End-carriages should be viewed holistically: As a key sub-assembly in any and all overhead cranes, customers should question the wisdom of attempting their own end-carriage assembly using individually sourced wheel-blocks, because wheel alignment is critical, and this is a specialised process.
The advice comes from Condra, a company well known for delivering durable, robust sub-assemblies to rival crane manufacturers.
“Putting it simply, they come to us because we last longer,” quipped a company spokesman.
End-carriages are the “feet” at either end of the overhead crane. They support the girders and hoists, and move them along the rails. However, wheel wear can cause excessive and escalating end-carriage maintenance costs, the result of one or both of two factors: mis-alignment of the wheels at each end of the end-carriage, and/or distortion of the rails caused by heat.
The spokesman cautioned that wheel alignment within the end-carriage should not be confused with alignment of the end-carriages at either end of the girder, which is a much simpler process that most manufacturers would be able to carry out.
It is to avoid misalignment within the end-carriage – the end-carriage wheels themselves – that Condra recommends sourcing the end-carriage as a completed sub-assembly from a single company.
“Wheel alignment is a very specialised and delicate process,” the spokesman explained. “Get it wrong, and the steel-on-steel nature of the crane’s wheeled movement will result in rapid wheel wear and increased maintenance costs.”
The second cause of wheel wear, rail distortion, is more difficult to counter because it is caused by the very high temperatures that accumulate in the upper levels of all factories, where the rails are located.
Although periodic wheel replacement is inevitable because of rail distortion, Condra has minimised its cost through careful design of the wheel-block, fixing the wheels in position by means of a simplified bolt arrangement that allows quick and easy removal for exchange. Stocks of service exchange units, held either on site or by Condra according to customer preference, minimise downtime.
From the customer’s perspective, ordering an end-carriage from Condra as a completed assembly – aligned, tested and ready to work – is a simple process.
The design office needs only to know the load and how fast this load has to move. Armed with this data, Condra will supply a recommended configuration of wheel, motor, gearbox and brake for the wheel-blocks, a fully designed end-carriage recommendation, and a recommended rail. Should the rail not be available for any reason, Condra will adjust the wheel diameter and, if necessary, the motor and gearbox to suit.
“So, just tell us what you want to move and how fast you want to move it, and Condra will come up with the solution,” said the spokesman, explaining that the design process, simplified from the customer’s side, nevertheless involves for the design office very careful end-carriage design and component selection.
“Some 20 000 design combinations are possible,” explained the spokesman.
“Wheels, for example, come in ten different off-the-shelf diameters from 63mm to 630mm, each offered with the flange on either side, or flangeless, and in widths from 30mm to 125mm to suit the rail. There are also different motor powers and mounting arrangements for the wheel-blocks, and the overall end-carriage varies in length depending on the customer’s girder arrangement,” the spokesman explained.
“What we have done is to simplify as far as possible what is actually quite a complex process, to make the customer’s life easier.”
Condra generally uses wheels of larger diameter than its competitors, to reduce loading and decrease rolling resistance. The result is longer component lifespan and lower overall lifetime cost.
“With our design, it is not necessary to change the end-carriage wheels every two years,” explained the spokesman. “They last a lot longer.”
Condra’s end-carriages are among several component assemblies offered to crane manufacturers worldwide. Hoists, crabs, bottom blocks, cable-loop systems and enclosed conductor systems are also available.
Hoists are supplied with capacities of up to 500 tons.
All are manufactured to customer specification for final assembly, making unnecessary the need to transact with multiple suppliers. A twelve-month guarantee is standard.