Method for reducing the occurrence of cracks in graphite molds

When we are making graphite molds, we will heat treat them in order to make them have good characteristics. However, when processing, it is easy to cause damage to the product because of cracks, and how to reduce this situation. Let's analyze it here.

The cause of the problem:

1. Serious shrinkage of graphite network cementite;

2. There is mechanical processing or cold plastic stress in the graphite mold;

3. Improper operation of die heat treatment;

4. The mold shape is complicated and difficult, the thickness is uneven, the oil sharp Angle and the threaded hole make the thermal stress and organizational stress too large;

5. The temperature is too high to make the die quenching overheating or burning too much;

6. The tempering of the graphite mold after quenching is not timely, or the tempering holding time is not enough;

7. After heat treatment of the EDM mold, the hardened layer has high tensile stress and micro-cracks.

What if we reduce these problems:

1. Strictly control the internal quality of graphite raw materials;

2. Remove mesh. Strip. Chain cementite, perfect calcining and nodulating annealing process;

3. The mold after machining should be stress annealed (>600℃) before heating and quenching;

4. For molds with too complex shapes, they should be in the risk part. Thread holes and thin walls should be filled with asbestos and quenched by stage or isothermal quenching.

5. When the mold is repaired or refurbished, it must be annealed or tempered at high temperature;

6. Strictly control the quenching heating temperature and time to reduce overheating and overheating;