LEEA Foundation Certificate (Global) Course Workbook PDF

LEEA – Foundation Certificate (Global) – Course Workbook There were a few variations along the way. The original BS grade 40 was used at a factor of safety of 5:1 and because of that, it could either be in the normalised condition or hardened and tempered. To make the distinction the mark 04 was us...

LEEA – Foundation Certificate (Global) – Course Workbook There were a few variations along the way. The original BS grade 40 was used at a factor of safety of 5:1 and because of that, it could either be in the normalised condition or hardened and tempered. To make the distinction the mark 04 was used for normalised and 40 for hardened and tempered. Later the factor of safety was reduced to 4:1 so it had to be hardened and tempered and again to make the distinction, grade M was used. So all three have the same breaking strength but the heat treatment and rating varied. Once all grades of chain were hardened and tempered, the letters and numbers became interchangeable and expressed as M(4), S(6) and T(8). However, when we started the European standards programme in the late 1980s, we agreed to use the number grades for medium tolerance chain for chain slings and the letter grades for fine tolerance chain for hoists. At the same time, we started using the terms medium tolerance and fine tolerance. Previously chain for hoists was termed calibrated to make the distinction but in practice, all machine-made chain is calibrated as part of the manufacturing process, the distinction is one of accuracy. When applied to components other than chain, the grades are not defined strictly by stress levels, rather by being compatible with the same grade of chain so whilst the maximum stress levels may be of a similar order, it is the manufacturer who decides on most of the dimensions (within the confines of the dimensional envelope) and therefore the stress level. Hence ‘Kuplex’ can use the same components for grades 8 and 10. Notes: 31 Page © LEEA Academy - FOU (Global) Workbook v 1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Course Workbook Basic Machines Types of Machines There are two categories when it comes to machines, these are: Simple machines Compound machines Simple machines A lever is an object that acts as a pivot point that multiplies the force that can be applied to another object. The wheel and axle is a rod attached to a wheel that can multiply an applied force. A pulley consists of a wheel on an axle with a rope running over the wheel. Pulleys are used to change the direction of an applied force. The inclined plane is a flat surface with ends at different heights. Inclined planes reduce the amount of force required to move an object. Wedges are triangular-shaped and used to separate, hold or lift an object. Screws are cylindrical shafts with grooves that pass through or move other objects through rotational force. Compound machines A collection of simple machines working together. Compound machines are the most common type of machine and do more complex work than individual simple machines. They perform more work and therefore offer a greater advantage than simple machines alone. Compound machines may consist of various and innumerable combinations of simple machines. For example, a mobile crane’s mechanisms would include levers (the jib/mast), pulleys (sheaves), screw (limit switch), wheel and axle (drive train wheels) etc. Lifting equipment is manufactured using multiple combinations of basic machines in order to carry out a particular task. Notes: 32 Page © LEEA Academy - FOU (Global) Workbook v 1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Course Workbook Weight and Force (F) Although not strictly true, we will consider weight and force to be equal and expressed in the same units. In a lifting machine, a small weight or force is used to lift a larger weight or force. We call the force required to do the lifting, the effort. We call the force being lifted, the load. Simple machines provide mechanical advantages. They make our work easier by increasing the amount of work done with a certain amount of effort, or by decreasing the amount of effort required to do the same work. Question: Using the image above, calculate the turning point. (Select one answer) □ 0.5Nm □ 10.2Nm □ 2Nm □ 9.08Nm Notes: 33 Page © LEEA Academy - FOU (Global) Workbook v 1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Course Workbook Mechanical Advantage (MA) When the force and effort in a machine are equal, a state of equilibrium exists. Any subsequent increase in effort will move the load. In more complicated machines, e.g. a hand chain hoist, the effort required to move a load is usually much smaller than the load. Their relationship is known as the Mechanical Advantage. The mechanical advantage allows the device to perform the taskfor which it was designed. Consider… Consider the Mechanical Advantage of a simple winch. By increasing the lines of cable between the winch and the vehicle being pulled, we can pull more than the working load limit of the winch. Example… ▪ 1t WLL winch and 1 line of cable = 1t Max. tow weight ▪ 1t WLL winch and 2 lines of cable = 2t Max. tow weight ▪ 1t WLL winch and 3 lines of cable = 3t Max. tow weight NOTE: this illustration does not consider friction. A chain hoist is operated by hand. An operator will pull down on one of the chain loops on one side of the chain. This will turn a pulley mechanism inside the chain hoist housing. When this pulley turns, it lifts up the end of the other chain, which usually has a hook on the end. By pulling down on one chain, the manual hoist is actually able to increase the mechanical work that is being done. This is caused by the gear ratio inside the manual chain hoist. Typically, the force exerted on the hand chain can be multiplied by the gearbox as much as 30 times. 