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Blast Nozzle
Blast Nozzle Basics
The selection of nozzle has an important influence on the efficiency of a blasting operation.
The shape of a nozzle’s bore determines the blast pattern, which differs for each application.
When selecting a blasting nozzle, you should take into account its shape and material. While the shape influences the velocity and the blast pattern, the material depends on the blasting media to be used, the desired service life, and the size of the blast job.
Nozzle shape
Among the many types of blasting nozzles, three are widely used.
The shape of the nozzle affects Velocity and Blast Pattern:
- Velocity
The long, tapered, converging entry of a venturi nozzle mixes the air and abrasive into the nozzle. The mix is then pushed into a narrow section in order to be forced out of the diverging exit end. These shapes greatly accelerate the air flow and particles/abrasives. The velocity of the abrasive as it exits the nozzle is nearly twice as high as in a straight bore nozzle (pos. 1).
The long venturi nozzle has a longer barrel, which gives the abrasive a higher speed and kinetic energy. Consequently, the impact is more aggressive and the long venturi nozzle works up to 10-15% faster than the standard venturi nozzle (pos. 2).
But nothing comes for free; long venturi nozzles (pos. 3) only work on full capacity when you fulfill the demands for compressed air. When there is too little air pressure, it is better to use standard venturi nozzles (pos. 2). - Blast pattern
A nozzle’s bore shape also determines its blasting pattern:
Straight bore nozzles (pos.1) create tight, varied blast patterns. The blasting pattern shows a harsh impact in the centre and little impact on the perimeter. This type of nozzle is best used for blasting small surface areas.
Venturi nozzles create wider and homogenous patterns and increase the velocity while lowering the abrasive consumption.
Long venturi nozzles with little air pressure have a small blast pattern. Increasing the air pressure gives a wider and thus better pattern, even allowing you to stand further away from the blast object. Long venturi nozzles are thus best used when blasting larger surfaces.
Nozzle material
The nozzle material selection depends on several factors:
- the abrasive you choose
- how often you blast
- the size of the blast job
- the rigors of the job site
Below, we provide some general application guidelines for various materials.
- Aluminium oxide ‘Alumina’ (ceramic) nozzles offer a reasonable lifetime at a lower price than other materials. They are a good choice for low-intensity applications where the unit price is a primary factor and the nozzle lifetime is less important.
- Tungsten carbide nozzles offer a significant long lifetime and value when rough handling cannot be avoided and mineral or coal slag abrasives are used.
- Silicon aluminium oxynitride (SiAlON) nozzles offer the same increased lifetime and durability as tungsten carbide but are only about half the weight. They are also better for handling aluminium oxide abrasives.
| Nozzle material | Steel shot/grit | Slag | Aluminium oxide |
|---|---|---|---|
| Ceramic | 20-40 hrs | 10-30 hrs | 1-4 hrs |
| Tungsten carbide | 500-800 hrs | 300-400 hrs | 20-40 hrs |
| SiAlON | 500-800 hrs | 300-400 hrs | 50-100 hrs |
