Trolleys

Trolleys are an important mechanism for bridge cranes. They are used to lift and transport cargos along the span.

Special aspects related to crane trolleys

In standard configuration, crane trolleys are frames on wheels. In addition, this structure can be completed with the following:

• cargo height and weight limiters that switch off the movement of a trolley at its maximum lifting point or in case of increased weight by 1/10 above the limit;
• a rule that regulates the movement along the span;
• buffers that support the device in case limit switches are out of order.

Electric drives or winches are used for the operation of trolleys. The manual version designed only for lightweight bridge cranes is rarely used. Rails are mounted for wheels, at the upper chord of a beam; the lower position can also be used in the double-girder crane.

Application

Carriers related to single-girder cranes are usually arranged according to the console type. Side rollers are used to hold this carrier on the beam. Rail ways intended for such carriers and their running wheels are installed above the main beam.

As far as the magnetic type is concerned, there are some slight differences. It includes a cable drum that is in contact with a lifting mechanism. When the magnet is lifted, it is possible to take a cable extending towards it.

A pair of drums firmly tied with an intermediate shaft is installed on the trolley of the same crane having the traverse beam non-rigidly fastened. Their position on the frame is determined by that of the traverse beam with respect to the bridge, through length and breadth. At the same time, the mechanism of movement of the crane trolley is installed from below, and the lifting and turning one – from above.

Characteristics

In most cases, crane trolley frames are made by welding (sometimes casting) from different kinds of rolled sections or steel sheets. Mechanisms are fastened onto pads mounted into the frame. Their contact surfaces should be treated very carefully. It is very important to properly prepare the surface of pads to which the movement mechanism's draw-out boxes are to be attached. If these requirements are not met, running wheels wear out and become unserviceable very quickly.

Load trolleys of maximum load capacity are equipped with a modular frame. Such trolleys are very massive, so ladders are provided for their maintenance.

How to choose trolleys

When you choose a crane trolley, consider the following:

• crane parameters: its type, lifting capacity, operation mode;
• a required trolley base and track;
• characteristics of railways;
• working conditions (in open areas or under roof);
• all mentioned limitations;
• design (standard, fire- and explosion-proof, for nuclear power plants).

If crane load trolleys are to be operated in contact with hazardous substances, each such device must be equipped with two brakes. It should be borne in mind that all of these factors determine not only the price of trolleys, but also their quality, reliability and safety.

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