I rounded out 2010 with a series of columns on the hazards of conveyors (“Analyzing Conveyor Designs for Safety,” Machine Design, Sept. 23, 2010, tinyurl.com/MDConveyorPt1; “When It Comes to Safety, Conveyors Are Machines, Too,” Machine Design, Oct. 21, 2010, tinyurl.com/MDConveyorPt2; “Ignorance of Conveyor Hazards Turns Lethal,” Machine Design, Nov. 18, 2010, tinyurl.com/MDConveyorPt3).
A reader recently responded to those columns. He’s a technical leader at a major consumer-products corporation that uses many conveyors of all widths, lengths, and speeds, so he had valuable suggestions for working safely with conveyors.
“I agree with your article with one exception: belt tracking. For the most part, the only way to track a belt is to do it while the conveyor is running. Belts have a natural camber that makes them to track to one side, and any splice is prone to misalignment that can cause a local tracking problem as the splice approaches a roller.
“I have seen maintenance people standing over conveyors for hours while belts find their true center. Rarely can we allocate such resources. It is common to see a belt track off after running for a day because it has stretched.
“Conveyor manufacturers are challenged to provide the lowest-cost equipment and often ignore the real world requirements for belt tracking. Our company has developed a proven method for guiding conveyor belts that I wanted to share with you, the conveyor manufacturers, and engineers and maintenance people in the field.
Most conveyor designs try to accomplish both take-up and steering tasks with a single roller at the opposite end of the conveyor from the drive roll, but this method doesn’t work reliably.
“John Shelton discovered the first law of web handling back in the mid-1960s: A web seeks to align itself perpendicular to the roller it is approaching. To take advantage of this phenomenon, we modify our conveyors by adding a steering roller with its far side fixed and its near side adjustable to steer the belt.
“For best results, locate the steering roller at the end of the longest run and equip it with self-aligning bearings. The steering roll’s plane of adjustment should bisect the included angle, and the free side of the steering roller must be easily accessible from a safe position outside the conveyor.
“The roller should be easy to move and lock down. Avoid arrangements like double-sided jack-bolts that are too cumbersome. Fine adjustments in either direction should be easy to make and encouraged over large changes. And maintenance people should wait seven full belt revolutions between adjustments.
“We have found that a well-designed steering roll improves our reliability, profit, and safety.”
Lanny Berke is a registered professional engineer and Certified Safety Professional involved in forensic engineering since 1972. Got a question about safety? You can reach Lanny at [email protected].