As a critical piece of equipment in steel rolling production lines, the grinding quality of CNC roll grinders directly impacts the final product quality. With continuous advancements in manufacturing technology, modern roll grinders are now capable of achieving high-quality, high-precision roll grinding. However, to achieve this goal, it is not only necessary to rely on the machine’s precision but also to select the appropriate grinding wheels, optimize grinding parameters, and use suitable grinding coolants. This article will delve into these key factors, revealing the secrets to improving the grinding quality of CNC roll grinders.
Factors Affecting Grinding Quality
Grinder Precision
The machining precision of a CNC grinder is the core criterion for evaluating its grade. Building upon the grinder’s inherent manufacturing precision, we can further enhance grinding accuracy by optimizing installation precision and strengthening the digital control system.
Inspection and Adjustment of Bed Way Surfaces
CNC grinding machines are typically mounted directly on a concrete foundation, with fine-tuning of installation accuracy achieved through shims. When inspecting the bed’s V-shaped guideways, we must ensure that straightness in both the horizontal and vertical planes is within 0.01 mm/m, while the contact point density must reach 12–14 points per 25 mm × 25 mm area. In addition, the perpendicularity of the saddle guideways must be controlled within 0.02 mm/250 m. For the bed’s flat guideways, we must also ensure that straightness in the vertical plane does not exceed 0.01 mm/m, and that parallelism with the V-shaped guideways is controlled within 0.02 mm/m.
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Inspection and Adjustment of Table Guideways
The straightness of the table’s V-shaped guideways within the vertical plane must be maintained at less than 0.01 mm along their entire length, while the contact point density must reach 10–12 points per 25 mm × 25 mm area. For the table’s flat guideways, we must ensure that their parallelism with the V-shaped guideways is within 0.02 mm/m and that they meet the corresponding contact point requirements.
Stability of precision is key to ensuring the high quality of CNC grinding machines. Through meticulous inspection and adjustment, we can ensure that the grinding machine maintains a high level of machining precision during long-term use, thereby providing customers with high-quality grinding services.
Inspection and Adjustment of the Clearance Between the Grinding Wheel Spindle and Bearing Shells
The clearance between the front and rear bearings of the grinding wheel head spindle is critical to the spindle’s stability and balance. To ensure precision machining, we must regularly inspect and adjust this clearance as needed. For hydrodynamic bearings, we adjust the contact points by scraping the bearing shell surface with a scraper, thereby controlling the clearance between the spindle and the bearing shell within the range of 0.0025–0.005 mm. For hydrostatic bearings, we monitor the pressure in the front and rear bearing oil chambers and make immediate corrections upon detecting any abnormalities.
Inspection and Adjustment of Grinding Machine Lubrication
The lubrication status of CNC grinding machines directly affects their machining accuracy. For example, the pressure values of the worktable guideways, the dovetail guideways of the grinding wheel head, and the hydraulic systems must all be maintained at optimal levels to ensure precision during the grinding process.
Grinding Wheel Selection
When selecting grinding wheels, multiple factors must be considered, including the material of the roll, the hardness of the grinding wheel, and the choice of bonding agent, to ensure the best grinding accuracy.
Abrasive Selection
Appropriate grinding wheels should be selected for different types of rollers. For example, alumina grinding wheels are recommended for hardened or non-hardened steel rollers, while silicon carbide grinding wheels are suitable for cold-hardened cast iron rollers, rubber rollers, copper rollers, and granite rollers. Additionally, for steel rolls made of different materials, it is necessary to further select a matching alumina grinding wheel.
Selecting Hardness
When selecting the hardness of a grinding wheel, if the wheel wears down rapidly, this typically indicates that the selected wheel is too soft. In this case, you can try increasing the longitudinal feed rate between the grinding wheel and the carriage to alleviate the wear issue. If this does not yield significant results, it is recommended to replace the wheel with a harder one.
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Selection of Bonding Agents
Bonding agents play a crucial role in grinding wheels. Ceramic bonding agents (code) are a common choice, offering excellent stability, water resistance, heat resistance, and low cost. Resin bonding agents (code), primarily composed of phenolic resin, produce grinding wheels with high strength and good elasticity, but they are not heat-resistant. Rubber bonds (designatedX) offer superior elasticity compared to resin-bonded wheels and provide some polishing effects, but they are not suitable for rough machining. Metal bonds (designated) are primarily used in the manufacture of diamond grinding wheels, offering high strength, good formability, and a certain degree of toughness.
Grinding Parameters
During the grinding process of the roll, grinding quality must be optimized by adjusting the roll-to-grinding wheel speed, the support plate feed rate, and the lateral feed amount, particularly by employing different strategies for the rough grinding and finish grinding stages.
Roll Speed
During the rough grinding stage, the roll speed should be controlled within the range of 28 m/s to 37 m/s. For finish grinding, the speed requirement is slightly lower, set between 25 m/s and 30 m/s.
Grinding Wheel Speed
For rough and finish grinding of cold-hardened cast iron rolls, the grinding wheel speed should be set within the range of 22 m/s to 38 m/s.
Table Longitudinal Feed Rate and Transverse Feed Amount
During the finishing stage, the table’s longitudinal feed rate should be set within the range of 85 m/min to 210 m/min, with the transverse feed amount controlled between 0.005 mm and 0.01 mm. For precision polishing grinding, the transverse feed amount must be further reduced.
Carefully select grinding wheels that are compatible with the specific material properties of the roll.
When fine-grinding rolls, start the grinding machine in advance and allow it to run idle for a few minutes.
For rolls with extremely stringent precision requirements, the roll speed can be flexibly adjusted during the fine-grinding process.
Key Operational Procedures and Precautions
Coolant Application
During the grinding process of rollers, particularly during the fine and super-fine grinding stages, coolant serves to cool, lubricate, and clean the workpiece. Using the appropriate coolant can extend the life of the grinding wheel and improve workpiece quality.
The Importance of Grinding Coolant
Coolant not only effectively dissipates heat generated during grinding but also lubricates the grinding process, reducing grinding resistance and grinding wheel wear.
Selection of Grinding Coolant
To address the high temperatures and fine chips generated during roller grinding, we must select a grinding coolant that provides lubrication, cooling, cleaning, and rust prevention.
Key Improvement Measures
The core measures for achieving high-precision roll grinding lie in using high-performance grinding heads, equipping high-precision roll grinding machines, and optimizing roundness, cylindricity, and roll profile accuracy to enhance grinding quality and meet modern market demands.
Roundness Issues
The roundness of the roller support journal directly affects the roundness of the roller surface after grinding.
Cylindricity Deviations
The lack of parallelism between the rotational axis of the workpiece roller and the longitudinal movement direction of the saddle, as well as straightness errors in the grinding machine bed’s guideways within the horizontal plane, can adversely affect the cylindricity of the ground roller surface.
Roll Profile Deviation
Modern CNC roll grinding machines are equipped with error compensation functions to meet roll profile accuracy requirements, but issues with roll profile deviation still persist.
Conclusion: As domestic quality requirements for slab shape continue to rise, optimizing production processes has become increasingly important. Improving the quality of roll grinding is key, as it directly impacts the final product quality. In an increasingly competitive market environment, enterprises must continuously optimize their technology and enhance their competitiveness to achieve healthy and sustainable development.