JEC COMPOSITES MAGAZINE - Issue #55 - February/March 2010 - 53

Vacuum integrity is absolutely critical in the infusion process, even more so than when used with prepregs or wet lay-up, which is why it is worthwhile using high-quality nylon film. Oven-cured processes The current advanced marine composite processes using prepregs require oven curing (70° to 85°C) with vacuum-assisted consolidation. The uniformity of heat distribution is quite critical. Hence, a maximum deviation of < ±2°C should be maintained in all control points. Trimarine has always preferred computer-controlled curing programs using appropriately-developed software to not only monitor the temperature profile of the component, but also actuate accordingly to maintain the correct amount of heat and air flow. Given the large mass of the components and moulds, it is not as straightforward to uniformly heat the curing polymer to the required curve as one might think from observing just a few thermocouple readings. It is important to have a large reserve of heating power and even more airflow to ensure optimum heat distribution, especially during the initial ramp, dwell and climb to the required curing temperature. Advanced infusion processes require post-cure at temperatures of at least +50°C. Such processes are more forgiving than prepreg curing and can be performed in simpler thermostatically-controlled ovens. heated blankets. In this area, series production projects have a neat advantage in that there are sufficient numbers of components to be built. This justifies the additional design effort needed to incorporate more bonded joints and thus eliminate the recourse to wet lay-up. Skills required Advanced composites require a skilled workforce. Typically, Trimarine operates with a force of 20-30 skilled workers with several years experience in composite prepreg lay-up, and at least half the workforce must have boat-building carpentry skills. This is necessary because there is a large amount of component fitting to be done in one-off construction. From the initial stages of master model or wood plug construction to the surface finishing of components, craftsman skills are impossible to substitute completely. Nowadays, the use of 3D milling of plugs and moulds, or even the laser or waterjet cutting of mould frames, has significantly reduced the need for a large number of skilled mould makers. In production boat building, the approach to repetitive series manufacturing originated a different kind of solution using a larger proportion of initially untrained labour which quickly adapt to the repetitive procedures and are relatively easy to substitute with new elements. In production boat building, the processes are more subdivided and there is less need for the workforce to understand the complete 'picture' of the product. Yard equipment Yards dedicated to the construction of advanced marine structures, due to their one-off nature, need flexible equipment capable of accommodating the different sizes of components. Lifting and moving equipment is ideally designed to minimise the time spent with such operations. Overhead bridge cranes equipped with rolling slings for quick rotation of large components are desirable assets. The installations should be equipped with air conditioning and heating to have a stable working temperature with controlled relative humidity. Centralised dust extraction is an important tool in minimising time wasted on cleaning the workplace and in the direct removal of dust particles when cutting or sanding laminates. Compressed air and vacuum equipment can be centralised but a series of portable vacuum pumps is always required. A large curing oven for hull and deck components is a necessity, coupled with one or more smaller ovens dedicated to flat components like bulkheads and partitions, in addition to an oven for long narrow components like girders, poles, beams, etc. A large heated panel press and a series of booths for cutting, sanding and painting smaller components can speed up the production of flat stock. A flat calibrated vacuum table is a fundamental piece of equipment for the production of large bulkheads. Having used flat vacuum tables with dimensions from 3x6 m to 6x12 m, the number and Carbon prepreg female mould tools for ACC Yacht Assembly and secondary bonding Secondary bonding is an unavoidable necessity in the assembly of component elements (hull-to-deck joint, bulkheads, girders, frames, beams, etc.) and often uses wet lay-up with or without vacuum consolidation. Given the one-off nature of most advanced marine projects, it is difficult to avoid such less desirable practices as wet lay-up. The tendency is to incorporate ever more joints designed so that they can be simply bonded with no need for secondary lamination and to limit prepreg secondary bonding to critical areas only. In such cases, localised heat-curing techniques have to be employed either by using improvised 'mini-ovens' or electrically- No55 February - March 2010 / jec composites magazine

JEC COMPOSITES MAGAZINE - Issue #55 - February/March 2010

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #55 - February/March 2010