Presentation on theme: "AND ELEMENTS OF MACHINES"— Presentation transcript:
1 AND ELEMENTS OF MACHINES UNIT 10SIMPLE MACHINESAND ELEMENTS OF MACHINESTECNOLOGIA INDUSTRIAL 1 BATXILLERAT
2 Mechanical systemsA machine is a system that is formed of one or more mechanical subsystems withmoving parts, and sometimes by other subsystems (electrical, electronic, optical, etc.), and that is designed to carry out a given task normally concerned with carryingout work or transforming energy.A mechanism is a set of mechanical elements that carries out guiding andtransmission functions related to the movements and forces within a machine.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.Mechanics
3 Statics of machines (I) 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.Equilibrium of a rigid solidA 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.Moment of a force with respect to a point:
4 Statics of machines (II) Couple of forcesTwo 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 (Γ) or simply couple.Free body diagramThe free body diagram is a drawing of the body being studied isolated from the rest of the bodies with which it is in contact..
5 Simple machines (I) Lever Inclined plane A lever is a rigid bar that rests on a point of support or fulcrum.Lever rule:Inclined planeδ: rolling coefficient in m.F: force to be applied in the centre of the wheel in N.N: normal equivalent to the weight (Gr) of the wheel in N.rr: radius of the wheel in m.
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.
7 Simple machines (III) Differential pulleys Inclined plane 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.Inclined plane
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
9 Elements of machines (I) FixingsRivetRivetingRiveting with a through rivet
10 Elements of machines (II) Forms of rivetingOverlap jointJoint with cover plateJoint with two cover platesBolted jointsNut, washer and bolt
11 Elements of machines (III) The threadPitch.Handedness: right-handed, left-handed.Form: rounded thread, trapezoidal thread, etc.Characteristics of a threadPitchRight-handed and left-handed threadsDifferent thread geometries
12 Elements of machines (IV) Bolts, nuts and washersBolts 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 2–3 mm.Types of boltsGraphical representation of a bolt, a nut and their coupling
13 Calculation of jointsSimple jointsComposite joints
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:Transversal pinLatchExtruded axisLongitudinal pinsTapered pin
15 Tension spring or traction spring Springs and elastic jointsAny elements made of elastic material are called springs.Classification of springs:Tension spring or traction springTorsion springLeaf springCompression springSpiral spring
16 Types of rolling elements 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 bearingTypes of rolling elements
17 Bearings (II) Types of bearings Rigid ball bearing Bearing with angular contactCylindrical roller bearingTapered roller bearingNeedle bearing
18 Lubricants Types of bearing: A lubricant is a substance capable of reducing the friction that exists betweenthe elements in contact with one another in a machine when the move with respect to one another.Reduces the friction between the moving parts.Acts as a coolant.Supports the aggression of possible contaminants that mix with the lubricant.Characteristics of a lubricantHydrodynamic lubrication: consists of maintaining a film of lubricant between the parts so that these are effectively floating.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.Lubrication