The issue of friction vs. impact in pneumatic conveying is mainly about how much damage a pneumatic conveying system can sustain from the bulk material being conveyed over time. Understanding these types of wear will also allow you to protect the components in your system that are most susceptible to impact and friction forces.
By identifying and protecting the vulnerable components in a system, the wear and tear process can be minimized, as can breakdowns, repairs, periods of downtimes, and, of course, cost.
What is Friction in Pneumatic Conveying?
Friction is produced when two surfaces slide past each other, creating an abrasive force that causes the particles on the surfaces to scrape together. This happens in pneumatic conveying systems when loose particles of the bulk material, like grains or plastic pellets, come into contact with the inner walls of the components, such as the elbows, couplings, tubes and pipes.
Frictional abrasion can become intense when the bulk material is moving at a high velocity. This abrasive friction becomes even worse when the particles change direction, which is why the insides of pneumatic elbows and other curved components are particularly susceptible to friction damage. If these parts are left unprotected, frictional abrasion can cause damage straightaway.
Different types of bulk materials have different levels of abrasiveness, and this is known as friction coefficient. For example, steel has higher friction coefficient than polyethylene pellets. The coefficient also has effects on the pressure inside the pneumatic system. Therefore, it’s an important factor in designing the system and whether it should be a dense phase or dilute phase design.
How to Recognize Impact in Pneumatic Conveying Systems
Just as with frictional abrasion, the bends in your pneumatic conveying system, particularly the elbows and other curved fittings, will be the most vulnerable to impact damage if left unprotected. Impact wear can result in the breakdown of your system if unchecked, so it’s important that you’re able to identify this.
Unlike frictional abrasion, particle impact damage usually presents as a hole or dent caused by the collision of particles in one particular area. You can typically see this happening right at or just off of the tangential line. Impact damage is the area where the particles of the bulk material collide with the back of components, and is particularly obvious on elbows that have a short radius. This happens because the moving particles don’t have sufficient time to slow down in these areas.
The speed of the bulk material and the pressure inside the pneumatic system also affect the impact force of particles, causing them to hit harder in certain places. Some amount of energy is lost during this impact, meaning that the impact force can also affect the material itself: if the impact is sufficiently strong, it could cause the larger particles on the material to break and shatter.
Key Differences in Friction vs. Impact in Pneumatic Conveying
Although both can simultaneously damage pneumatic components, there are some key differences between friction and impact in a pneumatic systems:
- Friction wear causes abrasion while particle impact wear causes a dent or hole
- Velocity is the main factor of friction while energy is the main factor of impact
- Impact wear mainly occurs in smaller areas while friction wear occurs over larger areas
- You can reduce friction wear if you use abrasion resistant linings, such as ceramic linings, and/or reduce the system’s speed
- You can reduce the impact wear by reducing the energy or pressure of the conveying air
Changing the radius of the elbow can also affect impact wear as the energy becomes dissipated
