Transfer pot

Urea-formaldehyde moulding powders may be transfer moulded. Pressures of 4-10 ton/in (60-150 MPa), calculated on the area of the transfer pot, are generally recommended. 

Transfer moulding uses an additional pot/ram section built into the top of the mould. A pad of rubber compound sufficient to fill the cavities, plus an allowance for the transfer pad remaining in the transfer pot, is put into the pot and the mass transferred into the individual cavities. 

In addition to in-mould transfer pots, loose pots are also used which sit on top of a mould. These save on mould costs and weight but some excess compound can escape between pot and mould surface. 

FIGURE 2.3 Molding cycle of a pot-type transfer mold, (a) Molding compound is placed in the transfer pot and then (b) forced under pressure when hot through an orifice and into a closed mold, (c) When the mold opens, the sprue remains with the cull in the pot, and the molded part is lifted out of the cavity by ejector pins. (After Frados, J. ed. 1976. Plastics Engineering Handbook, 4th Ed., Van Nostrand Reinhold, New York.)... 

RTM was described May 1957 (at the BPF Reinforced Plastics Conference), in a paper on work dating from 1954 at Bristol Aircraft, Filton, UK. It is basically a liquid resin version of compression transfer molding a process in which a charge of compound is placed in a transfer pot and is injected into a closed mold, usually by a plunger system. The method allows the compound to be suitably prepared melt and then transferred fast and accurately into the mold, in which the required reinforcement has already been placed, in suitable form. 

Fig. 6-2. Front view of a 64-capacity (integrated circuits) mold, showing layout, top-transfer pot, and plunger used in a transfer molding system. (Courtesy of Hull Corp.)...

A pre-weighed quantity of DMC is placed in a heated transfer pot by hand. A punch or ram compresses the material and causes it to flow into the heated tool cavity where it cures. The tool is mounted between the platens of a press. 

The original process used a single ram, both to close the mold and to transfer the resin from the pot to the mold cavity this was a manual operation. The preferred process at present uses one ram to close the mold and another auxiliary ram to transfer the resin from the pot to the mold cavity this is semiautomatic. A third process, which is used occasionally, uses a screw preplasticator to warm the resin and feed it to the transfer pot this is completely automatic. 

Cull kol [ME, fr. ME cuillir, fr. L colligere to bind together] (13c) n. (1) A rejected material or product. (2) In transfer molding, the material remaining in the transfer pot after the mold has been filled. A certain amount of cull is usually necessary for the operator to be confident that the cavity has been properly filled. 

Figure 6.9 High-frequency preheater with roller electrodes to raise temperature of preforms prior to placing in cavities of compression mold or in transfer pot of transfer mold. Preheating shortens cure time and minimizes mold...

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. 

Transfer pots to cabinets or greenhouse, remove plastic bag to harden plant, leave plants to self-pollinate and harvest seeds from mature brown pods after 2 months. 

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 moulding material is heated until plastic in a transfer pot from which it is pushed by a plunger through a series of runners into the heated split mould where it cures. Fig. 15.9. The two halves of the split mould are attached to the heated platens of a hydraulic press in the same way as for compression moulding. 

An interesting development is the TMS (Turner, Moore and Smith—Avon Rubber, Wiltshire, UK) Rheometerwhich is based on a Mooney machine, but the rubber is injected into the closed cavity by means of a transfer pot mounted directly above the cavity. By this means, rubber with freshly created surfaces can be made to fill the cavity and a control maintained on the pressure inside the cavity. This arrangement gives reproducible results at shear rates of up to... 

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