Testing Nails

The wood pallet and case industry in the USA for some 40 years has successfully used the MIBANT (Morgan Impact Bend Angle Nail Tester) method  to demonstrate nail bending resistance. The MIBANT test method is an impact hammer drop test with a fixed weight striking a nail held in a small vice. The angle of bend (MIBANT angle) is measured after the hammer drop and this is used in US pallet design and software.

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Torque applicators used in nail bending tests

Nail strength for the European pallet and case industry was largely ignored except for building Europallets, as explained in earlier pages. Following a CEN initiative for nail bending tests in building and construction, ISO commenced work in the 1990s and pallet and case designers can now quickly rate nails for bend strength against ISO 12777-1: 1997 Determination of bending resistance of pallet nails. PalletLink provided the Convenor for the ISO nail standard drafting committee and retains a strong interest in nail quality.

Details of how nails perform in these European standards are now available from some nail suppliers. Tested against EN ISO 15629 nails can be rated ‘high’, ‘medium’ or ‘low’ quality which relates solely to their bending strength and not to their visual appearance. That is a sound method to use when specifying nails for pallets and cases. The ISO protocol for nail tests is a method which was intended to complement the older Mibant nail bend test method which is required as part of keyboard input to the PDS (Pallet Design System) software.

PalletLink frequently undertake nail quality tests for members and the test rigs we use are the Rockhi Robiment and the Verus 127, both of which conform to EN ISO 12777-1. Nail testing using this method is a fast, internationally recognised method that unlike the Europallet nail tests (not a recognised international method) does not use wood in the specimen tests. This makes it less liable to the introduction of errors which arise from the use of a naturally variable material. The MIBANT measures nail bend strength as an angle of bend measured after the elastic limit and so the bend strength angle (MIBANT angle) mixes plastic modulus with elastic modulus. It also tests nails near the head where annular rings are absent and the nail is strongest and so for European ring nails can give a misleadingly high result. The ISO 12777-1 tests at the rings where the ring nail is weakest, which is a better evaluation of European ring nails.

The oldest method used for nail strength uses ultimate tensile strength in kN/mm² which is the original steel mill quality method using an ASTM (USA standards body) standard which is the normal method of trading plain steel stock for wire products. Although it defines the steel's ultimate tensile strength accurately in kN/mm² (or in the USA in tons/in²) it is only accurate when stock wire was 9 or 12mm dia at manufacture. Also it is obtained by pulling wire in a tensile testing machine which is not relevant to wood packaging.

Although quoted in occasional wood packaging specifications, ultimate tensile strength (UTS) in kN/mm² is of little value to our industry. The correlation between nail bending resistance in Newton.metres and the ultimate tensile strength is widely known to be poor. The ISO wood pallet committees in the early 1990s decided that they needed a relevant, more modern nail bending resistance test, hence we now have ISO 12777 Part 1. This measures nail bending resistance which is important to performance of pallets and cases in terms of resistance of joints. Bending resistance of finished nails takes simpler equipment and is a faster and more accurate test than relying on UTS of wire at pre-manufacture stage.

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PDF52d Nail assessment for pallet or box manufacture. (PDF 50kb)
PDF52e Testing nails for USA performance criteria including MIBANT angle (PDF 30kb)
PDF52h Methods of measuring strength of nails for wood pallets and packaging (PDF 27kb)
PDF52j International strength levels for pallet & box nails. (PDF 72kb)
PDF52m Mibant, Rockhi, Verus - nail bending test methods (PDF 56kb)
PDF52r Rockhi Robiment Nail Tester - Instructions for Use. (PDF 211kb)
Excel64n Nail bending strength test procedure ISO 12777 (Excel 20kb)
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