When using the welding method to repair tractor cast iron parts, in addition to selecting the appropriate welding method according to the actual situation, the following points should also be noted:
First, welding preparation
Before welding, all welding contaminants, such as rust, oil, paint, etc., must be completely removed. If the wall thickness of the weldment is less than 25 mm, weld cracks of about 4 mm in diameter shall be drilled. Some welds also need to choose groove type according to wall thickness and process requirements.
Second, the choice of electrode and its diameter
Different types of cast irons should use their corresponding welding rods; their diameters are mainly determined by the thickness of the weldment's welding complement; in order to prevent the generation of white mouth and fire-fighting organizations and reduce the heat-affected zone, small-diameter electrodes are currently used.
Third, the choice of power polarity
In the DC arc welding, in order to avoid excessive penetration, the weldment overheats and burns through, use the reverse polarity connection, namely the weldment connects the cathode, the welding rod connects the anode.
Fourth, the choice of current intensity
When the current is too large, the penetration depth increases, and the weld metal components and impurities diffuse into the molten pool to change the performance of the weld; current is too small will affect the stability of the arc, easy to produce slag inclusions, pores and other defects; the choice of current strength should be based on cracks or defects Conduction in the space of the weldment, at the same time should also consider the electrode brand and diameter.
Five, welding operation points
In order to reduce the cracks, local overheating in the welding area should be avoided as much as possible. Long cracks should be intermittently and intermittently welded. In order to reduce the penetration depth, small currents, fine electrodes should be selected, and short butt welding should be used as far as possible; Such as nickel-based electrodes, copper-iron electrodes, immediately after welding, use a round-headed small hammer to tap the weld to relax the welding stress, remove cracks and pores; each small welding wave should not span both sides of the slope at the same time. It is beneficial to the free contraction of the unwelded part and to avoid that the arc stays on both sides of the groove for too long; the welding layer should cover the underlying layer to anneal the bottom layer and change its processing performance.
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