640° C (6) is that with the rapidly decreasing temperature
of the hot streak after impact (14), there is insufficient lag
time (7) to allow the ignition of the gas mixture.

IMPACTING FORCES

Except for a single data point overlap (figs. 8 and 10),
no ignition occurred where final radial forces were at or
below 380 Ib and all ignitions occurred when the final
radial forces were at or above 320 Ib. A similar pattern

holds for the final tangential forces. Figures 9 and 11
show, in general, ignitions occurred for final tangential
forces greater than 53 lb. Figures 10 and 11 show that a
relationship exists between streak temperature, final forces,
and likelihood of ignition. While Rae (9) reported an in-
verse relationship between time and the square of the slid-
ing load, this research found no one-for-one relationship
between number of impacts to ignition and impacting
forces,

CONCLUSIONS

1, The three polycarbonate resins (LEXANS 141, 500,
and 3412) and the ultra-high-molecular weight polyeth-
ylene (Special A-R) caused no ignitions at any of the three
speeds, but do not have sufficient strength to hold the
carbide tip during coal cutting,

2. The Zn-Al alloy (ZA 27) caused no ignitions at any
of the three speeds, but, while significantly stronger than
the four plastics, was deemed not to have sufficient
strength to hold the carbide tip during coal cutting.

3. The nitrided Nb-Ti-W alloy (NICON) caused ig-
nitions on every trial at all three speeds and was, there-
fore, considered dangerous to use as a coal-cutter material
in underground mines.

4, The 1018 steel and the 10Ni-90Co cast alloy caused
some ignitions at the lowest speed (400 sfpm) and was,
therefore, not recommended for coal-cutter materials in
underground mines.

5. The A2 tool steel had a similar performance record
as the 4340, There were no ignitions at the lowest speed,

but there were ignitions on every trial at the two higher
speeds. Since A2 tool steel is more expensive than 4340,
there are no reasons to justify substitution of A2 for 4340.
6. The two Ni-base cast alloys were shown to be less
likely to cause an ignition than 4340.
7. Some interrelationships between test parameters
were also found for the steels:

a, All ignitions occurred where the hot streak tem-
perature was 860° C or higher.

b. As speed increased, the likelihood of ignition
increased.

c. As speed increased, the temperature of the hot
streak at ignition rose.

d. In general, ignitions occurred at or above 320 Ib
final radial force and 53 1b final tangential
force.

REFERENCES

1, McDonald, L. B., and W. H. Pomroy. A Statistical Analysis of
Coal Mine Fire Incidents in the United States From 1950 to 1977.
BuMines IC 8830, 1980, 42 pp.

2. Kawenski, E. M, G. C. Price, and C. R. Stephen. Frictional
Ignition of Gas by Continuous Mining Machines in Underground Coal
Mines. MSHA IR 1110, 1979, 12 pp.

3, Nagy, J. The Explosion Hazard in Mining. MSHA IR 1119, 1981,
© pp.

4, Rae, D., B. Singh, and R. Danson. The Size and Temperature
of a Hot Square in a Cold Plane Surface Necessary for the Ignition of
Methane. SMRE Res. Rep. 224, 1964, 35 pp.

5. Mason, W., and R. V. Wheeler. ‘The Ignition of Gases. Part Il,
Ignition by Heated Surfaces, Mixtures of Methane and Air. J. Chem.
Soc. (London), v. 121, 1922, pp. 2079-2091.

6. Powell, F. Ignition of Gases and Vapors. Ind. Engr. Chem, v.61,
No. 12, 1969, pp. 29-37,

7. Naylor, C. A., and R. V. Wheeler, The Lag on Ignition of
Firedamp. SMRB Pap. 9, 1925, 16 pp.

8. Burgess, M. J, and R. V. Wheeler. The Ignition of Firedamp
by the Heat of Impact of Hand Picks Against Rock. SMRB Pap. 62,
1930, 18 pp.

9. Rae, D. The Importance of Working and Wear Process in the
Ignition of Methane by Friction. SMRE Res. Rep. 236, 1966, 49 pp.

10. Bowden, F. P., and K. E. W. Ridler. Physical Properties of Sur-
faces III - The Surface Temperature of Sliding Metals. Proc. Royal Soc.
(London), v, A154, No. 883, May 1936, pp. 640-656.

11. Powell, F,, and K. Billinge. Ignition of Firedamp by Friction
During Rock Cutting. Min. Eng, (London), v. 1134, No. 176, May 1975,
pp. 419-426.

