JPH04100690A - Method for repairing electric weld bead cut part - Google Patents

Abstract

PURPOSE:To obtain the exhaust steel pipe for internal combustion engines having excellent corrosion resistance and good quality by cutting away the electric weld beads of the Al (alloy)plated steel pipe, then setting the thermal spraying distance between a thermal spraying gun or torch and the cut part at a specific distance and thermally spraying Al (alloy) to this cut part. CONSTITUTION:After the electric weld beads of the Al (alloy)plated steel pipe are cut away, the thermally spraying distance between the thermally spraying gun or torch and the cut part is set at 20 to 80mm and the Al (alloy) is thermally sprayed to this cut part. The sufficient corrosion resistance is obtd. if the surface of the repaired part is fully coated with the Al (alloy) without exposing the base metal. The thermally spraying is much better in the overall corrosion resistance rather than plating as the method for coating the repaired part. The repaired part is coated with the thermally sprayed film of the Al (alloy) at a sufficient film thickness in this way to prevent the exposure of the base metal and the adhesive strength of the thermally sprayed film is improved. The secure film which does not easily peel is formed to prevent the secondary exposure of the base metal. The sufficient corrosion resistance is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for repairing a cut portion of an electric resistance welding bead.

[Conventional technology]

Conventionally, galvanized steel pipes,
Aluminized steel pipes, stainless steel pipes, etc. are used.

Corrosion of exhaust steel pipes for internal combustion engines is broadly divided into internal corrosion caused by condensed water caused by condensation of exhaust gas, and external corrosion caused by internal combustion engines being used in humid environments. There is a strong desire for an exhaust steel pipe that has excellent corrosion resistance against such corrosion.

[Problem to be solved by the invention]

By the way, in the galvanized steel pipes mentioned above, pitting corrosion occurs in a short period of time, and in the case of stainless steel pipes, pitting occurs due to local corrosion in low grade stainless steels such as I3Cr, which have insufficient corrosion resistance. If stainless steel, which has components with sufficient corrosion resistance, is used as a material, a significant increase in cost may become a problem.

For example, Japanese Unexamined Patent Publication No. 55-'121
As described in Japanese Patent No. 04, aluminum-plated steel pipes have been developed and used.

However, even in aluminum-plated steel pipes, the outer surface bead of the ERW weld diameter is cut off during the manufacturing process, so there is no plating layer on this cut part (the steel pipe base material is generally left bare). Therefore, corrosion resistance is still insufficient.

Techniques for repairing such bead cut portions include, for example, Japanese Patent Laid-Open No. 1211559/1982 and Japanese Patent Laid-open No. 135/1983.
Although plating repair techniques disclosed in Japanese Patent No. 61 are also known, these repair techniques still do not have sufficient corrosion resistance.

The present invention enables perfect repair of bead cutting parts, and furthermore -
The present invention provides a method for repairing a cut portion of an electric resistance welding bead, which can provide an exhaust steel pipe for an internal combustion engine with excellent layer corrosion resistance at a low cost.

[Means to solve the problem]

In the present invention, after cutting and removing the electric resistance welding bead 1 of aluminum or alloy aluminized steel pipe, the spraying distance between the thermal spray gun or torch and the cut part is set to 20 to 80 mm, and aluminum or aluminum alloy is applied to the cut part. This is a method for repairing a cut portion of an electric resistance welding bead, which is characterized by thermal spraying.

[For production]

In order to obtain an exhaust steel pipe for internal combustion engines with excellent corrosion resistance, the present inventors have conducted experiments and studies on a method of covering the cut portion of the ERW weld bead. Alternatively, sufficient corrosion resistance can be obtained by coating with aluminum alloy, and the method of coating the repaired area is as follows:
We found that thermal spraying has far better overall corrosion resistance than plating, and that by combining these findings, we can further improve the corrosion resistance of exhaust steel pipes for internal combustion engines.

According to the research conducted by the present inventors, all conventional thermal sprayed repair products for ERW parts have little effect on improving corrosion resistance, and are not much different from unrepaired ERW steel pipes. The reason for this is that the thermal sprayed coating is extremely thin and the base material is often exposed, and the surface is not completely covered.
This is because the base material is exposed due to peeling due to mechanical loads such as processing steps. Therefore, the aluminum or aluminum alloy thermal spray coating is coated with a sufficient thickness to prevent base material exposure, and the adhesion of the thermal spray coating is improved to create a strong coating that does not peel off easily and prevent secondary base material exposure. By doing so, sufficient corrosion resistance can be obtained.

As a result of further research, the present inventors found that thermal spray repaired products with a sufficient film thickness have much better overall corrosion resistance than plated repaired products.

In many experiments, good corrosion resistance results have been obtained for straight pipes that have not been subjected to any processing such as bending or expansion, regardless of whether they are thermally sprayed or plated. However, when processed, i.e., when actually used as an exhaust steel pipe for internal combustion engines, the corrosion resistance of the plated repaired product is markedly rusted and its corrosion resistance is greatly reduced.
It was found that thermal sprayed repaired products with sufficient film thickness exhibit excellent corrosion resistance with no red rust, similar to untreated products.

This is thought to be due to the difference in the essential adhesion mechanism between plating and thermal spraying.

