Cold Isostatic Pressing

Most tungsten carbide products are manufactured by powder metallurgy through raw material preparation, milling, pressing, and sintering. For pressing, there are many different methods. Take tungsten carbide rods as an example, we can not only produce tungsten carbide rods by mold pressing, but also produce by extrusion pressing, and isostatic pressing. And in this article, we are going to talk about one method of pressing, cold isostatic pressing.

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What is cold isostatic pressing?

Cold isostatic pressing is a method of processing materials, which is quite similar to metal mold pressing. Cold isostatic pressing functions based on Pascal’s law, which states that pressure applied in an enclosed fluid is transmitted in all directions throughout the fluid without any change in the magnitude of the pressure.

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Cold isostatic pressing includes compacting powders by enclosing them in an elastomer mold which has low resistance to deformation. Liquid pressure is then applied uniformly to the mold to compress it. At the end of the process, a highly compact solid will be left.?

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Cold isostatic pressing can be used for plastics, graphite, powder metallurgy, ceramics, sputtering targets, and other materials and processes.

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Advantages of cold isostatic pressing

1. Uniform Density

Cold isostatic pressing ensures that materials have a uniform density. This means that there will be uniform shrinkage when the material is going through other processes such as sintering. The uniform density can be attributed to the fact that the pressure used in CIP reaches every part of the material with equal magnitude.

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2. Uniform Strength

Since the pressure used to compact the materials is equal in all directions, the material has uniform strength. Materials with uniform strength are usually more efficient than those without uniform strength.

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3. Versatility

CIP can be used to produce difficult shapes which can not be produced by other methods. In addition, it can be used to produce large-sized materials. The only limitation to the size of materials produced by this method is the size of the pressure vessel.

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4. Corrosion Resistance

Cold isostatic pressing improves the corrosion resistance of a material. Thus materials that undergo this process have a longer lifespan than most other materials.

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5. Mechanical Properties

The mechanical properties of cold isostatic pressed materials are improved. Some of the properties improved include ductility and strength.

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6. Powder Metallurgy

Cold isostatic pressing is used in powder metallurgy. It is used for the compacting step of powder metallurgy that comes just before the sintering step. In powder metallurgy, CIP is often used to produce complex shapes and dimensions.

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7. Refractory Metals

CIP is used to produce refractory metals. They include tungsten, molybdenum, and tantalum. Tungsten, for example, is used to manufacture wires for filaments in the lamp industry. Generally, refractory metals have a high melting point and are resistant to wear and tear.

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8. Sintering

Cold isostatic pressing usually comes right before sintering. Cold isostatic pressed products usually have a high green strength that allows them to be sintered faster than other materials.

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Types of cold isostatic pressing

Cold isostatic pressing also has two different types. One is wet bag isostatic pressing, and the other one is dry bag isostatic pressing. In the wet bag isostatic pressing, the powder is filled in a mold and sealed tightly. After filling the mold with powder, the mold is submerged in the pressure fluid within the pressure vessel. Then isostatic pressure is applied to the external surface of the mold, compressing the powder into a solid mass. It takes from 5 to 30 minutes to process material using wet bag technology. Thus, it is relatively slow. However, high-volume pumps and improved loading mechanisms can go a long way in speeding up the process.

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In the dry bag isostatic pressing, the mold is fixed in the pressure vessel. The powder is filled in the mold while it is still in the pressure vessel. After this, isostatic pressure from the pressure liquid is applied to the external surface of the mold, compressing the powder into a solid mass with a compact microstructure. Dry bag technology is ideal for the mass production of materials. It is way faster than wet bag technology.

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In producing tungsten carbide rods, dry bag isostatic pressing is used. Dry-bag isostatic pressing can also be used to press tungsten carbide bars, but only for that under 16mm diameter. Otherwise, it will be easy to break. During the dry-bag isostatic pressing, the forming pressure is high, and the pressing process is fast. Tungsten carbide bars after dry-bag isostatic pressing have to be ground before sintering. And then it can be sintered directly. In this process, the forming agent is always paraffin.

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