I. Production Process of Granite Straightedge
Raw material screening and cutting
Material selection criteria: High-quality granite with a density of ≥2.7g/cm³ and a water absorption rate of < 0.1% (such as "Jinan Green" from Shandong and "Black Gold Sand" from India) should be selected. The mineral particles should be uniform (quartz particles ≤2mm), free of cracks and pores, and the hidden defect stones should be removed through X-ray flaw detection.
Rough cutting: Use a diamond circular saw to cut the blank into a blank that is 5-10mm larger than the finished product size. The flatness error of the cutting surface should be controlled within ±0.5mm.
2. Aging treatment
Natural aging: Place the green body in the open air for 6 to 12 months. Through the temperature difference between day and night and the changes in humidity, over 90% of the internal stress is released to prevent deformation in the later stage.
Artificial aging (optional) : Some manufacturers use a constant temperature furnace (100-150℃) for 24 hours to accelerate stress release, which is suitable for urgent orders, but the effect is slightly lower than that of natural aging.
3. Rough grinding and reference surface processing
Rough grinding and shaping: Use a 200-400 mesh diamond grinding wheel to grind the blank, remove the cutting lines, correct the flatness from ±0.5mm to ±0.1mm/m (100μm/m), and determine the reference surface.
Non-working surface treatment: Chamfer or coat the side and bottom surfaces (such as spraying anti-rust paint) to prevent edge cracking and moisture absorption expansion.
4. Precision grinding (core process)
The precision leap is achieved through hierarchical grinding, which is divided into three stages:
Rough grinding: Use 400-800 mesh abrasives (silicon carbide or diamond micro-powder) in combination with a granite grinding platform to correct the flatness to ±10μm/m, and the surface roughness Ra≤0.8μm.
Precision grinding: By switching to 1200-2000 mesh abrasives and combining with an electronic level (accuracy ±1μm/m) for real-time monitoring, the flatness has been improved to ±3μm/m, and the surface roughness Ra is ≤0.4μm.
Ultra-fine grinding (key to high-precision products) : By using W10-W5 grade micro-powder (particle size 5-10μm) and chemical polishing liquid, through the dual action of "mechanical grinding + chemical corrosion", the final flatness can reach ±1μm/m, and the surface roughness Ra≤0.2μm.
5. Precise detection and correction
Detection equipment: A laser interferometer (accuracy ±0.1μm) and an electronic level (resolution 0.001mm/m) are used to conduct full-range detection of flatness and straightness, and to draw an error distribution map.
Closed-loop correction: Based on the detection data, local supplementary grinding is carried out on the high-error area through a CNC grinding machine until the full-size error is controlled within the target range.
6. Surface protection and packaging
Protective treatment: Spray a nano-scale silica coating (5-10μm thick) on the reference surface, and apply an anti-corrosion wax layer on the non-working surface to prevent moisture absorption or oxidation during long-term use.
Precision packaging: It is packed in shockproof wooden cases with desiccants. During transportation, the temperature difference is controlled within ±5℃ to avoid precision attenuation caused by vibration.
Ii. Highest Precision Grade and Industry Standards
The accuracy of granite straightedge is based on the flatness error as the core index. According to the national standard (GB/T 4977-2018) and the international standard (ISO 2768-2), its accuracy grades and corresponding parameters are as follows:
Top laboratories can achieve ultimate accuracy:
Through nano-scale grinding techniques (such as magneorheological polishing and ion beam modification), the flatness of some high-end products can be broken through to ±0.5μm/m (i.e., the error per meter length does not exceed 0.5 micrometers), approaching the optical-grade plane reference. They are mainly used in extremely precise scenarios such as aerospace and metrology institutes.
Iii. Comparison of Factors Affecting Accuracy
Summary: The high precision of granite straightedge relies on the full-process control of "high-quality raw materials + ultra-long aging + graded grinding + harsh environment", among which the grinding process is the core for the breakthrough in precision. With the development of nanofabrication technology, its precision is gradually advancing towards the sub-micron level and has become an irreplaceable benchmark tool in the field of high-end manufacturing.
Post time: May-19-2025