Shenzhen Yonglian Spring Machine Sharing - Measures to Improve Spring Quality

Measures to improve the quality of springs:

(1) Deformation heat treatment—Combines both the deformation strengthening of steel and the heat treatment strengthening to further increase the strength and toughness of steel. Deformation heat treatment has high, medium and low temperature points. The high-temperature deformation heat treatment is quenching immediately after the austenite in the steady-state austenite state, and can also be combined with forging or hot rolling, ie quenching immediately after thermoforming. Deformation heat treatment has been used in automotive leaf spring production. (60Si2Mn)
(2) Isothermal quenching of the spring - for a small diameter or sufficient permeability of the spring can be isothermal quenching, it can not only reduce the deformation, but also can improve the toughness, and then a tempering after the isothermal quenching, can be Increase the elastic limit. The tempering temperature is the same as the austempering temperature.
(3) Relaxation of springs - The springs work under external forces for a long time. As a result of stress relaxation, there will be a slight amount of permanent (plastic) deformation. Especially for springs operating at high temperatures, the phenomenon of stress relaxation at high temperatures becomes more serious. The precision of the spring is reduced, which is not allowed for normal precision springs. Therefore, this type of spring should be relaxed after quenching and tempering. The spring is pre-loaded so that its deformation exceeds the amount of deformation that the spring may produce. Then heat above the operating temperature of 20C and hold for 8-24 hours.
(4) Low-temperature carbonitriding - The combination of tempering and low-temperature carbonitriding (soft nitriding) can significantly increase the fatigue life and corrosion resistance of springs. This process is often used in coil springs.
(5) Shot peening - Surface defects such as scratches, folds, oxidative decarburization, etc. tend to be stress-concentrated and fatigue fracture sources when the spring is in operation. If a small steel shot is used to spray the spring surface at high speed, not only the surface quality of the spring is improved, but also the surface strength is improved, and the surface is in a state of compressive stress, thereby improving the fatigue strength and service life of the spring.

Handling Precautions (1) Check whether the surface is decarburized or cracked before heat treatment. These surface defects will severely reduce the fatigue limit of the spring.
(2) Quenching and heating shall be specially done to prevent overheating and decarburization, to deoxidize the salt bath, to control the atmosphere of the furnace gas, to strictly control the heating temperature and time (3) To reduce the deformation, the loading method of the spring when heating the spring, the fixture form and Quench into the cooling method when cooling.
(4) As soon as possible after quenching tempering, heating should try to spoon. Rapid cooling after tempering can prevent temper brittleness and cause surface compressive stress and improve fatigue strength.

Quality inspection before heat treatment -
(1) The rolling surface of steel is often the surface after it is made into a spring, so there should be no cracks, folds, spots, hairline, bubbles, interlayers, and pressed oxide scales.
(2) Surface decarburization will significantly reduce the fatigue strength of the spring, and the depth of the decarburized layer shall be tested as specified.
After heat treatment--
(1) Observe the spring watch with naked eyes or low magnification magnifiers for cracks, pitting, and severe quenching deformation.
(2) The hardness and its uniformity are in compliance with the regulations. In mass production, it is permissible to check the hardness with a file, but care must be taken that the position of the scar does not affect the post-accuracy of the spring.
(3) The metallurgical structure should be a combination of the thorium or tortoise and sorbite.
(4) After the leaf spring is assembled, it is usually necessary to perform permanent deformation under load and static load deflection test.