LEEA Foundation Certificate (Global) Workbook PDF

LEEA – Foundation Certificate (Global) – Workbook Electric Chain and Wire Rope Hoists Modern electric power-operated hoists are normally fitted with low voltage control which is derived internall...

LEEA – Foundation Certificate (Global) – Workbook Electric Chain and Wire Rope Hoists Modern electric power-operated hoists are normally fitted with low voltage control which is derived internally within the unit by a transformer. This is usually in the range of 24 to 50 volts AC or DC and is often known as ‘Extra Low Voltage’. Older hoists and special purpose hoists may not have LV control. It should also be noted that it is common in many European countries to use mains voltage control. The two principal lifting media used with all power-operated hoists are: Short link round steel chain Steel wire rope HMPE and textile belt materials In hoists that use chain, the chain passes over a pocketed wheel with the slack side of the chain hanging loose. A collecting box may be used to house the slack chain, but as this sits below the body of the hoist it restricts the height that certain loads may be lifted. In hoists that use wire rope, the wire rope passes on and off a drum upon which it is stored. The range of lift is limited by the amount of wire rope that the drum can accommodate. Pneumatic Hoists Pneumatic power-operated hoists tend to be more limited in use than electric power- operated hoists, mainly due to the problems associated with the provision of a suitable air supply. However, they offer many advantages over electrically operated equipment and as a result are widely used in industries where the air is provided for other purposes or where the safety aspects associated with air- operated equipment are a major consideration. 91 Page © LEEA Academy – FOU (Global) Workbook v1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Workbook Hydraulic Hoists The hydraulic hoist provides smooth and accurate lifting and lowering operations and is very quiet in operation. An electric motor is used to run a hydraulic motor. The hydraulic motor is a mechanical actuator that converts hydraulic pressure and flows into torque, or rotation, which in turn moves the hoist. The advantages of this form of the machine are that the electric motor does not have to be physically near the fluid drive, so the system is virtually noiseless. They are regularly used in intrinsically safe areas, as is the pneumatic hoist. Electrical Controls Other control options, such as radio or infra- red controls, enable remote or central control. They are useful in areas where direct access may not be possible. Multi-point controls, usually wall-mounted, enable hoists to be controlled from several positions, which is useful in applications such as raising loads through several floor levels. Such arrangements must be suitably interlocked to prevent more than one control from operating at a time. A further essential requirement with this arrangement is the provision of emergency stop buttons to override all control positions until manually reset. Various examples of Electrical Controls 92 Page © LEEA Academy – FOU (Global) Workbook v1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Workbook Supporting Structures for Hoists and Light Crane Systems Built-in Runways These are usually runway beams supported by existing building structures. The ‘simply supported’ and ‘encastred’ type runways are most common. Suspended Runways These runways can also be suspended from suitable roof members or beams built into the building structure. 93 Page © LEEA Academy – FOU (Global) Workbook v1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Workbook Free Standing Runways Where no existing suitable supports are available, then free-standing runway structures are common. Special track systems (Light Crane Profiles) Special track sections are quite versatile and are often supplied in kits, sometimes referred to as light crane systems, which can be assembled in various configurations, such as simple runways, runways with switches, turntables, etc, and even low capacity bridge cranes. 94 Page © LEEA Academy – FOU (Global) Workbook v1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Workbook Switches and Turntables The use of runway switches and turntables allow the lifting appliance to be transferred from one runway system to another. Notes: 95 Page © LEEA Academy – FOU (Global) Workbook v1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Workbook Crane Systems Slewing Jib Cranes Slewing jib cranes are widely used in industry in conjunction with manual or power operated lifting appliances where a permanent facility is required to perform both lifting and limited moving operations. Typical examples of their use being over workbenches, in fitting and maintenance shops, over machine tools and in loading and unloading bays. They offer a wide area of floor coverage within the slewing radius of the jib arm and are ideal where full overhead travelling crane coverage may be either impracticable or uneconomic. They are often used to supplement overhead travelling cranes. Slewing jib cranes are often designed, supplied and tested without lifting appliances and it must be realised that a slewing jib arm becomes an effective crane only when fitted with a hoist, hoist and trolley or similar lifting appliance. Wall or Column Mounted: The jib arm, king post and bracing are assembled as a single unit. They may be either over - braced or underbraced in design dependent on the intended use and the location of the installation. Top and bottom bearing brackets fit onto the king post and these, in turn, are fixed to the supporting structure. Free Standing: The jib