SU1672345A1 - Magnetographic control - Google Patents

Abstract

This invention relates to non-destructive testing by a magnetographic method. The aim of the invention is to increase the sensitivity in controlling butt joints by increasing the level of the magnetizing field and reducing noise. To achieve the goal, the electromagnet is moved along the seam so that the direction of movement and the longitudinal axis of the working gap between the bias plates 6 make a given angle α, and the projections of the opposite points of the plates are located at the seam edges. 5 il.

Description

The invention relates to non-destructive testing, in particular to a magnetographic method, and can be used to control the quality of welded joints made by fusion welding.

The purpose of the invention is to increase the sensitivity in the control of butt welds by reducing noise and increasing the level of the magnetizing field.

FIG. 1 shows a device for implementing the method of magnetographic control, general view; Fig. 2 is a graph of the intensity of the floor on the sample surface versus the distance between the magnetizing plates; FIG. 3 shows the dependence of the sex of a defect on the angle of magnetization; Fig. 4 is a graph of the magnitude of the signal due to a defect as a function of the read angle of a tape recording; Fig. 5 shows the projection of the plates of the magnetizing system on the magnetizable product with a welded seam.

The device comprises a U-shaped core on which winding 1 is wound, wheels 2 for moving around the product, mounted on axles in sleeves 3 of supports 4 by means of screws 5, a biasing system in the form of plates 6 having a bevel at an angle p. The plates 6 are fixed with the possibility of movement in the vertical direction, and the poles 7 of the electromagnet - with the possibility of movement in the horizontal direction.

The method of magnetographic control is carried out as follows.

A magnetic tape (not shown) is placed on the surface of the product with a welded seam, and a magnetizing device with magnetizing plates 6 forming the working gap between them is placed and the device is moved along the test surface along the seam

(L

WITH

about vj

N3

J

SL

so that the direction of movement and the longitudinal axis of the gap between the plates make a given angle a, and in the process of moving the electromagnet along the seam, orient it so. so that the opposite points of the projection of the plates b, forming a working gap, located on the edges of the seam. After magnetization, the magnetogram is read, the results of the decoding of which determine the quality of the seam.

In the process of control, the distance between the plates with a bevel of the edge is chosen from the condition of creating a maximum magnetizing field on the surface of the magnetizable object. Fig. 2 shows the strength of the field on the surface of a magnetisable flat sample as a function of the distance between the plates. The maximum field strength on the surface of the flat sample is observed at a distance of 3-5 mm between the magnetizing plates. The maximum gender value in this case is increased by 2 - 3 times. Turning the device, orient it so that the projections of the working edges of the plates of the magnetizing system completely intersect the seam reinforcement, forming the minimum acute angle a with the longitudinal axis of the seam, and the opposite points of the plates are located on the seam boundary. This is due to the following. It is known that the field of a defect substantially depends on the orientation of the magnetizing field relative to the plane of the defect. It is maximal if the vector of intensity is perpendicular to the plane of the defect and decreases with increasing angle between the vector of intensity field and the normal to the plane of defect. The latter is illustrated by the graph shown in Fig. 3, the dependence of the sex of the defect on the angle of magnetization. It can be seen from the drawing that if the angle between the field strength vector and the normal to the plane of the defect is no more than 10 °, then the field of the defect is attenuated by no more than 20%. A further increase in a leads to a strong weakening of the sex of the defect.

The magnitude of the signal about a defect in reading a record is maximum if the reading direction coincides with the direction of the residual flow from the field of the defect. The dependence of the magnitude of the signal caused by the defect on the reading angle of the tape record is shown in FIG. 4. If the angle between the direction of the residual flow and the direction of mixing does not exceed 10 °, then the decrease in the signal does not exceed

20%. Therefore, the angle a between the projection of the working edges on the product and the longitudinal axis of the seam should not exceed 10 °, since the amplitude of the signal about the defect drops sharply (in

welds of products from low carbon and low alloy steels defects are oriented along the weld).

Figure 5 shows the projection of the plates of the magnetizing system on the magnetized product with a butt weld, I is the length of the plates, and is the width of the gap between them, b is the width of the seam. The dotted lines show the sides of the electromagnet poles, the dash-dotted lines indicate the seam roller edge. WG direction of the magnetizing floor. The arrow lv indicates that the magnetizing device moves along the seam. The minimum angle a for a given I is determined from the condition of complete intersection

projections of the working edges of the magnetizing plates of the weld bead. If the intersection is not complete, then not all the seam will be magnetized. The angle is determined from the equality sin a cos a.

.. a + b ,,

Or a arcsln -r-. Existing

U-shaped electromagnets have mm. Thus, arcsln $ - a 10 °

The field in the gap between the plates of the magnetizing system is oriented perpendicular to the working edges (along arrow H in Fig. 5)

Placing the plates of the magnetization system above the surface of the seam so. so that the projections of the working edges intersect the entire seam, and the opposite points of the plates that form the working gap are located on the edges of the seam and, moving them along with

an electromagnet along the seam above the angle a. the entire seam is magnetized and, at the same time, interference is eliminated. Thus, the proposed method allows: firstly, to create in the seam a much larger

5 field, secondly, exclude the occurrence of interference due to the displacement of the magnetizing system, thirdly, due to the fact that the angle between the vector of the intensity of the magnetizing field and the normal to

0 plane of defects not more than 10 °. achieve a defect floor close to the maximum at a given intensity of the magnetizing floor

Claims (1)

5 claims The method of magnetographic control, which consists in the fact that a U-shaped electromagnet with bias plates forming the working gap, is moved along the test surface in this way. that the direction of movement and the longitudinal axis of the gap constitute a predetermined angle a, about t and h, so that, in order to increase the sensitivity when monitoring butt welds, the electromagnet is moved along the weld and orient it so that The opposite points of the plates forming the working gap were located at the seam boundary. 20W l, im Fie g W 20 About 20 40 60 60 t ° Phie, 5