Evaluation of wet abrasive blasting methods

Wet blasting, like dry blasting, relies on an abrasive media delivered at high speed under pressure to remove surface contaminants and achieve a desired finish on a chosen surface. However, wet blasting mixes water into the blast media to enhance the levels of surface finish that can be achieved. There are a number of wet abrasive blasting methods and they all have their pros and cons.
 

Wet abrasive blasting methods

1)    Air abrasive wet blasting
There are several air abrasive wet blasting units:
        o    Slurry blasters
                    A slurry blaster is a dry abrasive blasting machine equipped with a nozzle to add water to the blast media just before it touches the surface. The first type encircles the blast stream with a curtain of water (halo ring) after it leaves the nozzle. The second type uses a water injection nozzle (WIN) to inject the water into the blast just before it reaches the nozzle. The water stream could also be sprayed into the abrasive stream beyond the nozzle.

        o    Venturi blasters
                    Venturi blasters store water and blast media in the pot. Under influence of the passing pressurized air stream, this mixture is sucked out of the pot (venturi effect). The volume of water and media in the blast stream is dependent on the amount of pressurized air.

        o    Vapour abrasive blasters
                    Vapour abrasive blasters combine water and abrasive in a pot under water pressure. This moist abrasive is injected into the air stream by hydraulic controls, affording an independent and fine control over the air pressure and the water/abrasive consumption rate. Vapour abrasive blasters can effectively blast at low pressures (30psi) but can also blast as high as 170psi. Vapour abrasive blasting units use only as much water and media as required by the application.

2)    (Ultra-)high-pressure water blasters

High-pressure water blasters produce a stream of water with a high velocity by passing a flow of pressurized water through a specially designed small orifice nozzle. High-pressure water blasting develops a pressure up to 5,000psi, which is insufficient for the removal of tight rust or mill scale from steel. For that you will need ultra-high-pressure water blasting that develops very high pressures of 30,000psi and more. High-pressure water blasting cannot be used for the surface roughening of steel itself. Abrasives must be added to the blast stream to increase its corrosive force.
 

Advantages & disadvantages of wet abrasive blasting methods

Considerations when using wet abrasive blasting

• The units that incorporate water into air abrasive blasting produce cleaning rates comparable to dry blasting and are very practical for field applications.
• High-pressure water blasting without sand is not capable of removing tight rust and mill scale under normal conditions.
• All wet blast units have a significantly lower dust reduction than dry blasting.
• The different types of wet abrasive blasting units vary in cost, portability, production capability, and adaptability to existing blast cleaning equipment. The best solution for your application depends on the size and type of job and availability of support equipment.
• In most cases the water should be enriched with inhibitors to prevent flash rust.

Vapour abrasive blasting, with 92% less dust

The Graco EcoQuip2 makes abrasive blasting more efficient and productive:

Faster

• No need to set pot pressure relative to blast pressure
• Easy to adjust blast pressure and to regulate media
• No need for containment and less clean-up
   

Cleaner

• Produces a fine mist
• Generates 92% less airborne dust than dry blasting
• Less toxic run-off
   

Greener

• Less media needed when compared to slurry or traditional wet abrasive blasting
• Less water needed when compared to Ultra-high pressure water jetting
• Less media needed, which equals less containment and clean-up