CONTROL OF THE THICKNESS OF ELECTROPLATED COATINGS BY AN ELECTRICAL METHOD

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP80-00809A000700030132-0
• Release Decision: RIPPUB
• Original Classification: R
• Document Page Count: 4
• Document Creation Date: December 22, 2016
• Document Release Date: October 17, 2011
• Sequence Number: 132
• Publication Date: November 17, 1951
• Content Type: REPORT

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r 50X1-HUM
CLASSIFICATION
CENTRAL INTELLIGENCE AGENCY
INFORMATION FROM
FOREIGN DOCUMENTS OR RADIO BROADCASTS
COUNTRY USSR
SUBJECT Scientific - Metals, testing
HOW
PUBLISHED Monthly periodical
WHERE
PUBLISHED Moscow
DATE
PUBLISHED Dec 1950
LANGUAGE
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CDrI/~/~G,UT/RL
REPORT
CD NO.
DATE OF
DATE DIST. ?1 Nov 1951
NO. OF PAGES 4
SUPPLEMENT TO
REPORT NO.
THIS IS UNEVALUATED INFORMATION
S. S. Palley
B. I. Kreps
Figures referred to are appended]
Realization of the control of the thickness of electroplated coatings is of
considerable significance.
The so-called drop method of control is in wide use at present.
The shortcomings of this method are: the necessity of having a number of
solvents for each type of coating, the length of the test, spoilage of the
surface being stulied,and the high degree of error in testing relative to the
accuracy of calculating the time of action of the drop, accuracy of preparing
a solvent of determined concentration, the temperature of the surrounding
medium, and other factors. All this may lead to an error of 100%, particularly
in the testing of coatings of less than 5fc-
Other methods for determining the thickness of coatings (gravimetric and
optical) are purely laboratory methods and can not be recommended for mass
.ont^ol use.
Magnetic thickness gages, whose principle of action is based on measure-
ment of the force pulling a permanent magnet from a ferromagnetic piece with
a nonmagnetic coating, are little sensitive to thin coatings.
Other devices, based on the measurement of secondary emf of a transformer
with an open magnetic circuit in which the resistance of the magnetic conductor
varies relative to the thickness of the nonmagnetic gap, i.e., the electro-
plated coating, also are not in widespread use. Experimental models of these
devices demonstrated low sensitivity to very thin coatings. In addition, the
devices are designed only for measuring coatings on parts made of ferromagnetic
materials and having a certain configuration.
NSBB
FBI
DISTRIBUTION
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The measurement of coating thickness with the aid of high-frequency eddy
currents is based on the different specific electrical conductivities of the
coating metal and the base metal.
If a bridge circuit is used containing the pure coating metal in one arm
and the part, coated with the same metal, in the other arm, then by selecting
the necessary supply frequency of the circuit and varying it evenly, the moment
at which the circuit balance is distributed may be observed.
The depth of eddy current penetration depends on the frequency; therefore,
while the depth of penetration into the retal is small, the eddy currents in
both arms are propagated in the metal of the coating and the circuit remains
balanced. The depth of penetration is disturbed as the frequency is changed.
The circuit balance is disturbed at some frequency, and it then becomes pos-
sible to judge the thickness of the coating layer. Apparatus operating on
this principle is quite complex and there are no industrial models of such
devices.
The authorshave developed an electromagnetic thickness gage, Type ZTMP-48,
based on the secondary-emf-measurement principle and using a control plate.
The apparatus facilitates highly accurate determination of any thickness of a
coating (except nickel) from 2 to 60/t..
Figure 1 shows the circuit diagram of the apparatus. The sensitive ele-
ment of the device -- the transmitting element D -- is a transformer with an
open magnetic circuit and, consequently, a variable transformation ratio dur-
ing measurement. The magnetic circuit of the transformer-transmitting element
makes contact with the ferromagnetic part, 1. The thickness of the nonmagnetic
coating, 2, on this part determines the resistance of the entire magnetic
circuit.
The value of the magnetic resistance of the coating layer is quite large
in comparison with the resistance of the magnetic materials.
