Mechanical ventilation, or assisted ventilation, is the medical term for artificial ventilation where mechanical means are used to assist or replace spontaneous breathing. This may involve a machine called a ventilator, or the breathing may be assisted manually by a suitably qualified professional, such as an anesthesiologist, Registered Nurse, respiratory therapist, or paramedic, by compressing a bag valve mask device.
Mechanical ventilation can be
Noninvasive, involving various types of face masks
Invasive, involving endotracheal intubation
Selection and use of appropriate techniques require an
understanding of respiratory mechanics.
Indications
There are numerous indications for endotracheal intubation
and mechanical ventilation (see table Situations Requiring Airway Control),
but, in general, mechanical ventilation should be considered when there are
clinical or laboratory signs that the patient cannot maintain an airway or
adequate oxygenation or ventilation.
Concerning findings include
Respiratory rate > 30/minute
Inability to maintain arterial oxygen saturation > 90%
with fractional inspired oxygen (FIO2) > 0.60
pH < 7.25
PaCO2 > 50 mm Hg (unless chronic and stable)
The decision to initiate mechanical ventilation should be
based on clinical judgment that considers the entire clinical situation and not
simple numeric criteria. However, mechanical ventilation should not be delayed
until the patient is in extremis.
Respiratory Mechanics
Normal inspiration generates negative intrapleural pressure,
which creates a pressure gradient between the atmosphere and the alveoli,
resulting in air inflow. In mechanical ventilation, the pressure gradient
results from increased (positive) pressure of the air source.
Peak airway pressure is measured at the airway opening (Pao)
and is routinely displayed by mechanical ventilators. It represents the total
pressure needed to push a volume of gas into the lung and is composed of
pressures resulting from inspiratory flow resistance (resistive pressure), the
elastic recoil of the lung and chest wall (elastic pressure), and the alveolar
pressure present at the beginning of the breath (positive end-expiratory
pressure [PEEP]
Resistive pressure is the product of circuit resistance and
airflow. In the mechanically ventilated patient, resistance to airflow occurs
in the ventilator circuit, the endotracheal tube, and, most importantly, the
patient’s airways. (NOTE: Even when these factors are constant, an increase in
airflow increases resistive pressure.)
Components of airway pressure during mechanical ventilation,
illustrated by an inspiratory-hold maneuver
PEEP = positive end-expiratory pressure.
Elastic pressure is the product of the elastic recoil of the
lungs and chest wall (elastance) and the volume of gas delivered. For a given
volume, elastic pressure is increased by increased lung stiffness (as in
pulmonary fibrosis) or restricted excursion of the chest wall or diaphragm (eg,
in tense ascites or massive obesity). Because elastance is the inverse of
compliance, high elastance is the same as low compliance.
End-expiratory pressure in the alveoli is normally the same
as atmospheric pressure. However, when the alveoli fail to empty completely
because of airway obstruction, airflow limitation, or shortened expiratory
time, end-expiratory pressure may be positive relative to the atmosphere. This
pressure is called intrinsic PEEP or auto PEEP to differentiate it from
externally applied (therapeutic) PEEP, which is created by adjusting the
mechanical ventilator or by placing a tight-fitting mask that applies positive
pressure throughout the respiratory cycle.
Any elevation in peak airway pressure (eg, > 25 cm H2O)
should prompt measurement of the end-inspiratory pressure (plateau pressure) by
an end-inspiratory hold maneuver to determine the relative contributions of
resistive and elastic pressures. The maneuver keeps the exhalation valve closed
for an additional 0.3 to 0.5 second after inspiration, delaying exhalation.
During this time, airway pressure falls from its peak value as airflow ceases.
The resulting end-inspiratory pressure represents the elastic pressure once
PEEP is subtracted (assuming the patient is not making active inspiratory or
expiratory muscle contractions at the time of measurement). The difference
between peak and plateau pressure is the resistive pressure.
Elevated resistive pressure (eg, > 10 cm H2O) suggests
that the endotracheal tube has been kinked or plugged with secretions or that
an intraluminal mass or bronchospasm is present.
Increased elastic pressure (eg, > 10 cm H2O) suggests
decreased lung compliance due to
Edema, fibrosis, or lobar atelectasis
Large pleural effusions, pneumothorax, or fibrothorax
Extrapulmonary restriction as may result from
circumferential burns or other chest wall deformity, ascites, pregnancy, or
massive obesity
A tidal volume too large for the amount of lung being
ventilated (eg, a normal tidal volume being delivered to a single lung because
the endotracheal tube is malpositioned)
Intrinsic PEEP (auto PEEP) can be measured in the passive
patient through an end-expiratory hold maneuver. Immediately before a breath,
the expiratory port is closed for 2 seconds. Flow ceases, eliminating resistive
pressure; the resulting pressure reflects alveolar pressure at the end of
expiration (intrinsic PEEP). Although accurate measurement depends on the
patient being completely passive on the ventilator, it is unwarranted to use
neuromuscular blockade solely for the purpose of measuring intrinsic PEEP. A
nonquantitative method of identifying intrinsic PEEP is to inspect the
expiratory flow tracing. If expiratory flow continues until the next breath or
the patient’s chest fails to come to rest before the next breath, intrinsic
PEEP is present. The consequences of elevated intrinsic PEEP include increased
inspiratory work of breathing and decreased venous return, which may result in
decreased cardiac output and hypotension.
