Application Research of Diamond Abrasive Belt in Thermal Spraying Layer Grinding

Abstract 1. Diamond abrasive belt and its grinding characteristics The hardness of high-hardness thermal spray coatings such as high-temperature alloys and special ceramics is generally above 1000HV0.2, and the coating thickness is between 0.1mm-0.5mm.
        1. Diamond abrasive belt and its grinding characteristics

The hardness of high-hardness thermal spray coatings such as high-temperature alloys and special ceramics is generally above 1000 HV0.2, and the coating thickness is between 0.1 mm and 0.5 mm. The thermal spray coating is hard and thin. In the grinding process, due to the high hardness of the thermal spray coating, diamond grinding tools are often used. However, due to the use of diamond-solid grinding-grinding wheel grinding, not only the power consumption is high, the grinding temperature is high, the workpiece is easily burned, and the surface and intrinsic quality of the workpiece are affected. Moreover, it is necessary to regularly trim the grinding wheel and it takes time. The use of ordinary abrasive grinding wheels and abrasive belt grinding, because of its low hardness, its cutting efficiency is lower or difficult to grind (see Table 1, Mohs hardness table for various substances).

Table 1. Mohs hardness table for various substances
Diamond has a Mohs hardness of 10 and is the material with the highest hardness found. It is especially suitable for processing non-metallic and non-ferrous metal difficult-to-machine materials with high hardness and brittleness. The diamond abrasive belt produced by the electroplating process has a high bonding strength between the diamond and the base fabric, and is arranged by using a grinding unit with a gap (see Fig. 1, arrangement of several diamond abrasive belt surface grinding units). The chip removal is better and the grinding temperature is lower, which not only ensures the surface quality of the workpiece, but also ensures the internal quality of the workpiece, thereby improving the fatigue strength of the component, prolonging the service life and improving the production efficiency. The grinding process of diamond abrasive belt also has the characteristics of less dust, less noise and low energy consumption, which is in line with China's energy conservation and environmental protection policies.

The surface quality of the diamond abrasive belt grinding workpiece is high, mainly in the phenomenon of small surface roughness, good residual stress state, and no micro crack or metallographic structure change on the surface. From the surface roughness point of view, the abrasive belt grinding has reached Ra0.01, which has achieved the effect of mirror grinding, and it is very easy to achieve the roughness value above Ra0.1mm. The test shows that when the other conditions are certain, when the linear speed of the abrasive belt is increased from 35m/s to 100m/s, the surface roughness of the grinding is reduced from Ra2.0μm to Ra1.5μm, and the precision is not achieved by ordinary abrasive tools. . Therefore, diamond abrasive belts and their derivatives are the best products for grinding high hardness thermal spray coatings.

        Second, diamond sand belt grinding processing plan and grinding process selection

Diamond sand belt is mainly used for the processing of rolls and shafts. Diamond grinding discs and diamond impellers are mainly used for grinding and polishing of planes, curved surfaces and complex profiles.

        (1) Diamond sand belt grinding processing thermal spraying layer scheme
Microhardness of carbide and several abrasives


540mm diameter × length 15m ceramic piston rod grinding processing plan

Process parameters of 540mm×length ceramic piston rod grinding process
Lathe model: 61125
Belt speed: 16m/s (1500rpm)
Belt specification: 60mm × 1950mm
Belt contact workpiece method: soft contact (non-contact wheel grinding)
Workpiece specifications: diameter 540mm × length 15m
Workpiece speed: 30 rpm
Grinding head speed: coarse grinding 60#, 200#, 2mm-3mm/rev; fine grinding 800#, 0.5mm-1mm/rev
Coolant: water
Workpiece spray material: ceramic coating
Spray coating thickness: 60μ
Initial roughness of spray coating: Ra0.4mm-0.6mm
Spray coating processing allowance: 25μ
After processing thickness of coating: 35μ
Figure 3, 540mm diameter × length 15m ceramic piston rod grinding processing site

  (II) Selection of grinding sandstone grinding process parameters

Figure 4, diamond abrasive belt grinding process flow chart

According to the above diamond belt grinding process (see Table 2, diamond belt grinding process parameter table), the grinding diameter of 540mm × length 15m ceramic piston rod, the grinding time is only 90 hours. In the first grinding process, due to the unreasonable design of the processing technology, the grinding time is as long as one month.
Table 2 Diamond abrasive belt grinding process parameter table

