Common Mechanical Engineering Terms

Ball and Detent A simple mechanical arrangement used to hold a moving part in a temporarily fixed position relative to another part. The ball slides within a bored cylinder, against the pressure of a spring, which pushes the ball against the detent, a hole of smaller diameter than the ball. When the hole is in line with the cylinder, the ball falls partially into the hole under spring pressure, holding the parts at that position. Additional force will push the ball back into its cylinder, compressing the spring, and allowing the parts to move.

Bearing The part of a machine within which a rotating or sliding shaft is held. In some bearing types, balls or rollers are used between the bearing surfaces to reduce rolling friction.

Bell crank A pivoting double lever used to change the direction of applied motion.

Boss A cylindrical projection, as on a casting or a forging. Usually provides a contact surface around a hole.

Broach To finish the inside of a hole to a shape other than round, as in a keyway. The tool for the process, which has serrated edges and is pushed or pulled through the hole to produce the required shape.

Burnish To smooth or polish by a rolling or sliding tool under pressure.

Bushing A smooth walled bearing (AKA a plain bearing). Also, a tool guide in a jig or fixture.

Cam A mechanical device consisting of an eccentric or multiply curved wheel mounted on a rotating shaft, used to produce variable or reciprocating motion in another engaged or contacted part (cam follower). Also, Camshaft.

Casting Any object made by pouring molten metal into a mold.

Chamfer A flat surface made by cutting off the edge or corner of an object (bevel).

Clevis A U-shaped piece with holes into which a link is inserted and through which a pin or bolt is run. It is used as a fastening device which allows rotational motion.

Collar  A cylindrical feature on a part fitted on a shaft used to prevent sliding (axial) movement.

Collet  A cone-shaped sleeve used for holding circular or rodlike pieces in a lathe or other machine.

Core  To form the hollow part of a casting, using a solid form placed in the mold  The solid form used in the coring process, often made of wood, sand, or metal.

Counterbore  A cylindrical flat-bottomed hole, which enlarges the diameter of an existing pilot hole.  The process used to create that feature.

Countersink A conical depression added to an existing hole to accommodate and the conic head of a fastener recessing it below the surface of a face.

Coupling A device used to connect two shafts together at their ends for the purpose of transmitting power. May be used to account for minor misalignment or for mitigating shock loads.

Die One of a pair of hardened metal plates or impressing or forming desired shape. Also, a tool for cutting external threads.

Face To machine a flat surface perpendicular to the axis of rotation of a piece.

Fillet A rounded surface filling the internal angle between two intersection surfaces. Also Rounds 

Fit  The class of contact between two machined surfaces, based upon their respective specified size tolerances (clearance, transitional, interference)

Fixture  A device used to hold a workpiece while manufacturing operations are performed upon that workpiece.

Flange (see bushing example)  A projecting rim or edge for fastening, stiffening or positioning.

Gage  A device used for determining the accuracy of specified manufactured parts by direct comparison..

Gage blocks  Precision machined steel blocks having two flat, parallel surfaces whose separation distance is fabricated to a guaranteed accuracy of a few millionths of an inch;

Gear Hobbing  A special form of manufacturing that cuts gear tooth geometries. It is the major industrial process for cutting involute form spur gears of.

Geneva Cam A device to turn constant rotational motion into intermittent rotational motion.

Gusset (plate) A triangular metal piece used to strengthen a joint.

Hasp A metal fastener with a slotted, hinged part that fits over a loop and is secured by a pin, bolt, or padlock.

Idler A mechanism used to regulate the tension in belt or chain. Or, a gear used between a driver and follower gear to maintain the direction of rotation.

Jig  A special device used to guide a cutting tool (drill jig) or to hold material in the correct position for cutting or fitting together (as in welding or brazing)

Journal  The part of a shaft that rotates within a bearing

Kerf  A channel or groove cut by a saw or other tool.

Key (Woodruff key shown)  A small block or wedge inserted between a shaft and hub to prevent circumferential movement.

Mechanical Engineering Terms

Keyseat  A slot or groove cut in a shaft to fit a key. Key rests in a Keyseat.

