The Right Abrasive for the Right Job

Choosing the right abrasive media for cleaning and peening surfaces is critical to achieving the desired surface finish, but the process can be complex and confusing.

 

By understanding the equipment available for the process, you can quickly narrow down your blasting media options. For example, glass beads are not suitable for use in a shot blast machine because they will shatter immediately.

 

Cleaning or peening?

 

The next question is an obvious, but crucial one that can further narrow down the selection of the right abrasive: What effect do you want to achieve?

 

What is the ideal surface finish?

 

While there are a wide variety of abrasives available, they generally fall into two categories:

 

Erosion materials are randomly shaped, angular particles used to cut and erode parts, primarily for cleaning and/or decontaminating surfaces.

Shot peening abrasives are almost always rounded and are used to knock or compress a surface, leaving it clean and creating pits. The shot peening process is specifically designed to improve fatigue strength in components that are subject to high alternating stresses, such as aircraft wings.

 

Abrasive Types

 

Here is a brief overview of common abrasive types and their applications:

 

Fused Corundum

 

This synthetic abrasive, available in three pure qualities, is known for its hardness, toughness, and sharpness. It is a very aggressive material that leaves a matte, etched surface.

 

White Corundum

 

With sharp, irregular grains, white corundum is well suited for machining hard surfaces, such as carbides and hardened steel, and for applications where contamination cannot be tolerated. Its high purity also enables its use in high-precision electrical components. However, its sharpness is also a disadvantage, and the pursuit of purity can also affect the life of the abrasive.

 

 

Brown Corundum:

 

Brown corundum is less pure than white corundum, making it tougher, longer-lasting, and more economical. At its purest, brown corundum is often used in the aerospace industry, often to remove residual coatings and to prepare surfaces before coating.

 

Pink Corundum

 

Pink corundum combines the toughness of brown corundum with the purity of white corundum. It is sharp and cuts quickly, making it an ideal choice for applications where contamination is strictly prohibited.

 

Metal Abrasives

 

This group of materials includes steel shot and grit, cast iron grit, high-strength cut wire shot, stainless steel shot, and aluminum shot. While shot peening is highly effective for hardening, an important factor to consider is the potential for surface contamination from the peening media – something that can happen when using steel shot to peen stainless steel surfaces.

 

It is also important to remember that most metal abrasives can cause considerable wear on grinding wheels and blasting equipment due to their density.

 

Plastics

 

Plastic abrasives are angular but, being relatively soft, do not attack surfaces. They are designed to deform on impact, cleaning coatings without damaging the surface.

 

Glass/Ceramic Beads

 

Glass and ceramic beads are primarily used to clean surfaces and achieve a satin finish with minimal stock removal or surface damage. They are completely iron and lead free, enabling contamination-free processing of non-ferrous parts.

 

Process Parameters

 

Choosing the right abrasive is undoubtedly an important step, but the work does not end there. People often blame the abrasive for poor finishes, but in reality, the problem lies with the machine setup or operating controls.

 

Poor performance can be related to a number of factors, including improper air pressure, cyclone and dust collector settings, and even worn machine parts. However, it is difficult to give universal operating parameters because abrasives used in the blasting process vary in performance and how they break down.

 

Recommendation: When looking for the cause of poor blasting performance, the entire process and all relevant parameters should be considered.

Importance of Maintenance

 

Most abrasives are only economical if they are recycled and reused, and most machines use pneumatic or mechanical methods to remove broken media from the abrasive. The machine must maintain a good supply of media, and the user must ensure that broken dust and debris are removed from the components from the system.

 

The media should be replenished in small but frequent amounts, as this will keep the abrasive in good condition and ensure consistent blasting results.