Performance and application of casting defect repairing machine

1 Introduction
Cast iron cast steel parts often suffer from surface blisters, blowholes and scratches during casting, machining and use. In the case where on-site high-temperature preheating is difficult to implement, repair welding by general welding methods (such as manual welding or argon arc welding) often causes hardening (or whitening) of the heat affected zone and even cracking. Whether it is possible to repair this type of surface defect with a relatively simple method has been a problem for welding engineers.

The emergence of the Japanese EDM welding machine has provided a new way of thinking to solve this problem. The biggest feature of the EDM welding machine is that the heat input is extremely small, so the damage to the base metal is also extremely small. The surface defects of the castings are repaired by the electric spark deposition welding machine, and the heat-affected zone hardening (or whitening) and the tendency of cracking are greatly reduced. However, the electric spark deposition welding machine made in Japan has a retail price of more than 200,000 yuan in China, which is difficult to promote and apply. In view of the current situation of defects in domestic castings, it is very necessary to develop a casting repair machine with low cost and good quality.

2 Introduction of new casting defect repairing machine

2.1 The composition of the welding machine The welding machine is mainly composed of two parts: the power supply and the welding torch.
The power supply includes a charge and discharge circuit, a control circuit, and a pulse trigger circuit.
The welding torch includes a normal welding torch and a bore welding torch.

2.2 Repair welding machine working principle

Under the protection of argon, the power supply section supplies high frequency pulses to the rotating electrode material, and when the end of the rotating electrode comes into contact with the surface of the workpiece, a discharge is generated. At the instant when the electrode is in contact with the workpiece to generate an electric spark, the temperature of the electrode contact region is as high as 7000-10000 ° C, and the electrode material is melted and deposited on the surface of the workpiece.

2.3 Main features
Thanks to the principle of electric spark deposition, this welder has excellent characteristics in terms of surface defects of repaired castings compared to conventional welding methods.

(1) Matrix deformation resistance and crack resistance

When the electric welding machine performs the spark discharge, it can generate 7000 ° C high temperature at the moment of discharge to melt and vaporize the end of the electrode material. However, since the discharge time is short, it is about 0.1 to 0.2 ms. The area of ​​the discharge is small, so the heat of discharge occurs only in a small area on the surface of the workpiece. As far as the entire workpiece is concerned, it is still at a normal temperature or the temperature is slightly increased, and the workpiece is not annealed and deformed.

Compared with the conventional welding method, since the metal and heat input deposited per discharge is extremely small, the heat-affected zone caused on the surface of the workpiece is inevitably extremely thin, and the residual stress formed in the heat-affected zone is low. In addition, the rolling effect of the electrode contact improves the heat-affected zone structure and stress distribution. Therefore, when the repair welding machine is used for repair welding, the surface of the casting does not crack even if it is not preheated. The welder was used to repair the gap of high-chromium white cast iron at room temperature. The outer dimensions of the notch were 18 mm long, 5 mm wide and 2.5 mm deep. After repair welding, no cracks were found in the casting. With the method of manual welding (the welding rod is Z308), once the arc is touched, the crisp cracking sound will soon be heard, and the welding cannot be performed at all.

(2) The way the sediment layer is combined with the substrate
The manner in which the deposited layer is bonded to the substrate depends on the reaction at the time of deposition and the reaction product. The discharge interval temperature during electrospark deposition is as high as 7000-10000 °C, which is enough to melt and vaporize the end of the electrode material and the surface of the substrate. The deposited layer obtained by condensation must be a new alloy formed by re-alloying the electrode material and the matrix material. Alloy layer. Therefore, the bonding mode of the deposited layer and the substrate is metallurgical bonding, and the deposited layer may also be referred to as a surfacing layer.

Since it is a metallurgical bond, there is a problem in that the electrode material and the matrix material match each other. If the metallurgical reaction between the two materials is weak, neither a solid liquid nor a compound can be formed, it will be difficult to obtain a deposited layer.

(3) Deposition efficiency
The welding machine has an input power of 1400W and a discharge frequency of 400-500Hz. Under normal circumstances, sand holes like mung bean size can be welded in only 3-5 minutes. The deposition efficiency can better meet the requirements of repairing the surface defects of castings.

(4) Operation and flexibility
The welding machine is easy to operate and does not require an operator with a high level of welding technology.

3 conventional repair welding process
First remove the oxide scale, rust, oil stains and stains on the surface of the casting to be repaired. If the surface defects of the casting are deep, the groove should be opened.

Selection of welding torch: If the defect is exposed outside, the ordinary welding torch should be used as much as possible; if the defect is located in the inner hole, or the defect is particularly fine, a small welding torch should be used.

The flow rate of argon gas was set at 5 to 1 OL/min.

Select the appropriate surfacing electrode and clamp it on the welding gun. The length of the electrode protruding nozzle can be controlled within 20mm.

At the time of surfacing, the end of the electrode is used to touch the surface of the casting and move. First, the surfacing is performed with a small output power. It is important to ensure that argon is continuously ejected from the nozzle to avoid oxidation of the electrode and the overlay.

Increase the output power for surfacing, at this time more sparks, the surfacing metal should show a bright metallic luster.

When the surface of the casting is too rough, use a trowel to level it and then weld it.

The surface of the surfacing can be machined by machining or benching.

4 Typical application examples
For a batch of gray cast iron flat plates processed for foreign trade, there are sand holes on the surface of some flat plates found before fine grinding. When the Z308 welding rod was used for manual welding repair, it was found that a bright ring of white light appeared around the solder joint after the fine grinding, and the gray cast iron flat plate was rejected. The reason is mainly that the heat-affected zone has obvious hardening during the welding process. The hardness of the hardened zone is much higher than that of the base metal and the weld. The hardening zone is grounder than the base metal and the weld. It is small, which is equivalent to grinding it, so that the finish of the place is obviously higher than that of the base metal and the weld.

When the repair welding machine is used to repair the sand hole, the material is made of nickel-based welding wire, and the conventional repair welding process is performed, and the repair of the surface of the gray cast iron flat plate is easily completed. The results of the fine grinding show that the surface of the cast iron plate does not have any bright spots, and the compactness of the repaired joint is superior to that of the cast iron.

5 Conclusion
The developed casting defect welding machine adopts the principle of electric spark deposition. When repairing the defects on the surface of the casting, the casting will not anneal and deform. Even if it is not preheated, the casting will not crack under normal conditions. The bonding mode of the deposited layer to the substrate is metallurgical bonding.

Insulation Gas Nailer

GT130B