wind turbine

A wind turbine is a rotating machine that converts the kinetic energy in wind into mechanical energy. If the mechanical energy is used directly by machinery, such as a pump or grinding stones, the machine is usually called a windmill. If the mechanical energy is then converted to electricity, the machine is called a wind generator, wind turbine, wind power unit (WPU) or wind energy converter (WEC).

This article discusses electric power generation machinery. Windmill discusses machines used for grain-grinding, water pumping, etc. The article on wind power describes turbine placement, economics, public concerns, and controversy. The wind energy section of that article describes the distribution of wind energy over time, and how that affects wind-turbine design. See environmental concerns with electricity generation for discussion of environmental problems with wind-energy production.

Wind machines were used for grinding grain in Persia as early as 200 B.C. This type of machine was introduced into the Roman Empire by 250 A.D. By the 14th century Dutch windmills were in use to drain areas of the Rhine River delta. In Denmark by 1900 there were about 2500 windmills for mechanical loads such as pumps and mills, producing an estimated combined peak power of about 30 MW. The first windmill for electricity production was built in Cleveland, Ohio by Charles F Brush in 1888, and in 1908 there were 72 wind-driven electric generators from 5 kW to 25 kW. The largest machines were on 24 m (79 ft) towers with four-bladed 23 m (75 ft) diameter rotors. Around the time of World War I, American windmill makers were producing 100,000 farm windmills each year, most for water-pumping.^[1] By the 1930s windmills for electricity were common on farms, mostly in the United States where distribution systems had not yet been installed. In this period, high-tensile steel was cheap, and windmills were placed atop prefabricated open steel lattice towers.

A forerunner of modern horizontal-axis wind generators was in service at Yalta, USSR in 1931. This was a 100 kW generator on a 30 m (100 ft) tower, connected to the local 6.3 kV distribution system. It was reported to have an annual capacity factor of 32 per cent, not much different from current wind machines.

The very first electricity generating windmill operated in the UK was a battery charging machine installed in 1887 by James Blyth in Scotland. The first utility grid-connected wind turbine operated in the UK was built by the John Brown Company in 1954 in the Orkney Islands. It had an 18 metre diameter, three-bladed rotor and a rated output of 100 kW.

Water turbine

A water turbine is a rotary engine that takes energy from moving water.

Water turbines were developed in the nineteenth century and were widely used for industrial power prior to electrical grids. Now they are mostly used for electric power generation. They harness a clean and renewable energy source.

Flowing water is directed on to the blades of a turbine runner, creating a force on the blades. Since the runner is spinning, the force acts through a distance (force acting through a distance is the definition of work). In this way, energy is transferred from the water flow to the turbine.

Water turbines are divided into two groups; reaction turbines and impulse turbines.

The precise shape of water turbine blades is a function of the supply pressure of water, and the type of impeller selected.

Reaction turbines

Reaction turbines are acted on by water, which changes pressure as it moves through the turbine and gives up its energy. They must be encased to contain the water pressure (or suction), or they must be fully submerged in the water flow.

Newton's third law describes the transfer of energy for reaction turbines.

Most water turbines in use are reaction turbines. They are used in low and medium head applications.

Impulse turbines

Impulse turbines change the velocity of a water jet. The jet impinges on the turbine's curved blades which change the direction of the flow. The resulting change in momentum (impulse) causes a force on the turbine blades. Since the turbine is spinning, the force acts through a distance (work) and the diverted water flow is left with diminished energy.

Prior to hitting the turbine blades, the water's pressure (potential energy) is converted to kinetic energy by a nozzle and focused on the turbine. No pressure change occurs at the turbine blades, and the turbine doesn't require a housing for operation.

Newton's second law describes the transfer of energy for impulse turbines.

Efficiency

Large modern water turbines operate at mechanical efficiencies greater than 90% (not to be confused with thermodynamic efficiency).

Die casting

 Die casting is the process of forcing molten metal under high pressure into mold cavities (which are machined into dies). Most die castings are made from nonferrous metals, specifically zinc, copper, and aluminum based alloys, but ferrous metal die castings are possible. The die casting method is especially suited for applications where a large quantity of small to medium sized parts are needed with good detail, a fine surface quality and dimensional consistency.

