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Machine A machine is a physical system using Power (physics), power to apply Force, forces and control Motion, movement to perform an action. The term is commonly applied to artificial devices, such as those employing engines or motors, but also to na ...
s include both fixed and moving parts. The moving parts have controlled and constrained motions. Moving parts are machine components excluding any moving fluids, such as
fuel A fuel is any material that can be made to react with other substances so that it releases energy as thermal energy or to be used for work. The concept was originally applied solely to those materials capable of releasing chemical energy but ...
,
coolant A coolant is a substance, typically liquid, that is used to reduce or regulate the temperature of a system. An ideal coolant has high thermal capacity, low viscosity, is low-cost, non-toxic, chemically inert and neither causes nor promotes corrosio ...
or
hydraulic fluid A hydraulic fluid or hydraulic liquid is the medium by which power is transferred in hydraulic machinery. Common hydraulic fluids are based on mineral oil or water. Examples of equipment that might use hydraulic fluids are excavators and backhoe ...
. Moving parts also do not include any mechanical
lock Lock(s) may refer to: Common meanings *Lock and key, a mechanical device used to secure items of importance *Lock (water navigation), a device for boats to transit between different levels of water, as in a canal Arts and entertainment * ''Lock ...
s,
switch In electrical engineering, a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another. The most common type of ...
es, nuts and bolts,
screw cap A screw cap or closure is a common type of closure for bottles, jars, and tubes. Usage A screw closure is a mechanical device which is screwed on and off of a "finish" on a container. Either continuous threads or lugs are used. It must be engi ...
s for bottles etc. A system with no moving parts is described as " solid state".


Mechanical efficiency and wear

The amount of moving parts in a machine is a factor in its
mechanical efficiency In mechanical engineering, mechanical efficiency is a dimensionless number that measures the effectiveness of a mechanism or machine in transforming the power input to the device to power output. A machine is a mechanical linkage in which force ...
. The greater the number of moving parts, the greater the amount of energy lost to heat by
friction Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction: *Dry friction is a force that opposes the relative lateral motion of t ...
between those parts. For example, in a modern
automobile engine , there were a wide variety of propulsion systems available or potentially available for automobiles and other vehicles. Options included internal combustion engines fueled by petrol, diesel, propane, or natural gas; hybrid vehicles, plug-in h ...
, roughly 7% of the total
power Power most often refers to: * Power (physics), meaning "rate of doing work" ** Engine power, the power put out by an engine ** Electric power * Power (social and political), the ability to influence people or events ** Abusive power Power may a ...
obtained from burning the engine's fuel is lost to friction between the engine's moving parts. Conversely, the fewer the number of moving parts, the greater the efficiency. Machines with no moving parts at all can be very efficient. An
electrical transformer A transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. A varying current in any coil of the transformer produces a varying magnetic flux in the transformer's c ...
, for example, has no moving parts, and its mechanical efficiency is generally above the 90% mark. (The remaining power losses in a transformer are from other causes, including loss to electrical resistance in the copper windings and
hysteresis Hysteresis is the dependence of the state of a system on its history. For example, a magnet may have more than one possible magnetic moment in a given magnetic field, depending on how the field changed in the past. Plots of a single component of ...
loss and
eddy current Eddy currents (also called Foucault's currents) are loops of electrical current induced within conductors by a changing magnetic field in the conductor according to Faraday's law of induction or by the relative motion of a conductor in a mag ...
loss in the iron core.) Two means are used for overcoming the efficiency losses caused by friction between moving parts. First, moving parts are lubricated. Second, the moving parts of a machine are designed so that they have a small amount of contact with one another. The latter, in its turn, comprises two approaches. A machine can be reduced in size, thereby quite simply reducing the areas of the moving parts that rub against one another; and the designs of the individual components can be modified, changing their shapes and structures to reduce or avoid contact with one another. Lubrication also reduces
wear Wear is the damaging, gradual removal or deformation of material at solid surfaces. Causes of wear can be mechanical (e.g., erosion) or chemical (e.g., corrosion). The study of wear and related processes is referred to as tribology. Wear in m ...
, as does the use of suitable materials. As moving parts wear out, this can affect the precision of the machine. Designers thus have to design moving parts with this factor in mind, ensuring that if precision over the lifetime of the machine is paramount, that wear is accounted for and, if possible, minimized. (A simple example of this is the design of a simple single-wheel
wheelbarrow A wheelbarrow is a small hand-propelled vehicle, usually with just one wheel, designed to be pushed and guided by a single person using two handles at the rear, or by a sail to push the ancient wheelbarrow by wind. The term "wheelbarrow" is mad ...
. A design where the
axle An axle or axletree is a central shaft for a rotating wheel or gear. On wheeled vehicles, the axle may be fixed to the wheels, rotating with them, or fixed to the vehicle, with the wheels rotating around the axle. In the former case, bearing ...
is fixed to the barrow arms and the wheel rotates around it is prone to wear which quickly causes wobble, whereas a rotating axle that is attached to the wheel and that rotates upon bearings in the arms does not start to wobble as the axle wears through the arms.) The scientific and engineering discipline that deals with the lubrication, friction, and wear of moving parts is
tribology Tribology is the science and engineering of interacting surfaces in relative Motion (physics), motion. It includes the study and application of the principles of friction, lubrication and wear. Tribology is highly interdisciplinary, drawing on m ...
, an interdisciplinary field that encompasses materials science,
mechanical engineering Mechanical engineering is the study of physical machines that may involve force and movement. It is an engineering branch that combines engineering physics and mathematics principles with materials science, to design, analyze, manufacture, and ...
,
chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds made of atoms, molecules and ions ...
, and
mechanics Mechanics (from Ancient Greek: μηχανική, ''mēkhanikḗ'', "of machines") is the area of mathematics and physics concerned with the relationships between force, matter, and motion among physical objects. Forces applied to objects r ...
.


