The characteristics of the drive for crane hoisting and lowering is
Right Answer is:
All of the above
Hoists are a means of transporting materials or passengers vertically by means of a moving level platform. Materials hoist come in basically two forms i.e static and mobile models. The hoist can be driven by petrol, diesel, or electric motor and can be of a cantilever or enclosed variety.
A crane is the type of machine mainly used for handling heavy loads in different industry branches: metallurgy, paper, and cement industry. By the construction, cranes are divided into overhead and gantry cranes
Torque and power requirements for crane and Hoist drives
Speed control is an essential feature in crane drives. It is required for allowing soft starting and stopping of the travel motions for enabling its correct positioning of the load. For the lifting drive the speed control in a wide speed range, from zero to nominal values, is required. Because of the precision when raising and lowering the load, the possibility of working at a very low speed and hold a load at the standstill is required, without using the mechanical brakes.
- Acceleration and retardation are more important than speed in most cases,
- Creep speeds are required for accurate positioning,
- There can be no overhauling, so braking is not a major problem; it is however required in both directions.
Hoist motion: This is required to lift and put loads without damage. The characteristics of this motion therefore are:
- A low hoist speed with an empty hook,
- The low lowering speed at all loads,
- High speeds in both directions – speed greater with light loads than with heavy loads,
- Steady braking torque in lowering direction,
- Power lowering is required for the light hook
- Emergency braking is required for the possible failure of mechanical brakes.
The nature of the duty cycle and the conditions under which it has to work form the basis of the requirements of the crane. In steel plants, the cranes to be used must satisfy the following:
- The crane must suitable for strenuous duty.
- The crane must be suitable for withstanding high ambient temperatures.
- It must be suitable for withstanding the conducting dust-laden atmosphere.
- It must give trouble-free operation.
- It must be provided with more rigid and additional safety measures.