SHORT PRODUCTION RUN

It can be said that basically the up-stream and down-stream procedures are similar in production lines whether calenders or extruders are used. For a given quantity of output, it is usually necessary to have more extruders than calenders. ITiis situation makes the extrusion fines more flexible and more able to handle relatively short production runs. The extrusion flexibility, when compared to calendering, includes ease of changing product thicknesses, widths, and materials. 

Polyurethanes find applications in a wide range of industries in competition with other plastics, ceramics, and metals. Cast polyurethanes are tough, abrasion resistant, have load bearing properties, and are chemical resistant. That makes them the first-choice materials in certain situations. The ability to be easily prototyped and have short production runs is a major positive factor for polyurethanes. 

Lessons may also be learned from applications of control systems in the food processing industries. These applications must satisfy hygiene requirements (including periodic cleaning and sterilization), time constraints imposed by product perishability, and requirements for accurate records of sources and operation histories of materials.21 The industry also experiences slim profit margins, short production runs, and frequent product changeovers—characteristics shared with many industrial bioprocesses. 

Calendering and extrusion lines (Chapter 5) produce film, sheet, and for applying plastic coatings to textiles, paper, or other supporting material. Table 9.1 provides comparison in fabricating PVC film. The extrusion process provides flexibility, when compared to calendering, that includes ease of changing product thicknesses, widths, materials, and provides for short production runs. 

Quality variations in the polymer produced in bstch reactors are often caused by slight variations in the reactor start up procedure. Furthermore, the polymerization rate may change considerably during the batch and this may give tempetature variations that are difficult to reproduce causing batch-to-batch variations in quality. These problems would be minimized with CSTRs if the continuous reactor system could be operated for at least several weeks before wall fouling and coagulum buUd up become critical and require reactor shutdown for cleanup. If an effective start-up procedure for a continuous reactor train is not available, the costs associated with offspec material could make continuous operation uneconomical. In addition, with a continuous reactor system one loses the flexibility of batch reactors when a multiproduct operation, with its short productions runs, is involved. 

Along with potting and encapsulating, one of the first two structural applications for epoxy resins was in tooling molds. For short production runs epoxy molds, drop hammers, stretch dies, jigs, and fixtures have replaced metal tools, especially in the aircraft industry and in automotive work. An epoxy tool can replace its metal counterpart on the basis of ease and speed of fabrication however, a resin-based tool will not have the durability of metal in long-term production runs. 

For easy maintenance and cleaning, all modern pellet mills are equipped with a hinged door in the front of the machine which can be opened to access the internal machine parts (Fig. 8.53), To also meet the demands of short production runs, a quick change pelleting cartridge (Fig. 8.54), which contains the die housing, the die, the... 

Vacuum bag moulding (autoclave process) Prepreg is encased in flexible bag a vacuum is applied to draw the prepreg against a mould surface. Heat is applied. Process carried out in autoclave Very large structures prototypes short production runs high fibre content... 

The cost of the mould is relatively low and practically any shape can be made. This means that hand lay-up is a cost competitive method to make individual articles and short production runs of complicated... 

Longer production runs are preferable instead of short production runs which need frequent stoppages of plant. These waste more fuel, power, and manpower every time the plant is started and stopped—moreover, the rate of production is less during starting and stopping at least for a few hours. Hence, try to minimise idle times between batches or convert present batch operations to continuous operations. 

Fibre reinforcement is laid down hand in the required arrarigement and shape, and resin k applied with a brush. Reinforcement can be in the form of rovings, a woven roving fabric, or a mat of randomfy arranged chopped fibres (chopped stand mat—CSM). The method is very versatile, but is also labour-intensive. It is therefore used for relative short production runs, for example in the building of small boats. 

The process is labour intensive, a typical production rate for the application of the laminate being about 3 kg/hour. However, it is very versatile and as the capital required for moulds is minimal, short production runs can be justified. The usual viable range of production quantity is from 1 to 500 components. 

Rotational Molding (Rotomolding). Liquid or powdered resin is placed in a closed, heated mold and rotated on two axes so that the resin coats the walls of the mold. This produces hollow products, ranging in size from golf balls up to 22,500-gal tanks. Capital investment is low, but operating cost is high, so it is best for short production runs. 

This method is preferred for relatively short production runs and large size objects. 

The use of CNC machine tools has radically changed the manufacturing industry. Curves are as easy to machine as straight lines, as well as parts with complicated contours and complex 3D shapes. The increased automation has resulted in improvements in consistency and quality together with a reduced frequency of errors. CNC also allows for more flexibility in the way workpieces are held, often avoiding the use of expensive jigs or fixtures required on conventional machines. Dimensional modifications can be done quickly and the time required to change over to a different part is reduced. Small batches or short production runs as well as parts needed in a hurry can be easily accommodated. 

Irregular discharges coming sporadically from relatively short production runs. These can cause acclimatization hazards for the activated sludge bacterial mass. 

Molds that are subjected to many, short production runs are also in danger of premature wear. Check the mold for hot spots and try to achieve uniform cooling. Make sure both mold halves are at equal temperature. A temperature variation in one section of the mold surface also can create a non-uniform flow front. 

Compression press capacities range to 100 tons (890 kN) for sm ler parts or parts with a short production run larger, and more automated, machines... 

Automatic machinery is available for high speed application. giving insertions up to the rate of thirty a minute. However, for short production runs, hand insertion equipment is comparatively easy to manufacture. 

Process flexibility is moderate tooling is dedicated, but changeover and setup times are short. Short production runs viable if section designed with part consolidation and integral fastening in mind. Minimum billet size = 250 kg (equivalent to 500 m). 

As silicone elastomers flow easily under pressure, the forces involved in moulding can be lower than other elastomer types. Many prototype or short production-run moulds can be made of relatively soft materials, though for normal production situations, hardened steel is preferred. Highly polished cavity surfaces may well prove adequate, but chrome plating is often specified. 

RP has progressed beyond the simple show and tell of a physical prototype to the ability to create functional prototypes for testing, customized products, and short production runs of standardized products. In addition, low-cost tooling can be built for fixtures, assembly tooling, and molds. 

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