The Corrugating Materials Quality Control Laboratory

A Brief Outline and Links to Test Instruments

It’s easy to believe that we all know about and understand the materials and product areas we work in, or associated with. But of course, that’s not always the case and there are occasions, when it’s nice to know there is a simple reference to call on.

At Tendring Physical Testing, we don’t believe there is such as thing as a ‘silly question’. If you don’t know the answer, then you don’t know the answer and you simply need to check in with someone who does.

So, here is our easy to read guide to the Corrugated Materials QA Laboratory.

Materials and Construction
Corrugated packaging board is constructed of front and back liners, with a fluting medium sandwiched between.

Board specifications vary with one, two or three walls, the linear frequency of the flutes and the quality of the materials themselves.

The manufacture of the corrugated board may be at a mill, integrated with the manufacture of the component materials, or based remotely, using purchased liner and fluting media.  So, the laboratory may be testing one, or more components, or the completed board.

Functionality
Corrugated board has two main functions:-

1. to form a strong container
2. to act as a cushioning material inside the container.

The first demands intrinsic strength, to maintain structure and form and to resist external forces, which might puncture, or crush it.  The second, protection, comes from inner board, which is constructed to absorb pressure from any deforming forces within the container.

The facing liner is often required to accept a printed image and the surface roughness should be enough to prevent slippage during stacking, but not too great, to prevent movement along conveyers. The fluting medium must be stiff, but formable, and not be abrasive when in contact with the fluting rolls.  Both must accept adhesive, without undue penetration.

Testing
Typically, tests required to establish these criteria are:

Grammage, thickness and moisture, to check component specification and machine runnability of the material.

Tensile strength, T.E.A. and elongation of the liners to ensure integrity on the corrugating machine and with tear, for general strength characteristics.

Bursting strength. This is a requirement for transit cases to conform with Railway Clearing House specifications, to which most are subject.

Crush tests. These are used to predict the performance of case components in use and include:

The Concora Medium Tester together with the crush tester (flat crush tester or electronic tensile tester with accessories) to measure the ability of the fluted medium to resist a specified vertically applied pressure without collapse or “leaning”.

Ring crush and edge crush to establish the force required to collapse the fluting medium and check specification. Flat crush of the combined board to check that it is within specification.

Pin adhesion test to establish the integrity of the glue lines, and accessories.

Compression strength of the combined board to establish the strength of the container when stacked etc.

Bending resistance of the liner and combined board to test the materials for stiffness under pressure.

Absorbtion using the Cobb Tester to establish the material’s ability to glue correctly and the top liner to accept print.

Roughness to establish that the container will stack correctly and not cause hold-ups on conveyers.  Also, that the surface will print effectively.

Friction test, used in conjunction with roughness to establish stacking and transport characteristics.

Puncture test, to test the combined board for resistance to penetration by sharp objects.

Abrasion test on the fluting medium to check that there are no abrasive materials such as silica present likely to cause excessive wear on the fluting rolls using the Taber abrader.

Box compression test, a final check on the resistance of the container to crush.