Understanding Gear Quality
Posted by: Janusz Roszczenko
We all know that the quality of gears in your mixer drive is very important. But do we know what exactly “gear quality” means? More importantly, does the engineer designing your mixer drive know?
Just in case… here are the basics.
The AGMA classification system for gear quality specifically defines various gear quality parameters including tolerance ranges for tooth spacing, profile variation, and lead (tooth alignment or helix angle) variation, runout, pitch, total composite error, and tooth-to-tooth composite error. There is an appropriate quality for each application depending on speed, acceptable noise, reliability, and cost. Quality numbers range from 3 to 15. The higher the number, the higher the quality. Typical grades for industrial gearing are Q8-10.
The higher the level of quality, the longer a gear system will last. Precision gears are capable of carrying more load while reducing transient loads. Precision gearing runs more quietly, lasts longer, and ultimately lowers operational costs by reducing input power requirements.
Gears need a smooth, accurate shape to carry their load. Think of each gear tooth as a cam, like those on an engine camshaft. They must be accurately spaced so that each is in the right place to pick up the load when the previous tooth rolls off its mate. If those cams are the wrong shape or out of place by just .001”, impact loads are added and gear life is shortened.
The choice of gear type is dependant upon a number of considerations involving physical space and shaft arrangement, load, gear ratio, and desired precision or quality level. In addition to the sizing of gear parameters, it is necessary to ensure that specifications and manufacture result in the desired gear quality. This includes not only tolerances, but an understanding of what comprises gear quality.
In order to avoid problems down the road, make sure that the engineers designing the gears that will be used in your mixer drive know and really understand what makes a quality gear.
About the author: Mr. Roszczenko has been with PMSL for 10 years. He has a MS and PhD in Mechanical Engineering. He holds 12 patents and is a working member of AGMA.