JPS58142253A - Manufacture of magnetic powder for magnetic powder flaw detecting - Google Patents

Abstract

PURPOSE:To high-precisely reproduce a defect indicating pattern, by a method wherein a magnetic powder has an appropriate magnetism, has a particle shape which is approximately spherical, has a magnetic nucleus located in the proximity of a center of a magnetic particle, and is uniformly covered with a binder. CONSTITUTION:A raw composition of magnetic powder is constituted such that 25-40wt% binder, consisting of an approximately equal part parafin and a thermoplastic resin, and 5-10wt% fluorescent pigment or 1-5wt% a fluorescent dystuff are added to 55-65wt% powder of tri-iron tetroxide with a particle size of 1-3mu. The mixture is placed in an enamelled receptacle to heat it to 110- 130 deg.C for fusion to form it into an uniform shape. Consecutively, the liquid material is sprayed into open air under a pressure of 1.0-3.0kg/cm<2> by means of a spray gun heated to 120-150 deg.C, and it is naturally cooled to obtain about 90 parts, based on 100 parts a raw material, of magnetic powder for flaw-finding. The employment of the method prevents the exposure of a magnetic nucleus and the occurrence of unevenness in magnetism.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing magnetic particles, which is used for flaw detection of materials such as mK brooms and billets, by exposing a defect indicating pattern using mK magnetic particles on the surface of an object.

To detect flaws on the surface of materials using magnetic particles, use non-fluorescent magnetic particles such as gray, black, or brown that have a good contrast with the skin color of the object, or emit fluorescent light when irradiated with a black light in a dark place. Fluorescent magnetic particles such as these are used, and the particles are dispersed onto the surface of the subject, and electricity is applied to the subject to magnetize the subject.

At this time, where there is a flaw, a defect indicating pattern made of magnetic particles is rounded and marked by visual inspection. Here, the point at which the defect indicator pattern appears on the bright W is the depth of the scratch,
It varies depending on the strength of the magnetic field on the surface of the subject and the magnetic strength of the magnetic powder used.

By the way, when detecting flaws in the rolling direction of a material by the magnetic particle flaw detection method, a shaft energization method is generally used as a method of magnetizing the test object. In this axial energization method, if the object to be inspected has a circular cross-sectional shape, only harmful defects can be detected by increasing or decreasing the current value, regardless of the area to be inspected or the waveform of the current being applied. . Therefore, in this case, it is effective to use magnetic particles with high defect detection characteristics. In contrast to slippage, when the object to be inspected has a rectangular cross-sectional shape, there is a significant difference in defect detection ability depending on the area to be inspected and the waveform of the applied current. In other words, the strength of the magnetic field at each location is 1! It is known that there is a relationship between H and the applied current 1 as follows: ``HR---(1)''. Here, Rti is the distance between the cross-sectional center point of the object and each part on the surface of the object. Therefore, in one plane of the material, the closer to the edge i, the larger R is.
The strength of the magnetic field is HF1m1. Furthermore, compared to alternating current, single-phase half-wave pulsating flow has larger differences depending on the region to be examined. Using this rounding and the appearance of a defect indicating pattern at the edge as a guideline, the current value for electromagnetizing the object is determined. On the other hand, when performing magnetic particle flaw detection by HIK inspection by an inspector, regardless of the level of skill of the inspector O, the inspector who marks the defect location with high accuracy is required to ensure that each defect indication pattern appears at wsi degree. Ru. This is because without blindness, some inspectors may overlook defects in the edges. Here, the relationship between the intensity ν of the fluorescent magnetic IIO light O deposited on the defect location and the magnetic field strengths X and O is as follows:
It has been reported that a relationship such as y = a logg-)b (a and b are constants) generally holds true. According to this, in the case of a relatively weak magnetic field near the limit where a defect indicating pattern is given, the strength of the fluorescence corresponding to changes in the strength of the magnetic field appears relatively sharply. As a result, there are differences in the quality of inspectors when marking defective areas. Therefore, it is conceivable to apply an excessively high magnetic field to alleviate the disparity in the appearance of defect indication patterns depending on the part of the square timber to be inspected. However, in such cases, the intensity of the magnetic field applied to the central part of the plane of the subject is very high, and the magnetic particles are attracted to non-harmful wrinkles and surface roughness, resulting in poor background. Even a harmless defect in the central part is strongly detected, resulting in a temporary marking that confuses the visual inspector 01iI. As a result, excessive damage is removed in the subsequent machining process, leading to uneconomical use of one-shot materials.

Therefore, it is necessary to accurately display defect indication patterns of the same degree as seen by the human eye without being affected by differences in each inspection area, such as the center or edge of a plane, and to avoid over-detection. The strength of the magnetic field, that is, the value of the current applied, is very hot and dull, while it has moderate O magnetism, the grain shape is close to spherical, the magnetic core is located at the center of the fine powder grain, and it is uniformly coated with the binder. Therefore, it is necessary to use magnetic powder for flaw detection. However, until now, we have not been able to provide magnetic particles for flaw detection that meet these conditions.

The present invention has been made for the purpose of providing a method for producing m powder for flaw detection that satisfies the above conditions.

The manufacturing method according to the present invention will be explained below.