Mere measurement of the transmitting element's secondary emf does not
give sufficient sensitivity; therefore, a differential measuring circuit 13
used. The secondary voltage of the transmitting element is rectified on the
Graetz bridge, M2, using copper-oxide rectifiers, and is connected so as to
oppose the voltage rectified on bridge, Ml. The galvanometer G measures the
difference in these voltages and is graduated directly in microns of thickness
of the electroplated coating. The indicator has two scales, one up to 35,ca
and the other from 30 to 60A
The switch, P, is included in the circuit for changeover to measurement
on the second scale. The switch disconnects shunt resistors Sh1 and Sh2 of
the indicator, increasing its sensitivity, and alters the resistance of the
rheostat, R4, so that the null point is shifted sharply to the left and the
base position of the needle is at 30,,.
To reduce the effect of circuit voltage fluctuations on accuracy of
measurement, a ballast resistor, b, is included in the circuit. The ballast
resistor stabilizes the voltage within *- 20% of the fluctuations on the
primary side. The indicator is a needle device with a sensitivity of 100,&+..a
on the scale. The entire circuit is supplied from a 220-v ac line.
The variable transformation ratio, which changes linearly with the thick-
ness of the coating, is, in absolute value, a complex function of the value of
the gap, geometrical configuration, dimensions of the magnetic circuit, and the
degree of saturation of the iron.
The value of the secondary voltage may be established experimentally. The
magnetic circuit shown in Figure 2 gives optimum sensitivity and has the ad-
vantage of small size.
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To be axle to use the apparatus for measuring any type of coating (except
nickel) on any metal, a method involving indirect measurement with the use of
a control plate is employed. The possibilities for application are thus extended
beyond ferromagnetic materials alone.
The control plate ie a 40-mm square, 4-5 mm thick, with a well-finished
surface. The material used for the control plate may be any untreated steel.
There is an opening in the upper part of the plate for a rack.
The control plate is placed in the electroplating bath along with a batch
of production parts.
As is known, the thickness of the coating does not depend on the material
in the parts being covered;, nor, in most cases, does the thickness depend
on the form of the parts. By carrying out measurements on the control plate
it is possible to find out the thickness of the coating on the production
parts. The control plate must be placed to the bath under exactly the same
conditions as the production parts.
To reduce error in the apparatus, the measuring plane of the transmitting
element and the surface of the control plate are thoroughly processed, since
rough places in the surfaces will prevent the magnetic circuit of the trans-
mitting clement from lying flush against the plane of the plate. This would
be equivalent to increasing the coating layer. To assure the desired quality
of the measuring plane of the transmitting element, the surface of the plane
is not finished until after the element has been completely assembled.
The graduation, and the testing of the operation of the apparatus, is
done by measuring the thickness of the control plate on an optimeter before
and after coating. Half the difference between these readings gives the true
value of the coating layer.
The control plates are used for an unlimited time, since any coatings,
after their thickness has been determined, can be removed galvanically. To
avoid production bottlenecks which might be caused by a lack of control plates,
50-100 plates should be prepared for each apparatus.
Measurement error on the apparatus does not exceed 2,u.. Thicknesses
from 2 to 60,u can be measured, and the process takes about 1 to 2 seconds.
50X1-HUM
Data on the Electrical Units in the Apparatus
1. Transformer T1i W1 -- 2,000 turns of PE wire, 0 0.02; W2 -- 200 tarns
of PE wire, 0 0.8; core, Sh 19; pack, 2 cm.
2. Transformer T2, W1 -- 150 turns PE 0 0.8; W2 - W3 -- 2,0.0 turns PE
0.12; core, Sh 10; pack, 1.5 cm.
3. Ballast resistor, Type 1B 10-17.
4. Transmitting: W -- 500 turns PE 0 0.06; W -- 2,000 turns PE 0 0.06;
for magnetic circuit dimensions, see Figure 2,
5. Resistance R1, R2, and R3 are adapted to the characteristics of the
copper-oxide rectifiers.
The Graetz bridges have four copper oxide elemenes each, Type 209 VK-1.
The needle indicator is Type M-494.
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?igure 1. Circuit Diagram of the ZT1 -48 Apparatus
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Figure 2. Magnetic Circuit of the Transmitting Element
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