The demonstration of intrinsic PEEP should prompt a search
for causes of airflow obstruction (eg, airway secretions, decreased elastic
recoil, bronchospasm); however, a high minute ventilation (> 20 L/minute)
alone can result in intrinsic PEEP in a patient with no airflow obstruction. If
the cause is airflow limitation, intrinsic PEEP can be reduced by shortening
inspiratory time (ie, increasing inspiratory flow) or reducing the respiratory
rate, thereby allowing a greater fraction of the respiratory cycle to be spent
in exhalation.
Means and Modes of Mechanical Ventilation
Mechanical ventilators are
Volume cycled: Delivering a constant volume with each breath
(pressures may vary)
Pressure cycled: Delivering constant pressure during each
breath (volume delivered may vary)
A combination of volume and pressure cycled
Assist-control (A/C) modes of ventilation are modes that
maintain a minimum respiratory rate regardless of whether or not the patient
initiates a spontaneous breath. Because pressures and volumes are directly
linked by the pressure-volume curve, any given volume will correspond to a
specific pressure, and vice versa, regardless of whether the ventilator is
pressure cycled or volume cycled.
Adjustable ventilator settings differ with mode but include
Respiratory rate
Tidal volume
Trigger sensitivity
Flow rate
Waveform
Inspiratory/expiratory (I/E) ratio
Volume-cycled ventilation
Volume-cycled ventilation delivers a set tidal volume. This
mode includes
The resultant airway pressure is not fixed but varies with
the resistance and elastance of the respiratory system and with the flow rate
selected.
V/C ventilation is the simplest and most effective means of
providing full mechanical ventilation. In this mode, each inspiratory effort
beyond the set sensitivity threshold triggers delivery of the fixed tidal
volume. If the patient does not trigger the ventilator frequently enough, the
ventilator initiates a breath, ensuring the desired minimum respiratory rate.
SIMV also delivers breaths at a set rate and volume that is
synchronized to the patient’s efforts. In contrast to V/C, patient efforts
above the set respiratory rate are unassisted, although the intake valve opens
to allow the breath. This mode remains popular, despite not providing full
ventilator support as does V/C, not facilitating liberation of the patient from
mechanical ventilation, and not improving patient comfort.
Pressure-cycled ventilation
Pressure-cycled ventilation delivers a set inspiratory
pressure. This mode includes
Pressure control ventilation (PCV)
Pressure support ventilation (PSV)
Noninvasive modalities applied via a tight-fitting face mask
(several types available)
Hence, tidal volume varies depending on the resistance and
elastance of the respiratory system. In this mode, changes in respiratory
system mechanics can result in unrecognized changes in minute ventilation.
Because it limits the distending pressure of the lungs, this mode can
theoretically benefit patients with acute respiratory distress syndrome (ARDS);
however, no clear clinical advantage over V/C has been shown, and, if the
volume delivered by PCV is the same as that delivered by V/C, the distending
pressures will be the same.
Pressure control ventilation is a pressure-cycled form of
A/C. Each inspiratory effort beyond the set sensitivity threshold delivers full
pressure support maintained for a fixed inspiratory time. A minimum respiratory
rate is maintained.
In pressure support ventilation, a minimum rate is not set;
all breaths are triggered by the patient. The ventilator assists the patient by
delivering a pressure that continues at a constant level until the patient's
inspiratory flow falls below a preset level determined by an algorithm. Thus, a
longer or deeper inspiratory effort by the patient results in a larger tidal
volume. This mode is commonly used to liberate patients from mechanical
ventilation by letting them assume more of the work of breathing. However, no
studies indicate that this approach is more successful than others in
discontinuing mechanical ventilation.
Noninvasive positive pressure ventilation (NIPPV)
NIPPV is the delivery of positive pressure ventilation via a
tight-fitting mask that covers the nose or both the nose and mouth. Helmets
that deliver NIPPV are being studied as an alternative for patients who cannot
tolerate the standard tight-fitting face masks. Because of its use in
spontaneously breathing patients, it is primarily applied as a form of PSV or
to deliver end-expiratory pressure, although volume control can be used.
NAMED the 'T Power H20,' the eco-friendly bike was created by Ricardo Azevedo in Sao Paulo. The design features a combination of water and a single, external car battery used to produce electricity and separate the hydrogen from the water molecule. The process, involving a pipe-system, results in combustion which subsequently creates the energy necessary to power the bike.
