In the early days of power-driven quarrying, the choice of gearbox was limited, with worm-driven ones usually the favoured option.
Although considered reliable, these gearboxes have high running costs, with efficiency ranging from 85 per cent to as low as 60 per cent. They also require precise mounting with correct alignment to work effectively, making them labour-intensive. The redeeming feature of the worm drive gearbox is its load-holding capacity, which is especially helpful when using any sort of elevating conveyor.
The introduction of helical gears in transmissions such as the shaft mounted speed reducer (SMSR) raised the standard on running costs, with efficiencies as high as 95 per cent becoming possible.
This hollow shaft gearbox is mounted directly on the conveyor head drum shaft, and is driven by an electric motor and vee-belt, thus eliminating the need for complex mounting structures to be custom-made. The belt alignment for such gearboxes operates on only one plane, which makes installation comparatively quick and easy. A torque arm, allowing for belt tension adjustment, holds the gearbox, and as long as you get your calculations correct, a simple change of pulleys enables economical adjustment of the final speed.
Unsurprisingly, this style of gearbox has been well received in the quarry industry, yet it has also produced new costs. The fretting and corrosion of shaft mounted gearboxes often make it impossible to remove a gearbox from its shaft without causing damage, and complete replacement is sometimes required.
A solution to this problem has come in the form of a tapered mounting bush that can lock the gearbox to the shaft with a key, ensuring 100 per cent drive. This advanced mounting bush not only makes removal and refitment a breeze, but also offers users greater economies by accommodating a range of shaft sizes on every gearbox. Such flexibility is a major benefit for standardisation and cost reduction, especially when running older, imperial-sized equipment in the metric age.
Helical level gearboxes
SMSR gearboxes, however, do have one drawback. Significant occupational health and safety risks and costs can exist with vee-belts, as correct and ongoing adjustment is necessary and belt guards need to be installed to prevent injury. Such guards can be clumsy and costly to manufacture, and failure to correctly refit them after servicing can occur.
A way to avoid these difficulties is by using the bevel helical gearbox.
This innovative gearbox uses no vee-belt, as the electric motor is directly coupled. Its right angle design allows for a more compact fitment that can run alongside the conveyor while still coupled to the conveyor head drum via a hollow shaft attachment.
Bevel helical gearboxes are very efficient, achieving in excess of 94 per cent power transfer, although their fixed ratio does make initial gearbox selection important, because they do not offer the same flexibility as the SMSR.
Anyone worried that the exact ratio they require may not be available will be pleased to know that speed correction can be made with the use of an electrical inverter or variable frequency drive.
Selecting the correct gearbox for your application can be a little tricky, however, as a clever user will want to take into account such factors as speed, service requirements and even thermal capacities, as most gearboxes now come from Europe and are made to operate at lower ambient temperatures than our tough Australian conditions.
In many ways, the bevel helical gearbox can be seen as the culmination of good design, efficiency and safety. It is one of the best gearboxes on the market, but there is still that old problem of fretting and corrosion that plagued the first SMSRs with parallel hollow shaft fitment.
Enter the Quicklock bevel helical gearbox with a tapered keyed mounting bush, available from Select Transmissions and Motors Australia. Designed specifically for the needs of the modern quarry market, it combines all the benefits of a mounting bush with the features of bevel helical gears and an externally mounted backstop, making it possibly the most flexible drive on the market.
Offering high efficiency, easy maintenance and reliable service, it is truly a top quality gearbox for the extractive industries.
So what is the right choice for gearing up production?
Operators need the gearbox that best fits their conditions and meets the high standards of efficiency, reliability, flexibility and quality. With all the choices now available, they should contact a specialist who can assess their specific situation and provide the most effective solution to keep production moving.
Source: HMA Group/Select Transmissions and Motors Australia