Transfer Moldings

The process differs from CM in that the plastic is heated to a point of plasticity in the pot before it reaches and is forced into the closed mold. This procedure facilitates the molding of intricate parts with small holes, numerous metal inserts, and so on. Less force is used, and less melt action occurs in the cavity (Fig. 6-2 and Table 6-2). 

Automation of the transfer/plunger concept is accomplished by the addition of a hopper-fed screw plasticator, in a system called screw transfer, which can replace the preform and preheat operations and automatically load the pot in CM (and is used to load a CM mold cavity). Conventional screw injection molding (IM) is another so-called transfer system (Chapter 

As explained in the IM chapter, for TSs the processor uses a screw compression ratio of one, the barrel heat is kept relatively low (below the curing/ hardening heat), and the mold is at a higher heat to permit final cure. 

Placing material in an open mold rather than injecting it into a closed 

Loading the mold 1. Powder or preforms. 2. Mold open at time of loading. 3. Material positioned for optimum flow. 1. Mold closed at time of loading. 2. RF heated preforms placed in plunger well. 

In compression molding, high pressures are applied at the mold, frequently hampering dimension stability of the product, mainly when more elements are introduced. In the method of transfer molding, the system com- 

TSs has experienced an extremely low total growth rate, whereas TPs have expanded at an unbelievably high rate. Regardless of the present situation, CM and TM are still important, particularly in the production of certain low-cost products as well as heat-resistant and dimensionally precise products. CM and TM are classified as high-pressure processes, requiring 13.8-69 MPa (2,000 to 10,000 psi) molding pressures. Some TSs, however, require only lower pressures of down to 345 kPa (50 psi) or even just contact (zero pressure). 

CM is the most common method of molding TSs. In this process, material is compressed into the desired shape using a press containing usually a two-part closed mold and is cured with heat and pressure. This process is not generally used with TPs. TM, also called compression-transfer molding is a 

Lead time typically days, depending on complexity of tool. 

Material utilization very good. Less than 3 per cent scrap typically. Scrap material cannot be recycled directly. 

Can mold around inserts and delicate cores easily. 

Lettering, ribs, holes, inserts and threads possible. 

Draft angles ranging 2-3 preferred, but can be as low as 0.5°. Minimum inside radius = 6 mm. 

---

Amino molding compounds can be compression, injection, or transfer molded. Urea molding compound has found wide use and acceptance in the electrical surface wiring device industry. Typical appHcations are circuit breakers, switches, wall plates, and duplex outlets. Urea is also used in closures, stove hardware, buttons, and small housings. Melamine molding compound is used primarily in dinnerware appHcations for both domestic and institutional use. It is also used in electrical wiring devices, ashtrays, buttons, and housings. 

The precerammed billets, already having appropriate tooth color, are loaded into a dedicated high temperature press and transfer-molded at 1100°C into phosphate-bonded molds. 

Figure 25 Schematic diagram of an injection/transfer molding machine [9]. (a) Hydraulic separation unit for upper mold plate, (b) Hydraulic separation unit for middle mold plate, (c) Shuttle system with automatic sprue nipple removal, (d) Brushing unit for cleaning middle mold plate, (e) Hydraulic ejector for automatic ejection.

The New ITM Injection-Transfer Molding Technique. Maschinenfabrik J. Dieffenbacher GmbH Co., Germany. 

C. F. Johnson, Resin Transfer Molding and Structural Reaction Injection Molding in Engineering Materials Handbook, Vol. 2, ASM, International, USA (1988). 

Injection Molding Extrusion Blow Molding Thermoforming Reaction Injection Molding Rotational Molding Compression and Transfer Molding Matched Mold Spray-up... 

Resin Transfer Molding Spray-up Hand Lay-up Mat-Preform Compound... 

Resin transfer molding With vacuum assisted RTM, this process can be called infusion molding. RTM usually uses liquid TS plastics that is transferred or injected into an enclosed mold usually at low pressures of about 60 psi (410 kPa) in which reinforcement... 

SCRIMP process This Seeman Composites Resin Infusion Process (SCRIMP) is described as a gas-assist resin transfer molding process. As an example glass fiber fabrics/ thermoset vinyl ester polyester plastic and polyurethane foam panels (for insulation) are placed in a segmented tool. A vacuum is pulled with a bag so that a huge amount of plastic can be drawn into the mold (Marco process approach). Its curved roof is made separately and bonded to the box with mechanical and adhesive fastening. It is similar to various reinforced plastics molding processes. 

Spray ing/bru shing/rolling Resin transfer molding Rotational casting Rotomolding Thermoforming Compounding/vulcani-zation... 

---