Secondary machining

Honeycomb core parts are usually supplied from the core manufacturer clean and packaged in such a way that additional cleaning is not necessary. If this is not the case or if secondary machining is necessary, the core detail is cleaned by vapor degreasing or emulsion cleaning to remove organic contaminants. 

Cooling water flow to the barrel jacket coolers for the secondary extruder removes the excess energy in the resin dissipated by the primary extruder and also the energy dissipated by the screw in the secondary machine. For a properly designed line, the performance of the secondary extruder determines the overall rate of the process. 

Hardness of Ore.—This is beyond the control of the operator, but its size is not. Formerly, the tendency was to feed ore up to 4 in. in size. The more recent practice is to reduce the size of feed, for operators arc determining the economic limitations of ball mills, and finding it preferable first to crush in secondary machines of approved type to 1 in. or finer. 

The large machines used for primary breaking reduce to rock to pieces 5- to 10-in. cube, a size at which they are properly sized for delivery to secondary machines. 

In these closing remarks I have touched on a very difficult subject, much more difficult than anything else in this book, and I shall not develop it any further here, beyond indicating briefly what is difficult about it. The essential problem is that all of the artificial systems that we know and understand depend on external agencies to keep them running. If a machine in a factory breaks down or wears out, it cannot repair or replace itself but needs some other machine, or some other factory, to do so. Of course, a large and sophisticated factory can include machines to maintain the primary machines, but that does not solve the problem, because these secondary machines are also subject to wear and tear, and need to be repaired or replaced themselves. Any simple-minded attempt to solve the problem thus leads to an infinite regress, in which each new step raises more problems than it resolves. 

An extension of conventional foiging known as precision foiging can be used to acquire geometric configurations very close to the final desired shape, thus minimizing secondary machining operations. 

The plastic (usually nylon) air intake manifold weighs half as much as one made from pressure-cast aluminium, and improves engine performance with its smoother inner surfaces, which minimize airflow resistance. The manifold is injection-moulded (see Chapter 7) and so secondary machining costs are eliminated. Additionally, because nylon is less thermally conductive than aluminium, the engine runs slightly hotter, which leads to a reduction in emissions the plastic manifold engines also have a shorter warm-up time. 

Adhesives ease tolerances, saving the cost of secondary machining and grinding. 

Melt-processible fluoroplastics can be molded into articles and stock shapes by extrusion, injection molding, transfer molding, and similar techniques. Polytet-rafluoroethylene cannot be processed by melt processing techniques due to its extremely high viscosity. This can be achieved by machining of molded stock shapes. Secondary machining can be used to finish parts that are molded by melt processing techniques. 

MIM, which possess such properties, offers a very attractive alternative over the conventional methods, such as investment casting, discrete machining and other ccmventional powder metallurgy process where secondary machining would be needed to create additional geometry. 

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