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Green body swelling in graphite electrode

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

Compression ratio definition in graphite electrode 

The compression ratio is the ratio of the cross-sectional area of the chamber of the extruder to the cross-sectional area of the extruded product during extrusion.

Small tonnage extruder can not press large size products

Small-tonnage extruders cannot press large-size products, and barely squeeze not only does not meet product quality requirements, but may also damage the press.
 

Large tonnage extruder is not suitable for small size products

The large-tonnage extruder (larger indoor diameter) is not suitable for pressing small-sized products, not only wastes the capacity of the press, but also the quality of the pressed blank.

Green body swelling in graphite electrode

Green body re-expansion is the phenomenon that the diameter or volume of the green body increases due to the elastic effect of the plastomer after the green body is demolded or extruded from the extrusion nozzle.
 

Reboom rate definition

The rebound ratio is an important parameter for designing the size of the extrusion nozzle or the size of the mold when molding. The size of the expansion is related to various process factors.
 

There are 5 factors that affect the size of the rebound.

  • 1. The greater the extrusion pressure, the greater the green back swelling.
  • 2. The green swell rate of the fine granule formula product is larger than that of the coarse granule formula.
  • 3. The shorter the length of the extruded nozzle shaped section. The extruded green body swells more.
  • 4. The faster the extrusion speed at the time of extrusion, the higher the rebound ratio of the extruded green body.
  • 5. The cooling time is short, and there are more gases in the paste.

Excessive expansion will cause cracks on the surface

Re-expansion leads to a decrease in green density, and excessive expansion is one of the causes of cracks on the surface of the green body.
 

Vacuum exhaust operation

Vacuum evacuation is an operation in which the paste in the material chamber is discharged by a vacuum pump during compaction or extrusion during the molding process.

Size of graphite electrode

Item Unit HP
300-500mm 550-700mm
Electric resistivity Electrode μΩm 5.5-6.8 5.5-7.0
Nipple 4.0-5.5
Bending strength Electrode Mpa ≥10.0 ≥8.5
Nipple ≥18.0
Elastic modulus Electrode Gpa ≤13.0
Nipple ≤15.0
Bulk density Electrode g/cm3 1.62-1.70
Nipple 1.72-1.80
CTE(100-600℃) Electrode 10-6/℃ 1.80-2.20
Nipple 1.50-1.80
Ash % ≤0.3

The paste will produce gas after mixing

The kneaded paste mass contains a certain amount of coal bitumen to decompose and volatilize the gas, and most of the gas can be discharged in the case of cooling, but a small amount of gas is still contained in the agglomerate of the paste, and these gases affect the density of the paste. And forming structural defects inside the green body and increasing the elastic back expansion of the green body.
 
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