Curing autoclave moldings

Autoclave molding has been particularly adapted for the cure of laminates of preimpregnated plies of continuous fibers (prepregs). A lay-up of... 

Chottiner, J., Sanjana, Z, N., Kodani, M. R., Lengel, K. W., Rosenblatt, G. B. Monitoring cure of large autoclave molded parts by dielectric analysis, p. 77, Proc. 26th SAMPE Symp., 1981... 

Autoclave molding, the process of curing thermoset resins at elevated temperature and pressure in an inert environment, has an important role in the fabrication of continuous fiber reinforced thermoplastics. While most companies view thermoplastics as an alternative to traditional autoclave long-cycle processing, they have come to accept the following reasons for the autoclave processing of thermoplastic matrices ... 

Dry layup n. The construction of a laminate by layering preimpregnated, partly cured reinforcements in or on a mold, usually followed by bag molding or autoclave molding. 

Curing can be performed in several devices heated mold (Figure 1-13), hot press (heated plates that are forced together), and an autoclave which is essentially a very large version of an ordinary kitchen pressure cooker as in Figure 1-21. 

The chapter is divided into a section on development of process cycles or plans and a section on in-process control. The tools to be discussed include design of experiments, expert systems, models, neural networks, and a variety of combinations of these techniques. The processes to be discussed include injection molding, resin transfer molding, autoclave curing, and prepreg manufacturing. The relative cost and difficulty of developing tools for these applications will be discussed where data is available. 

In traditional process control, models are often used to predict the deviation of the controlled variable from the desired state, the process error. This assumes that one knows the desired state. In complex batch processes, the desired state of the process is also dependent on history and changing dynamically. Further, most process models have to predict the outcome of an entire cycle to determine if the product will be good, so predictions are not available in real time, even for a slow process like the autoclave cure however, partial models have been used as virtual sensors to expand on the information available from sensors [38]. Saliba et al. used a kinetic model to predict the degree of cure as a function of time and temperature in a mold and used that predicted degree of cure to time pressure application and determine the completion of cure. Others [39] have used the predictions of models together with the measured progress of the process to predict future trends and even project process outcomes. 

In later stages, the technology developed and rubbers were compounded, mixed in mills, calendered in calenders, extruded in extruders, molded in hydraulic presses, cured in autoclaves and many hand operations of forming and curing became possible. State-of the art techniques of compounding were developed to produce rubber products of any shape and dimensions for many requirements. 

Depending on the resin preparation, the material in or around a mold can be cured with or without heat, and commonly without pressure. Curing needs include room temperature conditions, heat sources, vacuum bags, pressure bags, autoclaves, etc. An alternative is to use preimpregnated, B-stage TS polyester or sheet molding compound (SMC), but in this case heat is applied with low pressure via a impermeable sheet over the material. This process can produce compact... 

---