What's the Deal with Gear Drive Housings?

Article Tags:
drive housing
ductile iron
fabricated steel
gear drive
gear drive housing
grey cast iron
requirements for housing

The housing of a gear drive is the foundation for the unit and is the main barrier between the internal components and external abrasives. The housing may look like a simple casting or fabrication, but there are many considerations to its design.

One of the main functions of the housing is to support the torque loads produced by the motor and the internal loads which are produced by the operation of the components within the gear box. The internal loads created by the gearing are transferred to the shafts, which needs to be supported by the bearings, which need to be supported by the housing. Aside from supporting all of the loads, the housing ensures that the bearings are correctly positioned so that the shafts and gearing are aligned appropriately.

Any brackets for motors, coolers, or other accessories are connected to the housing. It must be designed to have enough material in the regions where these connections are made. It also needs to absorb any shock loading or vibrations imparted by them.

Lastly, the housing must be able to deliver lubricant to the bearings, dissipate heat from inside the gear drive by conducting it through the walls, and sometimes prevent oil from getting on seals (drywell applications). It may need to support other elements in the system as well – such as vertically mounted mixers.

When you are selecting a gear drive, the design of the housing will likely be fixed. You may be able to select the housing material, though. If so, consider the pros and cons.

1) Fabricated Steel

The pros of fabricated steel housing are that it is very strong and that it can be repaired and welded on. Unfortunately, the material and process makes it pricier than cast options.  Fabricated steel housings are used on modified or customized gear drives.

2) Ductile Iron

Ductile iron is less expensive than its steel counterpart, but cannot be repair welded and it is not as strong as steel. It is supplied as a casting to the gear drive manufacturer and is ideal for high volume products such as gearmotors.

3) Grey Cast Iron

Grey cast iron is the least expensive option of the three. Much like ductile iron, it will be supplied as a casting and cannot be repair welded. Unlike the other two materials, grey cast iron is brittle, will not give warning before failure, and can be sensitive to extreme cold.

In all cases, there is a chance that a poorly made housing will leak oil through the welds or pores in the housing. Quality manufacturers will pressure test their housings to ensure that leak paths do not exist.

If you are concerned about the housing dimensional fit or construction, work with your supplier. They should able to provide you with outline drawings or models during the quoting phase. Quality requirements for housings, such as inspections, should be communicated to the supplier through the PO.

Robin Olson

Robin is the Director of Applications Engineering at Rexnord Industries, Gear Group. In 1995, Robin joined Falk, which was acquired by Rexnord in 2005, and has previously worked in the Engineering Technical Services, Warranty, Product Engineering, and Marine Product groups during her career.  She is active in the American Gear Manufacturers Association (AGMA), acting as a contributing member of the Helical Gear Rating Committee, Chairperson of the AGMA 925 (Gear Surface Distress) subcommittee, and is honored to act as US delegate to ISO Working Groups 6 (Gear calculations) and 15 (Micropitting).  Robin holds a Bachelor of Science in Physics from the University of Wisconsin - LaCrosse and a Master of Science in Physics from the University of Wisconsin - Madison.