Section 3 Panel manufacturing process

3.1.1 This Section includes the minimum requirements for the elastomer and its base components at the time of installation.

3.1.2 Where pumping equipment is used it is to be maintained in accordance with the manufacturer's instructions. A valid certificate of calibration is to be retained in the quality control documentation to confirm the accuracy of the equipment.

3.1.3 Metered mixing equipment is to be calibrated for the mix quantities prior to the commencement of production, and at scheduled times thereafter subject to a minimum of one per shift.

3.2.1 The general level of workmanship, where no detailed requirements are given in this Chapter, is to be to the Surveyor's satisfaction.

3.3.1 The cavity surfaces are to be clean and dry, free from surface rust, degreased and grit free.

3.3.2 A minimum surface roughness of 60 microns and cleanliness to Swedish Standard Sa2.5 is to be achieved on the bonding surfaces before injection of elastomer. Alternative surface finishes will only be considered on an individual basis and will require validation by an agreed test program.

3.3.3 In general major structural welds are to be completed before injection into the cavity. These include lashing pots and other cargo securing details, and where highly loaded structural arrangements, such as crane foundations are welded directly to the sandwich support members.

3.3.4 Perimeter bars are to be welded on to the bottom plate in accordance with the construction plans to form the cavity walls. Any welds in way of the perimeter bars are to be ground smooth. See Ch 2, 6 Welding for welding requirements.

3.3.5 The required core thickness is to be maintained by spacers made of steel or elastomer or by any other suitable method arranged on the bottom plate in accordance with the design documentation.

3.3.6 Lifting arrangements are to be designed such that the steel plates and the finished sandwich panels are subjected to minimal distortion and unnecessary loads. Panels are to be adequately supported until the injected elastomer has cured to avoid distortion.

3.3.7 In general welding of the cavity being injected and cavities immediately adjacent is to be completed prior to any elastomer injection.

3.4.1 The material components are to be checked by the Builder, prior to injection, to ensure that the material base component's batch test certificates meet the requirements.

3.4.2 For each batch of material a minimum of three Shore D hardness tests are to be carried out on the cured elastomer injected on-site in accordance with DIN 53505. Each batch is to comply with the following (average of the results):

1. Shore D > 65 at room temperature.

3.4.3 The test samples may be prepared by any of the following methods:

1. an injection bucket shot preferably cured for 24 hours.

2. the centre of a 40 mm thick elastomer core cured for 24 hours, prepared from injection into a large mould at room temperature.

3. hand mixed components cured in a small heated mould according to specified time-temperature profile (130°C for at least 1 hour), tested at least 1 hour after removal from mould, at room temperature.

3.4.4 The pot life for each batch of the elastomer is to be determined by a test sample. A pot life between 360 – 450 seconds is to be achieved. Care is to be taken to ensure that the pot life is greater than the time it takes to fill the cavity.

3.4.5 The pot life sample core is to be visually examined and is to be free from surface defects and blemishes.

3.4.6 If the Surveyor has any cause for concern over the tests listed in this section or the batch properties, he may at any time, require samples of both elastomer and adhesion to steel samples to be prepared and tested.

3.5.1 Venting and injection holes are to be located in the top plate as shown on the design documentation.

3.5.2 The cavity formed by the steel plates and perimeter bars is to be air tight. Air tightness is to be demonstrated to the Surveyor's satisfaction, according to a mutually agreed schedule, prior to elastomer injection. When this test is performed, the procedure given in Pt 3, Ch 1, 9.6 Leak test procedures of the Rules and Regulations for the Classification of Ships, July 2022 are to be followed with the exception of that relating to the air pressure. It is recommended that the air pressure be raised to 0,02 MPa and kept at this level for about one minute. Any failed welds are to be repaired and retested.

3.5.3 Panel restraint beams are to be arranged in accordance with the design documentation.

3.5.4 Prior to any injection the relative humidity in the cavity is to be determined to confirm freedom from moisture. This process and the method to be used is to be part of the design documentation.

3.6.1 Injection is to be carried out when the cavity is deemed satisfactory as described above.

3.6.2 The top and bottom plates are required to maintain a temperature of not less than 50°C measured by contact thermocouple for a duration of 30 minutes in order to achieve satisfactory bonding of the elastomer to the steel. Depending on the ambient conditions it may be necessary to cover the sandwich panel with thermal blankets.

3.7.1 After completion of the injection, the injected elastomer is to be tested and the Surveyor is to witness the test. For each panel a minimum of one levelling funnel is to be Shore D Hardness tested after injection. The results are to comply with the requirement given in Ch 2, 3.4 Elastomer preparation, identification and characterisation 3.4.2.

3.7.2 After the injected elastomer has cured, the holes for high temperature pressure relief valves are to be drilled in accordance with the construction procedure report. In certain circumstances depending on the application, e.g. bottom shell, holes are not to be drilled.

3.7.3 The injection and venting holes are to be sealed by welding a steel disk into each hole.

3.7.4 Voids are to be brought to the attention of the Surveyor. The size of voids may be determined by tap-testing. The design documentation is to define the maximum allowable void size.

3.8.1 Voids larger than the maximum void size are to be repaired. Repairs are to be agreed with the Surveyor prior to being carried out.

3.8.2 The repair procedure is to be defined in the design documentation.

3.8.3 When modifications or repairs are required, that result in a procedure, which is different to the procedures given in the design specification, these procedures are to have prior agreement of the Surveyor.

3.8.4 Welding is to be carried out in accordance with the approved welding procedure, see Pt 3, Ch 10, 2.7 Welding procedures and welder qualifications of the Rules and Regulations for the Classification of Ships, July 2022.