The Graphite electrode and it's application in industry

What is the graphite electrode and it's application in industry?

Introduction

Graphite electrode refers to a kind of resistant material made by using petroleum coke and pitch coke as aggregate and coal pitch as binding agent through raw material calcination, crushing and grinding, batching, kneading, molding, roasting, impregnation, graphitization and mechanical processing. The high-temperature graphite conductive material is called artificial graphite electrode (graphite electrode for short), which is different from the natural graphite electrode prepared by using natural graphite as raw material.

advantage

(1) The increasing complexity of mold geometry and the diversification of product applications have led to higher and higher requirements for the discharge accuracy of the spark machine. The advantages of graphite electrodes are easier processing, high removal rate of electrical discharge machining, and low graphite loss. Therefore, some group-based spark machine customers abandon copper electrodes and switch to graphite electrodes. In addition, some special-shaped electrodes cannot be made of copper, but graphite is easier to form, and copper electrodes are heavier and not suitable for processing large electrodes. These factors have caused some group-based spark machine customers to use graphite electrodes.

(2) Graphite electrodes are easier to process, and the processing speed is significantly faster than copper electrodes. For example, the use of milling technology to process graphite, the processing speed is 2 to 3 times faster than other metal processing and does not require additional manual processing, while the copper electrode requires manual frustration. Similarly, if a high-speed graphite machining center is used to manufacture electrodes, the speed will be faster and the efficiency will be higher, and there will be no dust problems. In these processes, choosing tools with appropriate hardness and graphite can reduce tool wear and copper electrode damage. If you specifically compare the milling time of graphite electrodes and copper electrodes, graphite electrodes are 67% faster than copper electrodes. In general electrical discharge machining, machining with graphite electrodes is 58% faster than copper electrodes. In this way, the processing time is greatly reduced, and the manufacturing cost is also reduced.

(3) The design of the graphite electrode is different from that of the traditional copper electrode. Many mold factories usually have different allowances for roughing and finishing of copper electrodes, while graphite electrodes use almost the same allowances. This reduces the number of CAD/CAM and machine processing. For this reason alone, It is enough to improve the accuracy of the mold cavity to a large extent.

Processing

(1) Processing form of graphite material

There are three main types of graphite electrode processing: pressurized vibration method, numerical control automatic forming method and mechanical processing method.

(1) Pressurized vibration method: The pressurized vibration method requires a special machine tool, and the electrode master mold has the opposite shape to the electrode. The graphite material and the forming tool are placed relative to each other during processing, leaving a certain gap. The machining fluid, which is mixed with water and abrasive, is injected into it. While passing the machining fluid, the graphite and the forming tool are ultrasonically vibrated. Under the action of the abrasive impact force, the graphite is slightly exfoliated into the required shape. The abrasive is SiC, B4C or diamond. The coarser the abrasive, the faster the processing speed. When the machine tool is working, it adopts sealed and water curtain type for processing. It is suitable for EDM forming in mass production.

(2) Numerical control automatic forming method: The numerical control automatic forming method requires a dedicated graphite electrode forming machine, which adopts the numerical control method, has an automatic tool exchange device, and can accommodate multiple tools. In order to improve the processing environment, the graphite electrode is surrounded by a water curtain to prevent the graphite dust from dispersing. In addition, the wet machining method can also be used to prevent tool wear and graphite dust from scattering by water-soluble cutting fluid. The machine tool has a high-performance filter device, which can separate the cutting fluid and graphite chips, and can ensure continuous processing for a long time. It is an ideal special equipment for graphite electrode processing and is suitable for electrode processing for molds. However, its price is relatively high, and its application in China is not yet widespread.

(3) Mechanical processing method: The mechanical processing method is the main method adopted by the general domestic mold production units.

Graphite materials can be processed by turning, milling, drilling and grinding methods. In addition, graphite materials are prone to fly ash during mechanical processing, which will adversely affect processing equipment and operators.

(2) Processing procedures of graphite materials

1) Graphite immersion oil. Graphite materials should be immersed in engine oil for dozens of hours before machining, so that the oil can penetrate into the graphite material so that the ash will not fly up during machining and a smoother surface can be obtained.

2) Paint and mark. After the electrode is rough-processed on the contour surface, a thin layer of white paint is sprayed on the scribed surface and then scribed, so that the lines are clear and easy for mechanical processing.

3) Perform mechanical processing.

Application

(1) For electric arc steelmaking furnace

Electric furnace steelmaking is a big user of graphite electrodes. The output of electric furnace steel in my country accounts for about 18% of the output of crude steel, and graphite electrodes for steelmaking account for 70% to 80% of the total consumption of graphite electrodes. Electric furnace steelmaking uses graphite electrodes to introduce current into the furnace, and uses the high temperature heat source generated by the arc between the electrode end and the charge for smelting.

(2) Used in submerged electric furnace

The submerged electric furnace is mainly used for the production of industrial silicon and yellow phosphorus. Its characteristic is that the lower part of the conductive electrode is buried in the charge to form an arc in the charge layer, and the heat energy from the resistance of the charge itself is used to heat the charge, which requires current High-density submerged electric furnaces need graphite electrodes. For example, about 100 kg of graphite electrodes are consumed for every 1 ton of silicon produced, and about 40 kg of graphite electrodes are consumed for every production of 1 ton of yellow phosphorus.

(3) For resistance furnace

Graphitization furnaces for the production of graphite products, melting furnaces for melting glass, and electric furnaces for the production of silicon carbide are all resistance furnaces. The materials in the furnace are both heating resistors and objects to be heated. Generally, conductive graphite electrodes are embedded at the end of the resistance furnace. In the furnace head wall of the part, the graphite electrode used here is discontinuously consumed.

(4) Used to prepare special-shaped graphite products

The blanks of graphite electrodes are also used for processing into various crucibles, molds, boats and heating elements and other special-shaped graphite products. For example, in the quartz glass industry, 10t of graphite electrode blanks are required to produce 1t of fused tubes; 100kg of graphite electrode blanks are required to produce 1t of quartz bricks.