
fa)
5
3 ect KEY ; J
= Pneumatic percussion drill
4 Hydraulic percussion drill
82F e Pneumatic rotary drill 7
78 1 1 r L 1 1 1
0 125 250 500 1000 2,000 4,000 8,000 16,000

FREQUENCY, Hz

FIGURE 24.—Average frequency spectra: pneumatic and hydraulic percussion drills, pneumatic rotary drill.

yn oo OO Ff
T T e

foo)
oo
T

KEY
© Beginning
e End

SOUND POWER LEVEL, dBA
©
rs
T

125 250 500 1000 2,000 4,000 8,000 16,000
FREQUENCY, Hz

FIGURE 25.—Frequency spectra for pneumatic rotary drill: beginning versus end.

fos)
fo}


10

FIGURE 5.—Drill test rig in reverberation chamber, top view.

FIGURE 6.—Drill test rig in reverberation chamber, profile view


20

Pressure Analo .
transducer Volts (1-5 Vv) input card Digital output 0-24Vv
= pressure o-8l8 o-av Hydraulic
: Control
Rotation Data input Digital data valve
pressure Pc
Valve i ( )
Frequency Control Analog driver
= flow and data output card Hydraulic
rotation
Volts (1-5 V) = flow 0-24V motor

Frequency-
Rotation to-analog
Flow converter card
transducer HYDRAULIC DRILL SYSTEM
OV off, 24 Von
Air supply
Pressure Analog A OV off,
transducer Volts (I-5 V) input card oun 24 Von
= pressure n ( decrease,
Rotation Data input Digital data On- off Pressure
pressure PC bit
command Pneumatic
Frequency Control OV off, rotation
How and data 24 V on motor
input (increase
Volts (1-5 V) = flow pressure) | easing
Rotation Frequency- } valve
flow to-analog 4 Lead
Flow converter car —— Pilot valve
transducer Supply air

PNEUMATIC DRILL SYSTEM

FIGURE 15.—Drill rod rotation control system.

Flushing Water Control
Flushing water is controlled by a sim-
ple on-off command from the PC. When the
test operator issues the final "Start
Test" command through the XT keyboard
(see "Data Input and Startup Procedure"),
the PC activates a discrete output that
opens the water valve completely. Water
continues to flow to the drill until the
feed limit switch is closed following
drill retraction. Flushing water pres
sure is measured and recorded, but not
controlled, by the PC and XT during the
test. A manually operated pressure-
reducing valve is used to adjust water
pressure.

Other Drill Test Commands

The drill test program software permits
several other operator command choices
from the main test menu, as shown in the
"Executive commands" box at the top of
figure 10:

Exit program (Fl).--This results in

the display of the
menu of figure 9.
Master reset (F2).--This
holding registers that had previously
contained set points or test data and
changes the status word to that shown in
figure 10. Resumption of testing after a
"Master reset" command results in the

higher level option

nulls the PC


TEST APPARATUS FOR MEASURING SOUND POWER LEVELS OF
DRILLS

By William W. Aljoe,' Robert R. Stein,' and Roy C. Bartholomae’

ABSTRACT

This Bureau of Mines report describes in detail the design and opera-
tion of a test apparatus for measuring the sound power levels of drills
used by the mining industry. The two major components of the test ap-
paratus are a computer-controlled automated drill test fixture (ADTF)
and a large (45,000-f£t3) reverberation chamber that houses the ADTF.
Design specifications and performance capabilities of the ADTF and the
reverberation room are given. Initial test results for three types of
drills--a pneumatic percussion drill, a hydraulic percussion drill, and
a pneumatic rotary drill--are given to illustrate the types of experi-
ments that can be conducted with the test appartus.

IMining engineer.
2supervisory electrical engineer.
Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA.


It can be noted in figure 22 that the
drills differ significantly in sound
power output between 160 and 1,250 Hz.
This area is dominated by the noise pro-
duced by the exhaust of the pneumatic
drill. The difference would be even
larger if the pneumatic drill were not
muffled. At 1,000 Hz and above, the two
drills produce approximately the same

power spectrum. This is to be expected
as the noise in this frequency range is
characteristic of the drill body and
drill steel.

The sound power output at 1,250 to
8,000 Hz is largely a product of the ex-

posed drill steel. In particular, the
spectra from 1,250 to 4,000 Hz are almost
identical. This is not surprising be-
cause the two drills operate at about the
same frequency and the length of the
steel in both tests was the same. This
noise is not produced solely by the drill
itself, and in operating situations it is
inseparable from the drill body noise.

In the future, when tests for actual
drill sound power output are performed,
the drill steel noise will be eliminated
by removing the steel from the test.
This will be accomplished by using a
"dead block." The dead block is simply a
device that can absorb and dissipate the
energy produced by the drill, usually in
the form of heat. The drill will be
coupled to the dead block by a very short
section of steel that will be acoustical-
ly isolated from the test environment.
For the present, however, the dead block
is not being used so the effect of the
drill steel can be observed as it occurs
in the actual operation of the drill.

Research by Hawkes (12) shows that
noise produced by the drill steel is
caused primarily by bending waves in the

steel. These bending waves occur at many
frequencies above a critical frequency
and are calculated by the formla

fg =n? DC, [1-1-2(nD/L)?],
8 LZ

31

where fg = bending wave frequency, Hz,

n = mode number (1 for first
critical frequency),

D = drill steel diameter, in,
L = drill steel length, in,
and C, = speed of sound in drill

steel, 2 x 10° in/s.
These frequencies are
spaced sufficiently close together to
produce noise in all 1/3-octave bands
above the initial frequency.

Note in the above equation that the
bending wave frequencies are directly re-
lated to the length of the drill steel;
the longer the steel, the lower the first
critical frequency. The drill steel
used in the tests of the percussion
drills was 10 ft in length, resulting in
a first critical frequency of approxi-
mately 5 Hz, well below the 1/3-octave
band centered at 31.5 Hz. The contribu-
tion to the overall noise level occurs in
all bands measured but is considerably
larger at frequencies above 2,000 Hz
(fig. 23). This is of particular import-
ance up to 4,000 Hz because of the poten-
tial effects on hearing loss. The noise
levels drop over the course of a test due
to the entrance of the drill steel into
the hole. The section of steel that has
penetrated is shielded from the test en-
vironment, and the overall contributution
of the steel is thus reduced.

This type of information is particular-
ly useful when designing noise controls
for drills or when attempting to develop
noise-controlled operating procedures.
The time effects would be difficult to
observe with traditional data collection
methods but are easily noted by the reg-
ularly spaced intervals of data provided
by the test fixture's data collection
system

bending wave


card to activate the "unlock" side of the
hydraulic valve and deactivate the "lock"
side. The reverse takes place after the
carriage and boom have reached their set
points, thereby locking the rig in place
for the test. A timer loop in the PC
program delays execution of further steps

O V off, 24 V unlock

17

until the locking or unlocking process is
completed.

Feed Thrust and Hole Depth Control

The feed thrust and hole depth are con-
trolled by the pressure and flow, respec
tively, of hydraulic oil in the feed cyl-
inder. The upper portion of figure 13
diagrams the feed thrust control, and the

Hydraulic lower part describes the depth control.
Bit set control Since the area of the feed cylinder
tJ | valve piston is fixed, the feed thrust is pro-
PC | 7 portional to the hydraulic pressure on
— the larger (head) side of the piston.
Discrete’ The pressure transducer in figure 13
output sends a voltage signal to an analog input
card card, which intturn assigns a digital
O V off, 24 V lock value toa holding register in the PC.
During drilling, the PC program compares
this value to the set point and, depend-
ing on whether the pressure needs_ to be
. increased or decreased, assigns an appro-
Locking i «oa 1
cylinders priate digital value to an analog output
card. The voltage at the output card is
[pb sent to the Ledex driver, which increases
1 | or decreases the current to the "Forward"
side of the hydraulic control valve.
Foot jack This side of the valve then opens or
cylinder closes to increase or decrease the pres-
sure on the head side of the piston. The
digital output of the PC is constrained
within a relatively narrow range during
FIGURE 12.—Drill carriage lock system. the drilling mode to prevent the feed
Pressure Analog
transducer input card Digital output o-24y_ Forward
Volts (I-5 V) = pressure n Digital data 413=null 24v. Hydraulic
. O-8V f valve
Feed Data input 300 v=
pressure Total flow | PC retract 4V= null
counts
Valve
Analog driver
Flow- output card
int = flow (38/in) rf
Feed Pulses = flow in Discreve \
low output card 5 V= retract
High-speed Reset te ignal
Counter eset counter signa
Limit inter 9 Feed cylinder [{o)
switch
Off (open), on (closed) Bit set Forward =
(Feed retracted) — Retract
Discrete
input card

FIGURE 13.—Feed thrust and hole depth control system.


Direct Data Analysis and Graphics

Test Selection

Recall that all test data are stored on
floppy disks in files namea "TEST 7

DAT," with the blanks corresponding to
the four-digit test number assigned by
the XT. When data analysis is desired,
the test operator first makes sure the

correct test numbers are available on the
floppy disk by selecting option F4, "Di-
rectory of tests on A:" from the overall
software menu shown in figure 9. The

operator then chooses the data analysis
program (F2), which results in the dis-
play of the menu in figure 17. The test

or tests to be analyzed are selected by
entering the four-digit test number(s)
in fields 1 and 2 of figure 17 and press-—
ing the F9 "Retrieve tests(s)" key. Note
in figure 17 that tests 0178 and 0293
have been selected. Test 0178 is that of
a small, mffled pneumatic percussion
drill; test 0293 is that of a small, all-
rotary pneumatic drill. These two tests

will be used below to illustrate the
basic graphics capability of the data
analysis program. Further comparisons

between the two drills are contained in
the section of this report entitled "Ini-
tial Test Results."

23

Raw Data Retrieval

The "List test" and "Print test" op-
tions in figure 17 (function keys F7 and
F8) are used to retrieve all the data re-
corded during a given test. "List test"
displays the data only on the XT video
monitor; "Print test" also provides a
hard copy of this information. Figure 18
shows the data recorded for the first 45
s of test 0293. Descriptive information
is given at the beginning of the test
file, and the entry of new test parameter
values is documented at 15.7 and 26.3 s.
The top row of figure 18 shows all the
drilling parameters recorded during the
test andthe units in which they are
given. Sound power information is given
at 18.1 and 36.2 s; the first 21 values
in the string correspond to the twenty-
one 1/3-octave bands comprising the 100-
to 10,000-Hz frequency range, and the
final value is the overall (unweighted)
sound power level. Note that in this
particular test, the values for hammer
pressure and drill blow frequency appear
as dummy values of 1.0 and 0.0, respec~
tively, because of the all-rotary operat-
ing mode of the tested drill.

