TL;DR — Direct answer: A bearing factory needs clean, dry, oil-free quality air at 6 to 7 bar for grinding, superfinishing, assembly and testing, with a pressure dew point of 3 degrees C or lower and filtration to 0.01 micron so no oil, water or dust reaches a raceway, a grinding spindle or a measuring instrument. Size on the coincident peak of grinding and assembly lines, commonly 5 to 12 cubic metres per minute for a mid-size plant, and use a variable speed drive because grinding loads follow the production schedule. QiAir, a Chinese screw compressor manufacturer and supplier, builds oil-injected machines with multi-stage filtration and oil-free options for the cleanest bearing lines.

A bearing is a precision product measured in microns, and the air behind it has to match that standard. Grinding machines use compressed air for spindle control, wheel dressing and workpiece clamping, superfinishing lines use it for stone pressure and oscillation, assembly lines use it for pressing, greasing and sealing, and testing stations use it for noise, vibration and roundness measurement. A single puff of wet air can rust a raceway before it is greased, a trace of oil can contaminate a clean assembly, and a pressure dip can change the force on a superfinishing stone and leave a surface finish outside tolerance. The defect may only show up at final testing, by which time a whole batch is suspect. QiAir is a Chinese manufacturer and supplier of screw air compressors, and its machines for bearing plants are specified around air purity and pressure stability first and flow second.

QiAir screw air compressor
QiAir screw air compressor

The trap in bearing manufacturing is treating air as a background service while the grinding machine gets all the attention. Grinding is a batch process with sharp peaks when several machines change wheels together, assembly runs in steady shifts, and testing needs the cleanest air of all. The compressor must cover the coincident peak without sagging below 6 bar at the farthest grinder, and the treatment chain must hold the dew point and oil level steady through the hottest, most humid month. This guide maps the air users on a bearing line, explains how to size for grinding peaks, sets the filtration standard that protects raceways, and shows what to put on a sizing sheet for a China supplier.

Where Air Is Used: Grinding, Superfinishing, Assembly and Testing

Grinding is the heaviest user and the most sensitive to pressure. Air drives the grinding spindle auxiliaries, wheel dressing, workpiece clamping and coolant control, and any pressure swing shows up as a variation in surface finish or roundness. A grinding hall with ten to twenty machines can pull its peak in the first minutes after a wheel change, when several machines restart together, and a compressor sized on average flow will sag exactly then. Keep the pressure at the grinder within a narrow band, and fit a dedicated receiver near the grinding hall if the header run is long, because a local receiver is cheaper than upsizing the whole system.

Superfinishing, assembly and testing each add their own demand, and testing is the strictest of all. Superfinishing stones need steady air pressure to hold a consistent force on the raceway, assembly lines need dry air for pressing, greasing and sealing, and noise and vibration test stations need very clean air for their instruments and handling. A plant that runs deep-groove, tapered and spherical bearings on shared headers will see very different peaks by product mix, so the sizing exercise has to use the real production schedule, not a single representative day.

  • Grinding: spindle control, wheel dressing, clamping and coolant control sensitive to pressure swings.
  • Superfinishing and assembly: stone pressure, pressing, greasing and sealing where a dip changes the result.
  • Testing: noise, vibration and roundness measurement stations that need the cleanest, driest air in the plant.

Sizing for Grinding Peaks Without Oversizing the Plant

List every line with its flow at wheel change and at steady running, because the two are very different in bearing work. A mid-size plant with ten to twenty grinding machines and two to four assembly lines typically peaks at 5 to 12 cubic metres per minute at 6 to 7 bar, which is roughly a 37 to 75 kW screw compressor, and the peak usually lands in the first minutes after a wheel change when several machines restart together. A variable speed drive earns its keep here: it follows the batch pattern instead of loading and unloading a fixed-speed machine dozens of times a shift, and it keeps pressure within the narrow band that grinding control prefers.

Keep the pressure drop to the farthest grinder under 0.3 bar at peak, and fit a receiver of 500 to 1000 litres per 10 cubic metres per minute to absorb wheel-change spikes. A ring main helps when grinding, assembly and testing halls sit in different wings of the building. Log pressure at the grinding hall during wheel changes for a week, because that log is the honest record of whether the compressor is big enough, and it settles arguments faster than any catalogue figure. Never raise the set point to mask a sag: every extra bar adds roughly 7 percent to power use and hides the real fault, which is usually a clogged filter or an undersized pipe.

