High-Speed Units

High-speed units are normally separable. That is, the compressor frame and driver are separated by a coupling or gear box. This is opposed to an integral unit where power cylinders are mounted on the same frame as the compressor cylinders, and the power pistons are attached to the same drive shaft as the compressor cylinders. 

High-speed units are typically engine or electric motor driven, although turbine drivers have also been used. Engines or turbines can be either natural gas or diesel fueled. By far the most common driver for a high-speed compressor is a natural gas driven engine. 

Some induction heating furnaces must operate at frequencies higher than the supply frequency. Formerly, rotating motor alternator frequency converters were used. Now the avadabdity of high speed, high power sdicon controlled rectifiers for use in frequency converters has made rotary converters obsolete. Modem units operate at higher efficiency, cost less, require less factory space, and coordinate readdy with process controls (2). 

Rubber-mill chips are dissolved similarly to resins, to provide color concentrates. Dough mixer and chip concentrates must be diluted with solvent and other vehicles to make finished inks. Media milling is becoming a method of choice in both flexo and gravure ink manufacturing. Other high speed dispersing units, such as the Morehouse, Cowles, Kady, and others, are also used. 

Thermal or Flame Spray Process. The earliest experiments in metal spray used molten metal fed to a spray apparatus, where it was dispersed by a high speed air jet into tiny droplets and simultaneously blown onto the surface of the part to be covered. The metal solidified on contact. Modem processes use a more convenient source than premelted metal. Spray heads using a flame or an electrical arc to melt metal wires or powders directly are much more convenient. These are the only types used on a large scale in the United States. 

A variety of conical refiners were developed that involved modifications of the Jordan refiner. The Hydrafiner, for example, has a short, low taper, high speed rotor, and wide bars (10). The stock is driven through the refiner by an impeller which is fitted to the smaU inlet end of the rotor shaft. The Claflin refiner has a very short, high taper plug. Vanes that fit on the wide end of the plug draw the stock through the unit (11). 

Another development is the Inverform process and its more modem version, the Bel Bond (Fig. 8). In the Inverform unit, several pHes are formed on top of each other by consecutive, twin-wke forming units above a long carrying fabric. The Inverform process also is used for the forming of paper grades and is capable of moderately high speeds. Other versions of board machines involve mini-Fourdriniers and/or twin wkes which are placed on top of a carrying fabric. 

Single-punch machines produce approximately 100—150 tablets per minute. Depending on numbers of die per punch units, standard rotary presses can produce 5000 tablets/min, and even more with a double-sided rotary press. The newest high speed presses can achieve 12,000 tablets/min. 

The market for tar-based road binders has declined considerably for a variety of reasons. Less cmde tar is available and the profits from the sales of electrode pitch and wood-preservation creosote or creosote as carbon-black feedstock are higher than those from road tar. In most industrial countries, road constmction in more recent years has been concentrated on high speed motorways. Concrete, petroleum bitumen, or lake asphalt are used in the constmction of these motorways. In the United Kingdom, for example, the use of tar products in road making and maintenance had fallen from 330,000 t in 1960 to 100,000 t in 1975 and is less than 100 t in 1994, mainly based on low temperature pitch which is not suitable for electrode or briquetting binders, but which is perfectly satisfactory as the basis for road binders. 

High Speed Steels. Toward the latter part of the nineteenth century, a new he at-treatment technique for tool steels was developed in the United States (3,17) that enabled increased metal removal rates and cutting speeds. This material was termed high speed steel (HSS) because it nearly doubled the then maximum cutting speeds of carbon—low alloy steels. Cemented carbides and ceramics have since surpassed the cutting speed capabiUties of HSS by 5—15 times. 

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