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Mechanical properties of raw material

Release time:2019-12-06 From: Zhengnai Industry in China

Mechanical properties of carbon paste in graphite electrode

The change in mechanical properties over time is called mechanical relaxation, including stress relaxation, creep and dynamic mechanical properties.

Stress relaxation definition

Stress relaxation is the change in stress and modulus of an elastomer sample over time with constant strain.

The mechanical properties of carbon paste are affected by temperature

The mechanical properties of carbon paste are very sensitive to temperature, the temperature rises, the yield stress decreases, and the relaxation time is prolonged, which is important for the development of a reasonable extrusion process.

The essence of extrusion

The essence of extrusion molding is the elastic and plastic deformation process of the paste in the extrusion nozzle. The plastic deformation needs to occur when the applied pressure is large and the yield stress of the paste is forced to flow.

Charcoal plasticity related factors

The plasticity of the carbon paste has a great relationship with the formulation, and it is also closely related to the nature of the binder and the quality of the kneading.

The forming properties of carbon paste are special

The forming properties of carbon paste are special. After the formed green body, an anisotropic structure phenomenon in which density is uneven and heterogeneous often occurs.

Causes of cracks on the surface after molding

Due to the high elasticity of the carbon paste, a large internal stress is generated in the green body after molding, and the elastic aftereffect caused by the internal stress causes a dimensional change of the green shape, and in some cases, the green mold is released ( Cracks are formed on the surface after compression molding or extrusion (extrusion).

Causes of internal structural defects

If the plasticity of the paste is insufficient and the deformation speed is too fast during the extrusion process, a delaminated and sliding inner surface is generated in the green body, thereby causing internal structural defects.

One of the causes of cracking in green roasting

The density of each part of the green body is different, and internal stresses of different sizes and directions are generated inside the green body. This internal stress not only acts during molding or after molding, but also causes cracking of the green body during firing. 

Parameter of graphite electrode

Item Unit HP
Electric resistivity Electrode μΩm 5.8-6.6
Nipple 4.2-5.0
Flexural strength Electrode Mpa 10.0-13.0
Nipple 18.0-22.0
Elastic modulus Electrode Gpa 8.0-12.0
Nipple 14.0-16.0
Bulk density Electrode ≥g/cm3 1.62-1.66
Nipple 1.74-1.80
CTE(100-600℃) Electrode x10-6/℃ 1.6-1.9
Nipple 1.1-1.4
Ash   0.3

Plasticity when the paste is extruded depends on the binder

The plastic state of the paste extrusion depends to a large extent on the nature of the binder, ie the composition of the binder, the softening point, the change in viscosity after heating and the surface tension, and also on whether or not the lubricant is added.