Fluid knife

A board processing machine including a fluid knife for producing a jet of fluid which is wide and thin for use in the treatment of a board, the machine including at least one pair of rollers for feeding the board to a fluid knife pair including upper and lower fluid knives above and below a board path defined by the rollers, each fluid knife comprising:

• a body having a nozzle side with a nozzle surface, and
• at least one nozzle in the nozzle side of the body for producing the wide, thin jet of fluid,
• each nozzle defining by its orientation a mean, jet plane and
• each nozzle intersecting the nozzle surface of the body at a corresponding orifice, the mean jet plane dividing the nozzle surface of the body into a wing face and a lip face,
• the wing face having a dimension transverse to the jet plane which is greater than the lip face dimension transverse to the jet plane and
• the wing face sloping shallowly and the lip face sloping steeply when the body is arranged with the jet plane substantially vertical, the board processing machine being such that:
• in use a board passing along the board path is closely spaced from the at least one orifice, the board is drawn towards the fluid knife and the bulk of the fluid passes over the wing and not the lip, and
• the two fluid knives are relatively staggered along the board path.