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Production Procedures, Workmanship and Manufacturing Control

Section 2

3.2.3 When the laminate is applied in a mould a chopped strand mat of max. 450 g/m2 is to be applied next to the gelcoat.

3.2.4 Polyester resin is to be applied on each layer of reinforcement. Gas and air pockets are to be worked out of the laminate by regular rolling, generally before the next layer is applied. Rolling of the layers are to be made carefully, paying special attention to sharp corners and transitions.

3.2.5 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 interval sufficiently large to avoid excessive heat generation.

3.2.6 Curing systems are to be selected with due regard to the reactivity of the polyester and in accordance 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.

3.2.7 After completion of lamination the laminates are to cure for at least 48 hours at an air temperature of not less than 18oC. Curing at a higher temperature and a shorter curing time may be accepted on the basis of control of the curing rate.

3.3 Spray moulding

3.3.1 The term spray moulding is understood to mean the simultaneous deposit of polyester resin and fibreglass reinforcement. Manufacturers using this method are subject to special approval.

3.3.2 When approval of the spray moulding process is considered, special attention will be paid to production arrangement, ventilation equipment, the manufacturer's own quality control systems and other factors of significance to the quality of the finished product.

3.3.3 Spray moulding of structural members is to be carried out only by specially approved operators.

3.3.4 The equipment used for spray moulding is to give an even and homogenous build-up of the laminate. Any dosage devices are to ensure an even application of additives to the polyester resin. No fibres are to be shorter than 20 mm in length.

3.3.5 In addition to ensuring an even application during the spray moulding over the entire surface, regular rolling out of the sprayed-on layers is to be carried out. Immediately next to the gelcoat, the rolling out is to be done before the thickness of finished laminate reaches 1.5 mm and thereafter for every 2.5 mm of thickness of subsequent layers. The rolling out is to be done thoroughly to ensure adequate compression and removal of gas and air pockets. Special care is to be taken at sharp transitions and corners.

3.4 Sandwich lay-up

3.4.1Sandwich constructions can be fabricated either by lamination on the core (e.g. plug moulding), application of the core against a wet laminate or by gluing the core against a cured skin laminate.

3.4.2 Efficient bond is to be obtained between the skin laminates and the core and between the individual core elements. Approved tools for cutting, grinding etc. of various types of core material are to be specified in the production procedure. The bond is to be verified by shear or tensile testing.

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

3.4.4 Core materials with open cells in the surface are normally to be impregnated with resin before it is applied to a wet laminate or before lamination on the core is commenced.

3.4.5 When the core is applied manually to a wet laminate the surface is to be reinforced with a chopped strand mat of 450 g/m2 on plane surface and 600 g/m2 on curved surfaces. The core material is to be laid onto the pre-moulded skin as soon as possible after the laminate cure has passed the exothermic stage.

3.4.6 Frameworks for core build up are to give the core sufficient support to ensure stable geometrical shape of the construction and a rigid basis for the lamination work.

3.4.7 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.

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3.4.8 The core material is to be free from dust and other contamination before the skin laminates are applied or core elements are glued together.

3.4.9 Where a core is to be applied to an uneven surface, the Surveyor may request additional building up of the surface or contouring of the core to suit.

3.4.10 In general laminates are to be staggered by 50 mm per layer of reinforcement. Where very thin sandwich skins are adopted the rate of laminate stagger will be individually considered. The plans are to clearly show the staggering of successive plies in both the transverse and longitudinal directions.

3.4.11 Thermoforming of core materials is to be carried out in accordance with the manufacturer’s recommendations. Maximum temperature limits are to be strictly observed.

3.5 Secondary bonding

3.5.1 A secondary bonding is any bond between two GRP structures which is made after one or both of the individual structures has effectively cured.

Normally, the laminating is to proceed as a continuous process, as far as practicable, with the minimum of delay between successive plies. Where a secondary bond is required to be made, it is to be carried out in accordance with the resin manufacturer’s recommendation, details of which are to be incorporated in the builder’s quality control documentation. This will, in general, take the form of the area being lightly abraded and wiped with a suitable solvent, which is to be allowed to dry prior to laminating.

3.5.2 The surface ply of a laminate subject to secondary bonding and the first ply of the bonding laminate is normally to be of chopped strand mat to enhance the interlaminar strength of the laminate.

3.5.3 Surfaces in way of secondary bonding are to be clean and free from dust.

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

3.5.5 Consideration is to be given, especially in highly stressed areas, to the application of peel ply materials to obviate contamination of the exposed surface, and thereby reducing the abrading required to obtain a good secondary bond.If “peel strips” are used in the bonding surface the required surface treatment may be dispensed with.

3.6 Faults

3.6.1 All faults are to be classified according to their severity and recorded, together with the remedial action taken, under the requirements of the quality control systems. The documentation is to be made available during surveys and for works approval.

3.6.2 Production faults are to be brought to the attention of the attending Surveyor and a rectification scheme agreed upon.

3.7 Repair

3.7.1 Minor repairs are to be agreed with the attending Surveyor prior to being carried out. The builder is to incorporate details of the agreed repair procedures in the quality control system for the craft.

3.7.2 Where required, plans giving details of the proposed structural modifications or repairs are to be submitted for approval, prior to execution.

3.8 Inspection

3.8.1 It is the builder’s responsibility to carry out the inspections required in accordance with the accepted quality control system.

3.8.2 The Surveyors will monitor the builder’s quality control records and carry out inspections of work in progress during their periodical visits.

3.8.3 During inspections, all deviations are to be dealt with under the builder’s agreed quality procedures.

3.9 Acceptance criteria

3.9.1 Classification is dependent upon the work being carried out in accordance with the approved plans and the requirements of an accepted quality system.

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3.9.2 The workmanship is to be to the satisfaction of the attending Surveyor. This will include the verification of the quality control documentation and the remedial action associated with all defects and deficiencies recorded.

3.9.3 Proposed deviations from the approved plans are subject to IRS approval. An amended plan is to be submitted for approval prior to any such changes being introduced.

Section 4