To frost or decorate glass, a sandblaster with a 3 mm nozzle uses around 350 l/min at 4 bar, and a 4 mm nozzle around 600 l/min at the same pressure, as a rough guide. A frosting cabinet with a 3 mm nozzle runs on a 7.5 kW 4-in-1 screw compressor such as the K 75 (1.1 m³/min at 8 bar). A 4 mm sandblaster working at 6 bar in a workshop that already has other machines generally needs an S 220 PM (3.6 m³/min).
Sandblasting is just one of the stations in glass processing: find the others on our page on the compressor for glass processing and glazing.
What determines a sandblaster's air flow?
Only two parameters: the nozzle diameter and the pressure at the nozzle. Air flow increases with the square of the diameter: going from 3 to 4 mm multiplies the bore area by about 1.8. Pressure acts almost in proportion to absolute pressure: from 4 to 6 bar, the flow rises by about 40%.
The type of abrasive, the size of the cabinet or the make of sandblaster matter far less to the compressor. That is why the choice always starts with the nozzle.
How much air for each nozzle and pressure?
Indicative values for a new nozzle, in l/min of free air. The sandblaster's manual and the nozzle manufacturer's tables are the reference.
| Nozzle | at 3 bar | at 4 bar | at 6 bar |
|---|---|---|---|
| 2.5 mm | 190 | 240 | 330 |
| 3 mm | 270 | 350 | 480 |
| 4 mm | 480 | 600 | 850 |
| 5 mm | 750 | 950 | 1,300 |
Glass is generally blasted more gently than steel: around 2 to 5 bar depending on the thickness, the design and the effect you are after. An even frost on thick glass tolerates more pressure than fine etching on thin glass, which risks breaking through or shattering. Set the pressure at the station with a regulator; the rest of the network keeps its normal pressure of 7 to 8 bar.
Why does nozzle wear change everything?
The abrasive wears the inside of the nozzle, all the faster when the abrasive is hard and the nozzle material soft. A 4 mm nozzle worn out to 5 mm uses as much air as a 5 mm nozzle: about 1,300 l/min at 6 bar instead of 850, or more than 50% extra. The compressor, sized for the new nozzle, can no longer keep up, the pressure falls and the frosting becomes patchy.
Two simple habits:
- measure the nozzle regularly with a drill bit or a gauge, and replace it when it has opened up by around 1 mm;
- size the compressor with the margin from the configurator, which covers part of this wear.
The step-by-step calculation
Case 1: a frosting cabinet, 3 mm nozzle at 4 bar, near-continuous blasting.
- 3 mm nozzle at 4 bar: 350 l/min, counted at 100% because blasting is continuous.
- Dust-off blow gun counted at 50%: 75 l/min.
- Base total: 425 l/min.
- With the 25% safety margin: 531 l/min. With the 20% expansion margin: 638 l/min.
The K 75 gives 1,100 l/min at 8 bar: it covers the cabinet, the nozzle wear and a small cutting table. Its 420 L receiver exceeds the volume our configurator recommends, which is about one litre for every 3 l/min of demand.
Case 2: a glass workshop adding a 4 mm sandblaster at 6 bar. The workshop already uses 920 l/min before margins (cutting table, edging machines, washer, vacuum lifters, blow guns).
- 4 mm sandblaster at 6 bar: 850 l/min.
- Existing workshop: 920 l/min.
- Base total: 1,770 l/min.
- With the 25% safety margin: 2,213 l/min. With the 20% expansion margin: 2,655 l/min.
The K 150 (2.2 m³/min) is no longer enough. The S 220 PM, with its permanent magnet motor, delivers 3.6 m³/min at 8 bar: it covers everything with the reserve needed. As it is a standalone compressor, plan for a suitably sized dryer and filters.
The flow and pressure converter turns l/min into m³/min and into the CFM given in some sandblaster manuals.
Why must the air be dry for glass sandblasting?
The fine abrasive used for glass absorbs moisture. When wet, it sticks in the pot and the hose, flows out in clumps and leaves areas that are more or less frosted: the defect is immediately visible on a transparent surface. Water coming out of the nozzle can also leave rings on the glass and lift adhesive stencils.
- A refrigerated dryer is the minimum; it is built into the K series.
- If the sandblaster is in an unheated building, or the network runs outdoors, a desiccant dryer lowers the dew point further. See which air dryer to choose.
- Our compressors are oil-lubricated: the outlet filtration captures carried-over oil. A trace of oil on a stencil makes it lift, hence the value of a fine filter at the station.
Cabinet, open blasting or soft blasting?
For glass, the work is almost always done in a cabinet with extraction: glass and abrasive dust is fine and abrasive. The cabinet has little effect on air flow, which is still set by the nozzle; it only adds the cleaning of its filter. Our article on the blast cabinet covers these points in detail, and the page on the compressor for sandblasting gives the overall picture for blasting equipment.
The traps to avoid
- Choosing the compressor on a new nozzle with no margin. After a few weeks, the nozzle opens up and the pressure collapses.
- Blasting glass at the pressure used for steel. More pressure means more air used and a greater risk of breakage.
- Installing the compressor near the cabinet. The dust clogs its intake filter and its cooler. Put it in a separate, ventilated room.
- Stretching the servicing. First service at 500 hours, then every 1,500 hours; with sandblasting, check the intake filter more often too.
For your sandblaster, enter the nozzle diameter in the configurator, or send us its manual with a quote request.
For your trade: Compressor for glass processing, glaziers and double glazing.