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1銆丮ethods of reducing internal stress

1.Hammering and forging - mechanical method

When welding long cracks and surfacing layer, it is necessary to weld from one end to the other end. During welding, the weld and surfacing layer are in hot state, which can reduce the shrinkage of the weld and reduce the internal stress. When knocking, the effect is better when the welding metal temperature is 800 鈩�. If the temperature drops, the knocking force will also be reduced. If the temperature is too low, it is not allowed to knock around 300 鈩� to avoid cracks, The principle of forging method is basically the same as above, but the difference is that the weldment should be heated before hammering.

2.Slow cooling and preheating - thermal metho

This method is to put the workpiece to be welded in the furnace before repair welding and heat it to a certain temperature to prevent the heated workpiece from cooling rapidly during welding. The purpose of this treatment is to reduce the difference between the temperature of the repair welding part and the temperature of the base metal, so as to reduce the internal stress. The slow cooling method is to heat the welded workpiece to 600 鈩� and put it into the annealing furnace for slow cooling.

3.The law of "first breaking and then establishing"

When welding with ordinary carbon steel electrode, it is easy to produce cracks. This paper introduces a welding method of carbon steel electrode: cutting along the weld with small current, only slotting but not cutting through, welding while hot, because the local stress is removed during cutting, there will be no cracks, and the welding effect is good.

2銆丮ethods to reduce and prevent welding deformation

1.Preheating method

Preheating the weldment before welding can not only reduce the internal stress, but also reduce the deformation.

2.Pre adding reverse deformation method

According to the nature of the metal to be welded, the direction of shrinkage deformation after repair welding is estimated, and the workpiece is pre deformed by mechanical means before repair welding, so that the deformation after repair welding just offsets the pre deformation.

3.Water cooling method

Using cold water spray weldment, reduce the temperature of base metal, prevent deformation, put the weldment into the cold water tank, expose the repaired parts, so that the temperature of base metal will not rise, and the weldment will not deform.

4.Clamping method

The rigid fixture is used to fasten the weldment to prevent the deformation of the weldment, but this method will leave internal stress in the weldment, so it is mainly used for welding low carbon steel sheet with good plasticity.

5.Reasonable selection of welding specifications

Before welding, reasonable selection of welding specifications has a great influence on reducing the deformation of weldments. For example, with the increase of current intensity, the deformation of welding parts also increases accordingly. The welding sequence of welding seam is of great significance to reduce the deformation of welding parts. For structural welds, the welding between two connecting parts shall be welded finally. For cylindrical plate structure, longitudinal (axial) welds shall be welded first, If the weldment is composed of steel plate, the transverse weld of the steel plate shall be welded first, and the welding shall be carried out in the direction opposite to the general direction of welding.

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