The motorcycle does not need clean drinking water to run, and Azevedo demonstrated this when he went to the Tiete River, a river that is polluted, and filled the motorcycle up from that. He has been talking about the environmental benefits of his H20 motorcycle and of course the benefits of the cost associated with running a motorcycle that does not require fuel.
He said that one advantage of the motorcycle only using water to run was that it works with hydrogen that comes from the water and this means that the only thing that comes out of the exhaust pipe of the motorcycle is water vapour. He went on to point out that this is unlike a traditional motorcycle running on fuel which sends out carbon monoxide.
There are mainly two types of materials. First one is metal and other one is non metals. Metals are classified into two types : Ferrous metals and Non-ferrous metals.
Ferrous metals mainly consist iron with comparatively small addition of other materials. It includes iron and its alloy such as cast iron, steel, HSS etc. Ferrous metals are widely used in mechanical industries for its various advantages.
Nonferrous metals contain little or no iron. It includes aluminum, magnesium, copper, zinc etc.
Most Mechanical properties are associated with metals. These are
#1. Strength:
The ability of material to withstand load without failure is known as strength. If a material can bear more load, it means it has more strength. Strength of any material mainly depends on type of loading and deformation before fracture. According to loading types, strength can be classified into three types.
a. Tensile strength:
b. Compressive strength:
3. Shear strength:
According to the deformation before fracture, strength can be classified into three types.
a. Elastic strength:
b. Yield strength:
c. Ultimate strength:
#2. Homogeneity:
If a material has same properties throughout its geometry, known as homogeneous material and the property is known as homogeneity. It is an ideal situation but practically no material is homogeneous.
#3. Isotropy:
A material which has same elastic properties along its all loading direction known as isotropic material.
#4. Anisotropy:
A material which exhibits different elastic properties in different loading direction known as an-isotropic material.
#5. Elasticity:
If a material regain its original dimension after removal of load, it is known as elastic material and the property by virtue of which it regains its original shape is known as elasticity.
Every material possess some elasticity. It is measure as the ratio of stress to strain under elastic limit.
#6. Plasticity:
The ability of material to undergo some degree of permanent deformation without failure after removal of load is known as plasticity. This property is used for shaping material by metal working. It is mainly depends on temperature and elastic strength of material.
#7. Ductility:
Ductility is a property by virtue of which metal can be drawn into wires. It can also define as a property which permits permanent deformation before fracture under tensile loading. The amount of permanent deformation (measure in percentage elongation) decides either the material is ductile or not.
Percentage elongation = (Final Gauge Length – Original Gauge Length )*100/ Original Gauge Length
If the percentage elongation is greater than 5% in a gauge length 50 mm, the material is ductile and if it less than 5% it is not.
#8. Brittleness:
Brittleness is a property by virtue of which, a material will fail under loading without significant change in dimension. Glass and cast iron are well known brittle materials.
#9. Stiffness:
The ability of material to resist elastic deformation or deflection during loading, known as stiffness. A material which offers small change in dimension during loading is more stiffer. For example steel is stiffer than aluminum.
#10. Hardness:
The property of a material to resist penetration is known as hardness. It is an ability to resist scratching, abrasion or cutting.
It is also define as an ability to resist fracture under point loading.
#11. Toughness:
Toughness is defined as an ability to withstand with plastic or elastic deformation without failure. It is defined as the amount of energy absorbed before actual fracture.
#12. Malleability:
A property by virtue of which a metal can flatten into thin sheets, known as malleability. It is also define as a property which permits plastic deformation under compression loading.
#13. Machinability:
A property by virtue of which a material can be cut easily.
#14. Damping:
The ability of metal to dissipate the energy of vibration or cyclic stress is called damping. Cast iron has good damping property, that’s why most of machines body made by cast iron.
#15. Creep:
The slow and progressive change in dimension of a material under influence of its safe working stress for long time is known as creep. Creep is mainly depend on time and temperature. The maximum amount of stress under which a material withstand during infinite time is known as creep strength.
#16. Resilience:
The amount of energy absorb under elastic limit during loading is called resilience. The maximum amount of the energy absorb under elastic limit is called proof resilience.
#17. Fatigue Strength:
The failure of a work piece under cyclic load or repeated load below its ultimate limit is known as fatigue. The maximum amount of cyclic load which a work piece can bear for infinite number of cycle is called fatigue strength. Fatigue strength is also depend on work piece shape, geometry, surface finish etc.
#18. Embrittlement:
The loss of ductility of a metal caused by physical or chemical changes, which make it brittle, is called embrittlement.
Fluid dynamics is the study of how fluids behave when they're in motion. This can get very complicated, so we'll focus on one simple case, but we should briefly mention the different categories of fluid flow.
