The Ultimate Guide to Abrasives for Coated Abrasives
October 08 , 2024
Coated abrasives are essential in modern industrial manufacturing and processing, efficiently handling a wide range of materials to achieve fine surface finishes and rapid productivity. These abrasives are used in a wide range of applications such as metalworking, wood treatment, and automotive manufacturing to help improve product quality and extend tool life.
In coated abrasives, the abrasive is a core component that directly affects their cutting and grinding performance. The type, hardness and grit size of the abrasive determine the range of application and effectiveness of the abrasive. For example, aluminum oxides are suitable for general grinding, whereas diamonds are used for grinding ultra-hard materials. The combination of abrasive selection and processing ensures the efficiency and reliability of coated abrasives in a wide range of applications.
▶ Comparison of Common Abrasive Properties
The following is a comparison of the properties of several abrasives commonly used in coated abrasives:
◆☞ Brown Fused Aluminum
- Hardness: the Mohs hardness of brown corundum is about 8, which is moderate and can effectively cut various metal and non-metal materials.
- Abrasion Resistance: it has a strong grain structure with good compression and wear resistance properties, which maintains a stable cutting capacity during the grinding process.
- Thermal Stability: under high-temperature conditions (e.g. high speed grinding), it can still maintain its physical properties and will not be deformed due to temperature increase.
- Chemical Properties: good chemical stability, will not react with most materials.
◆☞ White Fused Aluminum
- Hardness: about 8 on the Mohs hardness scale, hardness similar to brown corundum, but with better-cutting properties due to its high purity and uniform particle shape.
- Wear Resistance: excellent wear resistance, long service life, and ability to maintain sharp cutting edges during the grinding process.
- Thermal Stability: maintains its performance even in a high-temperature environment, suitable for high-speed grinding.
- Finish: provides a higher surface finish for applications where the appearance of the final product is critical.
◆☞ Silicon Carbide
- Hardness: the Mohs hardness is about 9, which belongs to the super-hard material with strong cutting power.
- Abrasion Resistance: excellent abrasion resistance, able to effectively handle super-hard and brittle materials, suitable for high-precision grinding.
- Thermal Stability: it has good thermal stability and can maintain its physical properties under high-temperature conditions.
- Cutting: sharp particle shape provides good cutting results.
◆☞ Zirconia Fused Alumina
- Hardness: Mohs hardness between 8-9, higher, suitable for grinding a wide range of materials.
- Abrasion Resistance: excellent wear resistance, high toughness, and impact resistance, suitable for heavy-duty grinding.
- Thermal Stability: maintains performance at higher temperatures for extended use.
- Self-sharpness: gradually exposes new cutting edges during the grinding process, keeping them sharp.
◆☞ Ceramic Alumina
- Hardness: with a Mohs hardness of approximately 9, it is a harder material and is suitable for a variety of grinding applications.
- Abrasion Resistance: excellent wear resistance and self-sharpening, capable of maintaining long-lasting cutting ability during the grinding process.
- Thermal Stability: it remains stable at high temperatures and is suitable for high-speed grinding operations.
- Uniformity: ceramic alumina has a uniform grain structure that provides consistent grinding results.
◆☞ Diamonds
- Hardness: 10 on the Mohs scale, the hardest known material, capable of cutting ultra-hard materials with ease.
- Abrasion Resistance: extremely high wear resistance for use in extreme conditions and long service life.
- Thermal Stability: performs well at high temperatures but may oxidize at very high temperatures (over 800°C).
- Cutting Force: enables machining at very high cutting speeds, reducing machining time.
▶ The Manufacturing of Coated Abrasives
The production process for coated abrasives involves several key steps, combining materials and techniques to create effective sanding and grinding tools. Here’s an overview of the typical production process:
◆☞ Raw Material Selection
Abrasive Grains: The primary materials, such as aluminum oxide, silicon carbide, or zirconia, are selected based on the desired properties.
Backing Material: Common backings include paper, cloth, or film, chosen for their strength and flexibility.
◆☞ Abrasive Grain Preparation
Crushing and Sizing: Abrasive materials are crushed and sieved to obtain uniform grain sizes. This can involve various methods, including crushing, grinding, and air classification.
