Plastisols open molding

Open Molding. Plastisol is poured into an open mold, heated to gel and fuse, cooled to solidify, and stripped out from the mold. Typical products are auto air filters, oil filters, truck flaps, and place mats. 

Most of the plastisols are used in open molding. It is a very simple process to use. A measured amount of plastisol is poured into an open mold cavity. The mold and plastic are heated to gel and fuse the plastisol. The mold is then cooled so that it solidifies. It is stripped from the mold. Inserts can be placed in the liquid plastic before it is fused inserts can also be inserted in the mold before pouring. Two or more colors can be placed in different parts of the mold. 

This process resembles the open molding process except it is closed like a two-part compression mold (Chapter 14). A measured amount of plastisol is poured or pumped into the closed mold cavity, similar to close molding except that a slight pressure of about 5 psi (34.5 kPa) is applied. The mold is heated to fuse the plastisol then cooled. Later the mold is opened and the product stripped out. This process can provide for accurate thickness control, filling very complex shaped parts, and so on. 

The Vanderbilt process involves the mechanical frothing of air into a plastisol containing proprietary surfactants by means of an Oakes foamer or a Hobart-type batch whip. The resulting stable froth is spread or molded in its final form, then gelled and fused under controlled heat. The fused product is open-ceUed with fine cell size and density as low as 160 kg/m (10 lbs/fT). 

Rotational Casting. Like rotomolding, the plastisol is poured into a cold mold, which is rotated and heated to gel the plastisol onto the walls of the mold. It is then heated to fuse, cooled to solidify, opened, and the product removed. Typical products are volley balls, basketballs, dolls, and auto parts. 

Slush molding is used mainly with plastisols. It is usually a continuous operation. The mold (female) is filled above a specific pattern mark and passed through an oven that sets or gels the material in contact with the metal mold surface. These molds are electroformed copper or cast aluminum. The material in the center of the mold that is still a fluid is poured out of the mold with the mold returning to an oven for final fusion. Upon removal from the fusion oven, the mold is cooled and the finished product is stripped from the mold. Vacuum or compressed air can be used with large parts or with those of a complex geometry to assist in product removal. One part of the mold must be open to the atmosphere to permit pouring and product removal. 

Production of PVC and other plastics MCCPs and LCCPs Spray droplets volatilization waste waters 0.3-1.5% from extrusion, calendering, injection molding, coating 0.1-0.2% from open calendering of plastics and plastisol spread coating 0.05%/year to air and waste water... 

Slush casting is similar to slip casting (drain) of ceramics. The liquid is poured into a preheated hollow metal mold, which has the shape of the outside of the object to be made (Figure 2.43b). The plastisol in immediate contact with the walls of the hot mold solidifies. The thickness of the cast is governed by the time of stay in the mold. After the desired time of casting is finished, the excess liquid is poured out and the solidified plastisol with the mold is kept in an oven at 350°F-400°F (176°C—204°C). The mold is then opened to remove the plastic part, which now bears on its outer side the pattern of the inner side of the... 

In rotational casting a predetermined amount of liquid plastisol is placed in a heated, closed, two-piece mold. The liquid is uniformly distributed against the walls of the mold in a thin uniform layer (Figure 2.43c) by rotating the mold in two planes. The solidified plastisol in the mold is cured in an oven the mold is then opened, and the part is removed. The method is used to make completely enclosed hollow objects. Doll parts, plastic fruits, squeeze bulbs, toilet floats, etc. can be made by rotational casting of plastisols. 

Closed-cell foams result when the decomposition and gelation are carried out in a closed mold almost filled with plastisol. After the heating cycle, the material is cooled in the mold under pressure until it is dimensionally stable. The mold is then opened, and the free article is again subjected to heat (below the previous molding temperature) for final expansion. Protective padding, life jackets, buoys, and floats are some items made by this process. 

In order to make a hollow article, a split mold can be partially filled with a plastisol or a finely divided polymer powder. Rotation of the mold while heating converts the liquid or fuses the powder into a continuous film on the interior surface of the mold. When the mold is cooled and opened, the hollow part can be removed. Among the articles produced in this manner are many toys such as balls and dolls. 

Nitrosan ). This blowing agent is unique in that its low decomposition temperature permits the expansion of vinyl plastisol prior to gelation (93°C). Subsequent fusion at 177°C produces open-cell vinyl foam. Closed-cell foam can be produced by heating to fusion in a closed mold, releasing the pressure and subsequently heating in an oven at 100°C. 

Plastisol is poured into a preheated mold (one part of the mold has to be open). The mold is either filled to the top and excess is removed or a lesser amount can be added and the mold moved to cover all the desired surfaces and excess is removed. Thicker films or multilayer films may be produced by repeating the... 

The precise amount of plastisol needed for the part is put into the mold and the mold is closed. There are no openings in the mold, which is attached to a device capable of rotating in all dimensions to create a uniform internal coating. The arm and mold are put in an oven for fusion. Once the material is fused and cooled the mold is opened and the part removed. Balls and doll heads— and other nearly round parts— are most often rotomolded. Part properties are the same as that for slush molding. 

Molded Vinyl Foam With other materials such as urethanes and elastomers, most foam products are molded. They are either allowed to expand under low pressure to fill the mold, yielding an open cell stmcture, often with a skin (as in, e.g., crutch pads) or molded and thermoset under pressure and subsequently expanded in an oven, yielding a closed cell structure (as with foam rubber shoe soles or mattress components). The products of oven expansion, referred to as buns, can be skived and die cut to gaskets or seals. The latter process is also carried out with vinyl. Molds are filled with plastisol, fused and cooled under pressure, and then expanded in an oven at 100-120 °C, softening the polymer and enabling the trapped gas to expand. For highly defined shapes, this step can be carried out in a second mold. 

Rotational plastisol and powder molding now compete in production of automotive interior surface layers for PUR foam structures (e.g., instrument panels, crash pads, and arm and head rests). Tooling and compound costs generally favor the use of plastisols, increased antifogging requirements the use of powders. Powder technology also opens this area to polymers other than PVC future developments should be of interest. 

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