Fluids can flow steadily, or be turbulent. In steady flow, the fluid passing a given point maintains a steady velocity. For turbulent flow, the speed and or the direction of the flow varies. In steady flow, the motion can be represented with streamlines showing the direction the water flows in different areas. The density of the streamlines increases as the velocity increases.
Fluids can be compressible or incompressible. This is the big difference between liquids and gases, because liquids are generally incompressible, meaning that they don't change volume much in response to a pressure change; gases are compressible, and will change volume in response to a change in pressure.
Fluid can be viscous (pours slowly) or non-viscous (pours easily).
Fluid flow can be rotational or irrotational. Irrotational means it travels in straight lines; rotational means it swirls.
For most of the rest of the chapter, we'll focus on irrotational, incompressible, steady streamline non-viscous flow.
The equation of continuity
The equation of continuity states that for an incompressible fluid flowing in a tube of varying cross-section, the mass flow rate is the same everywhere in the tube. The mass flow rate is simply the rate at which mass flows past a given point, so it's the total mass flowing past divided by the time interval. The equation of continuity can be reduced to:
Generally, the density stays constant and then it's simply the flow rate (Av) that is constant.
Making fluids flow
There are basically two ways to make fluid flow through a pipe. One way is to tilt the pipe so the flow is downhill, in which case gravitational kinetic energy is transformed to kinetic energy. The second way is to make the pressure at one end of the pipe larger than the pressure at the other end. A pressure difference is like a net force, producing acceleration of the fluid.
As long as the fluid flow is steady, and the fluid is non-viscous and incompressible, the flow can be looked at from an energy perspective. This is what Bernoulli's equation does, relating the pressure, velocity, and height of a fluid at one point to the same parameters at a second point. The equation is very useful, and can be used to explain such things as how airplanes fly, and how baseballs curve.
Bernoulli's equation
The pressure, speed, and height (y) at two points in a steady-flowing, non-viscous, incompressible fluid are related by the equation:
Some of these terms probably look familiar...the second term on each side looks something like kinetic energy, and the third term looks a lot like gravitational potential energy. If the equation was multiplied through by the volume, the density could be replaced by mass, and the pressure could be replaced by force x distance, which is work. Looked at in that way, the equation makes sense: the difference in pressure does work, which can be used to change the kinetic energy and/or the potential energy of the fluid.
Pressure vs. speed
Bernoulli's equation has some surprising implications. For our first look at the equation, consider a fluid flowing through a horizontal pipe. The pipe is narrower at one spot than along the rest of the pipe. By applying the continuity equation, the velocity of the fluid is greater in the narrow section. Is the pressure higher or lower in the narrow section, where the velocity increases?
Your first inclination might be to say that where the velocity is greatest, the pressure is greatest, because if you stuck your hand in the flow where it's going fastest you'd feel a big force. The force does not come from the pressure there, however; it comes from your hand taking momentum away from the fluid.
The pipe is horizontal, so both points are at the same height. Bernoulli's equation can be simplified in this case to:
The kinetic energy term on the right is larger than the kinetic energy term on the left, so for the equation to balance the pressure on the right must be smaller than the pressure on the left. It is this pressure difference, in fact, that causes the fluid to flow faster at the place where the pipe narrows.
A geyser
Consider a geyser that shoots water 25 m into the air. How fast is the water traveling when it emerges from the ground? If the water originates in a chamber 35 m below the ground, what is the pressure there?
To figure out how fast the water is moving when it comes out of the ground, we could simply use conservation of energy, and set the potential energy of the water 25 m high equal to the kinetic energy the water has when it comes out of the ground. Another way to do it is to apply Bernoulli's equation, which amounts to the same thing as conservation of energy. Let's do it that way, just to convince ourselves that the methods are the same.
Bernoulli's equation says:
But the pressure at the two points is the same; it's atmospheric pressure at both places. We can measure the potential energy from ground level, so the potential energy term goes away on the left side, and the kinetic energy term is zero on the right hand side. This reduces the equation to:
The density cancels out, leaving:
This is the same equation we would have found if we'd done it using the chapter 6 conservation of energy method, and canceled out the mass. Solving for velocity gives v = 22.1 m/s.
To determine the pressure 35 m below ground, which forces the water up, apply Bernoulli's equation, with point 1 being 35 m below ground, and point 2 being either at ground level, or 25 m above ground. Let's take point 2 to be 25 m above ground, which is 60 m above the chamber where the pressurized water is.
We can take the velocity to be zero at both points (the acceleration occurs as the water rises up to ground level, coming from the difference between the chamber pressure and atmospheric pressure). The pressure on the right-hand side is atmospheric pressure, and if we measure heights from the level of the chamber, the height on the left side is zero, and on the right side is 60 m. This gives:
Why curveballs curve
Bernoulli's equation can be used to explain why curveballs curve. Let's say the ball is thrown so it spins. As air flows over the ball, the seams of the ball cause the air to slow down a little on one side and speed up a little on the other. The side where the air speed is higher has lower pressure, so the ball is deflected toward that side. To throw a curveball, the rotation of the ball should be around a vertical axis.
