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Clean connections for solar collectors

27 June 2011

High speed blind fastening technology has been adopted to meet the critical strength and contamination-free assembly requirements of a lightweight solar panel. Construction of the solar collector frame requires the secure fixing of an outer frame from one side only, without pre-punching or drilling to avoid compromising the structural integrity of the main frame. Additionally, the fastening technique has to work in combination with a silicone adhesive sealant and avoid any risk of contamination.

Working in partnership with energy efficient water heating systems manufacturer Clage GmbH, of Luneburg, Germany, fastening specialist Bollhoff, proposed its standard RIVTAC joining system to meet these specific production requirements.

The flat plate solar energy collector delivers very high energy yields - in excess of 80% - and weighs only 32.5kg due to its light weight geometry and materials. An aluminium frame is added as a final step in the manufacturing process to optimise strength and protect the solar cells and service connections. This is securely fastened at each corner with two RIVTAC fasteners.

Other fixing methods such as bolts and piercing rivets were evaluated but these were found to produce unwanted filings which could contaminate the silicone adhesive and have an adverse affect on frame strength.

To minimise application cycle time the RIVTAC fasteners are applied using Bollhoff’s portable high-speed pneumatic hand tool, which has a cycle time of less than one second. The fastener is presented to the components to be joined at high speed, penetrating both materials and causing a short-term rise in temperature in the joining zone, which improves flow. The materials being joined are displaced into the straight knurling on the tack shaft and achieve a close tolerance fit.

RIVTAC is particularly suitable for joints of aluminium, steel, plastics, non-ferrous metals as well as for mixed materials and multiple-layer joints.

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