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Porosity Testing – Gurley, Sheffield, Bendtsen

How to test surface porosity with 3 techniques

As you no doubt have already realized, corrugated is a thriving sector of the packaging industry. It’s a strong, lightweight, and low-cost option that’s particularly flexible when it comes to application, thanks to its suitability both as primary and secondary packaging. In fact, corrugated is enjoying such a boost in popularity that there is pressure on supply chains, upping the need for in-house quality control.

To maximize the performance for corrugated and paperboard, nothing compares to a tough testing regime and that includes testing for moisture permeability and water absorption. Surface porosity testing is an essential step in assuring product quality as it can affect everything from structural integrity to the performance of print.

Why test for water porosity?

As well offering insight into how well corrugated samples will maintain their integrity when exposed to water or dampness, permeance-based techniques are a key metric in determining the smoothness of the material’s surface.

Using permeance or porosity based smoothness or roughness testing techniques gives you greater insight into how corrugated materials will behave in humid environments.

3 key surface porosity tests

This integral part of the testing process has three popular techniques, each highlighting how corrugated materials will behave in damp climatic conditions or when exposed to water. Air permeance testing is a common method for determining the porosity of paper.

Gurley test

The Gurley porosity technique assesses the air permeance of paper and board using an air resistance tester. It is carried out using the Gurley apparatus and is suitable for papers and boards with an air permeance of between 0,1 µm/(Pa•s) and 100 µm/ (Pa•s) and is unsuitable for materials with rough surfaces, which can’t be clamped in a secure way that completely avoids leakage.

The test normally takes less than an hour. A test piece of paperboard or corrugated board is placed in the Gurley apparatus, which is filled with air that is compressed by weight of a vertical cylinder floating in liquid. The compressed air is forced through the sample and as it passes through, the cylinder falls. The amount of time it takes for a set amount of air to pass through the sample gives the formula for how porous the material is.

Sheffield test

The Sheffield technique is also used to measure the flow rate of air through a single sheet. It is generally used for sheets that are non-porous and dense and is an accurate way of working out the porosity of the paper’s surface. As with the Gurley test, it is not suitable for papers with rough surfaces, which can’t be clamped securely enough to ensure the absence of surface leakage.

It works by placing the paper sample into rubber clamping rings. Compressed air is passed through a flow measuring device then directed to the paper specimen test area. Air that passes through the sample escapes to the atmosphere through holes in the downstream clamping plate and the air flow is measured to determine the air permeance of the specimen.

Bendtsen test

This roughness and porosity test is based on a leak principle. A paper or paperboard specimen is clamped between a flat glass plate and a circular metal head. Air is then forced through the sample and the rate of airflow between the paper and head is measured in ml/minute. It is a commonly used testing technique with an adjustable testing time and water pressure. The sample used for testing is small, as in Gurley testing, which means they are often referred to as a spot test.

Alternative porosity testing techniques

There are other techniques to bear in mind too, such as the Bekk and PPS (Parker Print-Surf) methods. With such a wide range of testing solutions on offer, finding the right ones to match your setup and particular packaging needs can be tricky. That’s where we can help.

Paper porosity testing equipment at Industrial Physics

Ensure that porosity standards are upheld in corrugated or board products and packaging with the help of highly accurate and easy to use testing machines.

58-27 Bendtsen Porosity Tester

Capable of measuring both the roughness and porosity of paper and board, this compact product offers pressure compensation for improved precision and a 7-inch touchscreen with intuitive icons, making the testing process straightforward and easy to repeat.

In one machine, Bendtsen Roughness and Sheffield Smoothness instruments measure the roughness of a paper surface. Monitor desirable print and coating quality quickly and easily, with the 58-27 Bendtsen Porosity Tester.

Pocket Goniometer PGX+

This fast-working machine can measure the dynamic and static contact angle of a standard liquid on paper and board. The PGX+ is the ideal instrument to perform dynamic tests like absorption tests and it’s easily connected to the special PC software, so the tester can enjoy immediate feedback and make any adjustments to the testing procedure right away.  For a convenient way to test multiple paper surface properties in one handy machine, check out the Pocket Goniometer PGX+.

Find out more about the variety of different testing solutions for corrugated paper and board, from porosity or edge crush or short-span compression, available at Industrial Physics in our corrugated testing range.

Industrial Physics, your test and inspection partner

We’ve specialized in the design and manufacture of testing instruments for pulp, paper and packaging industries for almost 100 years and our constant desire to learn, expand and improve on testing techniques means we’re perfectly positioned to help you understand the various ins and outs of the QA processes available.

If you’d like to find out more about how Industrial Physics can offer you first class packaging inspection systems, just get in touch! A member of our team will reach out to discuss the various options available to help you find the surface porosity tests that will best suit your printing and packaging needs.