It's a little more complicated than that, actually. Although the picture here shows nice streamline flow as the air moves left relative to the ball, in reality there is some turbulence. The air does exert a force down on the ball in the figure above, so the ball must exert an upward force on the air. This causes air that travels below the ball in the picture to move up and fill the space left by the ball as it moves by, which reduces drag on the ball.
Friday, June 22,
2012, the Wankel rotary engine's last remaining and steadfast devotee,
Mazda, produced their final rotary engine in their Hiroshima plant. The
Wankel engine never really fulfilled its promises and hopes, though over
its history over 25 major automobile, motorcycle, tractor, and aircraft
companies, ranging from Suzuki to Rolls-Royce, were actively
researching, developing, and/or building the piston-less engine.
The
Wankel motor is one of those things that, for all its issues, was just
too pure and beautiful for engineers to ignore. With far fewer parts
than a regular reciprocating piston engine and a visually elegant
design, it's no wonder Mazda kept with it. For a given displacement, it
produces far more power than a given piston engine, at a much smaller
size and weight. It can rev faster and is inherently smooth, since the
motive force is rotational from start to finish— not the back-and-forth
hopping of a piston engine. The down side is that Wankels are always a
bit more fuel-gluttonous than a piston engine, and almost always have
dirtier exhaust. Poor fuel economy and more polluting are pretty much
the only strikes you need against you in our modern age, so the
mainstream Wankel is going away.
Felix Wankel was a gifted and
largely self-taught engineer. The fundamental concept behind the rotary
engine came to him quite early, as he is reported to have told friends
at the age of 17 he would build a new kind of car with "a new type of
engine, half turbine, half reciprocating. It is my invention!" I think I
remember saying similar things at 17, but replace "turbine" and
"reciprocating" with "boobs" and "magic".
Wankel's past was checkered, with periods in Hitler Youth and the
Nazi party, though he was forced out in 1932. After his first patent in
1929 for the engine, it wasn't until after WWII that development started
in earnest, thanks to a development deal with NSU in 1951. In 1957, an
NSU engineer built the first working Wankel motor without Wankel
knowing, which caused him to comment "you have turned my race horse into
a plow mare." Like a typical gearhead, I'm sure Wankel was imaging a
powerful racing motor instead of the practical lump made by NSU.
The NSU Spider was the first production Wankel-engined car, in 1964. A pretty little rear-engined roadster, it was sort of like the VW Type III convertible that was never made, with its under-trunk-floor engine position and two luggage compartments. Later NSU created the legendary Ro80,
a beautiful rotary-engined sedan that looked 20+ years ahead of its
time. Sadly, the Wankel proved to be the achilles heel of the car, with
issues with rotor-tip sealing causing some engines to fail as early as
30,000 miles.
Attempts from the Wankel's homeland were nothing
compared with the engine's longest and greatest patron, Mazda. Starting
with the lovely Cosmo back in 1967 (which had the first two-rotor Wankel) and ending this year with the advanced Renesis engine in the RX-8,
Mazda has built cars (and trucks) with rotary engines for 45 years, and
in that time managed to work out most of the major sealing and other
issues.
The final version of Mazda's rotary, the Renesis, made 238
HP out of 1.3 liters— very impressive. Less impressive is its fuel
consumption and emissions, the latter being the final, shiny coffin
nail, as the engine failed to pass the Euro 5 emissions tests. Mazda did release a limited run of a hydrogen-based rotary engine, but future development seems unlikely.
It's not totally
gone, though. The engine's just too elegant and simple to disappear
entirely, and is finding strange and novel niches in which to survive.
Like seat belts. The seat belt emergency pretensioner system in some
Mercedes-Benz and Volkswagen is actually a tiny Wankel motor driven by
an explosive charge. I need to comb the junkyards and see if I can find
one of those. Here's the patent on that.
Wankels
may also stick around in certain niche markets, like for snowmobiles,
since when they fail it's more gradual, and some power may still be
generated, for a time. This is unlike piston engines, who may throw a
rod and be done with it in a horrific moment of smoke and oil. For
snowmobiles, this is a big deal, since breaking down can mean much more
than an annoying afternoon. Much more as in lost noses and fingers to
frostbite or determined wolves. UAVs are also experimenting with small Wankels, since their simplicity and durability are big advantages for robot aircraft.
http://jalopnik.com
So why aren’t we all driving Wankel-powered cars? The problem lies in the pitfalls of the design. Fuel Economy: The Wankel’s combustion chamber is
long, thin, and moves with the rotor. This causes a slow fuel burn.
