As a rough guide, a PVC welder uses on average around 80 to 100 l/min with 2 heads and 150 to 200 l/min with 4 heads, and a corner cleaner around 200 to 300 l/min during production. A 4-head welder and corner cleaner together therefore account for about 0.4 to 0.5 m³/min, which a 7.5 kW 4-in-1 screw compressor such as the K 75 (1.1 m³/min at 8 bar) supplies with a generous reserve for the saw and the screwdrivers.
These two machines are at the heart of PVC window manufacturing. Our page on the compressor for PVC and aluminium window fabrication covers the whole workshop; here, we look in detail at how they use air and how to allow for it.
How does a PVC welder use air?
A PVC welder joins profiles cut at 45° by heating them against a heating plate, then pressing them against each other. Each cycle runs through several pneumatic movements:
- the clamps close on the profiles;
- the heating plate drops between the two ends;
- the carriages bring the profiles against the plate to melt them;
- the plate withdraws and the carriages press the ends together for the weld;
- after cooling, the clamps open.
A 4-head welder runs this cycle on all four corners of a frame at once: it therefore has roughly four times as many cylinders as a single-head welder. That is why its consumption rises with the number of heads. But the cycle lasts several minutes, a good part of which is heating and cooling with no movement: the average consumption remains moderate, with short bursts of demand at each movement.
How does a corner cleaner use air?
The corner cleaner takes the welded frame and removes the bead left by the weld, on the visible faces and in the gasket groove. It positions the frame, brings in knives and cutters, often several tools in turn, then blows away the swarf. Each corner takes around ten cylinder movements, and the blow-off comes on top.
The result: the corner cleaner uses air almost continuously as soon as the line is running, and often more than the welder. It is the machine to identify first in the calculation. If it is fitted with blow-off nozzles, their consumption can weigh as much as the cylinders. Our article on the air consumption of a blow-off nozzle gives orders of magnitude by diameter.
How do you convert litres per cycle into l/min?
Manuals give the consumption in two ways: in l/min, which is straightforward, or in litres per cycle (sometimes "Nl/cycle", litres of air at normal conditions). To convert:
consumption in l/min = litres per cycle × number of cycles per hour ÷ 60
Example, as a rough guide: a 4-head welder states 400 litres per cycle and welds 20 frames per hour.
- 400 × 20 = 8,000 litres per hour;
- 8,000 ÷ 60 = 133 l/min on average.
A corner cleaner states 70 litres per corner and handles 20 four-cornered frames per hour, so 80 corners:
- 70 × 80 = 5,600 litres per hour;
- 5,600 ÷ 60 = 93 l/min for the cylinders;
- add the blow-off: a nozzle open 30 seconds per corner at 150 l/min represents 150 × 0.5 × 80 ÷ 60 = 100 l/min.
- Corner cleaner total: about 193 l/min.
If the manual gives the consumption of a cylinder rather than of the machine, our article on the air consumption of a pneumatic cylinder explains the calculation from the bore and stroke. And the flow and pressure converter switches between l/min, m³/h and CFM.
The step-by-step calculation for a 4-head welder and a corner cleaner
Take the values above and add whatever else runs at the same time on the line:
- 4-head welder: 133 l/min.
- Corner cleaner: 193 l/min.
- Double mitre saw: 150 l/min, as a rough guide.
- One screwdriver and one blow gun, used intermittently and counted at half: 100 + 75 = 175 l/min.
- Subtotal: 133 + 193 + 150 + 175 = 651 l/min.
- 25% safety margin: 651 × 1.25 = 814 l/min.
- 20% expansion margin: 814 × 1.2 = 977 l/min, or about 0.98 m³/min (around 35 CFM).
The K 75, with 1.1 m³/min at 8 bar, covers this need. As soon as a profile machining centre or a second corner cleaner is added, you exceed its capacity: the K 110, at 1.7 m³/min, takes over. These are the margins our configurator applies.
What part does the air receiver play with these machines?
The average consumption does not tell the whole story. When the welder closes its clamps and presses its four corners, it draws far more than its average in a few seconds. If the corner cleaner blows at the same moment, the pressure in the network dips for an instant.
It is the air receiver that supplies these peaks. The compressor then refills it at its own pace. A correctly sized receiver stops a welder showing a pressure fault at the moment of welding, even though the compressor is more than sufficient on average. The 420 L receiver on the K 75 covers most lines with one welder and one corner cleaner. To check your own case, use the air receiver size calculator or our guide to sizing a compressed air receiver.
A small buffer tank at the welder, when the machine is far from the compressor, also steadies the pressure at the moment the weld is pressed.
What pressure for a welder and a corner cleaner?
Both machines most often need around 6 bar at their inlet. For the welder, stability counts more than the value itself: the force pressing the corners depends on the pressure, and a drop during welding gives an uneven weld seam. Set the compressor to 7 or 8 bar, and fit a regulator with a pressure gauge at the welder inlet to give it a constant pressure, set according to the manual.
The pitfalls to avoid
- Adding up the peaks. You size on average consumption. The peaks are the air receiver's job.
- Forgetting the corner cleaner's blow-off. It can account for half of its consumption.
- Letting the machine leak. A leaking solenoid valve or cylinder on a 4-head welder uses air day and night. Our article on compressed air leaks explains how to find them.
- Damp air. Water makes the clamps and carriages stick. The K 75 and K 110 include a refrigerated dryer and filtration.
To check the air flow of your line, run the calculation with the configurator or send us the manuals for your welder and corner cleaner with a quote request.
For your trade: Compressor for PVC and aluminium window fabrication.