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Enhance your employees’ product and industry knowledge with PTDA’s Tech Tips. This library of online tips, hints and techniques may be used to educate new and current employees on power transmission/motion control (PT/MC) products, technologies and concepts and serve as reference and reminder for more experienced staff. Tech Tips are based on the expertise of PTDA member companies and content from PTDA’s Power Transmission Handbook®, the definitive resource and training tool on PT/MC products.
Torque arm is a mounting device for gearbox and gearmotor with hollow shaft fixing to the machine like a conveyor. Torque arm always needs clearance to play and absorb shock load between gearbox body and fixing bracket at machine side. While standard type is rubber bushing which is soft and flexible, the other way to avoid early deterioration is the Belleville. Another type is disc spring, which is mostly made of metal, is a corn shape spring washer that absorbs shock load by its compression. Common industrial standard for dimension and spec follows JIS B 2706 and DIN 2093. Example of installation is shown below.
Without torque arm, a ‘shaft mounted’ gearbox would start rotating about itself instead of moving the conveyor belt. The torque arm provides support to the gearbox against the torque load. However, it should allow the gearbox to ‘float’ on the conveyor shaft. If the torque arm is mounted ‘rigidly’, with no wiggle room to the gearbox to adjust for the conveyor shaft runout, the bearings and seals of the gearbox would strain, and potentially succumb to fatigue. It is appropriate to utilize rubber bushings at the fixed end of the arm as a cushion. At the time of inspection, the gearbox should be able to wiggle about as the pulley rotates in operation. Also, it is important to make sure that the assembly does not interfere with any other components.
Cycloidal gearing is used in applications where low backlash and high torque-to-weight ratios are required. It differentiates itself from other gear reducers by having up to three cycloidal discs as the main elements generating the reduction. These cycloidal discs operate in a rolling motion allowing for constant contact which differs from other gearing where teeth slide against the interacting surfaces. The input shaft into a cycloidal gearbox drives an eccentric bearing that, in turn, creates the cycloidal motion. The perimeter of this disc is geared to a stationary ring gear housing and has a series of output shaft pins, or rollers, placed through the face of the disc. These output shaft pins directly drive the output shaft as the cycloidal disc rotates. The two main characteristics that stand out the most when it comes to a cycloidal gear reducer are high shock loads and high moments of stiffness. The unique design allows about 30 percent of the circumference of each cycloidal disc to be engaged. This allows heavy shock loads of up to five times the normal torque rating of the gearbox and the high moment of stiffness. These two characteristics make the cycloidal speed reducer an ideal choice for many applications in the machine tool industry as well as robotics.
It's important to consider ambient conditions such as:
Backlash, the clearance or play between mating gear teeth, is built into most speed reducers to let the gears mesh without binding and to provide space for a film of lubrication between the teeth. This prevents overheating and tooth damage. Even with zero backlash, applying a torque to a speed reducer creates mechanical deformation (yield) in the system. This distortion angle is typically measured on the output shaft with +/- 3% of the rated torque applied to the output shaft while the input shaft is locked in place. Backlash and lost motion are not the same thing. Lost motion is an umbrella term that covers any difference between the input motion and the output motion. It is the sum of all backlash and mechanical deformation. Lost motion is present in all speed reducers. Zero backlash is typically only achieved in cycloidal and harmonic gearing.
When mounting a sprocket or sheave to the gear reducer output shaft, always make sure the applied overhung or radial shaft load is below the capacity of the gear unit. Excessive overhung load or radial load applied to the gear shaft can lower bearing life or contribute to premature shaft fatigue.
Consider specifying helical-bevel gearing with superior surface finish, relatively low sliding friction and higher per stage gear efficiency versus worm gearing with high sliding friction, low efficiency and higher operating temperatures. Coupled with energy efficient or premium efficient low-intertia motors, the helical-bevel gear reducer or gearmotor can offer a significant reduction in energy consumption and result in significant cost savings, especially when there are numerous gearmotors or reducers in the factory or plant.
The gear reducer mounting position determines the lubrication fill quantity and the location of the oil fill-level, vent and drain plug. In some cases, mounting position may also dictate variations in assembly. Certain applications require reducers to be mounted on a slope or a rotation; this requires a special mounting position specification, since typical catalog mounting positions include only various forms of horizontal and vertical mounting.
Synthetic Gear Oils offer a number of advantages including the following:
Nature of the load, the environment and design type are three parameters commonly used in calculating the size of a gear drive. Gear rating and mounting position are additional factors to be considered.
Torque arms are used on shaft mounted gear reducers to prevent rotation by securing the gear box to the stationary part of the machine.
The correct amount of backlash in a gear set will depend on the gear design (shape), quality in terms of manufacturing, and application needed.