The instrument
in question — the RVT
-electronic tachometer —
is a radiowave
mneasuring instrument connected with the
object through
the microwave-band
elec-
Iromagnetic field.
important,
spreads
over
the
machines’
natural waveguiding elements such as the
engine
exhaust
pipe
to
the
turbosuper-
charger rotor, to the valves, etc.
All
this gives
the RVT instrument con-
siderable advantages over stroboscopes.
operator reduces the instrument’s readinc
to
ordinary
units
of measurement.
If
r
tational speed fluctuates more than thre
times
per
second,
the
automatic
spec
change tracking system goes on.
Radio Methods
More Convenient
Than Stroboscopic Ones
The RVT radiowave tachometer meas-
ures the
rotational parameters
of various
machine parts from any distances, practi-
cally
in any requisite frequency range, no
matter
what
materials
these
parts
are
made
of, and
irrespective
of
their shape
and
size. Electromagnetic energy passes
through dielectric walls and, what’s no less
Adequate Accuracy
The
radiotachometer
measures
ro-
tational speed with an accuracy to within
±0.017 s'
.
If the rotor carries an impeller
or a pinion, measurement accuracy can be
increased K times, where K
is the number
of blades or teeth. All
it takes
is a no less
than 3-mm blade or tooth pitch.
By
dialling
the number (from
to
99)
equal
to
that
of
blades,
teeth and
other
such
elements
of
a
rotating
object,
the
Many Uses
The radiowave principle of measureme
extends the range of the RVT tachometer
application considerably.
It
is suitable
f
measuring surface vibrations accurately
within 0.1
Hz, as well as running speed
cars,
for instance, from as
far as 600
away.
Combined with an oscillograph or with
recorder, the RVT instrument can be us>
for
measuring
relative
amplitudes
ai
phases
of
various
objects’
surface
Approved For Release 2001/03/07
: CIA-RDP96-00787R000500180031-6
BASIC SPECIFICATIONS OF THE RVT RADIOTACHOMETER
Measurement ranges:
rotational speed, s-1
vibration, Hz
1,6-104
— 2-1
Measurement ranges
Rotational speed, s—
Vibration frequency, Hz
1-10 1— 1,6-1
1,6-102— 1,6-103
1,6-1
3— 1,6-1
MO1 -*™5
Error:
S’**
±.0.017
JtO.17
_±1.7
—
Hz
—
—
—
±0.1
Minimal measure-
rement time, s
0.3
0.5
3.0
—
Automatic frequency change speed tracking range, %
+ 300 to —70
—
Maximum distance to object, m
Linear movement speed measurement:
speed, km/h
20—200
error, %
±1
Power consumption, W
Supply voltage, V:
a.c. (50 or 400 Hz)
220
d.c
12 or 24
Mass, kg
orations, as well as for periodic structure in-
tegrity checks. Such checks can reveal a
broken pinion tooth or a mechanical flaw in
a
turbocompressor
rotor
blade,
for
in-
stance.
fhe RVT Succeeds
Where Stroboscopic and
induction
Tachometers Fail
A typical application of the RVT radiota-
chometer is measuring the rotational speed
of
the
IC-engine’s
supercharger
com-
oressor. This is a very important job as any
deviation of the turbosupercharger’s work
rom
normal
impairs
the
technical
and
aconomic
indices
of
the
engines.
Such
measurements are essential to the devel-
opment and operation of aircraft engines,
oentrifuges,
turbines
of
various
kinds,
electric
motors (iow-power
ones,
in
par-
icular),
gyroscopes,
etc.
The RVT radiotachometer cuts down to a
hird
or even a
fifth
the time
it takes
to
neasure the rotational speed of the basic
dements of an internal combustion engine,
or instance. Measurement speed
is 10 to
times
higher
as compared
with
the
;troboscopic
method.
The RVT
radio-ta-
chometer measures the r.p.m. of the cen-
trifugal oil cleaner rotor in 6—8 sec, and of
the turbocompressor rotor,
in 10— 15 sec.
