A 22 kW screw compressor such as the S 220 PM, which delivers 3,600 l/min at 8 bar, runs about six air grinders non-stop, or four grinders and two chipping hammers. That figure assumes grinders at around 450 l/min, chipping hammers at around 400 l/min and a 25 % margin. The calculation below lets you redo the count with your own tools.
This article focuses on the fettling shop. For the other uses of air in foundries and forges, see our page on compressors for foundries and forges.
Step 1, each tool's consumption
Read the consumption on each tool's data sheet, at its working pressure. As a rough guide:
- air grinder: 450 l/min, the value used by our configurator, at about 6.3 bar;
- chipping hammer: around 400 l/min.
These are orders of magnitude. A large disc grinder uses more than a straight finishing grinder: the manufacturer's manual gives the right figure.
Step 2, how many run at the same time?
In fettling, grinders run almost without a break while the operator works the casting. Count them at 100 %. The chipping hammer is a borderline case: on a rough casting with many risers, it hammers continuously; if it only takes off a few burrs, it works in bursts. Our configurator counts tools used in bursts at 50 %, because the receiver absorbs the peaks.
Count one tool per operator at the station, not the number of tools hanging on the wall.
Step 3, the available flow
The S 220 PM delivers 3.6 m³/min at 8 bar. With the 25 % margin, the flow to share between tools is:
3,600 ÷ 1.25 = 2,880 l/min
That is the figure to compare with the sum of your tools.
Workable combinations
| Tools running at the same time | Total | With 25 % margin | On an S 220 PM at 8 bar |
|---|---|---|---|
| 6 grinders | 2,700 l/min | 3,375 l/min | yes |
| 4 grinders + 2 chipping hammers, continuous | 2,600 l/min | 3,250 l/min | yes |
| 4 grinders + 4 chipping hammers in bursts (counted at 50 %) | 2,600 l/min | 3,250 l/min | yes |
| 5 grinders + 2 chipping hammers, continuous | 3,050 l/min | 3,810 l/min | no |
In the last case, about 200 l/min is missing. You need a larger compressor or a second one. Above 22 kW, the S series goes up to 132 kW, on quotation.
For a smaller station, the S 150, 15 kW, delivers 2.2 m³/min at 8 bar, or 1,760 l/min after margin: three grinders, or two grinders and one chipping hammer.
Do not raise the pressure without a reason
A screw compressor delivers less flow at higher pressure. The S 220 PM goes from 3.6 m³/min at 8 bar to 3.2 m³/min at 10 bar. At 10 bar, the flow available after margin drops to 2,560 l/min: six grinders, which need 2,700 l/min, no longer fit.
If pressure is too low at the end of the line, the cause is almost always the network: pipes too small, quick couplings too small, hoses too long. Fix the network before touching the setting. Our article on how to calculate compressor pressure explains how to set the right value, and our guide to connecting a compressor to the air network helps choose pipe sizes.
Plan an air receiver
The S 220 PM comes without a receiver. Our configurator suggests about one litre for every 3 l/min of demand. For 3,375 l/min, that gives about 1,125 litres: take a 1,500 litre receiver, the next standard size. Our air receiver size calculator refines this figure based on your pressure settings.
The receiver smooths out the chipping hammer blows and lets water settle before the network. Fit it with an automatic drain.
Other points to watch
- Tool lubrication. Many grinders and chipping hammers need a few drops of oil in the air. Follow the tool manual: inline lubricator or manual oiling.
- Leaks. In a fettling shop, hoses lie on the floor and get damaged quickly. A leak uses air all the time, even at night. Our article on compressed air leaks gives the method to find them.
- Dust. Install the compressor away from the fettling station, with a clean air intake, and check its intake filter often.
For a first figure, enter your tools in the configurator. If your shop is already running, a compressed air audit measures actual consumption. Then send us your tool list with a quote request.
For your trade: Compressor for foundries and forges.