That is, plating has a metallurgical adhesion mechanism that involves reaction with the base material, and an alloy layer of the base material and plating components always exists at the interface. The alloy layer is extremely hard and brittle, and as a result of being processed, cracks can occur and propagate.
The opening leads to exposure of the base material.

On the other hand, thermal spraying uses a mechanical adhesion mechanism in which the coating material is applied to the base material in a molten to semi-molten state to create a close contact with the base material due to the so-called rivet effect, so there is generally no reaction with the base material. There is also no alloy layer. Coating thermal spraying is a characteristic of the soft coating material itself, and there is no particular cause for cracks to occur even if processing is applied.

The reasons for limiting the conditions and contents of the present invention will be explained in detail below.

In thermal spraying, thermal spraying materials such as powder or wire fly as molten or semi-molten particles, collide with the object to be thermally sprayed, and adhere to the object while being deformed, resulting in an uneven and porous surface. The research results of the present inventors show that in order to eliminate the exposure of the base material, increasing the density of the thermal spray material particles in a molten or semi-molten state can reduce pores in the formed film and increase the film formation rate. be able to.

As a specific method, this can be achieved by bringing the thermal spray gun or torch as close as possible to the object to be thermally sprayed, that is, by setting the thermal spraying distance to the shortest distance. The spraying distance is preferably 20 to 80mm; if it is less than 20mm, the spraying material will be affected by rebound, which may cause damage to the spraying gun or torch.
If it exceeds 80 mm, sufficient effects will not be obtained and the result will be insufficient.

The thermal spraying method is preferably a plasma arc wire type, an arc wire method, or the like. The reason for this is that other powder spraying methods use powder materials with a particle size of about 10 μm to 150 μm, so for aluminum thermal spraying, the amount of spraying is as small as 1 to 2 kg/hour, which increases the number of machines required. On the other hand, plasma arc wire thermal spraying or arc wire thermal spraying is economically advantageous and uses an aluminum wire rod with a thickness of about 1 to 2 mm, and the amount of thermal spraying is as large as 4 to 10 kg/hour.

〔Example〕

Next, the present invention will be explained in detail.

Outer diameter φ118.6~φ50.8mnn, thickness 1.2~L
6+nm Cr-containing j1596 material steel pipe was repaired by electric resistance welding bead cutting. Each repair method and film thickness are shown in Table 1 along with comparative examples.

The repair conditions in Table 1 are as follows.

Plating/Hot-dip aluminum plating, plating composition is aluminum plasma arc wire spraying and arc wire spraying containing 10% silicon.

Thermal spray material: 100% aluminum wire (JIS A
1070-WY) Wire diameter φ1.2 +n+r+ Wire supply speed -12 m/min The adhesion force evaluation method and corrosion resistance performance evaluation method in Table 2 are as follows.

Adhesion evaluation method: Based on the JISH8666 Ceramics Thermal Spraying Test Method (= J Adhesive Horn Test Method), apply adhesive to the end face of a φ40 x 110 mm round bar made of material 5S41 with a thickness of 300 to 800 μm and the same size as the test piece. The test pieces were glued together, and after drying and curing, a tensile test was conducted using a JISB772] tensile tester, and the tensile breaking load per unit sprayed area was taken as the adhesion strength.The adhesive used for adhesion was heat-curing epoxy. A resin adhesive was used, and after being cured for 5 hours at a drying temperature of 120°C, it was naturally cooled to room temperature and then subjected to a tensile test.

Corrosion resistance performance evaluation method Exhaust steel pipes coated and repaired under the conditions shown in Table 1 were manufactured, and these were installed as exhaust pipes of automobiles with gasoline internal combustion engines, and a corrosion resistance test was conducted by driving for two years.

Corrosion resistance performance was evaluated by dividing the straight pipe part of the exhaust steel pipe and the expanded pipe part expanded by 1.3 times, and evaluated by the ratio S of the area where red rust occurred to the total area of the outer surface for evaluation, and the following classifications were made.

×× ... 0.7≦S≦1.0 × ... 0.3≦S≦0.7 △ ・-・ 0.1 ≦S≦0.3 0 ・・ 0.05≦S≦0 .1 ◎ ... S<0.05 The overall evaluation was determined as the ratio S of the area where red rust occurred to the total area of the straight pipe and expanded pipe portion.

As can be seen from the evaluation test results in Table 2, the exhaust steel pipes 5 to 0 of the invention examples are shown to have superior corrosion resistance as exhaust steel pipes for internal combustion engines compared to comparative examples 1 to 4. There is.

〔Effect of the invention〕

According to the method of repairing the ERW bead cut portion of the present invention, a high-quality exhaust steel pipe for an internal combustion engine can be produced at a low cost, with excellent corrosion resistance in both straight pipes and expanded pipe parts.

can be provided.

Agent Patent Attorney Masaaki Akizawa 1 other person

Claims (1)

[Claims] After cutting and removing the electric resistance welding bead of the aluminum or alloy aluminized steel pipe, the spraying distance between the thermal spray gun or torch and the cut part is set to 20 to 80 mm, and aluminum or aluminum alloy is sprayed to the cut part. How to repair the cut part of the ERW welding bead.