And nine (9) important tips to observe when “air blasting” …. but firstly the principles!

Introduction 1

Venturi Fed / Suction Blast System

Venturi/suction blast cabinets and operating principles are by far the main method of delivery and are capable of many applications.  They are also generally the less expensive regarding  the initial investment, expenditure and running costs.

Venturi/Suction fed cabinets are easily adaptable; it is easy to change media, easy to maintain and have easy and simple controls.

Function

• Compressed Air is piped to the rear end of the blast gun, and placed through a given sized air jet nozzle, housed inside the rear of the blast gun. (See Diagram above)
• The air dispelled through the air jet, then passes over the media tube end, creating the venturie/suction effect; drawing the media up the tube from the hopper below.
• The air/media mixture is then propelled at speed through a media nozzle and out towards the work surface of the component to be processed.
• The distance between the end of the nozzle and work is normally between 125mm and 225mm, with a good recommended average of 150mm.
• It is important to set the air to media ratio correctly to optimise the work effort. This means that the flow of media is smooth and constant and this is adjusted at the air/ media pick up placed in or immediately below the media hopper.
• Various bore sized air jets and nozzles are available. Depending on the volume of compressed air available, the desired surface process can be achieved, be it critical, delicate or none critical; or the desire for more process speed (coverage), an appropriate air jet and nozzle size can be decided upon.

The advantage of a “venturi/suction blast system” is that it will provide:

• Most media can be employed. A venturie/suction blast machine produces most acceptable abrasive particle velocity and speed for most process requirements. Initial investment is much less than a pressure blast system and still means faster cleaning of tough contaminants.
• Stand-off distance. A good average stand-off distance between the end of the blast nozzle and component to be processed is 150- 160mm.
• Media types recommended. A Venturie/suction fed system is capable of succesfully blasting with most media types.  Limitations only occur when the choice of abrasive is extremely dense/heavy.  Larger sizes of blast media can also become problematic, as an insufficient number of paricles/second are incapable of passing through the delivery system, which limits the process speed.

Ra /Rz values enables the keying of the surface (e.g. higher Ra or Rz for bonding/adhesion).

• Peening/stress relieving.  A compressive strength and depth of peening is capable of being established but requires consistent and monitored controls applying for process verification.
• Production and productivity.  Venturie/suction fed systems will provide a greater flexibility with good overall productivity; an advantage over a pressure blast system.

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Post written by
Haydn Kitchen
Shot Blasting Technical Manager