Processing, thermosets molding

Molding or laminating at pressures below 200 psi. Process of molding plastic articles from powdered, granular or preformed plastics by fusing the material in a chamber with heat and forcing the mass into a hot chamber for solidification. Used primarily on thermosetting plastics. 

Being man-made, thermoset molding compounds may be processed, using various fillers, to give most any property desired in an end product. The basic resin itself will impart certain desirable results when compounded with fillers, which will produce an end product that may have superior electrical, physical, and heat resistant characteristics, etc. 

As stated, the basic resin system makes it possible to process a recommended molding compound for a specific end use or application. The general physical, electrical, specific properties, and their applications, may more clearly be understood if each type thermoset molding compound is examined. 

The time required to cure the materials is dependent entirely on the method of molding, mold temperature, and material temperature when introduced into the mold cavity. There are now four basic methods of molding thermoset molding compounds (1) Compression, (2) Transfer, (3) Injection, and (4) Extrusion—with the method most commonly used as rated. Very small quantities are processed by extrusion. All methods of molding may be done automatically or semi-automatically. In most cases, the injection method is practically all done automatically. 

ALLYL ESTER RESINS. The allyl radical (CH2CH=CH2) is the basis of the allyl family of resins. Allyl esters arc based on monobasic and dibasic acids and are available as low-viscosity monomers and thermoplastic prepolymers. They are used as crosslinking agents for unsaluraied polyester resins and in the preparation of reinforced thermoset molding compounds and high-performance transparent articles. All modem thermoset techniques may be used for processing allyl resins. 

These plastics represent at least 90wt% of all plastics consumed worldwide. Unlike thermoset plastics, they are in many cases reproccssable without any or serious losses of properties. There are those than can have limitations of heat-distortion temperatures, cold flow and creep, and are more likely to be damaged by chemical solvent attack from paints, adhesives, and cleaners. When injection molded, dimensional integrity and ultimate strength are more dependent on the proper process control molding parameters than is generally the case with TSs. 

Manzione, L. (1995) Processing epoxy molding compounds, in Thermoset Polymer Meeting for J. K Gillham s 60th birthday, Princeton, MA Princeton University. 

Chem. Descrip. Polyethylene wax CAS 9002-88-4 EINECS/ELINCS 200-815-3 Uses Rubber processing aid mold release agent for thermosetting plastics pigment cone, for plastics... 

Thermosets consist of densely crossUnked polymers, that can also be processed by injection molding. Thus produced articles are used in boats, in the automotive field and in the electrical industry (insulation). Thermoset moldings find particular apphcation, where their non-conductive properties and heat-resistance are essential. Injection molding provides a cost-effective mass-production process of articles for the electrical industry. 

While injection molding machines designed specifically for processing thermoset materials are available, a number of manufacturers offer replacement screw and barrel assemblies and stuffer hoppers to convert conventional thermoplastic injection moulding machines to process thermosets. 

Molding compound is transferred in the cold state by pressure from the material hopper into the main injection chamber. Here it can be preheated before injection into the heated mould tool. Injection, through a special nozzle, can be either by ram or screw pressure. If screw feed is used, the screw must be of the type designed to process thermosets as opposed to thermoplastics. 

Adherent Technologies Inc. [8] has developed a process for the reclamation of carbon fibers from carbon/epoxy composites. It has studied the depolymerization of thermoset carbon fiber reinforced epoxy matrix composites using a low temperature (20 min at 325°Q catalytic tertiary recycling reclamation process and has been able to obtain a product with 99.8% carbon and 0.2% residual resin, with only a loss of about 8.6% in fiber tensile strength. The process can be economically viable, provided sufficient scrap feedstock is available. Possible applications for the recovered fiber include thermoplastic and thermoset molding compounds. 

Scrap skrap [often attributive] [ME, fr. ON skrap scraps akin to ON skrapa to scrape] (14c) n. All products of a processing operation that are not present in the primary finished articles. This includes flash, runners, sprues, excess parison, and rejected articles. Scrap from thermosetting molding is generally not reusable. That from most thermoplastic operations can usually be reclaimed for reuse in the molder s own plant or can be sold to a commercial reclaimer. 

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