Machines Convention

Complementaiy medicine particularly charges that conventional medicine seriously neglects patients as whole integrated human beings (body, mind, spirit) and treats them too much as machines. Conventional practitioners may well feel uneasily... 

Syntactic foams are also available in sheet form, generally at thicknesses of 20-40 mils. Since it is impractical to machine conventional honeycomb down to this thickness range, this form of syntactic foam has found use in very thin sandwich structure fabricated with composite skins. 

There is an electronic circuit called a flip-flop. It consists of two transistors connected in such a way that, if a voltage is applied, one side of the circuit becomes active and the other side not if a second voltage is applied, the circuit flips so that the active side becomes inactive and vice versa. Thus, just as with a conventional switch for which one touch puts it on and a second touch turns it off, one touch of the flip-flop turns it on and a second touch turns it ojf. Addition of two binary numbers now becomes possible. Suppose we want to add 2 -(- 1 (= 3 decimal). First, the numbers must be converted into binary code (10 and 01) and these become switch settings in the machine, but we need four switches so that 10 becomes on, off and 01 becomes off, on (Figure 42.6). 

Forming and Machining. Articles can be formed below the melting point with conventional metal-forming techniques. 

Injection Molding. Matched metal molds are used in the fabrication of plastic closures, specialty packages, and botde preforms. In conventional injection mol ding the plastic resin is melted in an extmder which forces a measured quantity or shot into a precision-machined chilled mold after which the nozzle of the extmder is withdrawn. 

Variable Flow Rate Conventional variable clearance volume and valve lifting devices are impracticable at high pressures and, should it be necessary to vary the flow rate, use has to be made of variable speed electric drives or magnetic clutches. Integral steam and gas engines have been used and Burckhardt (168) developed an hydrauhc drive to provide an integrated variable capacity machine, but its efficiency is less than that of a straight mechanical drive. 

The automotive industry is the principal user of P/M forgings, primarily for transmission and differential components, but also for engine parts. Other markets are in power tools and farm machinery. Cost effectiveness is generally the reason for substituting P/M forgings for conventionally forged, cast, or machined parts. 

Extmsion accounts for about 30% of nylon produced and is used in various processes (24). Nylons can be extmded on conventional equipment having the following characteristics. The extmder drive should be capable of continuous variation over a range of screw speeds. Nylon often requires a high torque at low screw speeds typical power requirements would be a 7.5-kW motor for a 30-mm machine or 25-kW for 60-mm. A nylon screw is necessary and should not be cooled. Recommended compression ratios ate between 3.5 1 and 4 1 for nylon-6,6 and nylon-6 between 3 1 and 3.5 1 for nylon-11 and nylon-12. The length-to-diameter ratio, T/D should be greater than 15 1 at least 20 1 is recommended for nylon-6,6, and 25 1 for nylon-12. 

Urethanes are processed as mbber-like elastomers, cast systems, or thermoplastic elastomers. The elastomer form is mixed and processed on conventional mbber mills and internal mixers, and can be compression, transfer, or injection molded. The Hquid prepolymers are cast using automatic metered casting machines, and the thermoplastic peUets are processed like aU thermoplastic materials on traditional plastic equipment. The unique property of the urethanes is ultrahigh abrasion resistance in moderately high Shore A (75—95) durometers. In addition, tear, tensUe, and resistance to many oUs is very high. The main deficiencies of the urethanes are their resistance to heat over 100°C and that shear and sliding abrasion tend to make the polymers soft and gummy. 

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