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AMAZON multi-meters discounts AMAZON oscilloscope discounts Chain hoists, both manually and power operated, are a widely used type of hoisting equipment. Their simplicity, dependability, and relatively low cost have made them standard equipment in manufacturing plants, foundries, mills, refineries, repair shops, garages, and practically every phase of the construction field. This section describes the various types of chain hoists, explains their relative advantages and usual applications, and provides information on preventive maintenance, inspection, and upkeep. TYPES OF CHAIN HOISTS Manually Lever-Operated Chain Hoists (Pullers) These lightweight, portable tools can be used for pulling horizontally, vertically, or at any angle. A reversible ratchet mechanism, located in the lever, permits short-stroke operation for both tensioning or relaxing. An automatic friction-type load brake, sometimes known as a releasable ratchet, is often used to control the load and permit accurate positioning. Other types of lever-operated units utilize a ratchet and pawl-type of brake, which involves ratcheting in both directions, for load control. Lever-operated hoists are commonly available in both link and roller chain types, in capacities from 1/2 thru 15 tons. --- Spur-geared hoist. --- Puller or ratchet-level hoist with link chain. --- Multiple-reeved spur-geared hoist with link chain. --- Spur-geared single-reeved hoist with roller chain. Hand-Chain -- Manually Operated Chain Hoists These hoists are most frequently used for overhead lifting applications where the use of a powered hoist may not be practical. These would include many maintenance- or construction-type applications where a power source may not be readily available or the portability, load-spotting accuracy, or close-quarter capability of a hand-chain operated hoist may be required. There are a number of types and classes of hand-chain manually operated chain hoists available, ranging from heavy-duty, high-speed ball bearing spur-geared units, designed for heavy-duty industrial service, to much lighter-weight units with less efficient gearing and power trains designed for more infrequent service.
Heavy-duty, high-speed, spur-geared units, incorporating low-friction bearings and a Weston self-energizing disk-type load brake, typically have very high mechanical efficiency ratings, permitting operation at high speeds in the heavy-duty applications often encountered in industry. Separate hand and load chains operate over pocket wheels which are connected by a gear train and load brake. The brake is disengaged during hoisting by a one-way ratchet mechanism. To lower the load, the hand chain must be pulled continuously in the reverse direction to overcome the holding force of the brake. Modern hand-chain manually operated chain hoists utilize more compact designs and lightweight alloys to achieve much greater portability through a significant weight reduction as compared with earlier hoist models. Lower-cost, lighter-duty, spur-geared hand-chain manually operated chain hoists often incorporate gears which are not accurately machined, unlike those employed in high-speed units, and bushings are frequently used in place of low-friction bearings.
While these lighter-duty units are somewhat lower in cost, they also operate at mechanical efficiencies 30 to 40 percent lower than those required for high-speed industrial service. Further, these lighter-duty units will typically not withstand the more severe service encountered in rigorous industrial-type applications. Worm gearing is sometimes used in hoisting applications to provide an inexpensive power train incorporating a high ratio in a relatively small space. These types of power trains are approximately 60 percent less efficient than high-speed spur gearing, however. This is especially true if a high enough gear ratio is utilized to make the power train self-locking. A differential hoist is generally the simplest and least expensive chain hoist. It has an efficiency rating approximately 30 percent of that of a high-speed spur-geared unit. A dual-pocketed upper sheave and grooved single lower sheave are connected by an endless reeved chain for lifting and operating. The mechanical advantage is gained by the two upper sheaves differing by one link pocket so that more chain passes over the larger wheel than the smaller one to produce a net raising or lowering of the load. The difference in diameter of these two sheaves results in such a small turning moment on this combination that normal friction holds the load in the suspended position at any point, and this serves as the hoist braking means. An effort must be applied to either raise or lower the load hook. There are a number of variations to the hook-suspended hand-chain manually operated chain hoist, which are sometimes encountered, as follows: Low-headroom army-type trolley hoists are spur-geared units with an integral trolley to provide greatly reduced headroom for close-quarter operation. --- illustrates a low-headroom hoist with plain trolley. Hand-geared trolleys are also available. Twin-hook hoists are spur-geared hoists with two hooks which are operated simultaneously by one hand chain and are adapted to the handling of bulky objects which require two-point suspension. A twin hoist will lift a total load equal to the capacity marked on the hoist. The load often can be all on one hook or the other or divided any way between the two hooks. Typical extensions range from 3 to 16 ft. Extended-handwheel hoists have a handwheel extending from a