A: Todd Allison, Progressive Products, says:
Wear is one of the most common problems in pneumatic conveying, especially in the elbows you’re using in your system. Wear creates issues like shredding, pipe blocking and dusting, piling and bulking, friability, contamination, downtime, streamers, corrosion, and erosion. That’s why you should be using durable, cost-effective, wear-resistant elbows and other components that are right for your process.
There are a couple of different types of wear that are common in pneumatic conveying, and it’s important to recognize these so you can take steps to reduce the wear you’re experiencing in your system.
Three types of wear
Impact wear. During impact wear, bends in your system will see the brunt of the impact from particles. Impact wear usually appears as a hole that’s right at or just off of the tangential line where the material hits the back of the elbow where it’s straight. The back of the elbow takes all the impact without any opportunity to lose energy by sliding. This problem is especially visible on short radius elbows. Examples of materials that can produce impact wear include grain hulls and aggregates.
Sliding abrasion. Sliding abrasion will wear down the line components over a longer period of time. This abrasion type appears as a line of abrasion that looks like a long, even pattern. One item to note is that, at times, sliding abrasion will require longer tangents or flanges if the abrasion is occurring under the couplings.
If you think of a playground slide, you’ll better understand sliding abrasion. Rolling rubber balls from the top of the slide to the bottom will have an impact on the slide over time, whereas if you throw the balls hard at the bottom of the slide, the impact on that slide will be more severe more quickly. Fine powders such as silicates and plastic compound or resin are examples of applications where sliding abrasion occurs.
Corrosion. A less common type of wear is corrosion. I’ve found that when this problem arises, it’s usually in a process that conveys chemicals. This means that rather than using a ceramic-coated or ceramic-lined elbow, your solution probably has more to do with the alloy you’re using in your elbow. In this case, you may just need a stainless steel elbow to help prevent corrosion.
The most unusual corrosion example I’ve seen is a company that conveys oak chips. The sap produced by the wood was corrosive and had weakened the company’s regular steel elbows over time.
How to manage elbow wear
Ceramic-coated or ceramic-lined elbows are effective at managing wear and can take an incredible amount of impact from larger particles of the conveyed material traveling at high velocity.
There might be other elbow types that work better in your system or for the material you’re conveying, or you may need a specialty solution that’s geared toward solving your particular problem. Maximizing abrasion resistance as much as possible to reduce wear and save the time, effort, and expense it takes to replace elbows and other components in your system is important.
Progressive Products, Pittsburg, KS, is a manufacturer of abrasion-resistant pneumatic conveying line components, manifold parts, chutes, and storage containers.