Pultrusion quality control

Sumerak J E and Taymourian K (1989), Pultrusion quality control - A comprehensive approach , 44th Annual Conference, The Society of the Plastics Industry. 

Manufacturing methods for composites vary from manual to fully automated processes, whereby the latter have better quality control than the former. Wet layup, pultrusion, and filament winding are all discussed in some detail, while other techniques such as pull-winding, resin transfer moulding, vacuum bag moulding, and injection moulding are left to specialized composite materials texts. 

Incoming raw materials, specifically the matrix constituents and the fibre rovings and mats, should be inspected. Basic inspection includes checking the delivery notes and the labels of containers when the materials arrive. Visual inspection of raw materials is also recommended resins can be inspected for colour and the presence of contamination and gel particles (Evans, 2000) reinforcements can be checked for the presence of knots in the rovings, while simple mass measurements can be made for mats or fabrics. Some pultrusion companies have quality control and/or research and development laboratories where material characterisation tests can be performed (most often such control is executed by raw material suppliers). Fibre reinforcements can be subjected to tensile tests. The moisture content of the constituents (particularly the reinforcements and the fillers) can also be determined. The quality of incoming resins can be tested by means of thermal analysers (resin reactivity) and viscometers (resin viscosity and thixotropic index) (Owens Coming, 2003). 

Several pultmsion companies use Barcol hardness testers to assess the degree of cure of the produced parts. This enables the tracing of products with insufficient degree of cure of the resin matrix, which leads to lower mechanical performance. The quality control of pultruded produced parts can also include other mechanical characterisation tests which can sometimes be carried out in the laboratory facilities of pultrusion companies. EN 13706-3 (CEN, 2002) defines two grades of FRP pultruded profiles, specifying minimum values for material properties and the relevant test methods. The requirements for certain applications (e.g. petroleum and natural gas industries) can be stricter and often include aspects related to fire reaction and fire resistance behaviour, e.g. NBR 15708-1 (ABNT, 2011). 

Wu and Joseph (31) simulated the pultrusion heat transfer in die die and have determined the different conversion and temperature composite profiles for different pulling velocities. They point out the importance of automating the process by using an expert system in order to optimize the operations setpoints, manage emergency conditions and close the quality control loop with the information available, such as temperature measurement, product quahty, pulling velocity, pulling force requiied and the extent of reaction. 

To produce pultruded products with consistent and high quality, it is important to tailor and control the pultrusion process. To achieve a uniform degree of cure in the cross-section of a product, control of the temperature profile inside the pultrusion die is an essential aspect. Also, to achieve consistent fibre wetting, controlled flow and pressure build-up must... 

This paper will describe briefly the pultrusion process developed and built locally, its reliability or performance, the quality of prepreg combined with the controlling parameters and finally the preliminary results on its usage as laminates and reinforcement in thermoplastic composites. 

In 1968, Morgan joined a team at Courtaulds to manufacture carbon fibers and subsequently set up and managed a control laboratory to monitor production. He later became involved with production aspects relating to carbon fiber prepreg and pultrusion. Morgan took on the additional role of chief quality inspector in 1976 and gained approval for the production processes to Defence Standard 05-24, the forerunner of BS 5750. In 1980, he was appointed to Courtauld s Carbon Fibres division board as director with technical responsibilities. 

Various optimization studies on thermosetting as well as thermoplastic pultrusion parameters were conducted (Chew, 2004 Joshi et al, 2003 Kyaw, 2003 Li, 2001 Tat, 2006 Zaw, 2003) using the same FE/NCV method developed by Joshi and Lam (2001). Chew (2004) worked on cooling optimization in thermoplastic pultrusion whereas Tat (2006) studied the impact of mounting locations for the feedback thermocouples controlling heater temperatures. It was observed that if the thermocouples sense either the maximum or the minimum temperature on a hot die surface, the power input to the heater will be rather uneven and the process may not completely optimize. Joshi et al. (2003) looked for improved pultudate quality with the... 

A thermoplastic modifier in styrene offering excellent shrinkage control, superior surface quality and a broad processing latitude, formulated for use in SMC, BMC, wet moulding and pultrusion applications. 

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