Quality Control of Precision Granite Plates from Raw Materials to Finished Products

Applicable to 00, 000 grade precision granite (mainstream black granite such as Jinan Green), covering the entire process from mine material selection → raw material entry → rough processing → aging treatment → fine processing → grinding and scraping → inspection → packaging and delivery, with key control points for each process to ensure flatness, parallelism, perpendicularity, and internal stress stability.

I. Raw Material Mine & Raw Material Selection Control (Source Determines Stability)

1. Selección de minerales
   Prioritize gabbro / diabase (Jinan Green) with fine grains, uniform crystals, and dense structure; prohibit cracks, hidden cracks, inclusions, weathered layers, pores, yellow rust, and mineral vein impurities.

Key Point: Try to source the same plate from the same mine layer to avoid differences in the thermal expansion coefficient of different materials.

2. Raw Material Thickness Allowance
   Finished thickness 25-40mm processing allowance; large-sized bases must ensure sufficient thickness to reduce later deformation.
3. Initial Inspection of Raw Materials
   Use ultrasonic flaw detection to screen for internal hidden cracks; use naked eye strong light flashlight to check surface cracks; record the ore source number for traceability.

Risk: Internal micro-cracks in raw materials release stress after later fine processing, causing flatness to directly exceed the 000 grade.

II. Pre-treatment of Raw Materials and First Aging (Releasing Mining Stress)

1. After mine cutting, the raw material must first have the weathered skin and blast damage layer removed upon entering the factory.
2. Envejecimiento natural: Large-scale raw materials are left outdoors for 3-6 months to release internal stresses generated by mining, blasting, and cutting; for mass production with tight schedules, artificial aging in a constant temperature kiln can be used.

Strictly prohibit direct machine processing of raw materials upon entry, as they are extremely prone to slow warping and deformation later.

3. Re-inspection of raw material dimensions: Confirm length, width, and thickness allowances; mark crack and defect locations; defect locations must be within the processing removal range and cannot remain on the finished working surface.

III. Rough Processing Control

1. Cut to semi-finished product dimensions using large saws / gantry saws, leaving a 5-8mm fine processing allowance on each side.
2. Rough milling / grinding on each side to remove saw marks and chipped edges; roughly flatten the six sides.
3. Secondary Aging After Rough Processing (Very Critical)
   Rough processing removes a large amount of material, redistributing internal stresses. Semi-finished products are left in a constant temperature workshop for 7-15 days to release cutting stresses.

Many factories skip this step; the precision is qualified after grinding, but the flatness deviates after half a month.

4. Rough processing inspection: Check for hidden cracks and chipped edges; check overall geometric dimensions and ensure no obvious warping.

IV. Semi-finishing Stage

1. The gantry grinder grinds the six faces for semi-finishing, leaving a 0.08-0.15mm grinding allowance on each face;
2. Drilling, tapping, T-slotting, and assembly datum slotting are all completed in this process.

⚠️ Important: All holes, slots, and threaded holes must be completed before precision grinding.
If drilling and slotting are done after the working surface is ground, the impact stress will cause local deformation of the working surface, directly destroying the 000-grade accuracy.

3. After semi-finishing, let it rest again at a constant temperature for 2-5 days to release the stress caused by drilling and slotting.
4. Semi-finished product inspection: Dimensions, slot position, hole position tolerance; check for edge and corner chipping.

V. Precision Machining, Grinding, and Scraping (Determines the final accuracy grade)

Hard environmental conditions: Constant temperature workshop, temperature 20±2℃, temperature fluctuation ≤1℃/h, avoid direct sunlight, stay away from equipment vibration.

1. Precision grinding on a precision grinder, leaving a 0.015-0.03mm manual grinding allowance.
2. Manual grinding / scraping: 00/000 grade plates must be finely scraped to form oil-retaining micro-dimples, improving wear resistance and flatness accuracy.
3. Multi-face machining logic: Process the datum bottom surface first, then use the bottom surface as a datum to process the working surface to ensure parallelism; each vertical face relies on the right-angle datum to ensure perpendicularity.

Note: During the machining process, the workpiece must be placed on evenly distributed support points. Single-point loading is strictly prohibited to prevent the workpiece from bending under external force and rebounding/deforming after the supports are removed.

VI. Full Accuracy Inspection (Closed-loop before finished product leaves the factory)

The inspection environment is also a constant temperature of 20℃. Inspection tools: Spirit level, autocollimator, marble straightedge, dial indicator, height gauge, square.
Mandatory inspection items:

1. Flatness of the working surface (according to GB/T 2276 standard)
2. Parallelism of the working surface to the bottom surface
3. Perpendicularity of adjacent side faces
4. External dimension tolerance, T-slot straightness, hole position tolerance
5. Appearance: No cracks, no dents, no rust spots; edges and corners are safely rounded.
6. Issue an accuracy inspection record sheet, and archive each plate with its serial number.

Key point: Inspection cannot be done in one go. Re-test once after the grinding is completed and rested for 24 hours to confirm that the stress rebound does not exceed the tolerance before judging it as qualified.

VII. Protective Treatment

1. Clean off all dust and abrasives;
2. Apply a specialized stone protector to prevent seepage and oil stains, and avoid later oil absorption and discoloration;

Do not use ordinary paint, as it will affect precision testing.

VIII. Packaging, Transportation, and Delivery Control

1. Use a rigid wooden pallet at the bottom with multi-point uniform support, matching the actual support points during use as closely as possible;
2. Apply protective film to the working surface, reinforce the outer wooden crate, and prohibit direct pulling of the working surface during lifting;
3. Accompanying documents: Precision test report, product serial number, and installation support instructions.

Customer tip: Do not unpack and use immediately upon arrival; place it in a constant-temperature workshop for 48 hours before unboxing and re-testing.

IX. Summary of Major Failure Risk Points in the Full Process

1. Hidden cracks in raw materials not detected early → Cracking during use
2. Skipping multiple aging processes, stress not released → Slow warping of the finished product later
3. Drilling and grooving after grinding → Local deformation and loss of precision
4. Large temperature difference in processing and testing environments → Inaccurate measurements, false precision at factory exit
5. Unreasonable workpiece support during processing, pressure deformation, and elastic rebound after unloading
6. Incorrect support points during transportation, deformation due to handling compression