Processing, thermosets potting

Pot life The period of time during which a reacting thermoset plastic remains suitable for processing after mixing with a reaction-... 

The trickle impregnation process is a related process to thermoset plastic casting, potting, and encapsulation where it also uses a low viscosity liquid reactive plastic to provide the trickle impregnation. As an example, the catalyzed plastic drips on to an electrical transformer coil. Capillary action draws the liquid into its openings at a rate slow enough to enable air to escape as it is displaced by the liquid. When fully impregnated, the part is exposed to heat to cure the plastic. 

Once a thermoset is compounded for processing, it has a pot life that is also called working life. When the thermoset, has been mixed or compounded with a catalyst, its pot life is the time remaining in a usable condition. It is measured at room temperature or the temperatme to be encountered. This term should not be confused with shelf life. 

Nonelastomeric Thermosetting Polyurethane Curable mixtures of isocyanate prepolymers or monomers. Has good abrasion resistance and low-temperature stability, but poor heat, fire, and solvent resistance and weather-ability. Processed by reaction inj ection and structural foam molding, casting, potting, encapsulation, and coating. Used in heat insulation, auto panels and trim, and housings for electronic devices. 

CAS 21645-51-2 EINECS/ELINCS 244-492-7 Uses Flame retardant, smoke suppressanL processing aid, water resist, aid, antistat for wire/cable, elec, insulators, printed circuit boards, potting resins, molded and extruded polyolefins, flooring compds., conveyor belting, fabric coatings, polyester and aciylic pultrusion compds., thermosetting resins (BMC, SMC), PVC, EVA, EPDM, XLPE, EEA, thermoplastic elastomers, silicone rubber, NR, SR, acrylic resins, unsat. polyesters... 

Liquid A-stage thermosetting resins can be poured into finished form and simply cured in place. These processes are often called casting and sometimes distinguished as potting, encapsulation, and dip coating. 

Transfer molding n. A molding process used mainly for thermosetting resins and vul-canizable elastomers. The molding material, usually preheated, is placed in an open pot with a hole in its bottom atop the closed mold. The cross-sectional... 

Transfer, or plunger molding, is a process in which high-flow B-stage resins, such as epoxies, are liquefied under heat and pressure in a transfer pot, after which the resultant liquid resin is transferred under pressure into mold cavities. The transferred resin is then heated to form cured, final parts that are then removed from the mold. Although compression and transfer molding are used principally with thermosetting compounds, the processes are occasionally used with thermoplastic material, often thermoplastic composites. 

Figure T.8 Transfer molding process (a) the mold is closed and material is placed in the pot, (b) the plunger descends into the pot, causing material to melt and flow through runners into cavities, (c) after cure, the press opens, the plunger retracts and the parts are ejected with cull and runners. (Ref Hull, J.L., Processing of Thermosets , Modern Plastics Handbook, CA. Harper, ed., McGraw-Hill, New York, 2000)...

In the case of moulding thermosets, the uncured (initial) compound is usually placed first in the cavity of the mould, or the transfer pot of a transfer moulding process, and heated (to about 150 °C) to provide sufficient flow for mould filling. Pressure (approximately 13 MPa) is then applied for sufficient time to allow the resin to cure. 

The process is generally used for high-volume production, because the cost of a modern semiautomatic press of modest capacity, say 50-75-ton clamping force, may be as much as 50,000, and a moderately sophisticated self-contained multicavity mold may also cost 50,000. Typical applications include melamine dinnerware, toaster legs and pot handles, and electrical ontlets, wall plates, and switches— parts that require the rigidity, dimensional stability, heat resistance, and electrical insulating properties typical of thermosetting compounds. 

This technique is well-suited to the manufacture of cylindrical containers of low thickness. A variant of this technique, called molding by compression transfer, is widely used for the processing of thermosetting resins. It involves the preheating of the material to be molded in a simple mold ( pot of transfer ), permitting its fast thermal transfer then the matter of appropriate fluidity is introduced under pressure into the compression mold, and the curing of the thermosetting resin occurs. In this case, the amount of matter transferred into the mold should not be in excess. 

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