The ability to scan the entire set of
test data in this manner helps the test
operator in several ways: (1) Graphs

Analysis menu

Fl Plot hammer pressure
F3 Plot feed rate

F5 Plot spectrum

F7 List test

FQ QRetrieve test: 0178
@Retrieve test: 0293

F2 Plot feed thrust

F4 Plot sound power

F6 ‘Plot spectrum waterfall
F8 Print test

FIO. Exit

@X minimum @X maximum
@®Y minimum @Y maximum

FIGURE 17.—Data input menu for analysis program.


19

Pressure
transducer Volts (I-5 VV) j Analog Digital output -
= pressure input card 409-818 o-eay
iat - "
Hammer Control u~d data Digital 4°8V Hydraulic
pressure input values data PC drill
Fr Analog Valve
reavency Data driver Hydraulic
= flow input output card control
valve
Volts (1-5 V) = flow

Hammer Frequency-
flow to-analog
Flow converter card
transducer
HYDRAULIC DRILL SYSTEM
O Voff, 24 Von

Pressure Analog Discrete OVoff, Air supply

Wansducer Volts (1-5 V) input card output card | 24 Von valve
m = pressure in! n _J (decrease, Pneumati

lammer Control and data | [Digital data On- off bit pressure umatic
pressure input values PC | command drill
OV off, =
flow” Dota Zavor
input decrease

Pi -
Volts (1-5 V)= flow pressure] | regulating

Hammer Frequency- i valve

flow to-analog 4 Piles, '
Flow converter car oe lot valve
transducer Supply air

PNEUMATIC DRILL SYSTEM

FIGURE 14.—Drill hammer control system.

and retracting modes). Flow changes re~
sulting from motor load changes are mich
smaller in magnitude than the associated
pressure fluctuations, thus making a
f£low-based control system more
desirable.

Input signals
form of voltage pulses
flowmeters, converted to analog signals
by the frequency-to-analog cards, and
sent to the PC via analog input cards.
Output signals are generated by the PC
based on the difference between the ac—
tual flows and the set points. For hy-
draulic rotation, the "Forward" side of
the rotation valve is opened or closed
proportionally via the Ledex driver to
increase or decrease rotation flow. For
pneumatic rotation, the pilot valve pres-

are generated in the

from turbine

sure regulating system described for
Pneumatic hammers is employed; in this
case flow control is achieved through

pressure changes.

Another difference between the hammer
and rotation control systems is that re-
verse rotation is possible, although for-
ward and reverse rotation cannot be
achieved during the same drill test. Re-
verse rotation can be obtained simply by
reversing the hose connections to the
rotation motor.

Rotation flow is also monitored by the
XT to serve as a safety shutdown during
the drilling and retracting phases of a
test. A rotation flow of zero indicates
a stuck bit, which could cause damage to
the bit, drill rod, and perhaps the drill
itself. If the flow goes to zero during
the drilling phase, the test is aborted
and the retraction phase initiated. If
the flow remains zero (unsuccessful re-
traction), the PC goes into a null state
to allow the stuck bit to freed by
hand.

be


32

108
104

Pneumatic percussion drill

100
96
92

KEY
© Beginning
End

88

84

8005 250 500 1,000 2,000 4,000 8,000 16,000

108 — r
Hydraulic percussion drill

104

SOUND POWER LEVEL, dBA

100
96

92

1,000 2,000 4,000 8,000 16,000
FREQUENCY, Hz

250 500

FIGURE 23.—Frequency spectra for percussion drills, begin-
ning versus end of hole.

ROTARY VERSUS PERCUSSION DRILLS

A pneumatic rotary drill, the ALMINCO
Gopher, was also tested on the drill test
fixture. The intended uses of the Gopher
are roughly the same as for the two per-
cussion drills; however, rotary drills
operate at higher thrust levels than per-
cussion drills. This fact, combined with
the different control demands of a rotary
drill, allowed the test fixture to be
operated over a greater range of thrust
values than when testing percussion
drills alone. The Gopher drilled at a
rate of 1.57 ft/min under an average
thrust of 521 l1bf during the test se-
lected for comparison. The data re-
trieved from the tests of the rotary
drill provide some interesting contrasts
to both of the percussion drills.

The sound power spectrum of the rotary
drill is similar to that of the pneumatic
percussion drill from the standpoint of
the pneumatic exhaust, but it differs
from those of the percussion drills in

the relatively minor contribution of
drill steel noise. These observations
are evident in figure 24. The portion of
the spectrum from 200 Hz to 1 kHz is
greater in level for the two pneumatical-
ly powered drills than for the hydrau-
lically powered drill. The greater con-
tribution by the drill steel of the per-
cussion drills can be seen at 2 kHz and
above. The absence of drill steel noise
is also shown in the sound power levels
taken at intervals during the test.
The overall levels for the rotary drill
differ by less than 1 dB from beginning
to end, and the average spectra are ap-
proximately the same (fig. 25), indicat-
ing that noise radiated from the rotary
steel is not a major contributor to the
overall noise level.

Another good example of the types of
phenomena that can be observed is illus-
trated by the shape of the average test
spectra (fig. 24). A potential problem
with the rotary drill is revealed near
the center of the graph. It can be noted

from the graph that the portion of the
spectrum from which a majority of the
noise is produced is in a _ relatively

small range that differs from the predom-
inant noise of the percussion drills.
The span of frequencies in the 1/3-octave
bands centered from 800 to 1,600 Hz con-
tains over half of the total sound
energy. These frequencies overlap the
range of human speech. Hearing loss at
these frequencies greatly impacts func—
tional hearing ability. Based on the ob-
servation of overall levels alone, or
even individual narrow band spectra pro-
duced from recordings of field test, one
may conclude that the rotary drill is
less of a noise problem than the percus—
sion drills; however, by examining the
operation of the drill more closely, it
can be seen that a more thorough investi-
gation of the sources is necessary.

The positive side to this particular
observation is that the peak noise pro-
duced by the rotary drill has more poten-
tial solutions than the noise produced by
the percussion drills. The frequency
range of the noise, along with informa-
tion about the operating principles of
the drill, suggests that the noise arises
from the gear motor that drives the


14

issues a "Ready" message, and
operator to press F9 again.
The drilling rig then moves out to the
specified hole location, locks itself in-
to place with two clamping cylinders, and
pauses. The hole location is then
checked visually and, if satisfactory,
the operator presses F9 a third time to
start the drilling process. At any time
during the startup procedure or drilling
process, the operator can press the [Esc]
key, standard on all IBM and IBM-
compatible personal computer keyboards,
to halt the test and enter new input data
into the main menu. A closed-circuit
television system enables the operator to
monitor the entire sequence from the
safety of the control room and allows him
or her to terminate the test quickly
should problems occur.

the PC,
prompts the

Data Collection and Display

As soon as the drill test
checks the data input values and finds
them to be valid, it opens a file on the
XT floppy disk and writes the input data
to the file. These drill test files are
named "TEST +DAT", with the blank cor-
responding to the sequential test number

program

assigned by the drill test program. This
four-digit test number is then displayed
on the XT video monitor ("Run" in figure

10) and is used for all subsequent data
retrieval and analysis.
After drilling has begun,
the test is maintained by the process
controller (PC). As soon as the feed
thrust reaches its set point, the XT col-
lects data by reading the PC and the
sound measuring instrumentation at speci-
fied intervals and writing this informa-
tion to the floppy disk file. The opti-
mum sampling interval for data collected
from the PC was found to be 4s. Shorter
intervals are possible but would result
in rapid exhaustion of floppy disk space;
longer intervals could result in the loss
of important test data. The sampling in-
terval for sound power data was chosen to
be 18s. This interval allows the mlti-
plexer to scan 16 microphones for 1s
each and gives the sound power calculator
ample time to perform its computations
and store the data. These intervals,

control of

along with the maximum control parameter
values listed in table 1, can be changed
easily by the test operator. The F5
"Edit conrols file" key in figure 9 pro-
vides the operator with a menu that
enables these changes to be made from the
XT keyboard. Selected information is
also displayed on the XT video monitor,
as shown in figure 10. The data dis-
played immediately to the right of fields
10 through 13 allow the operator to com-
pare the actual values of the control
parameters with those of the set points.
The lower right section of figure 10 con-
tains the following information:

Status word.--This l6-digit binary
number contains information pertinent to
the movement and locking of the drill
test rig. It changes during the drill
movement sequence, with each digit either

identifying the status of a particular
hardware component critical to this pro-
cess (e.g-, limit switches open or

closed, input parameters valid or not) or
issuing a command to proceed to the next
step in the movement cycle (e.g., move
carriage and boom to set point, lock car-
riage). The status word is a valuable
troubleshooting aid if the drill rig
either fails to move on command or moves
incorrectly.

Test stage.--A string of text charac~
ters written to the display on the basis
of the status word. The four test stages
are collaring (drill rig moving to set
point and drill operating before feed
thrust reaches set point), testing (data
being collected), retracting, and moving
home.

Elapsed time.--The PC
when the feed thrust reaches the set
point and ends when the prescribed drill
depth is reached. This provides the time

timer starts

base essential for all posttest
analysis.

Drill frequency. ~-For percussion
drills, the number of blows per minute
(BPM) can be used to determine if the

drill is operating correctly and can also
affect the noise frequency spectrum.
Drill frequency information is supplied
to the PC via an accelerometer mounted on
the drilling rig and appropriate signal
conditioning equipment.


where SPL = sound pressure level at any For the drill noise research program
given point in an envisioned by the Bureau of Mines, sound
environment, dB, power is the quantity of greatest inter-
est because (1) it allows direct noise
PWL = sound power level of noise comparisons to be made among different
source, dB, types and models of drills, and (2) it
can be used to predict the sound pressure
Q = directivity factor (dimen- levels that will occur in other envi-
sionless) of the source, ronments, given their acoustical
whose value is dependent characteristics.
on the angle from the The directional property of a sound
acoustical center of the source describes its tendency to radiate
source to the measurement more noise in one direction than in
point, others. Directional properties are usu-
ally displayed in a graphical form called
r = distance from the source, a radiation pattern (fig. 3), showing
ft, sound pressure level at a fixed distance
from the source as a function of angle.
a = average absorption coeffi- It should be noted that figure 3 is for
cient (dimensionless) of illustrative purposes only; the sound
the acoustical environment, pressure levels in the figure do not cor—
including its boundaries respond to measured values for an actual
and objects located within drill.
it, From a purely diagnostic standpoint,
the most complete characterization of any
and S = total surface area, ft?, of noise source can be obtained by isolating
all reflecting surfaces it in an anechoic (free field) environ-
within the environment. ment, ise-, one in which no reflections
ANGLE FROM NOISE SOURCE
50° 60° 70° 80° 90° 100° 110° 120° 130°
W 3
we ae
2 40° 140° 8
3 a
vey
g 30° 3
°
3 is0° 2
3 5
© 20° 160° &
L w
W
a 10° | 70° 2
oO oO
2 2
* oe _ ig0°
100 90 80 Noise source 80 90 100

SOUND PRESSURE LEVEL, dB

FIGURE 3.—Typical noise radiation pattern.


