Contact molding cleaning

Potential adverse effects adhesion to hot metal surface, bubbling, increased mold cleaning frequency, lack of adhesion in joining processes, residue on the product surface, transfer to a material in contact, welding impairment... 

Parts molded from polycarbonate can be cleaned, disinfected, and sterilized by most methods known in practical operation. With some materials, caution is advisable if aldehydes or phenols are active ingredients. Under certain conditions, damage in the form of stress-cracks can occur under contact with cleaning, disinfectant, and sterilizing media. They result in a reduction in mechanical strength. Moreover, there also other effects not always visible, such as initial swelling or chemical degradation in the plastic that can also impair mechanical properties. 

Although more and more zinc sheet and strip are produced in continuous mills, some is stiU produced by rolling slabs cast in open or closed book-type molds made of cast iron (124—127). The casting temperatures are between 440 and 510°C, mold temperatures between 80 and 120°C. The contact surfaces of the mold must be smooth and clean to allow unrestricted shrinkage of the cast slab. Mold lubricant is not necessary, but if used should be held to a minimum. Slabs cast in open molds must be skimmed immediately to remove surface oxide. Rolling slabs are cast 1.87—10 cm thick. 

Bonding-cured polyurethane requires that both surfaces be clean and free from contamination, especially traces of mold release. The surface of the polyurethane should be roughened slightly and must be capable of making proper contact with the other piece. The polyurethane should be primed... 

Three basic schemes for the ultrasonic cleaning of the melt can be proposed (1) in a liquid bath of an ingot (the melt surface is in a contact with a waveguide-radiating ultrasonic system) (2) in a mold (oscillations transmit to the melt through mold walls) and (3) in an intermediate vessel placed in the flow of melt from a holding furnace to a mold (oscillations transmits to the melt according to the first scheme). 

Smooth surfaces of each polymer were also prepared (without additives) by pressing samples of the powdered polymers against a highly polished stainless steel surface in a Carver press at 16,000 p.s.i. Circular disks 1 inch in diameter and weighing several grams were formed in this way. PS and the PVeC copolymer were compressed at room temperature, PAM at 120° C.,and PMMA at 150° C. The pressure was maintained until smooth polymer surfaces were obtained. The mold and stainless steel piston were cleaned prior to use, so that contact angles could be measured on the polymer surfaces without further surface treatment. 

Epoxies, urethanes, cyanoacrylates, and thermosetting acrylics will result in bond strengths greater than the strength of the acrylic part. The surface needs only to be clean of contamination. Molded parts may stress crack when in contact with an adhesive containing solvent or monomer. If this is a problem, an anneal (slightly below the heat distortion temperature) is recommended prior to bonding. 

However, with welding some form of pretreatment may stUl be necessary. Certainly, the parts should be clean, and all mold release and contaminants must be removed by standard cleaning procedures. It may also be necessary to dry certain polymeric parts, such as nylon and polycarbonate, before welding so that the inherent moisture in the part will not affect the overall quahly of the bond. It may also be necessary to thermally armeal parts, such as acryUc, before solvent welding to remove or lessen internal stresses caused by molding. lA thout annealing, the stressed surface may crack or craze when in contact with solvent. 

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