Terry’s Moments Project: Shrink-Cracking Problem
June 8th, 1988
Series of 6 Prosyma Research Ltd reports to Terry’s
Reports dated 8th June 1988, 7th January 1989, 10th July 1989, 17th October 1990, 16th December 1991, 16th December 1992.
Introduction
Following the modifications to the mould cavity described in Report 1: “The Fragility Problem”, a trial was carried out at the Terry’s plant on 23rd September 1988. This trial involved the insertion of a small number of three types of mould cavity referred to as:
B – Original design
D – Terry’s rounded modification
F – SFB/Terry modification
The impact results from the three types broadly conformed to the results (Report 1) of the July laboratory trials, namely giving results in the order
D > F > B
with F nearer to D than to B. Also when deliberately broken in the normal way, the F type has shown the clearest breaks with no tendency for the moulding shell to crumple under finger pressure (as can happen with B types) or for the break to run into the shell (as happened with D types).
However, it was reported that a high proportion (around 30%) of F type bars in the plant trial were cracked before demoulding. It has always seemed likely that there are two linked problems in the cracking problem:
- cracking during and after demoulding
- cracking due to shrinkage in the final cooler prior to demoulding.
Basically the SFB modifications incorporated in design F are intended to correct (1) by reducing the chance of abnormally thin sections (< 0.8 mm) in the section between the shells (the weir section) and at the point where the back plate meets the open shell. These improvements appear to have been achieved in the F type.