Also, if one or more drilling parameters
are changed during the test, the effect
of these changes on all other parameters
can be displayed graphically.

Multitest Comparisons

The Lotus 1-2-3 graphics package can
display the results of up to six tests on

the same graph, versus only two for the
basic system graphics package. Para-
metric studies (where only one variable

is changed from test to test,
its effect on other variables) are there-
fore mich easier to perform. This cap-
ability also facilitates comparisons
among several different types and models
of drills.

Frequency Analysis

As mentioned above, the limited fre-
quency analysis capability of. the basic
system graphics package is one of its
greatest deficiencies. Spreadsheet anal-
ysis overcomes these deficiencies in the
Following ways:

1. The average frequency spectrum from
any portion of the test can _ be obtained
by judicious selection of the start and
stop times in the Lotus Formatter program
(fields 17 and 18 in figure 21). In this
manner a two-dimensional "spectrum water—

fall" can be created to observe how the
Spectra change during the course of a
test.

to observe |

29

2. A-weighting of the 1/3-octave band
noise levels can be performed quickly and
easily. An overall A-weighted level for
each spectrum can then be calculated and
displayed on the same graph as_ the 1/3-
octave band data.

3. Frequency rather than
can be displayed as the
graphs.

band number
X-axis of all

Analysis of Other Noise Tests

Since the Lotus Formatter can operate
on any data file created by the sound
measuring instrumentation, it can be used
to analyze noise information from any
test conducted in the reverberation cham—
ber. A separate noise test program al-
lows this instrumentation to be activated
through the XT, and causes it to write
the noise data to disk with a file name
of "NOIS .»DAT". The Lotus Formatter
program can then be used to convert the
data to a "xxx-PRN" file. The same 10-
step procedure described above is used
instead of the F9 “Extract drill test
data" command. As noted in figure 21,
drilling parameters cannot be converted
using the Fl10 command. One of the most
common uses of the noise test program is
to read the room correction factors from
the Bruel & Kjaer 7507 sound power cal-
culator. Knowledge of these room correc—
tion factors allows the sound pressure
levels to be calculated from the sound
power levels using the Lotus software.

INITIAL TEST RESULTS

To further demonstrate the abilities of
the automated drill test fixture, some
observations of the initial test data are
included. Three types of drills were
tested to help assure that the test fix-
ture was capable of performing as speci-

fied. A pneumatic percussion drill, a
hydraulic percussion drill, and a pneu-
matic rotary drill were all run in the
concrete test medium to compare perfor—
mance against the manufacturers' pub-
-ished data and to measure their sound
power levels in an operating situation.

All three drills are of the small

"hand-held" class for which noise control
technology has been difficult to
implement.

The general test scheme involves find-
ing the set of operating parameters that
results in the optimum penetration rate
for the drill being tested and measuring
the sound power level under these condi-
tions. However, drills designed to oper-
ate in soft rock perform better in the
concrete test medium than those designed
to drill hard rock. Therefore, it is
possible that the penetration rates pre-
sented here could be different if the


26

10

Test O178

105

100

95

85

80
110 — |

105

ZEEE_ .
100}
0 E-F—__

75
50 ERE

80) 6 " 16 al 26
FREQUENCY, !/3- octave band number

SOUND POWER LEVEL, dB

TIME, s

FIGURE 20.—Sound power spectrum and spectrum waterfall
graphs.

therefore, the "Xmax" (field 4) value in
the time-based graphs was set at 200 s so
that values of 50, 100, and 150s would
occur at the three computer-generated
subdivisions. Maximum and minimm values
for all the other parameters were chosen
in the same manner.

Hammer pressure (fig. 19).--Hammer
pressure for test 0178 (pneumatic percus-

sion drill) was set at 90 psi; the ADTF
achieved this pressure shortly after
startup and maintained it very con-
sistently throughout the test. Hammer

pressure for test 0273 was set at a nom-—

inal value of 1 psi (rotary drill).

Feed thrust (fig. 19).--Feed thrust in
test 0178 was set at 240 1bf and remained
there throughout the test. Feed thrust
in test 0293 was initially set at
200 1bf£; after the hole was collared,
thrust was increased to 500 1bf. Except
for the brief spike that occurred as the
ADTF adjusted to the higher set point,
feed thrusts remained fairly close to the
set point values.

Feed rate (fig. 19).--The abnormally
high feed rate at the start of each test

corresponds to the forward movement of
the drill before the bit contacts the
concrete. After collaring, both drills

achieved a fairly steady feed rate of 0.3
to 0.5 in/s, although the percussion
drill was somewhat faster. In test 0293,
an abnormally low feed rate occurred dur-
ing collaring because of the low feed
thrust; this rose markedly when the feed
thrust was increased.

Sound power (fig. 19).--Sound power of

the rotary drill (test 0293) was very
consistent at 105 to 107 dB through the
test. Sound power of the percussion

drill (test 0178) was around 115 dB at
the start of the test, but decreased as
the drill rod entered the hole. This ef-
fect did not occur in test 0293 because
the drill rod is not a major contributor
to rotary drill noise.

Spectrum (fig. 20).--The
band sound power levels in these two
tests were very similar at low frequen-
cies. The major difference between the
two spectra occurred at higher frequen-
cies, where the drill rod noise of the
percussion drill was more prominent.

Note in figure 20 that frequency data
are reported in "band number" rather than

1/3-octave

Hertz because this is the way the sound
power calculator reports frequency data
to the XT. In this case, band 1 corre-
sponds to 100 Hz and band 21 corresponds
to 10,000 Hz. However, since Hertz is
the universally accepted unit of fre-
quency measurement, the use of band num-

ber in graphs represents a major defi-
ciency of the basic system graphics. Two
other limitations of the basic system
graphics for sound power spectra are that
(1) only the final sample recorded during
the test is graphed when the F5_ key in
figure 17 is pressed and (2) the overall
sound power level cannot be plotted on
the same graph as the 1/3-octave band
data. As discussed in the next section,
all three of these problems can be re-
solved by using electronic spreadsheets
to look at frequency data.

Spectrum waterfall (fig. 20).--This
shows how the noise frequency spectrum
varies during a test. It can provide
useful qualitative information with re-
gard to frequency shifts during the
course of the test, but it is of little
value for quantitative comparisons. Ow-
ing to the complexity of the spectrum



/y=— Rock surface vibration

Av noise

Front centralizer vibration
Mid centralizer vibration

Piston-striking bar impact

Leakage air noise

Air motor noise
he Body noise

ff

[——- Exhaust noise

Feed vibration

Bit-rock impact

YA wa

Drill rod vibration

Feed screw rattle

Feed motor
noise

FIGURE 2.—Noise sources on typical jumbo-mounted percussion drill.

Furthermore, in most cases the quieted
noise levels were still above 100 dBA;
operator exposure would have to be lim-

ited to only 2 h/d to maintain compliance
with Federal noise regulations.

To date, the most effective means of
protecting the percussion drill operator
from noise overexposure has been to iso-
late him or her from the noise source by
using an acoustical cab. Noise reduc—
tions of up to 20 dBA have been achieved
through this technique, and in several
cases the noise level measured inside the
cab was below 90 dBA (6). Acoustical
cabs can be applied most successfully to
machine-mounted drills that are used in
areas of unrestricted headroom or where
remote control of drill positioning and
operation is employed. However, many
nining situations require the use of
3mall hand-held drills because of space
limitations; this precludes the use of
acoustical cabs. In fact, the hand-held
percussion drill remains the bulwark of

operations
flexibility,

ore

mining
compactness,

many underground
because of its

reliability, and low cost. Space limita-
tions and interference with drill opera-
tion (e.g., operator vision) also dis-
courage the use of acoustical cabs on

many types of jumbo-mounted drills.

Considering the high-energy nature of
percussion drilling, the limited success
of previous efforts to control drill
noise at its source, and the limited
practical application of acoustical cabs,
it is doubtful that the majority of per-
cussion drill operators will work ina
nonhazardous noise environment in the
near future. If the mining industry con-
tinues to use percussion drills, even
quieted models, as it has in the past, it
is reasonable to assume that numerous
noise overexposures will occur in the
years to come.

Despite the severity of the percussion
drill noise problem and the fact that all
percussion drills are inherently noisy,


INTRODUCTION

Percussion drills used in the mining
industry produce noise that can cause
exposures of 10 to 20 times the limits
allowed by Federal noise regulations.

Typical noise levels experienced by per-
cussion drill operators are 110 to 120
dBA. Approximately 60,000 percussion

drills are being used in the mining in-
dustry (1),3 and many more are used in
the construction industry. Given the
severity of the percussion drill noise
problem, it is not surprising that con-
siderable efforts have been made toward
its control.

The primary noise-generating mechanism

in all percussion drills is the repeated
hammering action of an oscillating steel
piston on the end of a_ long, slender
striking bar (drill rod). This action
causes vibration of both the drill rod
and the cylindrical piston housing,
thereby producing drill rod noise and
drill body noise. On pneumatic drills,
the high-pressure air used to oscillate
the piston is exhausted to the atmosphere
through ports inthe drill body, thus
producing air exhaust noise. Figure 1
depicts these three major noise sources
on a typical hand-held pneumatic (stoper)

drill. Figure 2 shows the various noise
sources associated with a _ typical
machine-mounted (jumbo) drill; however,

the drill body, drill rod, and air ex-
haust are still by far the most serious
noise sources on the drill.

Numerous attempts have been made in the
past by the Bureau of Mines and other re-
searchers to control percussion drill
noise through the use of retrofit noise
control treatments (2-6) and new drill
design features (7-10). These attempts
have been moderately successful, result-
ing in noise reductions of up to 15 dBA
at the drill operator position. Unfortu-
nately, some of the noise-controlled
drills were rather impractical from an
operation standpoint (e.g-, reduced
drilling rates, mffler freezing, exces-
sive weight and bulk).

3underlined numbers in parentheses re-
fer to items in the list of references at
the end of this report.

