As an important part of machine tool industry, machine tool industry plays an important role in the development of the whole national economy.In general, China's machine tool industry is in the best period of development since 1992, and the market is in short supply.Especially since entering the new growth period in 1999, the output value of China's machine tool industry has been increasing year by year, the product structure has been constantly adjusted, and the product quality has been improving day by day.The following table shows the growth of machine tool industry output value, metal cutting machine tool output and CNC metal cutting machine tool output since 1999:
According to the information obtained from the seminar on the market situation and countermeasures of China machine tool industry held in baoji on December 2, 2003, this year will be a bumper year for China machine tool industry. By the end of September, in terms of product output, the cumulative production of metal cutting machine tools has reached 222,000 units, an increase of 36.7% over the same period last year.Among them, as the key development of high-precision machine tools increased by 37.60%;Numerical control machine tools increased by 43.74%;Large machine tools grew by 87.90%.In addition, other such as forging machinery, woodworking machine tools also have a greater growth, it may be said that all the line of floating red.
Globally, the consumption of machine tools in China increased by 20.0% in 2002 compared with 2001, accounting for 19.2% of the total consumption of machine tools in the world, rising from the fourth place to the first place in the world.
At the same time, in the domestic machine tool industry production and operation continues to maintain a good situation, this year, China's machine tool imports also continue to grow, by the end of September, according to the customs statistics, China's machine tool imports have reached 2.96 billion yuan, increased by 35% over the same period last year.Moreover, some internationally renowned enterprises have entered China in the form of sole proprietorship and joint venture, taking advantage of China's cheap labor costs and various preferential conditions to seize the Chinese market.This fully shows that the international competition of machine tool industry in modern manufacturing industry has gradually penetrated into the hinterland of China.China will continue to be the world's largest importer of bearings and a major consumer.
Despite China's machine tool industry in recent years has made great progress, but in the current domestic and foreign machine tool market is extremely competitive situation, our country's machine tool industry competitiveness is not strong, mainly displays in our country is machine tools consumption is not power, large machine tools ownership but low level, the product structure is still backward, poor product innovation ability, machine tool reliability needs to be improved, etc.
The level of machine tool manufacturing in the world today is concentrated in the development of CNC machine tools, production capacity, CNC machine tools have become the mainstream equipment in the manufacturing industry, a country has a number of CNC machine tools, the level has become an important symbol to measure the comprehensive strength of a country.To achieve the goal of transforming China from a machine tool country into a machine tool production power, we must accelerate the pace of adjustment and intensify the development of new products.For this reason, the "tenth five-year plan" of the machine tool industry put forward to focus on the development of CNC machine tools, so as to promote the improvement of the overall level of the industry.The following total target has been set: by 2005, the output of CNC machine tools will reach 25,000-30,000, the output value will reach 6.5-7 billion yuan, and the market share of CNC machine tools will reach 50% (by value).From the current situation, the output target is expected to be achieved ahead of schedule in 2003.
Ii. Machine tool industry's demand for bearings
The use of rolling bearings in machine tools is mainly used in the following three parts: spindle, ball screw and general drive shaft.
As the basic accessory of machine tool, the performance of spindle bearing directly affects the machine tool speed, rotary precision, rigidity, anti-chatter vibration cutting performance, noise, temperature rise and thermal deformation, and then affects the precision and surface quality of the processed parts.Therefore, high performance machine tools must be equipped with high performance bearings.
The accuracy of linear bearing is generally divided into five grades: P0, P6, P5, P4 and P2. The precision of the bearing used for spindle of precision machine tools shall be P5 and its superior, while for spindle support of high-speed and high-precision machine tools such as nc machine tools and machining centers, P4 and its superior ultra-precision bearing shall be selected.
Spindle bearings for machine tools usually include deep groove ball bearings, angular contact ball bearings, cylindrical roller bearings, two-way thrust angular contact ball bearings, tapered roller bearings and thrust bearings.
With the rapid development of CNC technology, "compound, high-speed, intelligent, precision, environmental protection" has become the main trend of machine tool industry technology development.Among them, high speed machining can effectively improve the machining efficiency of machine tools and shorten the machining cycle of workpiece.This requires the machine tool spindle and its related components to adapt to the needs of high-speed processing.At present, the spindle bearings of CNC machine tools are basically limited to four structural types: angular contact ball bearings, cylindrical roller bearings, two-way thrust angular contact ball bearings and tapered roller bearings.
Along with the high-speed development of CNC machine tool spindle, ceramic materials (mainly Si3N4 engineering ceramics) due to its low density, high modulus of elasticity, small coefficient of thermal expansion, wear resistance, high temperature resistance, corrosion resistance and other excellent properties, so as to become the ideal material for the manufacture of high-speed precision bearings.Ceramic bearings have been more and more widely used, in view of the ceramic materials difficult to process, precision ceramic bearings are mostly rolling ceramic, inner and outer rings are still made of chromium steel mixed ceramic ball bearings.
Ball screw pair as a precise, efficient, sensitive transmission components, in addition to the use of high-precision screw, nut and ball, but also should pay attention to the selection of high axial stiffness, small friction torque, high operating accuracy of the bearing.Ball screw bearings were used in the past to support two-way angular thrust contact ball bearings, tapered roller bearings, needle roller and thrust roller combination bearings, deep groove ball bearings and thrust ball bearings.At present, the single row thrust angular contact ball bearing with 60° contact Angle is the most commonly used ball screw support. In addition, the accuracy grade is mainly P4 and its superior.
Machine tool installed on the general shaft of the rolling bearing, its requirements and selection and ordinary mechanical drive bearing is the same, only to meet the requirements of strength and life, the speed does not exceed the specified limit speed of the bearing.
Under normal circumstances, the machine tool bearing we mentioned refers to the machine tool spindle bearing and ball screw bearing, while the precision machine tool bearing refers to the spindle bearing and screw bearing with the accuracy of P5 and its superior P5.
Production of precision machine tool bearings
Precision machine tool bearing technology content is high, high added value, processing difficult, the world's major bearing companies have invested great energy in the development and development of precision machine tool bearing.At present, foreign manufacturers of precision machine tool bearings mainly include FAG company of Germany, SNFA company of France, NSK company of Japan, SKF company of Sweden, NTN company of Japan, etc.
Compared with developed countries, the overall level of China's bearing industry is quite different, especially in the development and development of precision bearings, due to the limitations of processing equipment, manufacturing process and related technologies