Analysis of current problems in roller production in China bearing industry

Analysis of current problems in roller production in China bearing industry

1. Technical indicators cannot meet the requirements

The National Standards of the People's Republic of China GB/T25767-2010 "Tapered Rollers for Rolling Bearings" and GB/T4661-2015 "Cylindrical Rollers for Rolling Bearings" clearly stipulate the parameter definitions and various accuracy indicators of tapered rollers and cylindrical rollers.

Cylindrical roller diameter tolerance and axial runout (GB/T25767-2010) unit is micron

Tapered roller surface roughness (GB/T25767-2010) Unit is micron

However, the current manufacturing level of the industry is restricted by various conditions. my country's bearing companies can only mass-produce G2-level cylindrical rollers and III-level tapered rollers, which cannot meet the supporting requirements of high-end bearings. Starting from the need to develop high-end bearings, the technical quality level of bearing rollers must reach: the ability to mass produce G1 grade cylindrical rollers, grade I tapered rollers and grade II spherical rollers.

2. Materials

The quality of bearing steel materials plays a vital role in the processing quality, service life and reliability of bearing products. With the introduction of advanced technology and equipment, the smelting level and metallurgical quality of my country's bearing steel have reached a higher level. In some technical and quality indicators, it has reached or is close to the advanced foreign level. However, the overall quality level is still far from that of developed countries. The larger gap manifests itself as:

1) Standard aspect

In the current bearing steel material standards, the quality of carbide particle size and distribution state is

The control situation has no content, resulting in a large gap in the size and distribution of carbide particles abroad. This is also a main reason why the service life and reliability of my country's bearing products are lower than similar foreign products. In addition, the inspection and rating method for non-metallic inclusions in "High Carbon Chromium Bearing Steel" (GB/T18254) currently has certain limitations for low-oxygen, high-purity bearing steel, and it is no longer possible to accurately evaluate the inclusions in bearing steel. Non-metallic inclusions have been graded by other inspection methods abroad. Therefore, only by making breakthroughs in the above aspects can the quality of my country's bearing steel and bearing products be improved. The raw materials of high-carbon chromium bearing steel rollers with a diameter greater than 60mm do not have reticular carbide requirements in GB/T18254, resulting in difficult to control the heat treatment structure.

2) The metallurgical quality stability of bearing steel is relatively poor.

For example, the oxygen content in bearing steel produced in my country is close to the level of advanced countries producing bearing steel abroad. However, the particle size and distribution of non-metallic inclusions in bearing steel are very uneven. In some fields, there is not even a single non-metallic inclusion. , appear in large numbers in some fields of view, and point-like non-deformable inclusions not only appear frequently, but also have larger particle sizes.

The plasticity of raw materials, the stability of chemical element composition, purity and particle structure are currently the bottlenecks that restrict the development of our roller industry, and they also restrict the life of bearings.

3. The gap between my country's bearing roller technology level and the international advanced level is highlighted in the bearing roller process equipment.

At present, foreign processing is basically in-line arrangement, while domestic bearing roller processing mostly adopts single machine, multi-process, and multi-step processing. In some links, the processing machine tools have poor accuracy and poor stability, and the processed bearing rollers have large dimensional differences. Problems such as inconsistent and unstable geometric accuracy lead to inconsistent conditions and unstable lifespan of the produced bearings. Among them, for roller forming, large domestic bearing companies, like foreign countries, use cold heading forming, but the cold heading equipment used is lagging behind that of foreign countries (multi-station cold heading machines), and the applicable roller size is also much smaller.

With the gradual improvement of the level of basic manufacturing industry, the manufacturing and imitation capabilities of domestic roller processing equipment have improved, and are at a different level compared with foreign countries. The design principles of machine tools, the materials used for processing, and the processing technology still restrict the performance of the equipment. At the same time, the auxiliary processing equipment of the grinding tool is also one of the main factors limiting the performance of the machine tool. Domestic equipment manufacturers are more concerned about how machine tools realize the grinding function. Protection of the service life of machine tools has not yet been put on the design agenda. Domestic machine tools have not yet implemented modular assembly and cannot guarantee equipment accuracy.

Due to the lack of breakthrough development in the digestion, absorption and re-innovation of imported equipment, it is impossible to stably mass-produce grade 0 and grade I high-precision rollers for high-end bearings.

