AIR VERSUS TURBINE – BALANCING BLASTING CAPABILITIES AND OUTCOMES
Blasting processes for surface finishing vary according to the size, quantity, composition, and desired finish of the work pieces in need of surface preparation. Air blasting and turbine blasting are two of the more common types of blasting. While there is some overlap between the two methods, each carries its own unique attributes and drawbacks.
When comparing these two blast methods, the number one thing to keep in mind is precision versus bulk. Air blasting provides precision surface preparation using a much smaller blast pattern compared to turbine blasting, which delivers large quantities of media over a wide blast pattern, thereby making it ideal for blasting large quantities of parts or larger individual parts.
Processing delicate or highly controlled work pieces is easily accomplished with air blasting’s small blast pattern and requires very little wear protection, thus reducing maintenance costs. Through the use of blasting lances, air blasting is also capable of cleaning the inside of some parts, with cylindrical parts giving the best internal blast results.
Any type of blasting media can be used with air blasting. Media handling on small to mid-size systems is entirely pneumatically controlled, allowing for more compact systems. Additionally, complete media change-outs are relatively easy on air blast machines as the vast majority of the media collects in a single location.
While air blasting’s small blast pattern offers precision, it also has some drawbacks.
Higher volume parts require more nozzles, blasting time, or both. If more blasting time is not an option, additional machines may need to be used. Blasting larger parts may require attaching linear actuators to nozzles in order to hit the full workpiece.
When a variety of parts require simultaneous processing, automation and part-on-part contact can be problematic. Unlike manual hand blast cabinets, automatic processing of different parts requires minimal programming, separate specifications for nozzle motion and blasting times and/or manual adjustments of nozzle positioning.
Air blasting uses more energy per pound of shot thrown than turbine blasting due to the use of a compressor. Depending on the compressor’s efficiency, approximately three times as much energy is used.
While larger media can be used with air blasting, larger media results in fewer pellets per pound and therefore less coverage per second of blasting due to the small blast pattern.
Boasting a much larger blast pattern, turbine blasting offers several benefits. The large blast pattern allows for rapid cleaning of large, complex parts or of large quantities of small to mid-size parts. The machines offer added versatility and the ability to handle many different types of parts with little to no adjustment as long as all of the parts have similar processing aims. Change outs in part fixturing and or adjustments to the cycle time or throughput speed provide additional versatility.
This method also offers higher energy efficiency since an electrical motor is used to propel the media unlike air blasting which relies on pneumatic force.
Limitations should be evaluated when considering turbine blasting as well, especially in respect to the type and life expectancy of media. Mineral-based media cannot be used in turbine blasting; the hardness of these medias would quickly tear through the turbine and other components. Even with non-mineral medias, turbine blast machines must be very well protected against the accelerated blast media. Due to the larger blast pattern and the tendency to blast with larger media to retain speed further from the turbine, these machines generally have higher maintenance costs and a greater need for spare parts.
Due to the high levels of abrasive throughput, mechanized media handling systems are required (i.e. auger screws, bucket elevators) as opposed to pneumatic systems. This leads to larger overall dimensions of the machine.
More media is thrust using turbine blasting resulting in greater consumption and fewer usable life cycles than media used in air blasting. The larger blast pattern also requires masking off work piece areas that should not be blasted. This method is also incapable of thoroughly cleaning the inside of parts.
Complete media change-outs of turbine blasting machines are difficult and time consuming as there are places where media is designed to sit without ever moving to reduce wear. These modification are fairly rare though and normally only necessary when the machine is being switched over to different blast applications. For example, a machine formerly used to strip paint being modified for peening.