Molding foamed plastics

Foam-injection molding Foam plastic sheathing Foam products Foam regulators Foam rheology... 

C. Sadr, Process and Apparatus for Molding Foamed Plastic Article, Canadian Patent CA 2,015,639(1993). 

Foamed plastics (qv) were developed in Europe and the United States in the mid-to-late 1930s. In the mid-1940s, extmded foamed polystyrene (XEPS) was produced commercially, foUowed by polyurethanes and expanded (molded) polystyrene (EPS) which were manufactured from beads (1,2). In response to the requirement for more fire-resistant ceUular plastics, polyisocyanurate foams and modified urethanes containing additives were developed in the late 1960s urea—formaldehyde, phenoHc, and other foams were also used in Europe at this time. 

Flexible foams are resiUent open-ceU stmctures with densities varying from 25—650 kg/m, depending on the choice of the raw materials. Most flexible foams are produced in the form of a slab or bun in a contiauous process in widths up to 2.4 m and thicknesses up to 1.2 m. A Hquid foamable mixture is pumped onto a conveyor, which moves through a tunnel where reaction and foaming occur (101). Similar mixtures can be placed in a mold and allowed to foam. This process is used in the manufacture of automobile seats (see Foamed plastics). 

The first area covers low volumetric flow rates, and entrance pressures below Pcr. This sector of two-phase flow in the molding machine is characterized by a complex non-linear dependence of reduced pressure on reduced volumetric flow rate. The structure of foam plastics obtained in this way was called shell structure by the authors in [20, 21] — the extrudate contains huge shell bubbles which are comparable to its section. As CBA concentration increases, or medium volumetric flow rate is increased at low CBA concentration, small bubbles materialize in the melt around the shell bubbles, and the structure becomes shell-bubble . Increase of the volumetric flow rate and the concentration of flowing agent neutralizes the difference in bubble size their lateral dimensions become smaller than their longitudinal ones. 

Many plastic products are decorated to make them multi-colored, add distinctive logos, or allow them to imitate wood, metal and other materials. Some plastic products are painted since their as-molded appearance is not satisfactory, as may be the case with reinforced, filled or foamed plastics. Painting or coating is also for product protection. The following section will discuss some of the secondary operations frequently used with plastics. Since plastics vary widely in their ability to be machined and to accept finishes,... 

For the preparation of the foam, a solution of 1 g technical sodium diisobutyl naphthalene sulfonate in 50 ml of 3% orthophosphoric acid is prepared. 20 ml of this solution are poured into a 11 beaker and air is stirred in with a fast running mixer until the cream-like dispersion has reached a volume of 300-400 ml.Then,20 ml of the prepared urea/formaldehyde resin are mixed in, whereby the resin must be evenly distributed. After 3-4 min the introduced resin gellifies into a molded article permeated with many water/air pores under the influence of the acidic catalyst. After 24 h,the crosslinking is completed. Drying for 12 h at 40 °C in a circulating air dryer yields a brittle thermoset foam.The foamed plastic obtained is hydrophobic and has a large internal surface. It can take up about 30 times its own weight of petroleum ether. 

Fig. 8. Effect of molding pressure P on the stress in compression (crc) for a carbonized foamed plastic made from a compound binder (wood resin, furfuryl alcohol, maleic anhydride) and phenolic microspheres 381...

Eq. (12) has commonly been used, e.g. in the analysis of mass and gas transfer in gas-filled systems. From this relationship it may be deduced that varies from 0 to 00 and that = 1 when G = 0.5. Systems for which G 4 0.5 are poorly gas-filled ( low-porous ) and those with G > 0.5 are highly gas-filled . The rule of reciprocals ( reversal rule ) facilitates the analysis of gas-filled structures such as foamed plastics by enabling the use of the so-called complementary gas-filled (porous, cellular) systems. The complementary systems relate to each other as a mold and casting or negative and positive . 

Dixon, S., "Polyurethane Foam Molding", British Plastics, 36 (1) 24-27 (January 1963). 

Laboratoryware, plastics Ladders, plastics Lamp bases, plastics Lamp shades, plastics Lenses, plastics except ophthalmic or optical Lifejackets, plastics Liferafts, nonrigid plastics Lock washers, plastics Machine nuts, plastics Microwaveware, plastics Molding of plastics for the trade, except foam Monofilaments, plastics not suited for textile use Netting, plastics Nuts, plastics... 

Special Processes. Several more recent developments have opened the possibility of special foam processes that may grow to tremendous importance and perhaps even change the entire concept of foamed plastics. These are structural foam, reaction injection molding (RIM), and syntactic foam. 

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