On mining sites, there is a need for rubber-tyred low-loaders to move large items of equipment from one part of the site to another. This is particularly the case for crawler-mounted equipment, where excessive undercarriage wear can occur during extended travel. Such items of equipment can weigh in excess of 300 tonnes.
To date, many of the low loaders used to transport such equipment have been supported on a multiplicity of tyres small enough in diameter to fit beneath the platform. It is quite common to use 32 wheels, arranged in four rows of eight wheels each. A complex system of load-equalisation apparatus connects the wheels together to ensure that the load is spread as evenly as possible over all of the wheels over a range of uneven road conditions, and brakes are provided for each wheel set.
There are a number of disadvantages associated with this approach. Firstly, the equalisation system cannot function over a sufficient range of wheel travel to accommodate severe road irregularities, resulting in tyre and suspension damage. Secondly, the spread of support over such a large area results in severe tyre scrub during cornering, again damaging tyres and suspension components. Thirdly, the large number of small brakes (typically 16) used leads to problems of uniform application, and these brakes are inherently unsuited for continuous retardation on downgrades, as they overheat quickly.
These shortcomings may be overcome by utilising single axle assemblies from large mining trucks in place of the multiple-axle designs currently in use. Tyre-scrub, and its attendant high maintenance costs for both tyres and suspension systems, is greatly reduced. However, the tyres from these machines, which are typically up to 4 metres in diameter, are too large to fit beneath a load platform with a reasonable loading height.
If they are installed outboard of the load platform, the vehicle becomes very wide, and cannot negotiate normal mine roads easily. If they are placed behind the load platform, it becomes impossible to load equipment over the rear of the load platform. While it is possible to load some types of equipment from the side, this is not feasible for long loads such as overburden drills.
To overcome these problems CMP Engineers has designed a patented swing wheel arrangement whereby standard off highway truck wheel assemblies are connected to the outer rear corners of the low loader via hydraulically actuated swinging arms for movement between a travel position behind the load platform and a loading position substantially outboard of the load platform. The swing axis is inclined so that the wheels swing upwards; clear of the ground as well as outwards.
This allows the load platform to be lowered all the way to the ground after the wheels have been swung outwards to facilitate easy loading. Jacks are included to raise the rear wheels clear of the ground before the wheel assemblies are moved into the loading position.
The use of large off highway wheels also permits the use of large enclosed oil-cooled disc brakes with spring applied emergency brakes. Such systems are designed to meet the requirements of Australian Standard 2958, providing safe and reliable fade-free braking and retardation in accordance with the requirements of this standard. Retardation on the trailer axles allows such low-loaders to descend long grades safely with full loads on board.
The SW300 has proved to be an outstanding success, and feedback from operators has been particularly supportive. It has reached 15,000 hours of operation without major problems giving significant grounds for confidence that the operational side has been suitably considered.
Based on the above principles, CMP Engineers has developed designs for low-loaders in excess of 450 tonnes in capacity. All designs are fully-engineered and utilise finite-element analysis techniques to identify areas of high stress. Castings have been used in many of these areas such as the swing arms, to produce fatigue-resistant structures.
We also have developed designs for converting existing multiple-axle low-loaders to large-tyred designs, and we would be happy to discuss with you any requirements for custom designs or modifications.