Keyway A slot cut into a hub to fit a key. A key slide in a keyway. See Broach.

Knurl  To roughen a turned surface, as in a handle or a knob.

Lug  Projection on (typically) a cast or forged part to provide support or allow mounting or the attachment of another component.

Neck  To cut a groove around a shaft, usually toward the end or at a change in diameter.  A portion of reduced diameter between the ends of a shaft.

Mechanical Engineering Terms

Pad  A rectangular or irregular projection, as on a casting or a forging. Usually provides a contact surface around a set of holes.

Pawl A device used to prevent a toothed wheel (ratchet) from rotating backwards, or a device that stops, locks, or releases a mechanism.

Pillow Block A bearing housing which typically mounts to a single planar face. May be split or unsplit to accommodate insertion /removal of the bearing.

Pinion A plain gear, often the smallest gear in a gearset, often the driving gear. May be used in conjunction with a gear rack 

Planetary Gears A gearset characterized by one or more planet gear(s) rotating around a sun gear. Epicyclic gearing systems include an outer ring gear (known as an annulus) with the planetary system.

Ratchet  A mechanical device used to permit motion in one direction only.

Relief  A groove or cut on a part used to facilitate machining.

Retaining Ring  A tool steel ring used in conjunction with a shaft groove or internal groove to located or control position of a component.

Rocker Arm  A pivoted arm-like lever used to transfer the application direction of a linear force.

Scotch Yoke Mechanism used to convert rotational motion to linear motion.

Sheave A grooved wheel used to accommodate a belt for the transmission of power. Sometimes referred to as a pulley sheave.

Shim A thin strip of metal inserted between two surfaces to adjust for fit.  

Shoulder A plane surface on a shaft, normal to the axis, produced by a change in diameter.

Mechanical Engineering Terms
Spline A cylindrical pattern of keyways. May be external (L) or internal (R)

Mechanical Engineering Terms
Spotface  a round machine surface around a hole on a casting or forging, usually to provide a contact surface for a fastener or other mating component.

Standoffs  A mounting designed to position objects a predetermined distance above or away from the surface upon which they are mounted.

Tap  To cut internal machine threads in a hole,  the tool used to create that feature.

Undercut  A cut having inward sloping sides,  to cut leaving an overhanging edge

Mechanical Engineering Terms
Yoke  A clamp or vise that holds a machine part in place or controls its movement or that holds two such parts together. A crosshead of relatively thick cross section, that secures two or more components so that they move together.

Mechanical Engineering Terms

How to select right Turbocharger Size for your car

Turbocharger Size

Turbo selection isn’t what it used to be. Once upon a time, self-proclaimed engineers were content to build an engine that produced massive power at high rpm, but drove like a dog at anything but. However, once hot-rodders figured out that anybody could bolt a junk turbo to any engine and make power, focus shifted from top-end force to overall driveability. With a little bit of extra work, anyone with a seventh-grade education can one-up the experts of yore and pick the perfect turbo for any application.

Turbocharger

 

  1. Assess your budget. Building a turbocharged engine isn’t about just bolting a giant huffer to the exhaust manifolds and calling it a day. The turbo might only cost you $500, but a good install doesn’t stop there. Turbochargers make power as a function of the engine’s original horsepower and torque, so building an engine to make more power before bolting the turbo onto it will likely yield benefits that compensating with huge boost won’t.

 

  1. Determine the required airflow in cubic feet of air per minute. Boost doesn’t make power, it just shoves more air through your engine. Because engines typically operate an air/fuel ratio of about 14 parts air to 1 part fuel, and because gasoline contains a certain amount of energy (about 114,000 British Thermal Units per gallon), you can make a direct correlation between airflow in cfm and horsepower. That ratio is about 150 cfm to 100 horsepower. As an example, let’s put together a 900 horsepower Chevrolet 350: For this application, you’ll need about 1,350 cfm of air.

