Mold-skinning

Recendy, storm doors have been constmcted of advanced thermoplastic composites. Stampable, glass-mat reinforced polypropylene sheet is used to create a high strength outer skin. These compression molded skins are welded together using a friction or ultrasonic process then injection molded with a polyurethane foam core to produce an insulated structure. New technology for window frames incorporate the pultrusion of frame channels to produce a thermoset composite channel that can be filled with fiber glass for further insulation enhancement (12,31,33,34,48,49,54—56,60—67). 

Duroplastic moldings usually have a highly resinous (low-filler) mold skin. Care must be taken not to damage this mold skin when treating, for example polishing the surface. 

Uses PU intermediate for flexible, water-resist, fabric coatings, microcellular foams which are resist, to HC soivs., polyether-based molded foam formulations to improve adhesion between the foam and vinyl mold skins Features Polyester polyol... 

In order to meet the great demands of application technology and the design department on the construction, surface structures, dimensional stability of the slush mold skins, electroplated molds are made available. The goal is reached by using a complex and expensive model technology. Figure 1.188 shows the principle path from CAD data to the finished electroplated mold shell. 

The TPU slush-molded skins were first introduced in the North American fleet (MY 1998, Chrysler LH-Series) by Textron. The growth for the slush molding process continues in Europe, North America, and Japan, but as shown in Figure 4, PVC slush is being challenged by ... 

In the high pressure process, a resia melt containing a chemical blowiag ageat is iajected iato an expandable mold under high pressure. Foaming begias as the mold cavity expands. This process produces stmctural foam products with very smooth surfaces siace the skin is formed before expansion takes place. 

The sandwich-type stmcture of polyurethanes with a smooth integral skin produced by the reaction injection molding process provides a high degree of stiffness as weU as exceUent thermal and acoustical properties necessary for its use in housing and load-bearing stmctural components for the automotive, business machine, electrical, furniture, and materials-handling industry. 

Uncured resins are skin sensitizers and contact should be avoided, as weU as breathing the vapor, mist, or dust. Novolak-based pulverized products generally contain hexamethylenetetramine, which may cause rashes and dermatitis. PhenoHc molding compounds and pulverized phenoHc adhesives must be controUed as potentially explosive dusts. In addition, they contain irritating or toxic additives. 

A mixture of PhenoHc MicrobaUoons and resin binder has a putty-like consistency. It can be molded to shape, troweUed onto surfaces, or pressed into a core. Curing gives a high strength, low density (0.144 g/cm ) foam free of voids and dense areas, and without a brittle skin. Syntactic foams are used in widely diverse appHcations, including boat flotation aids stmctural parts in aircraft, submarines, and missiles stmctural cores for waU panels and ablative heat shields for reentry vehicles and rocket test engines. 

Highest thermal performance with PPS compounds requires that parts be molded under conditions leading to a high level of crystallinity. Glass-filled PPS compounds can be molded so that crystalline or amorphous parts are obtained. Mold temperature influences the crystallinity of PPS parts. Mold temperatures below approximately 93°C produce parts with low crystallinity and those above approximately 135°C produce highly crystalline parts. Mold temperatures between 93 and 135°C yield parts with an intermediate level of crystallinity. Part thickness may also influence the level of crystallinity. Thinner parts are more responsive to mold temperature. Thicker parts may have skin-core effects. When thick parts are molded in a cold mold the skin may not develop much crystallinity. The interior of the part, which remains hot for a longer period of time, may develop higher levels of crystallinity. 

Acute effects of overexposure are as follows. Exposure to dust may cause mechanical irritation of the eye. PPS is essentially nonirritating to the skin, although freshly molded material may occasionally cause dermatitis. Inhalation of PPS dust may cause mechanical irritation to mucous membranes of nose, throat, and upper respiratory tract. 

The rigidi d thermoplastic sheet - Tiocess combines thermoplastic sheet vacuum forming with a spray-up or cold press molding process to add a thermoset composite stmctural backing to a decorative thermoplastic skin. Large parts such as bathtubs, hot tubs, recreation vehicle components, and camper tops have been produced by this process. 

Although the continuous casting of steel appears deceptively simple in principle, many difficulties are inherent to the process. When molten steel comes into contact with a water-cooled mold, a thin soHd skin forms on the wall (Eig. 10). However, because of the physical characteristics of steel, and because thermal contraction causes the skin to separate from the mold wall shortly after solidification, the rate of heat abstraction from the casting is low enough that molten steel persists within the interior of the section for some distance below the bottom of the mold. The thickness of the skin increases because the action of the water sprays as the casting moves downward and, eventually, the whole section solidifies. 

Semiflexible molded polyurethane foams are used in other automotive appHcations, such as instmment panels, dashboards, arm rests, head rests, door liners, and vibrational control devices. An important property of semiflexible foam is low resiHency and low elasticity, which results in a slow rate of recovery after deflection. The isocyanate used in the manufacture of semiflexible foams is PMDI, sometimes used in combination with TDI or TDI prepolymers. Both polyester as well as polyether polyols are used in the production of these water-blown foams. Sometimes integral skin molded foams are produced. 

Sanitary ware, including tubs, showers, combined units, basins, and toilet tank, may be made of thermoformed ABS or acryHc sheet, molded glass-fiber-reinforced polyester, or cast acryHc resins. The glass-polyester type dominates the tub/shower market. It is possible to install the units as a two-component system, assembled in place. Gel coats may be of thermoformed decorative acryHc skins. To reduce the smoke generated by fire, methyl... 

Figure 5 Optical micrographs of specimens injection molded at 180°C (a-d) and 280°C (e,t). Samples were taken from core (left) and skin region (right). (Sample codes as in Table 1.)...

The composites injection molded at the lower temperature (180°C) did not exhibit any skin/core effect, but rather contained fibers throughout. 

Figure 22 Distribution of fiber aspect ratio l/d and fiber number N versus fiber length class for skin and transition layer of the four groups of samples injection molded.

Table 5 compares the tensile properties of Vectra A950 in the form of dispersed fibers and droplets in the matrix by injection molding, microfibril by extrusion and drawing [28], injection molded pure thick sample and pure thin sample, and the pure drawn strand [28]. As exhibited, our calculated fiber modulus with its average of 24 GPa is much higher than that of the thick and thin pure TLCP samples injection molded. It can be explained that in cases of pure TLCP samples the material may only be fibrillated in a very thin skin layer owing to the excellent flow behavior in comparison with that in the blends. However, this modulus value is lower than that of the extruded and drawn pure strand. This can be... 

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