Production Molds

Polyimides for use ia molded products and high temperature films can be produced by the reaction of pyromelHtic dianhydride [89-32-7] and 4,4 -diaminodiphenyl ether [13174-32-8] ia DMAC to form a polyamide that can be converted iato a polyimide (13). DMAC can also be used as a spinning solvent for polyimides. AdditionaUy, polymers containing over 50% vinyHdene chloride are soluble up to 20% at elevated temperatures ia DMAC. Such solutions are useful ia preparing fibers (14). 

AppHcatioas of dibasic lead phthalate, coated grade, iaclude 90 and 105°C rated PVC electrical iasulation, plastisols, profile extmsions, calendered sheet, and molded products. The recommended range of usage ia viayl electrical iasulatioa is 5—7 parts pet huadred resia, depending oa the particular iasulatioa classiftcatioa to be met. Ia geaeral-purpose extmded and molded PVC stocks, approximately 3—6 phr of coated dibasic lead phthalate is suggested. 

Blow-molded products represent the biggest use of HDPE resins, at around 40%. Packaging appHcations account for by far the greatest share of this market. These include such products as botties (especially for milk, juice, and soap), housewares, toys, pails, dmms, and tanks. Expected aimual average growth rates for these appHcations are about 5—6%. Injection-molding products are the second largest appHcation, with approximately 20% of the HDPE market. These products include housewares, toys, food containers, pails, crates, and cases. 

Floor mats, carpet backing, and reHef mats have been traditional markets for ground mbber where the material adds resHiency at a lower cost compared to virgin compounds. Certain molded products have also been markets for ground mbber. An interesting use is the manufacture of lawn soaker... 

Injection-Molded Products. Numerous housings, electrical enclosures, and cabinets are injection-molded from rigid PVC. These take advantage of PVC s outstanding UL flammabiUty ratings and easy mol ding into thin-waHed parts. PVC has developed melt flow capabiUties to the point where it competes with essentially any other flame-retarded engineering thermoplastic and molds easier than most. 

HoUow mol ding as the name implies is a molded product with a hoUow center such as Easter eggs, bunny rabbits, and Santa Claus. The molds used in hoUow mol ding are divided in two halves and connected by a hinge. Chocolate is deposited into one half of the mold. The mold is then closed and rotated so that the Uquid chocolate completely coats the inside surface of the mold. After cooling the molds are opened and the piece removed. 

Portion of a mold that forms the outer surface of the molded product. 

A wide product range, from lightweight mats through flexible and semi-rigid, to rigid slab. Pipe sections, loose wool, blowing wool, molded products and mattresses. 

High-temperature work, fire protection, acoustics, sprayed fiber, molded products, cavity-wall insulation, loft insulation. 

A wide basic range of blankets, slabs, block and pipe sections, especially molded products, felts and gaskets. 

Rigid slabs, pipe sections, beveled lags and molded products. Also as a powder mix for use in wet cement form. 

Rigid slabs, pipe sections, beveled lags, molded products. 

Fig. 2-62 Example of directional shrinkage in an injection molded product.

They range from structural foam molded products (which come from the mold as completed molded products) incorporating low density cores and high density skins of the same materials to products vacuum formed of a plastics material, the core of which becomes cellular during the heating process (Chapter 8). RP translucent structural panels for curtain wall building construction using... 

A snap joint is economical in two respects it allows the structural member to be molded simultaneously with the molded product, and it allows rationalizing the assembly, compared with such other joining processes as screws. Table 3-4 provides a comparison of its advantages and disadvantages. Some examples of the various types and their design considerations are shown in Figs. 3-23 to 3-25. 

The geometry for snap joints should be chosen in such a manner that excessive increases in stress do not occur (Table 4-3). The arrangement of the undercut should be chosen in such a manner that deformations of the molded product from shrinkage, distortion, unilateral heating, and loading do not... 

These SPI tables can also be used as the basis for establishing standards for molded products between the designer, molder, and customer. Users will find that two separate sets of values are represented. Commercial values represent common production tolerances that can be achieved at the most economical level. Fine values represent closer tolerances that can be held, but at a greater cost. The selection of one or the other will depend on the application under consideration and the economics involved. 

Generally, the more discussed and technically reviewed residual stresses are in injection molded products. It usually occurs because melt in the cavity next to the cavity is cold and does not properly flow. Cause could be the melt and/or the cavity surface was cold. Their presence can often be detected by... 

Many injection molded products will influence the final product s performance, dimensions, and other characteristics. The mold includes the cavity shape, gating, parting line, vents, undercuts, ribs, hinges, and so on (Table 3-17). The mold designer must take all these factors into account to eliminate problems. At times, to provide the best design... 

Sharp corner As reviewed, and never to many times, when a drawing does not show a radius, the tendency is for the toolmaker while manufacturing a mold to leave the intersecting machined or ground surfaces as they are generated by the machine tool. The result is a sharp comer on the molded product. Such sharp comers on the insides of products are the most frequent property detractors. 

Parting line PLs on the surface of a molded product, which are produced by the parting line of the mold, when required can often be concealed on a thin, inconspicuous edge of the product. Doing so preserves the good appearance of the molding and in most cases eliminates the need for any finishing. 

Blind hole In regard to molding products that include holes, it is important to ensure that sufficient material surrounds the holes and melt flows property. A core pin forming blind holes is subjected to the bending forces that exist in the cavity due to the high melt pressures. Calculations can be made for each case by establishing the core pin diameter, its length, and the anticipated pressure conditions in the cavity (3). 

Tolerance Thermoformed products lack the dimensional accuracy of processes such as injection and compression molded products. 

Snap fits are widely used for both temporary and permanent assemblies, principally in injection and blow molded products. Besides being simple and inexpensive, snap fits have superior qualities. Snap fits can be applied to any combination of materials, such as plastic and plastic, metal and plastics, glass and plastics, and others. All types of plastics can be used (Chapter 3, DESIGN CONCEPT, Snap Joint). 

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