Hard board or medium density board, process for production thereof and means for practicizing the process

In a process for the preparation of building board selected from the group consisting of hard and medium density board made from lignocellulosic fibers, wherein an aqueous suspension of said lignocellulosic fibers having a consistency in the range of 1.0-4.0% is fed onto a moving wire screen of Fourdrinier type in a board machine for dewatering, whereafter the wet lap dewatered on said moving wire screen is subjected to the normal steps of pressing and baking, the improvement comprising introducing evenly across the width of the suspension an aqueous solution of a thermosetting resin into a central layer of said lignocellulosic fiber suspension having a consistency in said range near the headbox of said board machine such that the resin content of the central layer steadily decreases to that of the surface layers and such that there is no zone of the board having higher resin content than the central layer.

a process for the preparation of building board selected from the group consisting of hard and medium density board made from lignocellulosic fibers, wherein an aqueous suspension of said lignocellulosic fibers having a consistency in the range of 1.0-4.0% is fed onto a moving wire screen of Fourdrinier type in a board machine for dewatering, whereafter the wet lap dewatered on said moving wire screen is subjected to the normal steps of pressing and heat treatment, the improvement comprising introducing evenly across the width of the suspension a slurry of lignocellulosic fibers having a content of 1-15% by weight of a thermosetting resin into a central layer of said lignocellulosic fiber suspension having a consistency in said range near the headbox of said board machine such that the resin content of the central layer steadily decreases to that of the surface layers and such that there is no zone of the board having higher resin content than the central layer.

In a board making machine wherein a pulp slurry flow of a consistency of less than 4% is fed on to a moving wire screen, the improvement comprising a device for introducing a thermosetting resin solution into the pulp slurry flow in the direction of the slurry flow, said device comprising a straight pipe having the ends closed, the pipe being disposed in the slurry and transversely to the direction of the slurry flow and being provided with an internal partition plate provided with holes for distributing solution admitted to the pipe uniformly along the pipe, nozzles connected to the pipe and directed in the pulp flow direction, inlet means for feeding solution to the portion of the pipe other than that connected to the nozzles, and means for holding the device in position in the pulp flow.

In a board making machine wherein a pulp slurry flow of a consistency of less than 4% is fed on to a moving wire screen, the improvement comprising a device for introducing a thermosetting resin solution into the pulp slurry in the direction of the slurry flow, said device comprising hollow, elongated means having circular cross section said elongated means being disposed in the slurry flow and transversely to the direction of slurry flow and being provided with a partition wall which divides the hollow means into two chambers and which is provided with holes to uniformly distribute solution flowing from one chamber to the other, this latter chamber being provided with at least one slot in alignment along the elongated means to admit solution into a central layer of said pulp slurry flow in the same direction as this flow, the elongated means being surrounded by a matching turnable envelope having at least one slot matching said at least one slot in the elongated hollow means so that the flow through both said at least one slot can be controlled and means for feeding said elongated hollow means with solution and means for fastening the device in position in the pulp slurry on the board making machine.