Spring failure caused by improper manufacturing process

Mistakes and inaccuracies in the manufacturing process often cause spring failure. The most common technical defects and errors are: 1. Scratches of the tool; 2. Arc over-burning: sometimes during welding, sometimes during electroplating; 3. Hydrogen damage : Generally caused by improper pickling and electroplating process, or incomplete hydrogen flooding treatment after pickling or electroplating; 4. Incorrect firing process may cause cracks or scratches; 5. Incorrect heat treatment and operation.

1. Original condition: The spring is cold drawn from 60Si2Mn of á3mm, and the wire is wound into a coil spring with an outer diameter D=18.4mm and a pitch t=10mm. The two ends of the spring are directly energized to heat the head, and then the end faces are ground, and then 830e is quenched and 390e is tempered. The hardness is up to HRC50-56. The free height of the spring is 245mm, the assembly length is 163mm, and the working length is 103mm. The load under compression is 441N and 735N respectively. The design life requirement is more than 103 times. In fact, about 10% of the springs occur early. Low life break.

2. Observation and analysis: Observing the broken spring, it was found that the fracture was almost at the end of the electric chuck of the electric heating at the end, where there was an crater. Metallographic observations revealed large Wei's tissue. It shows that overheating occurred at the place of direct electric heating. The fracture is a fatigue fracture.

It can be seen that the working point has fallen in the safe area of ​​the first type of fatigue map, and SmaxmDb. Then why does the spring not break and break once? Because the mechanical properties of the spring wire are measured after the spring wire is directly quenched and tempered, and the compression force of the spring at 163mm and 103mm length is 45kg and 75kg respectively.

3. Conclusion: The spring has a low life fatigue fracture. The crack originates from the arc pit at the electrode of the electrically heated electrode, and because the quenching temperature is low (only 830e) is not sufficiently austenitized, the K1c value of the material after quenching and tempering is low, that is, the critical crack length a0. The reduction, plus the spring is working under high stress conditions, so early fractures often occur.

4. Improvement method: use coal stove or other furnace to perform / indirect 0 heating and head. The quenching temperature was increased from 830e to 890e, and the test proved that the spring life can reach more than 6,000 times.

Hospital Sliding Door

Door panel: door panel is made of stainless steel 304 with no frame. Core materials are paper honeycomb, aluminum honeycomb, PU, EPS and etc. The installation sites of door lock, door closer and hinge are reinforced with square tubes of more than1.5mmthickness which are compression moulded by special technology.