Hot pressing sintering process of boron nitride

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1) Adopt hot pressing furnace

2) Graphite mold
High purity graphite or electrode graphite for die body;High purity carbon rod for pressing column;Pressure head with high purity carbon blocks or high strength graphite;Bottom pad, with high purity carbon block or electrode graphite.

Graphite mold design should be according to the heat consumption of heat pressure to calculate the required resistance value, according to the resistance value to calculate the length of graphite mold and cross section area.However, hot-pressed BN products are mostly cylindrical, in different parts of the graphite mold its cross-sectional area is not the same, at the same time, BN product size is diverse, so it can not be a uniform formula to calculate the graphite mold cross-sectional area.

(3) The furnace charging
Hot pressing is a key process in hot pressing B N production, and furnace loading is an important part.Two points should be paid attention to when loading the furnace;

A, The graphite mold should be close to the bottom of the furnace.If there is a gap between them, it is easy to cause transverse cracks in the mold when pressurizing, and discharge will be caused when large current passes through at high temperature.
B. Tighten the side fastening screw of the furnace, otherwise longitudinal cracking of the mold will occur when pressurizing.

(4) Loading
Fill the hole with material, and continue to add material after compaction with aluminum or hardwood compression column, so that the density is about 0.9~1.0g/cm.If the surface is not high enough, you can add the pressure to meet the requirements.The cold pressing pressure should be 30~40kg/cm.

After loading, take out the aluminum or hardwood pressing column and replace it with high purity carbon pressing column.High strength graphite head was placed on the carbon pressing column and a press was used to apply a little pressure.A12O3 is used between the graphite head and the machine head.Insulation of powder and asbestos paper.

(5)Heat up and pressurize
Room temperature ~ 1300C, 30 minutes, 1300℃ start pressure, pressure 0-100kg/cm2
1300C~1700C, 30 min, pressure 100-250kg/cm2
Insulation at 1700℃ for 10-15 minutes, maintain pressure of 250kg/cm2
Power off, so that its natural cooling, pressure maintenance to 1000℃ below the stop pressure, do not unload pressure

(6)Loosen the electrode screws and side fastening screws at both ends of the furnace opening.Take the mold and push out sample B N with a cylinder smaller than the hole of the mold.