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Pressure Machining Repair of Diesel Generating Set Parts

Dec. 21, 2018

Diesel generator set pressure processing repair parts are the use of external force to plastically deform the metal, restore the geometry of the part, or move the metal of the non-working part of the part to the worn part to compensate for the worn metal and restore the original working surface of the part. Size and shape. According to the plasticity of metal materials, it is divided into two types: cold press processing at normal temperature and hot press processing under hot state. The following is a brief introduction to the repair of diesel generator sets - the upsetting method, the expansion method, and the reduction method in pressure processing.



Pressure Machining Repair of Diesel Generating Set Parts.jpg



 

1. It is a processing method that reduces the height of the part, increases the outer diameter of the part, or reduces the size of the inner diameter. Mainly used to repair non-ferrous metal sleeves and cylindrical parts. For example, when the inner diameter or outer diameter of the copper sleeve is worn, it is upset at a normal temperature by a special mold, and can be manually hammered using a press, a hand press or a hand hammer, and the direction of the force should be perpendicular to the direction of plastic deformation. , as shown in Figure 2-22. Repaired by upsetting, the shortening of the part after compression should not exceed 15% of its original height, and for larger loads it should not exceed 8% of its original height. In order to be thick and uniform, the ratio of height to diameter should not be greater than 2, otherwise this method should not be used.

 

2. The expansion method is a repair method that expands the aperture of the part, increases the outer diameter size, or expands the unimportant part of the metal to the worn part to restore the original size. For example, after the outer circumference of the hollow piston pin is worn, it is generally repaired with chrome plating. However, when there is no chrome plating equipment, it can be repaired by expansion method. The expansion of the piston pin can be carried out both in the hot state and in the cold state.

 

Fig. 2-23(a) is a mold for expanding the piston pin 2 by the cylindrical punch 1. In order to facilitate the punching, put the end of the cone and arc transition. 4 is the mold base, 3 is the expansion and contraction sleeve, its function is to prevent the wall damage and uniform tension. Figure 2-23(b) shows the die of the tapered punch expansion piston pin, which has the same meaning as before.

 

When the piston pin is in thermal expansion, it should be heated to 950~1000 °C and kept for 2~3h. At this temperature, it is immediately put into the mold and pressed on the press. Before the cold expansion. It should be heated to about 600 ° C and incubated for 1.5-2 h for annealing. After the piston pin is cooled, apply oil to the mold, and then put it on the press together with the mold to apply pressure. The expanded piston pin shall be heat treated according to technical requirements, and then the outer mesh shall be ground to meet the dimensional requirements. The expansion method is mainly applied to sleeve-shaped parts with outer diameter wear.

 

3. The reduction method is the opposite of the expansion method. It is a repair method that uses the die to squeeze the outer diameter to reduce the inner diameter. The outer diameter of the small sleeve can be repaired by metal spraying, copper plating or inserting. If the bushing is large, it can also be 3-4 copper rings on the outer diameter and then machined so that the inner and outer diameters meet the specified size requirements.

 

The size of the tapered hole of the mold is determined by the plastic deformation of the part material and the amount of compression required. When the plastic deformation property is low and the compression amount is large, the taper of the taper hole of the mold may be 10 degrees to 20 degrees; when the value of the compression amount is small, the taper is 30 degrees to 40 degrees; for the material with high plastic deformation property The taper can be 60 degrees to 70 degrees.

 

Diesel generator set parts often have residual deformation such as bending and twisting during use. The method of using external force or flame to make new plastic deformation of the part to eliminate the original deformation of the generator is called correction. The correction is divided into cold correction and thermal correction.

 

 

1. cold correction

 

Cold correction can be divided into pressure correction and cold correction.

 

1Pressure Correction Place the deformed part in the V-groove of the press with the convex surface facing up, press the part by pressure and bend it to 10~15 times. After 1~2min, remove the pressure and check the deformation. If you don't have a school, you can do it many times until you are straight.

 

In order to stabilize the deformation after pressure correction and improve the rigidity of the part, a qualitative heat treatment is required after the correction. The pressure correction is easy, but the accuracy of the calibration is not easy to control, leaving a large residual stress in the part, the effect is unstable, and the fatigue strength is reduced.

 

2Cold Work Correction Cold work correction is the use of a hammer to strike the convex surface of a part to cause plastic deformation. The metal of this portion is extruded and expanded to generate compressive stress in the plastically deformed layer. Think of this deformed layer as a compressed spring that has a thrust effect on the adjacent metal. The curved part is corrected by the deformation layer stress.

 

The correction accuracy of the cold correction is easy to control, the effect is stable, and the qualitative heat treatment is generally not performed, and the fatigue strength of the parts is not lowered. However, it cannot correct parts that have too much distortion. Usually, the bending of the part cannot exceed 9.03%~0.05% of the length of the part.

 

2. Thermal correction

 

Thermal correction generally involves rapidly heating the highest point of the curved portion of the diesel generator set to a gas-fired neutral flame to above 450 ° C and then rapidly cooling. As the metal of the heated portion expands, the plasticity increases with increasing temperature and, due to the hindrance of the surrounding cold metal, may stretch as the temperature increases. When cooled, the amount of shrinkage is proportional to the magnitude of the temperature drop, causing the amount of shrinkage to be greater than the amount of expansion, and the shrinkage force is large, relying on it to correct the deformation of the part.

 

When heat correction, the larger the diesel generator set parts are bent, the higher the heating temperature. The ability to correct the bending deformation increases as the heating area increases, and the heating area can be determined according to the deformation condition during the correction. As the heating depth increases, the ability to correct the deformation also increases. When the heating depth is increased to 1/3 of the thickness of the part, the correction effect is better. However, the heating depth continues to increase, the correction effect will be reduced, and all parts of the heat will not be corrected. In the calibration process, the heating depth is mainly determined by experience, and the parts must not be thermally permeable, and cooling measures should be taken if necessary.

 

The thermal correction is suitable for correcting large-size parts with large deformation and complex shapes, good correction and retention, little influence on fatigue strength, and application is common. For parts with higher requirements, flaw detection must be carried out after calibration. If cracks are found, measures should be taken to repair or scrap. Calibration can be performed on the press or with special tools or hand hammers.

 


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