Section 3 Manufacturing

301. Application

The hull structure, constructed in FRP, is to be in accordance with requirements in this chapter. The requirements, not mentioned in this chapter, are to be in accordance with requirements in the Rules for FRP Ship and Guidance for Approval of Manufacturing Process and Type Approval, ETC.

302. Manufacturing conditions

1. Storage of raw materials

(1) Storage premises are to be so equipped and arranged that the material supplier's directions for storage and handling of the raw materials can be followed.

(2) Storage premises for glassfibre are to be kept clean and as free from dust as possible, so that

the raw material is not contaminated. Glassfibre parcels are also to be protected against rain and moisture.

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heated up before use to the temperature of the moulding shop. Tanks for polyester are to be equipped and arranged so that the contents can be stirred every day.

(4) The glassfibre material is, whenever possible, to be stored for at least two days in storage

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(5) The storage temperature and the storage periods for resins and coating are to be within the lim- its specified by the material supplier.

(6) Core materials are to be stored dry and protected against mechanical damages.

Manufacturing conditions

2. (1) Manufacturing premises are to be so equipped and arranged that the material supplier's direc- tions for handling the materials, the laminating process and curing conditions can be followed.

(2) The air temperature in the moulding shops is not to be less than 18 ℃. The stipulated mini-

mum temperature is to be attained at least 24 hours before commencement of laminating, and is

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(3) The relative humidity of the air is to be kept so constant that condensation is avoided and is not to exceed 80 %. In areas where spray moulding is taking place, the humidity is not to be less than 40 %. The stipulated air humidity is to be maintainable regardless of outdoor air tem- perature and humidity.

(4) Air temperature and relative humidity are to be recorded regularly. In larger shops there is to be at least on thermohydrograph for each 1500 m where lamination is carried out. The location

of the instruments in the premises is to be as neutral as possible.

(5) Draught through doors, windows etc. and direct sunlight is not acceptable in places where lami- nation and curing are in progress.

(6) Manufacturing premises are to be kept clean and as free of dust as possible, so that raw mate- rials and moulds are not contaminated.

(7) The ventilation plant is to be so arranged that the curing process is not affected.

(8) Sufficient scaffoldings are to be arranged so that all lamination work can be carried out without operators standing on the core or on surfaces on which lamination work is taking place.

(9) During lamination of large constructions the temperature should be recorded at least at two lev- els vertically in the workshop and the curing system should be adjusted to compensate for pos-

sible temperature differences.

(10) Fabrication of flat panels are to carried out on a support lifted from the workshop floor level.

303. Production procedures and workmanship

1. Sandwich lay-up

(1) Efficient bond is to be obtained between the skin laminates and the core and between the in- dividual core elements. Approved tools for cutting, grinding etc. of various types of core materi- al shall be specified in the production procedure. The bond is to be verified by shear or tensile testing.

(2) All joints between skin laminates and core and between the individual core elements are to be completely filled with resin, glue or filler material.

(3) Core materials with open cells in the surface, should normally be impregnated with resin before it is applied to a wet laminate or before lamination on the core is commenced.

(4) When the core is applied manually to a wet laminate the surface shall be reinforced with a chopped strand mat of 450 g m in plane surface and 600 g m in curved surface. If vacuum is

applied for core bonding the reinforcement type in the laminate surface will be considered in each individual case.

(5) When a prefabricated skin laminate is glued to a sandwich core measures are to be taken to evacuate air from the surface between skin and core.

(6) The core material is to be free from dust and other contaminations before the skin laminates

are applied or core elements are glued together.

2. Manual lamination

(1) When the laminate is applied in a mould a chopped strand mat of maximum 450g m is to be

applied next to the gelcoat.

(2) The time interval between applications of each layer of reinforcement is to be within the limits specified by the material supplier. For thicker laminates care is to be taken to ensure a time in-

terval sufficiently large to avoid excessive heat generation.

(3) Curing systems are to be selected with due regard to the reactivity of the polyester and in ac- cordance with the supplier's directions. Heat development during curing is to be kept at a safe level. The quantity of curing agents is to be kept within the limits specified by the supplier.

(4) The reinforcement next to the core is normally to be a chopped strand mat of at least 300

3. g m . A lighter mat may be accepted provided proper bond is documented by testing.

Secondary bonding

(1) If a laminate subject to secondary bonding has cured for more than 5 days the surface should be ground. If resin containing wax is used grinding is required if the curing time exceeds 24 hours.