Date: 10/28/2019
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In this article, we detail the difference between cranes and hoists, what the components are and how they work. Understanding the basics will help you better communicate with your crane builder and ensure that you order a system that best suits your application needs. Ready to get started? Consult our Crane Designer today!
What is an overhead crane?
A crane is a complex machine that lifts, lowers and moves heavy or bulky loads. Cranes are equipped with components that provide the crane’s multi-directional mobility. A combination of the hoist, trolley and bridge motions provide full coverage of your factory floor.
Figure 1
What is a Hoist?
A hoist is a machine that performs a single task very well: lifting and lowering a load on a vertical plane (Figure 1, Motion 3). Hoists are situated on the primary horizontal beam of the crane, called the bridge girder. The hoist, when connected to the trolley (Figure 1, Motion 2), moves back and forth across the bridge girder. Chain hoists are excellent at lifting loads below 5 tons with little maintenance required, while wire rope hoists are the optimal choice for 5 tons and above. Single-reeved hoists use a single piece of rope on the rope drum, while double-reeved hoists provide true vertical lift through the use of two ropes on a single drum. With wider diameter rope drums, minimum hook drift, or lateral movement of the hook, on a single-reeved hoist can be achieved.
What is a Trolley?
The trolley is the mechanism that moves the hoist along the bridge girder of a crane. The hoist is moved horizontally along the top or underside of the bridge girder to position it above a load (Figure 1, Motion 2). There are three types of trolleys: low headroom, normal headroom and double girder trolley.
What is a bridge?
Cranes rely on end trucks to transport the bridge (hoist, trolley and girder beams) along the runway rail (Figure 1, Motion 1). The bridge motion adds the third leg of the multi-directional mobility to the crane, giving full hook coverage over the range of your building.
Crane electrification: How does a crane run?
The festoon is the wiring and support system that delivers power to a trolley and hoist across the bridge. Power is collected from the runway busbar and carried into the main bridge panel, which powers all the crane’s electronics. From there, festoon cables carry power to the hoist panel and the bridge drives, which run the hoist, trolley and bridge drive. For maximum productivity and safety, most operators rely on a pendant or radio to control the movement of the crane.
Customization: How do you choose the right crane components?
From the overall crane package down to the individual components, the equipment you select should be compatible with your unique building layout. To make the most of custom features and options, it’s helpful to understand the terms of measurement behind individual crane parts.
Span: The distance between the center point of the runway beams tells you the span, or the width, of the entire crane.
Trolley Gauge: In a double girder crane, the trolley gauge dimension is the distance from the center of one trolley rail to the center of the other trolley rail.
Headroom: The measured distance between the saddle of the hook and the bottom of the trolley wheels when the hook is raised to its upper limit is called the headroom. Low headroom hoists, like the SX low headroom hoist, provide maximum space efficiency when there is limited lifting distance. The headroom is also referred to as the C dimension.
R&M Materials Handling offers a broad portfolio of hoists and crane components with an extensive line of customizable features and components relied upon by crane technicians the world over. Use our distributor locator to find a local resource or contact us today to speak with one of our crane experts.