A machine that produces cardboard in a continuous sheet. Cardboard machines are divided according to function and design into four main types, fourdrinier (flat-screen), multi-cylinder, combination, and multi-cylinder with horizontal molding.
Single-ply cardboard weighing up to 500 g/m2 is produced on fourdrinier cardboard machines, which are virtually identical to paper machines, although they have a larger drying section because of their higher output (up to 850 tons per day). Such cardboard machines weigh about 4, 000 tons and are about 170 m long; the power of the motors that drive all their mechanisms is about 13 megawatts. A staff of five to six is required to operate such machines.
Multi-cylinder cardboard machines produce multi-ply cardboard weighing 600 g/m2 and more. The fourdrinier section of such machines consists of five to eight hollow cylinders 0.9–1.5 m in diameter (the cylinder walls are made from a fine metal screen). The cylinders are located in baths, into which the pulp is introduced continuously. Upon rotation of the cylinder, water passes through the screen within the cylinder and the matted fiber remains on the screen in the form of a layer weighing 40–100 g/m2. The individual layers are removed in succession by a conveyor belt and are joined into a continuous cardboard sheet. Machines have been constructed in which the pulp is introduced into the cylinder from an inlet device and reduced pressure is maintained within the cylinder.
The press section of the cylinder machines is divided into a preliminary section, with three to five pairs of roller presses, and a main section, with two to four pairs. The drying and cutting sections are similar to the fourdrinier machine. It is possible to produce cardboard made up of layers of different fibrous materials on such machines. For example, the outer layers may be of bleached fiber and the inner layers may be of waste paper or wood pulp. The output of cylinder cardboard machines is as high as 500 tons per day.
Combination cardboard machines are used mainly for preparing one-sided or two-sided lithographic cardboard (chrome-substitute type) weighing up to 500 g/m2. The fourdrinier section of the machine consists of flat screens in conjunction with four to six cylinders. The cardboard sheet in such machines is joined together on the flat screen before final drawing-off by a box or couch spindle. The width of combination machines is up to 4.2 m, and their output is up to 300 tons per day.
The screen section of cardboard machines with horizontal molding with a number of screens (Inverform type) consists of one lower screen and a number of upper screens located one on top of the other, with the number of upper screens equal to the number of cardboard layers. The pulp is introduced between the lower and upper screens, through which the dehydrated sheet is produced. The width of such machines is 6 m, and their output is up to 350 tons per day.