This article takes an in depth look at electric hoists.
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Electric hoists are devices designed for lifting, lowering, and moving materials and products. Powered by an electric motor and equipped with a controller to manage lifting settings, they are ideal for handling heavy loads. These hoists are particularly useful when conveyors and cranes are impractical or unsuitable for the task. Other hoist types include pneumatic (air) hoists, hydraulic hoists, and manual hoists, each distinguished by its driving mechanism.
Electric hoists are installed overhead to lift objects and need a power supply, making them most suitable for indoor environments. They are commonly used in settings like warehouses, automotive repair shops, machine shops, and manufacturing facilities. Designed to endure hazardous and high-temperature conditions, some electric hoists are also built for cleanroom applications, handling items like food and pharmaceuticals. Adhering to safety procedures is crucial when operating electric hoists across all environments.
By automating lifting and positioning tasks, electric hoists enhance operational efficiency and reduce manual effort, promoting better physical ergonomics in the workplace. They offer quicker operation compared to other hoist types and are more cost-effective and space-efficient than conveyor systems.
Manual chain hoists concentrate a low force with high travel input into a high force but low travel output. This is the cause of their slow operation. They utilize multiple gears with different number teeth inside their lifting mechanism, which is activated by pulling the hand chain several times. This principle is responsible for accomplishing the task of lifting a heavy object.
A manual chain hoist is installed above the object to be lifted, either by hooking or mounting it on a strong, stable frame. It operates with two chains: the hand chain, which is pulled manually, and the load chain, typically made of a robust material like steel, which actually lifts the load. The hand chain is considerably longer than the load chain. To begin, a grab hook is attached to the object. The operator, positioned safely away from the load, pulls the hand chain repeatedly. Each pull of the hand chain rotates the cog, which drives the driveshaft. The driveshaft turns a series of gears with varying numbers of teeth, concentrating the force from smaller, faster-moving gears to larger, slower-moving ones. This mechanical advantage turns the sprocket, which pulls the load chain and the attached object upwards as the chain shortens around the sprocket.
The ratchet mechanism at the back of the cog functions as the braking system for the hoist. The clutch engages with the ratchet’s teeth, preventing the cog from slipping and ensuring the load stays in place. When the cog turns in reverse, the clutch disengages from the ratchet, allowing the hoist to lower the load safely.
Manual chain hoists have largely been superseded by electric hoists, which require less manual effort for lifting tasks. Electric hoists achieve this by using either a chain or a wire rope to lift loads.
Electric chain hoists utilize a load chain for lifting. The lifting process is powered by an electric motor that converts electrical energy into mechanical energy to move the load. This motor is enclosed in a heat-dissipating shell, usually made from aluminum, and features a cooling fan to manage heat during prolonged operation, making it suitable for high-temperature environments.
To lift an object, an electric chain hoist is mounted above it on a sturdy frame. A hook attached to the end of the load chain secures the object. The lifting action begins when the operator activates the hoist motor. This motor includes a brake that controls the motor’s operation or holds the load in place by applying the necessary torque. During lifting, the brake continuously releases power to manage the vertical movement of the load.
The motor produces torque that is transmitted through a series of gears in the gearbox. These gears concentrate force to rotate the chain wheel, which moves the load. As the object is lifted, the load chain is collected in a chain bag, typically made from durable materials like nylon or plastic, to prevent tangling and ensure smooth operation. Regular lubrication of the load chain is necessary for optimal performance and safety.
Electric chain hoists are equipped with a limit switch that automatically halts the motor if the load exceeds the hoist's capacity. They can also move loads along a trolley system, and the controller allows the operator to adjust load positioning and engage emergency stops as needed.
These hoists are known for their low maintenance requirements and simpler installation compared to electric wire rope hoists. They are versatile and cost-effective, suitable for a range of environments.
Electric wire rope hoists lift loads utilizing a wire rope as the lifting medium. Wire ropes consist of a core that runs through the center of the wire rope and several strands of wire intertwined around the core. This construction forms a higher-strength composite rope. Wire ropes intended for hoisting applications are typically made from carbon steel, stainless steel, Monel, and bronze; these materials have high resistance to wear, fatigue, abrasion, and corrosion.
Electric wire rope hoists, similar to electric chain hoists, feature a hoist motor equipped with a braking system. They use a series of gears within a gearbox to amplify the torque from the motor. This amplified force is transferred to a spline shaft, which drives the winding drum. As the wire rope is drawn in to lift the load, it wraps around the winding drum. A rope guide ensures that the wire rope is properly aligned within the helical grooves on the drum's surface, preventing tangling. The wire rope also requires regular lubrication.
