SU744301A1 - Method of determining surface and subsurface defects of articles - Google Patents

Description

one

The invention relates to the field of surface quality control of rolling products in ferrous metallurgy.

At present, quality control of the surface of the rolled metal in the arterial meta-sturgeon is being carried out; ..-; - ;; As a rule, at the last stage, the perad-s: - a - before sending the consumer. d; d: iiJupoKO, the method used is visual. The controller-operator inspects the workpieces and marks the location of the defect, which is subsequently removed by emery or fire stripping.

The visual method, in which the sharpness of the operator’s vision plays a decisive role, cannot provide a complete picture of the defects. For this reason, when cleaning, it is often necessary to treat a surface that is many times greater than what is needed.

Recently, thermal methods have become widespread for quality control of materials and products.

A known method for the flaw detection of products, which means that the controlled area of the product is heated by passing for a certain time a constant-value current, is measured using a thermocouple

the temperature of heating and by the deviation of this temperature from the heating temperature of the defect-free zone is judged the presence of a defect (1.

The closest technical solution is a method for detecting surface and subsurface defects of products, based on the heating of the product by high-frequency currents and

10 registration of defects by the presence of a surface temperature gradient 2.

Known methods have a common drawback - they have low sensitivity and resolution.

15 to the detection of defects on the surface of metal products. They make it possible to detect defects (cracks, voids, inclusions, etc.), which are perpendicular to the direction of the heat flow and have a length comparable with the thickness of the product.

The aim of the invention is to increase the resolution and sensitivity of the method.

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To do this, the billet is heated with a current frequency at which the heating depth is equal to the thickness of the layer being monitored, and the billet is moved at a speed of 0.4-1 m / s. .

thirty

Taking into account the need to eliminate the formation of scale and a decarburized layer on the surface of rolling billets, the latter are not heated in accordance with the output. In this case, the penetration depth of eddy currents increases by not more than 20% and is inversely proportional to the square root of the frequency.

The essence of the proposed method for detecting defects is as follows. In thermal control methods, using traditional means of heating, the temperature gradient on the surface of the product, which is a criterion for the presence of a defect, is due to different rates of heat transfer on defective and defect-free parts of the product / On massive metal products, in particular rolling billets, to achieve a temperature gradient of more than a few tens of degrees, even for relatively large defects, usually fail.,

In the proposed method, the gradient of NT temeurur is created mainly not due to the different thermal conductivities on the defective and defect-free areas of the workpiece, but due to the uneven density of eddy currents on these areas.

In the area of the defect, a con centration of the magnetic field occurs, as a result of which the specific density of eddy currents becomes higher. All other conditions being equal, the greater the density of eddy currents corresponds to the greater temperature in the heated region.

The task of increasing the sensitivity of the Method is to ensure the maximum unevenness of the density of eddy currents in the places of defects. The maximum irregularity of the density of eddy currents in places of defects is achieved only when the thickness of the heating is equal to the depth of the predominant defect depth (the thickness of the layer to be monitored. The temperature gradient on the surface of the workpiece between defect and defect-free areas can reach several hundred degrees.

Providing the required thickness: heating is achieved by varying the frequency of the current. The required frequency is determined by known dependencies and tabular data.

As soon as the gradient of the temperature of the surface rises, it immediately tends to disappear due to the influence of the heat conductor and the body material. This effect must be minimized, for which it is necessary to reduce the time from the occurrence of the occurrence of the Gradient to the time of measurement, i.e. the time of removal of the test section from the heating zone. This segment is determined by the speed of movement of the monitored workpiece and the temperature measurement tools used. To control massive products such as rolled billets, there is a well-defined range of billet movement speeds. It is in the range of 0.4-1 m / s. At these speeds, modern means of measuring temperature makes it possible to detect the smallest cracks, voids and non-metallic inclusions in the surface layer of the workpiece.

Example. Blank - square 80 mm, Art. 65 g - ferromagnetic steel. The depth of the predominant defects - the thickness of the test layer is 0.25 mm. Local overheating is determined using a thermosensitive coating with a thermochemical conversion temperature of 250 ° C. Consequently, the average heating temperature of the entire surface at a speed of movement of the workpiece of 0.4 m / s (at least) should be 200-220 ° C. The thickness of the heated layer is 0.25-0.3 mm.

From the equality of the heating thickness (current penetration depth) to the depth of the monitored layer, the current frequency is determined by the method described above. It is equal to 9500 Hz.

Choose a 10-10 Hz machine frequency converter.

A single-turn inductor with a ferromagnetic magnetic core is made according to the shape of the blank with a gap of 5 mm. The inductor width is 15 mm.

According to the specified and obtained data (the size of the workpiece, the thickness of the heated layer, the speed of movement, the surface temperature, the structure of the inductor), the power of the converter is determined. It is equal to 92 kW.

The proposed method will allow to produce selective cleaning of blanks instead of solid, which gives a significant economic effect. This effect will be obtained by transferring auxiliary operations to detect and mark defects from the stripping section to the defectoscopy area. This also increases the machine time for stripping the metal.

Claims (2)

Invention Formula Method for detecting surface and subsurface defects of products, 5 mainly rolling billets, based on heating the surface of the workpiece with high frequency currents and detecting defects by the presence of a surface temperature Tyjsj gradient, characterized in that, to increase the breaking power and sensitivity of the method, the workpiece is heated with a frequency the current at which the depth of heating is equal to the thickness of the test layer, and the workpiece is moved at a speed of 0.4-1 m / s. Sources of information taken into account in the examination 1. USSR author's certificate 263969, cl. G 01 N 25/72, 1967. 2. US patent 3681970, cl. 73-154, 1970 (prototype).