Apparatus for coating running webs

A coater for coating a running paper or cardboard web, comprising wall means defining a coating chamber having an inlet end and an opposite outlet end, the chamber having an inlet opening at its inlet end for introducing coating substance into the chamber and being open against the web at its outlet end, the wall means including a web entrance wall that bounds the chamber in the upstream direction with respect to the path of movement of the web and is spaced from the web so as to define a slot for the web to enter the chamber, and a back wall structure that bounds the chamber in the opposite, downstream direction, said back wall structure including a doctor member that engages the web for forming a coating layer on the web, and the coater also comprising supply means connected to the inlet opening of the coating chamber for delivering pressurized coating substance into the coating chamber, the supply means including an inlet conduit which terminates at said inlet opening and which defines a flow path along which coating substance that is delivered into the coating chamber passes, the flow path having at least one sharp change of direction a short distance upstream of the inlet opening, the slot defined between the web entrance wall and the web being sufficiently narrow to limit the flow of coating substance from the coating chamber and thereby maintain the coating substance in the coating chamber under pressure, and the distance between the web entrance wall and the doctor member at the outlet end of the chamber being such that, at normal web running speed, the web moves from the entrance wall to the doctor member in a time of at most 0.3 s, the inlet opening being positioned to introduce coating substance into the coating chamber at a position that is closer to the web entrance wall than to the back wall structure, whereby the flow of coating substance in the coating chamber is, at a position close to the web entrance wall, divided into two branches, of which a first branch follows the web in its running direction toward the back wall structure and a second branch, which is of a considerably greater volume flow rate than the first branch, flows out from the coating chamber through the slot.