— Drill steet

Drill body———

Air exhaust

Scaie, in

FIGURE 1.—Noise sources on typical hand-held percussion
drill.


Overall sound power.--The XT reads
this value directly from the Bruel &
18 s,

Kjaer sound power calculator every
then resets the 7507 and the ml1tiplexers
for another sample. The PC is not in-
volved in this process. The sound power
levels displayed in figure 10 are linear
(unweighted) values. Although A-weighted
overall sound power levels would be more
desirable from a _ perceptual standpoint,
they cannot be obtained directly owing to
the recording and calculating techniques
used by the 7507.6 A-weighted levels can
be obtained, however, through posttest
analysis of the linear data.

Although the XT serves primarily as a
data collector during a normal test, the
operator can also enter commands in mid-
test through the XT keyboard. Most im-
portantly, the operator can terminate a
test at any time. It is also possible to
change one or more of the control para-
meters in fields 10 through 13. by typing
new values in the appropriate field(s)
and pressing the F9 key. The program
-esponds with a message "New Parameters

ent" on the monitor, and the XT records
che values and the time they were sent.
This capability is especially advanta-
geous because it minimizes the number of
holes needed to establish the optimum set
of operating parameters (i.e., the set
that yields the maximum penetration rate)
for a particular drill.

A typical drill test requires approxi-
mately 1,000 bytes of floppy disk space
per foot of hole. Therefore, data from
at least 30 tests (all 12-ft holes) can
be contained on a single 360-kb floppy
disk. Larger numbers of tests with shal-
lower hole depths can also be retained on
a single disk. Data collection and anal-
ysis is discussed later in this report.

©The A-weighting process simulates the
response of the human ear to sounds of
various frequencies. The 7507 can record
the desired 1/3-octave band sound power
levels only in the linear mode, so the
subsequent calculation of the overall
ound power level yields a linear value.

Control Subsystems

As described above, the ADTF consists
of four major elements--the IBM-XT micro-
computer, Westinghouse PC-700 process
controller, Ledex valve drivers, and the
various transducers and control valves on
the drilling rig. This section describes
how these elements function as a unit to
provide the required control of the
drilling process.

IBM-XT Microcomputer

The IBM-XT is a standard model witha
360-kb floppy disk drive, a 10-Mb hard
disk drive, a 256-kb random access memory
(RAM), and a serial port for communica-—
tions with the PC-700. All the drill
test software is permanently installed on
the hard disk. Other add-on cards are
installed for (1) a color monitor and
graphics printer, (2) programming the PC-

700, (3) interfacing with the Bruel &
Kjaer sound measuring instrumentation,
and (4) a real-time clock and calendar
function.

Westinghouse PC-700 Process Controller

a 4,136-kb memory and
can address 32 analog inputs, 32 analog
outputs, 256 discrete inputs, and 256
discrete outputs. The ADTF system uses
14 analog inputs, 12 analog outputs, 4
discrete inputs, and 16 discrete outputs.
The drill operating information is passed
to and from the PC via analog input
cards, two analog output cards, one dis-
crete input card, one discrete output
card, and four high-speed counter cards.
Four frequency-to-analog converter cards
are also located in the PC-700 cabinet;
although these are not addressed directly
by the PC, they are essential for PC con-
trol of flow-based processes. Power is
supplied by three sources--a 5-V supply
for the high-speed counters, a 15.8-V
supply for the input and output cards,
and a 5-V supply for the frequency~
to-analog converters.

The PC-700 has


be changed by the user during the

of a test if desired. The ADTF
allows the user to select an exact
hole location (following a preprogrammed
pattern), hole depth, and drill power
source (air or hydraulic) for each test.
The ADTF achieves this control through
the use of standard, comme rcially-
available hardware such as _ pressure,
flow, and position transducers, a pro-
grammable process controller, and a desk-
top microcomputer. Software designed
specifically for the purpose of drill
test provides the user with continuous
on-line information and interactive capa-
bility via the computer's cathode ray
tube and keyboard. Safety is ensured by
the presence of several types of auto-
matic and user-initiated shutdown modes.
By conducting drill noise tests in the
laboratory, it is also possible to exer-
cise almost complete control of the
drilling medium, bit type and sharpness,
drill rod length and type, and hole
‘ushing medium. These parameters can
most never be changed or controlled in
the field due to local geology, blasthole
size requirements, and other production
considerations. The capability of pro-
viding a relatively homogeneous drilling
medium (precast concrete or precut gran-
ite) is particularly advantageous when
assessing the effect of other drilling
Parameters on drill penetration rate.

also
course

also

CONTROL OF THE ACOUSTICAL ENVIRONMENT

The acoustical environment of an oper-
ating mine is rarely consistent because
the extent of the mine and the location
of the noise sources change almost daily
as mining progresses.

Irregular reflecting surfaces are often
present, and extraneous noise sources
(other pieces of mining equipment) add to
the difficulty of measuring the noise
produced by a drill. Microphone location

is another important factor to consider

when measuring drill noise in the field
because the sound pressure can vary
greatly from point to point within the
area of interest. Measurement of drill
noise in the laboratory allows for con-
trol of some of these variables, but the
experimental environment mst _ be chosen

carefully to assure that useful noise in-
formation is obtained in a_ practical and
cost-effective manner.

The two fundamental properties that de-
fine the noise-radiating capability of a
sound source are its sound power and di-
rectional characteristics. Sound power
is a measure of the rate at which acous-
tical energy is emitted by a noise
source; it is usually expressed as sound
power level, in decibels (dB), by the
formla

PWL = 10 log WactMret)s

where PWL = sound power level, dB,

Wact = actual sound power, w,

and Wre- = reference sound power,
10-12 wy.

distinction between
sound power level and sound pressure
level, the quantity most commonly asso-
ciated with noise, is that sound power

The most important

is a fundamental property of the noise
source itself. Conversely, the sound
pressure level is dependent on the

source, the
and the acous—
environment in

distance from the noise
direction from the source,
tical properties of the
which it is measured. The relationship
between sound pressure and sound power
levels can be quantified (11):

SPL = PWL + 10 log [(Q/4ar?)+(4/aS) ]
+ 10,


same sequence as the initial startup in
that the drill carriage and boom move to
the home position before moving out to
the selected hole location.

Move platform home (F3).--Moving the
drilling rig to its home position places
it close to the zero position, thereby
shortening the initial startup process
for the next test session. The home pos-
ition is also the most convenient one for
drill rig maintenance; therefore, this
command is usually issued at the end of a
drill test session or when a substantial
amount of mechanical work (e.g., changing
drills) needs to be performed on the
drilling rig.

Test without move (F4).--This command
starts the drilling process without mov~
ing the carriage or boom. It is used

most often when a_ successful move has
been completed but the maximum hole depth
has not been reached. For example, the
operator may notice a problem (e-g.,
stuck drill bit, leaking hose, etc.) and
terminate the test before the hole is
completed. The "Test without move" com
mand enables the test to be restarted

21

problem has been corrected without going
through the time-consuming move process.

HOLE LOCATION PROGRAM

The hole location program is a_ very
convenient means for managing the loca-
tions and depths of all holes drilled by

the ADTF. It can be accessed directly by
the test operator to change the actual
position of any row or column assignment
in the hole location grid, or to change
the depth (from the program's standpoint)
of any hole on the existing grid. It is
also addressed during the startup phase
of the drill test program to prevent the
use of a hole location that has already
been drilled to the maximum depth of
12 ft. These three functions of the hole
location program are described below.

Selection of Hole Position

The test operator gains direct access
to the hole location program by choosing
option F3 in the menu of figure 9, which
results in the display of figure 16, the

(with a new test number) after the hole location grid. The vertical hole
{Hole location program}—
FI Display location F2 Update location
@-@Location Feed |— @ Car @ Boom F6 Print locations
Feed 2— © Car © Boom @ Depth FIO Exit program
123456789 ll 2 13 1415 1617 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36
a4000000000000000000 000000000000000400
B000000000000000000 900000000000000000
co00000000000000000 000000000000000000
0000000000000000000 000000000000000000
—E000000000000000000 000000000000006600
F000000000000000000 o00000000000000000
G000013320000000000 000000000000000000
H000000000000000000 000000000000000000
!000000000000000000 000200000000000000
yv000200200000000000 006260505000000000
kK0000!15044000000000 o00000000000000000
Lo000000000000000000 000000000000000000
Mo00000000000000000 000000000000000000
Noo0o0000000000000000 000000000000000000
0000000000000000000 000000000000000000
P000000000000000000 000000000000000000
aq000000000000000000 000000000000000000
R000000000000000000 000000000000000000
Block | Block 2

FIGURE 16.—Data input menu for hole location program.


Information Circular 9166

Test Apparatus for Measuring
Sound Power Levels of Drills

By William W. Aljoe, Robert R. Stein,
and Roy C. Bartholomae

UNITED STATES DEPARTMENT OF THE INTERIOR
Donald Paul Hodel, Secretary

BUREAU OF MINES
David S. Brown, Acting Director


SYSTEM DESCRIPTION

The drill noise test apparatus consists
of eight distinct components, shown sche-
matically in figure 4:

1. A microcomputer (IBM model PC-XT,4
referred to as the XT) with hard-disk
storage of menu-driven programs for drill
operation and data analysis.

2. A programmable process controller
(Westinghouse PC-700, referred to as the
PC) with control cards for input, output,
and high-speed counting functions.

3. A  15-ft-long by 9-ft-wide by

(a) a rubber-tired carriage, (b) a pivot-
ing boom with two 10-ft-long feed chan-
nels, (c) the drills themselves, and (d)
the hydraulic and pneumatic control
valves and transducers. Figures 5-8 show
several views of the drill test rig and
drilling medium. The valves and trans-
ducers (fig. 8) are designed to meet the
capacities of the hydraulic and pneumatic
power sources listed in items 6 and 7
below.