spur-geared hoist and are designed for service which requires that the hand chain and operator be at a distance from the load being raised. Typical extensions range from 3 to 16 ft. Often, chain hoists are used to lift a load, the weight of which may be totally unknown. Because of this fact, many chain hoists are available with overload limiting devices designed to prevent the lifting of dangerous overloads. --- Differential hoist. --- Screw-geared hoist. ---Twin-hook hoist with link chain. --- Low-headroom trolley hoist with link chain. --- Extended-handwheel hoist with link chain. --- Lightweight electric chain hoist with push-button control and low headroom trolley. --- Electric chain hoist with roller chain and pendant rope control. --- Lightweight electric chain hoist with push-button control and hook suspension. Powered Chain Hoists Powered chain hoists are typically used for repetitive higher-speed lifting, as often encountered in production applications. Most powered hoists utilized electrical power, although quite a number of chain hoists are air-powered. Both types of powered units are equipped with either push-button or pendant rope controls. Both link-type chain and roller chain are utilized in powered hoists. Link chain has the advantage of being flexible in all directions, whereas roller chain is flexible in only one plane. Also, powered hoists are normally equipped with travel limit switches to restrict upper and lower extremes of travel, thus preventing the load hook from jamming against the bottom of the hoist or the chain from running out of the hoist. Electric chain hoists are available for use with most types of current. Many small-capacity models are equipped with single-phase 115-V motors, which can be plugged into a standard receptacle which receives a standard three-prong plug. Some manufacturers offer three-phase dual-voltage single-speed models as well as three-phase single-voltage two-speed models. Most single-speed dual-voltage units are reconnectible for operation on either 230 or 460 V, 60-Hz power. Two-speed units are generally built to operate on one specific three-phase voltage (i.e., 230 V, 460 V, etc.). Also, other voltages such as 575 V, three-phase, and 230 V, single-phase, as well as a large number of 50-Hz export voltages, are also readily accommodated. Powered hoists are generally available with a wide variety of suspensions and accessories. These units may be equipped with swivel or rigid hook, lug, plain trolley, hand-geared trolley, or powered trolley suspensions. Chain containers are often used to collect the unloaded loose end of the load chain at the hoist. A wide variety of power-distribution systems are also available to allow for travel of powered hoists on monorail or bridge crane applications. Often, powered hoist controls are integrated with trolley travel, bridge travel, mainline power disconnect systems, powered accessories, etc. Powered chain hoists, in capacities from 1/8 to 15 tons, are widely used throughout industry because of their convenience, relatively low cost, and durability. SELECTION OF CHAIN HOISTS In selecting either manually operated or powered hoists, certain considerations are basic and common to both types. --- provides a graphic comparison of the types of manual hoists used today for overhead lifting, each offering a varied range of mechanical efficiency and price and filling the need of a particular condition. --- illustrates the important performance and physical characteristics of both manually operated and powered hoists which must be considered in selecting a unit for a given use and specific installation. --- Comparison of hand hoists. --- Hoist installation check diagram. --- Load-chain gauging diagram. --- Hoist parts to be inspected and serviced. Intended use, safety, labor savings, portability, initial cost, and upkeep are all important factors to be considered in properly selecting a hoist for an application. With high labor costs for both operation and maintenance, low initial cost may not be the true measure of hoist value for a given application. Hoist capacity, in terms of the heaviest load to be lifted, is of prime importance. Headroom, height of lift, location and height of hand chain or push-button/pendant controls, lifting speed on powered hoists, type of suspension, travel speed on powered trolleys, hoist and trolley clearances, etc., are all factors affecting decisions on specific installations. ---is a self-explanatory diagram and checklist which will be found useful in selecting either a manually operated or powered hoist. Unusual atmospheric conditions, whether indoors or outdoors, may require sealed enclosures, weatherproof covers, or special protective coatings on the housings, chain, and other fittings. Under normal atmospheric conditions encountered in typical indoor applications, standard hoists are generally satisfactory. PREVENTIVE MAINTENANCE For all aspects of chain-hoist preventive maintenance, we suggest that the recommendations contained in ANSI/ASME Standards B30.16 and B30.21 be followed in detail. These ANSI/ASME standards rep resent an industry consensus published by the American Society of Mechanical Engineers, 22 Law Drive, P.O. Box 2300, Fairfield, NJ 07007-2300, which is nationally recognized and in wide use today. DESIGN/PERFORMANCE For additional detailed information on various types of chain hoists, the following standards are referenced: ANSI/ASME HST 1, Electric Chain Hoists ANSI/ASME HST 2, Overhead Manual Hoists ANSI/ASME HST 3, Manual Lever Chain Hoists ANSI/ASME HST 5, Air Chain Hoists Prev: Cranes: Overhead and Gantry |