harmonisation and standardisation in polymer selection

from a product design and material testing perspective . . .

A major headache for the design engineer, specifiers and moulders on a worldwide basis is the fact that test data published within polymer suppliers data sheets in most cases is simply unreliable. Rota Design argue that if the industry is to move forward the polymer suppliers must present us with accurate information about the performance of their products in both the short term and long term, and in addition, let’s have a harmonised testing and reporting procedure.

When we design a steel structure it is practice within the industry to calculate the loading imposed upon the beams and columns to enable us to select an appropriate grade of steel and suitable sections to achieve any given factor of safety. In support of this, we refer to national and international standards which set minimum characteristics for tensile and flexural strength etc. backed up with actual test certificates from the steel mill for a given batch of steel i.e. Certificates of Conformity.

The recently published Euro Norms for the construction industry specify the manner in which these calculations are to be undertaken and published. If we adopt this procedure we can be sure that the materials and sections selected are fit for purpose for the use intended and the structure will not fail under load. You may imagine the effects of the collapse of a building, tunnel, bridge or crane due to negligence of the design engineer.

When we draw a parallel with the rotational moulding industry and the manner in which the polymer suppliers feel fit to represent their products (or an alternative view maybe that they misrepresent their products), well, there is no comparison.

At the Nordic ARM conference held a Horsens in Denmark in February 2011, Norner, the well respected test establishment based in Norway, expressed their concern from a slightly different perspective, but with the same passion and intention of harmonising the data sheets so that comparison between different grades of polymers between different manufacturers can be made. Rota Design commends and welcomes this initiative.

So once we have harmonised test procedures and the method by which the test pieces are manufactured it will be easier to made comparative judgements on the most suitable polymer.

At present the best information on a given grade of polymer the industry has to rely on for structural plastic products is no better than sales literature.

pridicting failure using FEA
Difference in impact strength between compression moulded (CM) and rotationally moulded (RM) samples. 

The polymer suppliers who are conscientious in this respect are unfortunately tarnished by the less scrupulous. We need a technically sound platform on which to make our decision about the most appropriate grade of polymer and the polymer suppliers have to join the real world and trade on price, delivery, service etc. and not continue to hide behind voodoo and black magic!

Norner “We need to harmonise our test methods in order to make sure that datasheet values are comparable between suppliers” 

pridicting failure using FEA

Rota Design would prefer that all samples were manufactured on a laboratory rota moulding machine and not by injection of compression moulding. The physical characteristics published should then be representative of the minimum performance available if the polymer is processed at defined parameters.

I can hear the polymer suppliers moaning already, but I really don’t care; we all deserve better respect.

So many tanks and chambers being made now by rotational moulding as well as other structural plastic products such as pallets we have endured too many failures harming the reputation of the industry.

pridicting failure using FEA

Polymer suppliers, if we are going to move forward please present us accurate information about how your products perform in both in the short term and long term and in addition let’s have a harmonised testing and reporting procedure.

Only in this way will design engineers be able to decipher the maze of incomprehensible data that the polymer suppliers deem fit to impose upon us; data, which may have escaped your notice, is relative only to the first few minutes of life and NOT in any way relative to 20, 30 or 50 years being buried or loaded with a tonne on high bay racking for a year 20 metres in the air.

We take the rather extreme view that all polymer suppliers should be made to stand underneath the racking just to emphasise this point. Even a hard hat may not help them out of such a predicament! Sadly, I have to report that no offers have been received to date and nothing has changed.