Abstract: A moulding device having a moulding block with a moulding cavity formed therein. A chamber is connected to the cavity and has a mouth where the chamber is connected to the moulding cavity. A closing member is provided between the chamber and the cavity which is moveable from a first position in which the mouth of the chamber is sealed to allow the chamber to be charged with a molten substance while the piston is retracted to a second position which forms a narrow orifice such that a fine spray or jet or film of molten substance is forced at a high velocity through the narrow orifice to form a fine grain coating on the inner surface of the moulding cavity. The closing member can then be further retracted to provide for a second phase of molten substance injection which is carried out until the moulding cavity is full.