12. Guest, P. G. Ignition of Natural Gas-Air Mixtures by Heated
Surfaces. BuMines Tech. Pap. No. 475, 1930, 59 pp.

13, Blickensderfer, R.A. D. K. Deardorff, and J. B. Kelley. In-
cendivity of Some Coal-Cutter Materials by Impact-Abrasion in Air-
Methane. BuMines RI 7930, 1974, 20 pp.

14, Blickensderfer, R.A. Methane Ignition by Frictional Impact
Heating. Combust. Flame, v. 25, 1975, pp. 143-152.


UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT

°c degree Celsius
in inch

in/min _ inch per minute

ksi 10° pound per square inch
b pound

ug microgram

mg milligram

mil 10° inch

ms

psi
rpm
sfpm
vol pet
pet

millimeter

millisecond

pound per square inch
revolution per minute
surface foot per minute
volume percent

weight percent



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Table 3.—Compositions of nonpolymeric materials

‘Material

CURRENT RESEARCH

Steels:
1018 plain carbon steel
A2tool steel ......
4340 low-alloy steel...

PRIOR RESEARCH!
Rene 41 Ni alloy

Steels:
4130 alloy stool...
17-4 pH stainless steel .

Composition, pct

70+ Zn, 27 Ai, 2.25 Cu

87 Ni, 13 Co
90 Ni, 10 Co
90 Co, 10 Ni
50 Cb, 30 TI, 20 W

99+ Fe, 0.75 Mn, 0.18 C
90+ Fe, 5.25 Cr, 1.1 Mo, 1 C, 0.6 Mn, 0.25 V, 0.2 Si
96+ Fe, 1.8 Ni, 0.8 Cr, 0.7 Mn, 0.4 C, 0.3 SI, 0.25 Mo

52+ Ni, 19 Cr, 11 Co, 10 Mo, 3 Fe, 3 Ti, 1.51, 0.1C
99.9+ Fe

97+ Fe, 1.0 Cr, 0.5 Mn, 0.3 C, 0.3 S, 0.2 Mo
74+ Fe, 16.5 Cr, 4.3 Ni, 3.5 Cu, 0.5 SI, 0.4 Mn, 0.04 C

'Alloys used by Blickensderfer, Deardotf, and Kelley (13) are included for comparison with alloys used in current

Program.

EXPERIMENTAL PROCEDURES AND CONDITIONS

PROCEDURES

A sample of the shank material was loaded into the
flywheel of the ignition chamber. The chamber was in-
fused with natural gas to a7 vol pct concentration. The
sample was impacted against the sandstone at speeds of
400, 600, or 900 sfpm and a feed rate of 1 mil per impact.
The test was terminated at ignition or 300 impacts, which-
ever came first. A step-by-step sequence for the operation
of the frictional ignition chamber is given in appendix A.

TEST CONDITIONS

The independent test variables were shank material and
peripheral speed of the flywheel. The flywheel was rotated
at 400, 600, and 900 sfpm.

The controlled conditions were the sandstone (Ohio
Blue), the gas-air mixture (7 vol pet natural gas in air), the
feed rate toward the flywheel (1 mil per impact), and the
clearance angle between the sandstone and test material
(minus 3°).

Preliminary tests established the clearance angle that
was most likely to cause ignition to be between minus
T° and minus 4°. An angle of minus 3° (fig. 4), was
selected for all subsequent testing. Such a configuration

corresponds to a badly worn or damaged tool in an actual
continuous mining machine. Previous researchers have
shown that sharp cutting tools rarely, if ever, cause
frictional ignition, Only after a wear land developed on
the tool did ignition occur (14 15, 18).

Wear land L
‘on tool Sandstone
Negative
clearance
Feed per
impact (f)

‘Smeared layer \
of thickness (b)

Ejected rock
Particles

Tool velocity (v)

Figure 4.—Configuration of sandstone and tool: top, perspec-
tive; bottom, horizontal section.



INTRODUCTION

Many methane gas explosions in underground coal
mines are caused by frictional heating where coal-cutter
bits impact sandstone (1-3)? The ignition factors of air-
methane mixtures by heated surfaces have been studied for
‘over two centuries. The investigations have shown that:

¢ As the surface temperature increased, the size of the
heated area needed to incend methane decreased
@.

¢ The most incendive mixture was approximately
6.5 vol pct methane in air (5-6).

¢ The minimum temperature of the hot surface to
cause ignition was 640° C (5-6).

¢ A “lag time" existed between getting the surface
to a specific incendive temperature and the actual
ignition of air-methane mixtures (7).