Surface Treatment: Grains may be treated to enhance their performance, such as by coating them with resins or applying a specific texture.
◆☞ Bonding Agent Preparation
Resin preparation: Preparation of adhesives, usually phenolic or synthetic resins. This involves mixing chemicals and curing agents to form a stable binder.
◆☞ Coating Process
Application of Adhesive: The backing material is coated with the bonding agent using methods like roll coating, spray coating, or dip coating.
Grain Application: Abrasive grains are applied to the adhesive-coated backing. This can be done through a process like electrostatic spraying, where grains are charged to ensure an even distribution.
◆☞ Curing
Heat Treatment: The coated materials are cured in ovens to harden the adhesive and bond the grains to the backing. This step ensures durability and performance.
◆☞ Finishing Operations
Trimming and Cutting: The coated abrasive sheets are cut to size, and the edges are trimmed to prepare them for packaging.
Quality Control: Finished products undergo testing to check for adherence, grain uniformity, and overall quality.
◆☞ Packaging
Labeling and Packaging: Coated abrasives are labeled with specifications and packed for distribution, ensuring they are protected during shipping.
◆☞ Distribution
Logistics: Distribution of the final product to retailers and end users for a variety of applications such as woodworking, metalworking, and the automotive industry.
Each step in this process is crucial for producing high quality coated abrasives that meet specific performance criteria for different applications.
▶ Grain Size Analysis of Abrasives For Coated Abrasives
Abrasive grain size plays a vital role in coated abrasives, directly affecting grinding efficiency, surface quality, and machining accuracy. The choice of grit size varies according to the needs of different processes and is a central factor in sanding and polishing results. The following is a detailed analysis of abrasive grain size for coated abrasives in terms of the definition of grain size, classification of grain size grades, and their influence on grinding performance.
◆☞ Definition and Criteria of Abrasive Grit Size
- Abrasive Grain Size: the size of the abrasive particles, expressed in mesh or microns (μm). Commonly used grain sizes range from coarse (P12, P24) to very fine (P1000, P2500).
- International Standard: common grit size standards are FEPA (Federation of European Coated Abrasive Manufacturers) and ANSI (American Standard), with FEPA being the more common. The grit size range is usually divided into coarse, medium, and fine grits, each category corresponding to a different grinding application.
◆☞ Classification of Abrasive Grit Size
- Coarse Grit Abrasives (e.g. P12 to P60): large grain size, fast grinding speed, and high material removal capacity. Commonly used for primary machining, deburring, rough grinding of surfaces, removal of oxide layers, and weld seams.
- Medium Grit Abrasive(e.g. P80 to P220): the grains are more uniform and provide better surface quality while maintaining grinding efficiency. Suitable for medium machining, often used for surface finishing and intermediate sanding.
- Fine-grained Abrasives(e.g. P240 to P1200 and above): very fine particles, high surface finish, suitable for finishing. Commonly used in surface polishing and high-precision processing, such as mirror surface treatment, and precision mold processing.
◆☞ Abrasive Grain Size Analysis Methods
- Sieve Method: one of the most commonly used abrasive particle size testing methods, by placing abrasive samples on a screen with different apertures for vibratory sieving, according to the number and quality of abrasive particles passing through the holes on the screen to determine the distribution of abrasive particle size.
- Microscope Method: the microscopy method is a technique for directly observing and measuring abrasive particle sizes. It requires using a microscope to magnify and observe the abrasive particles, and then determining the particle size by measuring the dimensions of the particles visible in the microscope’s field of view.
- Laser Particle Size Analysis: laser Particle Size Analysis is a method of measuring the size distribution of abrasive particles using the principle of laser scattering. The size distribution of the abrasive particles is calculated by irradiating the sample with a laser beam and then measuring the intensity and angle of the scattered light.
◆☞ The Influence of Abrasive Grain Size on the Performance of Coated Abrasives
Grinding Efficiency
- Coarse Grit Abrasives: the highest grinding efficiency, due to large abrasive grains and sharp cutting edges, are suitable for the rapid removal of large amounts of material. However, this grit size may result in a rough surface that requires further grinding to achieve a smooth finish.
