Resin injection equipment

Broadly, RTM resin injection equipment is categorized based on its mixing capability and whether the flow rate or pressure is controlled. Based on mixing capability, they can be classified as  

The second type of classification depends on the injection boundary condition  

An ideal RTM resin injector should have the following features  

15 Inlet pressure Pnie,(f) and flow rate Q ie,(t) for two common types of injection boundary conditions (a) constant inlet pressure, and (b) constant inlet flow rate with an upper pressure limit. (Source. Reprinted with permission from reference 1, copyright 2010 CRC Press,Taylor Francis Group.) 

Multiple components of the polymer should be mixed accurately at the user s dehned ratio. The user may want to adjust the mixing ratio to achieve the desired gelation time (a.k.a. pot life) of the resin at different temperatures. 

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Application of the product is made by standard resin-injection equipment, having a minimum injection pressure of 0.4N/mm (4 bar). The method of application is almost the same as that of an epoxy crack-injection system. 

In the second process the reinforcement, accurately positioned and under tension, is drawn through a heated metal die where impregnation of the fibres and cure of the resin system takes place. Here, by the use of appropriate resin injection equipment, a short pot-life system can be used. Typical resin injection pressures are between 0.1 and 0.5 MPa. To... 

Figure 3.24 Diagram of resin injection equipment. Source Reprinted with permission from Symposium Fabricafion Techniques for Advanced Reinforced Composifes, Universify of Salford, Apr 1980. Copyrighf 1980, Elsevier.

Injection equipment consists essentially of two parts the injection and clamping units. The injection unit melts the polymer and injects it in the mold. The vast majority of modern injection presses use a reciprocating screw. As in an extruder, the screw rotates, melts the polymer and pumps it. Furthermore, in most injection molding units, the whole screw can also axially move forward, acting like a plunger to inject the resin into the mold cavity through runners and gates. 

Ethylene and acetylene are diluted with natural gas in the gas injection equipment and fed to the boiler plant to utilize the energy they contain. The resins can also be used for energy production with the aid of suitable incineration plants. Thus, the high calorific values of these by-products and wastes can be used to produce energy in the form of steam and electricity, thereby avoiding the environmental pollution that would result from the burning of fossil fuels. 

The press and resin transfer equipment for the RTM/LTM process are generally less expensive than for an injection press to make comparable size components, partly because RTM/LTM clamping and injection pressures are of the order of magnitude of only a few hundred pounds per square inch. Control systems have become highly sophisticated, however, bringing up the cost of equipment, and the long cycle times add to the cost of each item produced. 

Depending on the needs and expectations, one should dedde what type and capadty of the injection equipment to purchase. Usually, the initial investment cost of a flow rate-controlled injection equipment is higher than a pressure-controlled equipment. Figure 9.16a shows a flow-rate controlled injection equipment from Radius Engineering Inc. Its major components are (1) a resin cylinder (with a capacity of 2100 cc for this model) with a heater jacket, (2) an electric stepper motor which drives a piston at a desired resin flow rate, (3) a control console to input the process parameters and monitor process variables, (4) communication interfaces to control the equipment through a personal computer instead of the control console if desired and (5) a frame and stand with wheels. 

A pressure-controlled injection equipment from Composite Integration is shown in Fig. 9.16b. It is used for multiple component resin systems and stores the resin and catalyst in separate tanks and mixes them in the mixer head. After the injection is completed, a solvent flush system is used to prevent the cure of the resin in the mixer head. 

Srinivasagupta and Kardos (2004) developed an algorithm for economical design of the IP process, subject to controllability considerations. The multiobjective approach was able to determine the optimal values of the processing parameters such as heating zone temperatures and resin injection pressure, as well as the equipment spedfications (die dimensions, heater, puller and pump ratings) that satisfy the various objectives in a weighted sense. 

Both thermoplastics and thermosets can be formed by compression moulding (Fig. 24.5). The polymer, or mixture of resin and hardener, is heated and compressed between dies. The method is well suited to the forming of thermosets (casings for appliances, for instance) and of composites with a thermosetting matrix (car bumpers, for example). Since a thermoset can be removed while it is still hot, the cycle time is as short as 10 seconds for small components, 10 minutes for large tliick-walled mouldings. Pressures are lower than for injection mouldings, so the capital cost of the equipment is much less. 

Acetal resins may be processed without difficulty on conventional injection moulding, blow moulding and extrusion equipment. The main points to be considered are ... 

Polycarbonate melts adhere strongly to metals and if allowed to cool in an injection cylinder or extrusion barrel may, on shrinkage, pull pieces of metal away from the wall. It is therefore necessary to purge all equipment free of the resin, with a polymer such as polyethylene, after processing. 

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