Sandwich foam molding

Sandwich foam molding, also called coinjection molding may be considered a special form of sandwich molding. Two injection units are used to produce the skin and core as separate operations. First the skin material is injected then, through the same sprue, the core foamant is injected. The mold cavity expands, allowing the core to foam. This is a process that has been patented by ICl of Great Britain. 

In sandwich injection molding, two polymerizates in separate injection units are successively injected through the same channel into a mold. The second injected polymer blows the Hrst polymer up like a balloon and presses it against the mold walls. The process is especially suitable for enclosing foams in a more rigid coating or for enclosing cheap plastics in better quality materials. 

See also foamed plastic structural foam molding sandwich molding. 

Figures 8-3, 8-4 and 8-5 show some of the parts which incorporate the sandwich panel concept to improve stiffness. They range from structural foam molded parts (which come from the mold as completed parts) incorporating low density cores and high density skins of the same materials to parts vacuum formed of a plastics material, the core of which becomes cellular during the heating process for forming. Reinforced plastic structural panels for curtain wall building construction that have honeycomb cores or decorative cores are examples...

Within the limits set above the design can vary widely. The seat can be attached to the rest of the chair frame by leg supports at the four corners, or it can be cantilevered from the back with a floor pad support, or, in another version, from the front (Fig. 14-6). The seat construction can range from a formed sheet in two or three dimensions to one with rolled edges for reinforcement. It can have structural ribs molded in or it can be a sandwich panel construction made up of two molded parts cemented together. If can also be a structural foam molding, which is a sandwich panel construction. In each of the configurations there are tradeoffs of stiffness and strength which... 

Due to their particular sandwich-like structure formed by high density or even solid skins and a low-density foamed core (PU foams with this type of structure are also known as integral foams), molded flexible PU foams are commonly used in automobile interior parts, furniture cushions, or mattresses. 

Using several materials such as PP, glass-filled PS, and PS molded structural foam that is a natural sandwich panel material, the design procedure follows to determine the deflection and stress limitations of the material in each of the several designs. 

This low pressure process, also known as elastic reservoir molding, consists of making basically a sandwich of plastic-impregnated open-celled flexible polyurethane foam between the face layers of fibrous reinforcements. When this plastic composite is placed in a mold and squeezed, the foam is compressed, forcing the plastic outward and into the reinforcement. The elastic foam exerts sufficient pressure to force the plastic-impregnated reinforcement into contact with the heated mold surface. Other plastics are used. 

The physical properties for Reaction-Injection-Molded urethane foam cannot readily be determined because they are, as all sandwich structures, highly dependent on the particular shape of the article and the ratio of skin to foam or, in other words, the density distribution through the part. Typical densities for these new structural foams are 30 — 45 lbs./ft.3 with average moduli of elasticity of 120,000 — 250,000 p.s.i. The compression strengths are higher than those shown in Table VI for rigid foams without skins. 

Recently Sands et al.97) and Methven et al. 98) developed sheet molding compounds (SMC) and sandwich structures based on polyester syntactic foams. 

Figure 3.72 [27] presents the various types of foams and their corresponding characteristic density distributions. In integral foam, the unfoamed skin surrounds the foamed inner core. This type of foam can be produced by injection molding and extrusion and it replaces the sandwiched structure also shown in Fig. 3.72. 

In 1967, Imperial Chemical Industries (ICI) developed the sandwich or coinjection molding process for producing structural foam products. In this process, the first melt is... 

A special group of PU foams is structural foams that are made directly in their molds as either flexible or rigid foams.Structural foams are PU moldings that have a porous core and a nonporous outer layer of the same material and have been made in a single pass. These sandwich-style panels are used in construction applications. ... 

ICI Sandwich 3-stage injection molding short shot of solid polymer is followed by a second shot of foamable polymer and a third shot of solid polymer, forming a solid skin around a foamed interior. 

Some special types of foams are (1) structural foams (2) syntactic foams and multifoams and (3) reinforced foams. Structural foams (Figure 2.58c and d), which possess full-density skins and cellular cores, are similar to structural sandwich constructions or to human bones, which have solid surfaces but cellular cores. Structural foams may be manufactured by high pressure processes or by low-pressure processes (Figure 2.61). The first one may provide denser, smoother skins with greater fidelity to fine detail in the mold than maybe true of low-pressure processes. Fine wood detail, for example, is used for simulated wood furniture and simulated wood beams. Surfaces made by low-pressure processes may, however, show swirl or other textures, not necessarily detracting from their usefulness. Almost any thermoplastic or thermosetting polymer can be formulated into a structural foam. 

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