The ignition of firedamp, methane, and natural gas re-
sulting from the impact between metallic and rock mate-
tials has been investigated by many researchers. Some of
the results from the Safety in Mines Research Establish-
ment (SMRE) of England have shown that:

¢ An oblique, sliding impact between two materials
easily ignited air-methane mixtures (8).

© The time to ignition was an inverse function of both
the load squared and the speed of cutting to the
fourth power. (The load was applied to the sliding
metal sample perpendicular to the contact surface
between the sandstone and the metal.) (9)

¢ The temperature at the impact surfaces approaches
the melting point of the metal while the bulk of the
metal remains cool (10).

¢ There was no direct relationship found between
the lathe cutting forces and the ease of ignition as
the metallic sample cut a helical path into rotating
sandstone (71).

The U.S. Bureau of Mines also has been active in
methane incendivity research. Various Bureau researchers
have studied the effect of temperature and surface area
(12), the effect of different types of sandstone and other
rock materials (13-15), and the effect of near-tangential
impacts by coal-cutter steels and other cutting tool mate-
rials against rock (13-14, 16-17). They concluded that:

© Methane incendivity increased with cutting speed.

¢ The cause of ignition was the frictionally generated
hot streak on the sandstone immediately behind the
impact.

¢ The maximum temperature of the hot streak was
achieved within 2 ms and ranged from 1,200° to
1,400° C, but rapidly decreased to less than 800° C
within 40 msec after the impact.

© The steel shank is two to five times more likely than
the cemented carbide tips to cause gas ignition.

The work reported in this report compared the per-
formance of 4340, a coal-cutter shank material, against
possible substitutes for 4340 in the tool shank. Both
nonferrous metal alloys and polymeric materials were
investigated,

ACKNOWLEDGMENT

Strength requirement calculations for cutting of No. 6 coal are courtesy of George Laird, mechanical engineer, Albany

Research Center.

EXPERIMENTAL EQUIPMENT AND MATERIALS

EQUIPMENT

The frictional ignition chamber (FIC), shown in fig-
ure 1, was composed of 1/4-in steel walls with angle iron
braces. The FIC dimensions were 44 by 36 by 18 in.
There were two 1-in thick polycarbonate? viewing ports

Italic numbers in parentheses refer to items in the list of references
Preceding the appendixes at the end of this report.

3Reference to specific products does not imply endorsement by the
US. Bureau of Mines.

and one 16-in mylar plastic (1 mil thick) rupture-vent port.
The top-viewing port was a 14-in submarine type hatch
that allowed ready access for changing the shank materials
and sandstone blocks.

The shank material samples were 3/8 in square by
1-1/2 to 3 in long. They were mounted in a 24-in, 550-Ib
flywheel within the chamber (fig. 2). The flywheel was
driven by a hydraulic motor using a variable speed, vari-
able displacement hydraulic pump. The pump was driven
by a 15-hp electric motor. The rotational speed of the
flywheel ranged from 55 to 160 rpm (350 to 1,000 sfpm).


FRICTIONAL IGNITION OF NATURAL GAS-AIR MIXTURES
BY ALTERNATIVE COAL-CUTTER BIT SHANK MATERIALS

By L. Garner McDonald’

ABSTRACT

The U.S. Bureau of Mines tangentially impacted potential coal-cutter bit shank materials against
sandstone to investigate the potential of the materials to.ignite natural gas by a friction-generated hot
streak. The shank material samples were mounted in a 24-in, 550-Ib flywheel, which was rotated at
surface speeds of 400 to 900 sfpm. The sandstone was advanced toward the rotating flywheel at feed
rates of 1 mil per impact. The atmosphere mixture was 7 vol pet natural gas in air. Three grades of
polycarbonate resin, an ultra-high-molecular weight polyethylene, and a zinc alloy (ZA27) were among
the potential materials. None of these materials caused ignition of the methane at any of the three test
speeds (400, 600, and 900 sfpm), but the above materials do not have sufficient strength to hold a
carbide tip during coal cutting. Of the materials having sufficient strength to hold a carbide tip, three
nickel-based alloys proved less likely to cause a natural gas ignition than did iron-based alloys such as
4340 (a commonly used shank material for coal cutters).

‘'Metallurgist, Albany Research Center, U.S, Bureau of Mines, Albany, OR.


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INT.BU.OF MINES,PGH.,PA 29556


MATERIALS
The composition of the gas-air mixture used in the
experiment was 7 vol pct natural gas (natural gas com-
Position is given in table 1).

Table 1.Composition analysis of natural gas, volume percent
1.7-2.0 10,
7-1.0]} CO ..

