Pneumatic Conveying Elbow Degradation: 5 Factors to Keep in Mind

Gus Carrington

Gus Carrington About The Author

May 19, 2021

Why is it so important to take pneumatic conveying elbows into account when planning a bulk materials system? The answer to this question as a whole is something we’ve addressed on the AZO blog before, but what about elbows makes them unique when it comes to conveying?

We’ve gone over how the number of elbows, where they are located and how they are sized will affect a system’s success, but what about elbows makes them altogether different than the rest of the line? Ultimately, another reason that elbows are an overlooked concern in a convey system is that (unlike tubing) they wear out significantly when faced with flowing product. 

Material is the name of the game — we know you as a material handler would be lost without it (we would too). The bad news for elbows is that as material contacts a surface changing its direction, friction will eventually cause degradation on that surface. How long it will take an elbow to degrade is extremely dependent on what is going through the line (we hear reports from PVC plants who don’t change out their elbows for years vs. battery plants that change out elbows every shift). Whenever an elbow does fail, it will then be incumbent for someone in the facility to replace that elbow at that moment. 

Wouldn’t it be better to have some insight into when your convey line elbows are going to get worn down? Just think, you definitely wouldn’t want to halt production in the middle of a shift to swap one out (or be caught dead without a spare elbow in such an occasion). In this AZO blog post, we aim to put control in your hands (and elbows), so here are 5 factors to keep in mind when wondering when your elbows will give out.

The type of elbow will dictate how long it takes to degrade

The types of elbows (or degree of angles) come into play in the context of elbow degradation. A long-sweep elbow vs. a 90-degree elbow will behave differently against material that is conveyed through the line. Long angles will give you a more gentle curve, which typically minimizes the impact of the material on the elbow. An added bonus is that they also reduce the degradation of a mixed product (especially sensitive blends that contain color pigments). 

90-degree elbows are generally less expensive and easier to install than these long-sweep elbows, but the short radius of such an elbow will allow for abrasive product to wear down the elbow at a faster rate. 

“Angel hair” among other contaminates often found in granulate

A possible maintenance issue that long-sweep elbows have a tendency to introduce can be found in the plastics pellets industry, where pre-compounded pellets can hit the side of the elbow in a diluted stage to create extra “strings” of plastic. This is known as “angel hair” and can cause filter clogs downstream. If you find yourself facing this problem (and are using an AZO system), it might interest you to talk to one of our representatives about the specialized kit we offer that can be placed before a receiver to capture this excess “hair.” 

At this point, we’ll get out of your hair in order to continue explaining how material itself directly affects the life of a convey line elbow:

The type of material you convey through elbows dictates life span

Almost all of the material in a line hits the elbows in that line. For highly abrasive materials there's no such thing as preventing wear out, it’s going to happen. This may be obvious, but if you’re conveying particularly abrasive materials (like sugar, sand or diatomaceous earth), your elbows will wear out faster. Anything granular is typically abrasive to convey line elbows.

The first step in preparing for the future (in the context of setting up new elbows in your line) is understanding how long you can afford to delay that replacement. Abrasive material will present a quicker elbow turnaround, so to speak. On the other hand, fragile material presents a separate concern altogether. Causing damage or degrading a product mix becomes a possibility when product meets an elbow through the line. Ultimately, preventing this kind of de-mixing falls on the operator of the convey line, which brings us to our next point.

The operator’s expertise also plays a part in elbow degradation

When focusing on the quality of an end-product, we’ve argued that it will match the quality of the system that handles each of the ingredients making up that product. The quality of the product can also completely be affected by the person operating the conveying system. If that operator can’t convey the material to the specifications required, the material and convey system could be negatively impacted.

In other words, anyone can simply “move” material. It is how that material is moved that affects the quality of both the ingredients and the parts of a convey system in the long run. This is particularly true about convey line elbows. When both the potential exists that elbows could be worn down and products could degrade, the qualifications of those who are at the wheel of the conveying system will determine if the end-product and system itself is impacted positively or negatively.

Human errors do occur, but this is all the more reason for a company to explore their options in regards to implementing automation in their material handling processes

How long you are conveying affects the entire pneumatic process

Though the length of a system is a concern that applies to the integrity of a product blend more so than the elbows' longevity, this (in conjunction with the type of material) shapes an entire process. For instance, the act of manufacturing windows requires conveying a blended product that already has color in it. If you are conveying at, say, 1,000 feet through 8 or 9 elbows, that color could separate from the material. 

This could cause a cyclical chain reaction upstream: 

  •  The end-product is off-color, so...
  •  A great amount of scrap product is generated, and...
  •  (Avoidable) time and labor is used to clean the system in order to avoid more scrap from being generated 

(Not to mention, your elbow’s life span was chipped away by product that you weren’t even able to use). In summation, particularly abrasive materials are going to have more of an immediate impact on convey line elbows. If they have further to travel in the line, this could potentially lead to an elbow wearing down quickly. Already-abrasive materials (picking up velocity over a long distance) colliding against these elbows could create the perfect storm for elbow degradation. 

Pair all of this with an operator who doesn’t understand how to mitigate such degradation and you could potentially run through an elbow in no time, leaving facility workers surprised and unable to replace that elbow quickly (without significant downtime used to fix issues). One final factor that wastes resources and pertains to elbow degradation involves dust accumulation.

A final thought: dust represents scrap material and waste 

If a product degrades and turns into dust, that dust (formerly product) is going to get pulled out of the system. This alone may be intended (and a necessary move for minimizing dust in a convey system), but material that degrades this way is waste material. Essentially, you are reducing the amount of useful product. 

Furthermore, if you have a product that has high fat in it and the fat smears out, then you could actually clog the system. This can create a whole host of problems and roadblocks toward your end goal of creating a successful end-product (and protecting equipment i.e. convey line elbows along the way). 

AZO has more than seven decades of experience in handling raw materials and shaping ingredient automation to the benefit of various industries related to bulk material handling. Feel free to contact our sales team for any questions on how to help your plant and processes run smoothly. We also offer a free downloadable guide to answer a multitude of conveying queries you might have. 

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