Hand Operated Chain Hoists PDF

LEEA – Foundation Certificate (Global) – Workbook Hand Operated Chain Hoists Hand Operated Chain Hoists Manual chain hoists are very popular and are found in wide use throughout the world. This is because they can be used very effectively in the following applications where: ▪ A perma...

LEEA – Foundation Certificate (Global) – Workbook Hand Operated Chain Hoists Hand Operated Chain Hoists Manual chain hoists are very popular and are found in wide use throughout the world. This is because they can be used very effectively in the following applications where: ▪ A permanent installation for infrequent use is required ▪ A temporary installation for erection or maintenance purposes is required ▪ Precise location of the load is required ▪ A suitable power supply is not available The advances in material and manufacturing technologies have enabled much, smaller, lighter and more efficient chain hoists to be produced. Chain hoists use a pocketed wheel into which the load chain must fit, but freely enter and leave. The drive to the pocketed wheel is via a hand chain and screw brake mechanism. The free end of the load chain shall be fitted with a chain end stop to prevent it from passing through completely. All modern hand-operated hoists are fitted with an automatic brake which, when functioning correctly, is capable of arresting and sustaining the load at any position. Students will visit this subject in further detail in the LEEA Manual Lifting Machines Diploma. 81 Page © LEEA Academy – FOU (Global) Workbook v1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Workbook Combined types are usually combined with a purpose-made travelling trolley, although a direct connection to the supporting structure may also be possible. The connection between the hoist and the trolley or structure is usually rigid. Lower Capacity Hoists The lower capacity hoists (e.g. 500kg, 1t) lift the load on a single fall of load chain. Higher Capacity Hoists Higher capacity hoists may either be of similar design but with a larger frame or may utilise two or more falls of load chain. The very high capacity hoists may utilise a combination of a larger frame and multiple falls of load chain and may even have two or more frames linked by a yoke. Notes: 82 Page © LEEA Academy – FOU (Global) Workbook v1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Workbook Hand Operated Lever Hoists Hand-operated lever hoists are widely used since they can perform both lifting and pulling applications. The ability of the lever hoist to operate in any attitude makes the lever hoist a versatile tool, particularly for rigging. It can be used as an adjustable sling leg to enable a load to be balanced or for line adjustment when positioning - to give just two examples. Two basic types are available: one using fine tolerance (calibrated) short link steel chain, the other using roller chain. Advances in material and manufacturing technologies have enabled much, smaller, lighter and more efficient lever hoists to be produced. Lever hoists use a pocketed wheel into which the load chain must fit, but freely enter and leave. The drive to the pocketed wheel is via a hand chain and screw brake mechanism. The lever hoist will also have a change-over lever with a neutral position which allows the user to set the chain to the correct length (free-wheel facility). The free end of the load chain shall be fitted with a chain end stop to prevent it from passing through completely. Notes: 83 Page © LEEA Academy – FOU (Global) Workbook v1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Workbook Lifting and Pulling Machines - using a gripping action on the wire rope Commonly referred to as ‘jaw’ or ‘creeper’ winches in different regions, these winches are widely used throughout the industry for both permanent applications and temporary or rigging applications. They are used as pulling machines as well as lifting, which may permit a lower factor of safety and giving a higher working load limit when the winch is used for pulling. 84 Page © LEEA Academy – FOU (Global) Workbook v1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Workbook All jaw winches operate by the same general principle. Effort to the rope in a jaw winch is provided by two levers, which act via a lever and cam system on keys. Each set of jaws is made up of a top and bottom jaw which are brought together (clamped), or separated (unclamped), by half-moon-shaped keys actuated by levers known as jaw links. The wire rope supplied for use with a jaw winch should be considered as integral a part of the mechanism as a load chain of a chain hoist. Some ropes, which appear to be of the correct size, and which are accepted by the winch, may not be suitable. The efficiency and safety of the friction grip of the winch’s jaws depend entirely on the rope being the right diameter and constructed to withstand the crushing force of the jaws. With a rope diameter that is too small, the jaws will not grip the rope sufficiently. With a rope diameter that is too large, the rope may become stuck in the winch, putting the winch out of operation. It is therefore essential that only ropes approved by the manufacturer are used with the specified jaw winch. One end of the load rope is plain tapered and fused to allow entry into the machine. The other end has a terminal fitting for attachment to the load. 85 Page © LEEA Academy – FOU (Global) Workbook v1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Workbook Hydraulic Jacks Hydraulic jack bodies are commonly manufactured from aluminium, steel or cast iron. The material used affects the design, size, self-weight and capacity of the jack. Hydraulic jacks use oil and the body of the jack acts as a reservoir for the oil. When the jack is operated, the oil is passed through a system of non-return valves to the underneath of the lifting ram. When more oil is delivered through each stroke of the handle, the lifting ram is forced out of the chamber lifting the load. The load is lowered by opening a valve which allows the oil to return to the reservoir by the load pushing down onto the lifting ram. 86 Page © LEEA Academy – FOU (Global) Workbook v1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Workbook Mechanical Jacks There are several types of mechanical jack available. The ‘ratchet’, ‘screw’ and ‘journal’ jack most commonly found in service: 87 Page © LEEA Academy – FOU (Global) Workbook v1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Workbook Ratchet jacks The body of the jack contains a pair of pawls that engage in a rack. Operation of the jack causes the pawls to raise or lower the rack, which is fitted with a lifting head and toe, providing alternative positions for supporting the load. The full rated load may be supported on the head or toe. During the jacking operation, the operative effectively carries the load via the operating lever. At the end of each stroke, the load is sustained by a pawl. Screw jacks Consist of a single hollow casting with a square form female thread into which fits a male screwed shank. A swivel head is fitted to the shank to support the load. Directly turning the screwed shank causes it to raise or lower. Journal jacks Consists of a cast body that houses a bevel gear and screw mechanism. The operation of a ratchet lever turns the gears that drive a screwed shank. This in turn drives a running nut that is captive in the lifting journal and therefore causes the journal to raise or lower. Notes: 88 Page © LEEA Academy – FOU (Global) Workbook v1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Workbook Crane Forks and ‘C’ Hooks Crane forks and C-hooks are suspended from crane hooks but lift loads directly without the need for other lifting accessories. Whilst C-hooks are usually designed to lift a specific load, crane forks are of a more general nature and are usually supplied as a standard product. Although very different in design, crane forks and C-hooks have much in common, which enables them to be considered together. Differences will be noted where relevant. ▪ Crank forks: These are used to lift palletised or similar loads suspended from a crane hook. ▪ C – Hooks: These are used to lift hollow loads such as pipes, paper rolls or coils of steel. Fabricated from a profiled plate or rolled beam sections. 89 Page © LEEA Academy – FOU (Global) Workbook v1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Workbook Powered Lifting Machines (Appliances) Powered lifting machines are widely used in industry, often as part of a larger lifting installation, e.g. with an overhead runway, jib crane or overhead travelling crane, or where a permanent lifting facility is required. They may also be used for fixed position lifting applications or where a temporary powered lifting facility is required. Powered lifting machines are available with electric or pneumatic operation, but the most common in general use at the present time are electrically operated. Powered lifting machines are ideal for heavier or repetitive lifting applications as they offer the following advantages over manually operated chain hoists: ▪ Speed of operation ▪ Less fatigue for operatives, particularly on long lifts ▪ Operatives may be remote/away from the load Notes: 90 Page © LEEA Academy – FOU (Global) Workbook v1.6 Jan 2024