        (III) Characteristics of diamond sanding belt grinding processing plan
1. Advantages:
(1) The equipment is simple, easy to operate, and does not require expensive special grinding machines. It can be installed on the lathe tool holder of common specifications to work.
(2) The grinding and polishing speed is fast, the efficiency is high, and the grinding effect is good.
(3) Because of the special orderly arrangement of diamond particles on the surface of the diamond abrasive belt, the grinding is sharp and the chip removal is good, and no trimming is required. Processing requirements can be achieved by replacing abrasive belts of different sizes.
2, disadvantages:
The precision of such non-contact wheel grinding is slightly lower (in terms of cylindricity). If the contact wheel type grinding and polishing (contact wheel hardness 90) is used, the machining time can be greatly shortened and the machining precision of the workpiece can be achieved.

        (4) Determining the time and quality factors of processing:
1. The quality of the spray coating: the uniformity and roundness of the coating thickness, the uniformity and apparent quality of the surface roughness, the uniformity of the hardness, the porosity of the coating, and the microhardness.
2. Operator's operation level and operating habits: such as the feed pressure of the belt grinding head.

Plane and curved thermal spray coating

Some of the most advanced grinding methods are used in automotive stamping dies, steam turbine blades and aerospace components.
Diamond impeller grinding plane and curved surface: installed on pneumatic and electric mill, rotating speed 10000 ~ 20000rpm, high grinding efficiency, good effect, flexible and convenient operation.
Diamond grinding disc grinding plane: It is used on pneumatic and electric angle grinders. It has fast grinding speed and good smoothness.  
Diamond torque disc: 2 inches in diameter, 200#, 400# in high-speed pneumatic tools, tools, compact, flexible, fast loading and unloading.
Diamond impeller, grinding disc, torque disc product (see Figure 2, several common diamond abrasive belts and products) The most important characteristics of the grinding coating are: structural design flexibility, high hardness of diamond abrasive grains, sharp grinding, rigid and soft phase In addition, the coating will not be penetrated, and the surface is evenly polished and the consistency is good.
Figure 7 Diamond Thousand Wheels Polished Coating Photo

Figure 8. After polishing with a 180-mesh diamond thousand impeller, Ra 0.6-0.7

Figure IX, polished by 400 mesh diamond thousand impeller, Ra < 0.3
With the development of modern technology and industry, the performance of materials is increasingly demanding, wear-resistant and anti-corrosion is an important indicator. Some electroplating products, such as piston rods, due to the chrome plating process and the corrosion resistance of the chrome layer, are polished and sealed after spraying the ceramics, which greatly improves the corrosion resistance and service life of the piston rod. Plasma spraying technology is an effective means to obtain functional coatings on the surface of materials. It has the advantages of high production efficiency, good coating quality, wide range of materials for spraying, and low cost. Therefore, in the past ten years, the advancement of this technology and the production and application have developed rapidly, and it has been widely used in nuclear energy, aerospace, shipbuilding, petrochemical, machinery and other fields. In the welding technology science, thermal spraying technology such as supersonic and plasma, as a new high-tech industry, will play an increasingly important role in future material science research, it will replace some traditional welding processes and Materials to develop in a new direction. As a matching grinding technology, diamond abrasive belt and its derivatives are the best abrasive tools for processing high hardness thermal spray coatings.
Figure XI. Several examples of thermal spray layer grinding of domestic mechanical parts: roll processing of sheet mills; processing of printing rolls; processing of oil drill pipes; processing of aircraft engine blades, etc.

        Third, the conclusion

At present, compared with advanced countries, China's thermal spray coating processing technology is still relatively backward. Most factories in China still use diamond grinding wheel and diamond film vibration polishing process, which has low efficiency and is processed by diamond abrasive belt. There is no corresponding belt machine tool to match it, which has become the bottleneck for the promotion of diamond belt grinding technology. We have developed a belt machine that successfully cooperates with the lathe. We believe that through our unremitting efforts, we will make our own contribution to the adjustment of the industrial structure and innovation of the thermal spray industry in China. (Author: Zhengzhou Reiter Diamond Belt Co., Ltd. An Jianmin)

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