- Medium Grit Abrasives: a balance between efficiency and surface quality that removes material quickly while providing some surface flatness for general surface preparation work.
- Fine-grained Abrasives: slower material removal, but suitable for processes requiring high precision and detailed surface treatment. Due to the low grinding temperature, it is not easy to generate too much heat, avoiding material deformation or burns.
Surface Quality
- Coarse Grit: removes a large amount of material while leaving a rougher surface that often requires a subsequent process of fine grinding.
- Medium Grit Abrasives: moderate surface finish, able to remove machining marks, leaving a smoother surface, suitable for machining scenarios requiring medium precision.
- Fine-grained Abrasives: provide an extremely high surface finish and are suitable for processes requiring high surface quality, such as polishing and final machining of precision parts.
Machining Precision
- Coarse-grained Abrasive: due to the large abrasive grain and large cutting depth, it is easy to cause large errors on the surface, so the machining precision is lower.
- Fine-grained Abrasives: fine abrasive grains and shallow depth of cut enable better control of machining dimensions and surface precision, suitable for high-precision machining scenarios.
Thermal Effect
- Coarse-grained Abrasives: fast cutting speed, more frictional heat, easy to cause overheating of the material surface, may cause local burns or deformation of the material, especially in the dry grinding process is more obvious.
- Fine-grained Abrasives: smaller cutting volume, less frictional heat in the grinding process, so suitable for processing temperature-sensitive materials, such as high-strength steel or heat-resistant alloys.
◆☞ Factors in the Selection of Abrasive Grit Size
Workpiece Materials
Hard materials such as steel and titanium alloys are usually selected with coarser abrasives to improve grinding efficiency.
For soft materials such as aluminum alloys and copper, it is recommended to use medium or fine grit abrasives to reduce material deformation and improve surface quality.
Machining Process
- Rough Grinding Stage: coarse grit abrasives should be selected to remove material quickly.
- Medium Grinding Stage: the use of a medium grain size ensures a certain processing speed and also improves surface flatness.
- Fine Grinding and Polishing Stage: selection of fine-grained abrasives for high precision and smooth surfaces.
Processing Requirement
- If the goal is a high-finish, high-precision surface, a finer abrasive should be selected.
- Coarse-grained abrasives can be selected for machining with high removal requirements and low surface roughness requirements.
◆☞ Grain Size Marking and Application Cases of Coated Abrasives
In coated abrasives, the grit size is usually labeled, such as P100, P240, etc., to help customers select the appropriate abrasive tools.
Case Studies
- Metal Surface Polishing: initial polishing is usually carried out with P60-P80 coarse grit abrasives, followed by gradual surface finishing with P180-P320 medium to fine grits.
- Woodworking: grit sizes from P120 to P240 are typically used to sand wood to achieve a smooth surface finish.
- Precision mold processing: in mold polishing, fine abrasives with grit sizes of P600 or higher are commonly used for precision polishing to achieve a mirror-like finish.
◆☞ Abrasives for coated abrasives available from DOMILL:
- Brown Fused Alumina: DOMILL selects premium-grade brown fused alumina blocks from its own smelting plant for crushing and screening based on customer requirements. The resulting brown fused alumina abrasives are of high purity and exhibit stable chemical properties, making them well-suited for the production of standard coated abrasives. The related grades include A22 and A25.
- Available grit sizes: P12-P2000 can be customized according to the enterprise’s grain size requirements
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A22
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The abrasive is sharp, has a low build-up density, and is self-sharpening. The coated abrasives made from them are sharp, have good heat dissipation, and have high grinding efficiency, making them suitable for producing standard coated abrasives. They are ideal for hand sanding various metals and wood.
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A25
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The abrasive is polygonal with moderate packing density. The coated abrasives have good sharpness, durability, and high grinding efficiency, and are used for making abrasive cloth, abrasive paper, abrasive belts, and processing mild steel, alloy steel, and hardwood.