A Hew Circuit
for Measuring
the Reflected Signal
Modulation Spectrum
In
measuring
turbocompressor
rotor
r.p.m., a typical reflected signal modulation
spectrum
contains,
apart
from
the
fun-
damental harmonic the frequency of which
. equals the rotor rotational speed, a number
of harmonics with different frequencies —
components connected with the operation
of the turbine, with valve and engine piston
movements. The amplitude distribution
of
the harmonics depends,
in general, on the
incidence angle of the microwave
signal,
on the distance of its travel, on the shape of
the object, and other factors. Sometimes a
reflected signal
is superimposed by modu-
lations caused by the movement of several
components,
although
only
one
com-
ponent’s
rotational speed
is
to be meas-
ured.
The way out was offered by a transceiv-
ing aerial whose designing and right posi-
tioning relative to the rotating object invol-
ved a number of technical problems. We
have devised a method of filtering the
rt
fleeted signal modulation spectrum, of
fir
ding the requisite harmonic and of trac'kin
it automatically.
Measurement results are brought out
a four-digit indicator. An output to an an;
logue recorder is provided. As a result, th
instrument can be used for automatic cor
trol
of
most
various
objects'
rotation;
speed change dynamics.
The use of standard
microcircuits an
opto-isolators has simplified the instrumer
to a maximum.
No special
skills are required
for ope
ating an RVT tachometer.
Approved For Release 2001/03/07
: CIA-RDP96-00787R000500180031-6
/O009 3?
T SPEEDS
A/.M
F UP TO FIVE METERS PER SECOND
SHKARLET.
tt.C'-
nd. Sc. (TechJt—
ititute of/lntroscopy /
flO^r
16 new
ectromagnetoacousfical
MA) thickness gauges are
3e from the shortcomings
the priorart gauges.
The
M instruments are
mtactiess, they measure
e thickness of roiled stock
: any travel speed with a
gh accuracy and have a
imber of other important
ivantages.
The new method consists, essentially, in
(citing an
ultrasonic
oscillation
pulse
in
e metal article being rolled. The thickness
the article
is judged by the time
it takes
e pulse to pass through
it, bounce off the
oposite surface and return to the sensor
3 a reflected signal.
T iS
High Level
of Interference
Suppression
If the distance between the surface of
the article under test and the inductor/sen-
sor changes, that has no effect at all on the
accuracy
of
the EMA
instrument’s
oper-
ation. This is an important advantage of the
new
thickness gauge
over
the
ordinary
magnetic
and
electromagnetic
thickness
gauges.
The
neutralisation
principle
is used
to
prevent the EMA instrument from reacting
to any chance defects of the surface: the
“fault” signal is given only in case the rolled
stock thickness is indicated to deviate from
normal for five times at a stretch.
Finally, the instrument’s circuit provides
for suppressing the interference concomi-
tant
to
acoustical
wave
propagation
in
metal.
No matter how curved the surface of the
article under test may be,
this causes no
measurement
error. As a
result, the new
instrument
is best suitable for testing pipe
walls as well as sheet metal thickness.
Rolling Mill Operators’
Work Made Easier
The EMA thickness gauge gives accu-
rate
indications
of
positive and
negative
deviations
of
the
rolled
stock
thickness
from normal. The deviation
limits are
set
from
the
instrument’s
control
panel. The
EMA thickness gauge can be fitted into the
rolling
mill stand control loop to make the
operator’s work
easier. The EMA
instru-
ment can be connected with an automatic
device indicating,
in one way or other, any
faults in the rolled stock.
The new instrument has been patented
in the USA, the FRG, Japan and France.
leasurements
ontactless
The ultrasonic pulse is excited by means
f a pulsed electromagnetic field lasting for
oout 0.5 [xsec. The pulse oscillator induc-
>r
is
in a permanent magnetic field which
ermeates the article under test. Eddy cur-
3nts induced by the pulsed electromagne-
c field interact with the permanent mag-
etic
field and
thus
excite an
ultrasonic
/ave inside the material being tested. The
'ave extends
in depth, reaches the oppo-
ite surface and comes back causing
vi-
rations on the surface which generated this
ulse. The vibrating metal in the permanent
lagnetic field excites eddy currents which
ire picked up by the inductor now playing
he role of a sensor.
As we
see,
the
ultrasonic pulse
is
in-
iuced, and the bounced-off signal picked
ip,
without any
contact
with
the
article
inder test.
ligh Measurement Speed
ind Accuracy
Pulse
repetition
frequency
is
high
enough —
about
100
Hz.
