TL;DR — Direct answer: A heat treatment plant needs a screw compressor that holds 7 to 8 bar through furnace, quenching and atmosphere-control peaks, with a pressure dew point near 3 degrees C and filtration that survives furnace heat and scale dust. Size on the coincident peak of furnace controls and quenching loads, commonly 8 to 18 cubic metres per minute for a mid-size plant, with a large receiver to absorb quenching spikes. Keep the intake and dryer away from furnace heat, and protect pipework from vibration and thermal movement. QiAir, a Chinese screw compressor manufacturer and supplier, builds machines for this hot, intermittent duty.
Heat treatment is a process that forgives very little. A furnace holds a load at temperature for hours, a quench tank drops it in seconds, and the atmosphere inside the furnace must stay exactly as specified, or the parts come out soft, decarburised or distorted. Compressed air sits behind all of it: it drives burner controls, damper actuators and temperature-control instruments, operates quench agitation and transfer equipment, controls atmosphere gas mixing, and cleans parts between stages. A pressure dip at the wrong moment can disturb a furnace atmosphere, stall a quench transfer, or trip a burner, and a ruined heat costs a full furnace load. QiAir is a Chinese manufacturer and supplier of screw air compressors, and its machines are sized for the heat, scale and long cycles of heat treatment.
This is heat treatment, not forging: there is no hammer or press here, and the air users are the furnace, the quench system and the atmosphere controls around them. The sizing question is therefore about steady furnace loads plus sharp quenching peaks, and the reliability question is about heat and scale rather than impact. This guide maps the heat treatment air users, explains peak sizing, covers heat and dust protection, and sets out a sizing sheet for a China supplier.
Where Air Is Used: Furnaces, Quenching and Atmosphere Control
The furnace is the most critical user. Burner controls, damper actuators, temperature-control instruments and door operators all need clean dry air at a stable pressure, and a dropout can disturb a heat or trip a burner mid-cycle. Atmosphere control is the most sensitive user of all: air drives the gas-mixing valves and flow controls that hold the furnace atmosphere at the specified carbon potential, and a pressure swing can shift that atmosphere enough to change the case depth on a whole load. These are not high-flow users individually, but they are all sensitive to pressure stability, and that changes how the system should be designed.
Quenching adds the peaks. Quench tanks use air for agitation, transfer mechanisms and oil circulation control, and the load arrives in a sharp burst when a load drops into the tank. Tempering furnaces, washing machines and shot-blasting cabinets add their own intermittent demand, and a plant that runs carburising, nitriding and tempering on shared headers will see very different peaks by process mix. Map the quenching load carefully, because a transfer mechanism that stalls halfway into a quench tank is a safety issue as well as a quality one.
- Furnaces: burner and damper controls, instruments and door operators where a dropout can ruin a heat.
- Atmosphere control: gas-mixing valves and flow controls where a pressure swing changes case depth.
- Quenching and finishing: quench agitation, transfer mechanisms, tempering, washing and shot blasting.
Sizing for Furnace Loads Plus Quenching Peaks
Add up the steady furnace load first, then add the quenching peaks that coincide with it. A mid-size heat treatment plant with four to eight furnaces typically needs 8 to 18 cubic metres per minute at 7 to 8 bar, which is roughly a 55 to 110 kW screw compressor, and a variable speed drive suits the pattern well because furnace loads run all shift while quenching peaks in bursts. Keep a 15 to 20 percent margin for quenching spikes and for a future furnace, and put the margin in the receiver and the header as well as in the compressor, because a large receiver is what absorbs a quench peak without a pressure sag.
Keep the pressure drop to the farthest furnace under 0.3 bar at peak, and fit a receiver of 1000 litres per 10 cubic metres per minute, sited near the quench area where possible, to smooth the transfer spikes. A ring main helps when furnaces and quench tanks sit in different bays, and a dedicated small receiver near the atmosphere-control manifold can be cheaper than upsizing the whole header. Log pressure at the furnace instruments during a quench 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.
- Size on steady furnace load plus the quenching peaks that coincide with it, with a 15 to 20 percent margin.
