The aim of the Size Press is to apply a solution of starch, glue, or color to the dry surface of the paper. This operation improves the mechanical and printing features of the sheet. Other benefits can be to lessen the tendency to become dirty, to give more strength, and to reduce its permeability to air.
The impregnation of the sheet can take place on both sides or on one side only.
A series of jets with adjustable flow creates a sump between the two cylinders of the press and the side collecting tanks with a uniform concentration of the additive to be added.
The passing of the web in the NIP determines the impregnation of the sheet on one or both sides.
For web impregnation of the sheet on one side only, the size press is equipped with a lubrication system with a jet of nebulized water on the dry cylinder.
The machine is designed for semi-automatic working management.
The web coming from the pre-dryer section is guided by paper-guide rolls through the size press. Subsequently, while the cylinders rotate in synchronism of speed with the machine, the operator controls the closing down of the press.
The opening of the nozzles is automatic when the appropriate photoelectric sensors indicate the presence of a full-size web in the machine.
The approach of the cylinders is very fast, whilst the definite closure is slow; this is to avoid breakage of the paper.
The operator sets up the work pressure on the NIP and the PLC process runs all the sequences, the hydraulic unit, and its pumps in accordance with the safety procedures.
The use of the cleaning doctor in fixed or oscillating mode is chosen by the operator.