The moulding of plastic boat hulls should be carried out under controlled conditions if quality work is to be maintained. Workshop conditions are of vital importance if resin is to gain its maximum mechanical properties. It is not possible to lay down hard and fast rules for workshop conditions as each must be considered individually taking into account layout, type of production, local climate, etc.
An FRP yard can be broadly divided into two sections:
The plastic section comprising the moulding shop and its associated shops and stores handling the resins and reinforcements;
The fitting out shed and its wood machining shop, paint and general stores and a machine fitter's shop.
This chapter will only deal with workshop conditions of the FRP department.
The layout and facilities of the plastic section will be dependent on the type of production. For instance, separate rooms are provided for the gel spraying, trimming and post cure operations in works which mould hulls on a production line basis but are not found in smaller yards. In the early development of FRP boatbuilding some yards converted an old shed into a moulding shop and success came with experience. Newer entries to the industry have benefitted from advice given by technical sales staff of resin suppliers and Classification Societies and have been able to erect better equipped moulding shops.
It may be one or more bays of a larger work or may be a separate building. The exterior walls will be of some weather resistant material in association with a substantially framed structure, of steel, reinforced concrete or timber. Corrugated steel sheeting can be used for roof or walls but must be insulated against solar heating. Sometimes roof girders are increased in strength to carry additional loads from handling equipment, such as pulley blocks used to lift the moulding from the mould. The floor should be a damp-proof and dust-free material such as concrete or bituminous composition.
The insulation's function is to assist in maintaining a satisfactory working temperature. In very warm climates full use should be made of foil-faced insulation boards, spun glass insulation and corrugated aluminium. Windows, walls, doors and roofs need to be addressed as well as accounting for daily passage of the sun, natural shade and wind direction.
It is recognized that 18–21°C is the most suitable range for working temperatures in the mould shop when approval by a Classification Society is to be sought. Temperatures should not normally exceed 25°C but where a short moulding cycle of up to three days is used temperatures of up to 33°C may be satisfactory provided attention is paid to resin/catalyst ratios. Relative humidity should not exceed 80%. Above this level glass fibres may pick up moisture which will affect the cure and bond. In areas where humidity is consistently 70–100%, shift working may overcome these problems with moulding carried out at night. If approval by a Classification Society is sought, the question of an air conditioned mould shop should be addressed. A hygrometer and wet and dry bulb thermometer will allow the yard management to build up a record of local conditions and to allow for climate in production planning.
The shop atmosphere should be reasonably free from fumes and dust to permit comfortable and efficient working conditions. Up to about 5% styrene is evaporated during moulding and for 6–8 hours afterwards. The fumes are heavier than air and have to be drawn from the mould to the roof of the shop. The higher the roof, the less air changes are required. A ventilation system of several exhaust fans along the roof will also be required to remove solar heat.
Adequate ventilation should be provided in the spray area which is often in a separate area for gelcoating. Fans should not play on the moulding nor cause undue evaporation. In trimming and sanding areas, down draught ventilators which pull rather than blow overcome the problem of blowing dust over workers and wet laminates. Dust will retard and often inhibit resin cure and trunked extraction may have to be used with flexible suction ducts that can be held over cutting and sanding tools. A canvas pipe fitted to one of the roof extractors may be adequate. Dust removal from all surfaces prior to gelcoating and moulding is fundamental.
The shop should be adequately illuminated at moulding level by either natural or artificial lighting or by a combination of both. If allowed to play on a moulding or resin, direct sunlight will tend to cause premature gelling and excessive evaporation of the styrene both of which may cause permanent undercure. Fluorescent lighting should be installed well above mould surfaces as it emits ultra-violet radiations and has a similar effect to sunlight. Supplementary portable lighting may prove useful where fixed shop lighting does not illuminate secondary FRP work such as interior bonding.
The number of power points depends on the number of tools being used. Cables and hoses should be as short as possible to give better and easier handling of the equipment and will result in a less obstructed floor. Compressed air tools are usually lighter and more rugged than electrical power tools, they are also less likely to cause fire but are more expensive and require a constant source of compressed air. Equipment for resin spraying will need a compressed air system which should have a very low humidity level so that it does not contaminate the resin.
Figure 7 Examples of plant layout
The main shop doors should be large enough to allow the boats to be removed by handling equipment without the risk of damage. Steel doors are normally insulated to prevent heat gain. A heavy canvas curtain will prevent draughts but allow passage.
Cleaning in an FRP yard is a laborious and expensive business. It is essential for high quality work and the health of the worker, an untidy workshop will reflect itself eventually in the quality of workmanship. General cleaning may be carried out by one man dedicated to the task or by the work crew at the end of a shift.
The main problem is small pieces of discarded resin and glass which stick to footwear and are carried everywhere. Large pieces can be discarded directly into waste containers. Waxed hardboard panels can be positioned around spray equipment to prevent overspray adhering to walls and floors (particularly appropriate in rented accommodation). Entire floors waxed before operations commence and then covered in sections with a sacrificial layer of CSM is a means of scraping off congeled FRP. Covering with hardboard panels which can be thrown away is another method.
The cleaning of resin pots and moulding equipment is generally carried out in the resin preparation room by the resin mixer or his assistants so that they can be prepared for re-use. An extractor fan will be necessary for the styrene and acetone fumes. Brushes and rollers are also cleaned in acetone before washing in soap and water, but this time by the laminators themselves immediately after finishing a section.
For high technology laminating and mass production methods, some special equipment is necessary. For the general purpose moulder however, apart from the moulds themselves and lifting and moving equipment, no expensive equipment is required. A few specialized hand tools are necessary such as rollers for consolidating the wet laminate and catalyst or accelerator dispenser bottles.
Following tools are usually used for working FRP:
Electric drilling machine 13 mm chuck industrial quality
Hole saws 25 mm – 100 mm
High speed twist drills 3 – 18 mm
Jigsaw industrial quality with metal-cutting blades
Angle grinder hand held with 100 mm disc
Grinder discs carborundum for cutting
Grinder discs carborundum for grinding
Grinder discs disposable aluminium oxide 40 grit
Hacksaw 18/24 point blades
Rasp 250 mm half round
Files 250 mm flat, half round and round
Stanley knife and standard blades
Wood saw for foam cutting
Scissors tailoring quality for reinforcement cutting
Wet and dry abrasive paper 100 – 1 000 grit
Cork sanding blocks
Padsaw handles to accept hacksaw blades
Spirit levels 250 mm and 750 mm
Tape measures 3 m and 5 m
Rubber mallet 1 – 2 kg for mould release
Brushes 25 – 100 mm plain wood handles
Squeegees metal, rubber and plastic for resin and putty spreading
Masking tape 12 mm – 50 mm
Weighing scales to 20 kg
Buckets plastic or 5 L cans
Mohair rollers in various sizes for applying resin.
Laminating rollers, paddle or washer type for consolidating laminate.
Squeegee - flat, hard rubber pad 150 mm × 75 mm with tapered edge, replaces both of above.
Plastic graduated dispenser bottles for catalyst and accelerator.
Figure 8 Some hand tools