For a compressed-air shot blasting cabinet, the nozzle diameter decides the compressor. With a 5 mm nozzle, a 15 kW screw compressor such as the K 150 is usually enough. With a 6 mm nozzle, you need the S 220 PM, a 22 kW screw compressor that delivers 3.6 m³/min at 8 bar.
This article covers the shot blasting cabinet in a fettling shop. For all the air needs of a foundry, from core making to fettling, see our page on compressors for foundries and forges.
Air blast cabinet or wheel blast machine?
Check the type of machine first. A wheel blast machine throws the shot with a turbine: it uses little air, mainly for its controls and for pulse-cleaning its filters. An air blast cabinet throws the shot through a nozzle: the compressor gives the abrasive its speed, and it works without a break as long as the operator is blasting.
There are two kinds of air blast cabinets. In a suction cabinet, a venturi gun draws the shot in. In a pressure cabinet, the shot is pushed out of a pressure pot. For the same nozzle diameter, they do not use the same amount of air: the cabinet maker's data sheet is the reference.
The calculation, step by step
Step 1, the nozzle. Read the nozzle consumption on the cabinet data sheet. As a rough guide, at about 7 bar at the nozzle, common trade figures are 1,500 l/min for a 5 mm nozzle and 2,300 to 2,500 l/min for a 6 mm nozzle.
Step 2, the other air users. A cabinet also uses air outside the nozzle:
- the blow gun used to clean the parts, counted at 150 l/min in our configurator;
- pulse cleaning of the dust collector, given on the dust collector data sheet;
- door or basket cylinders, if there are any.
Step 3, the margin. Add 25 %, as our configurator does.
Example of a pressure cabinet with a 6 mm nozzle (indicative figures):
- 6 mm nozzle: 2,400 l/min
- blow gun: 150 l/min
- dust collector pulse cleaning, value taken for the example: 100 l/min
- total: 2,650 l/min, or 3,310 l/min with a 25 % margin
The S 220 PM delivers 3.6 m³/min at 8 bar, or 3,600 l/min, and 3.8 m³/min at 7 bar: it covers this need. Our flow and pressure converter switches between m³/min, l/min and cfm if your data sheet uses other units.
Which model for your cabinet?
| Cabinet | Need with margin | Model |
|---|---|---|
| 5 mm nozzle, single cabinet | around 2,200 l/min | K 150, 4-in-1, 2.2 m³/min at 8 bar |
| 5 mm nozzle, dryer and receiver already installed | around 2,200 l/min | S 150, 2.2 m³/min at 8 bar |
| 6 mm nozzle | around 3,300 l/min | S 220 PM, 3.6 m³/min at 8 bar |
| Two cabinets or an 8 mm nozzle | above 3,600 l/min | S series up to 132 kW, as an industrial project |
With a 5 mm nozzle, the K 150 runs close to its limit. If you plan a second nozzle or a larger one in the coming years, go straight for the S 220 PM.
Nozzle wear, the most expensive trap
Shot wears the nozzle all the time, angular grit especially. Air consumption follows roughly the square of the diameter. A 6 mm nozzle worn to 7 mm therefore uses about (7 ÷ 6)² = 1.36 times more air, a third more. In our example, the nozzle would go from 2,400 to about 3,270 l/min: even the S 220 PM could no longer keep up, and pressure would drop at the nozzle.
The rule of thumb: measure the nozzle bore at regular intervals and replace it before it has grown by a millimetre. That costs less than a bigger compressor.
Dry air, pressure and dust
- Water. Wet steel shot rusts, clumps in the hopper and blocks the metering valve. A refrigerated dryer after the compressor is essential. It is built into the K 150. For the S 220 PM, add the refrigerated dryer for 22 kW compressors and an automatic drain on the receiver. Our article on water in compressed air explains draining in detail.
- Pressure. Set the compressor to 8 bar to keep 6 to 7 bar at the nozzle. A long or narrow hose loses part of that pressure: place the compressor close to the cabinet, but never inside it.
- Dust. Install the compressor in a separate room with a clean air intake. Check the air filter often: near a shot blasting cabinet, it is the part that clogs fastest.
On our screw compressors, the first service is at 500 hours, then every 1,500 hours, with a reminder shown on the controller. 2-year warranty, spare parts available for 15 years.
For blasting outside a foundry, our page on compressors for sandblasting covers site and workshop blast machines. For your cabinet, send us its data sheet and nozzle size with a quote request: we will check the flow with you.
For your trade: Compressor for foundries and forges.