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SOP: Jenkins Bend Test for Tinplate

GIFSQ — Global Institute for Food Safety & Quality

Principle

Forming can bodies and flanging ends bends tinplate hard. A strip is gripped between rounded jaws and bent back and forth through a 180° arc until it starts to break. Two strips are tested every time — one along the rolling direction, one across it. Both the gap between the two readings and the level of the lower (“weak-way”) reading matter when judging how the plate will bend and flange.

Apparatus required

  • Jenkins alternating bend test machine: vice with jaws of radius 1.016 ± 0.025 mm (jaws preferably tungsten carbide to minimize wear); hand lever with a steel roller of diameter 9.525 mm, mounted on a floating spring-loaded fulcrum
  • Hand shears or guillotine

Procedure

Cut specimens about 60 mm long and 12.7 mm wide with hand shears or guillotine — cut two specimens, one with the long edge parallel and the other with the long edge perpendicular to the edge of the tinplate sheet, avoiding burring of edges

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Press the test piece between the jaws of the vice (jaw radius 1.016 mm ± 0.025 mm) until the ejector spring is compressed, then tighten the vice until the specimen is securely clamped

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Move the hand lever backward and forward alternately, bending and projecting the end of the specimen through 180°

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Continue the reverse bending until the first sign of fracture appears (not complete severance)

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Record the number of full reverse bends required to achieve fracture — this is the Jenkins Bend value

Interpretation

  • The higher “strong-way” count comes from the strip cut along the rolling direction and bent across it — across the grain
  • The lower “weak-way” count comes from the strip cut across the rolling direction and bent with the grain
  • How far apart these two counts sit shows how directional the plate is — a key input when judging whether it will form a clean flange
  • Cold-reduced and double-reduced plate is strongly directional; annealed plate shows much less difference

References

Ranganna, S., Handbook of Analysis and Quality Control for Fruit and Vegetable Products, 2nd edition.