Molds surface preparation

The mold is usually prepared with orifices to permit air trapped between the sheet and the mold to escape and ensure uniform, close contact of the plastic with the mold surface. By clamping the sheet beyond the perimeter of the piece, plastic may be drawn from the peripheral areas into the mold, ensuring uniformity. Both pressure and vacuum are employed to force the softened plastic sheet into the mold. 

Polyphenylene sulfide parts are commonly bonded together with adhesives. A suggested surface preparation method is to solvent-degrease the substrate in acetone, sandblast, and then repeat the degreasing step with fresh solvent. The polyphenylene sulfide surface that forms next to a mold surface is more difficult to bond than a freshly abraided surface. This is possibly due to a different chemical surface structure that forms at high temperature when the resin is in contact with the metal mold surface. 

Since one of the ultimate objectives of the RIM process, for its major market of automotive exterior part production, was a cycle time of 2 minutes or less, a great deal of effort was applied to mold construction and design. Continuous automatic operation of a molding station without interruption required improvements in mold release and mold surface technology. Originally, mold preparation following a shot was required due to the buildup of external release agents, which were necessary to enable easy removal of the part from the mold. 

Polyurethane RIM (PU-RIM) was selected for the Initial RIM application of automotive fascia not only because 1t provides the required damage resistance and other performance requirements, but also because the reactivity of the urethane raw materials, Isocyanate and polyol, provide acceptable productivity. Because the urethane mnomers can be nucleated, high quality sink free surfaces that are suitable for automotive exteriors are produced at the time of demold. Little, 1f any, post mold surface repair 1s needed 1n preparation for painting the RIM part. 

Matched male and female molds are employed, in a vertical press, giving good surfaces to both sides of the molding and a higher degree of dimensional and quality consistency than is usually obtained from hand lay-up operations. The molds are prepared and a release agent is applied. The reinforcement (usually tailored to size and shape) is then laid in the open mold and a charge of liquid catalyzed resin is poured over the lay-up. The mold is then closed, to allow cure to take place. 

Lubrication Mold release agents Ore flotation Paper manufacture Petroleum recovery Printing and printing inks Surface preparations Textiles Waterproofing Waxes and polishes... 

Air blasting and associated blasting processes can also be used to remove unwanted surface materials before painting or adhesive bonding. (See also surface preparation.) These processes can also be used as a finishing operation to remove unwanted gates, burrs, and other surface imperfections from molded plastic parts. 

Molded PPS items have applications in which chemical resistance and high-temperature properties are of prime importance. PPS has found significant use in high-release coating applications such as cookware and metal tire mold surfaces. Nonstick formulations can be prepared when a combination of hardness, chemical inertness, and release behavior is required. The largest end use is in electric/elec-tronic components including interconnection devices, coil forms, bobbins, yokes, and terminal boards. 

By careful apphcation of heat or solvent to a thermoplastic substrate, one may liquefy the surface resin and nse it to form the bond. With thermal or solvent welding, surface preparation is not as critical as with adhesive bonding. The bond strength is determined by diffusion of polymer from one surface into another instead of by the wetting and adsorption of an adhesive layer. However, with welding some form of pretreatment may still be necessary. Certainly, the parts should be clean, and all mold release and contaminants mnst be removed by standard cleaning procedures. 

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