4. Valve driver cards (manufactured by
Ledex, Inc., and referred to as the Ledex

6-ft-high drill test rig consisting of drivers) needed to operate some of the
larger hydraulic control valves that re-
4reference to specific products does quire a 24-V input potential.
not imply endorsement by the Bureau of
Mines.
Hydraulic power supply Hydraulic power supply
H a control box ia control cable
1
| oe f-Process controller (PC)
Control ! Micro- Frequency-to-analog
room —+4 COV computer {| converter cards
a) | =— High-speed counters 24-v
1 | | F<pOutput cards eipply
| D 1 Input cards ¥
| | | L=xc7215.8-V power supply NN
t--4------- - ‘—5-V power supply
Sound-measuring instrumentation ¥—PC output cable
Test chamber
eens Sale Siaee inks Se vate (reverberation
Terminal! [control Microphones room)
box valves Feet I
Feed
2

Test fixture

\

[=

CHydraulic lines (2)

\Vaive-driver and PC output cable ~ || | L com fare air line

‘input signal cable

Hydraulic power supply

Water supply

FIGURE 4.—Components of automated drill test fixture and contro! system.


occur and no other noise sources are
present. By measuring the sound pressure
at numerous points on a series of imagin-
ary spheres located at various radial
distances from the geometric center of
the noise source, it is possible to
determine both the sound power and the
directional properties of the source.
Unfortunately, this experimental approach
could not be pursued by the Bureau of
Mines because it would have been prohibi-
tively expensive, time consuming, and
impractical.

In terms of cost, practicality, and the
ability to obtain useful information on
drill noise, the Bureau of Mines deter-
mined that the reverberant environment
the best environment to choose. An

was
important feature of a_ perfectly rever-
berant environment is that the sound
pressure levels at all points are the
same due to the mltitude of sound re-
flections that occur at its boundaries
(walls). If only one dominant sound

surce is present in the environment, its

and power level can be calculated easi-
4y by comparing the measured sound pres—
sure levels to those produced by a refer~
ence source of known sound power. Most
importantly, it was possible to con-
struct, at a reasonable cost, a reverber-
ant environment (reverberation chamber)
capable of housing a full-sized drill
test fixture. In addition, the instru-
mentation needed to automatically calcu-
late drill sound power levels was afford-
able, the test procedures involved with
this setup were relatively simple, and
useful results could be obtained within a
reasonable time frame.

The greatest disadvantage of testing
drills ina reverberant environment is
the inability to determine the direction-
al nature of the noise source. The lack
of directional information makes it more
difficult to assess the relative noise
contributions of the drill rod, drill
body, and air exhaust. Also, potential

reductions that could result from
selection of the drill
insertion of

noise
the judicious
operator position or the
partial acoustical barriers between the
drill and the operator cannot be de-
tected. This disadvantage can be over-
come by conducting supplemental tests in
a semifree field (outdoors) with drills
that exhibit particularly strong direc-
tivity patterns.

DATA COLLECTION AND ANALYSIS

Collection of drilling data in the
field usually requires substantial human
effort such as constant visual monitoring
of pressure gauges, flowmeters, stop-
watches, etc. Noise monitoring in the
field is often performed only with hand-
held sound level meters. Extensive,
careful notes must be maintained to make
sure the data are recorded completely and
correctly. Even when data are recorded
electronically (strip chart recorders,
data loggers, or magnetic tape), consid-
erable human intervention is needed to
assemble and correlate the data for later
analysis.

The computer-controlled ADIF is the

ideal means for simplifying the task of
data collection and analysis. Signals
from permanently installed transducers

for flow, pressure, and position are con-
verted by the ADTF software into standard
units (cfm, psi, etc.) and are recorded
on a floppy disk at 4-s intervals. Sound
power levels are recorded at 18-s inter-
vals, and a continuous record of time
elapsed during the test allows for auto-
matic correlation of all test parameters.
All other information pertinent to the
test (drill type, hole size and location,
drill rod and bit type, etc.) is also
recorded on disk, and the computer as-
signs a specific test number to the en-
tire block of test data. This greatly
facilitates posttest analysis and
comparisons among different tests.


28

2 through 13. The
be created

character in fields
general names of the files to

by the Lotus Formatter (see item 5 below
for specific file names) are shown im-
mediately to the right of fields 2
through 13, and the parameter names are
displayed on the right of the file
names.

4. The disk drive to which the format—
ted files will be written is entered into
field 14. The hard disk (c): is the
default drive.

5. The specific names of the files to
be created by the Lotus Formatter are
chosen by entering any of the numbers 1
through 9 into field 15. For example, if
nonzero characters were entered in fields
2 and 9 and the default value of 1 were
left in field 15, the two files created
would have the names "HP1.PRN" and
"DDI.PRN." Up to nine Lotus-formatted
files for each parameter can thus be con-
tained on any one output target (floppy
or hard disk), and almost an unlimited
number of such files can be maintained
by renaming the files after they are
formatted.

6. The amount of drill test data to
be formatted is chosen by entering the
appropriate values in fields 16, 17, and
18. Since the Lotus Formatter program
uses the "Elapsed Time" parameter as a
key, field 17 (Start time) and field 18
(Stop time) determine the portion of the
test to be formatted. The default values
of 0.0 and 60.0 s are shown in figure 21.
Field 16 (Resample time), specifies the
interval at which the Lotus Formatter
program will recheck the "TEST .DAT"
file for new data. When the default val-
ue of 1.0 s is shown in figure 21, the
program interpolates between the actual
values recorded at 4- or 18-s intervals.

7. When all selections in fields 1
through 17 have been made, the F9 key is
pressed to perform the file conversions.

Confirmation messages and/or error mes—
sages appear at this time, including an
option to overwrite any "xxx.PRN" files
that are already located on the target
directory. Pressing F5 rather than F9
deletes from the target directory any
files whose names are the same as those

of the "marked" files.

8. The operator exits the Lotus For-
matter program, enters Lotus 1-2-3, and
calls in a special worksheet file that

contains A-weighting correction factors,
convenient column headings, and appropri-

ate axis labels for later graphs. This
serves as a template worksheet to which
the formatted drill test files will be
imported.

9. The cursor is moved to the area of
the worksheet in which the test data are
to appear, and the "File Import" proce-
dure of Lotus 1-2-3 is used to call in

This procedure is
file created

the formatted files.
repeated for each "xxx. PRN"
in steps 1 through 7 above.

10. The standard Lotus 1-2-3 file man-
ipulation and graphics options are uti-
lized to perform the desired analyses.
Examples of the use of Lotus graphics are

given in the section of this report
entitled "Initial Test Results."
Note that fields 2 through 11 corres-

pond to the drilling parameters listed in
figure 18. Fields 12 and 13 are special
Parameters that are created by the Lotus
Formatter software prior to conversion.
The "Average spectrum" (field 12) con-
sists of the logarithmic average of the
sound power levels in each of the twenty-
one 1/3-octave bands, with the number of
samples determined by the specified start
and stop times. For example, the default
values of 0.0 and 60.0 s would result in
the averaging of three sound power values
per frequency band (data at 18, 36, and
54s). Field 13 is analagous to field 12
except that the Lotus Formatter looks for
sound pressure data recorded from the
Bruel & Kjaer model 2131 digital fre-
quency analyzer.

Advantages of Spreadsheet Analysis

Multivariable Comparisons

The basic system graphics package can

only plot drilling parameters versus
time. With spreadsheet analysis, any two
Parameters ina given test can be com-

pared against each other. The most fre-
quent use of this capability would be the
comparison of sound power and hole depth.


waterfall graph, it can be displayed for

only one test at a time.

Expanded Data Analysis Through
Spreadsheets

Given the limitations of the basic sys-
tem graphics, a method for obtaining a

27

"File Import" function. For convenience,
the Lotus Formatter program and the stan-
dard Lotus 1-2-3 software are contained
on the hard disk.

File Conversion Procedure

The step-by-step procedure for convert-

more complete data analysis was desired. ing the "TEST DAT" files to Lotus 1-
The most effective approach was to con- 2-3 files is described below:

vert the test data files to electronic

spreadsheet files. Lotus 1-2-3 was 1. The test operator loads the Lotus
chosen as the spreadsheet program because Spreadsheet Formatter program into the
of its ready availability and compatibil- XT, which results in the display of the
ity with the IBM-XT. To avoid the manual menu shown in figure 21.

entry of test data into the spreadsheet 2. The four-digit test number of the
files, special software was written to test to be formatted is entered into
convert the individual parameters of the field 1 of figure 21.

“TEST -DAT" files into a format that 3. The parameters to be formatted
could be read by the lotus program's are selected by placing any nonzero
Spreadsheet Formatter

Fl Exit
FS Delete specific ??x. PRN files
F9 Extract drill test data FIO Extract noise test data
Test| © @ HPx. PRN| Hammer pressure Drill test only
@ HFx. PRN| Hammer flow "
@ RPx. PRN | Rotation pressure "
© RFx. PRN Rotation flow "
@© FTx. PRN Feed thrust "
@ FRx. PRN| Feed rate "
DFx. PRN| _ Drill frequency "
@ ODDx. PRN| Distance drilled "
@ FWx.PRN|~ Flushing water "
@ = SPx. PRN Sound power
@ ASx. PRN Average spectrum
@® PSx. PRN 2131 Average spectrum
@ Target directory: ® x=l
@ Resample time: |s @ Start time: Os Stop time + 60s

FIGURE 21.—Data input menu for Spreadsheet Formatter program.


it is important to note that some drills
generate more noise than others. Opera-
tor exposure to noise can be reduced by
choosing a less noisy drill or drilling
system. Factors that can affect the
noise produced by a drill include the
source of power (air or hydraulic), input
energy, degree of wear and leakage, drill
rod size and type, hammer and shank con-
figuration, means of drill steel rotation
(rifle bar or independent), and location
of the operator with respect to the
drill. The application and effectiveness
of noise control techniques are greatly
affected by these differences.

An in-depth understanding of drill de-
sign characteristics and their effect on
noise is an important part of any effort

to reduce the noise problen. The Bureau

of Mines, while continuing in this en-
deavor, does not possess the funding or
drill design expertise to embark on a

program to develop a drill or drilling
system that can solve the problem com-
pletely. However, with the aid of the

test apparatus described in this report,
it is possible for the Bureau to signifi-
cantly enhance the body of knowledge on
the subject of drilling noise. For ex-
ample, the test apparatus can provide
valuable but heretofore unavailable quan-
titative information on the sound power
levels produced by different types and
models of drills. Noise variations re-
sulting from differences in drill operat~
ing parameters can also be investigated
and quantified.

TEST SYSTEM CONSIDERATIONS

To conduct thorough, systematic studies
of drill noise, the researcher needs (1)
control of the parameters that affect
drill performance, (2) control of the
acoustical environment in which the drill
operates, and (3) a comprehensive, well-
organized data collection and analysis
system. The Bureau's test apparatus ful-
fills all three of these requirements.

CONTROL OF DRILL OPERATING PARAMETERS

The operation of a percussion drill is
affected by many parameters such as the
composition of the drilling mediun,
sharpness of the bit, type of bit used,
length and type of drill rod, number of
rod sections, drill feed force, supply
Pressure to the drill, wear condition of

the drill, and hole flushing medium. Un-
der actual drilling conditions in the
field, control of all these parameters is
a very difficult and sometimes impossible
task. In short, it can be said that no
two holes drilled in the field are ever
exactly the same.

