Preconditioning or “Scragging” for Compression Testing of Samples

In compression testing, “scragging” describes the process of preconditioning or exercising an object or material with elastic properties. Components such as springs, and objects such as tennis balls are scragged so that a representative measurement of their resistance to load can be obtained.

Since very few objects are single-use only, measurement of an object’s resistance to compression during operationally typical conditions is necessary. Scragging induces in a material or object physical conditions that approximate the state of the material or object during intended usage. For example, scragging a tennis ball would provide simulation of the conditioning experienced by the ball during play. Without prior scragging, a tennis ball – even fresh from its pressurized container – would display atypically low resistance in a compression test. Tennis players will precondition a ball by bouncing it several times prior to serve. Bouncing warms the ball, which raises its pressure, providing it with increased elastic performance, ideally resulting in a more powerful serve.

To the layman, such preconditioning processes might be simply recognised as “warming up”, which is a fairly accurate description. Depending on their temperature, elastic materials can exhibit differing resistance to force, so scragging a ball prior to compression testing allows for a more realistic reading of the ball’s elastic properties.

So what governs the preconditioning procedure? To what limits is a material or object to be scragged? Spring scragging will depend on the requirements of the manufacturer, who might stipulate a scrag count of several hundreds. Tennis balls might be scragged only a dozen times, but manufacturers will usually submit their samples to a regulations body that will perform scragging and testing to ensure the balls perform to official standards.

When scragging has been completed, a test of the sample’s resistance to compressive force will be taken. Scragging and testing are normally performed on the same machine. A motorised force testing stand fitted with load cell, self-levelling plate, digital gauge, and compression plates is a typical configuration. UK-based Mecmesin are long-established makers of such equipment. The sample is placed between the compression plates and the test is run manually, or through a computer using software such as Mecmesin’s “Emperor”, or via a programmable controller.

Eurofilm Mantzaris Chooses Mecmesin Tensile Tester

In 2011, leading producer of polyethylene (PE) films, Eurofilm Mantzaris SA, approached Mecmesin seeking a sophisticated but simple-to-use tensile strength testing device. Mecmesin, a British company, was delighted to offer Eurofilm Mantzaris its 30 years of experience in engineering force and torque testing solutions.

Eurofilm Mantzaris, which produces PE films primarily for packaging and agricultural applications, wanted its product to provide higher tensile strength at yield and break, and an elongation limit that meets the DIN 53455 standard. They also required a device that could automatically generate statistical calculations and report immediate feedback on the performance of individual specimens and batch trends.

After defining Eurofilm Mantzaris’s needs, Mecmesin supplied a MultiTest 0.5-i – a highly capable and popular test device driven by Mecmesin’s own powerful Emperor™ software. The device’s stand features extended travel, to accommodate the heights required in tension testing of PE film and similar highly elastic materials. The MultiTest 0.5-i tests elongation limit, tensile strength, and other material characteristics of polymer products against the specification of industry standards, which in the case of Eurofilm Mantzaris include the DIN 53455. In the test, a PE film sample is secured between two parallel grips that are steadily separated under the precise control of the test stand, stretching the film until rupturing occurs. The stand’s onboard controller records and plots the force applied against the deformation experience of the sample. Tests on the MultiTest 0.5-i are fully automated. The software accepts the test parameters and displays test progress graphically in real-time, revealing exactly how and when the film fails under tensile force. Mecmesin’s Emperor™ test software stores results and the raw data that produces them. It can also display a sample’s performance in simplified form, as a colour-coded “pass” or “fail”.

Eurofilm Mantzaris chose the MultiTest 0.5-i for its combination of affordability, usability, and sophisticated statistical programming capability.

“The MultiTest 0.5-i is a very good and reliable machine and the Emperor Software brings great advantages. It’s a very useful tool for these kinds of tests. It’s fully programmable and offers an in-depth analysis of results. It’s a precious tool for everybody involved, especially those who work with plastics and their mechanical performance.”
Nikos Michopoulus, Quality Control, Eurofilm Mantzaris S.A.

