Do you know the doctor blade detailed types and precautions?
Doctor Blade is a commonly used and important component in the papermaking process. The doctor blade is not only a simple cleaning tool, but also conducive to quality control, process optimization and equipment protection. It has a very important impact on paper quality and operating efficiency.
Types and Application Scenarios of Doctor Blades:
The doctor blade needs to be selected according to different parts of the paper machine, roller surface material, vehicle speed and other factors. According to the material of the blade, it can be divided into: composite doctor blade, polymer doctor blade, metal doctor blade, etc.
Composite doctor blade: Commonly used composite doctor blade are carbon fiber, glass fiber, and cotton fiber doctor blades. This type of blade is light in weight, high in strength, wear resistant and shock absorbing, has a small thermal expansion coefficient, and high fatigue strength. It is often used in high speed paper machines to reduce mechanical vibration, improve operating stability, and effectively extend the service life of rollers and bearings.
Polymer doctor blade: Commonly used blades of this type are HDPE doctor blade. This type of blade has low cost, good wear resistance, excellent corrosion resistance, and low friction coefficient. It is suitable for low speed, low load and high protection requirements.
Metal doctor blade: Commonly used are stainless steel doctor blade and phosphor bronze doctor blade.
Stainless steel doctor blades are commonly used economical scrapers with good corrosion resistance, strength, moderate price, easy processing and wide application. They are suitable for various papermaking processes (net section, press section, sizing section, etc.).
Phosphor bronze doctor blades are often used in the drying section of paper machines. They are resistant to high temperature, corrosion and wear and can effectively clean the roller surface.
Detailed Functions of Doctor Blades
The functions of doctor blades are more than just cleaning. They affect the appearance, physical strength, printing performance, coating quality, sizing effect of paper, and the operation and maintenance costs of paper machines.
(1) Clean the roller surface and remove impurities: remove fibers, condensates, metal powders, etc. in the slurry to prevent the influence of paper diseases (spots, streaks caused by uneven scraping by the doctor blade, broken ends, coating defects, uneven sizing)
(2) Control the coating amount and sizing amount: accurately control the amount of coating liquid or sizing liquid scraped by the doctor blade by adjusting parameters such as the doctor blade angle, pressure, and blade edge shape, thereby controlling the coating layer thickness and sizing amount.
(3) Adjust the moisture distribution of the paper web: the doctor blade scrapes off the free water on the roller surface and partially reduces the moisture content of the paper web (especially at the entrance of the pressing section and the drying section). The doctor blade can scrape off part of the water to reduce the burden of subsequent pressing and drying, and improve the dehydration and drying efficiency.
(4) Stabilize the paper web and prevent shaking: The stabilizing doctor blade uses a slight contact force to suppress the lateral or longitudinal shaking of the paper web when it is running at high speed, preventing the paper web from floating, wrinkling and breaking.
(5) Wrinkling of wrinkled paper: The doctor blade peels the paper sheet from the dryer cylinder through a specific angle and pressure, and uses the difference in adhesion between the paper and the dryer cylinder surface to cause controllable wrinkles in the paper.
(6) Extend the life of the roller surface: Timely scraping of impurities on the roller surface can reduce the wear and corrosion of impurities on the roller, reduce the accumulation of impurities on the roller surface to scratch the roller, extend the service life of the roller, and reduce the probability of replacing the roller.
