These days, some new upscale homes and buildings are adorned with formed concrete facades to give the stylish appearance of stonemasonry, but in a more practical and less costly way.
When one manufacturer of these stone fascias needed to transfer its 300-lb mold forms into a spray booth for release coating, they approached TKF Inc., Cincinnati, a company that designs and integrates conveyor-based material handling services and custom-engineered and manufactured systems.
“They needed ten extending, elevating fork transfers,” reports David Radford, design engineer and project manager at TKF Conveyors, “so we looked into the cost of purchasing these from a European manufacturer. The cost, however, was prohibitively expensive; the mechanism, without drives, controls, or frames would have cost more than $20,000 each. The answer was to design and build our own system.”
The biggest challenge was finding a precision linear motion device that could handle extreme loads. The 300-lb molds must be moved 96 in., so not including machine components, that is 28,800 in.-lbs of moment, and as much as 90,000 in.-lbs after factoring in remaining machine elements. In fact, Radford had four main considerations: capacity, deflection, cost, and reliability. After considering what is available in the marketplace, his team concluded that the Telescopic Rail from Rollon Corp., Sparta, N.J., was the only system that would withstand these loads.
Jeff Mowers, regional sales manager for Rollon comments, “The rail is a linear bearing that telescopes beyond its mounting structure. Before, drawer slides were simple bent-steel products suited for desk drawers, filing cabinets, keyboard trays, and other light-duty applications. Engineers were forced to use homemade solutions or double up on thicker gauge bent-steel drawer slides.” In contrast, the engineered telescoping bearings produce movement similar to that of drawer slides, but function like linear bearings.
Of equal importance is rail stiffness. When the molds are positioned in the spray booth, positioning tolerance is only plus or minus a quarter of an inch to ensure that the mold is completely covered by release coating. The Rollon rail in the new mold-moving design is made from induction-hardened and ground alloy steel, so it is stiff enough to provide accuracy needed. In addition, the rail enables a design comparable to designs available for purchase. However, item costs were kept down to about $13,000 and the finished system was designed and built for about half the price of a commercially available alternative.
The final consideration: reliability. “Any custom solution is a huge reflection on our company and, in the case of these 300-lb molds, failure could be extremely damaging to nearby personnel and equipment, not to mention the lost production,” Radford says.
“We worked closely with the Rollon team to ensure a safety factor of 2:1 because we have an old-school philosophy of building heavy and reliable one-off designs, rather than systems intended for mass manufacturing. The technical support from Rollon was of a high standard — we presented many design concepts, and their engineers were both helpful and knowledgeable. That adds value to a project like this, when high-quality products are matched with high-quality technical support.”