Failure

As mentioned, wear is a concern for moving parts in a machine. Other concerns that lead to failure include
corrosion Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engine ...
,
erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is distin ...
,
thermal stress In mechanics and thermodynamics, thermal stress is mechanical stress created by any change in temperature of a material. These stresses can lead to fracturing or plastic deformation depending on the other variables of heating, which include mater ...
and heat generation,
vibration Vibration is a mechanical phenomenon whereby oscillations occur about an equilibrium point. The word comes from Latin ''vibrationem'' ("shaking, brandishing"). The oscillations may be periodic function, periodic, such as the motion of a pendulum ...
, fatigue loading, and
cavitation Cavitation is a phenomenon in which the static pressure of a liquid reduces to below the liquid's vapour pressure, leading to the formation of small vapor-filled cavities in the liquid. When subjected to higher pressure, these cavities, cal ...
. Fatigue is related to large inertial forces, and is affected by the type of motion that a moving part has. A moving part that has a uniform rotation motion is subject to less fatigue than a moving part that oscillates back and forth. Vibration leads to failure when the ''forcing frequency'' of the machine's operation hits a
resonant frequency Resonance describes the phenomenon of increased amplitude that occurs when the frequency of an applied periodic force (or a Fourier component of it) is equal or close to a natural frequency of the system on which it acts. When an oscillatin ...
of one or more moving parts, such as rotating shafts. Designers avoid these problems by calculating the natural frequencies of the parts at design time, and altering the parts to limit or eliminate such resonance. Yet further factors that can lead to failure of moving parts include failures in the cooling and lubrication systems of a machine. One final, particular, factor related to failure of moving parts is kinetic energy. The sudden release of the kinetic energy of the moving parts of a machine causes overstress failures if a moving part is impeded in its motion by a foreign object. For example, consider a stone caught on the blades of a fan or propeller, or even the proverbial "
spanner A wrench or spanner is a tool used to provide grip and mechanical advantage in applying torque to turn objects—usually rotary fasteners, such as nuts and bolts—or keep them from turning. In the UK, Ireland, Australia, and New Zeala ...
/
monkey wrench The monkey wrench is a type of adjustable wrench, a 19th century American refinement of 18th-century English coach wrenches. It was widely used in the 19th and early 20th century. It is of interest as an antique among tool collectors and is sti ...
in the works". (See
foreign object damage In aviation and aerospace, foreign object debris (FOD), is any particle or substance, alien to an aircraft or system, which could potentially cause damage. External FOD hazards include bird strikes, hail, ice, sandstorms, ash-clouds or obje ...
for further discussion of this.)