Cleanliness: What Oil, Water and Dust Do to a Bearing

A raceway does not forgive contamination. Oil aerosol on a raceway before greasing changes the lubricant film and shortens bearing life, moisture in the air line rusts a freshly ground surface before it is sealed, and dust in the testing area can settle on a measuring instrument and skew a roundness reading. The standard that prevents this is a treatment chain, not a single filter: a pre-filter, a refrigerated dryer to a 3 degree C pressure dew point, a coalescing filter to 0.01 micron, and an activated-carbon filter where the process specification demands oil-free quality air. For the cleanest grinding and testing lines, an oil-free screw compressor removes the risk at source.

Maintenance is what keeps that chain honest. Change coalescing elements on pressure drop, not on a calendar guess, and test the air at the grinding hall and the testing station quarterly with a simple oil and moisture check. Drain condensate with automatic zero-loss drains, slope lines to drain legs, and keep the compressor room clean and ventilated so the machine does not breathe grinding dust or its own hot air. Grinding dust is fine and abrasive, so keep the compressor intake away from the grinding hall, check the intake filter weekly in the first months, and keep a spare on the shelf.

  • Fit pre-filter, refrigerated dryer, 0.01 micron coalescing filter and carbon filter where oil-free air is specified.
  • Consider an oil-free screw compressor for grinding and testing lines with the strictest cleanliness rules.
  • Test air at the grinding hall and testing station quarterly, and keep the compressor intake away from grinding dust.

Buying from China: Sizing Sheet for a Bearing Plant Compressor

QiAir is a Chinese manufacturer and supplier of screw air compressors, and a bearing order should start with a sizing sheet that names the product mix. Send the supplier the number of grinding machines and assembly lines, the coincident peak at 6 to 7 bar, the air-quality standard the process specification requires, ambient temperature and humidity, and the distance to the farthest grinder. Ask for a quotation that states the filtration grades and dryer duty explicitly, and ask whether an oil-free machine or a filtered oil-injected machine fits the specification better, with the cost and maintenance difference spelled out.

Agree the acceptance test before shipment: a full-load run at rated pressure, a dew point reading at the dryer outlet, and an oil-aerosol check at the final filter outlet. On arrival, install on a level plinth with clear cooler airflow, connect drains before the first run, and survey pressure at the grinding hall during a wheel change in the first production week. Keep a log of pressure, dew point and filter changes, and review it monthly, because a slow rise in dew point is the earliest sign that a dryer needs attention before bearings start failing.

  • Send the supplier grinder and assembly line counts, coincident peak, required air-quality standard and farthest-grinder distance.
  • Ask for filtration grades and dryer duty in writing, and compare oil-free against filtered oil-injected on total cost.
  • Accept on a full-load test plus dew point and oil-aerosol checks, then survey pressure at a wheel change in week one.

Frequently asked questions

What air quality does bearing manufacturing need?

Most bearing plants need dry air at a 3 degree C pressure dew point with coalescing filtration to 0.01 micron, and an activated-carbon filter where the specification demands oil-free air. For the strictest grinding and testing lines, an oil-free screw compressor removes the oil risk at source rather than filtering it out.

What size screw compressor does a bearing plant need?

A mid-size bearing plant with ten to twenty grinding machines and two to four assembly lines typically needs 5 to 12 cubic metres per minute at 6 to 7 bar, roughly a 37 to 75 kW screw compressor. Size on the wheel-change peak when machines restart together, and use a variable speed drive to follow the batch pattern.

Why does pressure stability matter for bearing grinding?

Grinding spindles, wheel dressing and superfinishing stones all respond to air pressure, so a swing changes surface finish and roundness. A variable speed drive, a receiver of 500 to 1000 litres per 10 cubic metres per minute, and a pressure drop under 0.3 bar to the farthest grinder keep the supply steady enough for consistent quality.

Related reading

QiAir is a Chinese manufacturer and supplier of screw air compressors. If you are sourcing a screw compressor from China — for a factory, a food plant, a construction site or a new production line — contact QiAir for a sized quotation, documented performance data and export support.