With the use of the McKee-formula, bending stiffness is important for the prediction of the box crush resistance. With the 4-point bending method, dependable stiffness values are measured in the machine and cross direction. This is particularly important for miniature flute corrugated board, where stiffness plays an increasing role, compared to standard flute heights.
With the knowledge gained from the bending units for structural materials, (aerospace, ceramics and high performance metals), Zwick developed a 4-point bending unit for carton and corrugated board. The result is a tool that is comparable to other existing solutions at a moderate cost. Another important point is that the bending unit can be used on the smallest machine, the zwicki-Line.
Compared to bending instruments which use dead weights for specimen loading, handling is uncomplicated and fast: the specimen is simply placed on the bending unit and the test is started. The stiffness is calculated automatically, taking in consideration of the elasticity limits.
Because of rotatable and swivable supports, shrinked or warped specimens can be tested within wide limits.
Tests are according to ISO 5628.
The advantages:
- Test time below 60 s
- The test graph allows a fast plausibility control even during the test
- Supports of the bending unit are optimized for the characteristics of carton or corrugated board
- Measured results are mostly independent of warp or shrink of the specimens caused by production. The test is performed within the elastic range of the specimen.