This level of versatility has placed die castings among the highest volume products made in the metalworking industry.
In recent years, injection-molded plastic parts have replaced some die castings because they are cheaper and lighter.Plastic parts are a practical alternative if hardness is not required and little strength is needed.

Process
There are four major steps in the die casting process. First, the mold is sprayed with lubricant and closed. The lubricant both helps control the temperature of the die and it also assists in the removal of the casting. Molten metal is then shot into the die under high pressure; between 10—175 MPa (1,500—25,000 psi). Once the die is filled the pressure is maintained until the casting has solidified. Finally, the die is opened and the shot (shots are different from castings because there can be multiple cavities in a die, yielding multiple castings per shot) is ejected by the ejector pins. Finally, the scrap, which includes the gate, runners, sprues and flash, must be separated from the casting(s). This is often done using a special trim die in a power press or hydraulic press. An older method is separating by hand or by sawing, which case grinding may be necessary to smooth the scrap marks. A less labor-intensive method is to tumble shots if gates are thin and easily broken; separation of gates from finished parts must follow. This scrap is recycled by remelting it.

The high-pressure injection leads to a quick fill of the die, which is required so the entire cavity fills before any part of the casting solidifies. In this way, discontinuities are avoided even if the shape requires difficult-to-fill thin sections. This creates the problem of air entrapment, because when the mold is filled quickly there is little time for the air to escape. This problem is minimized by including vents along the parting lines, however, even in a highly refined process there will still be some porosity in the center of the casting.

Most die casters perform other secondary operations to produce features not readily castable, such as tapping a hole, polishing, plating, buffing, or painting.

Pore-free casting process
When no porosity is required for a casting then the pore-free casting process is used. It is identical to the standard process except oxygen is injected into the die before each shot. This causes small dispersed oxides to form when the molten metal fills the dies, which virtually eliminates gas porosity. An added advantage to this is greater strength. These castings can still be heat treated and welded. This process can be performed on aluminum, zinc, and lead alloys.

Heated-manifold direct-injection die casting
Heated-manifold direct-injection die casting, also known as direct-injection die casting or runnerless die casting, is a zinc die casting process where molten zinc is forced through a heated manifold and then through heated mini-nozzles, which lead into the molding cavity. This process has the advantages of lower cost per part, through the reduction of scrap (by the elimination of sprues, gates and runners) and energy conservation, and better surface quality through slower cooling cycles.

Equipment
There are two basic types of die casting machines: hot-chamber machines (a.k.a. gooseneck machines) and cold-chamber machines. These are then rated by how much clamping force they can apply. Typical sizes range from 100 to 4,000 tons. The largest machines are as big as a house.
Hot-chamber machines rely upon a pool of molten metal to feed the die. At the beginning of the cycle the piston of the machine is retracted, which allows the molten metal fill the "gooseneck". The gas or oil powered piston then forces this metal out of the gooseneck into the die. The advantages of this system include fast cycle times (approximately 15 cycles a minute) and the convenience of melting the metal in the casting machine. The disadvantages of this system are that high-melting point metals cannot be utilized and aluminum cannot be used because it it picks up some of the iron while in the molten pool. Due to this hot-chamber machines are primarily used with zinc, tin, and lead based alloys.

Cold-chamber machines are used when the casting alloy cannot be used in hot-chamber machines; these alloys include aluminum, magnesium, copper, and zinc alloys with a large composition of aluminum. This machine works by melting the material, first, in a separate furnace. Then a precise amount of molten metal is transported to the cold-chamber machine where it is fed into an unheated shot chamber (or injection cylinder). This shot is then driven into the die by a hydraulic or mechanical piston. This biggest disadvantage of this system is the slower cycle time due to the need to transfer the molten metal from the furnace to the cold-chamber machine.
The dies used in die casting are usually made out of hardened tool steels because cast iron cannot withstand the high pressures involved. Due to this the dies are very expensive, resulting in a high startup cost. Dies may contain only one mold cavity or multiple cavities of the same or different parts. There must be at least two dies to allow for separation and ejection of the finished workpiece, however its not uncommon for there to be more sections that open and close in different directions. Dies also often contain water-cooling passages, retractable cores, ejector pins, and vents along the parting lines. These vents are usually wide and thin (approximately 0.13 mm or 0.005 in) so that when the molten metal starts filling them the metal quickly solidifies and minimizes scrap. No risers are used because the high pressure ensures a continuous feed of metal from the gate. Recently, there's been a trend to incorporate larger gates in the die and to use lower injection pressures to fill the mold, and then increase the pressure after its filled. This system helps reduce porosity and inclusions.

