The tungsten crucible crack analysis is quite important. If the problem that the bottom of crucible easily cracks is not solved, it will directly affect the yield of the crucible. Although powder metallurgy method producing crucible has many advantages including greatly saving metal consumption and reducing production cost, there are still many technical problems to be solved such as the bottom of crucible easily cracking.
There are many kinds of preparation methods to produce crucible, powder metallurgy method is widely used in rare earth industry mainly for smelting and electrolysis to produce rare earth metals and their oxides. The crucible has long life time, corrosion resistance, and can reduce the content of aluminum and tantalum in rare earth metals, it is very suitable for the production of high purity rare earth metals, the demand of crucible in rare earth industry is greatly growing.
In the production process, cracks are easy to appear in the following two stages:
1.0 Pressing stage
The tungsten crucible is pressed in cold isostatic pressing machine. The main cracks at the bottom of the crucible in the pressing stage include falling bottom, divergent cracking at the bottom, and small cracks on the outside of the bottom. They are mainly caused by powder proportioning, pressing pressure and the size of the fillet R at the bottom of the die mandrel.
2.0 Sintering stage
The cracks appearing in sintering stage is mainly because of sintering equipment and atmosphere. For example, the effect of sintering crucible in the 1300-2036-ww resistance furnace is better than that in the induction furnace. Because of the structure of the induction furnace, the bottom of the crucible is easily sintered impervious or uneven, which may lead to cracks.
The best ways to produce crucible are as follows:
1.0 Mix the recycled tungsten powder and the newly purchased tungsten powder with particle size of 3.0um ~ 4.5um evenly at a certain ratio, which will be most useful for production.
2.0 The pressing pressure should not be too high or too low, and it will be suitable during 170Mpa ~ 250Mpa.
3.0 The effect of staged heat preservation and sintering in hydrogen resistance furnace is obviously better than in other conditions, and the cooling rate should not be too fast at higher temperature.
4.0 It will be most suitable when the fillet R of mandrel is 16mm ~ 25mm, and the shore hardness of rubber used for rubber sleeve should not exceed 72.
If above mentioned can be avoided as far as possible in the production, the probability of cracking at the bottom of the crucible will be greatly reduced, then can improve the yield of the crucible.