First, the powder composition of the magnetic powder is 65 to 65% by weight, a powder of triiron tetroxide with a particle size of 1 to 100 kg, and 26 to 40% by weight of a binder consisting of equal amounts of paraffin and thermoplastic resin. and the weight of the fluorescent pigment is 5-16, and the weight of the fluorescent dye is 1-1.
It is made by adding S weight attack.

With reduced iron powder, the magnetism becomes too strong, and it is necessary to use a large amount of binder to moderately weaken it, and because it is difficult to reduce the particle size of iron powder to 10μ or less, a binder, The pigment easily peels off, and the peeled off material does not contain magnetic particles, resulting in variations in the product. Further, the proportions of paraffin and thermoplastic resin in the binder need to be approximately the same. This is because if the proportion of paraffin increases, the coated part of the product particles will become brittle, while if the proportion of thermoplastic resin OI increases, the viscosity will increase, causing problems in the subsequent melting and stirring process and spraying process. As the thermoplastic resin, a copolymer of vinyl acetate and ethylene (tn, y, 116° C.) or the like is used.

Next, put these mixtures in an enamel container, etc., and
Heat it to 10-180°C to melt it, and use a homomixer or the like to make it into a uniform liquid. The heating temperature differs slightly depending on the type of thermoplastic resin used.

Since the melting point of paraffin is about 4 to 15"C, it will completely melt at the above temperature.
This liquid portion is obtained using a spray gun heated to 0°C.

Here, the following steps are carried out using the spray granulation method.

That is, a mixture consisting of magnetic powder, binder and pigment is melted and kneaded into nine bales, dried to form a lump,
This is because the method of crushing and sifting this causes the exposure of magnetic nuclei O (ζ), resulting in variations in the magnetism of the product O.

The magnetic powder for magnetic particle flaw detection is manufactured by the method described above, and has a suitable magnetic property, a particle shape close to spherical 1tK, a magnetic core completely covered, and a magnetic core located at the center of the magnetic particle. We provide magnetic particles for magnetic particle flaw detection with good homogeneity of KaN.
-I was able to do that.

FIG. 1 shows the results of a magnetic particle flaw detection test using magnetic particles for flaw detection produced by the method according to the first aspect of the present invention. In the figure, (1
) C) The curve shows the test results when nine magnetic powders produced by the method of the present invention were used. The test conditions are as follows. The test liquid is prepared by adding 1 ton of magnetic tlPK dispersant for flaw detection and kneading it into a uniform paste, and then pouring it into water 11 and stirring to suspend and disperse it. Then, this test liquid is poured over the subject at a rate of 160 m//10 G-.

Magnetization is by a completely continuous method (illk energization). In the figure, the direction of the groove depth ratio on the horizontal axis is made to coincide with the axial direction of the subject. For comparison, track ml (g) shows the test results when magnetic powder for flaw detection, which has been commonly used in the past, was used. The strain rate of the test liquid is 0.6 F (magnetic particles)/l, and the other conditions are the same as above.

According to Fig. 1, the magnetic field strength is 0.01 at 600e when using conventional flaw detection magnetic particles with high defect detection characteristics.
! , 400· and a groove depth ratio of 0.07, a clear defect indicator pattern appears. As mentioned above, 1. This leads to poor background and excessive marking. On the other hand, the flaw detection defect indication pattern according to the present invention does not appear.

In addition, although the first intention shows a cross section of a square piece with one side (!r) of 0υ, when conventional magnetic powder for flaw detection with high defect indication characteristics is used, for example, the groove depth ratio at the edge (B) is 0. 1
6 is detected, the strength of the turtle's magnetic field is 190s and To
jl, then the strength H of the magnetic field at the center (mu) is
When the current is electromagneticized by alternating current, H=1170e from equation 0). Therefore, in the central portion (mu), groove depth ratios of o and io are detected.

This tendency becomes even more remarkable when electromagnetization is carried out using a single-phase half-wave pulsating flow. However, if large flaw detection magnetic particles manufactured by the method according to the present invention are used, those with a 4-groove stagnation ratio o of 16 or less in the center part (A) will not show any defect indicating patterns; Even when a strong magnetic field is applied, the pack ground is good and excessive! - It will not become a medium render. In addition, the rounding that can apply a strong magnetic field, the above-mentioned spreading, and the defect indication pattern of the highest degree regardless of the difference in the tested area,
There are no variations in marking due to individual differences among visual inspectors.

[Brief explanation of drawings]

FIG. 1 is a graph showing the results of nine flaw detection tests conducted using magnetic powder for flaw detection. Curve (1) is the case when magnetic particles produced by the method according to the present invention is used, and curve (2> is the case when conventional magnetic particles with high detection characteristics are used. ), (B) is a cross-sectional view of the square timber. Fig. 1 44σ or 1 gold Fig. 2

Claims (1)

[Claims] m1ll ~ Sttalene triiron tetroxide powder yI/lss ~
・b weight 1, binder 8s to 40 weight algae consisting of approximately equal amounts of paraffin and thermoplastic resin, and fluorescent family I
N1・weight-1* is fluorescent dye% 1 to 6 weight- and added,
Put these mixtures in a container and mix this with 110~11@
@0Kjlli Heat, melt, stir, and make a homogeneous liquid into a round shape, l!・For magnetic particle flaw detection, which is characterized by heating up to 1sO'''OK, spraying it into II atmosphere at a pressure of 1.0 to 10*/(If' (Z) using a nine-spray trout gun, and cooling naturally. Method of manufacturing magnetic powder.