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- Medium-temperature calcined brown fused alumina: DOMILL is the first enterprise in China to apply tunnel kiln to calcined abrasives. The medium-temperature calcined brown corundum abrasives for solidified abrasives are also roasted in a tunnel kiln instead of the rotary kiln used by many manufacturers, which enables the medium-temperature calcination temperature to reach 1000°C, allowing the removal of impurities in the abrasives more thoroughly, and its toughness, hydrophilicity, cleanliness, magnetic content, hardness and other qualities are significantly improved compared with those of general-purpose brown corundum. The relevant grades of medium-temperature calcined brown corundum for coated abrasives are AT22 and AT25.
- Available granularity: P12-P2000 can be customized according to the enterprise’s grain size requirements
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AT22
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The abrasive is sharp, with low packing density and self-sharpening. Its toughness, hydrophilicity, cleanliness, magnetic content, and hardness are significantly improved compared with A22. The coated abrasives made of it are sharp, with good heat dissipation and high grinding efficiency, and the abrasive cloth and sandpaper made of it are suitable for hand sanding of various metals and wood.
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AT25
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The abrasive is polygonal with moderate packing density. Its toughness, hydrophilicity, cleanliness, magnetic content, and hardness are significantly improved compared with A25. The abrasives made of it have high sharpness, good heat dissipation, improved durability, and high grinding efficiency, and the mid-range coated abrasives made of it are suitable for processing low carbon steel, alloy steel, hard bronze and hard wood.
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- High-temperature calcined brown fused alumina: DOMILL is the first enterprise in China to apply tunnel kiln to calcined abrasives. Calcined brown corundum is divided into medium-temperature calcined at 1050 degrees Celsius and high-temperature calcined at 1350 degrees Celsius, the temperature calcined abrasive is blue, and the performance index of the abrasive is better than that of medium-temperature calcined. High-temperature calcined brown corundum abrasive for coated abrasives is further improved in toughness, hydrophilicity, cleanliness, magnetic content, hardness, and other qualities compared with medium-temperature calcined, which is the peak of brown corundum, and the relevant grades are AB22 and AB25.
- Available particle sizes: P12-P2000 can be customized according to the enterprise’s grain size requirements
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AB22
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The abrasive is pointed, irregular, sharp particles, with low bulk density, after calcination treatment, its toughness, hydrophilicity, cleanliness, magnetic content, and hardness than AT22 significantly improved. The abrasives made of it have high sharpness, good heat dissipation, and improved durability; it is used for high-grade coated abrasives, making abrasive cloth, sandpaper, abrasive belts, processing of low carbon steel, alloy steel, and special wood.
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AB25
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The abrasive is polygonal, with moderate stacking density. Its toughness, hydrophilicity, cleanliness, magnetic content, and hardness are significantly improved compared with AT25; the abrasives made of it have high sharpness, good heat dissipation, and improved durability; it is used for high-grade coated abrasives, making abrasive cloths, sandpaper, abrasive belts, processing of low carbon steel, alloy steel, and special wood.
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- Coated brown fused alumina: Coated brown fused alumina abrasives refer to modified abrasives in which a certain amount of organic binder combined with special additives, or inorganic ceramic binder with special additives, is uniformly applied to the surface of the abrasive particles. The particles are then heat-treated at specific temperatures and times. The common coated brown fused alumina is red, while medium-temperature and high-temperature coated types differ. The related grades are ATR25 and ABR25.
- Available particle sizes: P12-P2500can be customized according to the enterprise’s grain size requirements
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ATR25
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Medium-temperature coated, bright red in color, with polyhedral-shaped particles and moderate bulk density. Compared to AT25, ATR25 shows significantly improved hydrophilicity, giving it strong adhesion, good sharpness, and excellent heat dissipation. It is primarily used in the production of high-end sandpaper, sanding cloths, and sanding belts for coated abrasives, suitable for polishing high-quality panels and processing low-carbon steel, alloy steel, and more. It ensures good grinding efficiency while maintaining durability.
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ABR25
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High-temperature coated, dark red in color, with polyhedral-shaped particles and moderate bulk density. Compared to ATR25, the toughness, hydrophilicity, cleanliness, magnetic content, and hardness of this product are significantly improved after high-temperature coating. It features strong adhesion and excellent heat dissipation. It is mainly used for the production of high-end coated abrasives and high-value non-woven abrasives, suitable for polishing high-quality hardwood panels and heavy-duty sanding of metals with abrasive belts.