 

  1. Calculate your engine’s non-turbo airflow in cfm. There are three ways to do this: You can either use an online cfm-to-horsepower calculator that takes engine displacement, efficiency and rpm into account, and you can extrapolate from the engine’s stock horsepower; or you can take the engine to a dyno room and check it. For our example engine, we’ll say that (in non-turbo form) it produces 300 horsepower at 5,500 rpm, at an 80 percent volumetric efficiency. The online calculator gives us 446 cfm airflow, and using the 150-cfm/100-horsepower ratio gives us 450 cfm.

 

  1. Divide your required airflow by your engine’s stock airflow to determine the required boost pressure ratio (the ratio of boost pressure to atmospheric pressure, which is about 14.7 psi). For the example engine, you arrive at a pressure ratio of exactly 3.00. Here’s a bit of trickery, though: Dividing desired horsepower by non-turbo horsepower will give you the same pressure ratio figure as going through this long-form cfm-to-horsepower-to-pressure ratio calculation. You only went this far to understand the factors that you’ll be dealing with in turbo selection from here on.

 

  1. Look through a manufacturer’s selection of “turbo maps.” A turbo map is a graph that indexes airflow to pressure ratio, and gives a visual representation of turbo efficiency at a given pressure ratio and cfm. You’ll see pressure ratio on the vertical axis and the airflow on the horizontal axis. A compressor map looks something like an elongated bulls-eye: the center of that bull’s eye is the compressor’s maximum efficiency range, which is where it makes boost without producing excess heat.

 

  1. Compare your engine’s required pressure ratio and airflow in cfm to various compressor maps and find one that puts your target airflow/pressure point in the center-to-upper-right-hand corner of the compressor’s maximum efficiency range (the center of the bulls-eye). Many times you’ll find airflow expressed in the metric “m3/s,” or meters cubed per second. To convert cfm to m3/s, multiply cfm by 0.00047. For our example engine, we’ll need to find a turbo that supplies full efficiency at a 3.00 pressure ratio at 0.6345 m3/s flow. Again, find a compressor where that point falls in the center-to-upper-right-hand corner of the turbo’s maximum efficiency range.

 

  1. Repeat Steps 2 through 7, using the engine’s peak torque rpm. The Chevy 350 in our example makes its peak torque at 2,000 rpm, where (according to the stock dyno graph) it makes 140 horsepower. Apply the 150-cfm/100-horsepower rule and you’ll find that this engine uses 210 cfm at that rpm. Multiply that airflow by the required pressure ratio (3.00) and you have your low-end boost response requirement. In addition to producing a 3.00 pressure ratio at 1,350 cfm (0.6345 m3/s), it should produce that same 3.00 PR at 630 cfm (0.2961).

 

  1. Search and search some more until you find a turbo that’s completely spooled up (producing a 3.00 PR, in this case) at your torque-peak airflow and maintains that PR through the engine’s horsepower-peak airflow. You’ll often find that, for larger engines like our 350, such turbos do not exist. No turbo out there will provide those PR and flow numbers over such a wide spectrum of airflow.

 

  1. Re-calculate for a multiple-turbo setup. If you can’t find a turbo to fit, divide your airflow figures by the number of turbos you want to use. Two turbos flow twice as much air as one, and smaller turbos have a wider efficiency range relative to absolute airflow than smaller ones. So, for our example 350, divide 1,350 cfm (0.6345 m3/s) and 630 cfm (0.2961) by two; now you need a pair of turbos that will provide a 3.00 PR at 675 cfm (0.3172 m3/s) to 315 cfm (0.1480 m3/s). That’s a spread of only 360 cfm for the little twin-turbo setup, versus 720 cfm for the single, big turbo setup — a much more achievable goal for any compressor.

Tip

  • If you got all disappointed when you got to Step 7 and found out that you’d have to do everything over again, then find a turbo that fit both requirements, then don’t feel bad. Some of the biggest names in the business don’t bother calculating the airflow spread from peak torque to peak horsepower. However, this little oversight just isn’t cool for modern turbo-engine builders. The modern turbo engineer understands that quality turbo selection is about performance throughout the engine’s entire operating range, not just at peak horsepower. Turbo lag is so 1980s.