Engines try to combat this by using twin (leading and trailing) spark
plugs. Even with the two plugs, combustion is often incomplete, leading
to raw fuel being dumped out the exhaust port. The small 1.3 liter 232
horsepower two rotor engine in the 2011 Mazda RX-8 gets worse fuel
economy (16 city / 23 highway) than the 6.2 liter 455 horsepower V8
engine used in the 2015 Corvette Stingray (17 city / 29 highway). Emissions: The unburnt fuel, along with burned oil
(described below) both result in terrible emissions from Wankel engines.
The emissions problems are one of several reasons the RX-8 was pulled
from production. Sealing:
Rotors use seals on the faces, seals around the central port, and most
importantly apex seals. The apex seal rides the wall of the housing,
sealing each of the three chambers formed by the rotor. The apex seals
are under extreme thermal and pressure stresses as they travel around
the engine housing. Failing apex seals are the primary cause of rotary
engines going down for overhaul. YouTube is littered with videos showing
the rotary overhaul process. Much like piston rings, these seals have to be lubricated. However,
due to the design of the rotary engine, there is no way to keep the oil
lubricating the seals out of the combustion chamber. Mazda engines
include an injector pump which pushes small amounts of oil right into
the engine housing, as well as into the air intake. This oil is
eventually burned, causing increased carbon and emissions over the life
of the engines. Overhaul interval: Rotary engines in general don’t last as long as piston powered engines. As explained eloquently by Regular Car Reviews,
the primary problem is with the seals. Browsing Mazda and rotary forums
shows people rebuilding somewhere between 50,000 and 100,000 miles.
However, this all must be taken with a grain of salt. The RX-7 and 8 are
after all, sports cars. While some people treat them gingerly, many
people drive these cars hard. Aftermarket performance parts like
turbochargers will also negatively impact engine reliability.
Gears are Power transmission elements. It is the Gears that decides the torque, speed, and direction of rotation of all the driven machine elements. Broadly speaking, Gear types may be grouped into five broad categories. They are Spur, Helical, Bevel, Hypoid, and Worm. A lot of intricacies are there in the different types of gears. Actually, The choice of gear type is not a very easy process. It is dependent on a number of considerations. Factors that go into it are physical space and shaft arrangement, gear ratio, load, accuracy, and quality level.
Gears may also be classified according to the position of axis of shaft:
a.Parallel
1.Spur Gear
2.Helical Gear
3.Rack and Pinion
b. Intersecting
Bevel Gear
c. Non-intersecting and Non-parallel
worm and worm gears
A number of gears are manufactured using different materials and with different performance specifications depending on the industrial application. These gears are available in a range of capacities, sizes and speed ratios, but the main function is to convert the input of a prime mover into an output with high torque and low RPM. These range of gears find use in almost every industry right from agriculture to aerospace, from mining to paper and pulp industry.
Some of the popular types of gears in use are :
Spur Gears
Spur Gear
Spur gears are straight-toothed gears having radial teeth used to transmit power and motion between parallel axes. These gears are widely used for speed increase or reduction, high torque, resolution for positioning systems.
These gears can either be mounted on a hub or a shaft. The gears are available in different size, design, shape and also offer a variety of features and functions to cater to different industrial requirements.
Materials Used Spur gears are fabricated from superior quality materials, like:
Metal- steel, cast iron, brass, bronze and stainless steel.
Plastic- acetal, nylon and polycarbonate.
Materials used to manufacture these gears are used keeping in mind certain factors including design life, power transmission requirements, noise generation.
Important Specifications to be Considered
Gear center
Bore diameter
Shaft diameter
Use of Spur Gears These gears find wide application in a number of fields including :
Automobiles
Textiles
Industrial engineering
Bevel Gears
Bevel Gear
Bevel gears are mechanical devices used for transmitting mechanical power and motion. These gears are widely used for transmitting power and motion between nonparallel axes and are designed to transmit motion between intersecting axes, generally at right angles. The teeth on bevel gear can be straight, spiral or hypoid. The gears are suitable when the direction of a shaft's rotation needs to be changed.
Materials used Materials used to manufacture these gears are used keeping in mind certain factors including design life, power transmission requirements, noise generation. Some of the important materials used are :
Metal - Steel, cast iron and stainless steel.
Plastic - Acetal and polycarbonate.
Important specifications to be considered
Gear center
Bore diameter
Shaft diameter
Use of Bevel Gear These gears find wide application in a number of fields including :
Automotive industry
Textile industry
Industrial engineering products
Helical Gears
Helical Gears
Helical gear is a popular type of gear having its teeth cut at an angle, thus allowing for more gradual and smoother meshing between gear wheels. The helical gears are a refinement over spur gears.
The teeth on helical gears are specially cut at an angle, so as to face the gear. As two teeth on the gear system engage, it starts a contact on one end of the tooth which gradually spreads with the gear rotation, until the time when both the tooth are fully engaged.