In addition to the dies there may be cores involved to cast features such as undercuts. Sand cores cannot be used because they disintegrate from the high pressures involved with die casting, therefore metal cores are used. If a retractable core is used then provisions must be made for it to be removed either in a straight line or circular arc. Moreover, these cores must have very little clearance between the die and the core to prevent the molten metal from escaping. Loose cores may also be used to cast more intricate features (such as threaded holes). These loose cores are inserted into the die by hand before each cycle and then ejected with the part at the end of the cycle. The core then must be removed by hand. Loose cores are more expensive due to the extra labor and time involved.

A die's life is most prominently limited by wear or erosion, which is is strongly dependent on the temperature of the molten metal. Aluminum and its alloys typically shorten die life due to the high temperature of the liquid metal resulting in deterioration of the steel mold cavities. Molds for die casting zinc last almost indefinitely due to the lower temperature of the zinc. Molds for die casting brass are the shortest-lived of all.Other failure modes for dies are:
Heat checking: surface cracks occur on the die due to a large temperature change on every cycle
Thermal fatigue: surface cracks occur on the die due to a large number of cycles

Advantages and disadvantages
Advantages:
Excellent dimensional accuracy (dependent on casting material, but typically 0.1 mm for the first 2.5 cm (0.005 in. for the first inch) and 0.02 mm for th each additional centimeter (0.002 in. for each additional inch).
Smooth cast surfaces (1—2.5 μm (40—100 μin.) rms).
Thinner walls can be cast as compared to sand and permanent mold casting (approximately 0.75 mm (0.030 in.).
Inserts can be cast-in (such as threaded inserts, heating elements, and high strength bearing surfaces).
Reduces or eliminates secondary machining operations.
Rapid production rates.
Casting tensile strength as high as 415 MPa (60 ksi).

Disadvantages:
Casting weight must be between 30 grams (1 oz) and 10 kg (20 lb).
Casting must be smaller than 600 mm (24 in.).
High initial cost.
Limited to high-fluidity metals.
A certain amount of porosity is common.
Thickest section should be less than 13 mm (0.5 in.).
A large production volume is needed to make this an economical alternative to other processes.

Engineering Metrology and Instruments

Engineering Metrology and Instruments

► Introduction:
Engineering Metrology:

- Measurement of dimensions such as length, hickness, diameter, taper, angle, flatness, profile and others.

Post-Process Inspection:

- Measurements taken after the part is produced
- Term inspection – checking dimensions and determining whether it complies with specifications.

In-process, On-line or Real-Time Inspection:

- Checking part characteristics while part is being produced.

Important concepts:

- Range of measurement:

The physical variables that are measured between two values.One is the higher calibration value H, and the other is Lower value L, The difference between H, and L, is called range.

- Sensitivity:

Is the smallest difference in dimensions that the instrument can detect.

- Accuracy:

The ability of a measurement to match the actual value of the quantity being measured.

- Precision:

The degree to which the instrument gives repeated measurements of the same standard.
The difference between precision and accuracy can be shown by the spread of shooting of a tar-get (as shown in Diagram below).

- Error:

The deviation between the results of measured value to the actual value.

- Correction:

The numerical value which should be added to the measured value to get the correct result.

Measurements Standards:

Two Standards
→ English Speaking Countries (English System):
Pound-mass, Foot, Second
→ Metric System (SI – System International):
Kilogram, Meter, Second

Measuring Instruments:

- classification of measuring instruments:
1- Length measuring Instruments.
- Direct measuring.
- Indirect measuring.
2- Angle measuring Instruments.
3- Instruments for surface finish.
4- Instruments for deviations.




