How White Fused Alumina Is Made: Fusion, Crushing and Grading
白色電融アルミナ (WFA), also called white fused aluminum oxide or white corundum, is a synthetic mineral produced by electric arc fusion of selected alumina. It is not an artificial gemstone and it is not made by simply calcining or grinding alumina powder. The fusion, cooling, crushing and classification stages create the abrasive grain sold for bonded abrasives, コーティングされた研磨材, 爆破, ラッピング, ceramics and refractories.
This guide follows the production route and explains how each stage can affect chemistry, 粒の形状, particle size and batch consistency.
1. Alumina Raw Material Selection
The process begins with selected alumina. Raw-material chemistry influences the final Al2○3 content and impurities such as Na2○, Fe2○3 and SiO2. The producer should define incoming inspection and storage controls to prevent mixing and contamination.
Industrial buyers should not treat high purity as a complete specification. The relevant impurity limits depend on the application: sodium may affect some abrasive and refractory systems, while iron contamination is especially important for clean blasting and color-sensitive products.
2. Electric Arc Fusion
Alumina is melted in an electric arc furnace at very high temperature. Controlled power input and furnace operation allow the charge to fuse into a dense aluminum oxide mass. After fusion, the material is cooled and solidifies into a crystalline block.
The purpose is to create fused alumina, not aluminum oxide glass or a gemstone. Furnace operation and cooling influence crystal development and the behavior of the material during later crushing.
3. Block Selection and Primary Crushing
The cooled block is broken into manageable pieces. Material from different zones may be separated according to the producer’s quality plan. Primary and secondary crushing then reduce the block into grain.
Crushing is not only size reduction. Crusher type, settings and repeated impact can influence particle shape, シャープネス, bulk density and the proportion of fines. A supplier producing different abrasive and refractory grades may use different processing routes.
4. Magnetic Cleaning and Contamination Control
Iron-bearing contamination can enter through handling and crushing equipment. Magnetic separation and clean material flow help control these particles. For stainless-steel blasting or other contamination-sensitive uses, the buyer may need a specific magnetic-material or iron-related limit instead of relying on the white color.
5. Macrogrit Screening
Coarser abrasive grains are classified by screens into controlled size distributions. FEPA F grades are used for bonded abrasives and general applications, while FEPA P grades are intended for coated abrasives. Refractory products may use mesh or millimeter fractions designed for aggregate packing.
The same number in two standards is not automatically equivalent. The order and COA should name the grade standard and test method.
6. Microgrit Classification
Fine abrasive microgrits require more precise separation than ordinary screening can provide. Depending on the grade and factory, classification may use wet processes or other controlled methods. The powder is then dried, deagglomerated where necessary and inspected.
For lapping and polishing, the coarse tail can be more important than the average size. Ask how oversize particles are controlled and whether the lot report shows the relevant upper limit, sieve residue or full particle distribution.
7. Final Inspection and Lot Release
A production lot should be released against the agreed specification. Depending on the application, testing may include:
- particle size distribution or sieve analysis;
- oversize or residue;
- Al2○3 and controlled impurities;
- bulk density;
- magnetic material;
- moisture, pH or electrical conductivity;
- microscope examination for particle shape or contamination.
The COA should distinguish actual lot results from typical product values. Retained samples are valuable when investigating a customer result months after shipment.
8. Packaging and Traceability
Finished WFA may be packed in lined 25 kg袋, bulk bags or customized export packaging. Fine powders require moisture and dust control. Labels should identify the product, grade, lot and net weight, and the lot code should connect the package to production and inspection records.
How Production Affects Performance
| Production control | Possible customer impact |
|---|---|
| Raw-material chemistry | 純度, color and refractory/abrasive compatibility |
| Fusion and cooling | Crystal and fracture behavior |
| Crushing route | Particle shape, sharpness and bulk density |
| Magnetic cleaning | Metallic contamination risk |
| 分類 | 切削速度, finish, packing and scratch risk |
| Drying and packing | 水分, flow, dispersion and storage stability |
Questions to Ask a Manufacturer
- Which grit standards and size ranges are produced on the line?
- Which chemistry values are guaranteed?
- How are magnetic contamination and abnormal coarse particles controlled?
- Is the sample taken from normal production?
- Can the supplier provide TDS, SDS, lot COA and retained samples?
- How are process or raw-material changes communicated?
For product properties and applications, read White Fused Alumina Powder: Properties, Grades and Applications. For supplier evaluation, see our WFA manufacturer qualification guide.
Send Yumo your grade, application and test requirements to request product data or a representative sample.
