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    boardmaking

    Board
    Board is usually defined as paper above an agreed substance (220–
    225g/m2 in UK, 250g/m2 in many other countries). It can be single-ply or
    multi-ply. The multi-ply structure consists of top liner, under liner, middle
    and back liner. Much of the making process is similar to paper. Points
    to note include:
    Furnish
    Basically the same as for paper, ranging from high-quality bleached pulps
    down to recycled waste paper. Stock treatment is basically the same as for
    paper. If waste paper is used, more cleaning and screening may be
    required. Board is generally given a lesser degree of beating/refining in
    order to ensure efficient drainage.
    The liner plies are often given conventional beating and refining to
    develop their strength while the middle stock is hardly given any mechanical
    treatment, just simply broken then lightly refined.
    Manufacture
    In multi-ply board, the plies may be combined on-machine or off-machine.
    In the case of on-machine boards, either Fourdrinier or vat process
    machines may be used.
    In the case of the Fourdrinier manufacturing process, the board is built
    up on the wire from a series of Inverform units, each of which contains a
    head box depositing successive layers on each other.
    The vat boardmaker, on the other hand, consists of a number of vats or
    cylinder units, in-line, in each of which revolves a large hollow cylinder.
    Each cylinder picks up a layer of stock and deposits it on the underside of
    a moving felt which carries the first ply of board. The layers are built up
    progressively; and at the end of the wire the board is removed for drying.
    In the case of off-line finishing, the resulting boards are known as
    pasted boards to distinguish them from the homogenous product which
    comes off a single machine. A number of webs of board are unreeled in
    parallel to each other; adhesive is applied to the top surface of all but the
    top sheet; and a pressing cylinder finally brings all the reels together, joining
    them to create a single reel of thicker board. The edges are slit to provide
    flush edges to the new reel.
    Finishing
    The range of operations in finishing corresponds to those for paper and can
    include: calendering, supercalendering, coating, slitting, sheeting, conditioning
    and, finally, packing for despatch.

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