The Process of Cold Isostatic Pressing (CIP)
Before the mold is assembled, the size, shape and surface condition of the mold should be checked. If the metal touches are scratched, rusted, deformed, bent, etc., it will make the compact unable to be demoulded or cause defects such as marks on the surface of the blank. Surface treatments should be repaired or replaced at any time. The plastic sheath has been used for a long time and is easily deformed. It is difficult to maintain a certain shape and should be replaced at any time. The surface of the mold should be kept clean and dry to ensure that the powder is not contaminated.
The basic requirements for powder filling are: strive to make the powder filling density high and uniform. In order to increase the filling density of the powder, the powder is usually granulated. The granulation method is commonly used spray drying method and compression method.
Spray drying granulation method to make spherical granules with uniform composition and good fluidity. The pressing method is to press the powder in advance, and then crush it and sieve it, so that the powder presents a particle size distribution of different sizes.
During the powder filling process, the powder with larger particles is easy to roll on the surface of the smaller particles, and most of them are concentrated at the edge of the mold cavity, resulting in segregation of the powder particle size in the mold cavity, resulting in uneven compression ratio during molding, and compaction Size and shape will be difficult to control. In order to avoid the phenomenon of uneven accumulation of coarse and fine particles caused by the powder falling freely, the usual method is to fill the powder from the bottom of the mold cavity through the charging funnel, place the mold on the lifting platform, or hang the hopper on the lifting platform. on the device. In order to increase the filling density of the powder, keep the filling density consistent, and ensure the repeatability of the filling process, manual compaction and mechanical vibration are often used to achieve this. Small blanks and small batches are suitable for manual compaction; large compacts and large batches of production are suitable for mechanical vibration. It is better to vibrate while loading the material.
After the powder filling is completed, the charging port is sealed with an end plug, some use varnish as the adhesive to seal, or no adhesive is required, and it is best to use elastic bands for external bundling, so that during the compression deformation of the end plug , still has the function of fastening and sealing, and will not fall off. It is also effective to use iron wire to bind.
In order to improve the quality of the green compact, some products are larger in size. Before the sheath is sealed, a sponge pad or filter paper for filtering is placed between the powder and the end plug to prevent the powder from being taken away during pumping, such as using rubber The cover of the end plug can be inserted into the sponge pad through the rubber plug with the medical injection tube. The other end of the injection needle tube is connected with the vacuum system, which can realize the degassing of the powder in the cover. After the injection needle tube is taken out, the rubber stopper can Self-sealing, the easiest degassing device.
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