Improve the quality of China's diamond tools from the craft
China is also a large ceramics producing country. In 1999, the total output of various types of ceramic tiles was 1.6 billion square meters (33.6% of the world's total output), and the total consumption was 1.3 billion square meters (30.8% of the world's total consumption). There are more than 1,000 diamond and diamond tool manufacturers. In 1999, the annual output of diamonds exceeded 750 million carats, making it a major diamond producer. Diamond saw blades have been able to meet domestic demand. Nearly one-third of the products are exported, forming a certain competitive strength in the DIY market.
Although China has entered the ranks of major powers in the above aspects, it is not yet a strong country. With the integration of the global economy and China's entry into the WTO, how to make China a powerful country in the production of diamond tools is an important issue facing our counterparts. According to our practice and investigation, we only put forward some views on improving the quality of diamond tools in China.
1. Providing high-strength diamond diamonds with stable mass production, coarse particles and good thermal stability for diamond tool manufacturing. Grade quality, particle size and concentration have a decisive effect on diamond tools. In China's diamond synthesis, the six-sided top small tonnage high-strength process has matured, the six-face top large tonnage large cavity process has been continuously improved, and the two-side top synthetic diamond has also begun to take shape. The powder catalyst synthesis, carbon, and pyrophyllite block raw materials are continuously produced. perfect. Therefore, for the manufacture of diamond tools in China, high-strength diamond with stable performance, coarse particles and good thermal stability is possible. Foreign diamond companies, in addition to the SDA+, SDB, DSN, MBS, ISD series, DeBeers launched BKI, BK30, BK60, BK70 diamonds for the Chinese market, South Korea's Rijin company launched six-sided synthetic SDS series diamonds, all worthy of China Learn from peers.
2. Using strong carbide forming elements to improve diamond holding force A key factor in improving the cutting efficiency and life of diamond saw blades is to increase the holding power of the carcass to diamond. The carcass has a good grip on the diamond, the diamond will not fall off prematurely, and has the largest protruding height, sharp cutting and high efficiency.
There are generally three ways to increase diamond holding power:
(1) Improve the mechanical holding power. This is because the metal powder shrinks during sintering, forming a compressive stress to hold the diamond. The compressive stress is generated due to the difference in thermal expansion coefficient between diamond and the carcass metal, which is caused by volume change during sintering or crystal formation and growth. Due to the limited yield strength of the carcass, the resulting compressive stress and mechanical holding force are limited.
(2) Adding a small amount of strong carbide forming elements such as Cr, W, Mo, etc. to the powder, because of its good wettability and affinity for diamond, carbides are formed at the interface between diamond and the carcass metal during sintering to achieve diamond The combination of sub-gold is conducive to strengthening and improving the holding power.
(3) The surface of the diamond is plated with a layer of strong carbides to form metal elements such as Cr, Ni, Ti, W, and the like. This is a process that has been adopted in recent years. To this end, Yanshan University has specially developed and produced three types of vacuum micro-evaporation titanium plating equipment.
According to experimental research and use at home and abroad, the most effective conditions and scope of diamond plating technology are:
1 is suitable for high grade diamond, the effect is more obvious;
2 The order of improvement of the holding force in the pure drill carcass is: Cr plating > Ti plating > unplated diamond.
3MBS-960Cr2 chrome diamond is suitable for Co-based carcass, low-iron low-bronze carcass and WC carcass.
4MBS-960Ti2 titanium-plated diamond is suitable for drilling bronze-based carcass and iron-based carcass.
5 Tungsten-plated diamond is used in cutting asphalt, concrete concrete (GreenConcrete) and reinforced (reinforced steel) saw blades.
6 nickel-plated diamond is suitable for resin bond grinding wheel, and its effect is as follows: needle-shaped nickel-plated diamond > nickel-plated diamond > unnickel-plated diamond.
7 Silver-plated diamond is suitable for grinding precision resin bond grinding wheels for tungsten carbide cemented carbide tools. Because the price of silver is not very expensive, it is suitable for high-precision grinding, and its thermal conductivity is good, suitable for oil-cooled grinding of hard alloys. At the same time, silver is a good lubricant, which can reduce the friction between the grinding wheel and the workpiece, and the heat is not large.
The plating of strong carbide forming elements such as Ti, Ni, W, Cr, etc. improves the diamond holding power, mainly due to:
1 plating metal can prevent oxidation, graphitization and thermal corrosion of diamond under certain temperature, pressure and sintering time conditions. The author carried out TG (thermogravimetric) analysis on different metal-plated diamonds and found that diamond began to lose weight and graphitize at around 800 °C. When diamonds such as Ti, W, and TiN are plated at 900 ° C, 925 ° C, and 940 ° C, weight loss and graphitization begin. It shows that the diamond is coated with metal to prevent oxidation and graphitization, and can withstand thermal shock and thermal decomposition. It has obvious protective effect on high temperature sintered carcass.
