TL;DR — Direct answer: A die casting plant needs clean, dry air at 6 to 7 bar for die spraying, core blowing, trimming and shot blasting, with a pressure dew point of 3 degrees C and filtration to 0.01 micron so no oil or moisture reaches a die surface, a spray nozzle or a cast part. Size on the coincident peak of die spray and shot blast, 8 to 18 cubic metres per minute for a mid-size plant, roughly a 55 to 132 kW screw compressor with a variable speed drive. QiAir, a Chinese screw compressor manufacturer and supplier, builds fixed and variable speed machines with dry-air treatment for die casting plants.
A die casting plant is a hot, fast and dirty environment, and compressed air is used at every step. Molten aluminium or zinc is injected into a steel die, the die is sprayed with release agent, cores are blown clean, the casting is trimmed, shot blasted and inspected, and then it moves to machining. A pressure dip at the die spray nozzle leaves release agent uneven and causes soldering, where the casting sticks to the die, moisture in the spray air causes porosity in the casting, and a weak shot blast line leaves scale on parts that must be machined. The air system has to survive heat, metal dust and oil mist and still deliver dry air. QiAir is a Chinese manufacturer and supplier of screw air compressors, and its machines for die casting plants are specified around high flow and heat tolerance first and oil control second.
The mistake buyers make most often is sizing air on the casting machines alone and forgetting shot blast and trimming. Die spray runs in short bursts at every shot, core blowing is intermittent, and the shot blast line draws a heavy, continuous flow while it runs. Add them together at peak and the real demand is typically 25 to 35 percent higher than the first estimate. This guide maps where the air goes in a die casting plant, explains how to size for spray and blast peaks, sets the dry-air standard that protects castings, and shows what to put on a sizing sheet for a China supplier.
Where Air Is Used: Die Spray, Core Blowing, Trimming and Shot Blast
Die spraying is the most sensitive user. After every shot, the die is sprayed with a water-based release agent carried by compressed air, and the spray must be even and fine, because too much release agent causes porosity and too little causes soldering. Spray nozzles clog fast in a die casting shop, so fit a dedicated filter close to the spray station and check nozzle pressure weekly. Core blowing uses short, powerful air blasts to clear cores and vents, and the demand spikes at every cycle, several times a minute on a fast machine.
Trimming, shot blast and handling take the most air. Trim presses use it for clamping and ejection, shot blast machines use it for media blasting and dust extraction dampers, and robots and handling equipment use it for grippers and part transfer. Shot blast is the heaviest single user: a blast cabinet running continuously can draw 3 to 6 cubic metres per minute on its own. Metal dust and die release mist are everywhere, so air tools and valves need filtration that survives them, and any open blow-off nozzle wastes air fast. A plant that maps every user, including the cleaning lances used at die change, usually finds 25 to 35 percent more demand than the original estimate.
- Die spray: release agent atomisation after every shot, sensitive to pressure and nozzle condition.
- Core blowing and trimming: short powerful blasts to clear cores, plus trim press clamping and ejection.
- Shot blast and handling: continuous media blasting, the heaviest single air user, plus robot grippers.
Sizing for Die Spray Bursts and Shot Blast Demand
List every machine with its flow at peak and at steady running, because the two differ sharply in die casting work. A mid-size plant with four to ten die casting machines, two trim presses and one or two shot blast lines typically peaks at 8 to 18 cubic metres per minute at 6 to 7 bar, which is roughly a 55 to 132 kW screw compressor, and the peak usually lands when the shot blast line runs at full load while several casting machines spray together. A variable speed drive earns its keep here: it follows the shot pattern of the casting hall instead of loading and unloading a fixed-speed machine dozens of times a shift, and it holds pressure within the narrow band that spray nozzles prefer.
Keep the pressure drop to the farthest die casting machine under 0.3 bar at peak flow, and fit a receiver of 1000 to 2000 litres to absorb spray and core-blowing spikes. A ring main helps when the casting hall, trim shop and blast area sit in different parts of the building. Log pressure at the farthest spray station during a full production run 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.
- Size on the coincident peak of die spray and the shot blast line, not on casting machines alone.
- Use a variable speed drive for casting-shop loads, and keep far-end pressure drop under 0.3 bar.
- Log farthest-spray-station pressure during production for a week to prove the sizing in real use.
Heat, Metal Dust and Moisture: Protecting Dies and Castings
Heat is the first problem in a die casting shop. Ambient temperature near the casting machines can reach 40 to 45 degrees C, and a compressor breathing that hot air loses capacity and runs hotter, so site the compressor in a cooler, ventilated room away from the furnaces, and size the cooler for the worst summer day, not the average. Metal dust and die release mist are the second problem: fit a heavy-duty intake pre-filter, check it weekly, and keep the intake away from the shot blast area. A clogged intake filter is the most common cause of a slow capacity loss that looks like a sizing fault.
Moisture in the spray air causes porosity in castings, and oil in the air contaminates the die surface and the release agent film. 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 for oil vapour, with a final point-of-use filter at each spray station. Drain condensate with automatic zero-loss drains, slope lines to drain legs, and test the air at the farthest spray station quarterly for oil, moisture and particles.
- Site the compressor in a cooler, ventilated room away from furnaces, and size the cooler for the worst summer day.
- Fit pre-filter, refrigerated dryer, 0.01 micron coalescing filter and carbon filter, with a final filter at each spray station.
- Protect the intake from metal dust with a heavy-duty pre-filter, and test spray-station air quarterly.
Buying from China: Sizing Sheet for a Die Casting Plant Compressor
QiAir is a Chinese manufacturer and supplier of screw air compressors, and a die casting order should start with a sizing sheet that names the machine count. Send the supplier the number of die casting machines, trim presses and shot blast lines, the coincident peak at 6 to 7 bar, the air-quality standard the die spray stations require, ambient temperature near the casting hall, and the distance to the farthest machine. Ask for a quotation that states the dryer type and filtration grades explicitly, and ask whether an oil-free machine or a filtered oil-injected machine fits the die spray 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 farthest spray station during the first full 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 castings start failing inspection.
- Send the supplier machine, press and blast-line counts, coincident peak, ambient temperature and farthest-machine distance.
- Ask for dryer type and filtration grades 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 the farthest spray station in week one.
Frequently asked questions
What pressure does a die casting plant need?
A die casting plant needs clean, dry air at 6 to 7 bar for die spraying, core blowing, trimming, shot blasting and part handling. Keep far-end pressure drop under 0.3 bar, because a pressure dip at the spray nozzle leaves release agent uneven and causes soldering, and size on the coincident peak of die spray and the shot blast line.
Why must die casting air be dry?
Moisture in the spray air causes porosity in castings, and oil contaminates the die surface and the release agent film. A pre-filter, refrigerated dryer to a 3 degree C pressure dew point, 0.01 micron coalescing filter and carbon filter in series protect the spray stations, and an oil-free screw compressor removes the oil risk at source.
What size screw compressor does a die casting plant need?
A mid-size die casting plant with four to ten casting machines, two trim presses and one or two shot blast lines typically needs 8 to 18 cubic metres per minute at 6 to 7 bar, roughly a 55 to 132 kW screw compressor with a variable speed drive. The shot blast line alone can draw 3 to 6 cubic metres per minute, so count it honestly.
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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.