Therefore,
neasurements can be made
at
a
rolled
stock travel speed
of up to 5 m/sec. The
oasic error does not exceed 2% over the
.hickness range of 3 to 15 mm, with scale
inearity guaranteed.
Schematic Diagram of Thickness Gauge
- Magnetic circuit
• Pole piece
• Supply source
Excitation coil
• Constant magnetic field coil
- To detector
• Pick-up coll
. Switch
• Tube
.......
- Capacitor supply source
Approved For Release 2001/03/07
: CIA-RDP96-00787R000500180031-6
FOURTEEN NEW
FLAW DETECTORS
V. KLfU
v- v- KlJUYEV. Dr. Sc. (Tech.),
General
Director,
Spektr
Research
and
Production
Amalgamation,
-
O-S. SEMENOV
CandTscT(Tech.)7\aborator.
Chief, Institute off Introscopy
j
l.SBMEWt/
i. 1*!!* AttaftYuMn«.nm, .j, MX
-to &K 9009 32
me
instruments
which
de-
tect flaws
in
ferrous and non-
ferrous
metal
articles
by
the
eddy current or constant mag-
netic field method keep improv-
ing.
In this article we dwell on
new flaw detectors using these
methods.
Many
of
these
in-
struments have no parallels
in
world practice, and others are
much simpler and more reliable
than
the
prior-art
ones.
They
offer new ways of checking for
higher product quality.
The VD Flaw Detectors
for Checking
Quantity-Produced
Articles
These
instruments
check
wire, pipes, round billets, round
and hexahedral rods from 0.05
to 200 mm
in
diameter,
and
: square
billets from 50x50
to
250x250 mm
in cross section
for surface defects by the eddy
current
method. A
distinctive
feature of this method
is that
it
i brings equally accurate results
; for
ferrous
and
non-ferrous
: metals. The article under test is
: Put
either
through
a
ring
on
which
transducers
rotate,
or
through
a
stationary
trans-
ducer.
As compared with the prior-
art flaw detectors with rotating
transducers, the instruments of
the VD series are more reliable,
simpler
in design and take less
time to maintain. Testing pipes
and rods with a curvature of up
Ft c
Wft
to 5 mm per one meter of length
is no problem at
all. Variations
in
the clearance between
the
transducer
and
the
surface
under test within ±2 mm have
no effect on the flaw detector’s
sensitivity, as distinct from the
prior-art
models.
Hence
the
possibility
to
test oval-shaped
as well as round articles.
The
VD-40N,
VD-41N,
VD-43N
and VD-60N
flaw
de-
tectors are fitted with a facility
pinpointing
the
flaws
in
the
rolled articles under
test. They
provide
for sorting the articles
into
three
categories:
“OK",
“Reclaimable
spoilage”,
“Re-
ject”.
The VD-30P flaw detector
can by right be described as
universal.
It
gives
invariably
accurate
indications
over
a
wide range
of diameters,
con-
figurations
and
metal
grades
thanks to
its easy-to-detach
in-
terchangeable
transdi
with
the
appropriate
dian
of the through hole and to
cial
filters.
Indications
are
livered to counters, a
rapic
tion automatic recorder
a;
computer.
The
VD-10P
and
VD
flaw detectors test wire n
of
any
material
with
ele<
conductivity ranging from
60 Mohm/m. The result ana:
unit
indicates
the
length
number of the inadequate
<
lity sections and
their loca
in
the wire
coil. The same
formation
is
delivered
to
printer and to the programm
unit which controls the grac
assembly
of
the
autom
machine
making
various
t
cles out of tested wire.
The design of these flaw
tectors’
transducers
me
special
mention.
Usu
transducers
intended
for
t
BASIC SPECIFICATIONS OF THE VD-SERIES FLAW DETECTORS
Detector model
VD— 10P
VD— 20P
VD— 30P
VD—40N
VD— 41
N
VD—43N
VD— 60N
Transducer type
Stationary
Rotary
Object configuration
round
round
round
annular
hexahedral
round or annular
square
Diameter, side length, mm
0,05—0,2
0,2-0,
1—47
30—120
10—50
100—200
50—250
Minimum size of flaw
detected, in depth:
mm
% of diameter
1-2*
0.2-0.5**
0.5***
j Maximum object travel speed, m/s
5.0
5.0
3.0
1.5
1.0
depending on diameter;
less for sized articles, more for hotl-rolled articles;***
including those on edges.