2The plated strong carbide element can form a carbide alloy at the interface between the diamond and the carcass under sintering conditions, which is beneficial to the chemical bonding and metallurgical bonding between the diamond and the carcass metal, greatly improving the holding force of the carcass on the diamond, and the tungsten plating X-ray analysis of the diamond revealed that a WC phase had formed on the diamond surface.
3 can increase the static pressure of diamond by 5% to 20%.
4 diamond plating metal can improve the friction of diamond, while the latter helps to increase the holding power.
3. Using ultrafine powder and prealloyed powder In the production of special saw blades, ultrafine metal powder and prealloyed powder should be used. The refinement of the metal powder is advantageous for lowering the sintering temperature and increasing the hardness. The use of pre-alloyed powder prevents premature loss and segregation of low-melting metals, favors the elastic limit and yield strength of sintered products, increases the holding power of diamonds, and reduces sintering temperature and holding time. China Shanghai Materials Institute, Beijing Artificial Crystal Institute, Changsha Metallurgical Materials Institute and Central South University of Technology Powder and Metallurgical Institute have done a lot of work in this regard. South Korea's ultra-fine powders and pre-alloyed powders from BASF, UM, INCO, Fum-Tunge, and Kennametal are widely used in the production of high-grade saw blades.
4. Promote granulation process in the production of cutter head The granulation process has been widely used in the production of cemented carbide and ceramics in China. In recent years, it has also been widely used and developed in the production of diamond cutter heads. The advantage of powder granulation is that the segregation of diamond is reduced, the distribution is more uniform, the cutting performance of the cutter head is improved, the fluidity of the powder is increased, the application of the volumetric cold press process is made possible, and the ordinary cold press process is better, reducing The harm of dust to workers. The disadvantage is that investment and process procedures are added, and binders are added during granulation, which may have an adverse effect on welding, sintering and carcass performance. The advantages and disadvantages of various granulation methods are shown in the table below.
Disadvantages: need to be cleaned, no diamond, only one metal, large equipment.
Rolling method: Advantages: easy to operate, good paraffin adhesion, spherical. Disadvantages: The granulation process is unstable, contains diamond, and is difficult to granulate. It needs to be sieved.
Extrusion screening method: advantages: fast speed, less binder, easy to operate. Disadvantages: no diamond, need to be screened, shape is not uniform, the pass rate is 20% to 40%.
Manual screening method: advantages: simple, low investment, can contain diamonds, and the production volume is small. Disadvantages: It is difficult to select the binder, the labor required is heavy, and the shape is irregular.
Pressure sieving and rolling method: Advantages: stable process, easy to clean, automatic, diamond-containing, one-time granulation optional. Disadvantages: It is difficult to choose a binder, and more flux is needed.
Low-speed mixing high-speed cutting method: advantages: can be automated, the size of the particle can be artificially controlled. Disadvantages: no diamond, the amount of granulation can not be too small, the pass rate is 70% to 80%.
Germany Feiyu Company introduced GA180 and GA240 granulators, and its granulation process is composed of mixing → adding binder stirring → scraping and sieving → rolling granulation. This method is used to increase the cold pressing speed of the cutter head by 3 times, the die life by 1 time, and the cold press cost by 2/3.
South Korea Dixex Company launched CA-10 granulator, the process consists of dry mixing with binder → low-speed mixing (25 ~ 28r / min) → high-speed cutting (2300 ~ 2800r / min).
In order to granulate, Germany developed GB300, 400, 500 type binder, Korea used Olycox, China WS-120 granulating agent developed by Nanjing Sishang Science and Trade Center is a white group spheroidal powder with a density of 1.068g/cm3. The thermal decomposition temperature is 320-350 ° C, and the residual ash after sintering is <0.01%. It has replaced imported binder and has been widely used in various diamond tool factories.
5. Promoting vacuum protection atmosphere in sintering process Hot pressing sintering process and equipment sintering is a key process in the production of diamond saw blades. Its quality will affect the density, hardness and cutting performance of the saw blade, and the technical performance of the sintering equipment. Affect the production cost, product and quality of saw blades. Recently, we conducted a survey on the overall sintering furnace of diamond saw blades. The comparative sintering tests were carried out using the same formula powder in several representative furnace types. The results show that:
(1) Hydrogen protection, pressureless sintering, and furnace and bell furnace are suitable for the production of low-grade small-size saw blades, which have a large single output, but the saw blade has a low life;
(2) CSF500 hot-pressing sintering furnace, the furnace temperature distribution is uniform, and the nitrogen-protected pressure-sintered saw blade has high hardness and high density. Sharp and long-lasting when sawing, it can produce high-grade saw blades, and can produce multi-species and multi-species saw blades;
(3) RYL series medium frequency atmosphere protection hot press sintering furnace has superior design performance and is suitable for mass production of single specification saw blade, but the adaptability to many varieties is poor, and the furnace temperature distribution needs to be further improved;
(4) After the SF500 and ZBRY-2 sintering furnaces are perfected, they are a promising sintering equipment.
