Allied Colloids are producers of flocculating gel which absorbs moisture in nappies etc. During the manufacturing process, a chemical reaction is induced in a cocktail of chemicals and they are transformed into a jelly-like consistency inside large tapered cauldrons. The cauldrons are then inverted to allow the gel to drop out.
The problem stemmed from the fact that the consistency of the gel was such that it was difficult to drop out. As the gel moved down the cauldron a vacuum was formed above it which made it even more difficult. What was needed was a non-stick surface which was also chemically resistant. The obvious choice is a fluoropolymer with their unsurpassed non-stick capability and blanket chemical resistance. A number of different solutions were tried – including PTFE spray, loose and bonded linings in FEP into the existing steel cauldrons. All had a very limited degree of success and none achieved the customer’s goal – defined as being able to withstand 1000 inversions. The primary reason for failure was the divergence in the expansion rate when exposed to elevated temperature of the steelwork and the lining giving rise to a breakdown in the bond between the two surfaces.
A solution had to be found which would deliver a fluoropolymer lined vessel, able to withstand the repeated temperature cycling and offer the non-stick surface to encourage the gel to drop out.
Working closely with Northern Plastics in Bradford (part of the Ardeth group of companies), Holscot’s proposal was to create FEP/GRP vessels constructed using glass backed FEP, overwrapped with GRP. The two materials would form a homogeneous layer which would expand at a similar rate and avoid the problems seen with lined steel options. It was proposed that the existing stainless steel vessels could be cut down and part of them used as a support collar.
Northern Plastics provided a Mandrel onto which Holscot built the lining with FEP laminate exposing the glass fabric on the outside, Holscot used its proprietary welding and themoforming techniques to achieve this and Northern Plastics completed the vessel with multiple layers of fibre glass and resin to comply with the British Standard.
The completed trial vessel was subjected to the 1000 inversions without showing any signs of distress and Holscot/Northern Plastics went on to complete over 60 cauldrons.
In 2013, after nearly 20 years of service, Holscot has again been involved in manufacturing replacement cauldrons.