Important factors that should be considered in the selection of any blast media for a particular application is the material and chemical composition, its hardness, its density, its shape, screen size and last but not least, the hardness of the component to be blasted.
The term ‘media’ as used in mechanical surface finishing refers to the free flow abrasive or non-abrasive type of media which carries out the process required on the component.
So, what can be considered and used as a blast media?
Anything! That can be projected through a blasting system.
Media Characteristics to be considered include
- Density
- Media shape
- Media size
- Media hardness
- Media breakdown
Put another way and in context various materials have a range of hardness which can be compared as per the MOH’s scale:-
In choosing which blast media to work with we suggest the following basic rules:
- Choose the least aggressive media that will do the work planned. This will result in less wear and lower equipment maintenance expense.
- Use the smallest media particle/granular size that will do the work. The more impacts per second – the faster the process is achieved.
- Find the lowest blast pressure or turbine speed that will do the work. This offers the benefits of energy savings and reduced compressed air requirements, as well as less abrasive consumption, wear and tear and subsequent lower maintenance costs.
Availability
It’s important to ensure that the abrasive selected for a project can be easily obtained in sufficient quantities. Many abrasives are naturally occurring minerals or by-products from other industries and may not be available locally without the addition of transport costs.
Cost
The cost of the abrasive is a critical part of any job. Often the cost of freight to transport the abrasive from manufacturer to the customers’ site can determine your choice. Also important is its friability or breakdown rate.
The blasting pressure, hardness, malleability and size of the abrasive determine its blast recycling capabilities.
Many types of finish may be obtained by the selection of abrasive and by the adjustment of air pressure in the blasting unit. The more commonly used medias are:
- aluminium oxide
- white aluminium oxide
- urea and other plastic abrasives
- corn cob grit
- walnut shell grit
- glass beads
- pumice
- crushed glass grit
- silicon carbide
- steel grit
- steel shot
- chilled iron grit
Blast Media Choice and Use
- Glass beads can be used to texturise, descale or remove light burrs and flash leaving a smooth bright satin finish.
- Use at 40 to 80 PSI.
- Abrasive grits can be used for more aggressive work leaving a dull satin finish and are useful for creating a good key on the surface for bonding.
- Use up to 90 PSI.
- Walnut shell grit can be used for deflashing thermoset plastics without destroying the original polish surface.
- Use 30 to 80 PSI.
Comparison guide showing the material Hardness in (MOH’s), Vickers Hardness or Rockwell “C” Scales.
Rösler branches offer an evaluation service for any new or existing applications.
Complete our online form at www.rosler.com
Post written by
Haydn Kitchen
Shot Blasting Technical Manager