In-Line Shaft Connection for Longer Life
By James Hu, PE, Director of Engineering
Most clarifier and thickener drive units consist of three speed reducers--primary, secondary, and final. Various torque transmission methods can be used to link one reducer to the next. However, for speed and torque transmission between the primary and the secondary gearboxes on clarifier and thickener drives, the choices are often limited to chain connection for parallel shafts and spline connection for in-line shafts.
The following table compares these two designs. It is not hard to see that in-line shaft designs are superior to the chain designs. The real challenge is to incorporate in-line shaft arrangement thus eliminating parallel shaft configuration. One example of this technology evolution is the invention of rear axle differential box now common to most all automobiles throughout the world today. This made it possible to use an axial shaft instead of a chain to transmit torque from the engine to the rear axle. Using in-line arrangement in clarifier drive unit designs is superior and it has proven on DBS drive units for over twenty years.
| Life | 15,000 hours on a conservatively designed when properly lubricated chain | 150,000 hours or more with little maintenance |
| Bearing Capacity | Very critical due to the overhung loads from the sprockets; Bearing failures are common with the chain designs | No load on the bearings; bearing capacity is not critical |
| Smoothness of Operation | Non-uniform speed due to chordal action | Uniform speed with no dynamic acceleration |
| Safety | Chain guard is required | Totally enclosed; no exposed moving parts |
| Cleanliness | Messy grease/oil in the chain and sprocket area, openings routinely collect dirt and contaminants | Totally enclosed; no exposed grease |
| Speed Reduction | Yes | No |
| Maintenance Cost | Frequent lubrication; replacement of chain every two years and replacement of sprockets every two to five years | None |