Machining and finishing

In addition to the previously noted safety factors associated with these processes, there are additional needs for dust control and ventilation for dissipation of various vapors from pressing, tempering/heat treatment, and machining and finishing operations. 

The uncured compacts are presintered in vacuum or in a stream of neutral gas (Ar, H2) at 800-1400°C. Presintering ensures the removal of the organic binder to avoid later contamination of the sintering furnace by pyrolysis of the by-products. It also facilitates machining and finishing, which are difficult and expensive after final sintering because of the hardness of borides. 

Except for vertically suspended pumps (see 5.3.2 2), shafts shall be machined and finished throughout their length so that the TIR is not more than 25 pm (0.001 in.). 

After cooling, the graphitized blocks are removed from the furnace, cleaned, and inspected to determine whether property specifications have been met. Typical load-to-load cycles of an Acheson furnace are 30 days, making the process both time and capital intensive. After machining and finishing, the blocks are ready for delivery to the customer. For some materials the total manufacturing time may be as much as 5 months. 

Polysulfones have been used satisfactorily in a wide range of products, including consumer, medical, automotive, aircraft, aerospace, industrial, electrical, and electronic applications. Like other engineering thermoplastics, they are replacing metals in a variety of applications because they can be injection molded into complex shapes at reduced cost since costly machining and finishing operations can be avoided. Table 15.15 lists some of the applications of polysulfones. 

In many fields of use polysulfones have replaced or are replacing metals, ceramics, and thermosetting plastics, rather than other thermoplastics. Since commercial polysulfones can be injection molded into complex shapes, they avoid costly machining and finishing operations. Polysulfones can also be extruded into film and foil. The latter is of interest for flexible printed circuitry because of its high-temperature performance. 

PES is madnly replacing metals - sometimes because there is a saving in materials costs as, for ocample, in the replacement of stainless steel or brass, but more often PES is used because of its ability to injection mould coiq>lex shapes, and so avoid costly machining and finishing operations which are often necessary with die case metal. 

This section will discuss the megor machining and finishing operations commonly used in the manufacture of plastic products ... 

Terry A. Richardson, Machining and Finishing, Modem Industrial Plastics, Howard W. Sams Co., New York, 1974. 

Figure T.9 Two tumbling methods (a) parts being tumbled in a revolving drum and (b) parts being tumbled on an endless revolving belt. (Ref Richardson, T.A., Machining and Finishing Modem Industrial Plastics, Howard W. Sams Co., New York, 1974)...

TIFYA 65, Machining and Finishing of Aluminum and the Production and Handling of Aluminum Powders... 

Spray-buff with 175-r/min 12-in rotary floor machine and finish restorer... 

Machinability Data Center. 1980. Machining Data Handbook, 3rd ed. Cincinnati, OH The Machinability Data Center. A classic work in the field, this two-volume set is a compendium of data for the machining and finishing of materials into various types of machine parts, both simple and complex. 

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