1) Length measuring Instruments:

1.1) Rules and tapes: (Direct measuring)

Rules and tapes are the simplest way of measuring larger dimensions. Steel rules are generally only available to measure dimensions up to 1 metre. Beyond this, steel tapes (measuring to 30 m) or an ultrasonic rule (measuring to 10m) are used.
The steel rule is undoubtedly the simplest instrument available for measuring length.
Measurement accuracy is only modest using standard rules, which typically have rulings at 0.5mm intervals, but the best rules have rulings at 0.05mm intervals and 
a measurement resolution of 0.02 mm. When used by placing the rule against an object, the measurement accuracy is much dependent upon the skill of the human measurer and, at best, the inaccuracy is likely to be at least 0.5%.


1.2) Vernier caliper: (Direct measuring)
The vernier calipers found in the laboratory incorporates a main scale and a sliding vernier scale which allows readings to the nearest 0.02 mm. This instrument may be used to measure outer dimensions of objects (using the main jaws), inside dimensions (using the smaller jaws at the top), and depths (using the stem). 

How to read vernier calipers?

When a length is measured the zero point on the indicating scale is the actual point of measurement, however this is likely to be between two data scale points. The indicator scale measurement which corresponds to the best-aligned pair of indicator and data graduations yields the value of the finer additional precision digit.
- Example: 
The reading is 34.60 mm.
In figure shown, the first significant figures are taken as the main scale reading to the left of the vernier zero, i.e. 34 mm. The remaining two digits are taken from the vernier scale reading that lines up with any main scale reading, i.e. 60 on the vernier scale.



1.3) The Micrometer: (Direct measuring)

The micrometer screw gauge is used to measure even smaller dimensions than the vernier calipers. The micrometer screw gauge also uses an auxiliary scale (measuring hundredths of a millimeter) which is marked on a rotary thimble. Basically it is a screw with an accurately constant pitch (the amount by which the thimble moves forward or backward for one complete revolution). 

Take as an example: the micrometers which have a pitch of 0.50 mm (two full turns are required to close the jaws by 1.00 mm). The rotating thimble is subdivided into 50 equal divisions. The thimble passes through a frame that carries a millimeter scale graduated to 0.5 mm. The jaws can be adjusted by rotating the thimble using the small ratchet knob. This includes a friction clutch which prevents too much tension being applied. The thimble must be rotated through two revolutions to open the jaws by 1 mm.


How to read Micrometer?

In order to measure an object, the object is placed between the jaws and the thimble is rotated using the ratchet until the object is secured. Note that the ratchet knob must be used to secure the object firmly between the jaws, otherwise the instrument could be damaged or give an inconsistent reading. The manufacturer recommends 3 clicks of the ratchet before taking the reading. The lock may be used to ensure that the thimble does not rotate while you take the reading.

- Example: 
The reading is 7.38 mm.
In figure shown the last graduation visible to the left of the thimble is 7 mm and the thimble lines up with the main scale at 38 hundredths of amillimeter (0.38 mm); therefore the reading is 7.38 mm.


1.4) Calipers: (Indirect measuring)

These are used to transfer the measured dimension from the workpiece to a steel rule. This avoids the necessity to align the end of the rule exactly with the edge of the workpiece and reduces the measurement inaccuracy by a factor of two. In the basic caliper, careless use can allow the setting of the caliper to be changed during transfer from the workpiece to the rule. Hence, the spring-loaded type, which prevents this happening, is preferable.

Types of calipers:
1- Inside caliper: are used to measure the internal size of an object.
2- Outside caliper: are used to measure the external size of an object.
3- Divider caliper: are used in the process of marking out suitable workpieces.


2) Angle measuring Instruments:

Measurement of angles is one of the less common measurement requirements that instrumentation technologists are likely to meet. However, angle measurement is required in some circumstances, such as when the angle between adjoining faces on a component must be checked. The main instruments used are protractors and a form of angle measuring spirit level.

