Edge Crush Test (ECT) of corrugated cardboard

  • Mecmesin

The humble cardboard box is the unsung hero of countless deliveries every day. By using simple test methods such as the Edge Crush Test (ECT), companies benefit from understanding the maximum weight a box can withstand and the overall stacking strength.

ECT gives a good picture of overall strength, enabling cardboard and box manufacturers to better maintain and improve quality control testing, during formulation, processing and production.

Over the weeks of COVID-19 lockdown confinement there has been a surge of home deliveries, with even online retail giants struggling to fulfil demands and hiring fleets of new workers.

Hearing the knock at the door to receive a package provides a small sense of normality and pleasure to many. And it is the humble cardboard box which is neatly and safely enabling the widespread distribution of goods.

Beyond household deliveries, cardboard is also an object serving on the frontline of public health services, enabling mass deliveries of vitally needed medical equipment.

Modern production and shipping have changed drastically, and the testing methods we use to measure a package’s strength have changed accordingly. These days, much of the shipping is done as boxes on pallets, delivering goods from one business to another business (B2B).

Testing the edge wall of a box for its stacking strength is the most sensible and reliable measure of how well the box will hold its form under the vertical weight during transit.

Evolving test methods from Mullen Burst Test to Edge Crush Test (ECT)

For many years the Mullen Burst Test had been the main industry standard for the grading of corrugated board packaging. It required a minimum board base weight. However, as more recycled content is now used in the manufacture of corrugated board, it was discovered that recycled board of the same weight did not always perform so well in the Mullen Burst test.

This was despite the fact that these ‘recycled board’ cases still had very good compression and damage resistance qualities, as evidenced in the Edge Crush Test (ECT).

The Mullen Burst Test measures the force required to puncture the face of corrugated board and is reported in pounds per square inch (psi), boards are thus rated accordingly eg #275.

As such, this test was favoured by companies with heavy, awkward-shaped contents requiring protection where the liner-board must not burst outwards.

Box type Bursting test ECT Max. load per carton
Standard 200# 32 ECT 40 lbs
Heavy duty 275# 44 ECT 65 lbs
Heavy duty
double wall
275# 48 ECT 80 lbs

However for companies who simply wish to know the maximum weight a box can withstand, then knowing the overall stacking strength is the primary concern - this is where the Edge Crush Test comes into its own and has become the more common test nowadays.

ECT is a measure of the edgewise compressive strength of corrugated board. It is measured by compressing a predefined section of board on its edge between two rigid platens.

This compression is performed perpendicularly to the direction of the flutes until the board collapses and a peak load is reached.

This load is reported as force per unit width (lb/in, kN/m, etc). When reported as an ECT value (eg 44 ECT) this relates to a minimum strength value and corresponds to pounds per inch width (lb/in).

Since the edges and corners of a box are mostly responsible for bearing the load, it gives a good picture of material strength allowing cardboard manufacturers to perform quality control, and box manufacturers to select the most appropriate materials and processes to produce their protective packaging

A proper ECT-rated corrugated board provides an equivalent level of strength to a Mullen Burst rated board, but typically uses less material.

Fewer raw materials, meaning lower energy requirements and reduced pollution, are features associated with properly sized ECT-rated cartons incorporating increasing amounts of recycled content.
International standards for measuring crush force in the Edge Crust Test (ECT)

There are a number of international standards from various standards authorities, which address the subject of measuring the crush force by the Edge Crush Test.

A variety of methods are in use in different parts of the world. These can be classified into three groups as follows:

  • Those in which a carefully cut rectangular test piece is tested without any special treatment or modification (eg ISO 3037 “Corrugated fibreboard — Determination of edgewise crush resistance -unwaxed edge method”).
  • Those in which the edges of the test piece to which the force is applied are waxed, to prevent the test result being influenced by “edge effects“ (eg ISO 13821 “Corrugated fibreboard — Determination of edgewise crush resistance — waxed edge method”).
  • Those in which the test piece edges are not waxed but the shape of the test piece is such that the length is substantially reduced at a point midway between the loaded edges, in order to induce the failure to occur away from those edges (eg FEFCO 8, TAPPI T838 and TAPPI T839)

Developing testing solutions for Edge Crush Test (ECT) of corrugated cardboard

Mecmesin has worked together with both producers and users of corrugated cardboard to supply cost-effective and easy-to-use ECT test systems.

A software-controlled compression tester, featuring a rigid loading column and precision loadcell, is equipped with rectangular plattens. Two free-standing guide blocks serve to support the corrugated test specimen thus keeping it parallel to the plattens.

The test programme controls the tester to descend at a constant speed until a set-load is reached at which point the guide blocks can be removed. The tester then continues further until the corrugated board collapses and the software automatically calculates the Edge Crush Resistance value in the desired unit of measurement (lb/in, N/mm).

Bench-top models of ECT Compression Testers are available in capacities of 2.5kN - 10kN depending on the range of board to be tested.

Test standards

ISO 3037  Corrugated fibreboard - Determination of edgewise crush resistance (unwaxed edge method)
TAPPI T 839  Edgewise compressive strength of corrugated fiberboard using the clamp method (short column test)

See also

Cosmetic packaging pull-off test

A bench-top testing system was required to repeatably test the pull-off force on a variety of cosmetic containers. The system needed to allow a relatively high volume of containers to be tested with the minimum level of training required for users. Mecmesin's solution avoided the risk of damaging the loadcell by excessive torque on tightening the collet grip, and the lipstick barrel was first inserted in the grip and then connected to the gauge by a flexible chain-link.

Food packaging made from thermoformed plastics and intended for freezing, requires testing to ensure optimum functionality when closing and sealing the container. The closing effort of the lid is measured by using a motorised force tester controlled by software together with a custom-designed fixture to hold standard-sized ice cream tubs. In addition the ‘top-load’ crush strength of the container itself can also be tested on the same machine to guarantee it is rigid enough to avoid buckling and spillage when the lid is applied.

Mecmesin develops Combi Cork-i Extraction Tester for leading Scottish whisky

To improve the quality and storage of a premium product, the R&D team at a leading Scottish whisky maker needed to optimise the design of their bottle stoppers. They decided that the strength and performance of their reusable stoppers could be ensured by systematic testing of the characteristics of both portions of the stoppers. Working closely with the R&D team, Mecmesin developed the Combi Cork-i Extraction Tester, an innovative multi-function cork extraction testing system that tests both phases of de-corking synchronously.

Greek beauty product manufacturer guarantees production quality by updating to Mecmesin's digital torque testers

A manufacturer of a wide range of skin, hair-care, make-up and sun-care products based in Greece needed to replace their outdated torque testers with up-to-date digital torque testers to guarantee production quality and to ensure their products remained sealed. Mecmesin supplied the company with two Tornado 10N.m digital torque testers, which have the ability to test tamper-evident closures, an intrinsic part of their specification.

  • Jo Webb
  • Product Info
  • English
  • Created 20 Jul 2020
  • Modified 05 Aug 2020
  • Hits 347