The sandstone used in the investigation was a fine-grain
quartzitic sandstone called Ohio Blue from McDermitt,

Chy... she bh

0.15-0.2 j| CO,.. <0.1
CHy.. 24 281} CH, Hy

<1 2 <t

OH. The sandstone is a dark gray, clayey, feldspathic,
very fine-grain sandstone with some parallel bedding. It
has a clastic texture consisting of rounded grains of quartz,
some feldspar, and trace amounts of muscovite, pyrite, am-
phiboles, pyroxenes, and diatoms, The cement is mostly
argillaceous material.

The materials investigated in this program were three
steels, a zinc based alloy, three nickel-cobalt alloys, a
nitrided niobium-titanium-tungsten alloy, and four poly-
meric materials (table 2). The compositions of the metal-
lic alloys investigated here and, for comparison, four alloys
investigated by Blickensderfer, Deardorff, and Kelley (13)
are shown in table 3.

Table 2-Properties and descriptions of test shank materials

Material Tool UTS, YS, _Elongation, Hardness
No. ksi ksi pot
METALLIC ALLOYS
ZA2T sandoast Zn alloy? so... eee ee eee eee 1 5864 53-54 36 HB 110-120
NCo cast alloys:
87NI-13C0 2 ND ND NOD ND
SONI-10Co . 63 ND ND NO NO
10NI-90Co ... 6 ND ND ND NO
NICON nitrided refractory metal alloy? . 68 ND NO ND ND
Stools:
1018 plain carbon steel ...... 69 5860 (82-54 1525 HB 116-126
A2 tool steel, quenched and temp 70 285 230 4 HRC 58
4340 low-alloy steel, quenched and tem; 571 235 210 15 HRC 48
POLYMERIC MATERIALS
Polycarbonate resins:
Lexan 141, medium viscosity’ . 2 95 9 110 HRM 70
Lexan 500, high rigidity, toughness, and impact
3 96 8 10-20 HRM 85
4 16 ND 46 HRM 91
6 56 ND 470 HRM 67

HB Brinell hardness.
HRC Rockwell C hardness.
HRM Rockwell M hardness.
ND Not determined.

UTS —_Uttimate tensile strength.
YS Yield strength.

'Material test sample number.

2Provided by Noranda Corp. through the auspices of the Zinc Institute, inc.

3Provided by Fansteel Corp.

4A commonly used coal cutter shank steel,
SProvided by General Electric Co.
“Provided by Industrial Plastics, inc.


RI} 9417 REPORT OF INVESTIGATIONS/1992

Frictional Ignition of Natural Gas-Air Mixtures
by Alternative Coal-Cutter Bit Shank Materials

By L. Garner McDonald

UNITED STATES DEPARTMENT OF THE INTERIOR

BUREAU OF MINES


1,000 T r) T T
300 ; & T T
; 1 ae oan ® ;
SO 250+ D1 case (no ignition) # 900 F
E © 13 cases (no ignition) =]
& 200 A Average <
~ x
wu
2 150% & 800 °
no # QO
5 100 F ¥ °
< = a4 °
= sof x 700 Sime
0 n 1 1 fl a A Average
400 500 600 700 800 900 j : ; .
CUTTER SPEED, sfpm 600

400 500 600 700 800 900

Figure 5.—Effect of speed on number of impacts to Ignition of CUTTER SPEED, sfpm
7 vol pet natural gas-alr mixture for steels Impacting sandstone. ———
Averages are calculated assuming ignition occurred at 300 Im- Figure 6.—Effect of speed on streak temperature of 7 vol pct

pacts for each ‘no Ignition’ case, natural gas-air mixture for steels Impacting sandstone.
ve
IGNITION TTS xs ccee IGNITION
No oNMON = CVO © pian NOIGNTION SOCK ° tem
8 coses:
600 700 800 900-1000 Y °TM 0 200 400-600-800 1000
STREAK TEMPERATURE, ‘C FINAL RADIAL FORCE, tb
Figure 7.—Etfect of streak temperature on ignition of 7 vol pet Figure 8.—Etfect of final radial force on ignition of 7 vol pet
natural gas-air mixture for steels impacting sandstone. natural gas-alr mixture for steels impacting sandstone.
ad XX TXT RX
g re
3 900 + sion ko HK sition region x 4
$00 | vey 4
3 o ee)
, Cte (tin
IGNITION x m- 00 9 0 © 2am ow te) 1
NO IGNITION yg No ignition region
Boo tet Pe,
L 4 0) 200 400 600 800 1,000
20 40 60 80 100120 FINAL RADIAL FORCE, Ib

FINAL TANGENTIAL FORCE, ib

Figure 10.—Effect of final radial force on streak temperature
Figure 9.—Effect of final tangential force on ignition of 7 vol in 7 vol pet natural gas-alr mixture for steels Impacting
pet natural gas-air mixture for steels impacting sandstone, ‘sandstone.