Warnings

  • When you do turbocharge your vehicle, make sure to support it with other modifications, as the turbo will probably make other parts of your car break.
  • It would be a good idea to install forged pistons, increase injector capacity, a higher flowing fuel pump, a new exhaust system, head studs, and forged connecting rods.
  • Installing a turbocharger yourself, and making it live, is a very difficult and in depth project. If you’re a beginning mechanic, it is not recommended that you try this unless you have someone experienced helping you.
  • The increased power of your vehicle can also make other parts of your car break. It could snap your axles, bend your drive shaft, break the rear end in a RWD car, and even bend your car from the increased torque. Be sure to upgrade the other parts of your car at the same time as you install the turbocharger, or else you could end up with a powerful car sitting in the driveway because there’s no way to put the power down.

Refrences

Differences Between Rotary & Reciprocating Compressors

Rotary and reciprocating compressors are both components of gas transfer systems. They both have the same purpose–to bring a gas into the system, inhale exhaust, then repeat the process. They both do this by changing the pressure at certain points in order to force gas in and exhaust out.

Pistons

One key difference is that reciprocating compressors use pistons while rotary compressors do not. A reciprocating compressor has a piston move downwards, reducing pressure in its cylinder by creating a vacuum. This difference in pressure forces the cylinder door to open and bring gas in. When the cylinder goes back up, it increases pressure, thus forcing the gas back out. The up-and-down motion is called a reciprocating motion, hence the name.

Rollers

Rotary compressors, on the other hand, use rollers. They sit slightly off-center in a shaft, with one side always touching the wall. As they move at high speeds, they accomplish the same goal as the reciprocating compressors–one part of the shaft is always at a different pressure than the other, so gas can come in at the low pressure point and exit at the high pressure point.

Advantages and Disadvantages

Reciprocating compressors are marginally more efficient than rotary compressors, generally being able to compress the same amount of gas with between 5 and 10 percent less energy input. However, since this difference is so marginal, most small-to-medium level users are best off using a rotary compressor. Reciprocating compressors are more expensive and require more maintenance, so it is often not worth the extra cost and headache for such a small difference in efficiency.

Large users, however, are generally best-served by reciprocating compressors. These are users for whom 5 percent represents a substantial figure, often substantial enough to justify the added expense.

Comparison Between Reciprocating and Rotary Compressors

Comparison between Reciprocating and Rotary Compressors can be done in aspects like pressure ratio, handled volume, speed of compressor, vibrational problem, size, air supply, purity of compressed air, compression efficiency, maintenance, mechanical efficiency, lubrication, initial cost, flexibility and suitability.

 

S.no
Aspect
Reciprocating Compressors
Rotary Compressors
1 Pressure Ratio Discharge Pressure of air is high. The pressure ratio per stage will be in the order of 4 to 7. Discharge pressure of air is low. The pressure ratio per stage will be in the order of 3 to 5.
2 Handled Volume Quantity of air handled is low and is limited to 50m3/s. Large measure of air handled can be handled and it is about 500 m3/s.
3 Speed of Compressor Low speed of compressor. High speed of compressor.
4 Vibrational Problem Due to reciprocating section, greater vibrational problem, the parts of machine are poorly balanced. Rotary parts of machine, thus it has less vibrational problems. The machine parts are fairly balanced.
5 Size of compressor Size of Compressor is bulky for given discharge volume. Compressor size is small for given discharge volume.
6 Air supply Air supply is intermittent. Air supply is steady and continuous..
7 Purity of compressed air Air delivered from the compressor is dirty, since it comes in contact with lubricating oil and cylinder surface. Air delivered from the compressor is clean and free from dirt.
8 Compressed efficiency Higher with pressure ratio more than 2. Higher with compression ratio less than 2.
9 Maintanence Higher due to reciprocating engine. Lower due to less sliding parts..
10 Mechanical Efficiency Lower due to several sliding parts.. Higher due to less sliding parts.
11 Lubrication Complicated lubrication system. Simple lubrication system.
12 Initial cost Higher. Lower.
13 Flexibility Greater flexibility in capacity and pressure range. No flexibility in capacity and pressure range.
14 Suitability For medium and high pressure ratio.
For low and medium gas volume.
For low and medium pressures.
For large volumes.

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