Extending the life of drive trains in heavy industry
06 May 2015
Your choice of power transmission couplings for heavy duty drive trains can have a big impact on the reliability and life expectancy of these installations.
We examine the merits of one particular type – rubber-in-compression. And where safety is concerned, we also take a look at mechanisms that prevent potential catastrophic consequences of inclined conveyor drive failure.
Selecting rubber-in-compression couplings as a cure for vibration and shock loading on arduous applications in the metal manufacturing industries not only cuts maintenance and downtime but also reduces operating costs and extends the life of the machinery and equipment to which the couplings have been fitted.
Excessive vibration and massive shock loading are common problems on plant and equipment in metal manufacturing that can damage machinery, cause premature failure and significantly increase maintenance costs. Not only can it result in damage to the machinery being driven but also to the motor and the component parts of the power transmission system.
One of the easiest and most cost-effective solutions to this problem is to fit rubber-in-compression type flexible couplings. The benefit of rubber-in-compression couplings is that there is no metal-to-metal contact and torque is transferred via pre-compressed rubber elements that damp vibration, eliminate backlash, and ensure that the natural frequency of the drive train does not coincide with the running speed.
They comprise two round, metal sections fitting one inside the other with what looks like the paddles of a paddle steamer projecting inwards from the outer section and outwards from the inner. Rubber blocks are placed in the spaces between the paddles and, as the outer section is turned by the engine, it drives the inner section through the rubber blocks. As this happens the rubber is compressed - hence the term rubber-in-compression. These components are maintenance free and the rubber blocks are usually good for at least ten years of service.
Typical applications for rubber-in-compression couplings in metal manufacturing include rolling mill drives, table roller drives, coilers, ladle cranes, piercers, pilgar mills, pickling lines and edger drives.
Cement manufacturers can also cut maintenance and downtime by fitting rubber-in-compression couplings on similar arduous applications like grinding mills, kilns, conveyors, crushers and fans. Rubber-in-compression couplings are particularly reliable for heavy-duty, arduous applications because they are intrinsically failsafe and maintenance free, thanks to their design and construction.
There are no wearing components in a rubber in compression coupling, as there are in gear, or other types of metallic coupling. Due to the fact that the rubber blocks are totally encased in metal they can only change shape during operation and will not wear or fail, thus ensuring reliable operation at all times, even on the most arduous applications. The couplings are also maintenance free, eliminating the need to shut down plant and equipment for lubrication.
The rubber blocks in the couplings eliminate backlash and are carefully selected for each application to significantly reduce vibration, shock loading and torque amplification that would otherwise reduce the life of plant and equipment, causing premature fatigue failure.
Halifax based Renold Hi-Tec Couplings, a specialist manufacturer of torsionally flexible couplings, can supply a range of rubber-in-compression couplings for high torque applications in industries from steel making, through mining and marine to power generation.
Safety of inclined conveyors
Sprag clutch holdbacks with central torque arm are suitable for arduous, heavy-duty applications such as inclined belt conveyors and bucket elevators where reverse running due to loss of drive could have catastrophic consequences. If drive is lost, these devices instantaneously prevent any runback.
Inclined conveyors are commonly found at mines, quarries, cement and steel works. Most of them tend to be extremely long and the weight of material on them at any one time can be enormous. If the drive stalls and the conveyor back-drives then it will accelerate due to gravity until its load has been dumped at the bottom.
If a fully loaded inclined conveyor runs backwards then it will tend to run much faster than it runs forward. This isn't a problem for the conveyor and the bearings but it can be catastrophic for the components on the other side of the gearbox. The out-of-control conveyor would drive the gearbox the wrong way, changing its speed-reducing role to one of a speed-amplifier.
This would overload the components in the drive train that would have been sized for normal operating conditions when the conveyor runs forward. If a fluid coupling is fitted in order to provide a soft start for the conveyor, its aluminium casing would be put under massive centrifugal loads, sufficient to make the whole thing explode like a bomb, spreading shrapnel and hot oil everywhere.
To prevent such a catastrophic occurrence, another Renold division - Renold Clutches & Couplings - can supply the SH sprag clutch holdback, which is normally positioned on the end of the conveyor headshaft. If the drive fails or is stopped when the conveyor is loaded this device instantaneously prevents any runback, thanks to the clutch’s high quality sprag elements being in constant contact at all times with the inner and outer races of the holdback clutch element.
Renold SH sprag clutch holdbacks are suitable for applications such as inclined conveyors in mining, quarrying and aggregates, materials handling and on apron feeders in mining applications. The high quality components ensure long unit lifetime and low operating costs.
Able to accommodate large bores, of up to 20in (500mm), the SH series offers high torque capacity within a compact design, while the dimensionally interchangeable one-piece central torque arm is designed for ease of replacement.
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