In some circumstances, a simple protractor of the sort used in school for geometry exercises can be used. However, the more sophisticated form of angle protractor shown in the figure provides better measurement accuracy. This consists of two straight edges, one of which is able to rotate with respect to the other. Referring to the figure, the graduated circular scale A attached to the straight edge C rotates inside a fixed circular housing attached to the other straight edge B. The relative angle between the two straight edges in contact with the component being measured is determined by the position of the moving scale with respect to a reference mark on the fixed housing B. With this type of instrument, measurement inaccuracy is at least š1%. An alternative form, the bevel protractor, is similar to this form of angle protractor, but it has a vernier scale on the fixed housing. This allows the inaccuracy level to be reduced to š10 minutes of arc.

The spirit level shown in Figure is an alternative angle-measuring instrument. It consists of a standardspirit level attached to a rotatable circular scale that is mounted inside an accurately machined square frame. When placed on the sloping surfaces of components, rotation of the scale to centralize the bubble in the spirit level allows the angle of slope to be measured. Again, measuring inaccuracies down to š10 minutes of arc are possible if a vernier scale is incorporated in the instrument.

3) Gages:

Gauge blocks, also known as slip gauges, consist of rectangular blocks of hardened steel that have flat and parallel end faces. These faces are machined to very high standards of accuracy in terms of their surface finish and flatness. The purpose of gauge blocks is to provide a means of checking whether a particular dimension in a component is within the allowable tolerance rather than actually measuring what the dimension is. To do this, a number of gauge blocks are joined together to make up the required dimension to be checked.


The pictured below accessories provide a set of holders and tools to extend the usefulness of the gauge block set. They provide a means of securely clamping large stacks together along with reference points and scribers.

Slip gauges are made from a select grade of carbide with hardness of 1500 Vickers hardness. Long series slip gauges are made from high quality steel having cross section (35 x 9 mm) with holes for clamping two slips together.

Grades:

They are available in various grades depending on their intended use:
• reference (AAA): small tolerance (± 0.00005 mm or 0.000002 in) used to establish standards 
• calibration (AA): (tolerance +0.00010 mm to -0.00005 mm) used to calibrate inspection blocks and very high precision gauging 
• inspection (A): (tolerance +0.00015 mm to -0.00005 mm) used as tool room standards for setting other gauging tools 
• workshop (B): large tolerance (tolerance +0.00025 mm to -0.00015 mm) used as shop standards for precision measurement 



Plug gages:

(a) Plug gage for checking size or diameter of internally threaded part.
(b) Plug gage for checking taper of internally threaded part.
(c) Ring gage for checking size or diameter of externally threaded part.


Ring gages: 

(a) The Metric Trapezoidal Ring Gage.
(b) American Standard Adjustable Ring Gage.



Snap gage:

- Snap gage gages diameters, lengths, and thickness.
- The adjustable limit snap gage is used to check outside diameter.
- There are a various types of snap gages: 
→ adjustable snap gage.
→ adjustable roll snap gage.
→ dial indicator snap gage.



4) Comparative length-measuring instruments:

4.1) Dial indicator:

A dial indicator is used to measure shaft runout, shaft thrust, gear backlash, flywheel face runout, flywheel housing concentricity, and valve seat concentricity. You can mount a dial indicator on a test stand or, with clamps and a magnetic base, directly on the equipment to be measured. Figure shows a typical dial indicator with mounting accessories, Most dial indicators have components such as a bezel, indicator pointer, tool post and clamp, magnetic toolholder, and sensor button that are used in taking measurements. 

