A long time ago, after a piece of automotive leaf spring heat treatment, the craftsmen would continue to beat and slam it with a hammer. At that time, the craftsmen did not know that the result of doing so would extend the service life of the leaf spring by a factor of six. Now, this fact has been fully understood by engineers.
This intensive process technology is also applicable to cylindrical coil springs (round springs), torsion bars, designed to improve and improve spring fatigue strength and stress corrosion fracture strength to varying degrees. Other aircraft and automotive components, such as connecting rods, crankshafts, rocker arms, planetary gears, gear wheels, aero-engine blades, landing gear, and driveshafts, will strengthen the process as a necessary step in the production process and have established strict technical specifications. . Let me briefly explain what happens when a part is strengthened.
Principle of strengthening the process
The strengthening process utilizes the impact of the high velocity moving projectile flow on the metal surface to create a cyclic plastic strain layer on the surface, thereby causing a favorable change in the microstructure of the layer and introducing the surface layer into the residual compressive stress field. The microstructure and residual compressive stress field of the surface layer are two strengthening factors to improve the fatigue fracture and stress corrosion fracture resistance of the metal material and its spring to improve the reliability and durability of the spring.
Reinforcement is a "cold treatment" process that is different from the hot processing of metal parts at high temperatures. The compressive stress layer typically extends from 0.005" to 0.030" deep below the surface of the material. If necessary, the depth of the compressive stress layer can also be increased by changing process parameters such as pellet size, spray/projection velocity, spray/projection angle, spray/projection time, and the like.
Two important parameters for evaluating the enhancement effect are strength and coverage. Coverage (100%, 200% or greater) is mainly based on visual inspection, while strength is measured using representative spring steel coupons (ie Almen test strips)
Intensity measurement
The Part Proofing Tool (PVT) is designed to hold the test piece at specific locations where the test piece simulates the location of the part where the part has strength requirements and must be tested for strength. The intensity ranges from 0.015 to 0.030 (on the 'A' rating) depending on the application.
Spring Strengthening Equipment Type
Spring-strength equipment can be divided into two types:
—— Centrifugal blade shot blasting equipment
—— Pneumatic nozzle type shot peening equipment
The advantage of the previous week is that the speed is fast and the output is high. It is more suitable for the strengthening treatment of parts with high capacity requirements such as leaf springs and round springs. It can eject more areas in a shorter time and make the parts to be sprayed more. Fast to saturation intensity.
A shot peening device for a continuous chain conveyor system is suitable for leaf spring reinforcement, a plurality of throwing heads are aligned with the upper surface of the leaf spring, and the left and right sides are ejected
A continuous pass type shot blasting device with a finger shaft is suitable for round spring strengthening, and there is a rotating roller in the blasting chamber, which drives the round spring edge to rotate and pass, in the process, a plurality of throwing heads are aligned with the same Shot blasting is performed.
Springs of relatively small size, such as valve springs for engine valves, are suitable for reinforcement with track-type shot blasting equipment
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