Before you use that shiny new electric hoist, consider this. Hoists that are not equipped with variable speed controls can be hazardous to your health and the health of your molten metal pump. Recently, I have heard a range of complaints regarding poor speed control with electric hoists. In most cases, the speed is to too fast and placement control is difficult or “jerky”.
When introducing a pump into a well of molten metal, you must have precise control of the pump position to preheat the pump a few cm above the melt. As the pump enters the melt, a smooth slow motion is needed to prevent splashing and reduce thermal shock. Introducing a pump into the melt requires half a dozen carefully controlled steps to prevent thermal shock and position the mounting points of the pump. Slow smooth motion is needed to reduce splashing of molten metal and reduce stresses on the pump.
When a pump is immersed in molten metal, it is generally buoyant. As a pump is lifted from the melt, it will be stressed by it’s own weight for the first time since being immersed. Latent thermal damage from lowering a pump into the melt too fast may not become a problem until the pump is lifted above the melt. Fast or abrupt hoist movements could result in a structural failure of the pump over the melt.
- Manual hoists offer a good deal of control when raising and lowering a pump, but the lack of remote control results in working with hot chains.
- Air chain hoists are a good compromise between benefits of a powered hoist and maintaining precision speed and placement control.
- Electric chain hoists with variable speed controls are available, but low cost units lack the desired control.
- Remote control pendants (available for both air and electric hoists) are highly desirable so that the operator can stand a safe distance from the pump well.
- A trolley mounted hoist allows the pump to be guided to a service area and also allows the hoist to be parked away from the furnace to reduce thermal exposure to extend hoist life.
Alway follow your company’s safety rules. Molten metal, heavy pumps, and power hoists present a range of hazards that must be taken seriously.