The gears are available in different sizes, shapes and designs to meet the customer specifications.
Materials Used These gears can be manufactured from superior quality materials including stainless steel, steel, cast iron, brass etc. depending on the application.
Use of Helical Gears These gears are used in areas requiring high speeds, large power transmission, or where noise prevention is important.
Automobiles
Textile
Aerospace
Conveyors
Worm Gears
Worm Gear
Worm Gear
A worm gear is a type of gear, engaging with a worm to significantly reduce rotational speed, or allowing higher torque to be transmitted. The gear can achieve a higher gear ratio than spur gears of the same size.
Materials Used Worm gears can be constructed from a number of materials depending on the end application. Some of the popularly use materials are :
Brass
Stainless steel
Cast iron
Aluminum
Hardened steel
The gears can operate under difficult conditions and have the ability to achieve large speed reductions. The gears also transmit high loads at high speed ratios.
Types of Worm Gears
Non-throated
Single-throated
Double-throated
Use of Worm Gears These gears find application in :
Electric motors
Automotive components
Differential Gears
Differential Gear
Differential gears are referred to an arrangement of gears, connecting two axles in the same line and dividing the driving force between them. One axle is allowed to turn faster than the other. These gears are often used in automotive industry for allowing a difference in axle speed on curves.
In automobiles, the gear system allows the wheels to rotate at different speeds and simultaneously supplying each of them with equal torque. The gears are specially designed to create a differential and consist of pinion and turnable gears.
Types of Differential Gears
Straight Line Differential Gears
Rotary Differential Gears
Materials Used The gears are manufactured using materials including :
Aluminum alloys
Cast iron
Stainless steel
Use of Differential Gears The gear is extensively used in the automobile industry for effective and efficient working of vehicles. These gears do not create noise and also help in speed differential.
Ground Gears
As generally seen grinding is most of the time conceived in context of quantity fabrication of superior quality gears as a form of secondary refining procedure. We incline to forget that grinding is essentially a basic process in the step towards production of case hardened gears. Moreover, the teeth of precision-engineered fine-pitch gears completely ground from the blank itself.
The advent of trawling also led to the development and manufacturing of Ground Gears. Ever since then ground gears have made substantial improvement in the terms of designing and component accuracy. These gears assure high transmission accuracy and deliver superior efficiency, greater load capacity, and correction of profile and durability.
Ground gears can be made using different materials, such as cast iron, carbon steel, alloy steel, hardened steel, bronze, and more.
Advantages of Ground Gears Ground Gears offer various advantages to its users, some of which are:
High Precision: Achieving high precision is not a difficult task for ground gears since in the grinding process, there is little removal of material in the final pass.
Superior Surface Finish: Grinding makes the surface of ground gears more shiny than that obtained from any other machining technique.
Improved Flexibility: Hardened steel alloys can be used to developed into ground gears that gives its added flexibility.
Minimal Surface Stress: There is minimum residual surface stress in ground gears.
Minimal Wear and Tear: Ground gears have minimal wear and tear that results in prolonged life.
Limitations of Ground Gears Though ground gears offer multiple benefits and advantages, they too have some limitations:
There is a limit to grinding procedures and that is to ferrous material.
Hard metals can be grind in an efficient and better way than the soft ones.
In case of worm or helical gears, grinding may not be the ideal solution. This is due to the reason that it often involves deviations in terms of removal and profile.
Gear grinding machines are not as popular as hobbing machinery.
Grinding demands higher costs, as it is a secondary operation.
Applications These gears find wide application in a number of fields including :
High Speed Rotation: Ground gears are ideal for uses in applications that need noise and vibration resistance in the case of high-speed gear drives. An example can be that of ground spur gears.
Positioning: CP Racks and Pinions are recommended for perfect positioning applications. In these cases, ground gears are used in calculating for reducing pitch errors.
Kiln Girth Gears
Kiln Girth Gears
Kiln girth gears are large diameter / large module gears that are manufactured using large gear cutting machines. The girth gear of a rotary kiln comes with a diameter of 6384 mm with 56 module and 112 teeth. These gears are very difficult to fabricate using the conventional techniques of gear cutting. In manufacturing of these gears, teeth cutting is done using face mill cutter on a horizontal boring machine, which generally reduces the time taken in teeth cutting to one-third of the original one.
The kiln girth gears come under the category of industrial gears and the commonly used material for these gears is 42 Cr Mo 4. These gears are widely used in cement industry, sugar industry and other industrial purposes and applications.
Engineered to precision, kiln girth gears are known to deliver superior efficiency and flawless performance and their overall life depends on proper alignment and lubrication. These gears are easy to install and take less time as compared to others.
