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Product surface crack regulations

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

Green defect type

Green defects are defects in the appearance of the green body or internal non-compliance with technical standards. The green defects are generally observed with the naked eye. If necessary, the surface of the green body is struck with a small hammer to determine whether there are defects such as internal delamination, and defects that do not meet the technical standards of the process are treated as waste.

Graphite electrode Supplier

Our company has a special storage warehouse and storage method to ensure the safety of graphite electrode storage.

There are 3 kinds of cracks on the surface of the electrode green body.

The crack on the surface of the electrode green body can be divided into three types: longitudinal crack, transverse crack and reticular crack.

Longitudinal crack definition

Longitudinal cracks are cracks that appear along the length of the green surface

Lateral crack definition

The transverse crack is a crack appearing along the circumferential direction of the surface

Mesh crack definition

Crisscross  crack  called mesh crack

Product surface crack regulations

It is generally stipulated that longitudinal cracks or transverse cracks with a length of 10 mm or more are not allowed on the surface of small-sized products. Cracks of 1 mm or more and 50 mm or more in length are not allowed on the surface of large and medium-sized products.

There are 3 main reasons for cracks in graphite electrode

The main causes of cracking are:
  • 1. The kneading temperature of the paste,
  • 2. The temperature of the cooling material,
  • 3. The control of the molding operation is unreasonable.

Hemp surface definition

The surface of the product is a continuous or large area of rough scratches on the surface of the product. Generally, the width of the surface of the green surface shall not exceed one quarter of the circumference of the electrode, and the depth shall not exceed the allowable deviation of the rated diameter.

There are 4 main reasons for producing pockmarks.

The main reasons for producing pockmarks are: 1. The temperature of the extruded nozzle is too low, 2. The surface of the extrusion nozzle is not smooth or has a hard block, 3. The surface of the green pallet is not smooth or has a hard material. Block, 4. The surface of the skin produced by the "fish scales" due to friction during the extrusion of the green body.

Size of RP graphite electrode

Item Unit RP
300-500mm 550-800mm
Electric resistivity Electrode μΩm 7.5-8.6 7.5-8.8
Nipple 4.5-6.0
Bending strength Electrode Mpa ≥7.5 ≥6.5
Nipple ≥16.0
Elastic modulus Electrode Gpa ≤9.0
Nipple ≤13.0
Bulk density Electrode g/cm3 1.54-1.62
Nipple 1.70-1.78
CTE(100-600℃) Electrode 10-6/℃ 2.20-2.60
Nipple 1.50-1.90
Ash % ≤0.3

Adhesive performance

The surface of the green body is stained with a hard block and embedded in the surface layer of the green body when it is not sufficiently cooled. The reason is that the pallet of the green plate receiving table or the roller felt pad rolling to the water tank is not slag removed in time.

There are 5 reasons for bending and deformation.

The causes of bending and deformation are mainly 1. The binder content of the paste is more, 2. The water is not cooled in time after pressing, 3. The temperature of the cooling water is higher, 4. The roller path is deformed, 5. The green body is in Insufficient cooling time in cold water