Production process of molded graphite (1)

A typical production-process flow diagram for molded graphite is shown in fig.5.2. The production steps are as follows.

producton process flow diagram of molded graphite

fig.5.2-producton process flow diagram of molded graphite

Milling and sizing: filler and binder are ground or milled to the particle-size requirement which may vary from 1 um to 1.25 cm. A batch usually consists of more than one size. This allows better control of the packing characteristics and optimizes the density of the final product. Table 5.1 lists the grain size of various grades of molded graphites and its effect on properties.

Table 5.1. Particle sizes and characteristics of graphite grades

Grade Grain size properties
Medium grain Up to 1.25 cm Low density
Low thermal expansion
Low strength
High permeability
Fine grain 0.05 to 0.15 cm Medium density
Medium thermal expansion
Medium strength
Medium permeability
Micrograin <1 um to 75 um High density
    High thermal expansion
    High strength
    Low permeability

Mixing: filler and binder are weighed in the proper proportion and blended with large mixers into a homogeneous mix where each filler particle is coated with the binder. Blending is usually carried out at 160-170C, although temperatures may reach as high as 315C on occasion. When mixing at lower temperatures, volatile solvents such as acetone or alcohol are often added to promote binder dispersion.

The final properties of the molded product are controlled to a great degree of the characteristics of the filler-binder paste such as: (a) the temperature dependence of the viscosity, (b) the general rheological behavior, and (c) the hydrodynamic interaction between filler particles.


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