The mechanized world is dominated by rotating shafts, each designed to turn at a particular speed and torque. On one end of the shaft, quite often, is an electric motor — the prime mover. On the other end is the load. In between, keeping both sides happy, are gears. Keeping gears happy is the focus of this month’s discussion on productivity. Hear why gears are likely to fail and what you can do to prevent it. Also learn where gear technology is headed, and what this means for designers and end users alike. It’s all on the following pages — waiting for you.

Productivity

What is “productivity” and how do gears contribute to it?

Philip/Thomson: Machine “up” time and component life determine productivity. Compared to belts, pulleys, and other reduction methods, gear drives last longer and are easier to maintain, increasing the “productivity” of each motion axis.

Dave/SEW Eurodrive: Productivity is the volume of products produced in a specified time.

John/Alpha: It’s the ability to process goods in a timely manner at the lowest possible costs. In drive components, it’s tied to speed and power requirements.

Roger/Poly Hi Solidur: Webster defines “productive” as “yielding or furnishing results, benefits or profits.” Gear drives, in and of themselves, contribute to productivity by efficiently transmitting rotary power from one location to another and by reducing or increasing speed and torque. Rack and pinion systems have the added benefit of converting rotary motion to linear or vice versa.

Fred/Forest City Gear: In a world driven to reduce costs and come to market quicker, we are all dependent upon mechanisms that get us to the end result faster and more accurately. This translates to more precise mechanical products, servodrives, stepper motors. It follows that gear accuracy must improve commensurately. Also, at higher speeds inaccuracies generate more noise, which certainly doesn’t help productivity.

Paul/Falk: Productivity is the ability to accomplish more work with fewer resources. Something as subtle as how a component mounts can be a factor. A shaft-mounted gear drive, for example, doesn’t require a significant foundation — no large investment to build a support structure — saving time and money.

Tom/Mijno: Productivity is performing a process quickly and precisely. Gear drives contribute by converting power (force and motion) into a more usable form than the source is able to provide.

Steve/Danfoss Bauer: The simplest definition is the economical conversion of resources, whether human, energy, financial, space, or material into profitable sales, be it goods or services. Gear drives have held a place in “productivity” since an ancient carpenter hammered pegs into a wooden wheel to produce a cog.

Mike/Emerson: The term productivity generally implies “doing more with less” or “getting more for less” and this has certainly been the trend in the gearing industry. “Power density” has become a popular term referring to squeezing more torque from a smaller envelope. This has been accomplished primarily through optimization of gear tooth geometry, improvements in materials and heat treatment, and post heat treatment finishing of gear teeth to achieve higher quality levels.

Limiting factors

What elements most often limit machine productivity?

Philip/Thomson: What typically limits planetary gearheads are the bearings. Bearing life, in turn, is a function of loads and speeds associated with the application.

Dave/SEW Eurodrive: Gear failures are usually caused by overloads, shock loads, poor maintenance, and incorrect sizing.

John/Alpha: Limiting factors include heat, radial loading on output bearings, speed at input bearings, and torque for planetary bearings. Heat from oil churning and seal friction worsens with increasing speed.

Roger/Poly Hi Solidur: There are two modes of failure that affect spur gears; surface and fracture fatigue. Because individual spur gear teeth act as cantilevered beams, power capacity is based on material bending strength. With heavily loaded all-polymer gears, keyway failure may also be a concern.

Keith/Rockwell Automation: Many gear failures are due to applying the incorrect reducer to the required load. A gear reducer must be sized according to required torque based on speed and motor horsepower. Shock loads must also be considered. Other common causes of failure include contamination, seal wear, and improper installation and maintenance.

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