Word Meaning More Information
blade micrometer Blade micrometer is a measuring device that has a thin blade to reach inside narrow recesses. 
Blade micrometer is used for measuring where the standard micrometer spindle could not be accommodated.
combination set Combination set is used as a rule, a square, a miter, a depth gage, a height gage, and a level. The combination set consists of: blade, center head, protractor head, combination square head, scribe, and spirit level.
comparator Comparator graphically displays and measures dimensions and shapes that would be difficult to measure with regular tools. Optical measurement is a different and valuable aid to quality control. Capable of magnifying an object hundreds of times.
depth micrometer Depth micrometer measures depth of holes, slots, and other recesses. 
These micrometers come as a set with interchangeable rods to accommodate various measurements.

dial indicators Dial indicators check alignment of machine components; show the variation of the object being measured. There are 2 types of dial indicators:

a. Balanced reading (has figures in both directions from the zero)
b. Continuous reading (numbered continuously) 
Continuous reading dial indicator
disc micrometer Disc micrometer measures forming tools, cutting edges, narrow slots. 
This micrometer finds its application in measuring flanges and hard to reach areas.
gage block set Gage block set is also known as "Jo Blocks". Precision-round square or rectangular blocks are made of steel, chrome, or tungsten carbide. Gage blocks are used for:
- calibration and inspection of precision instruments
- to set comparators/indicators
- setting of sine bars
- precision layout
- machine setups
micrometer Micrometer is used to measure materials. It is available in metric and inch systems. The most common are the outside and inside micrometers. 
Available in different shapes and sizes
outside caliper Outside caliper measures an outside surface. Rules are also used for transfer measurements with calipers. It is used for semi-precision and comparison measurement. They depend on "feel" to measure a part.
plug gage A type of "Go" or "No-Go" gage used to admit or refuse the inside dimension of an object.

There are three types:
- plain cylindrical
- cylindrical taper
- thread plug gage They are mounted at the ends of an aluminum handle. "Go" in one end and "No-Go" on the opposite end.
ring gage A type of "Go" or "No-Go" gage used to admit or refuse the outside dimension being checked. 

There are three types:

- plain ring gages
- taper ring gages
- thread ring gages 
screw thread micrometer The 60 degree comparator micrometer is usually called a screw thread comparator micrometer or pitch micrometer. 
The pitch diameter, the most important measurement of a screw thread.
sine bar Sine bar is used for checking angles, typically used with gage blocks. The sine bar is a precision bar that has been hardened and then ground and lapped to very precise dimensions. It is also used for machine setups.
snap gage Snap gage gages diameters, lengths,and thickness. 

Various types of snap gages:

- adjustable snap gage
- adjustable roll snap gage
- dial indicator snap gage
square A square has two straight edges that form a right angle. A machinist uses several types of squares for a variety of jobs. A square is used for inspecting squarness and laying out work.
surface gage Surface gage is a scribing tool that draws lines parallel to a surface. When combined with test indicator, flatness, parallelism and heights may be inspected. Surface gages are designed for a variety of uses. The main uses are for scribing lines, transferring measurements and for probing surfaces in inspection work.
universal bevel protractor Universal bevel protractor is used to lay out, measure, or check angles. 
Vernier caliper Vernier caliper is a precision measuring tool capable to read within .001 inch. Used for inside, outside and depth measurements. A Vernier caliper consists of a beam with a fixed measuring jaw, a sliding jaw witht he Vernier scale, and a mechanism for making fine adjustments.
Vernier gear-tooth caliper Vernier gear-tooth caliper measures gear teeth using two Vernier scales. 
Vernier height gage It is rugged and reliable tool that gives precise and dependable measurements over long vertical ranges. It is also used for precision layout.

