Hoists and Cranes for Hot Molten Metal Service
CRANE 1 receives many requests for hot metal hoisting applications each year. The proper selection of the hoist with proper hot metal features is vital to ensure the safety of the operator and the longevity of the equipment.
Design and special feature requirements for overhead hoists and cranes for use in hot molten metal or material applications are specified in various standards.
Among these are:
CMAA Standard 70
CMAA Standard 74
ANSI 830 Series
It is generally the responsibility of the hoist manufacture to interpretation the requirements necessary for their equipment to properly meet hot molten metal applications. That provides assurance that all components are suitable for use in this demanding environment
HOT METAL HOIST FEATURES
The specific items that often need to be addressed in order for most crane equipment to meet the standards of hot metal use are outlined below:
1. Hoist Limit Switches
A geared upper and lower limit switch shall be provided. A power circuit upper limit switch shall be provided Power Circuit Upper Limit Switch must cut the power to the entire hoist, opening up a disconnect switch.
2. Hoist Ropes
Hoist rope shall have an independent wire-rope, wire-strand, or other temperature-resistant core. Hoistrope shall have a design factor of at least 8:1 based on the nominal breaking strength of the rope andthe hoist or crane rated load. 3 Wraps of rope must remain on the drum at the lowest hook level.
3. Hoist Brakes: Each independent hoist unit shall have one of the following arrangements:
- Two holding brakes (one of which is mounted on a gear reducer shaft) plus control braking means shall be provided. Each brake shall have a torque of at least equal to a full load hoisting torque at the point that the brake is applied.
- If the hoist has a mechanical load brake or a controlled braking means that provides emergency braking in the lowering direction on loss of power, only one holding brake is required. The holding brake shall have a torque rating at least equal to 150 % of the full load hoisting torque at the point that the brake is applied.
4. Trolley Restraining Lug
Trolleys (and end trucks) shall be provided with restraining lugs to limit the drop of the trolley or hoist to one inch in the event of wheel or axle failure.
5. Bolts in Tension Restraining Means An independent restraining means shall be provided to minimize the drop of any load-supporting member held in place solely by a bolt in tension. All swivel trolleys require modification to comply with this requirement.
6. Warning Device: All power-driven travel mechanisms, trolley, and crane shall have an approved warning device (flashing warning light or audible device).
USE OF ELECTRIC CHAIN HOISTS in HOT METAL APPLICATIONS
Electric Chain Hoists are certified for Hot Metal use by some manufacturers of hoists. The use of these hoists in hot metal applications often causes unseen changes to the properties of the load chain due to the exposure to heat altering the tempering the steel chain. These changes are difficult to detect in load chain, while the effect will be easily noticeable in wire ropes due to deformation. For that reason, we recommend extreme caution in the use of chain hoist for hot metal.