How are black polished pebbles processed?

The polishing process for black polished pebbles is relatively complex, involving multiple stages of treatment. Each step requires meticulous operation to ensure the stone's luster and quality. Below, I will detail the entire polishing process from raw stone to finished product:

1. Material Selection and Raw Stone Preparation

The quality of black pebbles depends on the selection of raw stones. First, manufacturers must collect black pebbles from quarries or beaches. Key considerations during selection include:

Stone Hardness: Black pebbles typically require relatively hard stone to achieve optimal polished results.

Grain Size: Select appropriate pebble sizes based on customer requirements, commonly including small grains, round shapes, and irregular forms.

After selection, these raw stones are transported to the processing plant for subsequent treatment.

2. Cleaning and Screening

Raw stones carry soil, sand particles, and other impurities, necessitating thorough cleaning:

Dirt Removal: Submerge stones in water tanks to flush away surface soil and debris.

Screening and Grading: Use screening equipment to classify pebbles by size, retaining those suitable for polishing while discarding broken or irregularly shaped stones.

3. Rough Processing (Cutting and Grinding)

Cleaned and screened pebbles undergo preliminary surface rough processing. This aims to remove surface irregularities and achieve greater smoothness.

Cutting: Larger pebbles may require initial mechanical cutting to achieve desired size and shape. Smaller pebbles typically do not need cutting.

Initial Grinding: A grinding machine (typically using sand belts or discs) performs initial grinding to remove surface roughness. Coarser grit sandpaper (e.g., 60-80 grit) is used at this stage.

4. Medium Grinding (Surface Leveling)

After initial surface roughness removal, further medium grinding is required.

Sandpaper Grinding: Use finer grit sandpaper (e.g., 150-300 grit) for medium grinding to further flatten the surface, making the stone smoother and free of noticeable scratches.

Detailed Inspection: At this stage, workers inspect every part of the pebble to ensure the surface is uniform and free of obvious defects.

5. Fine Polishing

This is the most critical stage of the entire processing, as the polishing treatment determines the final appearance of the pebbles. Through this process, the surface of the pebbles will achieve a brilliant luster.

Polishing Machine Usage: Pebbles are typically placed into polishing machines equipped with polishing pads, polishing liquids, and polishing compounds.

Polishing Compound Selection: Choose the appropriate compound based on the pebble's material. Common compounds include emery paste and aluminum oxide paste, which enhance the pebble's luster.

Grinding Process: Inside the machine, the pebbles rotate with the polishing pads. Through prolonged grinding, the surface gradually becomes smooth and shiny. During this process, progressively finer polishing powders and liquids (such as 3000-5000 grit abrasive powders) are used to enhance surface gloss.

Temperature and Humidity Control: During fine polishing, ensure proper temperature and humidity control within the equipment, as overheating or excessive dryness may compromise polishing results.

6. Final Inspection and Finishing

After polishing concludes, the pebbles undergo a final inspection focusing on:

Surface Gloss: Verifying the pebble surface is uniformly smooth and achieves the required gloss level.

Shape Inspection: Ensuring the pebble shape meets specifications with no excess cutting marks.

Size Consistency: For batch-processed pebbles, checking each pebble's dimensions for uniformity.

Any imperfections are manually refined by workers, potentially requiring localized re-grinding or polishing on specific surface areas.

7. Cleaning and Drying

After polishing and inspection, pebble surfaces typically retain polishing compound residue. To remove these residues, the stones undergo additional cleaning:

Water Wash: Thoroughly clean the pebbles with clean water or specialized detergent to remove residual polishing compound, impurities, and moisture.

Natural Drying: After washing, the pebbles must dry naturally in a dry, well-ventilated environment to prevent residual moisture from affecting quality.

8. Packaging and Shipping

Following meticulous polishing and cleaning, the finished black polished pebbles are ready for packaging. Depending on customer requirements, pebbles can be packaged individually or in bulk, typically using:

Bagged: Smaller pebbles are divided into mesh bags, plastic bags, or cardboard boxes.

Wooden Crates: Large bulk orders are usually packed in wooden crates to ensure the stones remain undamaged during transit.

Finally, the packaged pebbles are shipped, delivering the products to customers according to their specifications.