- Use a variable speed drive for the steady-plus-burst pattern, and site a receiver near the quench area.
- Log furnace-instrument pressure during a quench for a week to prove the sizing in real production.
Heat, Scale and Dry Air in a Heat Treatment Shop
A heat treatment shop is hot, and a compressor that breathes furnace air will run hot, use more power and age its oil faster. Site the compressor in a separate room or a ventilated enclosure away from furnaces, duct the intake from a cooler, cleaner place, and duct the hot discharge air outside so the machine never re-breathes its own exhaust. Scale dust is abrasive, so check the intake filter weekly in the first months, keep a spare on the shelf, and watch the pressure drop across it as the honest measure of dust load.
Dry air protects furnaces, quench systems and atmosphere instruments from corrosion and sticking. A pre-filter, a refrigerated dryer to a 3 degree C pressure dew point and a coalescing filter are the minimum, and a point-of-use filter at the atmosphere-control manifold is cheap insurance. Slope lines to drain legs, fit automatic zero-loss drains, and drain the receiver until the automatic drain proves itself. In winter, watch for condensate in outdoor runs to the furnace hall, and lag or trace-heat any line that can fall below the dew point, because a frozen condensate leg can starve a furnace instrument without warning.
- Site the compressor away from furnaces, duct intake from clean cool air and discharge hot air outside.
- Check the intake filter weekly against scale dust, and keep a spare in stock.
- Fit pre-filter, dryer and coalescing filter, add a point-of-use filter at atmosphere controls, and drain every low point.
Buying from China: Sizing Sheet for a Heat Treatment Plant Compressor
QiAir is a Chinese manufacturer and supplier of screw air compressors, and a heat treatment order should start with a load sheet rather than an average-flow figure. Send the supplier the furnace count and types, the coincident peak at 7 to 8 bar, the quenching peaks, the atmosphere-control requirements, ambient temperature near the compressor room, and the distance to the farthest furnace. Ask for a variable-speed quotation with the part-load curve, and ask the supplier to confirm the receiver recommendation in writing, because the receiver is what makes or breaks quenching performance.
Agree the acceptance test before shipment: a full-load run at rated pressure and temperature, a dew point reading at the dryer outlet, and a simulated peak-draw test if the supplier can run one. On site, install on a level plinth with flexible connections, clear cooler airflow and drains connected, then survey pressure at the furnace instruments during a quench in the first week. Keep a log of pressure, temperature and filter changes, and review it monthly, because a slow rise in discharge temperature is the earliest warning of a choked intake or a tired cooler.
- Send the supplier furnace count and types, coincident peak, quenching peaks and farthest-furnace distance.
- Ask for variable-speed pricing with the part-load curve, and confirm the receiver recommendation in writing.
- Accept on a full-load test plus dew point reading, then survey furnace-instrument pressure during a real quench in week one.
Frequently asked questions
What size screw compressor does a heat treatment plant need?
A mid-size heat treatment plant with four to eight furnaces commonly needs 8 to 18 cubic metres per minute at 7 to 8 bar, roughly a 55 to 110 kW screw compressor, plus a large receiver near the quench area to absorb transfer spikes. Size on steady furnace load plus the quenching peaks that coincide with it, and verify pressure at the furnace instruments during a real quench.
Why is the receiver so important in heat treatment?
Quenching draws a sharp burst of air when a load drops into the tank, and the transfer mechanism needs that air instantly. A large receiver supplies the peak while the compressor refills it at a steady rate, so pressure stays stable and the transfer completes on time. Without enough receiver volume, even a large compressor sags on every quench.
How do I protect a compressor from furnace heat and scale?
Site it away from furnaces in a ventilated room, duct the intake from clean cool air and the hot exhaust outside, and check the intake filter weekly against scale dust. Fit a pre-filter, refrigerated dryer and coalescing filter, use flexible pipe connections at vibration points, and drain every low point automatically.
Related reading
- How to Choose the Best Screw Air Compressor Manufacturer in China for Your Factory
- Two-Stage PM VFD Screw Compressors: How a Top China Supplier Cuts Factory Energy Costs
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.