Aninnovative carburized case-hardening process that increases the strength of precisiongear racks, including the tooth flanks and root, maximizes power density,stiffness and performance. The Strong Line class of gear racks from AtlantaDrive Systems Inc. enables designers to use smaller rack sizes, compared to traditionalgear racks, and can increase the performance of existing systems.

"What is revolutionary is that thisis the first rack on the market that is completely case-hardened withroot-hardened teeth. It achieves the maximum power density, since there isn'tanything more you can do to the rack to increase the power it can transmit,"says John Entwistle, vice president of engineering with Atlanta Drive Systems. "Fordesign engineers, it decreases the size of the rack required in applications. Themore power-dense rack makes it possible to have smaller designs, and the rackrequired for an application typically drops down a size. In existingapplications, the new rack increases the capabilities and performance of thedesign."

"By completely case-hardening the rack, youharden the root as well as the sides and back of the rack and the mountingholes. This allows the back surface of the racks to be used with cam followerroller bearings for guiding the axis," Entwistle continues. The racks areprecision ground on the teeth and all sides to achieve extremely accurate pitchdeviation and parallelism. Rack mounting holes are optimized for maximumholding force to insure the rack remains stationary under high forces.

Racks are typically sized based onthe acceleration and torque needed for a machine to ramp up-to-speed. The newracks allow the design to push harder during acceleration and carry more mass.With root hardening, the rack is also stiffer and there is less deflectionunder load.

Entwistle says there is more demandfor hardened racks now, especially with machine tool and aerospace customerswho need the stiffness and power density that the rack provides. With this newproduct, we are showing a way to increase the forces that a rack can transmitand increase the performance of a machine.

With a simple, soft milled gear rack, thelimits to the amount of force that can be transmitted are based on the bendingand pitting strength of the teeth. Because the teeth are soft, the limit is thepitting strength or contact pressure between teeth. Hardening the teethincreases the allowable contact pressure and changes the limit from pitting strengthto bending strength.

There are racks available on themarket where the flanks are hardened to increase the allowable contactpressure. So the only way to further increase the capacity of the rack is toroot-harden the base of the teeth. But it's very difficult to reach between theteeth with an induction hardening process, and is expensive and difficult tocontrol.

With rack-and-pinion applications, Entwistlesays there are always several solutions for a machine, at several differentprice points. The hardened racks provide a high-end solution for engineersdesigning high-performance machines. The Strong Line gear racks are availablein straight and helical versions, and can be combined with precision pinionsand servo reducers to create an ultra-high-precision rack-and-pinion drivesystem.