A typical HIP cycle for a hotloading coldwall HIP unit is as follows

1. The powder-filled compacts would be placed on fixturing designed to hold the load at elevated temperatures. Some compacts can be self-fixtured by attaching a lifting device to the container.

2. The compacts and fixtures are placed into a furnace and heated to the desired temperature at a controlled rate or progress through a series of preheat and high-temperature furnaces to a hold point. Because the thermal conductivity of loose powder is much less than that of fully dense material, long hold times are necessary to ensure the entire cross section of the largest compact in the load is thoroughly heated and ready for HIP.

3. Once heated, the compacts and fixture are lifted from the furnace and placed into the pressurizing vessel. The load may be protected with insulating material during the transfer to prevent cooling prior to placement in the HIP unit.

4. The lid is placed on the vessel and sealed.

5. A pressure valve is opened, and gas at high pressure is released from a reservoir into the densifying chamber until there is equalization in both tanks. The vessel is held at these conditions for a set period of time, which is usually short, and thus lends itself to high production rates.

6. The gas is pumped from the densification chamber back into the storage reservoir, and the connecting valve is closed.

7. The lid is removed from the HIP chamber, and the load is removed.

8. The load is cooled to room temperature either in air or in another chamber (e.g., a furnace) at a predetermined rate to protect the parts from undesirable reactions or microstructural phase transformations.

0 0

Post a comment