In the laboratory, however, it is pos-
sible to control these parameters such
that any drilled hole is repeatable.
More importantly, it is possible to se-
lectively change only one parameter from
hole to hole to determine its effect on
noise and penetration rate. The computer
controlled automated drill test fixture
(ADTF) facilitates this process by auto-
matically maintaining the supply pres-—
sure, rotation flow, and feed force spec-
ified by the user. These parameters can


18

from lurching forward at the start of
drilling, when the actual and set point
pressures are far apart. A dead band

around the set point is also included to
prevent the feed pressure from oscillat—
ing rapidly when the actual and set point
pressures are very close but not
identical.

Hole depth is measured and controlled
by the flow of hydraulic oil through a
positive-displacement flowmeter in the
line leading to the head side of the feed
cylinder. This flowmeter generates 38
voltage pulses per inch of feed travel,
which are transmitted to the high-speed
counter. The counter tallies the pulses
and assigns the total count during a test
to a PC holding register for comparison
with the count corresponding to the drill
depth set point. A normal test ends when
the two counts are equal; at this point
the XT commands the PC to. stop drilling
and retract the feed.

To initiate the retraction phase, the
PC sends a digital value of 300 to the
analog output card, which then sends an
input voltage of 3 V to the Ledex driver.
fhe subsequent Ledex output is 5 V to the
"Retract" side of the hydraulic control
valve. This causes oil to flow to the
rod side of the feed piston at a slow,
constant rate to retract the drill. When
the drill reaches the fully retracted
position, the limit switch on the feed
(fig- 6) closes mechanically. The PC
then sends a null value (413) to the ana-
log output card, thus stopping the feed,
and sends a discrete output to the high-
speed counter to zero the actual count
for the next test.

Drill Hammer Control

Two different types of drill hammer
control systems are shown in figure 14;
the top portion describes the analog con-
trol system for hydraulic drills, and the
lower part shows the discrete control
system for pneumatic drills. The two
systems are similar in that pressure is

used as the process control variable,
‘ith flow being recorded in the PC for
informational purposes only. However,

controlling pressure is
as described below.

the method for
somewhat different,

Pressure control for hydraulic hammers
involves the same basic sequence as feed
thrust control. Voltage from a pressure
transducer is converted to a digital sig-
nal and compared to the set point in the
PC, which assigns an output that eventu-
ally results in the opening or closing of
a hydraulic valve. In the case of hammer
pressure, only one side of the valve is
activated because a reverse hammer func—
tion is not required. As with feed pres-

sure, the PC's digital output range is
limited to prevent hammer pressure
surges, anda dead band around the set

point is included.
Pressure control for

includes the same type of

and PC comparisons as for

pneumatic hammers
analog input
hydraulic ham-

mers, but the output involves three dis-—
crete control circuits. One circuit
serves only to turn the main air supply
valve onor off, as determined by the

pneumatic~hydraulic choice entered into
the XT (field 2 of figure 10). The other
two circuits operate the pilot valve that
controls the pressure-regulating valve
(figure 14). After the PC compares the
actual pressure to the set point, it
opens one side of the pilot valve and
closes the other. If the actual pres—
sure is less than the set point, the PC
opens the side that increases the pres-
sure in the regulating valve. If the
actual pressure is greater than the set
point, the PC opens the opposite side of
the pilot valve, reducing the pressure in
the regulating valve. Reaction time of
this system is very rapid and a dead band
is included, so the amount of air vented
to the atmosphere is minimal.

Drill Rod Rotation Control

Drill rod rotation control (fig. 15) is
very similar to hammer control for pneu-
matic and hydraulic drills, as can be
seen by comparing figures 14 and 15. The
major difference is that flow rather than
process control

pressure serves as_ the

variable, with pressure being recorded
for informational purposes only. Flow is
the preferred control variable for rota-
tion because the load on the rotation

considerably during the
test (collaring, drilling,

varies
of a

motor
course


9. Dutta, P. K., and W. N. Patterson.
Development of Prototype Quiet Hard Rock
Stoper Drill, Volume I (contract
HO113034, Creare Products, Inc. ). Bu-
Mines OFR 128-85, 1985, 63 pp.; NTIS
PB 86-139722.

10. Patterson, W. N. Development of

Prototype Quiet Hard Rock Stoper Drill,
Volume II (contract HO113034, Creare
Products, Inc.). BuMines OFR 20-86,

1986, 37 pp-; NTIS PB 86-165073.

US. GOVERNMENT PRINTING OFFICE 1987 605.017/60126

35

ll. Beranek, L. L. Noise and Vibra-
tion Control. McGraw-Hill, 1971, 650 pp.
12. Hawkes, I., D. D. Wright, and

P. K. Dutta. Development of a Quiet Rock

Drill, Volume 2: Sources of Drill Rod
Noise (contract JO155099, Ivor Hawkes
Associates). OFR 132-78, 1977, 77 pp.;

NTIS PB 289 716.

'NT,-BU.OF MINES,PGH, ,PA. 28607


Test 0293

Drill tested: GOPHER Pneumatic or hydraulic: P Feed: | Hole size: | 7/5"
Drill steel: I" HEX Bit type‘-POS R__ Location: 1-02

Comments: retest GOPHER at optimum settings

Time, Rotation | Distance | Hammer} Feed |Feed| Drill _|Hammer | Rotation] Flushing
5 flow, | drilled, pressure, thrust, rate, frequency, ght pressure, water,

g/ct in psi in/s ps
; Hammer pressure = | Rotation flow = 100
Values: Feed thrust = 200 Distance drilled = 48
0.1 | 102.1 0.1 | 201.6] 0 0 0 90.4 | 525
41] 1023] 45 | 204.1} 1.1 0 0 82.1 | 60
8171018) 6 I 199 | 0.4 0 0 83.6 | 61
12.1] 85.4] 6.3 | 209.3} 0.1 0 0 76.7 | 60
157 New Hammer pressure = | Rotation flow = 120
. values: Feed thrust= 200 Distance drilled = 48
16.1 | 86.2] 65 I 188.6} 0.1 0 0 78.7 | 601!
Sound power, 81.2, 83.4, 85.4, 87.7, 92.5, 92.1, 97, 93.5, 91.6, 96.8,
18.1 dB: 93.8, 97.5, 94.9, 88.9, 973, 92.3, 91.2, 88.9, 85.9,
86.2, 105.4
20.2] 1169] 67 I 201.6] 0.1 0 0 100.2 | 604
242 | 117.2 7 I 201.6} 0.1 0 0 97.8 | 607
263 New Hammer pressure = | Rotation flow = 120
: values: Feed thrust = 500 Distance drilled = 48
2827) 1126} 81 | 739 | 03 0 0 97.3 | 61
323] 1139] 97 | 522 | 0.4 0 0 101.7 | 607
Sound power, 83, 85.6, 87, 89.7, 95, 95.5, 99.3, 95.7, 93.5,
36.2 dB: 100.6, 97.5, 98.6, 99.2, 93.2, 96.1, 94.7, 93.8,
92.4, 90, 90.2, 90.9, 107.8
36.5] 112.3 {| 11.3 | 532.3} 0.4 0 0 99.7 | 606
406] 112.1 | 12.5 0.5 |558.1} 0.3 0 0 97.8 | 609
447] 114.4 | 13.8 | 4806} 0.3 0 0 99.2 | 606

Note: the notation g/cf for rotation flow reflects
fact that flow is measured in gpm for hydraulic
drills and cfm for pneumatic drills.

FIGURE 18.—Printout of drill test data.


ii

10.
ll.
12.
13.
14,
15.
16.
17.
18.
19,

20.
21.
22.
23.
24.

25.

ILLUSTRATIONS~~Continued

Main data input menu for drill test program...
Drill rig carriage and boom positioning system.
Drill carriage lock System...eereseereeeececece
Feed thrust and hole depth control system...
Drill hammer control systeme.-cesscesseeees
Drill rod rotation control system..-.+.-.+-
Data input menu for hole location program..
Data input menu for analysis program...

Printout of drill test data.....e..ee-
Graphs of hammer pressure, feed thrust, feed rate, and sound power versus

elapsed times. cecece cece eee rercceevcceecccsccrevee
Sound power spectrum and spectrum waterfall graphs
Data input menu for Spreadsheet Formatter program.
Average frequency spectra: pneumatic and hydraulic percussion drills
Frequency spectra for percussion drills, beginning versus end of hole.
Average frequency spectra: pneumatic and hydraulic percussion drills,
Pneumatic rotary drille.ccecwcceeccercceecccccverscveccvcvececevces

Frequency spectra for pneumatic rotary drill: beginning versus end..

TABLE

Maximum values and accuracy of ADTF control parameterS.ceeceeccececevecces

13

UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT

cfm cubic foot per minute in/s inch per second
dB decibel Kb kilo byte
dBA decibel, A-weighted kHz kilohertz
ft foot lbf pound (force)
f£t2 square foot Mb megabyte
£t3 cubic foot min minute
ft/min foot per minute pet percent
gpm gallon per minute psi pound (force) per
square inch
h/d hour per day
s second
Hz Hertz
v volt

in inch



ll

FIGURE 8.—Drill test rig in reverberation chamber, control valves and process sensors.


Data Input and Startup Procedure

Data input begins when the operator en-
ters the drill test program and is pre-
sented with the menu shown in figure 10.
The circled numbers in figure 10 denote
the fields in which test data are entered
by the operator, as described below:

Fields 1, 4, 5, 6, and 9 are text en-
tries for documentation purposes; they
facilitate later analysis but do not di-
rectly impact the test itself.

Field 2, entered as P or H, identifies
whether the drill to be tested is pneu-
matic or hydraulic. Field 3, entered as
1 or 2, identifies the feed channel on
which the test drill is mounted. This
information allows the appropriate set of
control cards in the PC to be activated
during the test.

Fields 7 and 8, respectively, specify
the vertical (rows A through N) and
horizontal (columns 1 through 36) hole
location. Field 3 is also important in
this regard because, for the same hole

vation on the wall, the actual amount

carriage and boom movement is dif-
terent for each feed. The operation of
the hole location program is discussed in
more detail later in this report.

Fields 10, 11, 12, and 13 are the main
control parameters governing the
operation of the drill during the test.