Industrial Applications Some of the important applications of girth gears include:
Heavy Machinery Industries
Metal Casting Industries
Metal Processing Industries
Construction Industries
Precision Gears
Precision gears are custom-made actuators that can be designed for varying uses and applications. These gears are generally used in applications under conditions of light loading. Precision gears are generally preferred for their precise, smooth, compact, noiseless and reliable performance.
Precision gears can be manufactured as per the customer's drawings or based on a functional description depending on the type of application. The different types of precision gear products include, - spur gears, helical gears, worm gears, anti-backlash gears, cluster gears, clutch gears, face gears, planetary gears, gear assemblies, gear boxes, bevel gears, miter gears, metric gears, internal gears, idler gears, gear rack & pinion, worms, worm shafts, splines, spline shafts, se shafts, and more. These gears can be manufactured as per the exact customer specifications or according to application need.
The quality and performance of a precision gear depends on the quality of blank in which it is cut. Thus it is essential to hold tight tolerances without grinding.
Precision gears are known for their trouble free superior performance, long service life, and excellent surface finish and customization capability. These gears are used in a variety of industrial applications, such as heavy machinery Industry, metal casting, metal processing, construction, and more.
Rack Gears
A rack is generally used for converting rotational motion into linear motion. It is a flat bar onto which the teeth of a pinion gear are engaged. It is a kind of gear whose axis is at infinity. These gears are designed to accommodate a wide variety of applications.
Materials Used A variety of materials are used keeping in mind the application. Some popularly used materials are :
Plastic
Brass
Steel
Cast Iron
These gears ensure quieter and smoother operation. The mechanism provides less backlash and greater steering feel.
Use of Rack Gear The gear is commonly used in steering mechanism of cars. Other important applications of rack gears include :
Construction equipment
Machine tools
Conveyors
Material handling
Roller feeds
Sprockets
A sprocket is a gear having metal teeth that meshes with a chain. Also known as a cog wheel, it is a small toothed ring that can fit onto the rear wheel. It is a thin wheel having teeth that engage with a chain.
Materials Used A variety of materials can be used to manufacture superior quality sprockets used in different industries. Some of the materials used are :
Stainless steel
Hardened steel
Cast iron
Brass
Use of Sprockets This simple gear finds application in diverse areas including :
Food industry
Bicycles
Motorcycles
Cars
Tanks
Industrial machines
Movie projectors and cameras
Segment Gears
The segment gear, as the name suggests, is basically a gear wheel. These gear wheels are composed of a large number of pieces that are small parts of a circle. A segment gear is connected to the arms or trappings of the water wheel.
The segment gear comes with a part for receiving or communicating the reciprocating motion from or to a cogwheel. These gears also comprise of a sector of a circular ring or gear. There are also cogs on the periphery.
Segment Gears are available in various finishes, such as untreated or heat-treated and can be designed as a single component or as an entire system.
Applications Segment gears, which are basically gear wheels, are used in variety of industrial uses and applications. These gears offer various advantages such as improved flexibility, superior surface finish, high precision and minimum wear and tear. Some of the uses of segment gears include:
Defense
Rubber
Railways
Planetary Gear
Planetary gear is an outer gear that revolves around a central sun gear. Planetary gears can produce different gear ratios depending on which gear is used as the input, which one is used as the output.
Materials Used The gears can be constructed from a variety of materials including :
Stainless steel
Hardened steel
Cast iron
Aluminum
The gears are suitable for reduction of high RPM electric motors for use in high-torque low RPM applications. These gears are used in precision instruments because of their reliability and accuracy.
Use of Planetary Gears These gears are the most widely used gears having diverse applications including :
Sugar industry
Power industry
Wind turbines
Marine industry
Agriculture industry
Internal Gear
An internal gear is a hollow gear with teeth cut on its internal surface. The teeth in such a gear project inwards instead of outwards from the rim.
Materials Used There is a variety of materials being used to manufacture internal gears depending on the end application. Some of the popularly used materials are :
Plastic
Aluminum alloys
Cast iron
Stainless steel
The teeth in such gears can either be spur or helical. The internal teeth have a concave shape with a base thicker than that of an external gear. The convex shape and a strong base help in making the teeth stronger and also creating less noise.
Advantages of Internal Gear
The gears are specially designed to accommodate a wide range of equipment.
The gears are cost-effective and ideal for a broad range of light-duty applications.
The non-binding tooth design ensures smooth and quiet operation.
Use of Internal Gears
Light duty applications
Rollers
Indexing
External Gear
One of the simplest and most used gear units, external gears are extensively used in gear pumps and other industrial products for smooth functioning. These gears have straight teeth parallel to the axis. The teeth transmit rotary motion between parallel shafts.
Materials Used The gears can be constructed from a variety of materials including :
Stainless steel
Hardened steel
Cast iron
Aluminum
The kind of material used in manufacturing these gears depends on the end use they are being put to.
Use of External Gears These gears are used in diverse fields including :
Coal industry
Mining
Steel plants
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