| M-Real in Tampere, Finland developed a new multi-layer material “Avenira” for the production of folding boxes. But there was one problem: how to predict its crush resistance. For standard corrugated board, three test methods are used to predict the box strength. The aim for M-Real was to create only a single test that would enable the box strength to be predicted directly.
M-Real's idea was to utilize the buckling theory of a panel and to simulate the edges of a box by the test rig. Some discussions resulted in a simple test rig that met the desired requirements: the specimen is held by a V-notched frame, which simulates the box's edges (Fig. 1). For constant test conditions, the force that holds the specimen in the V-notched frame must be constant. A screw driven, constant force-applying counter jaw was the solution (Fig. 2).
Once the specimen is placed into the rig, a compressive test, called the Avenira Compression Test (ACT), is performed. The specimen will buckle like a box under compressive load, allowing the box crush resistance to be determined at given dimensions of the folding box from the test result, which is the maximum strength (Fig. 3). The whole rig works very accurately because of the guided compression plunger. This unit fits into all Zwick testing machines (Fig. 4).
The ACT method is in everyday use at M-Real. Based on the ACT measurements, M-Real is able to position their new Avenira material inside the carton and micro-corrugated world. The ACT method even allowed M-Real to improve the strength of their new material. Used in production control, they achieved a high-strength consistency, as well. The primary aim, the box strength prediction of folding boxes, which is dependent on different packaging materials, has also been met.
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