13

Input values are assigned the units shown
in figure 10. In the case of field 12,
rotation flow, the units depend on field
2; gpm is assumed for hydraulic drills

and cfm for pneumatic drills. Table 1
lists the maximmm allowable values of
these parameters and the accuracies

achieved by the ADTF control system.
After all data have been entered, the
operator presses the F9 function key
(fig- 10) to continue the test. The pro-
gram checks the input values for confor-
mance with the above requirements, issues
an error message if this is not the case,
and allows the operator to correct the
erroneous data. If the inputs are valid,
the program loads the input values into

TABLE 1. - Maximum values and accuracy
of ADIF control parameters

Parameter Maximum Accuracy
value pet
Hammer pressure 5,000 psi 5
(hydraulic).
Hammer pressure 350 psi 5
(pneumatic).
Feed Thrust.....--. | 12,000 1bf 4
Rotation flow 50 gpm 5
(hydraulic).
Rotation flow 1,000 cfm 2
(pneumatic).
Distance drilled... 144 in 3

{ Main menu}

Executive Fl Exit program F2 Master reset Date: September |5, 1985
commands _| F3 Move platform home F4 Test without move Time: 13:18:35
FQ Start test FIO Data analysis Run: XXXX
Test docu- [- @ Drill tested: @® Pneumatic or hydraulic: @ Feed:
mentation |] @ Hole size: © Drill steel: © Bit type:
L@-® Location: ® Comments:
Set Actual Status 000! 1000 0000 0000
[ © Operating hammer pressure psi XXXX Teststage iw www ee ee
Control _| @ Feed thrust Ibf XXXX Elapsed time tae
Parameters @® Rotation flow* g/cf XXXX Drill frequency BPM
L. @ Distance drilled in XXXX — Sound power Lee dB

*The notation g/cf for rotation flow reflects the

—_ On-line information —t

fact that flow is measured in gpm for hydraulic

drills and cfm for pneumatic drills.

FIGURE 10.—Main data input menu for drill test program.


CONTENTS

Abstract.
Introduction..
Test system considerations.
Control of drill operating parameters.
Control of the acoustical environment..
Data collection and analysis..........
System description......
System operation..
Drill test program...
Test sequence..-.-.+
Data input and startup procedure....
Data collection and display......+-.
Control subsystems.....-
IBM-XT microcomputer...
Westinghouse PC-700 process controller
Drill rig positioning control
Carriage lock control...

Feed thrust and hole depth control.

Drill hammer control....

Drill rod rotation control.
Flushing water control..

Other drill test commands..

le location program...-.- o.
Selection of hole position
Validation of input data..
Selection of hole depth.
Data analysis program...
Direct data analysis and graphics.
Test selection.....

Raw data retrieval.
Basic system graphics.
Expanded data analysis through spreadsheets..
File conversion procedure.......
Advantages of spreadsheet analysis.
Initial test results....
Pneumatic versus hydraulic percussion drills.
Rotary versus percussion drills......
Discussion.
References..-+++--

ILLUSTRATIONS

1. Noise sources on typical hand-held percussion drill...
2. Noise sources on typical jumbo-mounted percussion drill.
3. Typical noise radiation pattern.....
4. Components of automated drill test fixture and control system.
S. Drill test rig in reverberation chamber, top view....sseeeeeee
Drill test rig in reverberation chamber, profile view....-....--
» Drill test rig in reverberation chamber, rear view showing control room....
8. Drill test rig in reverberation chamber, control valves and process
SOENSOLEs se secccccccccccccccccecseceeeeeces

9. Drill test software program selection menu......-...+-



34

This type of noise can sometimes
the rotors

drill.
be attenuated by redesigning

and reduction gears to shift the fre-
quency into a more tolerable range.
It should be pointed out again that

these are merely observations of selected

test data and are in no way statistically
representative of the way the drills
behave, especially in terms of penetra-
tion rate.

DISCUSSION

The automated drill test fixture is a
very powerful tool for studying the noise
characteristics and operational perfor—-
mance of percussion and rotary drills.
The unique feature of the ADTF is that it
is housed within a _ large reverberation
chamber to allow the easy calculation of
drill sound power levels. Sound power
data are not usually provided by drill
manufacturers, so the ADIF can _ supply
drill users with information that has
previously been unavailable. If noise is
a consideration when selecting a drilling
system, this information can be very
valuable.

The ability to achieve control over all
important drill operating parameters is a
key advantage of the ADTF. Test condi-

tions can thus be reproduced exactly or
changed to study the effect of one or
more parameters on the overall perfor-

mance of the drill. Diagnostic work of

this type can provide useful information
on drill penetration rate as well as
noise. The ability to change drilling

when examining
Each drill mst

media is very important
drill penetration rate.

be tested in the medium for which it was
designed (soft, medium, or hard rock) in
order to make valid comparisons of drill
penetration.

Initial tests conducted with the ADIF

confirmed that it is capable of achiev—
ing the desired process control and data
recording functions. The data analysis
software greatly facilitated the inter-
pretation of these initial tests. Gen-
eral observations were made with respect

to the noise produced by pneumatic per-
cussion, hydraulic percussion, and pneu-
matic rotary drills. A much more exten-

sive testing program with each of these
drills must be conducted before defini-
tive comparisons can be made.

REFERENCES

1. Patterson, W. N., G. G. Huggins,
and A. G. Galaitsis. Noise of Diesel-
Powered Underground Mining Equipment:
Impact, Prediction, and Control (contract
HO346046, Bolt Beranek and Newman, Inc. ).

BuMines OFR 58-75, 1975, 227 pp.; NTIS
PB 243 896.

2.  Visnapuu, A., and J. W. Jensen.
Noise Reduction of a Pneumatic Rock
Drill. BuMines RI 8082, 1975, 23 pp.

3. Summers, C. R., and J. N. Murphy.

Noise Abatement of Pneumatic Rock Drill.
BuMines RI 7998, 1974, 45 pp.

4. George, D. L., and N. J. Matteo.
Development of Noise Control Technology
for Pneumatic Jumbo Drills (contract

HO395029, Ingersoll-Rand Research, Inc. )-

BuMines OFR 100-81, 1980, 61 pp.; NTIS
PB 81-237414.
5. Dixon, Ne. R-, and M. N. Rubin.

Development of a Prototype Retrofit Noise

Drills (con-
and Newman,
1982,

Control Treatment for Jumbo
tract HO387006, Bolt Beranek
Inc. )- BuMines OFR_ 111-83,
106 pp-; NTIS PB 83-218800.

6. U.S. Mine Safety and Health Admin-
istration. Noise Control Abstracts.
Compiled by MSHA Health and Safety Tech-

nology Centers, Denver, CO, and Pitts-—
burgh, PA, 1983, 45 pp.
7. Dutta, P. K., and P. W. Runstadler,

Jr. Development of Commercial Quite Rock
Drills (contract JO177125, Creare Pro-
ducts, Inc. ). BuMines OFR 143-84, 1984,
114 pp.; NTIS PB 84-232644,

8. Dutta, P. K., and W. N. Patterson.
Development of Noise Control Technology
for Jumbo Drills (contract H0395025,
Creare Products, Inc. ). BuMines OFR 21-
86, 1985, 67 pp.: NTIS PB 86-165081.


22

positions (hole rows) are denoted by the
letters A through R; the horizontal posi-
tions are given by columns | through 18
(left-side concrete block) and 19 through
36 (right-side block). Operator control
of hole position is achieved by entering
information in the circled fields 1
through 6 in figure 16. Fields 1 and 2
are the row and column assignments, re-
spectively, of the hole to be considered.
Fields 3 through 6 contain the desired
number of counts (38 counts per inch) to
be issued by the position transducers en
route from the home position to the hole.
Fields 3 and 4 are the carriage and boom
counts for feed 1, while fields 5 and 6
are for feed 2. These data are then
placed into the appropriate PC holding
registers by pressing the "Update loca-
tion" (F2) key. A current listing of the
counts for each hole location can be ob-
tained by pressing either Fl (output to
video monitor) or F6 (output to printer).

The entire hole location grid was pre-
programmed in this manner to remain with~
in the confines of the two existing con-
crete blocks. Spacing between adjacent
rows and columns was set at 4 in, and the
pattern was staggered by 2 in (i-e.,
even-numbered columns were shifted 2 in
downward from odd-numbered columns) to
provide an actual hole spacing of about
4.5 in. Under normal circumstances, the
test operator would have no reason to
change the preprogrammed hole positions.

However, an important exception occurs
when considering the use of drilling
media other than the concrete blocks.

For example, a granite test block was in-
serted into the wall between the concrete
blocks, and previously unused hole loca-
tions around the perimeter of the con-
crete blocks were utilized to establish a
hole pattern on the granite block. The
only constraints on hole position are the
physical travel limits of the carriage
and boom.

Validation of Input Data

At the end of each drill test, the
drill test program automatically enters
the hole depth (in feet) into the
hole location program. If the operator

subsequently specifies a hole location
that has already been drilled to the max-
imim depth (e-g-, location G-5 in figure
16) or asks for a depth that would exceed
the maximum at that location (e.g-, a 7-
ft hole at location J-21), the drill test
program issues an error message. Testing
cannot proceed until the error is cor-
rected by specifying either another hole
location or a shallower hole depth.

Selection of Hole Depth

During the initial programming of the
hole location grid, the depth of each
hole was set to zero via field 7 of fig-

ure 16. Subsequent drill tests resulted
in the assignment of actual hole depths
to various locations. In some cases,
however, it is desirable for the operator
to arbitrarily assign hole depths through
the hole location program For example,
a very large drill hole at a particular

location may interfere with adjacent
holes if the holes are not perfectly
straight; damage to the drill rod or

drill could result if the holes intersect
within the block. Therefore, even though
the actual depths of the adjacent holes
are zero, the operator may wish to enter
a depth of 12 ft into the hole location
program (field 7 of figure 16). This
will cause an error message to appear if
the operator tries to select these holes
for drill tests. The hole depth selec-
tion feature also allows easy re-
initialization after the concrete blocks
are replaced.

DATA ANALYSIS PROGRAM

The drill test software possesses very

powerful analytical capabilities. Any
drilling parameter stored to disk can be
studied and compared graphically to any

analysis pro-
the overall

main drill
similtaneous

other variable. The data
gram can be called in from
software menu (fig. 9) or the
test menu (fig. 10) for
analysis of any two tests. The data re-
corded to disk can also be converted
easily to commercially available spread-
sheet files (Lotus 1-2-3) for subsequent
analysis using the spreadsheet software.


Library of Congress Cataloging in Publication Data:

Aljoe, William W.
Test apparatus for measuring sound power levels of drills.
(Information circular/United States Department of the Interior, Bureau of Mines; #161)

Bibliography: p. 34-35.
Supt. of Docs. no.: 1 28.27: 9166.