Word	Meaning	More Information
blade micrometer	Blade micrometer is a measuring device that has a thin blade to reach inside narrow recesses.	Blade micrometer is used for measuring where the standard micrometer spindle could not be accommodated.
combination set	Combination set is used as a rule, a square, a miter, a depth gage, a height gage, and a level.	The combination set consists of: blade, center head, protractor head, combination square head, scribe, and spirit level.
comparator	Comparator graphically displays and measures dimensions and shapes that would be difficult to measure with regular tools.	Optical measurement is a different and valuable aid to quality control. Capable of magnifying an object hundreds of times.
depth micrometer	Depth micrometer measures depth of holes, slots, and other recesses.	These micrometers come as a set with interchangeable rods to accommodate various measurements.
dial indicators	Dial indicators check alignment of machine components; show the variation of the object being measured. There are 2 types of dial indicators: a. Balanced reading (has figures in both directions from the zero) b. Continuous reading (numbered continuously)	Continuous reading dial indicator
disc micrometer	Disc micrometer measures forming tools, cutting edges, narrow slots.	This micrometer finds its application in measuring flanges and hard to reach areas.
gage block set	Gage block set is also known as "Jo Blocks". Precision-round square or rectangular blocks are made of steel, chrome, or tungsten carbide.	Gage blocks are used for: - calibration and inspection of precision instruments - to set comparators/indicators - setting of sine bars - precision layout - machine setups
micrometer	Micrometer is used to measure materials. It is available in metric and inch systems. The most common are the outside and inside micrometers.	Available in different shapes and sizes
outside caliper	Outside caliper measures an outside surface.	Rules are also used for transfer measurements with calipers. It is used for semi-precision and comparison measurement. They depend on "feel" to measure a part.
plug gage	A type of "Go" or "No-Go" gage used to admit or refuse the inside dimension of an object. There are three types: - plain cylindrical - cylindrical taper - thread plug gage	They are mounted at the ends of an aluminum handle. "Go" in one end and "No-Go" on the opposite end.
ring gage	A type of "Go" or "No-Go" gage used to admit or refuse the outside dimension being checked.	There are three types: - plain ring gages - taper ring gages - thread ring gages
screw thread micrometer	The 60 degree comparator micrometer is usually called a screw thread comparator micrometer or pitch micrometer.	The pitch diameter, the most important measurement of a screw thread.
sine bar	Sine bar is used for checking angles, typically used with gage blocks.	The sine bar is a precision bar that has been hardened and then ground and lapped to very precise dimensions. It is also used for machine setups.
snap gage	Snap gage gages diameters, lengths,and thickness.	Various types of snap gages: - adjustable snap gage - adjustable roll snap gage - dial indicator snap gage
square	A square has two straight edges that form a right angle.	A machinist uses several types of squares for a variety of jobs. A square is used for inspecting squarness and laying out work.
surface gage	Surface gage is a scribing tool that draws lines parallel to a surface. When combined with test indicator, flatness, parallelism and heights may be inspected.	Surface gages are designed for a variety of uses. The main uses are for scribing lines, transferring measurements and for probing surfaces in inspection work.
universal bevel protractor	Universal bevel protractor is used to lay out, measure, or check angles.
Vernier caliper	Vernier caliper is a precision measuring tool capable to read within .001 inch. Used for inside, outside and depth measurements.	A Vernier caliper consists of a beam with a fixed measuring jaw, a sliding jaw witht he Vernier scale, and a mechanism for making fine adjustments.
Vernier gear-tooth caliper	Vernier gear-tooth caliper measures gear teeth using two Vernier scales.
Vernier height gage	It is rugged and reliable tool that gives precise and dependable measurements over long vertical ranges. It is also used for precision layout.

Casting defect

The defects in a casting may be due to pattern and moulding box equipment, moulding sand, cores,gating system or molten metal. Some of the defects are:

1: Mould shift

It results in a mismatching of the top and the bottom parts of the casting , usually at the parting line.

2: Swell

It is an enlargement of the mould cavity by molten metal pressure resulting in localized or general enlargement of the casting.

3: Fins and Flash

These are thin projections of the metal not intended as a part of casting. These usually occurs at the parting line of the mould.

4: Sand Wash

It usually occurs near the in the gates as rough lumps on the surface of a casting.

5: Shrinkage

It is a crack or breakage in the casting on the surface of the work piece, which results from unequal contraction of the metal during solidification.

6: Hot Tear

It is an internal or external ragged discontinuously in the metal casting resulting just after the metal has solidified.

7: Sand Blow or Blow Hole

It is smooth depression on the outer surface of the casting work piece.

8: Honeycombing or Slag holes

These are smooth depression on the upper surface of the casting. They usually occur near the ingates.

9: Scabs

These are patches of sand on the upper surface of the casting component.

10: Cold Shut and Misruns

These happens when the mould cavity is not completely filled by the molten and insufficient material or metal.

11: Run-outs and Bust-outs

These permit drainage of the metal from the cavity and result in incomplete casting.