6. The use of hot isostatic pressing and high-temperature brazing in the production of diamond wire saws For nearly a decade, diamond wire saws have been creatively applied in quarrying and construction projects, making diamond wire saws from quarry to stone processing plants. From large-scale cutting to dressing, from sheet metal cutting to processing of shaped products and various applications in construction engineering, it has a 10% share of stone cutting worldwide and has a growing trend.
There are several main features in the development process:
(1) The bead production method consists of electroplating single layer and double layer metal diamond beading, to hot pressing sintering and high temperature brazing beading, so that the application range of the wire saw is expanded from marble to granite and concrete.
(2) The diameter of the wire saw is reduced from 10 to 12 mm to 6 to 8 mm, which improves the cutting efficiency and reduces material consumption.
(3) The development of the CNC controlled wire saw machine makes it possible to make a multi-wire saw, so that the wire saw machine can enter the plate factory, which can effectively cut the plate and the special-shaped products, and can replace the frame saw and the bridge plate saw machine.
(4) The hot isostatic pressing process is used for beading production to improve the density, hardness, strength and service life of the bead.
Hot isostatic pressing (HIP) is to place the sintered product in a hot isostatic press with an inert gas Ar (argon) as the pressure transmitting medium, the temperature rises to 1320 ~ 1400 ° C, and the gas is thermally expanded to produce 80 ~ 150MPa pressure, the bead is placed in the glass wrap for a certain period of time.
Hot isostatic pressing reduces porosity in the article and increases density, strength, impact toughness and performance. China's Beijing Iron and Steel Research Institute, Central South University of Technology Powder and Metallurgy Institute, Beijing Nonferrous Metal Research Institute, Zhuzhou Cemented Carbide Factory have hot isostatic pressing equipment.
(5) Adopting single-layer high-temperature brazing diamond beading This process is a new patented technology introduced by Taiwan Taiwan Grinding Wheel Manufacturing Co., Ltd. (KNIKInc.). The diamonds are arranged in high-temperature brazing beads with reasonable distribution, chemical bonding and metallurgical combination. Diamond Strong control and high standing. The diamond usage can be saved by half, the sawing speed is 2 to 4 times that of the ordinary saw blade, the cutting life is equivalent, and the saw blade cost is reduced.
7. Active development of high-end laser welding special saw blade Laser welding saw blade has many advantages in the United States and Europe, has been 15 years of history, the world's diamond tool industry has 300 laser saw blade production line, There are more than 20 articles in our country. Therefore, to develop the production capacity of existing equipment, to develop high-end laser welding special saw blades, occupying the international market is our development goal.
(1) Laser generators are constantly improved and updated. Foreign countries have developed from cross-flow and fast axial flow to the third-generation plate. With a power of 2 to 2.5 kW, China has developed a lateral flow of gas, a longitudinally constrained discharge excitation, a multi-fold laser cavity, and a low-absorption optical element laser generator. Their characteristics are: high power, low gas consumption, low operating cost, low maintenance workload, reliable operation, good beam quality, small spot size and improved welding quality.
(2) The fixing method of the saw blade base and the cutter head is changed from manual to fully automatic, with high precision and reliable operation. The United States, Italy, Germany, South Korea and China have different fixed methods, including manual fixtures, magnetic fixtures, pneumatic fixtures, and rolling fixtures.
(3) No solder is needed, but a reasonable transition layer formula must be used to match the performance with the working layer and the substrate to improve the welding strength, penetration and porosity and crack.
(4) Develop a reasonable working layer formula. Generally, Fe-based, Co-based, and Ni-based carcasses are easily welded, and it is difficult to weld a carcass containing too much Cu, Sn, W, Wc, and Pb.
(5) In order to meet the needs of asphalt and curing concrete processing, we developed helical teeth, high and low teeth, knife-shaped teeth and hard alloy reinforced teeth.
(6) Pay attention to the research on the sintering process of laser saw blade, choose reasonable sintering temperature, pressure and time, and control the sintering atmosphere and temperature, which is an important factor to ensure the quality of laser welding.
(7) Select reasonable welding process parameters, control welding power, angle, speed, offset, aspect ratio, and ensure welding quality and strength.