The harsh environment, with highly abrasive dusts, requires fans built to a high standard, frequently from specialised steel alloys such as Hardox or Hastelloy. Halifax has wide experience of fabricating impellers from a wide range of special materials to meet the arduous conditions found in the minerals and aggregates industries. Self-cleaning and the handling of high temperature gases is a frequent requirement and deep-groove ball and roller bearings may be employed to withstand the end thrust that is normally experienced with impellers fitted with back plates.