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UNIT 10 SIMPLE MACHINES AND ELEMENTS OF MACHINES TECNOLOGIA INDUSTRIAL 1 BATXILLERAT Slide 2 Mechanical systems A machine is a system that is formed of one or more mechanical subsystems with moving parts, and sometimes by other subsystems (electrical, electronic, optical, etc.), and that is designed to carry out a given task normally concerned with carrying out work or transforming energy. A mechanism is a set of mechanical elements that carries out guiding and transmission functions related to the movements and forces within a machine. Mechanics Statics: the analysis of aspects related to the equilibrium of applied forces. Kinematics: studies the equilibrium of applied forces. Dynamics: the analysis of forces and the consequent movements. Slide 3 Statics of machines (I) Moment of a force with respect to a point: A rigid solid is a body of a given mass in which the distance between any two points does not vary regardless of the applied forces. Equilibrium of a rigid solid Equilibrium of a material point (particle) Newton's first law: when the sum of the forces acting on a body is zero, the body remains at rest or in uniform motion in a straight line. Slide 4 Statics of machines (II) The free body diagram is a drawing of the body being studied isolated from the rest of the bodies with which it is in contact.. Free body diagram Couple of forces Two forces of parallel but opposite direction, equidistant from a point O, generate a moment about the point O called a moment of a couple of forces () or simply couple. Slide 5 : rolling coefficient in m. F: force to be applied in the centre of the wheel in N. N: normal equivalent to the weight (G r ) of the wheel in N. r r : radius of the wheel in m. Simple machines (I) Lever A lever is a rigid bar that rests on a point of support or fulcrum. Inclined plane Lever rule: Slide 6 Simple machines (II) Winch A winch consists of a horizontal cylinder whose ends rest on two pads. Two bars, in the form of handles, are attached to the ends of the cylinder, so that the cylinder can be turned, wrapping around it cord or cable from which is suspended a load. A differential winch is a variant of the winch with two concentric cylinders of different diameter so that, when a weight is being lifted, the larger cylinder rolls on the cord while the smaller cylinder rolls it off. Slide 7 Simple machines (III) Inclined plane Differential pulleys A system of differential pulleys is a machine formed by three pulleys: two fixed and concentric, of different diameters and fixed on the same axis, and one mobile. Slide 8 Simple machines (IV) Screw A thread or a screw is an inclined plane that runs up a cylindrical surface. Comparison between a screw and an inclined plane Slide 9 Elements of machines (I) Fixings Rivet RivetingRiveting with a through rivet Slide 10 Elements of machines (II) Forms of riveting Overlap joint Joint with cover plate Joint with two cover plates Bolted joints Nut, washer and bolt Slide 11 Elements of machines (III) The thread Different thread geometries Characteristics of a thread Pitch. Handedness: right-handed, left-handed. Form: rounded thread, trapezoidal thread, etc. Right-handed and left-handed threads Pitch Slide 12 Elements of machines (IV) Bolts, nuts and washers Types of bolts Bolts and nuts are used to join two parts in such a way that they can be assembled and disassembled. They must be standardised (ISO). A washer is a part, generally ring-shaped and made of mild steel, whose external diameter is greater than that of the nut by 23 mm. Graphical representation of a bolt, a nut and their coupling Slide 13 Calculation of joints Simple jointsComposite joints Slide 14 Pins Pins are pieces, generally made of steel, that fit in hollows or grooves of a given geometry made in the axis and in the hole. Pins according to the type of force: Extruded axis Latch Longitudinal pinsTapered pin Transversal pin Slide 15 Springs and elastic joints Any elements made of elastic material are called springs. Classification of springs: Compression springSpiral spring Torsion springTension spring or traction spring Leaf spring Slide 16 Bearings (I) A bearing is an intermediate element mounted between two parts of a mechanism that turn with respect to one another to ensure that the friction between them is minimal but at the same time ensuring that they remain joined. Parts of a bearing Types of rolling elements Slide 17 Bearings (II) Rigid ball bearing Bearing with angular contact Types of bearings Cylindrical roller bearing Tapered roller bearing Needle bearing Slide 18 Lubricants Types of bearing: A lubricant is a substance capable of reducing the friction that exists between the elements in contact with one another in a machine when the move with respect to one another. Characteristics of a lubricant Reduces the friction between the moving parts. Acts as a coolant. Supports the aggression of possible contaminants that mix with the lubricant. Hydrodynamic lubrication: consists of maintaining a film of lubricant between the parts so that these are effectively floating. Lubrication With oils: is used when the temperature and the speed of the elements are high. With greases: is used in the maintenance of bearings. Mineral oils. Synthetic lubricants.