Selection and use of cooling lubricants for stone sawing
1. The Mechanism of Action of Cooling Lubricant
Cooling lubricants significantly enhance the cutting conditions during stone processing. They are primarily composed of emulsifiers and base oils, hence they are also referred to as lubricants. When dissolved in water, these substances typically form an emulsified state, which is why they are known as emulsified rinses. The mechanism by which cooling lubricants function during stone cutting is complex and involves both physical and chemical processes.
1.1 Mechanism of Action on Diamond
(1) Lowering the Temperature at the Diamond-Rock Interface
Cooling lubricants act as surfactants that adsorb onto the surface of diamond-like rock, forming a lubricating film that enhances the interface's lubricity. This reduces frictional resistance, resulting in less heat generation during sawing. Consequently, the interface temperature decreases, reducing the rate of diamond oxidation or graphitization. This helps maintain the hardness and strength of the diamond. Studies show that a 0.2% concentration of cooling lubricant can reduce the friction coefficient by over 60% compared to water. Additionally, the directed adsorption of lubricant molecules on the diamond and rock surfaces creates a lubricating film that further reduces friction.
(2) Accelerating Thermal Diffusion at the Diamond-Rock Interface
Diamonds are oleophilic and hydrophobic. The low surface tension of the cooling lubricant solution (32.5×10â»Â³ N/cm), which is about 50% less than that of water, improves its wettability. This allows for faster thermal diffusion at the interface, reducing the heating time of the diamond and minimizing oxidation or graphitization. This improves the working environment of the diamond, reducing wear and extending its life.
1.2 Mechanism of Action on Metal Bond
The diamond block (cutting head) is made by mixing and sintering diamond particles with metal powders. During the sawing process, new diamonds are exposed due to the wear of the metal binder. The wear of the bonding agent is a key factor affecting the blade’s lifespan.
(1) Reducing Friction at the Binder-Rock Interface
Cooling lubricants not only adsorb on the diamond surface but also on the metal binder, improving the lubricity of the binder-rock interface. This reduces friction and wear. Laboratory tests show that using 0.2% cooling lubricant can reduce binder wear on rock to 1/10 of that when using clean water, creating favorable conditions for the binder to protect the diamond.
(2) Enhancing Stone Powder Precipitation
Cooling lubricants contain polymeric precipitants that help aggregate fine stone powder, causing it to settle quickly. This reduces the concentration of stone powder in the coolant, minimizes wear during recycling, and prevents premature diamond loss, thereby extending the cutter head’s life.
1.3 Reducing Saw Blade Deflection
During sawing, the blade may deflect, increasing current and preventing further cutting. This occurs due to either substrate deformation or friction between the blade and rock walls. Using cooling lubricants forms a thick lubricating film at the interface, reducing the friction coefficient from 0.38 to 0.1, thus reducing resistance and controlling vibration, which extends the blade’s life.
2. Composition of Cooling Lubricants
A complete stone-cutting lubricant should include emulsifier, lubricating oil, and precipitant. Depending on the application, only two of the three components may be used. Each component has different types, and their performance varies accordingly.
2.1 Emulsifier
Emulsifiers are mainly surfactants, consisting of hydrophilic and lipophilic groups. They reduce surface tension and change the system’s interfacial state. Surfactants can be classified into anionic, cationic, amphoteric, and non-ionic types based on their hydrophilic structure.
2.2 Lubricating Oil
Lubricating oils are categorized into mineral, animal/vegetable, and synthetic oils. Mineral oils are the most commonly used due to their availability, cost-effectiveness, and stability. Synthetic oils offer unique properties but are more expensive and less widely used.
2.3 Precipitant
Precipitants help flocculate stone powder, making it settle quickly. Inorganic precipitants like NaCl work by neutralizing the charge on particle surfaces, while organic ones like polyacrylamide use polymer bridging to cause aggregation.
3. Selection of Cooling Lubricant
3.1 Choosing the Right Type
Selecting the right cooling lubricant involves considering factors such as raw material availability, quality, consumption, and cost. Anionic lubricants are preferred for granite due to their ability to repel stone powder and reduce friction. Sodium alkyl fumarate is ideal due to its low cost, good performance, and wide availability.
3.2 Quality Considerations
Choosing high-quality products from reliable manufacturers is crucial. Ensure the product meets safety standards, has no harmful effects, and maintains a weakly acidic pH. Regular checks and proper storage are essential to maintain effectiveness.
4. Proper Use of Cooling Lubricant
Using cooling lubricants requires a circulating water system and sedimentation tank. The size of the sedimentation tank depends on annual output. Regular replenishment, pH control, and water quality monitoring are essential for optimal performance.
5. Conclusion
Cooling lubricants play a vital role in reducing friction, lowering temperatures, and extending the life of diamond blades. A well-formulated lubricant, combined with proper usage, improves efficiency, reduces costs, and ensures long-term performance. By selecting the right components and maintaining optimal conditions, users can achieve significant improvements in their stone-cutting operations.
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