Tea bag integrity

Customised engineering example

Some of the simplest applications may not seem so obvious when you face them. A string and tab on a tea bag? Commonly stapled in place, the tensile test should be on the clipping of the string, not the tear strength of the bag itself.

For our client, Mecmesin devised the simple 'tea bag hook' to do just this. A small part, a simple test, but now done efficiently and consistently for daily quality assurance and brand protection.

To hold the other end of the complete product, the paper tag, a small plane vice grip is used. A choice of jaw faces enable secure location without damage to the material or failure within the material at a location away from that of the fastening.

For this solution, a motorised tensile tester was used, controlled by a digital force gauge. Constant elongation speed is readily achieved to ensure accuracy and repeatability combined with the simple set-up procedure.

Tea bag material wet tensile strength

Extending the quality control regime for the tea bag with tag product, some customers have implemented strength testing of the bag material itself. Should the pull-of loads be too light, further tests may enable the manufacturer to optimise the design and rectify any issues.

The bag material is likely to be paper or similar natural fibres. The wet tensile strength of this type of material is usually tested to a TAPPI T456 or related international standard suitable to paper 'food wraps'. One variation is the 'Finch' type of test, requiring a specific design of fixture including a cup to saturate a loop of material of specific dimensions. 

Heated water

Adding more relevance to the environmental conditions of the wet saturated bag material specimen, a system to also heat the water may be employed. To completely meet safety considerations, the hot water and the test stand should be located with a safety enclosure.