What is isostatic pressing of graphite?

What is isostatic graphite?

Isostatic graphite is an ultra-fine grain graphite used for applications where the mechanical properties of other fine grain graphites are inadequate.

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The term "isostatic graphite" stands for isostatically molded graphite. This means that the raw material mixture is compressed into rectangular or round blocks in a Cold-Isostatic-Press (CIP).

Compared to other technologies such as extrusion or vibration molding, this technology can produce the most isotropic form of artificial graphite. Additionally, isostatic graphite generally has the smallest grain sizes of all artificial graphites.

CGI and ESM series are isostatically pressed graphites which are produced by the method of Cold Isostatic Pressing (CIP). This very fine grain graphite material allows high densities to be achieved.

Properties of isostatic graphite

• high strength
• excellent resistance to thermal shock
• high temperature and oxidation resistance
• low electrical resistance
• good corrosion resistance
• precise machining
• low content of impurities

Manufacturing process of isostatic graphite

Isostatic pressing is a multi-stage process and enables the production of blocks with an extremely homogeneous structure, maintaining consistent physical parameters across all sections and points.

1. COKES

Coke is produced in oil refineries by heating hard coal (600-1200°C) in a specially designed coke oven, using combustion gases and limited oxygen availability. It has a higher calorific value than conventional fossil coal.

2. PULVERIZING

After raw materials are checked, they are pulverized to a specific grain size. Special machines grind the material, transferring the fine coal dust into bags sorted by grain size.

PITCH

Pitch, a by-product of coking hard coal (heated without air at 1000-1200°C), is a dense black liquid.

3. KNEADING

Once the coke milling process is complete, it is combined with pitch. Both raw materials are mixed at high temperatures so that the coal melts and combines with the coke grains.

4. 2ND PULVERIZING

After mixing, small carbon balls are formed and must be milled again to achieve very fine grains.

5. ISOSTATIC PRESSING

Once the fine grains are ready, the pressing stage follows. The powder is placed in large molds corresponding to the final block sizes. The powdered carbon in the molds is exposed to high pressure (over 150 MPa), which applies equal force and pressure to the grains, ensuring symmetrical arrangement and even distribution. This method allows for uniform graphite parameters across the entire mold.

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6. CARBONIZING

The next and longest stage (2-3 months) is baking in the furnace. Evenly pressed material is placed in large furnaces reaching temperatures of 1000°C. The temperature is constantly controlled to avoid defects or cracks. When baking is complete, the block achieves the desired hardness.

7. PITCH IMPREGNATION

At this stage, the block can be impregnated with pitch and burned again to reduce its porosity. Impregnation usually uses pitch with lower viscosity than the binder pitch, allowing precise gap filling.

8. GRAPHITIZING

During graphitization, the carbon atoms' matrix is arranged orderly. The blocks are heated to about 3000°C. After graphitization, density, electrical conductivity, thermal conductivity, and corrosion resistance are significantly improved, enhancing machining efficiency.

9. GRAPHITE MATERIAL

After graphitization, all graphite properties, including grain size, density, and strength, must be inspected.

10. MACHINING

Once the material is fully ready and inspected, it can be manufactured according to customer documentation.

11. PURIFICATION

If isostatic graphite is used in industries like semiconductors, silicon monocrystalline, and atomic energy, high purity is required. Impurities are removed chemically. Typically, the graphitized product is placed in a halogen gas and heated to about 2000°C.

12. SURFACE TREATMENT

Depending on its application, graphite surfaces can be milled for smooth finishes.

13. SHIPMENT

After final machining, the finished graphite detail is packed and shipped to the customer.

Graphite plates

We can deliver our isostatic graphite in these forms:

- Graphite blocks

- Graphite plates

- Graphite rounds

- Graphite tubes

- Graphite sections

- EDM graphite electrodes for EDM process

- Graphite casting dies

- Graphite tools and accessories

- Graphite parts according to drawing

Our machined isotatic graphite products can also be purified to <5ppm on request.

For further information on available dimensions, isostatic graphite grades, and prices, please feel free to contact us. Our engineers will be pleased to advise you on the right material and answer all of your questions.

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