This is the second blog in a three-part series on plastics in conveyors. Click here to read the first article: Why Use Plastics in Conveyors?
Why use plastic paddles in drag conveyors? Manufacturers have produced twin-chain drag conveyors for decades. Originally, these conveyors were little more than a steel connection between two chains and a bolted-on, plastic paddle, which dragged on the conveyor floor. When we set out to design a drag conveyor for woody biomass, we saw potential in a twin-chain design but knew it needed improved.
Step One: Reduce Friction and Wear
The first thing we wanted to do was to get the paddle off the floor due to the wear and friction it produced. We accomplished this by placing the conveyor chains on plastic wear strips, which lifted the paddle assembly. After we did this, our initial thought was to change the paddle material from plastic to steel.
But then we shot videos of drag conveyors moving wood. What we learned led to a series of design changes that brought us back to plastic paddles.
Step Two: Fix Problems with Wedging
While shooting videos, we repeatedly observed that wood would wedge between the paddles and the floor, lifting the paddles and twisting both them and the chains. This increased friction and wear at the floor and chains.
To limit lifting and twisting, we captured the chains between upper and lower wear strips. Capturing the chains limited their movement as well as the movement of the paddles attached to them.
But limiting movement was only half the problem. We still had to stop material from wedging under the paddles. To stop the wedging, we came up with a unique paddle design: a paddle with fingers. The fingers work like a leaf rake, shearing and pushing material as it clumps together. The design worked. Wedging was no longer a problem.
Customers often ask us how much product goes through the fingers. They’re concerned the design isn’t efficient. Their concerns are unwarranted, however. Virtually nothing gets through the fingers. We size the fingers to match the product being conveyed so that the product packs in front of them. Depending on the material, the fingers range from fine-toothed to flat to shark like.
Step Three: Make the Paddles Better
We were still working with steel paddles up to this point. Once we came up with the finger design, however, we thought, “Wouldn’t it be nice if the fingers had some elasticity so they could flex?” Flex would help prevent the paddles from breaking, were they to encounter an obstruction. Plastic in the solution then.
Plastic weighs less than steel so that means we can carry more material with less power.
Finally, if for some reason a piece of paddle breaks off, it will not damage downstream processing equipment like hogs, nor jamb in boiler grates or ash systems.
There are a lot of twin-chain drag conveyors out there still designed like they were decades ago: a steel connection with a solid plastic paddle dragging on the floor. But a better design is available. So why, when you’re working to improve efficiencies and be smart with your money, would you purchase something you know is less efficient and is costlier in the long run? Save yourself the trouble that comes with conventional drag conveyor designs and reap the benefits of a SMART Conveyor™ from Biomass Engineering & Equipment.
Stay tuned for the final edition to this series: Plastic Components—What, Where, and Why?