What is isostatic pressing of graphite?

What is isostatic graphite?

Isostatic graphite is an ultra-fine grain graphite that excels where the mechanical properties of other fine grain graphites fall short.

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The term "isostatic graphite" refers to graphite that is molded isostatically. This involves compressing the raw material mixture into rectangular or round blocks using a Cold-Isostatic-Press (CIP).

Compared to other methods like extrusion or vibration molding, this technique produces the most isotropic form of artificial graphite. Additionally, isostatic graphite typically has the smallest grain sizes among all artificial graphites.

The CGI and ESM series of graphites are formed through Cold Isostatic Pressing (CIP), resulting in graphite with very fine grains and high density.

Properties of isostatic graphite

• High strength
• Exceptional resistance to thermal shock
• High temperature and oxidation resistance
• Low electrical resistance
• Good corrosion resistance
• Precise machinability
• Low impurity content

Manufacturing process of isostatic graphite

Isostatic pressing involves multiple stages, producing blocks with extremely homogeneous structures and consistent physical properties through each section and point.

1. Cokes

Coke, a component produced in oil refineries by heating hard coal (600-1200°C), has a higher calorific value than conventional fossil coal. This transformation takes place in a specialized coke oven using combustion gases and limited oxygen availability.

2. Pulverizing

Raw materials are checked and pulverized to a specific grain size, creating very fine coal dust sorted into special bags by grain size using specialized machinery.

Pitch

Pitch, a by-product of coking hard coal without air at 1000-1200°C, is a dense black liquid essential to the next processing steps.

3. Kneading

Post-pulverizing, the coke is mixed with pitch at high temperatures, which causes the coal to melt, combining with the coke grains.

4. 2nd Pulverizing

The carbon balls formed from mixing are milled again into very fine grains.

5. Isostatic Pressing

The fine grains are then pressed into large molds corresponding to the final block sizes. High pressure (over 150 MPa) is applied symmetrically to achieve uniform grain distribution, ensuring consistent properties across the entire block.

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6. Carbonizing

The longest stage (2-3 months) is the baking process. The uniform material is placed in large furnaces heated up to 1000°C. The temperature is carefully controlled to prevent defects or cracks, resulting in a block of desired hardness.

7. Pitch Impregnation

The block may be impregnated with a lower viscosity pitch and baked again to reduce porosity. This step ensures better filling of the gaps.

8. Graphitizing

Graphitizing involves heating the blocks to about 3000°C, facilitating the transition from carbon to graphite. This step significantly enhances density, electrical conductivity, thermal conductivity, and corrosion resistance.

9. Graphite Material

Post-graphitizing, all graphite properties, including grain size, density, and strength, are inspected to ensure quality.

10. Machining

Once inspected, the graphite material can be manufactured according to customer specifications.

11. Purification

For applications in the semiconductor, silicon monocrystalline, and atomic energy industries, high purity is crucial. Impurities are chemically removed by heating the graphitized product in halogen gas at about 2000°C.

12. Surface Treatment

Depending on its application, graphite surfaces may be milled to achieve smooth finishes.

13. Shipment

After final machining, the finished graphite products are packed and shipped to customers.

Graphite Plates

We offer isostatic graphite in various forms, including:

- Graphite blocks

- Graphite plates

- Graphite rounds

- Graphite tubes

- Graphite sections

- EDM graphite electrodes for EDM processes

- Graphite casting dies

- Graphite tools and accessories

- Graphite parts according to drawings

Our machined isostatic graphite products can be purified to <5ppm upon request.

For more details, dimensions, isostatic graphite grades, and prices, feel free to contact us. Our engineers are ready to provide material recommendations and answer your questions.

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