Electric wire rope hoists come with similar positioning controls and safety features as electric chain hoists.
These hoists are designed to handle heavier loads and achieve greater lift heights, making them suitable for heavy-duty and rapid lifting tasks. They can support and lift loads for extended periods, although, in some cases, the wire ropes may not be as durable as load chains. Additionally, electric wire rope hoists tend to be more expensive than their chain counterparts.
Winches and hoists are designed to lift or move heavy loads safely and easily. Though they have similar functions, they are engineered differently to perform different tasks. Unlike hoists that lift loads vertically, winches are designed to move loads horizontally over inclines and flat surfaces.
Winches and hoists share similar constructions, both designed to wind cable to create tension for moving heavy objects. Like hoists, winches can be operated manually or electrically and feature a steel drum wrapped with cable.
Winches are equipped with a gear braking system that secures the load when the cable is not being pulled, which is particularly useful on inclines. Unlike hoists, which lift loads vertically using a wire rope or chain attached to a sling or load mechanism, winches pull or drag loads horizontally.
The hook on a winch attaches directly to the load. To connect it, the operator disengages the locking mechanism, pulls out the cable, and hooks it onto the load. Often, the hook may go through a section of the load, with the cable acting as a sling. This method is not permitted with hoists.
When operating a winch, the motor gradually pulls the cable to achieve the desired tension. Adhering to the winch and cable's load capacity is crucial to avoid cable snaps or breaks, which can be hazardous to anyone nearby.
People often confuse winches and hoists, sometimes using the terms interchangeably. The main difference lies in their functions: a hoist lifts vertically, while a winch pulls horizontally. This distinction is also reflected in their respective components.
Winches can also serve as lifting devices for lighter loads by using pulleys. For floor-mounted winches, the cable is threaded through a pulley to achieve vertical lifts. Other winches can be mounted on beams or walls and connected to a pulley system, and can be operated either electrically or manually.
High-capacity winches are commonly used in shipyards, with capacities ranging from 10 or 15 kN to over 200 kN. These winches often come with various drum configurations to suit different needs.
Electric hoists can be categorized based on the suspension method used to position them above the load:
Hook-mounted hoists feature a top hook that allows them to be temporarily attached to a trolley or beam clamp. This is the most basic suspension method. The top hook typically includes a safety latch to prevent the load from swaying or unintentionally falling off.
Lug-mounted hoists are attached by bolting their top to a wall or overhead beam, securing them firmly in place for lifting operations. While they are fixed in their location, they can sometimes be adjusted or moved to different positions if needed.
Trolleys are attached to electric hoists to enable them to move along the length of a beam, allowing for precise positioning and transportation of the hoist from one location to another.
Push-type trolleys, also known as plain trolleys, allow electric hoists to move horizontally by manually pushing or pulling the hoist along the beam. This type of trolley is less accurate in positioning and requires significant effort, whether the hoist is loaded or unloaded.
Geared trolleys are operated using a hand chain, which must be pulled repeatedly to move the hoist along the beam. This manual operation allows for controlled movement but requires physical effort from the operator.
Electric travel trolleys are equipped with an electric motor that moves the hoist automatically over a specified distance. The travel direction and speed are controlled through the electric hoist’s control system, providing high precision and ease of use with minimal effort.
The bridge that supports and allows the trolley to move is constructed from beams. It is essential that both the bridge and its structural frame are robust enough to handle the combined weight of the electric hoist and the load. The specifications and dimensions of both the beam and the electric hoist trolley must be properly matched to ensure smooth operation. Common beam types used in hoisting systems include I-beams, wide-flange beams, and patented track beams.
Specifications such as the rated capacity, working load limit, and duty cycles are crucial for engineers and operators to choose an electric hoist that meets the specific lifting requirements.
The rated capacity represents the maximum weight a hoist can handle before it risks failure. This capacity depends on the motor's power, the rigidity of the hoist assembly, and the strength of the load chain or wire rope.
The working load limit is the maximum weight a hoist can safely lift. It is calculated by applying a safety factor to the minimum breaking load. This safety factor considers the hoist’s construction, potential risks to operators, and the operating environment.
The duty cycle indicates the amount of time a hoist can operate under normal conditions before needing a rest period. For example, if a hoist is used for one minute and then turned off for 99 minutes, the duty cycle is 1/100 or 1%. Operating a hoist beyond its duty cycle can lead to accelerated wear and reduced service life.
Lifting speed and travel speed are crucial specifications that impact productivity and turnaround times. Here’s a closer look at these factors:
Lifting speed is the rate at which the load is raised or lowered. Electric hoists can have either a fixed or adjustable lifting speed, controlled via the hoist's controller. Slower speeds are used for delicate, heavy loads or precise positioning, while faster speeds are suitable for rapid production and transportation. Moderate speeds are typically used for loading and unloading.
