Flex Cracking Resistance
Versie Rons
This property is desirable when comparing candidate films during the material selection process. Good flex crack resistance will reduce the propensity of the package developing holes during the distribution cycle thereby destroying the package integrity.The sample (size 200 by 280 mm) is attached to the Gelbo flex-tester mandrels. The flexing action consists of a twisting motion combined with a horizontal motion (compression), thus repeatedly twisting and crushing the sample. For polymeric film, the number of predetermined strokes is typically set at 1000, after which the sample material is examined. The formation of pinholes is determined by use of a blue dye solution (Toluidine Blue) and allowing it to stain through the pinholes onto an absorbent white backing. The number of pinholes is a measure of the flex crack resistance of the material and is reported as, for example, 3 pinholes/1000 flexes.
As with all of the different properties of various base materials, some elastomers perform better than others in terms of flex resistance and, whilst the inherent characteristics of a polymer can be improved through the inclusion of additives, it is important to develop an understanding as to which base elastomers offer the most suitable properties.
The term flex resistance does not mean resistance to flexing or bending, rather, the ability to withstand numerous flexing cycles without damage or deterioration. Flex-crack resistance is the ability to withstand a number of flexing cycles without experiencing the occurrence of surface cracks as a result of stress. Most commonly, rubber products and components are damaged by repeated flexing cycles in the form of surface cracks.
In selecting a rubber which can withstand flex resistance for use in any particular application, it is necessary to understand the different base elastomers available and, as such, which can be used as a base for developing a unique blend to meet the requirements of a specific product or component.
Primarily utilising 12 different elastomers for the manufacture of rubber sheeting, reinforced rubber sheeting and rubber coated textiles, our technicians are on hand to help inform decisions and to help make the research stage that little bit more straightforward.
Please note: Whilst most main rubbers are outlined below, our capabilities and experience allow us to manufacture a much wider range of blends and formulations. The inherent characteristics of a polymer can be improved through the inclusion of additives, including the flex resistance properties.
Natural Rubber
Whilst not suitable for use in instances where the product or component will be exposed to ozone, oils or solvents, natural rubber offers excellent flex resistance alongside superior resistance to tear and abrasion, good tensile strength, high tear strength and good flexibility at low operating temperatures.
Polyurethane
Most formulations of polyurethane offer extremely high flex resistance and can be expected to outlast other base elastomers where this is an important requirement of a particular product or component. It is possible to enhance this base material through the inclusion of additives to further improve the flex resistance as well as to enhance other such characteristics as necessary, depending upon the operating environment.
When analysing the requirements of any given product or component, the selection of the correct base material is often required to be a compromise between a number of different factors including individual usage specifications and the economics of any particular blend.
Here at White Cross Rubber Products, our expertise and capabilities allow us to manufacture a wide range of blends and formulations dependent upon a number of characteristics including the operating environment and economic factors. Should you be looking for in-depth, backed up information and data surrounding the flex resistance of any number of our main elastomers, or wish to discuss your specific needs and requirements, we welcome you to give our technicians a call on 01524 585200.
Gelbo Flex Testing is intended to subject a target material to the fatigue of repetitive twisting, crunching, and flexing motions under controlled conditions. The material can then be examined for the presence of any flex cracks or pinholes. To perform a Gelbo test, packaging material is repeatedly twisted and crushed and then evaluated for flex failure. The flexing action performed during the test consists of a twisting motion combined with a horizontal compression motion that provides repetitive strain to test the flex resistance of the flexible barrier material for the entirety of the test. Flex failure is typically determined by the appearance of pinholes or integrity failures in one or more plies of a multi-ply structure, or the breakdown of barrier properties. The commonly used standard for Gelbo flex testing is ASTM F392, though it can vary. The number of cycles in a Gelbo test typically range from 2700 cycles (Condition A) down to 20 cycles (Condition E) to simulate everything from full flexing to partial flexing.
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