Plant dumps DIY for engineered conveyor belt cleaners

by Bill Hoogewind

With a cost-consciousness, do-it-yourself approach that has become a way of life for many competitive regional concrete suppliers, Raineri Ready-Mix in St. Louis waged a constant battle with conveyor-belt carryback, armed with brooms and shovels.

Ultimately fed up with the arduous, wasteful and sometimes risky routine of manually removing carryback fallout, the plant cautiously agreed to try a new design of head-pulley precleaner engineered for simplicity and economy and found an immediate payoff.

At the St. Louis plant, six material bunkers hold up to 350 tons of the most frequently specified crushed stone, alluvial gravel and sands, lined up over a 265-foot tunnel conveyor. The tunnel belt carries batch-required quantities of these materials to an open pit for transfer onto a 147-foot incline conveyor, which carries the materials to the top of the batching plant. A hopper above the transfer allows front-end loaders to add various specialty materials such as colored aggregates stored in surge piles nearby. Both belts typically run at about 750 fpm.

"Our sand and aggregates typically contain a little clay and hit the belts with 4 percent to 10 percent moisture, so they can get pretty sticky," says secretary and treasurer Chris Raineri. "Both the tunnel and incline belts were originally installed with belt cleaners, but their design forced the cleaners to be positioned where carryback material cleaned off the belt fell short of the transfer hopper and landed on the ground." 

Routine cleanup essential
The tunnel-to-incline transfer, he points out, occupies a concrete-walled pit in which the incline belt's tail pulley is only 8 inches above the concrete floor. At least once a week, sometimes twice, the fallen carryback material built up to a point that demanded removal.

The pit walls are only a few feet from the transfer, which makes tight quarters for shovelwork, so cleaning out the pit would take eight to 10 man-hours at a labor cost of $360 to $440.

"Worse than the cost, was the need to have people in there shoveling next to a moving belt,” he says.

Still, cleanup was essential, otherwise the carryback would find its way onto the return side of the belt and start building up on the pulley faces, which leads to tracking problems, slippage on the drive pulley and belt damage due to rocks grinding into the bottom cover. 

Belt-cleaner droppings created a different problem atop the incline conveyor. That belt deposits its load into a turnhead diffuser that rotates to guide different materials into one of six narrow vertical hoppers, from which selected amounts are drawn out at the bottom in proportions specified for each batch.

"Up there, the cleaned-off material would drop outside the turnhead and fall into the wrong hopper,” says Raineri. “The only way to deal with that was to keep one hopper out of use so it could accumulate whatever was falling. Since we could never be sure exactly what was in that hopper, we'd just end up saving it until we got an order for 'lean' concrete, a low-strength mix used for ground stabilization under construction sites."

The original-equipment cleaners had other problems, too, he adds. They used a pair of flat, half-inch rubber blades, mounted atop compression springs. These springs were supported by an extended arm that held the blade assembly against the belt using leverage applied by a counterweight at the opposite end of the arm.

"That design did a fair job of cleaning but needed a lot of maintenance because the rubber blades wore out quickly, and if not replaced promptly would allow their metal base to damage the belt,” he says. “In addition, material dropping off the belt would clog the springs and diminish the blade's ability to conform to the belt.  Maintenance was difficult because everything had to be done down underneath the belt.

"We had no choice but to keep these cleaners working as well as possible," says Raineri. "Otherwise, carryback would shake off all along the length of the tunnel, where cleanup is much more difficult than in the pit. On the incline, carryback would shake off as the belt traveled over plant buildings, so somebody would have to go up and clean off the roof a couple times a year as well.  Some of that carryback is corrosive, so it can't be left on conveyor framework or it'll start eating away at the steel. In the end, what didn't shake off the belt would just stick around to contaminate the next batch.

"We were able to improve on those cleaners a bit with whatever we could do quickly and cheaply, including trying different kinds of belting material for blades, but we never eliminated the need for shoveling,” he says.

New cleaner design tried
During a meeting with Jason Schicker, the plant's representative from A-L-M Inc., a local distributor of conveyor belting and accessories, Raineri's chief mechanic Kevin Vermillon learned about a belt cleaner that sounded like a solution to this problem. Recently introduced by Flexco as one of its Rockline conveyor products designed for the aggregate industry, called the EZP1 Precleaner, this unit mounts across the forward face of the conveyor head pulley to clean off carryback immediately below the conveyor discharge point so that material could follow the discharge into the transfer.

"We were pretty skeptical at first, but what we had wasn't working well and this Rockline cleaner had some special features that made sense, so we agreed to give it a try,” says Vermillon.

Among the most promising features were the blade shape and sizing, he says. Rockline's ConShear blade is a single piece of polyurethane molded with a claw-shaped cross section having a faceted profile. Its geometry allows the blade to continually renew a sharp shearing edge every time blade wear reaches a new facet, which keeps cleaning efficiency high throughout the life of the blade.

No more shoveling
Our original twin-blade system would wear into good cleaning contact after about 8,000 cubic yards, then would be good for maybe another 40,000 yards -- about five or six months -- might even last a year if we were lucky, Raineri says.

"This Rockline unit with just one blade did a far better cleaning job right from the start, and after 40,000 yards, blade wear still looked negligible,” he says. “Most important, we aren't routinely sending anyone in to shovel out the transfer pit anymore, because now all of that carryback is coming off the belt into the transfer.

"Similar story on the incline belt," he says. "Now that the cleaner fallout is going where it's suppose to, we can load that sixth hopper with specialty materials and shorten the time on preparing those orders.”

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