Engineering News : Page 8 of 10

and welded using a pulse TIG welder. This produced a hermetic seal, eliminating the need for O rings.

ASCO delivered eight solenoid valves within six weeks, and Smith's experiment functioned as expected during flight.

Plate design doubles bearing load capacity

Port Washington, NY - Thomson Industries' patented Super Smart Ball Bushing(TM)(SSBB) linear bearing series offers designers twice the load capacity or eight times the travel life of its older Super Ball Bushing(TM) (SSB) bearings. "We see this as a leapfrog technology in the world-wide linear bearing market," claims inventor Al Ng, chief engineer, Core Products.

SSBB bearings achieve greater performance by increasing the number of bearings and contact areas, and reducing friction. First, dual-track bearing plates with ball-conforming grooves replace single-track grooved plates. This roughly doubles the bearing count and maximizes the number of bearings in the load zone, which helps SSBB bearings handle full load capacity when installed in slightly out-of-round housing bores.

Second, the two-track, pivoting bearing plates self-align in roll, pitch, and yaw. To self-align in roll, the bearing plate's smaller outer radius rides against the larger radius of the ring. This allows it to roll against the ring and evenly distribute the load to each of its two ball tracks.

Pitch self-alignment occurs because the precision ring's convex undersurface allows the bearing plate to rock along the longitudinal bearing axis plus or minus 0.5 deg. This attribute assures smooth ball entry and exit in the load-carrying zone and optimum ball loading from end to end. It also compensates for misaligned housing bores and shaft deflections.

Each bearing plate also rotates about its center to prevent skewing of the ball tracks relative to the shaft (yaw). This minimizes friction and maximizes bearing life.

A comparison of equally sized SSB and SSBB bearings illustrates the SSBB's performance gains. A 5/8-in. bore SSB bearing has a 450 lb. maximum dynamic load capacity, while the same bore SSBB bearing rates 620 lb.; a 1.5-in. bore SSB bearing has a 2,000 lb. capacity, while the same bore SSBB bearing hits 3,880 lbs.

Ng believes his design will find many applications in motion control, such as pick-and-place devices, robotic arms, assembly machines, machine-tool guides, and ultrasonic welders.

--Russell King, Contributing Editor

Urethane tape reduces ambulance costs

Manasquan, NJ -Building custom emergency vehicles is very labor-intensive-and costly. But by using mounting tape to bond body panels on ambulances and similar vehicles, engineers at PL Custom Emergency Vehicles are reducing assembly time and improving reliability.

To bond the aluminum body "skins" to the tubular aluminum frames of ambulances and similar vehicles, PL engineers use a 0.030-inch-thick dense foam tape from Norton Performance Plastics Corp., Granville, NY. Norton supplies Normount(R) urethane tape with acrylic adhesive on both sides.

"Compared to welding or riveting, we're probably saving 40 man-hours per vehicle," estimates PL General Manager Robert Stevenson. The tape also eliminates the rework necessary to correct distortion caused by welding heat, and eliminates rattles and galvanic corrosion, say engineers.

The company first switched to liquid adhesives. However, mounting tape offers the advantage of needing only alcohol to pre-treat

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