RESULTS AND DISCUSSION

The effect of cutting speed for each material tested on
ignition and number of impacts to ignition are summarized
in table 4. The raw data for all of the materials and
variables are tabulated in appendix B, Figures 5 through
11 show the effects of speed, temperature, and cutting
forces on likelihood of ignition.

ALLOYS

The materials evaluated for possible replacement of
steels in coal-cutter shanks were three grades of polycar-
bonate; one grade of wear-resistant, ultra-high-molecular
weight polyethylene; three cast Ni-Co alloys; a nitrided
Nb-Ti-W alloy and a cast zinc alloy. For comparison pur-
poses, three grades of steel—1018 plain carbon steel, 4340
alloy steel (currently used shank material), and A2 air-
hardened tool steel were also tested. The ignition results
are shown in order of likelihood of causing an ignition and
are summarized as follows:

1, The nitrided Nb-Ti-W alloy (NICON) caused natural
gas ignitions on every test run at all three speeds (400,
600, and 900 sfpm).

2. The 1018 steel and 10Ni-90Co cast alloy caused
ignitions at all three speeds, but only at 900 sfpm did they
cause ignitions on every trial.

3. The A2 tool steel and the 4340 alloy steel caused no
ignitions at 400 sfpm, but resulted in ignitions on every
trial that was run at 600 and 900 sfpm.

4, The 87Ni-13Co and 90Ni-10Co cast alloys caused no
ignitions at 400 sfpm, and did not result in ignitions on
every trial at either 600 or 900 sfpm.

5. The four polymers and the cast zinc alloy caused no
ignitions on any trial at any of the three speeds.

Alloy steels such as 4340 and 4130 are the most com-
mon shank materials currently used. These two steels,
with proper heat treatment, have yield strengths above
200,000 psi (19). The five materials that caused no igni-
tions have yield strengths less than 25 pet of this value.
ZA27 has a yield strength of 54,000 psi (20). The ultimate
tensile strengths for LEXAN 141, 500, and 3412 are 9,500,
9,600, and 16,000, respectively (22). The Special A-R
polyethylene has an ultimate tensile of 5,600 psi (22).
Simple calculations using resultant force measurements
from Roepke and Voltz (23) for the cutting of Illinois
No. 6 coal gave strength requirements of 20,000 psi. This
value does not include any dynamic affects, such as impact,
or softening by frictional heat, which can increase the
strength requirements by an order of magnitude. It is not
uncommon for the carbide tip to be torn from the steel
shank of commercial cutters and the shank near the tip to
be badly deformed. This suggests that conditions occur
that, on occasion, can exceed the 200,000 psi yield strength
of the common shank materials. The strength of the four
polymers and the zinc alloy are too low to hold carbide
tips during the cutting of coal.

Table 4.Number of impacts and ignitions for shank materials evaluated in this research (In order of likelihood of Ignition)

NICON 10-N+ = 10184340 AZ_—«7NI- «SON ZAQ7.Zn _ Polycarbonate resins Special
alloy 90Co carbon alloy tool.» -13Co.-«10Co.— alloy Lexan Lexan Lexan ARpoly-
steel _steel__stee! 141-500-3412 __ ethylene
Cutting speed,
sfpm:
400... 200" 320 908-315 310 348355 808810804804 ND
190" 311 307-301 909 308881 305 = 02ND ND ND
170* 304 306 300-304 308322 ND ND ND ND ND
159* —253* 304 = ND = 902,304.06 ND ND ND ND ND
ND ND 301 = ND 300 ND 202 ND ND ND ND ND
ND ND 144" =ND ND ND OND ND ND =ND ND ND
114" 307 313° 162" 150" 315314 810 8208135 304
108" 190" 150*147*# 137" 314810 ND 304 = NDsND ND
93* 153 131" S*112* 81408. ND ND =ND ND ND
se" 150", 118" 55* 96180" 129" ND ND ND ND ND
6or 192" o2* 56" 118306. 320 32565818820 333
s7* 190" 96" 53* ag" 237" = a7ak 07H (1S 307
see 96* ey 47*# 74" 230" 24st 307-332 810809 304
si* 66* 37*33* ge 2te* = ttt* 306. 82107808 ND
ND 63* NO ND ND 183" = 80303. 312, ND ND
ND ND ND ND ND 130 = 77* 304 307, = ND sND ND
Ignitions pertria: 1 0.69 087 073 062 043 0.40 00 00 00 00 00
ND Not determined.

