Drag Conveyor Paddles: Steel vs. Plastic

Drag Conveyor from Biomass Engineering & Equipment

A typical drag conveyor comes equipped with steel paddles. Although a standard throughout much of the industry, such a design comes with drawbacks. Steel paddles are expensive, difficult to manipulate, can corrode, bend, and can damage other machines down the line if broken. So, we’ve decided to chuck standard designs and opt for a different paddle material—plastic.

Plastic Conveyor Paddles: Part of a System

While it’s tempting to simply compare plastic paddles to steel, the plastic paddles are part of a system and really need to be considered as such. The combination of the plastic paddle, the “fingers” (paddle design element), the plastic wear strips, the engineered paddle frame, and the chain all work together to deliver the most efficient and effective conveyance system ever created for difficult bulk materials.

As part of this system, the paddle’s fingers, for example, break up the material so it flows rather through the conveyor than packing together. Think of one of these paddles as a rake—loose material packs in front of the fingers while material that wants to pack passes through—to be picked up by the next set of fingers.

The fingers help in other ways. They prevent tapered pieces of wood from wedging under the paddles. They also are able to flex if they contact an obstruction. This reduces stress on the paddle frame, chains, and wear strips. They also spring back into shape under most conditions, whereas steel paddles will bend and stay bent.

They also reduce the overall friction load within the conveyor. Because the material doesn’t pack together, the conveyor mustn’t strain to move it. And because the paddles don’t touch the floor, there isn’t friction between these parts. This reduces wear, as well, and increases the life of the floor plates and the paddles.

While it may seem counterintuitive to design a gap between the paddles and the floor, due to friction, material doesn’t simply lie under the paddles; it moves with the rest of the material. Providing space under the paddles also helps ensure the material doesn’t pack and cause an obstruction. It furthermore allows the machine to keep material flowing evenly.

Direct Comparison of Steel and Plastic Paddles

If you’re looking for a straight comparison of plastic verses steel, however, we won’t disappoint. Here are four ways which plastic paddles outperform steel paddles in drag conveyors.

Cost: Steel vs. Plastic

That plastic paddles cost less than steel paddles shouldn’t much explaining. Industrial-grade plastic costs less purchase and is easier to cut and mill than steel. Not only does plastic cost less in bulk, but it’s easier to work with during the fabrication process. The more complex a metal part becomes, the more its price increases—exponentially so. Steel is not easy to work with and is much more difficult to shape than plastic. Greater complexity means more welding, grinding, shaping, die work, etc. With plastic, the price increases at a slow, steady rate with complexity because retooling machines is typically all that’s required.

So, when a paddle breaks in your conveyor (not that this has ever been a problem with our conveyor paddles), ask yourself: do you want to pay for custom-milled steel or custom-milled plastic?

Performance: Corrosion

Significant differences between steel and plastic conveyor paddles arrive in their performance. Due to weatherization, acidic rain, and the moisture and chemicals in the material being conveyed, conveyor paddles can corrode over time, losing their ability to conveyor material effectively.

Plastic doesn’t face this problem. It doesn’t rust.

Performance: Weight

Plastic also surpasses metal paddles also in terms of weight. We use high-density polyethylene for our paddles, which has a specific gravity between 0.93-0.97. Stainless steel has a specific gravity of 7.7, so it weighs nearly eight times as much as plastic. That weight difference means the conveyor using plastic paddles can run more efficiently because its not using as much energy to move its own components. It also makes transportation and installation easier. Replacing parts is easier, too, because maintenance technicians won’t have to wrestle with heavy parts.

Performance: Downstream Damage

The biggest advantage of plastic paddles as opposed to metal ones really comes in their ability to mitigate damage if part of a paddle breaks off. Companies will often push their conveyors to the limit, and it’s not surprising that machines break as a result of the abuse. In this event, were the part to fail be a steel paddle, the steel could damage equipment downstream, dulling or breaking blades and other components.

A broken plastic paddle is less likely to cause trouble. Chippers and hogs, for example, won’t be damaged from a piece of polyethylene.

Equipped with fingered plastic paddles, SMART Conveyors from Biomass Engineering & Equipment are the right choice for bulk material handling. We’ve implemented our conveyors to move everything from DDGS at ethanol plants to pellets to wood chips to recycled tire rubber, and we’re ready to take on the next challenge.

Contact us today to learn how our equipment can meet your needs.

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