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PLASTICEL - 47004

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		The polyester resin used to laminate the various layers, for example, produces heat during the hardening phase. Part of this is dispersed in the air, but part is absorbed through the surface of the mould and transferred to the structure. The ideal way of making a mould (and the plug that precedes it) of high quality is to design a construction process using just one material, with no screws and without using fillers or marine putty. All materials, from wood to synthetic foam to fibreglass, have their pros and cons. The important thing is to know how they behave and handle them correctly.

		Environmental conditions: the plug and all the materials to be used must first be conditioned . Fibre reinforcing materials, balsa wood and ply are hygroscopic and must be stored in damp conditions. The humidity tends to condense on the surfaces and on the fibres, especially at low temperatures and in still air. The heating system in the mould building department must heat the environment evenly at the possibly without raising dust. The ideal solution is slow speed hot air or floor heating. In summer cool the air should be fed in from above, and it's advisable to water cool the roofing. To ensure correct and complete hardening and degassing of the resin and the gelcoat the finished mould must be kept in a controlled temperature environment (at not less that 20°C) before use. The higher the temperature the faster the mould would be ready to use. Seasoning and curing must be taken into account in the mould design phase. Times and temperatures can be estimated on the basis of the materials, the working environment conditions and the processes to be followed.

		Construction: Laying down the gelcoat is the most critical phase of the entire process: the gel-coat is the mould itself. Laminates and frames serve to support the mould surface and keep in position. They must be rigid, homogeneous and have no thermal bridges. For the first layer of fibreglass, it's best to use mould resins that are high HDT(), isophthalic, di-cyclopentadiene, vinyl ester or Low Profile. The first reinforcing layer must contain plenty of resin that is perfectly laid down and well hardened. There should be no air bubbles, dry fibres or obvious overlaps. It's advisable to lay down the second layer singly too. The reinforcement should be of medium weight, and you must always check the impregnation ratio. Low Profile resins are being increasingly used. This system allows large thicknesses to be built up in few hours without surface shrinkage problems. Three or four mats are impregnated at a time with resin, to form thicknesses of 4mm wet on wet. Resin impregnation is a rather difficult job, and cut-and-spray machines are usually used. The best results are obtained when the low profile resins are applied at temperatures of not less than 25-28°C. () What it means HDT?: Is a measure of polymer's resistance to distortion under a given load at elevated temperatures. The deflection temperature is also known as the "heat deflection temperature", "deflection temperature under load" (DTUL) or "heatdistortion temperature" (HDT).

		Making the structure rigid: The mould laminate must be rendered rigid to ensure adequate dimensional stability of the working surfaces. The entire structure must stand up to deformation caused by the thermal and mechanical stresses (both static and dynamic) it is subjected to during the moulding cycle. To avoid the risk of scarring of the mould surface, the laminate must be correctly hardened. Only later can it be made more rigid with ribs or expanded material. Large flat surfaces must be far more rigid than is demanded of the moulded article. The main techniques used for this are ribbing with wood or expanded material and sandwich with balsa wood or expanded material.

			C/Muntaner, 525 08022 Barcelona(Spain) Tel.+34 934 18 29 29 Fax.+34 934 18 54 71 plasticel@plasticel.es 11

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