to 8' (2.4-m) thick concrete walls and large doors that attenu- ate the radiation from traveling beyond the treatment room. “We’ve manufactured and installed nearly 100 of the direct shield doors, since I’ve started working with Pitts Little,” said Bargeron. “Each door, and radiation-shielded vault, is designed specifically for the needs of the customer so they vary in dimension and design. They range from 24,000 to 30,000 lb [10,886–13,607 kg] each, and block gamma rays from entering the environment and absorb neutrons resulting from radiation treatments.”
The original design of these unique sliding doors used a style of bearing that helped the doors slide quietly open and shut, but the bearings became difficult and expensive to or- der. Bargeron and Walter Little, president of Pitts Little, made the decision to redesign the doors and turn to a new supplier. They contacted Osborn’s Load Runners division (Brooklyn Heights, OH) and requested a new, specialized roller from Load Runners to replace the old bearing part. Osborn’s Load Runners division features a full line of cam followers, idler rollers and rail systems in all standard configu- rations: plain, flanged and v-groove. In addition to its standard products, the company designs and manufactures custom- ized products with special geometries, seals, lubrication and/ or materials—all to exacting customer specifications. “I was familiar with Osborn, and have used both Osborn and Load Runners’ products for the past 20 years,” said Bargeron. “I know that they make superior products that are well-designed, good-looking and sturdy.
Four custom, small-diameter, low-friction steel rollers, paired in two separate trolleys roll on an Osborn Load Runners’ hard, round polished steel bar for very low-friction movement. Low friction reduces the power needed for a belt drive to move the heavy door and makes it easier to manually push or pull the door open in the event of a power outage.
“The first door that the new rollers were needed for weighed 28,000 lb [12,700 kg] and was 2" [51-mm]-thick. It had 6" [152 mm] of solid lead to block gamma rays and 11" [279 mm] of borated, polyethylene sheets that absorb neutrons inside of it,” said Bargeron. “It needed to slide reliably, electronically and manually, and it was imperative that it be quiet so that our customers could effectively provide patient comfort.” Previous door designs used ballscrew actuators or chains to open and close the doors. These methods caused them to be noisy and unreliable. Osborn’s engineers designed a small Load Runners bearing roller to fit the specifications that Bargeron and Pitts
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