NOTE.—Asterisk indicates ignition of gas mixture occurred.


Figure 1.—Frictional ignition chamber. Note: 6-in hydraulic
cylinder located outside explosion chamber (left-center).

Figure 2.Sandstone holding fixture and flywheel. Sandstone
block and shank material are in test position (lower center).
Note: 3-1/4-in hydraulic cylinder is located inside chamber
(upper center),

The sandstone block was secured to a steel-holding
table that could be moved radially, tangentially, or axially
to the flywheel. The table was advanced radially by a 6-in
bore hydraulic cylinder. A micrometering valve on the
cylinder head inlet port controlled the sandstone block
feed rate from 0 to 2 ipm (actual test feeds were set to
advance the sandstone toward the flywheel at 1 mil/rev).
The location of the 6-in cylinder projecting from the left
end of the FIC is shown in figure 1,

The sandstone holding table also had the capability to
be advanced tangential to the flywheel using the 3-1/4-in
hydraulic cylinder shown in figure 2, Axial motion to the
flywheel was accomplished by a manually operated screw
drive. The screw drive and 3-1/4-in cylinder were used to
position the sandstone so that four to six kerfs could be
made on each side of the sandstone block.

Pressure transducers were located at the side ports on
the head of the two hydraulic cylinders (6-in bore radial
feed and 3-1/4-in bore tangential motion), Pressure
measurements from the transducers were fed through sig-
nal conditioners to a digitizing oscilloscope and micro-
computer analyzing system where they were converted to
radial and tangential forces and stored on 5-1/4-in floppy
disks. Figure 3 shows the oscilloscope-microcomputer
analyzing system.

Figure 3.—Frictional ignition chamber with oscilloscope and
microcomputer analyzing system for determining radial and
tangential impact forces.


CONTENTS

Abstract
Introduction .
‘Acknowledgment
Experimental equipment and materials
Equipment ...........0seeeee ’
Materials .. .
Experimental procedures and conditions .
Procedures ....
Test conditions .
Results and discussion

Temperature .

Impacting forces
Conclusions .
References .
Appendix A. Fr ional ignition chamber operating procedures
Appendix B.—Frictional ignition data table

1, Frictional ignition chamber

2, Sandstone holding fixture and flywheel

3. Frictional ignition chamber with oscilloscope and microcomputer analyzing system for determining radial
and tangential impact forces..............

4. Configuration of sandstone and tool ...

5. Effect of speed on number of impacts to ignition of 7 vol pet natural gas-air mixture for steels
impacting sandstone ...... 0. sccsce cece ee eee teen nent eee e eee eee EAA ERR

6, Effect of speed on streak temperature of 7 vol pct natural gas-air mixture for steels impacting sandstone.

7. Effect of streak temperature on ignition of 7 vol pct natural gas-air mixture for steels impacting
sandstone

8. Effect of final radial force on ignition of 7 vol pct natural gas-air mixture for steels impacting sandstone .

9. Effect of final tangential force on ignition of 7 vol pct natural gas-air mixture for steels impacting

SANSOME eee eee e eee eee e eee EEE EEE EEE EE ee EE EEE EEE E EE EEE EEE EE
10. Effect of final radial force on streak temperature in 7 vol pet natural gas-air mixture for steels
impacting sandstone
11, Effect of final tangential force on streak temperature in 7 vol pet ‘natural gas-air mixture ‘for steel
impacting sandstone 0.0... .. 0c eeseeseeeeee eee e cece teeter tent eee e eee e tent eee eeeens
TABLES
1, Composition analysis of natural gas
2. Properties and descriptions of test shank materials
3. Compositions of nonpolymeric materials . . saws
4, Number of impacts and ignitions for shank materials evaluated in this research
5. Number of impacts and ignitions for shank materials cited in reference 13 . .
B-1, Frictional ignition data... 0.0.0... c sees esse eee eeeeee esses eee e essen eeees

Page

BR erermamnauuunannnne


10

15, Hartmann, I. Friction Ignition of Gas by Mining Machines,
BuMines IC 7727, 1955, 17 pp.

16, Blickensderfer, R.A. J. E. Kelley, D. K. Deardorff, and
M. I. Copeland. Testing of Coal Cutter Materials for Incendivity and
Radiance of Sparks. BuMines RI 7713, 1972, 17 pp.

17. Kelley, J. E,, and B. L. Faulkner. Ignitions in Mixtures of Coal
Dust, Air, and Methane From Abrasive Impacts of Hard Minerals With
Pneumatic Pipeline Steel. BuMines RI 8201, 1976, 19 pp.

