The study of pre alloy powder used in diamond saw blades

Transcription

1 The study of pre alloy powder used in diamond saw blades Alloy is a kind of substance with metallic properties composed of a metal and another metal or other several metals or nonmetals. Alloy is generally prepared by homogeneous fused components liquids and then condensed. It s known as pre-alloy powder by melting a variety of metals into sprayed low melting point alloy powder. The property of diamond tool matrix is one of the key factors affecting the cutting performance of diamond tools. Therefore, the suitable process technology to modulate or mediate the property of matrix material has special significance to the stability and quality improvement of diamond tools. From the composition of matrix material, at present the process is to mechanically mix the metal powder and pre alloyed powder and then press and sinter. Its advantages are: large adjustable range of the combination and performance, but there are more affecting factors by using element powder. Thus, it is not easy to control the sintering quality of the matrix. The pre alloyed powder comes up with the shortcomings of mechanical mixing matrix powder which is widely used in the diamond tool production. Comparison of elemental powder matrix and pre alloyed powder matrix: diamond tool matrix uses pre alloyed powder and mainly comes with mechanical mixing matrix powder which is widely used in the diamond tool production. At present, most of diamond products in China are added in the form of single element mixed powder and the advantage of mechanical mixed powder matrix is easy to adjust the components ration. However, as the diamond is easy to be carbonized at high temperature, the sintering temperature of the diamond products is comparatively low (most under 1000 C), and the melting point of most the of metals especially the high strength metal

2 is higher than 1200 C, so their alloy has a high melting temperature. So, the matrix of the products produced under lower temperature sintering is mostly pseudo-alloy, namely most of the high melting point metals are melted or fused and formed into alloy with other small amount elements. And, in the sintering process, a large part of the low melting point metals are destroyed or volatile and cannot reach the performance requirements of the original matrix formulation design. Because most of the metal elements in the matrix have not played their advantages after the sintering, for example, cemented carbide sintered at 1520 C, the flexural strength of which reaches 1400~2000pa, but the tungsten cobalt matrix sample sintering at 950~1000 C has a flexural strength of less than 1000pa. What s more, the mixed powder is easily oxidized which seriously affects the sintering properties of the matrix. In order to further improve the physical mechanical properties of diamond matrix, pre alloyed powder of matrix powder emerges as the times require. To improve the mechanical property of the matrix For the mechanical mixing single metal powder, all the metals have their own melting temperatures which are of large differences, such as cobalt, nickel and titanium whose melting points are higher than 1400 C, but the melting temperatures of tin and zinc are only 230 C~420 C. The sintering temperature of diamond tools are generally at 700~1000 C. Too high temperature is easy to cause the diamond carbonization, thereby reducing the service life of diamond tools. In the sintering temperature of 700~1000 C, low melting point metals have already melted even some occurred burning phenomenon, and for high melting point metals, the matrix produced under low sintering temperature are mostly pseudo-alloy, namely most of the high melting point metals exist in elemental form and cannot play their roles so as not to meet the requirements of the original designed matrix alloy formulation. The metals are not fully alloyed in this kind of matrix: the particles of

3 each metals spread through solid melt, creep and bind in weak force, which affects the mechanical strength of diamond tools. If making the bond metals into pre-alloy powder, the alloy power has a single melting point, which can be controlled and chosen through adjusting the composition ratio. Pre-alloy powder is much more evenly than mechanical mixed powder and its property is also improved as completely alloying. In diamond sintering process, as long as the temperature rose above the liquidus phase line of pre alloyed powder which is functioned as adhesive composition, the powder will fuse and the sintering process is over, thereby, avoiding the drawbacks of most often appearing composition segregation and low melting point metal fusing and enriching easily as well as easy to oxidize and violate etc in the mechanical mixing power, thus ensuring the quality of diamond tools and improving the property of diamond tools greatly. To improve the matrix alloy holding force to the diamond Chinese diamond tools often have the package undesirability problem, leading to diamond off phenomenon. The current commonly methods is to add small amount of chromium and titanium etc. in the matrix, because they are elements of strong carbide and forming a thin layer of Cr3C2 or TiC between diamond and chromium powder, titanium powder which forms a certain bonding force between titanium, diamond powder and also keeps certain combination force with alloy matrix, so as to improve the holding force of matrix to diamond. But due to the combination of chromium powder, titanium powder in matrix alloy itself is a kind of loose combination, the effect by using the titanium powder, chromium powder to improve the matrix of diamond is limited and cannot solve the problem of matrix to diamond package insert fundamentally. The most fundamental way is to solve the wetting angle problem between matrix and diamond.

4 powder oxidation and dirty problem To solve the metal The metal powder is generally 200 fine grains in diamond tools and some of the metal powdersare easy to oxidize or get dirty, such as copper powder, titanium powder, manganese powder etc, which are hard for long time preservation, for example titanium powder is to be preserved in vacuum packaging. The sintering activity of oxidized metal powder is greatly reduced, seriously affecting the quality properties of diamond tools. For the pre alloy powder, because some antioxidant elements (such as chromium powder) are introduced, it improves the antioxidant capacity of the whole alloy and solves the long time preservation problem. Easy to meet the matrix property requirements The high antioxidant ability, good sintering property, fully alloying and homogeneous microstructure of pre alloy powder greatly improve the compressive and flexural strength of sintering products and easily meet the performance requirements of diamond tools matrix.

5 Beneficial to avoid heat damage to diamond and save energy Through the control of the pre alloy production process, it can obtain ultrafine and sub micron grade pre alloyed powder, which is good to improve the powder sintering property and greatly reduces the required activation energy of the metal element in the sintering process, lowers the sintering temperature in the diamond tools production, and shortens the sintering time, all of which are beneficial to avoid the heat damage and save energy. To simplify production process and reduce errors By using the pre alloy powder, the burdening is simplified as the weighing and mixing 2-3 powder ingredients, which decreases the error probability when weighing. It has loose requirements for the sintering temperature and sintering pressure when using pre alloy powders at the same time, which greatly reduces instability problem of diamond tool quality property because of the different production standards To prevent technology loss and contain leakage Through the use of pre alloy powder which is independently designed, developed, and produced or designated processed, it s good for technology security and prevents the business technology loss with the technical staff mobility. To improve the diamond tool quality and lower the cost It can improve the matrix holding force to the diamond tools, improve its sharpness and extend the life of the tools by using pre alloyed powders as the matrix of the diamond tools. Under the same performance, pre alloy powder application can reduce the diamond concentration of 15% to 20% so that the production cost is much cheaper.