Pressed Products

Isostatic Pressing at Almath

Isostatic pressing is a dry powder forming method. As the name suggests it uses equal pressure from all directions to press powder into the desired shape. It has the advantage over other pressing and forming techniques as it can press large shapes, high aspect ratio shapes and thick walls. The even pressure distribution ensures predictable, even shrinkage that avoids distortion and cracking.

The excellent powder density distribution and compatibility with machining techniques makes it particularly suitable for very large crucibles (up to 270mm high, 200 mm wide), crucible holders, or any technical ceramic component. The dry nature of the process makes it highly suited for forming magnesium oxide, which are sensitive to hydration. Almath can offer fully dense and porous crucibles in MgO, alumina and a variety of zirconia materials.

Complex technical ceramic components can be made by pairing it with Almath’s machining techniques. The strong binder systems used in isostatic pressing, and even density distribution make it possible to press blanks that can then be machined to any shape. This means highly complex shapes at demanding tolerances can be achieved.

Key differences between pressing and slip casting

Almath has traditionally manufactured crucibles through slip casting. This is a wet process where water from the slip is pulled into plaster moulds leaving behind a part that is then dried and fired. In isostatic pressing, binders are mixed with the ceramic powder. In this process the powder forms free flowing granules that fill moulds easily. These powders then bond together when pressed to produce the desired shape that can be easily handled and machined. Almath designs and manufactures its own tooling to rapidly turn around and optimise iso-pressed designs.

Iso-static pressing is more ideally suited to higher volumes than slip casting, as less drying of the parts and moulds is needed. The process can also manufacture wall thicknesses and sizes that are commercially prohibitive by slip casting. Iso-static pressing also opens up new design features for crucibles, as the cross-section does not need to be uniform, unlike slip casting. Similarly, features can be machined onto pressed parts to achieve almost any design

Almath Materials

Magnesium Oxide: Almath offers a fully dense, high purity, (99.2% MgO + Y₂O₃). Isostatic pressing avoids the introduction of water during manufacture, which MgO is known to react to increasing the design flexibility. MgO is ideally suited for melting alkali materials. Our high purity, pressed MgO crucibles are frequently used in the nuclear and green steel industry.

Alumina: Our standard alumina is a 99.8% alumina, which is fully dense. This has a low glass phase content for increased strength, toughness and durability. The high purity nature makes it ideal for high purity calcination and other high temperature process where contamination is paramount, such as in battery and biomedical fields.

Zirconia: Almath can offer a range of zirconia materials, stabilised with Yttria, Lime or magnesium oxide. Zirconia is ideal for higher temperature use than magnesium oxide and alumina and is compatible with acidic materials at high temperature.

ZTA: Our standard ZTA uses 10% zirconia added to alumina to cost effectively improve strength and toughness. We are able to increase the zirconia percentage to 30%, according to customer requirements.

Materials Development: Almath is able to develop any material to the required specifications. We are able to tailor porosity and composition and in the last year have developed several pressable grades of Ca stabilised zirconia and zirconia silicate.