Kinetic energy of the moving parts of a machine

The
kinetic energy In physics, the kinetic energy of an object is the energy that it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its accele ...
of a machine is the sum of the kinetic energies of its individual moving parts. A machine with moving parts can, mathematically, be treated as a connected system of bodies, whose kinetic energies are simply summed. The individual kinetic energies are determined from the kinetic energies of the moving parts'
translation Translation is the communication of the Meaning (linguistic), meaning of a #Source and target languages, source-language text by means of an Dynamic and formal equivalence, equivalent #Source and target languages, target-language text. The ...
s and
rotation Rotation, or spin, is the circular movement of an object around a '' central axis''. A two-dimensional rotating object has only one possible central axis and can rotate in either a clockwise or counterclockwise direction. A three-dimensional ...
s about their axes. The ''kinetic energy of rotation of the moving parts'' can be determined by noting that every such system of moving parts can be reduced to a collection of connected bodies rotating about an instantaneous axis, which form either a ring or a portion of an ideal ring, of radius a rotating at n
revolutions per second The cycle per second is a once-common English name for the unit of frequency now known as the hertz (Hz). The plural form was typically used, often written cycles per second, cycles/second, c.p.s., c/s, or, ambiguously, just cycles (Cy./Cyc.). The ...
. This ideal ring is known as the ''equivalent flywheel'', whose radius is the ''radius of gyration''. The
integral In mathematics Mathematics is an area of knowledge that includes the topics of numbers, formulas and related structures, shapes and the spaces in which they are contained, and quantities and their changes. These topics are represented i ...
of the squares of the radii all the portions of the ring with respect to their mass \int a^2 dm, also expressible if the ring is modelled as a collection of discrete particles as the sum of the products of those mass and the squares of their radii \sum_^n m_k \times a_k^2 is the ring's moment of inertia, denoted I. The rotational kinetic energy of the whole system of moving parts is \frac I \omega^2, where \omega is the
angular velocity In physics, angular velocity or rotational velocity ( or ), also known as angular frequency vector,(UP1) is a pseudovector representation of how fast the angular position or orientation of an object changes with time (i.e. how quickly an objec ...
of the moving parts about the same axis as the moment of inertia. The ''kinetic energy of translation'' of the moving parts is \frac m v^2, where m is the total mass and v is the
magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...
of the
velocity Velocity is the directional speed of an object in motion as an indication of its rate of change in position as observed from a particular frame of reference and as measured by a particular standard of time (e.g. northbound). Velocity is a ...
. This gives the formula for the ''total kinetic energy of the moving parts of a machine'' as \frac I \omega^2 + \frac m v^2.


Representing moving parts in engineering diagrams

In
technical drawing Technical drawing, drafting or drawing, is the act and Academic discipline, discipline of composing Plan (drawing), drawings that Visual communication, visually communicate how something functions or is constructed. Technical drawing is essent ...
, moving parts are, conventionally, designated by drawing the solid outline of the part in its main or initial position, with an added outline of the part in a secondary, moved, position drawn with a ''phantom line'' (a line comprising "dot-dot-dash" sequences of two short and one long line segments) outline. These conventions are enshrined in several standards from the
American National Standards Institute The American National Standards Institute (ANSI ) is a private non-profit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States. The organi ...
and the American Society of Mechanical Engineers, including ASME Y14.2M published in 1979. In recent decades, the use of
animation Animation is a method by which image, still figures are manipulated to appear as Motion picture, moving images. In traditional animation, images are drawn or painted by hand on transparent cel, celluloid sheets to be photographed and exhibited ...
has become more practical and widespread in technical and engineering diagrams for the illustration of the motions of moving parts. Animation represents moving parts more clearly and enables them and their motions to be more readily visualized. Furthermore, computer aided design tools allow the motions of moving parts to be simulated, allowing machine designers to determine, for example, whether the moving parts in a given design would obstruct one another's motion or collide by simple visual inspection of the (animated) computer model rather than by the designer performing a numerical analysis directly.


See also

* Kinetic art — sculpture that contains moving parts *
Movement (clockwork) In horology, a movement, also known as a caliber or calibre (British English), is the mechanism of a watch or Clock, timepiece, as opposed to the ''case'', which encloses and protects the movement, and the ''clock face, face'', which displays the ...
— the specific name for the moving parts of a clock or watch


References


Further reading

* * {{cite journal, title=Method of diagramming for moving parts fluid controls, id=ANSI/NFPA T3.28.9-1976, publisher= National Fluid Power Association and
American National Standards Institute The American National Standards Institute (ANSI ) is a private non-profit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States. The organi ...
, year=1976 Machinery