18. Allsop, G., and R. V. Wheeler. Ignition of Firedamp by Pyrites,
During Coal-Cutting. Trans. Inst. Min. Eng. (London), v. 96, 1939,
pp. 310-316.

19. American Society for Metals. Metals Handbook, 8th e4,, v. 1.
Metals Park, OH, 1961, pp. 498.

20, Wigotsky, V. (ed.). Zine Casting Alloys Stand Tough. Design
Eng, v. 35, No. 5, May 1982, 4 pp.

21. G. E, Plastics Group,
sheets for Lexan regions (Pittsfield, MA) LEXAN Properties Guide
(CDC-662B), 3 pp.

22, Industrial Plastics, Inc, Product data sheets for UHMW products
(Washougal, WA), June 1983, 2 pp.

23, Roepke, W. W., and J. I. Voltz, Coal-Cutting Forces and Primary
Dust Generation Using Radial Gage Cutters, BuMines RI 8800, 1983,
2 pp.

2, Titman, H. A Review of Experiments on the Ignition of In-
flammable Gases by Frictional Sparking. ‘Trans. Min. Eng. (London),
¥. 115, 1955-56, pp. 536-556.



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Library of Congress Cataloging in Publication Data:

McDonald, L. Garner.
Frictional ignition of natural gas-air mixtures by alternative coal-cutter bit shank
materials / by L. Garner McDonald.
P. cm. — (Report of investigations; 9417)
Includes bibliographical references (p. 9).
Supt. of Docs. no.: I 28.23:9417.
1. Mine explosions~Prevention. 2. Coalbed methane—Combustion. 3. Coal-

cutting bits—Testing. 4. Friction. I. Title. I. Series: Report of investigations
(United States. Bureau of Mines); 9417.

TN23.U43_ [TN313] 622 s—de20 [622.82] 91-10788 + CIP



Report of Investigations 9417

Frictional Ignition of Natural Gas-Air Mixtures
by Alternative Coal-Cutter Bit Shank Materials

By L. Garner McDonald

UNITED STATES DEPARTMENT OF THE INTERIOR
Manuel Lujan, Jr., Secretary

BUREAU OF MINES
T S Ary, Director


1,000 I EL 2k 72

Mixed Xx Ignition region
2 region x xX x
900+ 7
2 Oo xx
ra
&
S 800+ vey 7
fi oO X 1 ease (Ignition)
x D2 cotes (ignition)
$ 70+ Goa qi 1 team (e eaten) |
E a © — 2 caves (no ignition)

No ignition region

600 in 1 1 1 n i in 1 1 J
1 8930 5070s si‘ «30

FINAL TANGENTIAL FORCE, Ib

Figure 11.—Effect of final tangential force on streak temper-
ature In 7 vol pet natural gas-alr mixture for steels impacting
sandstone.

Of the remaining materials in table 4, the NICON,
while surely strong enough, too readily causes ignitions at
all cutting speeds to be used as a coal-cutter material.
The 1018 carbon steel with a maximum yield strength of
only 54,000 is not strong enough to hold the carbide during
coal cutting. The 10Ni-90Co cast alloy causes some igni-
tions at the lowest cutting speed and is composed primarily
of the strategic and expensive metal cobalt. The A2 tool
steel is more expensive than 4130 or 4340 without provid-
ing any extension of tool life or improved safety from
reduced likelihood of ignition. The 87Ni-13Co and 90Ni-
10Co alloys are shown to be less likely to cause an ignition
than any of the steels in table 4, This improved safety of
nickel-based alloys is confirmed in table 5 obtained from
the data of Blickensderfer, Deardorff, and Kelley (13).
The nickel-based alloy Rene 41 was shown to be less likely
to cause an ignition than the three iron-based alloys—
Armco Iron, 4130 steel, and precipitation hardening stain-
less steel with composition of 17 Cr and 4 Ni (13).

CUTTING SPEED

Many researchers have reported that as cutting speed
increases, the ease of ignition increases (5, 11, 14, 24), In
this research, as the speed of the steels increased, the
likelihood of ignition increased from 7 pet at 400 sfpm, to
92 pet at 600 sfpm, and 100 pet at 900 sfpm. Furthermore,
the number of impacts required to get an ignition dropped
as speed was increased. Figure 5 shows this drop in im-
pacts as a function of speed. To get natural gas ignition
at 900 sfpm generally required about 69 impacts; while
at 600 sfpm the requirement was 137 impacts; and by
400 sfpm the ignition of natural gas required 292 impacts.

