In the past, copper was widely used as an electrode mat […]
In the past, copper was widely used as an electrode material in electrical discharge machining. However, with the rise in copper prices and the advancement of graphite technology, the price of graphite materials has gradually declined, and graphite has become more and more commonly used as an electrode material for electrical discharge machining. So why does graphite have the opportunity to replace copper machine tools? This is because compared with copper, graphite materials have many advantages.
1. Mechanical processing. The graphite deceleration layer and the reflection layer are made of finely-processed blocks. Graphite masonry has various holes for fuel rods, control rods, instruments and tests. These holes have accurate dimensions. In addition, all graphite block masonry can prevent neutron flow and cooling gas leakage. For this reason, the processing of nuclear graphite requires higher precision than the processing of any graphite products. In fact, the accuracy is required within a few wires. In order to ensure the accuracy of product processing, a special high-precision processing machine is provided.
2. High purity. The purity of nuclear graphite moderator is one of the most valued properties. First, petroleum coke and coal pitch with high purity and low impurity content are selected as raw materials. The boron content in the raw material impurities should be low, because the 1 × 10 boron content is equivalent to increasing the cross section of lmb. High temperature graphitization. Most metal impurities volatilize at 2800 ～ 3000 ℃, and boron is difficult to remove because it is higher than 3000 ℃. Form B4C3. The requirements for the boron content in the raw materials are extremely strict. In addition to the raw materials, it is also very important to reduce foreign impurities and reasonable process systems through more than 10 processes in the production.
3. High density. Nuclear graphite should have a higher density, generally controlled at about 1.79 / cm, which basically meets the requirements of the graphite stack. The volume density of graphite represents the effective moderation rate of the moderator, and the density decreases the number of atoms per unit volume , The slowing rate will be reduced.
4. Small anisotropy. When graphite is used in nuclear reactors, Wigner growth due to thermal expansion and irradiation due to temperature rise. This phenomenon is very large in the direction perpendicular to the direction of extrusion, but small in the direction parallel to the direction of extrusion, so the graphite block cannot expand in the same proportion as the original shape. Therefore, the structure of the anisotropic expansion of graphite in the moderating layer composed of many graphite blocks cannot be ignored. Graphite anisotropy is mainly due to the extremely anisotropic nature of graphite crystal structure. On the other hand, the arrangement of coke particles during extrusion molding also has a decisive influence on the anisotropy of the product, so measures should be taken to reduce the anisotropy during the molding process.
Low density and small mass
The graphite density is only 1/5 of that of copper, and the UHP Graphite Electrode can greatly reduce the load during spark machining.
Smaller thermal expansion rate
The thermal expansion rate of graphite is 1/4 of copper, which can effectively reduce the deviation caused by electrode heating deformation.
The cutting resistance of graphite material is small, and its processing efficiency is about twice to three times that of copper. The use of graphite material can reduce the processing of electrodes.
It is easier to realize the processing of thin rib pattern
The processing of copper electrodes generated by cutting heat is prone to thermal deformation, because of the plastic nature of the material, elastic deformation will easily occur during processing of thin rib patterns, causing processing vibration; and graphite itself is sintered from particles, and its heat-resistant and brittle material Features can reduce processing deformation and vibration.
Outstanding EDM roughing effectiveness
The melting point of copper is 1083 ℃, and the temperature at the time of discharge can reach 1100 ℃. The use of copper electrodes is easy to wear, and the graphite will sublimate at 3550 ℃, so the adoption of high power graphite electrode is easier to withstand large currents, and it can also achieve a slighter Electrode consumption.
The reason why the graphite machine replaces the copper machine is shared here for everyone. As an EDM electrode processing material, compared with copper, the graphite electrode has less electrode consumption, fast discharge processing speed, good mechanical processing performance, light weight, and small thermal expansion coefficient. Such advantages have been gradually recognized and accepted by everyone.