Approved For Release 2001/03/07
: CIA-RDP96-00787R000500180031-6
V
stationary
fiaw
sctors
have
proved
efficient means
of
*d stock testing
(1).
table
flaw detectors
very convenient
for
ting
various
items
[t on the workbench,
ng the assembly and
mting
of
large-size
sles
and
construc-
s (2).
BASIC SPECIFICATIONS OF THE MD-SERIES FLAW DETECTORS
Detector model
MD-10F
MD-901
MD-1001
ducer tvpe
Rotary
Rotary and stationary
Stationary
under test....
Pipe
—
__
Sheet
Hot-rolled strip
dimensions, mm:
neter
thickness
30— 160
up to 12
—
h
—
_
:ness
560—2,500
^
500
0.4— 3.0
1-6
detectable crack:
—
, mm
. % of metal
0.2 and over
—
ness
—
travel
3, m/s
up to 3
0.5— 5.0
0.5—10.0
—
.
.
—I
indicator
is
an
j
Approved For Release 2001/03/07
: CIA-RDP96-00787R0005001 8003-1 -6
ting thin wire are made by hand
The
new
transducers
do
not
require
handwound
coils
and
are much
longer
lasting
than
the prior-art ones.
The MD Flaw Detectors
for Testing Steel
Sheets and Pipes
In many cases the eddy cur-
rent method proves less effec-
tive than that of constant mag-
netic field. This is true of testing
thick
rolled
sheets
and
pipes
when inner as well as surface
flaws are to be detected. Such
sheets and pipes can best be
tested,
at the
rate of their ma-
nufacture, with the MD flaw de-
tectors depending on constant
magnetic
field
for
their
oper-
ation.
The
MD-10F
flaw
detector
comes complete
with
devices
for magnetizing a pipe perpen-
dicular
to
its
axis
(circularly)
and
for
rotating
transducers
around
a
pipe. An
electronic
system
processes
the
signals,
coming in from the transducers
and delivers commands to
tjpe
sorting mechanism,
with
data
on the outer and inner flaws of
the
pipes
arriving
separately.
The MD-10F flaw detector has a
self-checking unit which signals
any mechanical failure and any
disturbance of control settings.
The MD-901 flaw detector is
intended
for
testing
rolled
sheets
in
crosswise
and
lengthwise
metal
cutting
lines,
it sorts out good sheets
from faulty ones and indicates
the location of flaws.
Magnetic field dispersions
in
the
flaw areas
are
picked up
both by stationary transducers
and
those
rotating
parallel
to
the metal sheet. Depending on
the rolled stock width there can
be one transducer or several of
them. A special electronic
cir-
cuit
precludes
mistakes
con-
nected
with
changes
in
clea-
rance between the transducers
and
the
metal
article
being
tested.
The MD-1001 welded
joint
jndjcajor^ Js_.gr]
^instrument
which
delivers
signals
to
the
automatic system
of a contin-
uous
steel
sheet
rolling
mill.
The
information
it
furnishes
about the joint helps adjust roll-
ing
speed
and
prevent
metal
strip breakage.
The instrument can
also be
used
in
continuous
pickling
lines,
automatic
weld
cut-out
machines and other such units.
An
important
distinguishing
feature of the MD-1001 indicator
is its high noise immunity which
precludes
the
generation
of
spurious
signals. An ingenious
layout of the transducers and a
new
method
of
information
processing make
it possible to
single out the weld’s magnetic
field
only,
"ignoring"
single
or
group
flaws.
The
instrument
comes complete
with a sheet
magnetizing device.
Portable Universal
Flaw Detectors
for Transport and
Heavy Engineering
Surface defects — cracks,
nair
seams,
laps
and
other
defects of ferrous and non-fer-
rous metals on planes 30 mm
and more
in diameter are de-
leted
quickly and
accurately
ay
the VD-20N-D
instrument.
: itted out with a
rotary
trans-
fucer and using the eddy cur-
ent method,
it finds flaws from
12 mm deep and 10 mm long
wen on
articles with an
elec-
rically non-conductive coating
jp to
1 mm thick. The flaw de-
ector is equipped with a defect
ndicator
lamp. A more
accu-
ate information about the sur-
ace being
tested can be
ob-
ained from the screen of a ca-
hode-ray
tube. As
the
trans-
lucer
is moved over the metal
urface by hand, the instrument
as a special electronic circuit
a
preclude
spurious
signals
nd
misses
which
might
be
aused
by
variations
in
the
learance
between
the
trans-
ucer
and
the
metal
being
>sted.
