Nailplates / Shearplates
Nailplates have long been used in bearer pallet repair in North America, for top-frames and export packing but were rarely used in Europe in the timber packaging industry until the potato storage box industry discovered that they were an ideal way to eliminate diagonal timber bracing in 1000kg storage boxes for high stacking. Placed on sides and ends they do this by locking together several sawn timber boards which then exhibit high panel shear strength in a similar manner to a thick plywood box side. They are now widely used in that industry (see 31c & 31f below)
Nailplate (top), shearplates (center),
with a coach-bolt and washer needed
when using the shearplates
Nailplates are an authorised alternative to damaged bearer replacement in EN ISO 18613: 2003: Pallets for materials handling - repair of flat wooden pallets, they do this in an effective way but are still little used in commercial European pallet repair where block pallets are the norm.
Box designs in sawn wood strengthened by appropriate length and width nailplates when tested for compliance with BS 7611 meet the tough lateral load test requirements that ensure normal storage loads of 8 tons will be safe. PalletLink has carried out tests on potato storage box designs using nailplates and results are available on the POTATO BOX page. However, although nailplates are more efficient, less troublesome alternatives to timber bracing, they do require special machinery to apply them to sawn wood in the form of a hydraulic press with several tons capacity.
Shearplates are widely used in timber house building, but not often in the timber packaging industry. They are circular, with a diameter of 40 or 50mm, tightly sandwiched between two timber boards or battens and when drawn together with a coachbolt and nut the joint exhibits high shear strength. One shearplate at a joint is equal to several ring nails, but unlike nails they can be tightened as wood shrinks during drying over the early life of a structure. Their use in the timber packaging industry is restricted to special constructions such as export cases, skids and packing cases and crates. We are able to supply members with working loads for shearplates for various end uses.
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31c Proposed revision to BS 7611 - 1992 Potato Storage Boxes (PDF 37kb)35f Using punched steel nailplates in one tonne potato boxes (PDF 44kb)