Tungsten Copper Powder Injection Molding Research

Based on conventional molding process and combines plastic molding industry technology, PIM (Powder Injection Molding) has excellent applicability in some tungsten copper products with small size and complex shape or structure. So we study from mixing, injection, degreasing, sintering and several key process of tungsten copper powder injection molding, and analyze and summarize the advantages of the process and the defects.

The first is the selection of the binder and the preparation of mixture. Binders can reduce caking of the powder, which has good flowability, and plays the role of maintaining the shape of the body until degreasing sintering. Thus the choice of the binder is injection molded in a key ring, it should meet the deformation and cracking does not occur before the product sintering defect, and easy to be removed. Now more use thermoplastic or some polymers as binders, such as paraffin, stearic acid, HDPE, EVA and so on. In the process of mixing, paraffin and stearic acid are liquid phase, which does not destroy the nature of the binder. In addition, wherein the order of addition of powder and a binder is the final state of the blank has a certain influence. The next is granulating, and select particles about 2-3mm for injection molding.

Many parameters of injection molding should be perfectly controlled, such as the temperature, the pressure, the speed and so on. Theoretically, in the process of injection molding, the temperature and pressure are the largest influencing factors of molding properties. In order to press tungsten copper powder mixture into the mold cavity, the temperature inside the injection machine must be high enough so that moderate viscosity mixing, the two-phase does not separate. For injection pressure (to overcome the flow mixing cavity flow resistance, provide filling speed and compaction of the melt) and speed in the experiment demonstrated that there is an optimal match range, pressure and speed should not be too large or too small. From the figure above, we can also find the optimum temperature range for injection, injection pressure and speed. Since the injection process to fill the cavity is more complex, many parameters must be well controlled, once appear unreasonable control can cause a variety of defects. We introduce some common defects and the corresponding solutions: 1. Under-injection, it refers to the injection process feed can not fill the mold cavity, the corresponding solution is three-pronged approach from the injection temperature, feeding quantity and viscosity of the feed itself causes analyzed; 2. The pores, it is the most common type of defect, the corresponding method is to pay attention to whether the injection and mixing of air entrainment and make adjustments, check the injection speed, the injection pressure, etc; 3. Unstable quality, it should be considered that whether the powder is uniform and the segregation with the binder.

Tungsten Copper Power Properties Test

Tungsten copper powder properties itself will directly affect the final performance of tungsten copper products so that the test of tungsten copper powder raw material becomes vital. At present, laser particle size analysis, transmission electron microscope, differential scanning calorimetry are the main test methods, next we will introduce and analyze them by theory and working principle.

Laser particle size analyzer judges the size of particles by distribution (ie, scattering spectra) by the diffraction space or scattered light particles. The method combines Fraunhofer with Mie scattering theory, when a bunch of laser irradiation wavelength λ in the small spherical particles of a certain size, the beam encounters a barrier, diffraction and scattering phenomenon will occur. Generally, when the particle size is less than 10λ, the main phenomenon is scattering, while the particle size is greater than or equal to 10λ, the main phenomenon is diffraction.

The most widely used laser particle size analyzer currently usually uses 500-700nm wavelength laser as a light source, which test particles size above 5μm is relatively accurate. For particle size of less than 5μm by Mie theory is mathematically corrected, which means that for the sub-micron or nano-scale particles have a certain measure of error. In addition, theoretical model of laser particle size analysis is based on spherical particles and mono-disperse condition, and thus for the particle shape and particle size distribution will have a greater impact on the final results of particle size analysis. The more irregular shape of particle, the wider particle size distribution, the final error will be greater. For tungsten-copper composite powders, the water as a dispersant and add ethanol for grinding, after 30 minutes of ultrasonic cleaning in distilled water dispersion of particle size analysis.

Next, we introduce transmission electron microscope (TEM), which is a kind of high-powered high-resolution microscope. Compared with common optical microscope, it uses electromagnetic field as lens and was widely used in super-fine grain, aggregates and some nano-scale material testing. Furthermore, since the electron beam penetration is weak, so the specimens for electron microscopy of ultrathin sections shall be made about a thickness of about 50nm, which require ultra-microtome machining. For tungsten-copper powder, the thickness is more than 100nm, if the sample is required and the powder milled sample was dissolved in ethanol, in an ultrasonic cleaning after the suspension of the dispersed drops in the electron microscope with a copper medium carbon film, powder morphology was observed after drying.

