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**Abstract**
1. Diamond Abrasive Belt and Its Grinding Characteristics
High-hardness thermal spray coatings, such as high-temperature alloys and special ceramics, typically have a hardness above 1000 HV0.2, with coating thickness ranging from 0.1 mm to 0.5 mm. These coatings are both hard and thin, making them challenging to process. Traditional diamond grinding wheels are often used for this purpose. However, they tend to consume more power, generate higher temperatures, and risk damaging the workpiece surface or internal structure. Additionally, frequent dressing of the wheel is required, which increases processing time. In contrast, ordinary abrasive belts and sanding belts offer lower cutting efficiency and may struggle with such hard materials (as shown in Table 1, the Mohs Hardness Scale).
Table 1. Mohs Hardness Scale for Various Substances
[Image: Mohs hardness chart]
Diamond has a Mohs hardness of 10, making it the hardest known material. It is especially suitable for machining non-metallic and non-ferrous materials that are hard and brittle. Diamond abrasive belts produced via electroplating technology exhibit strong bonding between the diamond particles and the base fabric. They are arranged using grinding units with gaps, allowing for better chip removal and lower grinding temperatures. This not only ensures good surface quality but also preserves the internal integrity of the workpiece, enhancing its fatigue strength and service life. Furthermore, diamond abrasive belt grinding produces less dust, noise, and energy consumption, aligning with China’s environmental protection and energy-saving policies.
[Image: Diamond abrasive belt arrangement]
The surface quality achieved through diamond abrasive belt grinding is exceptionally high, characterized by low surface roughness, favorable residual stress distribution, and no micro-cracks or changes in the metallographic structure. In terms of surface roughness, abrasive belt grinding can achieve Ra 0.01, effectively reaching mirror-like finishes. It is easy to achieve values above Ra 0.1 mm. Tests show that increasing the linear speed of the abrasive belt from 35 m/s to 100 m/s reduces surface roughness from Ra 2.0 μm to Ra 1.5 μm, something that standard abrasive tools cannot achieve. Therefore, diamond abrasive belts and their derivatives are the best options for grinding high-hardness thermal spray coatings.
[Image: Surface roughness comparison]
**Second, Diamond Sand Belt Grinding Process Plan and Selection of Grinding Parameters**
Diamond sand belts are primarily used for processing rolls and shafts. Diamond grinding discs and impellers are mainly used for grinding and polishing planes, curved surfaces, and complex shapes.
(1) **Diamond Sand Belt Grinding Plan for Thermal Spraying Layers**
[Image: Microhardness of carbide and various abrasives]
**540mm Diameter × 15m Ceramic Piston Rod Grinding Plan**
Process parameters for the 540mm × 15m ceramic piston rod grinding process:
- Lathe model: 61125
- Belt speed: 16 m/s (1500 rpm)
- Belt specification: 60 mm × 1950 mm
- Contact method: Soft contact (non-contact wheel grinding)
- Workpiece size: 540 mm diameter × 15 m length
- Workpiece speed: 30 rpm
- Grinding head speed: Coarse grinding 60#, 200#, 2–3 mm/rev; fine grinding 800#, 0.5–1 mm/rev
- Coolant: Water
- Workpiece spray material: Ceramic coating
- Spray coating thickness: 60 μm
- Initial roughness of coating: Ra 0.4–0.6 mm
- Processing allowance: 25 μm
- Post-processing coating thickness: 35 μm
[Image: 540mm diameter × 15m ceramic piston rod grinding site]
(II) **Selection of Grinding Process Parameters**
[Image: Diamond abrasive belt grinding flow chart]
According to the above diamond belt grinding process (see Table 2, diamond belt grinding parameter table), the grinding of a 540mm × 15m ceramic piston rod took only 90 hours. In the first process, due to an unreasonable design, the grinding time extended to one month.
Table 2: Diamond Abrasive Belt Grinding Parameter Table
[Image: Process parameter table]
(III) **Features of the Diamond Sanding Belt Grinding Plan**
1. **Advantages:**
- Simple equipment, easy to operate, and does not require expensive special grinders. It can be installed on standard lathe tool holders.
- Fast grinding and polishing speed, high efficiency, and excellent results.
- The orderly arrangement of diamond particles on the belt allows sharp cutting and good chip removal, eliminating the need for dressing. Different sizes of abrasive belts can be replaced to meet various requirements.
2. **Disadvantages:**
- Non-contact wheel grinding has slightly lower precision (in terms of cylindricity). Using contact wheel grinding (with wheel hardness of 90) can significantly reduce machining time and improve workpiece accuracy.
(4) **Determining Processing Time and Quality Factors**
1. **Quality of the spray coating:** Uniformity of coating thickness, surface roughness, hardness, porosity, and microhardness.
2. **Operator skill and habits:** Such as the feed pressure applied during belt grinding.
[Images: Surface quality before and after polishing]
**Plane and Curved Thermal Spray Coatings**
Advanced grinding methods are widely used in automotive stamping dies, steam turbine blades, and aerospace components.
Diamond impeller grinding for planes and curved surfaces is installed on pneumatic or electric mills, rotating at 10,000–20,000 rpm, offering high efficiency and smooth results. Diamond grinding discs are used on pneumatic and electric angle grinders, providing fast grinding and smooth finishes. Diamond torque discs (2 inches in diameter, 200# and 400#) are compact, flexible, and quick to load and unload.
Diamond impeller, grinding disc, and torque disc products (see Figure 2, common diamond abrasive belts and products) have key characteristics: flexible structural design, high diamond grain hardness, sharp cutting ability, and a balance between rigidity and softness. The coating remains intact, and the surface is evenly polished with good consistency.
[Images: Polished coating photos, surface roughness after polishing]
With the advancement of modern technology and industry, material performance demands are increasing, with wear resistance and corrosion resistance being critical indicators. Electroplated products like piston rods benefit from ceramic spraying and subsequent polishing, greatly improving corrosion resistance and service life. Plasma spraying is an effective method for obtaining functional coatings on material surfaces. It offers high production efficiency, good coating quality, and cost-effectiveness. Over the past decade, this technology has developed rapidly and is now widely used in nuclear energy, aerospace, shipbuilding, petrochemicals, and machinery. In welding technology, thermal spraying techniques such as supersonic and plasma will play an increasingly important role in future material science research, replacing some traditional welding processes and driving new development directions. As a complementary grinding technology, diamond abrasive belts and their derivatives are the best abrasive tools for processing high-hardness thermal spray coatings.
[Image: Examples of domestic mechanical parts with thermal spray layer grinding]
**Third, Conclusion**
Currently, compared to advanced countries, China's thermal spray coating processing technology is still relatively backward. Most Chinese factories still use diamond grinding wheels and diamond film vibration polishing, which are inefficient. There is no matching belt machine tool for diamond abrasive belt grinding, creating a bottleneck for its promotion. We have developed a belt machine that successfully works with lathes. We believe that through continuous efforts, we will contribute to the industrial restructuring and innovation of the thermal spray industry in China.
(Author: Zhengzhou Reiter Diamond Belt Co., Ltd. An Jianmin)
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