Worm Gear: (02:16 - 31.03.2011) In worm gears, the axes are non- intersecting and the planes containing the axes are normally at right angle to each other. Worm- gear is a special case of a crossed helical gear or spiral gear in which the shaft angle is 90o. The hand of helix is the same for both mating gears. To get large speed reduction in skew shafts and to transmit a little higher load than usual spiral gear, use of worm and worm gears can be made. Worm gears have wide application in hoisting equipments, due to the itself locking ability.
A single-enveloping worm gear set has a cylindrical worm with a throated gear wrapped around the worm and there is a line contact between the teeth.
A double-enveloping worm gear set has both members throated and wrapped around the worm each other and there is a area contact between the teeth.
The worm gear is normally the driven member of the pair and is amde to envelop (or wrap around) the worm. The axis length of the worm is increased so that at least one or two threads, called as teeth, complete the circle on it.
The worm is a member having the screwlike thread and worm theet are frequently named as threads. Worms in common use have 1 to 8 teeth, and, as well as there is no definite relation between the number of teeth and the pitch diameter of a worm. Worms may be designed with a cylindrical pitch surface as shown in the figure. A worm can be single, double or triple start.
(Theory of Machines and Mechanisms - II, H.G Phakatkar, p.636-637)
Response Surface Methodology: (03:41 - 31.03.2011)
Response surface methodolgy (RSM) is a collection of statistical an d mathematical techniques useful for developing, improving, and optimizing processes. It also has important applications in the design, development, and formulation of new products, as well as in the improvement of existing product designs.
The most extensive applications of RSM are in the industrial world, particularly in situations where several input variables potentially influence some performance measure or quality characteristics of the product or process. This performance measure or quality characteristics is called response. It is typically measured on a continuous scale, although attribute responses, ranks, and sensory responses are not unusual. Most real-world applications of RSM will involve more than one response. The input variables are sometimes called independent variables, and they are subject to the control of the engineer or scientist, at least for purpose of a test or an experiment.
(Response surface methodology: process and product optimization using designed experiments ,Raymond H. Myers,Douglas C. Montgomery,Christine M. Anderson-Cook, 3rd Edition, p.1)
Potentiometer: (18:11 - 31.03.2011)
A potentiometer is a device that is designed to measure an unknown e.m.f by comparing it with known e.m.f. The konwn e.m.f may be obtained from a standart cell or any other standart cell. If any one of the e.m.f.s is known, then other unknown e.m.f can be obtained by only comparison of unknown e.m.f with known e.m.f. i.e a standart e.m.f.
The result obtained with potentiometer are with high degree of accuracy, because the e.m.f measurement is done by comparison method and result is not dependent upon the deflection of pointer actually. Thus,the degree of accuracy totally depends upon the accuracy with which the reference voltage is known.
The potentiometer makes use of balance or null condition for the unknown e.m.f. measurement, then under the balance condition no current can flow through any element in the branch consisting the unknown e.m.f. Thus the potentiometer can measure e.m.f of source which is not dependent on the source resistance. As no current flows the branch consisting unknown e.m.f., there is no voltage drop across source resistance.
The main application of the potentiometer is to measure e.m.f., it can also be used for the current measurement by measuring voltage due to unknown current across known standart resistance. Then by ohm's law, the unknown current can be obtained. Along with this the potentiometers can also be used for the calibration of voltmeters and ammeters, for testing of energymeter and wattmeter, for the measurement of self resistance.
There are two types of potentiometers; namely
1) D.C. potentiometer
2) A.C. potentiometer
(Electrical Measurements & Measuring Instruments, K.A.Bakshi A.V.Bakshi U.A.Bakshi, 1st Edition, 2007, p. 5-1)
Coextrusion: (18:38 - 31.03.2011)
Coextrusion is the simultaneous extrusion of two or more polymers through a single die where the polymers are joined together such that they form distinct, well-bonded layers forming a single extruded part. Coextrusion has been applied in film, sheet, tubing, blown film, wire coating, and profile extrusion.
Advantages of coextrusion are better bonds between layers, reduced materials and processing costs, improved properties, and reduced tendency for pinholes, delamination and air entrapment between the layers. Another advantage is that it is often possible to reuse scrap material and locate it in an inside layer of the extruded product. so that it does not affect the appearance of the product. An obvious disadvantage of coextrusion is that the tooling is more difficult to design and manufacture and, therefore, more expensive.. Further, it requires at least two extruders and it takes more operational skill to run a coextrusion line.
(Polymer extrusion, Chris Rauwendaal, 4th Edition, p.567)
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