Machining operations

The U.S. Bureau of Labor Statistics (20) has Hsted 416,000 persons employed as welders, cutters, and welding machine operators, with 90% employed in the fields of manufacturing, services, constmction, and wholesale trades. The same report projects a decline in employment for welders job prospects remain good, however, as the number of qualified workers entering the market is expected to balance workers leaving the field. 

Machining. Magnesium is the easiest of all stmctural metals to machine (120). Because of this machinabiUty, it is sometimes used in apphcations where a large number of machining operations are required. The machinability of magnesium alloys relative to that of other metals based on the lowest power required to remove 16 cm of metal and when magnesium is assigned a value of unity, is (120) ... 

Modem practice is to maintain the white water system as closed as possible, ie, as much water as is compatible with efficient machine operation is recycled. The loss of fibers and inert furnish components, particularly clay, has been gready reduced. Eiber losses, however, stiU occur into the white water, and greater economy of operation may be achieved if these fibers could be recovered. Thus, it is common to design a fiber-recovery system into the white water cycle. The three general types of save-all fiber recovery are based on filtration (qv), dotation (qv), and sedimentation (qv). If these are operated efficiendy, the net fiber loss can be less than 1%. 

The cutting tool is an important component of the machining system. Consequendy, tool materials significantly affect machining operation productivity. Other elements include cutting conditions, tool geometry, and the characteristics of the work material, nature of parts produced, machine tool, and support system. 

During machining operations, eye protection is recommended during grinding operations, NIOSH-approved respirators for metal fumes and dust are recommended (177). Fine powder of Co is known to cause dermatitis and pulmonary disorders in humans. Most manufacturers supply safety information with their products (178). These should be followed strictly for the welfare of the personnel on the shop floor. 

Many improvements have been made to streamline performance and to reduce machine operation labor. Some of these are tensionless jigs using variable speed electric motors with built-in drag for brakes, automatic reversing equipment, and automatic temperature and level controls. These machines are widely used for goods that are easily creased, such as fabrics consisting of filament acetate, heavy filament nylon, or cotton duck. They are also convenient for small dye lots and for sampling purposes. 

Another extremely popular machine of this type is the jet dyeing machine which conserves energy by reducing the cloth-to-Hquor ratio to 1 10 or lower as compared to 1 20 for the winch. In this machine, the fabric which is in a rope form is transported by movement of the dye Hquor through a Venturi jet. This method provides intimate contact between the dye Hquor and each meter of material. The machine operates at 40—135°C. 

Mechanical Expanders Reciprocating expanders are very similar in concept and design to reciprocating compressors. Generally these units are used with inlet pressures of 4 to 20 MPa. These machines operate at speeds up to 500 rpm. The thermal efficiencies (actual enthalpy difference/maximum possible enthalpy difference) range from about 75 percent for small units to 85 percent for large machines. 

It kg Avg Instant oz gr Package setup, supply FiUing- machine operators Package closers PaUetizers, loaders, attendants Package conveyorized Automatic palletizing Filling machine System ... 

Cleaning Supercritical fluids such as CO9 are being used to clean and degrease quartz rods used to produce optical fibers, produc ts used in the fabrication of printed circuit boards, oily chips from machining operations, and precision bearings in militaiy applications, and so on. Here, CO9 replaces convention chlorocarbon or chlorofluorocarbon solvents. 

Whenever the process machine operates at the same speed as its driver, the two can be directly coupled. This direct couphng stiU allows for a variable speed, through acuustments of the speed or the driver. Steam turbine speed can be easily adjusted, and electric motor speed can also be varied by the use of special drives that vaiw the frequency of the power applied to the motor. Wdiether the speed is fixed or variable, direci coupling of two machine shafts presents the problem of accommodation of misalignment. To this purpose, machines are coupled through a.flexible coupling. 

Vlanv process machines operate at speeds diFFerent From the one oF their drivers. Typical oF cases where the machine rotates. dower than the driver are reciprocating compressors typical examples oF machines rotating/ js / er than the drivers are centriFiigal compressors driven bv electric motors. In either case, ear. are used to match the two speeds, (iears can also be designed to accommodate shaFts that... 

V( = zero phase seqtience p.ti. reactance n = no. of machines operating in parallel... 

By the harmonic flux and frequencies Increased iron losses in the inductive machines, operating on such a system, due to saturation effects (equations (1.12) and (1.13). 

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