Finally, thermal analysis, which refers to a change in endothermic or exothermic reactions that take place through the heating and cooling process and the quality of the material, the components was analyzed and identified substance. It includes that differential scanning calorimetry (DSC), which measuring thermal transitions within the material and relevant to the relationship between temperature and heat flow. The shape of the melting peak on DSC curve reflects the particle size distribution; the information can be drawn melting enthalpy crystallinity. Themogravimentric analysis (TGA) records that temperature changes and the time the sample quality, measurable by TGA analysis of injection molding material at different temperatures of weight loss situation, and in order to determine the heating rate of heat degreasing.

Tungsten Copper Used in Vacuum Switch

Tungsten copper composite material has high hardness, high melting point, high strength and sweating property so that it can be widely used in high temperature, military fields, aeronautics and astronautics, vacuum switch, electronic packaging, EDM electrode and so on. Here we highlight tungsten-copper composite material in vacuum switch electrical aspects. Theoretically, vacuum switch is a kind of pressure in the vacuum system for the protection of the automatic controller, small size, excellent performance, stability, ease of maintenance and long service life. It can be widely used in various industrial automation environments, such as water utilities, petrochemicals, railways, military, pipelines, ships and so on.

When the vacuum pressure is greater than the set point, the controller will automatically cut off the circuit, signals, to ensure the normal operation of the system. When the pressure in the system is higher or lower than the safe pressure, pressure sensor immediate action within the controller, the controller makes contact on or off, the device stops working; When the pressure within the system to a safe pressure range of the device, the pressure sensor inside the controller reset immediately, the contacts within the controller turned on or off, the device is working properly. In order to adapt some high-voltage as well as vacuum switch electrical demand, related researchers developed special vacuum switch of tungsten copper. It can be perfectly adapt to flammable, explosive, high temperature and low temperature, moisture, corrosive environments, and gradually dominate the high-voltage (6-35V) grid and electrification equipment.

Tungsten copper composite materials require extremely low gas containing impurities (such as oxygen O2, N2 gas, etc.), it requires the use of a low gas content of raw materials and special process (high temperature sintering, vacuum infiltration, vacuum degassing, etc.) prepared. n these vacuum tungsten copper contact materials, in addition to conventional grades, the proportion of copper tungsten contact material has also developed a number of high-low tungsten copper tungsten copper, tungsten W is usually its content> 85%, such as W-10Cu, W-15Cu, etc., when asked tungsten copper material used in the case of low value when the closure, which can also add some other low melting point metal (such as antimony Sb, bismuth Bi, tellurium Te).

In contrast, there is a high copper content (60% -90%) of tungsten copper alloy, wherein W-70Cu Tungsten copper alloy products have been tested and Vickers hardness reaches1100MPa and 80% -85% IACS of high conductivity, and at 600 ℃ can still maintain a high hardness and conductivity, stable performance. Therefore, It also gradually replace some of the precious metal contacts (such as silver contacts, etc.), which significantly reducing the cost of the contact material. Overall, with the application of tungsten-copper composite materials more widely, for its new tungsten copper alloy materials research is also developing, such as tungsten copper with gradient structure, nano-crystalline tungsten copper, tungsten copper deformation processing, tungsten copper used in vacuum, tungsten copper with high or low content of tungsten, which replace the conventional materials in EDM, micro electronics, high temperature, military fields gradually. However, there are some problems of tungsten copper products in china, includes less high-end products, low utilization, the research and production are disjoint.

Tungsten Copper Contact for Air Breaker

Tungsten copper contact for air breaker is an important component in low-voltage distribution network and electric drive system, which can prevent it from overloading based on contacting and breaking circuit.When the general overload circuit, the overload current can not make the electromagnetic release of action, but can make the heat element to produce a certain amount of heat, to promote the bimetal heating up bending, push the lever to hook and lock release, the tungsten copper The main contact breaking, cut off the power. When the line short-circuit or serious overload current, short-circuit current exceeds the instantaneous trip setting current value, the electromagnetic release to produce a large enough suction, the armature to attract and hit the lever, so that the hook around the shaft seat rotation and lock release, The buckle under the action of the reaction force spring will be three main contact breaking, cut off the power.

According to different applications, tungsten copper air breaker can be divided into main contact, auxiliary contact and alarm contact.