34 Page © LEEA Academy - FOU (Global) Workbook v 1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Course Workbook Having established that the relationship between of the load (W) to the effort (P) is the mechanical advantage, this is represented by a simple formula: So if we know the load that is to be lifted and the amount of effort that has to be applied to the machine in order to do so, we can calculate the mechanical advantage. Note: we do not use any particular units of measure for a mechanical advantage as this is a simple mathematical ratio. Question: Select from the options below which one is the correct Mechanical Advantage calculation if the load is 300kg and the Effort is 50kg. (Select one answer) □4 □6 □3 Velocity Ratio (VR) Are machines can move large loads by applying small amounts of force. Unfortunately, as we all know, you never get something for nothing and in order to move the load a short distance, it is necessary for the effort to travel a greater distance. Having established that the relationship between these movements is called the Velocity Ratio, this can be represented by the following formula: Velocity Ratio = Distance moved by effort ÷ Distance moved by load (or DME ÷ DML) Notes: 35 Page © LEEA Academy - FOU (Global) Workbook v 1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Course Workbook Question: Select from the options below which one is the correct Velocity Ratio calculation if the distance moved by effort is 75m and the distance by load is 3m (Select one answer) □ 25 □ 30 □ 10 Efficiency (EFF) Are machines are designed to waste as little energy as possible. This means that as much of the input energy as possible should be transferred into useful energy stores. Efficiency indicates how good a machine is in transferring energy input to useful energy output. A very inefficient device will waste most of its input energy. A very efficient device will waste very little of its input energy. The following formula can be used to establish the relationship between the Mechanical Advantage and Velocity Ratio to establish the Efficiency of a machine: Efficiency = MA ÷ VR x 100% Question: Using your answers above, what is the Efficiency calculation? (Select one answer) □ 16 □ 24 □ 12 Notes: 36 Page © LEEA Academy - FOU (Global) Workbook v 1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Course Workbook ▪ ▪ ▪ Polymers and Natural Fibres Polymers There are two types of polymers: Natural Polymers: Such as shellac, wool, silk and natural rubber have been used for centuries. A variety of other natural polymers exist, such as cellulose, which is the main constituent of wood and paper. Synthetic Polymers: Are materials such as synthetic rubber, resin, nylon, polyvinyl chloride (PVC or vinyl), polypropylene, polyamide, polyester, high modulus polyethylene (HMPE) and others. Notes: 37 Page © LEEA Academy - FOU (Global) Workbook v 1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Course Workbook Polymer products are lightweight which makes them ideal for moving around from job to job. The properties of polymers can be altered by introducing additives such as plasticisers and stabilisers. In the lifting equipment industry, polymers are commonly used for roundslings and flat webbing slings, ropes, gears, bushes and sheaves. Nylon compounds, often in association with latex and rubber, are also used to manufacture wear seals, pressure seals and oil seals. Natural Fibres Fibre rope slings are the traditional form of textile sling whose origins are recorded in the earliest history of lifting equipment. Although their use has declined in recent years in favour of the newer forms of textile slings, i.e. flat woven webbing slings and roundslings, they may still be found in general use throughout the industry. Natural fibres are produced from grasses and other leaves that are spun to form ropes. Fibre rope slings are produced from cut lengths of rope which are then hand spliced. Common natural fibres for rope slings include manila, hemp and sisal. Notes: 38 Page © LEEA Academy - FOU (Global) Workbook v 1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Course Workbook Heat Treatment There are various reasons for carrying out heat treatment. Heat treatment is the process of heating and cooling metals to change their microstructure and to create the physical and mechanical characteristics that make metals desirable for specific applications. The temperatures metals are heated to, and the rate of cooling after heat treatment, attribute to a metal’s final properties and can: ▪ Increase the strength (hardening a material) ▪ Decrease the strength (soften a material) ▪ Complete or surface hardening of a material ▪ Toughen a material by tempering ▪ Relieve stresses in a material ▪ Anneal a material after cold working to soften it, or to refine its grain structure Although each of these processes bring about different results in metal, all of them involve three basic stages: heating, soaking, and cooling. These 3 stages are used accordingly by the manufacturers to gain their desired properties. Hardening and Tempering as being the most common form of Heat Treatment. Heat treatment of steel is normally a two-step process. 1) Hardening 2) Tempering Heat treatment can therefore change properties of materials, such as Toughness Brittleness Ductility 39 Hardness Page © LEEA Academy - FOU (Global) Workbook v 1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Course Workbook Stress and Strain It is unlikely that you will need to carry out stress calculations as a lifting equipment examiner. However, it is important to understand their effects on equipment being examined and tested. - LEEA Stress There are forces acting on lifting equipment when it is under loaded conditions. Strength is therefore an important mechanical property of any lifting equipment. It is related to how much force can be applied to the equipment before it eventually breaks. The load (force) applied to the equipment and its cross-sectional area is the resultant stress in the material. It is the stress which controls whether a material will fail. The stress is found by dividing the (load) force by the cross-sectional area. In simple terms, when calculating stress, a force is usually spread over a given area resulting in a pressure of magnitude force unit ÷ area unit. Strain When a load (force) is applied to lifting equipment, it will respond by changing its shape. This is known as strain. Take an elastic band for example. If you hold it at its ends in a relaxed state, it will show no signsof extension, but as you apply an opposing force to the elastic band between your hands, it willbegin to stretch. This extension of the elastic band is known as strain. 