There is not a lot of information in the literature about
the relationship between speed and temperature, but it has
been proposed that the increase in ignition probability with

speed is because of an increase in area of the hot streak
exposed to the gas, not because of higher temperature
(14). The current research found that as speed increased,
temperature increased (fig. 6). Thus the increasing likeli-
hood of ignition with increasing speed is caused not only
by the increased hot streak area, but also by an increase in
temperature of the hot streak,

‘Table 5.—Number of impacts and ignitions for shank
materials cited in reference 13

Feed, 4130 17-4pH Amco Rene
mils per — alloy _—stainiess Fe 4
impact steel__ steel
Cutting speed,
sfpm:
WO... 08 308 326 250 300
3 190 130 137 137
450 ee 08 178* 2 333 w2
3 161 7 131 50"
6 61 60 61 115
12 » KJ 31 26*
600 ...... 08 175* 166" 79" 300
3 154* 126 126 124
6 or 24* 73 4a"
12 30" 16" 32" c-J
750.2... 08 172" 6 170* 310
3 165 92 120* 115*
6 a 20 75 38*
12 14* 23 32" 2"
900... 08 76* 93* 125* 5
3 ‘55* 86 108* 128
6 63 14* 48 40"
12 "1" * 24e 2a
1100 ..... 08 70* 103* 143* 305
3 132* 74 ov 136
6 28* 18* 53 60
12 et a 15* 10*
Ignitions per trial: 073° 050 050 0.41

NOTE.—Asterisk indicates ignition of gas mixture occurred.

TEMPERATURE

A definite relationship was found between ignition oc-
currence and hot streak temperature (fig. 7). No ignitions
occurred below hot streak temperatures of 860°C. Powell
(6 reported a minimum temperature of 640° C for a non-
friction heated surface to cause methane-air mixture ig-
nition. Blickensderfer (14) found maximum temperature
for friction caused hot streaks to be 1,200°-1,400° C at
2 ms after impact, but the hot streak rapidly cooled to a
maximum of 800° C by 40 msec after impact. Naylor and
Wheeler (7) showed that there is a "lag time" between
getting a surface to a specific temperature and the ig-
nition of methane-air mixtures, also the lower the specific
temperature, the longer the “lag time." The most likely
explanation of why there were no ignitions between the
860° C of this research and the minimum temperature of


il

APPENDIX A.—FRICTIONAL IGNITION CHAMBER OPERATING PROCEDURES

Normal operating sequence for the frictional ignition
chamber:

1, Sandstone was loaded into the holding fixture. All
sandstone was held in a drying oven at 140° C until ready
for loading.

2. Shank material sample was weighed and loaded into
the flywheel,

3. Ignition chamber was sealed by closing the top port
and installing the 1 mil mylar rupture diaphragm.

4. Natural gas was charged into the chamber until the
gas-air mixture was 7 vol pct natural gas. Natural gas vol-
ume was measured by a wet test (flow) meter. As the gas
entered at the top of the chamber, a small vent was open-
ed at the bottom to allow air to escape, thereby maintain-
ing ambient air pressure in the chamber. The vent was
closed when gas infusion was completed.

5. Gas and air were mixed thoroughly in the chamber
with a spark-resistant safety fan for a minimum mixing
time of 5 min.

6. The flywheel hydraulics were engaged and the
wheel set to the desired speed by adjusting the pump
flow.

7, The flywheel was disengaged and all accumulators
charged,

8. The sandstone radial feed rate was set to provide
1 mil per impact.

9. The oscilloscope-microcomputer was engaged for
acquisition of cutting force data.
10. The flywheel was engaged again, and the sandstone
was moved radially toward the flywheel.
11. Ifignition did occur within 300 impacts, the test was
terminated and pressurized air vented into the chamber to
expel all combustion products before the top port was

12. If ignition did not occur within 300 impacts, the
flywheel was stopped and a spark plug was energized to ig-
nite the air-gas mixture. Pressurized air was vented into
the chamber to expel all combustion products. For safety
teasons, the number of impacts was limited to just over
300, The test samples extended 0.375 in from the flywheel
and, at 1 mil per impact, 300 impacts left a safe operating
distance between the sandstone and the flywheel.

13. The test sample was removed; sample and sand-
stone were examined for amount and type of smears; test
sample was then cleaned and weighed, and the kerf chord
length on the sandstone was measured,

14, Throughout the run, two observers noted the color
of the hot streak on the sandstone just behind the test
sample. If ignition occurred, then the color of that impact
was logged. If no ignition occurred, then the color was
recorded at impact number 300.