Isostatic Pressing

Isostatic pressing

    Isostatic pressing is a defined as the loose aggregate of powders into a rigid shape by the application of uniform hydrostatic pressure to the powders that contained in a flexible rubber container. It is also called as “Biaxial pressing"

Steps involved in Isostatic pressing:

Step 1:        Select the ceramic powders

Step 2:        Filling the mould with powder

Step 3:        Apply load on the mould to press

Step 4:        Pressurize and hold the mould

Step 5:        Depressurize and remove the mould

Step 6:        Removal of compact powder

Step 7:        Sinter the compact powder

Types of Isostatic pressing:

There are two types of isostatic pressing. They are as follows:

• Wet Bag Pressing
• Dry Bag Pressing

Wet Bag Pressing

    Wet bag isostatic pressing consists of a steel chamber and hydraulic fluid contained in it. Then, the flexible rubber mould filled with powders is submerged into the pressure vessel. Inside the rubber mould, powder gets compressed by the application of pressure to the fluids. During this process, deformation takes place so that pressure is transmitted uniformly to the powder and then compaction occurs. After pressing, the flexible rubber mould is removed.  Hydraulic oil, glycerine and water are the non compressible fluids which are used for isostatic pressing. The walls of the chamber are made using by elastomer like silicones, rubber, neoprene and butyl rubber. This method is suitable for the compaction of complex as well as large shapes.

Wet bag isostatic pressing

Advantages

• Uniform density
• Tooling cost is lower
• Various shapes per cycle

Disadvantages

• Cycle time is 5-30 minutes
• Automation is difficult
• Longer cycle time
• Labour requirement is higher

Dry Bag pressing

    Dry bag isostatic pressing is able to operate easily than the wet bag isostatic pressing. In dry bag isostatic pressing, mould is permanently fixed into the pressure vessel and the mould is an intrinsic part of vessel. After the mould is filled with powder, pressure is applied between the fixed mould and the wall of pressure vessel. This type of pressing is followed to achieve a higher production rate. This method is suitable for producing hollow tubes, ceramic pipes and spark plugs.

Dry bag isostatic pressing

Advantages

• Production rate is higher
• Cycle time is lesser than one minute

Disadvantages

• Higher tooling cost
• One part at a time (automated)

Advantages of Isostatic pressing

• Good uniform density
• Better compaction
• Does not required any lubricants
• Light weight of the machine
• Pressure distribution is programmable with good accuracy
• Upgraded functionality
• Safe to use
• Formation of defects is much severe than uniaxial pressing

Disadvantages of Isostatic pressing

• Slower than uniaxial pressing
• Pressing parts may require post machining
• Delamination and fracture can occur (if the pressure is released rapidly after the compaction process and this happened due to spring back effect)

Applications of Isostatic pressing

• Food
• Chemicals
• Cutting tools
• Fabrication of cone classifiers, radomes and cathode ray envelopes
• Explosives
• Aircraft fittings