The Institute for Consultancy, Research, System Planning and Packaging (BFSV) at Hamburg University of Applied Sciences (HAW) has been engaged in consultancy and research in the fields of packaging and transport of goods, together with planning and optimization of transport logistics systems, for over 50 years. The Institute is unique in Germany in both its form and orientation and in its attachment to the university.

Cross-border and intercontinental goods flows have increased significantly in the wake of globalization, with the consequence that the protective function of corrugated corrugated boxes increasingly has to be adapted to accommodate changes in the loadings experienced during the boxes’ life-cycle. With this in mind BFSV has commenced a project which is putting the present-day quality characteristics of heavy-duty corrugated board as used for transport packing to the test, while seeking to establish a basis for a modern, practically oriented quality definition for heavy-duty corrugated board.

An important sub-project involves determining the loading on corrugated board; both static / short-term  and dynamic / long-term during the board’s entire service life.

What is the procedure today if a corrugated board must be specified according to quality? DIN 55468 uses three properties - bursting strength, puncture resistance and edge crush resistance – to determine the type of corrugated board.

Two things are expected of a corrugated box:
• the higher the grade of corrugated selected, the greater strength it should possess;
• boxes with the same dimensions and made of the same grade of corrugated board should possess the same strength regardless of manufacturing process.

Tests at BFSV have shown that this is unfortunately not so. Therefore BFSV has set itself the goal of finding a way out of these contradictions and providing heavy-duty corrugated board specifications that enable it to
• meet the above expectations;
• be adequate for transport requirements over its lifetime.

So what makes a corrugated box what it already is today as far as its basic functions are concerned: a reliable, cost-effective form of packing, which moreover complies with strict environmental requirements?

Firstly the factors ‘moisture’ and ‘storage’ must be included in the specification. The relevant values  are provided by tests for wet bursting strength, wet adhesion tests and – at the planning stage – a long-term test which provides information on the strength of transport packing under continuous static load.
 
It is also the case that transport packing bows out under loading; in other words it is subjected to compressive and bending forces and therefore provides good protection if it is made of compression and flexure-resistant materials. From this perspective, it is logical to include stiffness in the parameters for corrugated board. Why this logic was not applied to corrugated board classification much sooner is easily explained. Stiffness in this case is determined using a 4-point bending test, which, compared to other tests, is not entirely straightforward.  

Apart from the purely physical parameters which must be observed, the properties of corrugated board must also be considered. Corrugated board can be distorted in two directions from production (twist and warp) and must not be exposed to any local deformations at the load application points during the test. A series of precautions are therefore necessary if the bending test on corrugated board is to be reliable. Zwick has carried out pioneering work in this area with its bending test kit for corrugated board in combination with its numerically controlled testing machines.

 
Once the basic data have been specified in the Test Program only the nominal thickness of the corrugated board needs to be entered; the machine takes care of everything else. A particular advantage is that even when changing to a weak, unknown type of corrugated board, no overloading of the specimen can occur, as outer fiber strain is monitored during the entire test for its limit value of 0.03%. The bending deformation transducer may only travel 0.1 mm during the test, but thanks to  direct measurement (without lever transmission) and high resolution (in the nanometer range), measurement of small deformations presents no difficulty.

Summary

The tests carried out demonstrate the following points. Classification of corrugated board to DIN 55468 does not correspond to the range of use of heavy-duty corrugated board as required today. To describe the behavior of corrugated board according to humidity, additional parameters must be incorporated into the classification. To describe the long-term behavior of corrugated board requires creep testing, for which modified ECT and flexure tests are suitable.

Puncture resistance determined by the puncture test has no overall consistent significance with regard to the performance of heavy-duty corrugated board.
 Bending stiffness as determined by the 4-point bending test has overall consistent significance with regard to the performance of heavy-duty corrugated board and can be measured quickly and easily using today’s testing machines.

Dipl.-Ing. Wolfgang Reimers of BFSV:
“The tests have brought us a great deal nearer to our aim of developing a new performance standard for heavy-duty corrugated board, which includes the quality and transport purpose of the board. An important step forward here was incorporating stiffness in the performance data. Our Zwick Z020 and  its flexure test kit have supplied us with valuable data in this respect.“