Wheel sizes

Wheel sizes Wheel diameters range from 1.75 in. for eold helium expanders up to 55 in. for eompressor impellers. 

This section will focus upon the crystallization principles used to produce commercially synthetic diamond grit abrasives. The size of particles discussed here are within an envelope of about 850-200 pm for grits used mainly in stone and concrete sawing (saw sizes) and from about 200-50 pm used for grinding applications (wheel sizes). 

They are built in sizes up to 1500 hp and may be obtained in standardized frames up to 1000 hp with wheel diameters from 12 to 36 in. Rotational speeds vary from 600 to 7200 rpm or higher the lower speeds apply to the larger wheel sizes used with direct-connected turbines, and the hi er speeds are favored in geared units. The bucket speed usually falls between 250 and 450 ft/s in direct-coimected turbines operating at 3600 rpm and may exceed 600 fl/s in geared turbines. 

Roulette wheel selection In this selection variant the probability for selecting a chromosome is proportional to its fitness. The idea can be illustrated when we imagine a roulette wheel, where a slot is allocated to each chromosome and the size of the slot is chosen with respect to the quality of the chromosome. When the wheel is spinning the chromosomes with a better quality are more likely to be chosen than those of a minor quality. Figure 9-28 illustrates this procedure,... 

Figure 9-28. Roulette wheel selection. The size of each sector is equivalent to the fitness of the corresponding chro iTiosoiTie.

Bonded abrasive products are made as wheels, disks, cylinders, sticks, blocks, and segments, all of which are defined n.yiSyi-B74.2-1974, "USA Standard Specifications for Shapes and Sizes of Grinding Wheels." This bulletin is sponsored by the Grinding Wheel Institute it is obtainable from most wheel manufacturers. 

Typically, dry potassium nitrate is pulverized in a ball mill. Sulfur is milled into cellular charcoal to form a uniform mix in a separate ball mill. The nitrate and the sulfur—charcoal mix are screened and then loosely mixed by hand or in a tumbling machine. Magnetic separators may be used to ensure the absence of ferrous metals. The preliminary mix is transferred to an edge-mimer wheel mill with large, heavy cast iron wheels. A clearance between the pan and the wheels is required for safety purposes. The size of this gap also contributes to the density of the black powder granules obtained. Water is added to minimize dusting and improve incorporation of the nitrate into the charcoal. The milling operation requires ca 3 to 6 h. 

The wisest fan choice is frequently not the cheapest fan. A small fan operates well on its curve but may not have adequate capacity for maximum flow control, future needs, or process upset conditions. It may be so lightly constmcted that it is operating near its peak speed with no provision for speed increases in the future, if needed. As fan size is increased, efficiency generally improves and wheel speed is lower. These factors decrease operating cost and provide reserve capacity for the future. However, it is also possible to oversize a fan and impair its performance. 

Preferably, the wheel cover of the present invention may be easily applied without extended mechanical or manual effort merely by adhesively applying the cover to the wheel spokes or rim. Once in place, the wheel cover may be shrunk to size so as to provide a tightly fit cover. 

Pulpstones. Improvements have been made in the composition and speed of the grinding wheel, in methods of feeding the wood and pressing it against the stone, in control of power to the stones, and in the size and capacity of the units. The first pulpstones were manufactured from quarried sandstone, but have been replaced by carbide and alumina embedded in a softer ceramic matrix, in which the harder grit particles project from the surface of the wheel (see Abrasives). The abrasive segments ate made up of three basic manufactured abrasive siUcon carbide, aluminum oxide, or a modified aluminum oxide. Synthetic stones have the mechanical strength to operate at peripheral surface speeds of about 1200—1400 m /min (3900 to 4600 ft/min) under conditions that consume 0.37—3.7 MJ/s (500—5000 hp) pet stone. 

Hquid is fed into center of spinning disk, cup, or wheel, and spreads out toward rim produces a 360° spray pattern and relatively uniform drop size used in spray drying and cooling appHcations... 

The bulk of synthetic industrial diamond production consists of the smaller crystal sizes up to 0.7-mm particle size (25 mesh). This size range has wide utihty in industry, and a significant fraction of the world s need for diamond abrasive grit is now met by synthetic production yielding thousands of kilograms per year. Because the raw materials are plentiful, synthetic production could, if necessary, supply the world demand for diamond abrasive. Development work continues in order to improve size and utility of the manufactured product and to realize the full potential of diamonds at minimum cost. An appreciable increase in performance has been obtained by coating the diamonds with a thin layer of nickel or copper, before incorporating them into wheels. The thin layer of metal apparendy improves adhesion and heat transfer. 

An impulse-type turbine experiences its entire enthalphy drop in the nozzle, thus naving a very high velocity entering the rotor. The velocity entering the rotor is about twice the velocity of the wheel. The reaction type turbine divides the enthalphy drop in the nozzle and in the rotor. Thus, for example, a 50 percent reaction turbine has a velocity leaving the nozzle equal to the wheel speed and produces about V2 the work of a similar size impulse turbine at about 2-3 percentage points higher efficiency than the impulse turbine (0 percent reaction turbine). The effect on the efficiency and ratio of the wheel speed to inlet velocity is shown in Fig. 29-27 for an impiilse turbine and 50 percent reaction turbine. 

---