Thomas Broadbent & Sons, Limited, of Huddersfield, manufacture heavy duty decanter centrifuges which are used extensively in the chemical, petrochemical, mining and mineral treatment and other process industries throughout the world. The numerous applications include the separation of crystalline and granular solids from liquids, the drying of fine solids and the classification of solids according to particle size.
Our illustration shows a conveyor component and complete Broadbent decanter used in the production of polyvinyl chloride, the moving assembly and other parts in contact with the process fluid being made entirely of FERRALIUM 255 super duplex stainless steel (UNS S32550, Alloy 255, DIN 1.4507, ASTM F61). In common with many processes of this kind the retention of some chlorides under slightly acid conditions within the slurry from which PVC powder is finally separated and the elevation temperature can cause stress corrosion cracking and blistering of the standard 18/10 and 18/10/3Mo austenitic stainless steels previously used.
The danger of stress corrosion cracking is significantly reduced by using FERRALIUM 255 alloy which has proved its superiority over austenitic stainless steels under these arduous conditions thus greatly increasing service life.
The conveyor is an Archimedian spiral approximately 4’0” in length, tapering from 2’0” to 2’6” in overall blade diameter, formed and welded from ¼” FERRALIUM 255 plate. The spiral is carried on a central tube if 1’5” diameter rolled and welded in ½” plate. The weldability of FERRALIUM 255 alloy is clearly demonstrated in this conveyor component fabricated by F. Pedley & Sons Limited, of Chadderton, Lancs.
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