The MD-40K flaw detector
is
ary convenient
for checking
the quality of coarse threads
of steel components like studs,
rods,
bolts and hooks. The
in-
strument
is
fitted with a set of
transducers
which
make
it
possible to check on threads 30
mm and over (pitch from 1.5 to
12 mm). The instrument detects
flaws more than 0.5 mm deep
and
over
10 mm
long.
The
transducer
is moved consecu-
tively along the thread fillets for
the
purpose.
The
procedure
can be
easily
mechanized,
if
necessary.
The MD-41K
flaw
detector
reveals fatigue cracks in gear
transmissions
with
pitches
of 4.5 to 8 made of ferromag-
netic
materials.
This
instru-
ment, with
its electronic circuit
similar to that
of the MD-40K,
comes complete with a set of
transducers for checking gears
over
the
entire
above-
mentioned range of pitches. A
transducer
is placed
in a gear
tooth space
by
hand. An
ad-
vantage
of
this
instrument
is
that with
it gear wheels can be
tested without the gear
trans-
mission being taken apart be-
cause there
is no need for any
special preparation of the
arti-
cles under test. The instrument
detects flaws more than 2 mm
deep and over 10 mm long.
The
magnetographic
method
of
testing
welded
joints in pipelines up to 1,420
mm in diameter, with pipe walls
up to 20 mm thick is more con-
venient — and much safer for
the servicing personnel — than
the
radiographic
one.
The
magnetographic
method
con-
sists
in placing a piece or ord-
inary ferromagnetic tape 35 or
50.8 mm wide on
a
joint and
recording
the
flaws’ magnetic
field
on
it
by
passing
a
per-
manent magnet along the joint.
The new UV-30G flaw detec-
tor
reads
the
information
re-
corded on tape — the leakage
fields of the weld’s flaws — and
reproduces
it on the screen
ol
the cathode-ray tube. Besides,
test
results
are
recorded
on
paper tape. This method of tes-
ting
is 5-7 times more efficient
than the X-ray or radioisotopic
ones.
UP TO A THOUSAND
INTEGRATED CIRCUITS
A new semi-automatic
solder-
ing device is 3 to 10 times more
efficient
than
conventional
equipment.
Add to this the excellent qua-
lity of soldered joints, the opti-
mum conditions of solder mel-
ting,
extraordinary
soldering
efficiency
(it takes a mere 0.3
sec to solder one lead), the ab-
sence
of
solder
“jumpers”
between leads, the light weight
and compact size.
applies
precisely
dosed-os
amounts of solder to their enc.
—
all
in one working stroke!
The
semi-automatic
solderir.
device and
the
integrated
ci
cuit
preparation
facility
hav
been patented
in the USA,
th
FRG,
Great
Britain,
France
Japan and other countries.
nZAAtt
Another merit of the device is
a simple and efficient facility to
prepare
microcircuits
for
ass-
embly.
It
bends
microcircuit
leads,
trims them
to
size and
*Sijr
l
**!•#*•
£«'•
|
Esa
e®
. y .
\
4:
BASIC SPECIFICATIONS OF THE SEMI-AUTOMATIC
DEVICE FOR SOLDERING INTEGRATED CIRCUITS
AND FACILITIES FOR PREPARING THEM
Semi-automatic device:
Efficiency, Integrated circuits per hour
UP ,0
Soldering temperature, 0°
about sou
Temperature maintenance accuracy, 0° C
J?
Maximum printed card size, mm
*10 x
Overall dimensions of the semi-automatic
soldering device, mm..
x 220
Mass, kg
Power consumption, W.
Integrated circuit preparation facility:
Press effort,
Rod stroke, mm
Solder wire diameter, mm....
Overall dimensions of facility, mm....