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- White fused alumina: The white fused alumina series is made from alumina powder, which is melted in an electric arc furnace at temperatures exceeding 2000°C and then cooled. The resulting abrasives are dense, with uniform crystals, high purity, and high hardness. Abrasives made from white fused alumina are suitable for grinding high-carbon steel, high-speed steel, and quenched steel, and can also be used in the production of coated abrasives. The related grades include WA22 and WA25.
- Available particle sizes: F12-F2500 can be customized according to the enterprise’s grain size requirements
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WA22
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With a sharp shape and low bulk density, the coated abrasives made from it are sharp, have low toughness, and offer high grinding efficiency, making them suitable for the production of sandpaper, nylon wheels, and sponge sanding pads.
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WA25
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With a polyhedral shape, relatively regular particles, and sharp edges, it has a moderate bulk density. Coated abrasives made from it offer good hardness, moderate toughness, and high grinding efficiency. Sandpaper, nylon wheels, and sponge sanding pads made from it are more wear-resistant than those made with WA22.
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- Monocrystalline Fused Alumina: is an abrasive produced from high-purity alumina using a high-temperature smelting process. It features a nano-layered structure with strong toughness, high hydrophilicity, and high hardness. The crystal grains are fully developed with layered bonding, allowing sharp cutting edges to form during grinding and cutting. Compared to standard abrasives, it offers longer life, higher grinding and cutting efficiency, and better surface finish. The related grade is MA22.
- Available particle sizes: P12-P220 can be customized according to the enterprise’s grain size requirements
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MA22
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It has a blue, sharp shape with low bulk density and high sharpness, mainly used for producing high-end coated abrasives, high-demand hardwood polishing, and heavy-duty metal abrasive belt grinding. It is suitable for hard and tough-to-grind metal materials such as stainless steel, high-vanadium high-speed steel, heat-resistant alloy steel, and workpieces prone to deformation and burning.
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▶ Storage and handling of abrasives for coated abrasives
◆☞ Storage Conditions
- Temperature: Abrasives should be stored in a cool, dry place, away from high temperatures which can affect the physical properties of the abrasive.
- Moisture: Keep humidity levels low to prevent moisture in the abrasive, as moisture can cause the abrasive to clump or reduce its performance.
- Sunlight: Avoid direct sunlight as UV rays can cause damage to some abrasives.
◆☞ Packaging: Abrasives should be packaged in well-sealed packaging materials, such as polythene bags, paper bags, or drums, to prevent external contamination during storage and transport. Packaging materials should have sufficient strength and durability to withstand shock and vibration during transport.
◆☞ Labels: The name, specification, date of manufacture, shelf life, and other information of the abrasive should be clearly marked on the packaging to facilitate management and use.
◆☞ Transport: During transport, ensure that the abrasive packaging is intact and avoid collision and extrusion. At the same time, the appropriate mode and means of transport should be selected according to the nature of the abrasive to ensure transport safety.
◆☞ Safe handling and environmental protection measures
- Safe Handling: When handling abrasives, wear appropriate personal protective equipment (PPE), such as dust masks, gloves, etc., to prevent injury from abrasive dust. At the same time, relevant safety operating procedures should be observed to ensure the safety of personnel and equipment.
- Environmental Protection: Environmental protection should be emphasized in the storage and handling of abrasives. The storage environment should be kept clean to avoid pollution of the environment by abrasive dust. During transport, effective measures should be taken to prevent the leakage of abrasive dust into the environment. In addition, discarded abrasive packaging and transport equipment should be properly disposed of in accordance with applicable regulations to minimize environmental impact.
▶ Why Choose DOMILL as the ideal abrasive supplier?
As a professional supplier of abrasives with 30 years of industry experience and technology accumulation, DOMILL provides integrated services from R&D, and production to sales to ensure that customers can obtain the most suitable products for their needs. In addition, DOMILL also has strong R&D capabilities and the ability to guarantee stable delivery of large quantities, which can meet the diversified needs of customers. By choosing DOMILL as your abrasive supplier, you will gain a reliable, professional and innovative partner for your success in industrial manufacturing.