1) Cylindrical roller production process route:

Cold heading - Soft channeling - Soft grinding outer diameter - Soft grinding end face - Heat treatment - Shot blasting - Polishing - Line production in hard grinding workshop - Coarse grinding outer diameter - Double end face 1 - Fine grinding outer diameter - Double end face 2 - Polishing /End surface grinding - final grinding 1 - final grinding 2 - super fine - cleaning - photoelectric appearance inspection - sorting - oiling - packaging.

2) The main equipment is: cold heading machine, finishing machine, outer diameter grinder, end surface grinding machine, and super-finishing machine.

3) Tapered roller processing technology:

Cold heading - Soft channeling - Soft grinding outer diameter - Soft grinding end face - Heat treatment - Shot blasting - Polishing - Online production in hard grinding workshop - Grinding outer diameter (coarse grinding, fine grinding) - Grinding ball base surface (coarse grinding, fine grinding) Grinding) - final grinding outer diameter (1 to 3 times) - super fine outer diameter - cleaning - appearance inspection (photoelectric, manual) - oiling - coding - packaging.

4) The main equipment is: cold heading machine, outer diameter grinder, spherical surface grinder. Among them, there are many forms of spherical surface grinding, mainly disc grinding and Fan Cheng method grinding. Fan Cheng method grinding has slightly higher accuracy, but It is less efficient and suitable for larger rollers, and of course there are other grinding methods. Roller outer diameter super precision machine, cleaning equipment, photoelectric appearance inspection, oil coating and packaging, etc.

Roller multi-station cold heading machine

The imitation Soviet roller cold heading machine that has been used for many years is very backward and must be completely eliminated. The imported roller multi-station cold heading machine has high processing precision and high processing efficiency, but it is expensive and ordinary enterprises cannot afford to purchase it. In recent years, some domestic equipment manufacturing companies have made great efforts to digest, absorb and innovate the imported roller multi-station cold heading machines and have made certain progress, but there is still a big gap between them and the international advanced level.

Roller cylindrical grinder

Technical features of the introduced high-precision CNC roller cylindrical grinder, such as servo CNC, rigid support of grinding wheel and guide wheel, large diameter and wide width grinding wheel, large diameter and wide width guide wheel, application of combined grinding wheel, grinding wheel Technical features such as dual servo interpolation dressing and automatic compensation, and guide wheel on-machine self-dressing have been deeply studied, digested, absorbed and re-innovated, and a high-precision CNC roller cylindrical grinder that has reached the international advanced level has been developed and applied.

Roller cylindrical super-finishing machine and special super-finishing guide roller grinder

Conduct in-depth research on the technical features of the introduced high-precision roller cylindrical CNC super-finishing machines, such as the application of large-diameter and wide-width super-finishing rollers and large reciprocating and small oscillating oscillators, digest and absorb them and innovate again, and the research and development applications will reach the international advanced level. Horizontal high-precision roller cylindrical CNC super precision machine.

A special super-precision guide roller grinder is developed and applied. After the guide roller grinding process, a special profile for the roller support is formed, so that the roller can pass the super-precision to achieve the logarithmic curve convexity or modification required by the design.

Roller ball surface grinder

At present, there are various types of roller CNC ball surface grinders introduced from many countries. Some types have high processing accuracy but low processing efficiency, and some types have high processing efficiency but low processing accuracy. We should conduct in-depth research on various types of imported spherical surface grinders, learn from others' strengths, focus on independent innovation, and develop roller CNC ball surface grinders that are suitable for my country's national conditions, have high processing accuracy and processing efficiency, and are cost-effective.

Online roller appearance automatic inspection and non-destructive testing equipment

At present, domestic testing instruments are relatively backward. Foreign inspection equipment keeps pace with the times and relies more on computer control. However, domestic mature and basic online testing technologies and equipment are not widely used. Many still rely on manual appearance inspection, which affects production efficiency and product quality.

Roller grinding super automatic production line

At present, most domestic professional roller manufacturers or bearing factories have installed many automatic roller grinding and super-automatic lines after equipment transformation in recent years. However, most of them are due to accuracy problems of the equipment itself, resulting in long connections and large floor areas, which affects the roller grinding process. production efficiency and product quality.

Digital testing instruments

Research and develop special digital instruments and equipment for all major technical indicators of roller rolling surfaces, ball base surfaces, end surface pockets, and chamfers.

However, the equipment's performance stability, precision retention, connection technology and system integration capabilities are far behind the international advanced level. In particular, the introduction, digestion, absorption and reinvention of key equipment for roller processing have not made breakthrough progress, so that they cannot be stabilized. Mass production of Class I cylindrical rollers and Class I tapered rollers for high-end bearings.