Mass,
kg.,
700
0.3— 0.6
150 x CO
x 100
Approved For Release 2001/03/07
: CIA-RDP96-00787R000500180031-6
W ULTRASONIC
R OBSTETRICS
KOROLYOV ,
(Tech.),
of Department,
ite of Introscopy
early diagnosis problem
/ed by various methods,
masonic method (UZ) be-
rtainly the most suitable
)r use
in
obstetrics and
oology.
ew instrument, Malysh
DM),
has been
devel-
specially
for
obstetri-
Its ultrasonic converter
continuous
ultrasonic
tions
to
the
patient's
irough a layer of contact
The
signals,
reflected
internal
structures,
are
up by the converter, with
quency of the oscillations
ed
from
moving
struc-
'the
heart,
blood
vessel
etc.) differing from that of
dilations
reflected from
ary structures (the Dop-
: ect). As distinct from the
;copic
methods,
the
ul-
c converter
is not affec-
usual acoustic noises
in
se.
design
of
the
amplifier
etector
of
the
Doppler
icy
signal
ensures
the
ioise ratio necessary for
sending minimum-power
ultra-
sonic
signals
to
the
patient's
body.
Radiation
intensity does
not exceed 10 MW/cm
, which
totally
precludes
any
harmful
effects on the foetus.
The Malysh can be used for
diagnosing
palpitation
and
cardiac disorders
in the foetus
and for localizing the placenta.
Palpitation
is detected as early
as
in
the
8th-1 Oth
week
of
pregnancy. Thanks to the con-
verter fitted with focussing len-
ses of a special design, the
lo-
cality
of the moving
structure
control
has
been
sharpened,
and
their
differentiation
im-
proved.
In
these
character-
BASIC SPECIFICATIONS OF DEVICES FOR
ULTRASONIC MEDICAL INVESTIGATIONS
Malych
Ekran
area under examination, mm.
Any
400 x 300
1 resolution, mm:
depth
2,5
rntal
4,0
ing frequency, MHz
3,0
2,5
storage time, min
—
consumption, W
1,5
500
supply
From batteries
From 220 V mains
250
Left — the Malysh por-
table
instrument;
right
—
the Ekran stationary
tomograph with two
di-
splay
units
(screen
sizes: 23 and 50 cm
in
diagonal).
istics, the Malysh
is superior to
the
prior-art instruments
of
its
kind.
The Ekran (UI-20EM) pulse
ultrasonic tomograph
is of a
still
wider
diagnostic
lati-
tude.
It shows sectional roent-
genograms
of
internal
organs
on a display unit screen.
Upon
being
processed,
the
echo
signal
proceeds
to
the
memory unit where an image is
formed by scanning. A vidicon
is used as a memory
cell;
in-
formation about the converter’s
co-ordinates and the
reflected
pulse amplitude
is delivered to
the
intermediate
picture
tube.
The
final signal shaped on the
vidicon
target appears on
the
videomonitor screen as a
half-
tone
image.
This mode
of
to-
mograph
operation
is
usually
referred to as the “B” mode.
Besides,
the image can be
formed
in
the
“A”
and
“M”
modes.
In the former mode, the sig-
nal is formed on the screen only
along the
line scanned by the
ultrasonic
converter
at
the
moment. On the horizontal, the
visual
display
unit
screen
shows
the
value
of
the echo
pulse, and on the vertical — the
distance
inside the body from
the converter’s point of contact
with
the
skin.
This method
is
commonly used
in encephalo-
graphy
to
study
brain
struc-
tures.
What the “M” and “A” modes
have in common
is the immobi-
lity of the converter. The differ-
ence between the modes is that
in the "M" mode the echo am-
plitude shows
as
bright
lumi-
nance
in the appropriate point
of
the
screen, and
the
ampli-
tude of
this or that structure’s
movement — as a “hump"
ris-
ing
over
the scan
trace.
This
mode
is used chiefly
in cardio-
logy for examining heart valves
and walls.
Two visual display units with
23 and 50 cm screens
(diag.)
broaden the sphere of the
Ek-
ran
device’s
application
con-
siderably.
In
particular,
it
is
used for diagnosing kidney,
liv-
er and other troubles, localizing
stones,
tumours
and
inflam-
mations.
It enables oncologists
to determine the size and posi-
tion
of metastases more con-
fidently.
A
distinguishing
feature
of
the Ekran device
is
its conver-
ter of a new design which en-
sures
high pulse
resolution
of
the device.
Approved For Release 2001/03/07
: CIA-RDP96-00787R000500180031-6