Travel speed refers to the rate at which the trolley moves along the beam to transport the load. Electric hoists can have a single travel speed or an adjustable speed, managed through the hoist controller.
Electric hoists can be employed as standalone units or integrated into structural frames and tracks as part of a comprehensive lifting system. The various types of lifting systems include:
Engine hoists, or engine cranes, are used to assist the workers in the installation and maintenance of engines of automobiles. They are designed to lift the engine under the automobile hood. Their electric hoists are mounted on top of the rigid and portable structural frame. The structural frame has wheels installed at its base to easily maneuver the hoist over the automobile, as well as to transport it around the machine shop. Its portability makes it suitable for outdoor applications. The structural frame of some engine hoists is foldable, so it can save space when it is stored.
The installation of overhead cranes is planned during the early stages of a building‘s construction, as they require a much greater amount of structural support. Overhead cranes lift the heaviest loads at the highest lifting heights in an enclosed facility.
In overhead cranes, there are two parallel end trucks mounted on runway beams . The runway beams are also responsible for supporting the entire overhead crane and the load. The end trucks travel along the rails of the runway beams together with the bridge and the electric hoist. The electric hoist travels across the length of the bridge. The bridge can either be a single girder or a double girder bridge. A single girder bridge crane has one trolley that moves across a single girder beam, while the double girder bridge crane has two trolleys that move the electric hoist synchronously across two girder beams. The bridge and the end trucks are positioned perpendicularly with each other. This arrangement enables the electric hoist to move left and right (via end trucks), and forward and backward (via the bridge). Lifting and positioning parameters are controlled remotely.
A jib crane has a lifting fixture that primarily consists of two large beams constructed to form a cantilever. The mast, or pillar, is the vertical beam of the fixture that supports the reach. The reach, or boom, is the horizontal beam of the fixture wherein the electric hoist travels to position the load. There are three types of jib cranes:
Floor-mounted jib cranes are self-supporting structures with a large mast fixed to the floor. These cranes are designed to support the loads of primary cranes and come in various types and designs to enhance lifting capabilities. For instance, drop-mounted cantilever jib cranes feature an adjustable boom that allows for modifications in lifting height. Many floor-mounted jib cranes are capable of rotating up to 360°.
In some contexts, floor-mounted jib cranes are also known as base-mounted hoists. They perform a similar function, being positioned on the floor for vertical lifting. These hoists operate along a load line that moves through a heel and crown block at ground level or the rooster head of a gin pole.
The primary purpose of a base-mounted hoist is to lift and lower materials. These hoists are equipped with a rope drum, gearbox, motor, brake, and control panel. To ensure durability and strength, base-mounted hoists are constructed from steel, typically bolted or welded together, with load capacities ranging from half a ton to ten tons or more.
Wall-mounted jib cranes are attached to a wall or column that must be structurally sound to support them. Their range of rotation is typically limited to 200°. There are two main types of wall-mounted jib cranes: cantilever wall-mounted jib cranes, which provide maximum clearance both above and below the boom and apply minimal force to the supporting column, and tie-rod supported wall-mounted jib cranes, which use a wall bracket and a tie rod for support. With no additional support structure beneath the boom, these cranes allow the electric hoist to travel the full length of the reach.
Articulated jib cranes feature a mast and two boom arms connected by joints that allow them to flex or fold. These cranes can be installed on the floor, ceiling, wall, or a bridge crane. The primary boom arm, which supports the load, can rotate up to 360°, while the rotation of the secondary boom arm varies based on the crane’s mounting location. Articulated jib cranes offer flexible load movement in multiple directions.
Gantry cranes are versatile lifting devices featuring a horizontal overhead bridge supported by legs. The electric hoist moves along the bridge’s length. Mobility is achieved by equipping the legs with wheels or by having them run along a track. Unlike bridge cranes and jib cranes, gantry cranes do not rely on the building’s structure for support and can be used outdoors. They are also capable of operating beneath bridge cranes to handle some of their load.
Monorail cranes are specialized overhead cranes used in production facilities and machine shops for repetitive lifting and positioning tasks. They are designed to transport loads within confined spaces. The electric hoist trolley moves along the outer flange of a single I-beam that is mounted on the building's ceiling structure.
Workstation cranes offer an ergonomic solution for lifting and moving objects within a compact workspace. They resemble overhead cranes but are supported by free-standing columns rather than being integrated into the building's structure. With a smaller frame and limited lifting heights, workstation cranes are a cost-effective choice for light to medium-duty applications.
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