15 minutes rated Motor is suitable for
Right Answer is:
Light duty cranes
SOLUTION
Classification of Cranes
Cranes for foundries, steelworks, and power stations generally require creep speeds on hoist motion for accurate load spotting. Cranes for material handling plants should be designed for higher operating speeds and duty cycles than any general workshop cranes. For steelworks, cranes must be selected to operate round the clock with higher operating speeds and low creep speed.
The classification of various types of cranes is mainly based on the following factors:
(i) Nature of the work it has to perform, e.g. handling of hot ladles, for transport of ingots, for the handling of raw materials, etc.
(ii) The duty factor: This is the time it has to work compared to the total working period of the shop and frequency of starting the crane. In a steel plant, they may be divided into 4 groups:
- Light duty cranes (15% duty factor), e.g. cranes for compressor plant, refrigeration plant, power plant, service building light warehouses, Light duty cranes where service requirements are infrequent. light duties cranes work for (1,000 hr/year) i.e 2.75 hours per day. Here the 15% duty cycle means the signal is on 60% of the time but off 40% of the time. If the duty cycle is rated for 15 minutes, it means the motor can be safely operated for 15 minutes before it must be shut down to be allowed to cool.
- Medium duty cranes (25% duty factor), e.g. handling materials in auxiliary and repair shops, machine shops, and general industrial use both indoor and outdoor application.
- Heavy-duty cranes (40% duty factor): The cranes of foundries, forging shops, cast houses, production line cranes.
- Continuous duty cranes (above 40% duty factor): These are for the major part of the production line: cranes for bulk material handling, soaking pit cranes, charging cranes.