40 Page © LEEA Academy - FOU (Global) Workbook v 1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Course Workbook The Tensile Test The tensile test, also known as the tension test, is probably the most fundamental type of mechanical test you can perform on material. ▪ The Tensile Test This tensile test reveals a great amount of information about the material and quantifies the important properties of the material. ▪ Why is this test important? Lifting equipment examiners need to know these properties and how they are determined in order to understand various material specifications and relate these to their suitability for making lifting equipment. A standard size specimen of the material to be tested is machined to a predetermined size. The cross-section of the specimen is usually round, square or rectangular. For metals, a piece of sufficient thickness can be obtained so that it can be easily machined - a round specimen is commonly used. For sheet and plate stock, a flat specimen is usually used. From the tensile test, we can use the results to determine how a material will react under tensile loading. Typical properties revealed include the elastic limit, yield point, ultimate tensile strength and elongation/reduction in the cross-sectional area of the material under test. A tensile load is applied to the specimen until it fractures. During the test, the load required to make a certain elongation on the material is recorded. A load/elongation curve is plotted by a recorder so that the tensile behaviour of the material can be obtained. 41 Page © LEEA Academy - FOU (Global) Workbook v 1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Course Workbook From a tensile test, a stress/strain, or sometimes known as a load/extension curve can be produced. Five definite points can be seen as the line of the graph: A. Limit of Proportionality B. Elastic Limit C. Yield Point D. Tensile Strength E. Ultimate Breaking Stress Question: What is meant by the term, ‘local necking’? (Select one answer) □ a. When a material under tensile load exceeds its maximum tensile strength, a reduction in material cross-sectional occurs which is known as local necking. □ b. When a material reaches its elastic limit, the measured reduction in cross-sectional area is called the local necking yield. Notes: 42 Page © LEEA Academy - FOU (Global) Workbook v 1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Course Workbook Tensile Test Definitions: There are some key phrases/terms used regarding tensile test – see below: Limit of Initially as the force is applied the stress and strain are proportional Proportionality until point A is reached. This is the point at which the graph is no longer a straight line. This point is known as the Limit of Proportionality. The Elastic Limit This is the point up to which the material remains elastic. Within the elastic limit, the test piece will return to its original dimensions if the load is removed. (With mild steel this point practically corresponds with the Limit of Proportionality. This is not generally true of other materials or for materials that have been overstrained). When this point has been exceeded the extension is permanent and is referred to as Plastic Deformation. Yield Point Slightly above the elastic limit, the Yield Point is reached when a sudden permanent extension, B to C, occurs without any increase in load. (Sometimes there is a slight drop in the load, due to the extension, giving an upper and lower yield point). Tensile Strength The Tensile Strength is reached at this point. When this is passed the cross-sectional area becomes noticeably smaller and ‘necking’ occurs. This is the point of maximum load. Ultimate Breaking This is the actual breaking load where an increase in stress is obtained Stress with a reduction in load. Although the value is smaller than the tensile strength this gives a false impression of what occurred. From points D to E the section of the test piece considerably reduces as it ‘necks’ - thereby effectively increasing the stress. However, as the graph records the stress as load over the original cross-sectional area, it appears to decrease. There is a clear difference between a ductile material and a brittle material under the same tensile test. A brittle test piece withstands deformation until the stress applied is at a relatively high level. It then yields, deforms and fractures. A ductile test piece withstands deformation but yields at a lower level of stress than the brittle test piece. This is because the ductile material is not as strong as the brittle material. The ductile material then continues to elongate, reaching its maximum tensile stress and eventually fracturing. 43 Page © LEEA Academy - FOU (Global) Workbook v 1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Course Workbook Shear, Tension and Compression Loading conditions: lifting equipment may be subjected to single or multiple types of stress: Single shear – forces acting across a material o Example: A lifting lug on a waste skip being lifted Double shear – forces acting across a material in two areas o Example: A shackle pin under load Compression – a pushing force o Example: A jack body under load Tension – a pulling force o Example: A chain sling under load 44 Page © LEEA Academy - FOU (Global) Workbook v 1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Course Workbook Torsion – a twisting force o Example: A rotating gearbox shaft driving a hoisting appliance Notes: 45 Page © LEEA Academy - FOU (Global) Workbook v 1.6 Jan 2024