RU1776980C - Method of electroconductive coating thickness measurement - Google Patents

Abstract

A method for controlling the thickness of coatings relates to a measurement technique and can be used to automate coating processes. The purpose of the invention is to increase the accuracy of control. The method consists in coating the wire, heating the transition from the coated part to the uncoated, creating a temperature difference, measuring the thermoelectromotive force and judging the thickness of the coating. 3 ill.

Description

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The invention relates to non-destructive testing, in particular to determining the thickness of coatings, and can be used to automate the application of thin films and coatings.

A known method for determining the thickness of coatings is the measurement of thermoelectromotive force.

The disadvantage of this method is the low accuracy of the measurement.

Closest to the present invention is a thermoelectric method for controlling the thickness of coatings, which consists in measuring the thermoEMF that occurs when heating at the junction of the coating with the base metal to determine the thickness of the coating.

The known method has a low accuracy control due to the uncertainty of the temperature distribution on the part and

the effect on the thermopower of the electrode pressure on the surface being monitored.

The purpose of the invention is to improve the accuracy of control.

The goal is achieved in that in the method consisting in measuring the thermopower, the coating is applied to the wire, a temperature gradient is created at the points of transition from the coated part to the non-coated, the thermopower is measured, which is used to determine the thickness of the coating.

In comparison with the prototype, thermopower is measured, which occurs at the transition from the coated part to the uncoated one. Thus, the claimed method meets the criteria of the invention of novelty.

Technical solutions for determining the thickness of a coating using the thermoelectric effect are known. However, in the claimed method, the place of transition from the coated part to the uncovered part has its own VJ

Vj

ABOUT

H

00

about

With the spa thermocouple, direct heating of this place exempts the proposed method from the listed disadvantages. In addition, the optimal choice of the diameter of the wire according to the schedule allows to increase the accuracy of indirect measurement of coating thickness. This allows us to conclude that in accordance with the technical solution the criterion of significant differences.

In FIG. 1 shows a diagram of a device that implements the proposed method; in FIG. 2 is a graph of thermoEMF versus coating thickness; in FIG. 3 is a graph for determining the optimum wire diameter.

A device based on the proposed method comprises a coated wire 2, heaters 3 made in the form of tubes, terminals 4, potentiometer 5.

The wire 1 coated on it 2 passes through the heaters 3 and through the terminals 4 is connected to the potentiometer 5.

The claimed technical solution is illustrated by the following examples of specific performance.

Example 1. When using the proposed method for controlling the thickness of a coating deposited on a wire, coated wire 1 is placed at the transition points from the coated portion to the uncovered portion in the heaters 3 (as shown in Fig. 1). A temperature difference is created and a thermoEMF signal is recorded by potentiometer 5. The thickness of the coating is determined by the graph shown in FIG. 2.

Example 2. When using the proposed method for automatic control of the coating processes on wire 1, a coating portion 2 is applied, placed at the transition points from the coated portion to the uncovered portion in the heaters 3 (as shown in Fig. 1). A temperature difference is created and a thermoEMF signal is recorded by potentiometer 5. The thickness of the coating is determined by the graph shown in FIG. 2.

Since the measurement of the coating thickness is indirect, the measurement error is determined by the formula

AS-AE /

where AS is the error in measuring the thickness of the coating;,

And E is the measurement error of thermopower.

Therefore, in order to improve accuracy

measuring the thickness of the coating and bringing the coefficient - g in the formula (T) to max

the optimal value, the wire diameter is selected according to the schedule (Fig. 3), which is described by the function

fifteen

2R2ATd2 (Ki -K2) (S + d) Rl (S2 + 2dS + (R2 / Ri) d2) f2;

(2)

where AT is the temperature difference created by the heaters, ° С;

d is the diameter of the wire, microns; 20 Ki, 2 coefficients of thermoEMF, respectively, of the material of the wire and coating;

S is the thickness of the coating, microns;

Ri, R2 - specific electrical resistance of wire material and coating, Ohm mm2

m

Thus, for example, when applying a coating with a thickness of 2.5 microns, the maximum ordinate and the corresponding optimum wire diameter d 0.3 mm are determined from the graph (Fig. 3) 30.

Thus, the use of the proposed method will improve the accuracy of monitoring the thickness of the coating. For example, in the range of 0-1 μm, the relative measurement error is ± 5% at a confidence level of Student distribution of 0.99, 40

Claims (1)

The claims A method of measuring the thickness of an electrically conductive coating, comprising 45 that they measure the thermoEMF arising from heating at the junction of the coating with the base metal, characterized in that, in order to increase the accuracy of measurements, the coating is applied to the wire50, and the thermoEMF is measured at the junctions from the coated part of the wire uncovered. U. -U -s. (M to J S § 5 1 1.5 3 S.HKM 9ig.z