Main contact: In the event of a serious overload or short circuit fault, the coil in series with the main circuit will produce a strong electromagnetic attraction to the armature to attract the top of the open hook, so that the main contact disconnected. When the power supply voltage returns to normal, it must be re-closed to work, which achieves the pressure loss protection;

2. Auxiliary contact: It is the circuit breaker main circuit point, a mechanical linkage on the mechanical contact, mainly for the circuit breaker sub-state display, connected to the circuit breaker control circuit through the circuit breaker of the separation, the implementation of related electrical control or interlock;

3. Alarm contact: Mainly used for the circuit breaker load overload short circuit or other fault free tripping.

Tungsten Copper Contact for SF6 Breaker

Tungsten copper contact for high-voltage breaker is kind of oil-free switchgear that uses SF6 gas as arc quenching medium and insulating medium. It has better performance in arc extinguish and insulation than oil circuit breaker and has high requirement of application, management, operation of SF6. So it main used for the voltage level of 110kv.

It composed of porcelain column structure: It also known as blocks, a plurality of identical unit interrupters and pillar insulators can be used to form the circuit breakers of different voltage levels. The circuit breaker consists of three independent single-phase and one hydraulic, electrical control cabinet. Each phase consists of two pillars of porcelain sets of four interrupters (fracture) in series. In each pillar porcelain top of the unit is equipped with two unit interrupter, 120 ° angle V-shaped arrangement, the two parallel capacitors are arranged horizontally.

Tank structure: Using the advantages of box-type multi-oil circuit breaker, the circuit breaker and the transformer together, compact structure, anti-seismic and anti-fouling ability. It is generally three-phase split-type, single-phase from the base, insulated porcelain casing, current transformers and single-break interrupter with the shell composition. Each phase is equipped with a hydraulic mechanism and a control cabinet which can be operated individually and can be operated in three phases by means of electrical control.

Characteristic

1. As insulating gas, SF6 has many advantages, is colorless, tasteless, non-toxic, non-flammable inert gas and has performance in cooling arc. Especially cooling effect under high arc temperature;

2. The chemical effect of SF6 gas itself is very stable, and has a very high dielectric strength;

3. Blocking effect: give full play to the effect of air blowing arc, interrupter small size, simple structure, breaking current, arc time is short, breaking capacitor or inductor current without re-ignition, over-voltage;

4. Long electrical life: 50kA full capacity of continuous breaking up to 19 times, the cumulative breaking current up to 4200kA, maintenance cycle is long, suitable for frequent operation;

5. Good sealing performance: SF6 gas has lower water content, arc chamber, resistance and pillar into separate air separation, on-site installation without opening, after installation with automatic connection; installation easy maintenance, and to prevent dirt and moisture Into the circuit breaker inside.

Tungsten Copper Contact for Electronic

Tungsten copper contact for electronic has excellent wear and corrosion resistance and mainly used for controlling electron motion in vacuum, air or solid. So it has a wide range of application, such as electronic components, connectors, semiconductor discrete devices, electro-acoustic devices, laser devices, electronic display devices, optoelectronic devices, sensors, power supplies, switches and other electronic chemical materials and parts.

1. Wedge-type Contact: By the use of double-headed bolt sets of spring pressure in the conductive seat on the pairs of contact and wedge-shaped contact block composition, the general wedge-shaped contact block as a moving contact. When the moving contact is contacting with the static contact, the contact surface will be cleaned by the friction. Its high electric stability, self-cleaning effect, increase the number of contacts and wedges may increase the rated current, but also increased the size of the horizontal, so the assembly is difficult;

2. Insert-type Contact: Static contact is composed of multiple trapezoidal fingers. There are two types of flexible conductive sheet and non-flexible conductive sheet. A flexible conductive piece of the socket, a finger on the groove, groove embedded in the insulating sleeve, into the coil spring, in order to ensure that the finger on the conductive rod pressure, the other end of the spring ring support, along the conductive rod (moving contact) around to adjust the touch finger position slightly.

China's electronic components production has accounted for more than 39% of the world. The major products include capacitors, resistors, electro-acoustic devices, magnetic materials, piezoelectric quartz crystal, micro-motor, electronic transformers, printed circuit boards. So tungsten copper contact for electronic also has a lot of the demands. With the expanding scale of China's electronic information industry, the Pearl River Delta, Yangtze River Delta, the Bohai Bay region, part of the central and western regions of the four major electronic information industry base initially formed. These areas of electronic information enterprise concentration, the industry chain is more complete, with considerable size and supporting capacity. However, there are some problems in electronic components industry, such as excess low-end products, and high-end products mainly rely on imports; lack of core technology, low product profits; inadequate investment for technology development.