Extruded Products
November 13th, 1984
Part 4, Polymer Engineering, Open University Press, ISBN 0 335 10668 4
S F Bush with G Weidmann
Introduction
Polymer engineering is about making things. This and subsequent units show how the properties and processing knowledge of polymers acquired in the previous three units can be applied to realistic design problems.
It will be readily appreciated that, in any practical situation, a design for a product or component will have to fulfil a multitude of conditions. Usually only some of these can be defined in precise, let along strictly mathematical, terms. Nonetheless there is a systematic way of designing which can embrace both quantitative and qualitative factors, and this is outlined in Section 3. The subsequent discussion is then carried out within the framework of this design procedure and with reference to it.
While the quantitative analysis needed to attain the required processing and product performance will usually be one or more of a few types, the variety of qualitative factors which might possibly be involved is almost endless, as those who have experience of engineering projects or design will be aware. That being so, the qualitative, circumstantial factors can only be illustrated by case studies and the text is based around two of these. One case study, in Section 2, examines the failure of a polypropylene vessel in a chemical plant, whilst the other, on the design of a gas pipe, forms a theme which runs through a large part of the unit.
The earlier units have covered the basic aspects of polymer behaviour in the fluid state and have indicated how this behaviour influences product performance. More evidence of this relationship will be seen as this unit develops. The important point is that the analysis of polymer behaviour will now be made more specific and applicable to real cases. To do this takes a little time, so that most of this unit will be taken up with two matters of central importance in this branch of polymer engineering:
- stresses and failure conditions in extruded products
- melt flow and heat exchange in extruders and within dies and channels.
Both these matters will be dealt with in the context of the overall design procedure as applied to practical cases.