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Graphite Electrode Machining

Release time:2019-11-04 From: Zhengnai Industry in China

Graphite electrode processing

The graphite electrode processing is divided into two independent processing parts of the electrode body and the nipple. The electrode body processing includes three units of operation such as outer circle of the vehicle, machining of the end face, machining of the connecting thread in the nipple hole, and cutting of the half buckle. The joint processing includes the outer circle of the car, the processing of the male thread on the outer round surface, the flattening of the two end faces and the processing of the half buckle and other three unit operations.
The graphite electrode processing is divided into two independent processing parts of the electrode body and the nipple. 


 

Electrode processing characteristics

Graphite electrode is a kind of non-homogeneous brittle material. Its hardness is not high, it is easy to cut, and it can be processed into products with higher precision and different shape. The surface finish of the processed product is affected to some extent by the particle size of the product. The influence of the composition.
 

The graphite particles with different sizes are produced during cutting

The cutting heat is generated when the graphite electrode is cut, but the coolant or protective lubricating fluid is not needed on the processing surface. At the same time, it will produce a certain impact vibration, so high-speed steel or carbide tools with better resistance to shock and vibration are generally used .
A large amount of dust is generated during the cutting process, which not only pollutes the environment, but also affects the health of the operator. Moreover, some impurities such as silicon carbide in the graphite dust will cause certain wear on the machine tool components, so the machine tool for cutting the graphite electrode must be installed with high efficiency. Dust collection equipment.
For graphite electrodes, the higher the cutting speed, the more prolonged the continuous use time of the blade.


 

Electrode processing quality standard requirements

The threading precision of the joint hole and nipple conforms to the standard, ensuring that any electrode of the same specification and any nipple of the same specification can achieve a reliable connection without loosening the trip.
The torso of the electrode body is perpendicular to the end surface, ensuring that the upper and lower electrodes are connected in a straight line, and there is no obvious gap between the end faces.
The electrode body is kept concentric with the nipple hole.
 

Graphite electrode machining

After calcination and graphitization, the size of the formed blank varies, sometimes bending and deforming to a certain extent, bumping or falling, and the surface is rough and uneven because of some fillers or other impurities. It must be properly machined to cut off a layer of skin, and achieve the required external diameter size and surface light. Cleanness. Because graphite electrodes are continuously used in electric arc furnace, it is necessary to cut both ends flat, then process the nipple holes with nut threads on both ends, and process the nipples with corresponding size and outer common threads with specially prepared nipple blanks for connection.
Machining is the last step in the production process of graphite electrodes.

Size of UHP/RP Graphite electrode

Item Unit UHP RP
300-500mm 550-600mm 700-800mm 300-500mm 550-800mm
Electric resistivity Electrode μΩm 4.6-6.2 4.5-6.0 4.5-5.8 7.5-8.6 7.5-8.8
Nipple 3.5-5.0 3.4-4.5 3.3-4.3 4.5-6.0
Bending strength Electrode Mpa ≥10.5 ≥10.0 ≥10.0 ≥7.5 ≥6.5
Nipple ≥20.0 ≥22.0 ≥23.0 ≥16.0
Elastic modulus Electrode Gpa ≤14.0 ≤14.0 ≤14.0 ≤9.0
Nipple ≤20.0 ≤22.0 ≤22.0 ≤13.0
Bulk density Electrode g/cm3 1.66-1.73 1.68-1.74 1.54-1.62
Nipple 1.75-1.82 1.78-1.85 1.70-1.78
CTE(100-600℃) Electrode 10-6/℃ 1.20-1.50 1.10-1.50 2.20-2.60
Nipple 1.10-1.40 1.00-1.30 1.50-1.90
Ash % ≤0.3

 

Graphite electrode processing accuracy

In order to ensure the reliable connection of the graphite electrode in the electric arc furnace, it is not loose, does not trip, and is not easy to break. The graphite electrode processing must achieve high precision. The accuracy of the dimensional deviation and the shape of the thread in the Chinese graphite electrode quality standard only specifies the maximum value of the positive deviation of the electrode nipple hole diameter and the maximum value of the negative deviation of the nipple diameter. The end face gap of the two electrode nipples is not more than 0.5 mm, and the electrode The deviation between the center line of the body and the nipple hole is not more than 3mm, but it is not clearly defined in other aspects.
 

Graphite electrode machining accuracy deviation type

Graphite electrode processing requires high accuracy, but in actual processing, it is often caused by defects in the quality of the billet, or processing machine tools, tools, measuring tools and processing operations and other reasons that the processing accuracy can not meet the requirements. The center line of the electrode body does not coincide with the center line of the nipple hole, and the upper and lower ends of the electrode are not coincident. Problems such as non-parallel surface or the center line of the electrode body is not perpendicular to an end surface, deviation of pitch, deviation of taper, deviation of thread angle or thread angle center line, etc.


 

Graphite electrode processing equipment

The graphite electrode processing method is divided into two types using ordinary lathe processing and using a specially designed combined machine tool. The outer circle, end face and thread processed by the ordinary lathe cannot achieve high precision, and the processing efficiency is relatively low. However, according to the investment comparison, the price of ordinary lathe is much lower. For example, the ordinary lathe is properly modified, the rigidity is increased, the transmission gear ratio is adjusted, the maintenance is usually meticulously maintained, and the reasonable cutting parameters are specified. The appropriate tool is selected, the operation is serious, and the machining can also be processed. A graphite electrode with an accuracy that meets the standard. The use of specially designed combined machine tooling equipment is a highly efficient and highly accurate processing equipment, but at the same time expensive.
 

Processing tool selection

The tool is an important condition in the machining process of the product. The choice of tool material, tool shape and sharpening angle and cutting parameters are important reference standards when selecting tools.
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