What are the types of scrapers in paper machines?

The scraper is a common mechanical device in paper machine, which can be divided into two types: one is the scraper for cleaning such as rolls (including the wire section/press section rolls, drying cylinders, calender rolls, take-up rolls); The other type is functional scrapers, such as coating scrapers, creping scrapers, etc.

(1) Net scraper

The wire section includes the Fourdrinier wire section, the nip former and the hybrid wire section, and the doctor blades are used on the breast roll, couch roll, inner wire guide and outer wire guide. The scraper of the breast roll requires a baffle to ensure that the white water goes directly from the scraper seat to the white water pan, and for the inner guide roll, the nozzle of the white water receiving pan must be directed from the scraper to the forming fabric. For the external guide roll of the Fourdrinier paper machine, no special water treatment device is required, and the water directly flows into the white water tray of the wire part. For twin-wire formers and hybrid formers, a special design is required to use the entire white water pan to catch water and remove fibers from the drum. When the inner or outer mesh guide rolls are self-deflecting rolls or tensioning rollers, special brackets are required to ensure that the doctor blade and the roll are kept in a fixed relative position during operation.

(2) Scraper in the press section

The main function of the scraper on the top press roll is to promptly remove the broke generated when the transfer sheet breaks on the press roll. When the sheet breaks suddenly on the press roll, if the sheet is not transferred from the roll in time, the fabric (press felt) will be burned out and cannot be used. The function of the scraper to remove paper sheets is also to use the scraper blade to achieve the cleaning function of the roller. Therefore, the design of the scraper base must be very strong, and it should also include a table or sheet transport device for catching the cleaned sheets.

The scraper on the felt guide roller can make the fabric get the best free cleaning, especially the scraper on the guide roller that touches the felt paper page is more effective. Because shredded paper, fines, and other small solids in contaminants are transferred from the press felt to the smooth roll surface, the doctor blade removes these contaminants, preventing them from accumulating too much and contaminating the press fabric. The doctor blade usually also includes a chip catcher in this position to prevent chips from falling onto the press rolls.

Intermediate press roll blades are often used with a spray system to remove contamination and water film from the roll surface.

(3) Scraper in dryer section of paper machine

Cylinder scrapers are installed at the exit of each cylinder to keep the cylinders clean, thereby improving the heat transfer efficiency between the cylinder surface and the paper.

(4) Calender scraper

When installed on the bottom of the calender or on the bottom roll of the calender, the function of the scraper is to remove the paper sheets caused by the paper breaks and make them directly into the broke pit. Because of the function of removing sheets, the scraper holder must be of a durable design. The scraper of the intermediate roll is preferentially used to clean the contamination of the roll.

(5) Coiling cylinder scraper

The function of the scraper in this position is to scrape the sheet on the take-up cylinder in the event of a paper break. Because the sheet needs to be scraped, a durable scraper device must be used.

The doctor blade removes contamination and water from the roll/dryer face by holding the blade in a fixed position, swinging back and forth under the same pressure, such as on a smooth press roll to remove debris from paper breakage. When used for guide roll cleaning, and in conjunction with a spray system, the doctor blade is an effective tool for keeping fabrics clean, as most machine surface contamination is transferred from the fabric to the smooth rolls. Paper machine blades are often used to remove these contaminants to prevent them from building up and recontaminating or damaging fabrics.