The pressure and temperature during operation are high, and the use conditions are poor, which is easy to break. After the spring is broken, the plunger is stuck. If the toothed rod is adjusted at the high speed section before the spring is broken, the plunger always maintains a large flow rate and the oil supply is easy to cause the speeding. If the toothed rod is adjusted at the low speed section before the spring is broken, the oil supply may be insufficient after the broken spring. The power is reduced. The main reason for the breakage of the plunger spring was to analyze the spring breakage, and collected a total of 51 springs from 17 injection pumps, which were analyzed from materials, processes, equipment, personnel and environment. According to the requirements of the drawings, the plunger spring selects 50CrVA steel wire according to GB5220), and processes the springs of different periods into 10 samples 1) fuel injection pump body; 2) oil outlet valve seat; 3) oil outlet valve; 4) plunger Set; 5) adjust the rack; 6) drain plug; 7) camshaft; 8) tappet; 9) plunger spring; 10) plunger; 11) spring lower seat; 12) spring upper seat plunger The oil pump is tested for tensile strength. It can be seen that except for the lower limit of the tensile strength of the sample 1, the other tensile strengths are all qualified. The retraction rate of the other 10 samples was not less than 40%, which met the standard requirements. The hardness of the broken spring sample was measured after grinding. It is known that the breaking spring hardness also meets the requirements of the drawings. By sampling the broken spring, the geometry also meets the drawing requirements. When analyzing the apparent mass of the spring, it was found that the sectional shape of the 51 pieces of the spring was 30b60b, and the metallographic structure under the 500-fold metallographic phase microscope. It can be seen that the fracture section that occurs during use is a typical fatigue fracture, and the fatigue source occurs at the corrosion surface of the spring surface. Corrosion products at the pits are corroded for the surface of the spring. There are 27 pieces of cracks from the outside of the 51 pieces of springs, which have different degrees of rust. These rusts cause the surface of the spring to form pits. When used, the stress concentration is first formed on the inner side surface of the spring (the most stressed), which becomes the source of fatigue; Over time, the cracks continue to expand, eventually leading to breakage. It can be seen that the apparent quality of the spring is the direct cause of the spring breaking. After investigation and analysis, the reasons for affecting the apparent quality of the spring are 4. The apparent quality of the raw materials was found by visual inspection of the existing 50CrVA steel wire, and the surface was visually observed to be crusted and rusted. No cracks were observed by surface penetration, but cracks were observed on the surface by acid immersion. According to statistics, there were more engine break springs in 1996. After further investigation, it was found that the 1105kg steel wire purchased from a steel mill in 1996 was found to have poor appearance quality, using 685kg and 420kg for return processing. In the past, the surface of the machine was scratched and scratched. The plunger spring was always wound on the lathe. Due to the limitation of the mandrel and the clamping, the surface of the spring after machining was scratched. We randomly selected a spring being processed for acid. Dip test, found that the scratch depth is more than 40Lm. The anti-rust measures during the processing of the parts are poor. The original plunger spring is quenched and tempered, and the anti-rust treatment is not taken after the tempering, because the salt bath quenching spring is very easy to rust, although the rust is removed afterwards. Some places with severe rust will form dents on the surface of the spring, which will easily form a source of fatigue when used. Plunger spring section shape physical plunger spring section 500 times shot peening effect Poor shot peening is an effective way to improve the fatigue strength of the spring. Shot peening produces residual compressive stress on the surface of the spring, and reduces stress concentration and sensibility, thus extending its work. life. However, some shot blasting machines cannot rotate and the shot peening effect is poor. In addition to the above reasons, the plunger spring is broken. There are still some reasons for the inspection of the product, inspection process and testing equipment.
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The column is a problem of spring damage and disposal