Equipment
* MultiTest 0.5-i (column height: 1200mm)
* ILC-S 100N loadcell
* Emperor™ software
* Parallel grips (provided by Eurofilm Mantzaris)

Mecmesin Systems Test Beauty Product Closures

A Greece-based manufacturer of skin, hair-care, make-up, and sun-care products has recently replaced their outdated torque testers with up-to-date digital torque testers supplied by Mecmesin, a British company with over three decades of experience in engineering force and torque testing systems. The beauty manufacturer, whose wide ranging key lines include numerous well-known personal care products, acquired the torque testing devices to ensure consistency in production quality, focusing on the integrity of seals, which are vital to leak prevention and maintenance of product quality.

The manufacturer required torque testers with the ability to test the tamper-evident closures of various plastic and glass bottles and pots for slip and bridge torque. In addition, the torque testers had to feature clear, intuitive controls, easy-to-read pass/fail indicators, onboard memory for storage of statistical test data, and waterproofing to withstand the splashing that is common on the production floor.

Mecmesin supplied the company with two Tornado 10Nm digital torque testers. These devices are comfortably capable of testing the torque required to open tamper-evident closures, which is a critical specification in the design of packaging for personal care creams and liquids. The Tornados are fitted with a four-peg clamping frame (shown in the illustrations). These frames provide the versatility required by the manufacturer, since their adjustability allows them to secure a large variety of containers while their seals undergo torque testing. During the test, peak torque readings are clearly displayed, and operators have the option of exporting the test data to a statistical printer or other output device.

Mecmesin’s Greek distributor, George Gousoulis and Co., provided the manufacturer with several after-sales services, including training and technical instruction. The manufacturer was pleased to say that reliability and value for money were their main reasons for their choosing Mecmesin’s Tornado digital torque tester.




Plastic pot placed on Mecmesin Tornado torque tester




Equipment
• Two Mecmesin Tornado 10Nm digital torque testers
• One Mitutoyo DP1VR printer

Mecmesin Screwdriver Tests Torque of Cereal

The Netherlands’ top agricultural and horticultural school, the University of Applied Sciences HAS Den Bosch, in conjunction with Wageningen University, another leading Dutch institution, acquired a Mecmesin Static Torque Screwdriver and Advanced Torque Gauge to help in their research into improving the yield and quality of Teff, a gluten-free cereal.

Teff – Latin name: eragrostis tef – originates in Ethiopia but is currently grown in Europe, the United States, and elsewhere. Teff contains no gluten but is rich in protein, calcium, fibre, and iron, so is potentially important as a health food product and as a wheat alternative for sufferers of coeliac disease.

But teff has struggled to bring growers commercial benefits. The quantities of Ethiopian-grown teff sold on world markets are low, and the cereal failed to grow well in the early stages of its introduction to Europe. Researchers at Wageningen University discovered that a major cause of inhibited yield was the lodging (permanent displacement) of plants. Several field trials were conducted to identify the causes of this lodging.

The University of Manchester supplied the Centre for Crop Systems Analysis in the Netherlands with a Mecmesin torque testing screwdriver to perform tests in the field. For over 30 years, Mecmesin, a UK-based maker of torque and force testing devices, has been providing innovative and affordable measuring solutions for a broad range of applications.

In these tests, entire plants were measured and the three largest shoots carefully removed. The centres of gravity of the entire plant and each separate shoot were obtained by balancing the plant/shoot on a thin, smooth metal tube and measuring the distance between balance point and base end. The gravitational moment of plants, shoots, and panicles under 0, 3, 45, and 60 degrees was obtained using a custom-designed lodging meter, made from a highly sensitive Mecmesin digital torque screwdriver that reads up to 1.5Nm of torque in steps of 0.0001Nm.

The Dutch researchers adopted the Mecmesin device on the advice of their colleagues at Manchester University and praise it warmly for its simplicity and usability.

“The Mecmesin digital torque screwdriver was simple and straightforward to operate and it was very helpful that the user guide PDF was on the net.”

Sander H van Delden, Teacher/Researcher at the Department of Plant-Soil Interaction, HAS Den Bosch, Wageningen University

Equipment
• Static Torque Screwdriver – recommended for torque applications requiring fewer than 180 degrees of rotation
• Advanced Torque Gauge – for reading of torque and storage of test data

Mecmesin torque testing screwdriver, enclosed and fitted with lightweight metal tube to measure dislodging torque of teff shoot


For details about the study in which the Mecmesin device was used, please see Delden, S.H. van; Vos, J.; Ennos, A.R.; Stomph, T.J. (2010). Analysing lodging of the panicle bearing cereal teff (Eragrostis tef). New Phytologist 186 (3). - p. 696 - 707.