Everyone has an opinion about the Rubber Sheeting they buy and not simply that it's too expensive or not as good as 'in the old days'. Common questions we are asked in relation to Rubber Sheeting materials involve hardness queries, thickness tolerances and surface finish. The problem in trying to respond too many of these issues relate to variances in methodology, equipment available, individual interpretations of standards and quite simply custom and practice.
I thought it would be a good idea to ruminate through a blog on these issues and more importantly publish how MacLellan Rubber assess, measure and approve its own materials, with a view to these ruminations being a guideline for Storage; Hardness Measuring, Thickness Measuring and Handling, many of which relate to British and European Standards and where appropriate common sense.
I may not be right about everything but in publishing this and follow up articles we hope to clarify some of our customers concerns and remove some of the areas of conflict that can so easily arise.
The Customer is of course always right, it's just that they are not always correct!
I thought we should start with one of the most common issues which impacts on quality concerns which is the Storage of Rubber Sheeting. The principal thing to remember is that we are dealing with a vulcanised rubber which is an elastic product and susceptible to changes in the physical properties if storage conditions vary. Areas which are readily affected by incorrect storage and handling are hardness, flexibility, surface cracking and deterioration. Long term implications of incorrect storage and handling may be a reduction in performance characteristics such as elongation, tensile strength and compression set
These are covered by standards such as BS3734, ISO 2230 amongst others but the main points to follow are:
Store in a Cool environment - Optimum temperature will be 10 C, but shouldn't be below 0 C or exceed +30 C as the polymerisation within the material may start to break down. Where temperatures do drop below 0o C you should allow the material to warm slowly before commencing work on it.
Store away from Direct Sunlight - Exposure to UV will cause materials to harden and crack.
Material should be wrapped in an opaque, non-reactive packing material for best practice.
Store away from Heat Sources - Extreme Heat will cause material to soften and degrade.
Maintain Humidity - A relative humidity between 45 and 75% is optimum. Low humidity may cause material to harden and crack.
Store in a Relaxed Condition - Rubber Sheet may take on a compression set or deformation if stored incorrectly or under load. Ideally store standing on its end rather than lying on its side. Re-roll the material so that it is tightly coiled and retains some rigidity. If the material has to be laid on its side then avoid putting too much load on top which will crush the material and may effect some compression set.
Despite following these recommendations we need to remember that vulcanised Rubber Sheet still has a defined Shelf Life after which there can be no expectation that it will perform to anything like the stated characteristics such as elongation or tensile strength.
ISO 2230:2002 amongst other standards categorise materials into one of three groups to determine their initial shelf life when stored correctly and an extension period that can be agreed if the material is show to be in good condition. These are summarised accordingly:
|Classification||Polymers||Initial Storage Period||Extension Period|
|Group A||BR,NR,IR,SBR||5 Years||2 Years|
|Group B||CR,NBR,IIR,HNBR||7 Years||3 Years|
|Group X||EPDM,FKM,Q,VQM||10 Years||5 Years|
For a full list of Polymers by Classification please refer to our website.
Note shelf life is dependent upon correct storage conditions and cannot be taken for granted. Incorrect storage conditions may reduce the shelf life by as much as 50%.
As a final point in this blog, I should say that all of the team at MacLellan Rubber are regularly updated on changes to standards that affect our business and are willing to provide advice and recommendations where appropriate.
I hope that this first instalment gives all of those with the time and inclination to read it something to consider, whether or not you agree with the statements made. If you do, we look forward to working with you. If you don't I guess we will potentially have more discussions in the future.