Graphite Dies The graphite mold used in hot-pressing diamond geodes is taken as an example, and the damage of graphite mold is decomposed into four types by industrial field observation and experiment:
1. Oxidation crack type
This type of damage is the most. In the air, when the graphite material is heated to a certain temperature when the oxidation began. The oxidation initiation temperature of the different graphite materials is different, and the oxidation initiation temperature of the artificial graphite material is about 450 ℃. The higher the temperature, the faster the oxidation rate. The oxidation products of carbon are CO, CO2 gas, so that as the oxidation progresses, the graphite material is gradually consumed. Artificial graphite is a kind of porous dispersion structure material. With the progress of oxidation, the pores become larger and larger, Graphite Dies the structure becomes loose and the mechanical strength is greatly reduced. In the industrial field, you can clearly observe the mold surface off the toner, the surface becomes rough, mold Bi thinner, when the graphite material is oxidized to a certain extent, in the case of pressure, along the mold wall vertical cracks And damaged. In fact, Graphite Dies in order not to cause waste of sintered material, experienced operators always avoid the emergence of mold fracturing situation, the mold is oxidized to the extent of danger is no longer used. Improve the antioxidant properties of materials, is the key to reduce such damage.
2. Mold hole size becomes large and small
Graphite Dies About 30% of the mold, the use of several times, because the hole becomes larger, the size of ultra-poor and scrapped. It was observed in use that the inner bore of the mold was not in full contact with the air and was not substantially oxidized or slightly oxidized. In the hot press, the graphite mold hole into the sintered carcass material and drill pipe, at high temperatures in the carcass material in the metal binder in the molten or semi-molten state, although the vast majority of metal melt is difficult to spontaneously So that under the pressure, the molten metal will be squeezed into the inner wall of the mold surface,Graphite Dies with the graphite material adhesion. In addition to the composition of the sintered carcass material, the adhesion and the porosity of the graphite material, the size of the pores and the mold wall finish there is a significant correlation. As a result of this adhesion, when the sintered parts are cooled and demolded, the inner wall of the mold tends to adhere to some metal residue, which must be removed before the next use of the mold. In the industrial production site,Graphite Dies this cleaning tool is the use of metal blade tools such as artificial scraping, which caused the mold hole size larger or increased wall roughness, accelerated mold damage. Reduce the adhesion of metal melt, improve the material's wear resistance is the key to reduce such damage.
3. Beat stripping damage type
As a result of (2), sometimes caused by the sintered body can not be pulled out from the mold, only by repeatedly tapping the mold, drill pipe before stripping. In this way, sometimes due to beating to make the mold up and down the edge or the outer wall surface of the block, causing defects in the next sintering,Graphite Dies these flawed places will accelerate oxidation. At the same time, these places are also the focus of mechanical stress. This requires the stone cunning material structure should be fine, high strength.
4. Bottom wall fracturing type
Graphite Dies Due to the low mechanical strength of the graphite material or the design of the mold is unreasonable, the bottom or the wall strength is not enough, can not withstand the hot pressing pressure, when the pressure is added to a certain extent, along the bottom of the mold and mold wall connecting the stress concentration part of the horizontal crack , In the case of material strength is not enough, mold wall or mold bottom also cracks.