1. Rock-drills—Noise. I. Stein, Robert R. II. Bartholomae, R. C. III. Title. IV. Series.
Information circular (United States. Bureau of Mines); 9166.

TN295.U4 ITN279] 622s (622’.8] 87-600273



30

drills were tested in a hard drilling

mediun.

Several points should be noted about
the test data. Most importantly, the
number of tests to date is too small to

generate statistically valid results con-
cerning the behavior of the drills under
differing operating conditions. Second,
the primary purpose of these tests has
simply been to verify the capabilities of
the ADTF in terms of process. control,
data collection, and test analysis; how-
ever, operation of the test fixture has
still yielded some interesting informa-
tion. The confirmation of the contribu-
tion of the drill steel to the overall
noise level in percussion drills is one
factor that can be noted from the avail-

pneumatic drill developed under contract
with the Bureau of Mines (9-10). Its
valveless design, independent rotation,
and integral mffler make the QHR drill
one of the quietest in its class. A Tam-
rock HH-50 was chosen to represent hy-
draulically powered percussion drills.
This drill also has independent rotation

and is capable of accommodating either
water or air flushing, as is the QHR.
The sound power spectra of these two

drills are shown together in figure 22.
The QHR and the HH-50 are in approxi-
mately the same weight and power-output
class and give a fairly good comparison
between the two different power sources.
During the tests chosen for comparison,
the QHR drilled at a rate of 1.95 ft/min

able data. under an average thrust of 245 Ilbf and
the HH-50 drilled at a_= rate of
PNEUMATIC VERSUS HYDRAULIC PERCUSSION 2.20 ft/min under an average thrust of
DRILLS 277 1lbf. Although they are not typically
used for concrete drilling, button bits
The drill used for the tests of pneu- were used to maintain bit consistency
matic percussion drill was a Technologi- during testing.
cal Enterprises QHR drill, a quieted
aie) T T T T T T T
lo6 fr 7
a L 4
2102
id se}
W 98 4
lu
4
o - 4
G 94
je)
a2 90F- |
a
5
Q r 4
8 86 KEY
= Pneumatic percussion drill
got 4 Hydraulic percussion drill
78 i 1 1 i L 1 1
O° 125 250 500 000 2,000 4,000 8,000 _ 16,000

FREQUENCY, Hz

FIGURE 22.—Average frequency spectra: pneumatic and hydraulic percussion drills.


generated by the software are more easily
interpreted with the availability of hard
numbers, especially when input parameters
are changed during a test, (2) particu-
larly interesting portions of a test can
be isolated for more detailed analysis,
and (3) data anomalies that sometimes oc~
cur at the start of a test are easier to
identify.

Basic System Graphics

The function keys Fl through F6 in fig-

25

variable. Function key F5 plots the 1/3-
octave band sound power levels versus
frequency, and F6é provides a simulated
three-dimensional graph with frequency as

the X-axis, 1/3-octave band sound power
level as the Y-axis, and time as the Z-
axis. Figures 19 and 20 are examples of

these graphs for tests 0178 and 0293.
Fields 3 through 6in figure 17 are
used by the test operator to define the
range of values to be displayed on the X-
and Y-axes of each graph. These values
are entered before pressing the function

ure 17 are used to display graphs on the key for the desired graph. If these
XT video monitor; hard copies are ob- fields are left blank, the range is de-
tained easily by pressing the "Print termined by the actual minimum and maxi-
screen" key of the XT keyboard when the mum values contained inthe data. In
graph is displayed. Function keys Fl figures 19 and 20, ranges were selected
through F4 provide graphs that utilize such that all test data would be dis-
the indicated test parameter as_ the de- played on easily readable axes. For
pendent (Y-axis) variable and elapsed example, the total elapsed time in each
time as the independent (X-axis) test was slightly greater than 150 s;
100 T T — 800 T Y
preteen ne
a fi xX
Test O178 -
wr 75th 7 ‘B 600} |
iva ' .
5 ' E
n t n
8 ' =) Test 0293
wo sof 4 400F
a -
a
Wi 3 mye
2 ast 4+ 200 XO 4
c=? Test O178
= pm 0293
° 50 100 150 200 ° 50 700 150 200
1.00 125 - 1 —
2
i % 120+ :
2 rsh id
sg it > isk J
a VI Test 0178 a
E H \ «
< | 4 Hof 4
1 w _
« 4 F as
a
in ! a josp 7 Test 0293 1
a I
ir 4 = |
B i00f |
rr)
A 95,
° 50 100 150 200 ° 50 100 150,
TIME, s

FIGURE 19.—Graphs of hammer pressure, feed thrust, feed rate, and sound power versus elapsed time.


5. A sound measurement system consist-
ing of an array of microphones suspended
from the ceiling of the reverberation
room and instrumentation to calculate
sound power levels. Figure 7 shows some
of the sound measuring instrumentation in
the control room adjacent to the rever-
beration chamber.

6. A remotely controlled hyraulic
power source capable of providing up to

35 gpm of flow at 5,000-psi pressure.
This is sufficient to operate most cur-
rently available hydraulic percussion
drills.

7. A compressed air source capable of
providing 1,200 cfm of flow at 100-psi

pressure. This is sufficient to operate
most currently available pneumatic drills
with the exception of down-the-hole
drills.

8. A flushing water
suppression.

source for dust

The first four components combine to
form the automated drill test fixture
(ADTF); the other four provide vital sup-
ort functions and are accessed by the
«aDTF during its operation. The drilling
rig and microphones are located inside
the reverberation chamber, the XT and
sound measuring instrumentation are lo-
cated inside the control room adjacent to
the chamber, and the PC and valve drivers
are located in cabinets immediately out-
side both the test chamber and control
room. The hydraulic power pack and air
compressor are located remotely so that
their noise contribution to the test
chamber is minimal.

All eight components are
the operation of pneumatic
all but the air compressor
for hydraulic drills.
drills can be mounted on the ADTF at
once, only one drill at a time can be
operated. The advantage of having two
feeds is that a pneumatic and hydraulic
drill can operate in consecutive tests

required for

drills, and
are required
Although two

without having to dismantle and reconnect
numerous fluid supply connections. Both
percussive-rotary and all-rotary drills
can be tested on the ADTF using the same
test program and procedures.

The primary drilling medium consists of
two 6- by 6- by 12-ft concrete blocks
(compressive strength approx. 6,000 psi)
inserted into the chamber wall; see fig-
ures 5 and 6. Provision has also been
made to drill into granite or another
drilling medium either by replacing the
concrete or by inserting the medium into
the wall between the two concrete blocks.
All drilling takes place in the horizon-
tal direction, with a maximum depth of 12
ft governed by the confines of the build-
ing in which the reverberation chamber is
housed.

The reverberation chamber and sound
measurement system meet the criteria of
ANSI S1.31-1980, "Precision Methods for
the Determination of Sound Power Levels
of Broad-Band Noise Sources in Reverbera-—
tion Rooms." The chamber itself is 60 ft
long by 34 ft wide by 22 ft high and is
constructed of filled concrete block with
nonabsorptive paint covering its interior
surfaces. Exhaust fans and floor drains
provide a clean working environment with
consistent acoustical properties. The
sound measurement system consists of (1)
an array of 20 randomly spaced micro-
phones positioned at 9 to 11 ft above the
chamber floor, (2) two 8-channel mlti-
plexers (Bruel & Kjaer model 2811) to
provide access to 16 of the 20 micro-
phones during any single test, and (3) a
Bruel & Kjaer model 7507 sound power
calculator. Alternatively, if sound
pressure rather than sound power were the
desired quantity, a Bruel & Kjaer model
2131 digital frequency analyzer could
serve as the third component of the sound
measuring system. This system was
qualified using the test procedures in
section 8 of the ANSI S1.31-1980.


12

SYSTEM OPERATION

The operator activates the drill test
system by turning on the process control-
ler (PC), the sound power measurement
system, and the microcomputer (XT).
Turning on the XT with no floppy disk in
place automatically loads the disk oper-
ating system (DOS) from the hard disk.
At the DOS prompt, the operator loads the
drill test software and is presented with
the menu shown in figure 9.5 The func-
tion keys Fl through F6 on the XT key-
board are used to access the various op-
tions. The three major elements of the
drill test software--the drill test pro-
gram, analysis program, and hole location
program--are described in this section.

DRILL TEST PROGRAM

Test Sequence

Prior to running a drill noise test,
the operator starts the hydraulic power
pack and air compressor (if required) and
adjusts them to operating pressures that
are at least as great as those that will
be required for the test. A typical
drill noise test sequence follows:

1. The test operator loads the drill
test program (Fl in figure 9) and enters
descriptive information and control para—
meters (set points) into the XT.

2. The drill test program checks the
input values and, if consistent with sys—
tem limitations, loads them into the PC
along with a command word to start the
test.

3. The PC moves the drilling rig to
the selected hole location, locks the
carriage, and pauses for an operator com-
mand to proceed. When this command is
issued, the PC starts the drilling pro-
cess, and the sound measurement system is
activated. Throughout the test, the PC
handles the task of reading the pressure
and flow transducers, comparing their
values to those of the set points, and

5tThroughout this report, graphs and
menus such as figure 9 have been modified
slightly to conform to Bureau of Mines
publication standards.

opening or closing valves to maintain the
set points as closely as possible.

4. When the feed thrust reaches the
set point, the XT starts to collect in-
formation from the PC at intervals speci-
fied by the test operator. It continues
to do so until the hole depth reaches the
set point or the operator terminates the

test. At this point the XT instructs the
PC to stop drilling and retract the
drill; the sound measurment system is
also deactivated, and the data are

written to a file on a floppy disk in the
A: disk drive unless the operator de-
cides the test was invalid.

5. When the drill reaches its origi-
nal, completely retracted position, the
system waits for a new test command to be
entered into the XT.

6. The operator either analyzes data
from the test just completed or enters
new data for another test. If no other
tests are needed but data analysis is de-
sired for one or more previous tests, the
operator exits the drill test program,
enters the data analysis program (F2 in
figure 9), and calls in the desired test
numbers. Pressing the F4 key allows the
operator to check the directory of the
disk in the A: drive.

7. If no subsequent tests or data
analyses are desired, the operator issues
a command that moves the rig to a home
position (conveniently located to permit
drill maintenance or removal), exits the
drill test program, and shuts down the
ADTF and power sources.

Choose option:
Fl - Drill test program
F2 - Analysis program
F3 - Hole location program
F4 -
FS -
F6 -

Directory of tests on A:
Edit controls file
Exit to DOS

FIGURE 9.—Drill test software program selection menu.