arm and supporting column are assembled as a single unit which includes all mountings and bracing. They may be either over-braced or underbraced in design dependent on the intended use and the location of the installation. The supporting column is usually manufactured from a square box section, fabricated sections or tube dependent on the required angle of slew. The angle of slew and intended use will also affect the design of the king post and mounting structure. Free standing jibs are available with a wide variety of slewing angles. They may have a full 360° angle of slew, allowing for continuous rotation if a tubular column is used, or be limited to 270° angle of slew if a square box or similar section column is used. 96 Page © LEEA Academy – FOU (Global) Workbook v1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Workbook Mobile Gantries: a mobile gantry is normally used in areas where it is not cost-effective to have a permanent installation. A mobile gantry is a free-standing structure comprising a runway beam and two supports or A-frames assembled in a goalpost-like configuration. The supports are usually mounted on wheels or castors to enable the structure to be relocated by man-power only; they may however be mounted on free-standing feet requiring the structure to be dismantled for transportation. Goalpost Gantry: This consists of a runway beam, often in the form of a manufacturer’s branded track section, with single column supports. Lateral stability is provided by a base member on which the column is mounted. This design is limited to light loads, usually up to 500kg, and light - duty applications. ‘A’ Frame Gantry: this is the most common type of mobile gantry. It consists of a runway beam, usually of standard rolled steel section, with supports in the form of an ‘A’. Lateral stability is given to the structure by the shape of the supports. This design is available in all capacities, usually up to 5 tonnes. 97 Page © LEEA Academy – FOU (Global) Workbook v1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Workbook Adjustable Height Gantry To provide limited variations to the erected height of the runway, an adjustable height gantry has telescopic supports enabling the runway to be raised or lowered to suit differing site conditions. This facility is not intended for use under load but is to allow for varying lifting height requirements only. This design is available in all capacities, usually up to 5 tonnes. Foldaway Gantry Designed for easy dismantling and storage. They are intended for applications where regular dismantling and transportation is necessary or where the usage is such that long periods of storage occur. This design is usually limited to loads of up to 2 tonnes. 98 Page © LEEA Academy – FOU (Global) Workbook v1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Workbook Self-Erecting Gantry Designed with the provision of hand winching mechanisms that allow the structure to be assembled horizontally on the floor. Operation of the winches pulls the side members of the ‘A-frame supports together until the gantry is in its operating position. Additional locking structural components are then inserted making the structure rigid. This design is usually available in higher capacities from 2 tonnes upward. Crane Supporting Structures Tracks Tracks will generally be constructed as ‘top (Gantries) running’ or ‘under-slung’. Top running gantries are supported in various ways. Crane Tracks: Generally manufactured from standard constructional sections. For top running cranes a rail section is usually welded to the top flange of the track beam. For underslung cranes, the crane will run on the bottom flanges of the beam. Dependant on the crane type the track will either be suspending from a cross beam known as a carrier beam or fitted directly to the tops of the supporting columns. Crane or Track Rails: Depending on the duty, the rail will have a profile similar to one of those shown below, but more often than not for light duties, this will be a square bar. These rails are normally fixed by intermittent welding and if not welded with the rail securely clamped to the beam weld, cracking will occur in service. Bridge and Gantry Cranes: Bridge and gantry cranes provide a means of lifting and transporting loads over the area covered by the crane. Some bridge and gantry cranes may use manual effort to lift, lower and move the load. However, it is more usual for some, or more typically all, of the crane’s motions to be electrically powered. There are four main types: ▪ Top running bridge crane ▪ Under-slung bridge crane ▪ Semi-portal gantry crane 99 ▪ Portal gantry crane Page © LEEA Academy – FOU (Global) Workbook v1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Workbook Top Running Bridge Crane Distinguished by running on the top of rails which are part of the crane supporting structure. Under-Slung Bridge Crane Distinguished by running on the bottom flanges of the cranes tracks. Because of the under-slung arrangement, the bridge of this type of crane can have a cantilever at one or both ends. Two or more such cranes running on parallel sets of tracks can be fitted with latching mechanisms to facilitate the transfer of loads from one crane to another. Portal Bridge Crane: Distinguished by running on a low-level track, usually at ground level, with the bridge girder or girders supported on legs. The bridge of this type of crane can have a cantilever at one or both ends. Semi-Portal Bridge Crane: A combination of a top running bridge crane and a portal bridge crane. The bridge of this type of crane can have a cantilever at the end of the span supported by the legs. 100 Page © LEEA Academy – FOU (Global) Workbook v1.6 Jan 2024