As abrasive is recycled and re-used within your pipe shot blasting machine it is affected by impact. It will gradually reduce in size as a result of a combination of: splintering, spalling (peeling), deformation (i.e. rounding) or smoothing (i.e. grit becoming blunt).
As your abrasive changes, so will your process along with the result you achieve.
Where you are working with angular abrasive (i.e. grit) the rounding of the abrasive angles will produce a less-impacted surface, with a reduced and smoother profile. This will affect paint adhesion properties.
Similarly where you are using a round steel shot, should a percentage of that shot be broken and splintered the surface will change from a satin appearance to a more matt finish. More importantly still, if you are using shot to generally ‘peen’ a surface and remove tensile stress, the impact of broken / splintered abrasive introduces the risk of worsening the stress factors, rather than improving the present state. This introduction could result in components performing badly (increased risk of failure through fatigue and shortened life expectancy).
Whilst an abrasive type and size should be defined when a machine is first installed or components are introduced, sometimes this doesn’t happen, things change. and what can happen is abrasive being used on parts harder than it is. Instead of deforming and/or hardening this can result in the abrasive ‘shattering’. This same effect is achieved where empty blast machines are run (or parts loadings are lower than prescribed) allowing the abrasive to have a direct impact on a hardened wear plate. Similarly where abrasive can be sat and/or exposed to the elements it can become corroded, change its properties, etc… and this again can have a detrimental effect on both the machine (increased wear and spare parts usage and maintenance costs) and the process result sought.