Deeply understand the production process of brown corundum powder
Standing three meters away from the electric arc furnace, the heat wave wrapped in the smell of burnt metal hits you in the face – the bauxite slurry at more than 2200 degrees in the furnace is rolling with golden red bubbles. The old master Lao Li wiped his sweat and said: “See? If the material is one shovel less coal, the furnace temperature will drop by 30 degrees, and the brown corundum that comes out will be as brittle as biscuits.” This pot of boiling “molten steel” is the first scene of the birth of brown corundum powder.
1. Melting: The hard work of taking “jade” from the fire
The word “fierce” is engraved in the bones of brown corundum, and this character is refined in the electric arc furnace:
Ingredients are like medicine: bauxite base (Al₂O₃>85%), anthracite reducing agent, and iron filings must be sprinkled as a “matchmaker” – without it to help with melting, the impurity silicates cannot be cleaned up. The proportioning books of old factories in Henan Province are all worn out: “Too much coal means high carbon and black, while too little iron means thick slag and agglomeration”
The secret of the tilted furnace: The furnace body is tilted at a 15-degree angle to allow the melt to naturally stratify, the bottom layer of pure alumina crystallizes into brown corundum, and the upper layer of ferrosilicon slag is scooped away. The old master used a long pick to poke the sampling port, and the splashed molten droplets cooled and the cross section was dark brown: “This color is right! The blue light indicates that the titanium is high, and the gray light means that the silicon is not completely removed”
Quick cooling determines the outcome: the melt is poured into a deep pit and poured with cold water to “explode” into pieces, and the water vapor makes a popcorn-like crackling sound. Fast cooling locks lattice defects, and the toughness is 30% higher than that of natural cooling – just like quenching a sword, the key is “fast”
2. Crushing and shaping: the art of shaping “tough guys”
The hardness of the brown corundum block just out of the oven is close to that of diamonds. It takes a lot of trouble to turn it into a micron-level “elite soldier”:
The rough opening of the jaw crusher
The hydraulic jaw plate “crunches” and the basketball-sized block is broken into walnuts. Operator Xiao Zhang pointed at the screen and complained: “Last time a refractory brick was mixed in, and the jaw plate broke a gap. The maintenance team chased me and scolded me for three days”
The transformation in the ball mill
The ball mill lined with granite rumbles, and the steel balls hit the blocks like violent dancers. After 24 hours of continuous grinding, dark brown coarse powder gushed out of the discharge port. “There is a trick here,” the technician tapped on the control panel: “If the speed exceeds 35 rpm, the particles will be ground into needles; if it is less than 28 rpm, the edges will be too sharp.”
Barmac Plastic Surgery
The high-end production line shows its trump card – Barmac vertical shaft impact crusher. The material is crushed by self-collision under the drive of the high-speed rotor, and the micro powder produced is as round as river pebbles. A grinding wheel factory in Zhejiang Province measured: for the same specification of micro powder, the traditional method has a bulk density of 1.75g/cm³, while the Barmac method has a bulk density of 1.92g/cm³! Mr. Li twisted the sample and sighed: “In the past, the grinding wheel factory always complained about the poor fluidity of the powder, but now it complains that the filling speed is too fast to keep up.”
3. Grading and purification: precise hunting in the world of microns
Classifying particles 1/10 of the thickness of a hair into different grades is a battle of the soul of the process:
The mystery of airflow classification
0.7MPa compressed air rushes into the classification chamber with powder, and the impeller speed determines the “admission line”: 8000 rpm screens out W40 (40μm), and 12000 rpm intercepts W10 (10μm). “I am most afraid of excessive humidity”, the workshop director pointed to the dehumidification tower: “Last month, the condenser leaked fluorine, and the micro powder clumps and blocked the pipeline. It took three shifts to clean it.”
The gentle knife of hydraulic classification
For ultrafine powders below W5, water flow becomes the classification medium. The clean water in the grading bucket lifts the fine powder at a flow rate of 0.5m/s, and the coarse particles settle first. The operator stares at the turbidity meter: “If the flow rate is 0.1m/s faster, half of the W3 powder will escape; if it is 0.1m/s slower, W10 will mix in and cause trouble.”
The secret battle of magnetic separation and iron removal
The strong magnetic roller takes away the iron filings with a suction force of 12,000 gauss, but it is helpless against the iron oxide spots. The trick of the Shandong factory is: pre-soak with oxalic acid before pickling, convert the difficult Fe₂O₃ into soluble ferrous oxalate, and the impurity iron content drops from 0.8% to 0.15%
4. Pickling and calcining: the “rebirth” of abrasives
If you want brown corundum micropowder to withstand the test in the high-temperature grinding wheel, you have to pass two life and death tests:
Acid-base dialectics of pickling
Bubbles in the hydrochloric acid tank surge to dissolve metal impurities, and concentration control is like walking on a tightrope: less than 15% cannot clean rust, and more than 22% corrodes the alumina body. Lao Li held up a PH test paper to impart experience: “When neutralizing with alkaline washing, you must accurately pinch PH=7.5. Acid will cause burrs on the crystals, and alkaline will cause the surface of the particles to powder.”
The temperature puzzle of calcination
After calcination at 1450℃/6 hours in a rotary kiln, the ilmenite impurities decompose into rutile phase, and the heat resistance of the micropowder soars by 300℃. However, due to the aging of the thermocouple of a certain factory, the actual temperature exceeded 1550℃, and all the micro powders that came out of the furnace were sintered into “sesame cakes” – 30 tons of materials were directly scrapped, and the factory director was so distressed that he stamped his feet.
Conclusion: Industrial aesthetics between millimeters
In the twilight workshop, the machines are still roaring. Lao Li dusted off the dust on his work clothes and said: “After working in this industry for 30 years, I finally understand that good micro powders are ‘70% refining and 30% life’ – ingredients are the foundation, crushing depends on understanding, and grading depends on carefulness.” From bauxite to nano-scale micro powders, technological breakthroughs always revolve around three centers: purity (pickling and impurity removal), morphology (Barmac shaping), and particle size (precise grading).
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