UNIT 10

SIMPLE MACHINESAND ELEMENTS OF MACHINES

TECNOLOGIA INDUSTRIAL 1 BATXILLERAT

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.

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.

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

(Γ) or simply couple.

δ: 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.

Simple machines (I)

Lever

A lever is a rigid bar that rests on a point of support or fulcrum.

Inclined plane

Lever rule:

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.

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.

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

Elements of machines (I)

Fixings

Rivet

Riveting Riveting with a through rivet

Elements of machines (II)

Forms of riveting

Overlap joint Joint with cover plate

Joint with two cover plates

Bolted joints

Nut, washer and bolt

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

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 2–3 mm.

Graphical representation of a bolt, a nut and their coupling

Calculation of joints

Simple joints Composite joints

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 pins Tapered pin

Transversal pin

Springs and elastic joints

Any elements made of elastic material are called springs.

Classification of springs:

Compression spring Spiral spring

Torsion springTension spring or traction spring

Leaf spring

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

Bearings (II)

Rigid ball bearing Bearing with angular contact

Types of bearings

Cylindrical roller bearing

Tapered roller bearing

Needle bearing

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.