According to Malcolm Lewis, Managing Director of Bonfiglioli Transmission (Aust) , gearbox failure can be prevented by maintaining a speed reducer in top condition while ensuring correct installation, proper use and regular checking.
Given the importance of gearboxes in industrial processes, Malcolm Lewis recommends key steps to ensure long-lasting and trouble-free operation.
Correctly selected, installed and regularly maintained speed reducers or gear motors should operate satisfactorily for years. But there are key steps to prevent malfunctioning and excessive maintenance.
For instance, one should consider the characteristics of the driven load while selecting a gearbox so that adequate service factors are applied to the design to ensure sufficient safety factor for the application.
While installing the gearbox, one should ensure rigid, flat mounting surfaces and accurate shaft alignment. Where possible, flexible couplings must be installed as these will help compensate for any shaft misalignment. It is also advised to choose a shaft-mounted configuration if it is compatible with the application being considered.
A torque limiting device such as a fluid coupling may be installed for applications where DOL starting is specified, helping to reduce stresses on the gearbox by providing a ‘soft start’.
For applications where overloading cannot be avoided, or when a peak torque cannot be estimated accurately, a torque limiting device such as a clutch may be installed. Such devices are highly effective when installed between the speed reducer and the electric motor. It is also important to select a properly rated electric motor to suit the application.
Input or output shafts in some applications may be exposed to radial loadings generated by the application or by an external power transmission component such as a belt, chain or gear. To minimise the overhung load and preserve the life of the bearings, the transmission pulley, sprocket or pinion should be of the largest diameter compatible with the transmission ratio. It should also be located as close as possible to the shaft shoulder to minimise the load offset.
Most gearboxes are supplied for a specific orientation or mounting position that will govern oil level and position of sight glass among others. It is critical that the gearbox is installed in the orientation advised to the manufacturer at the time of order.
Once the drives are properly specified and installed, one should ensure before startup that the service plug positions match the configuration specified on the order. Except for life-lubricated gear units, it is normally advisable to double-check lubricant levels.
There are several important do’s and don’ts for lubrication. For starters, it is important to adhere to the manufacturer’s specifications when filling oil with regard to oil type, quantity, viscosity and any additives. Additionally, both ambient temperature and duty cycle play a role in the selection of optimal lubricant viscosity.
Though more expensive, synthetic oils are generally preferred to mineral oils as they allow for extended change intervals, lasting up to three times as long as mineral oils. Their higher viscosity rating maintains their properties unaltered across a broader range of ambient temperatures.
Gear reducers must be kept away from heat to minimise thermal radiation. This can be achieved by installing suitable guards or forced ventilation systems if required. Additionally, the fan cowl of the electric motors must be kept clean and free of obstruction, avoiding dust accumulation over time, which inhibits cooler operation.
Gear units must be installed with sufficient free space all around to ensure effective natural airflow, as well as to facilitate routine maintenance according to the manufacturer’s instructions.
Commissioning and disassembly
Prior to commissioning, speed reducers are sometimes painted to customer requirements. One should be careful about avoiding solvent spills on the rubber oil seals, which can be done by protecting them with rubber tape or grease.
Whenever the reducer has been partially or fully disassembled for maintenance, the gaskets and oil seals must be replaced with brand new ones.
It is also important to strictly follow all applicable safety regulations in force during maintenance or installation, which must only be performed by qualified personnel.