The Types Of Doctor Blade You Need To Know

By Function & Application Scenario

Cleaning Doctor Blade

Forming Section Doctor Blade

Used for cleaning forming wire rolls, couch rolls, breast rolls, and similar components. These doctor blades are responsible for scraping away fibers, fillers, and fine impurities that remain on the wire surface during the dewatering process of the wet paper web. Through that, the doctor helps prevent wire clogging, enhances dewatering efficiency in the forming section, and improves sheet uniformity.

The material used for wire section doctor blades typically requires resistance to abrasion and hydrolysis, as well as moderate hardness and blade angle to avoid damaging the wire fabric.

Press Section Doctor Blade

Due to the unique nature of dewatering via pressing, the material used for the press section doctor blades must be water resistant, wear resistant, and possess a certain degree of elasticity to withstand the high pressure and high moisture environment of the press section. In particular, the doctor for grooved rolls requires a specialized design to ensure effective cleaning deep within the grooves.

Dryer Section Doctor Blade

The dryer section blade, also called the drying cylinder doctor blade, is primarily responsible for cleaning the surface of the drying cylinder. This dryer section blade is one of the most critical blades. Due to the high operating temperatures and severe wear associated with drying cylinder blades, they require materials that possess high heat resistance, abrasion resistance, and a low coefficient of thermal expansion—such as ceramics or special alloy steels. The quality and selection of the drying cylinder blade directly impact the drying efficiency of the paper web, its surface quality, and operational safety.

Coating Doctor Blade

Coating blades are utilized in various components of coating machinery such as coating rolls, air knives, and blade coating heads. The precision of the coating doctor blade's edge fabrication is a critical factor influencing both the coating process and its resulting quality.

Given the extremely high precision requirements involved, a manufacturing process for coating blades capable of minimizing errors (such as CNC machining) must be employed.

Regarding material selection, it is highly advisable to choose coating doctor blades that are resistant to corrosion by the coating fluid, possess excellent wear resistance, and feature a smooth surface finish.

Naturally, for more sophisticated coating applications, a metering doctor blade represents a superior choice. For instance, a metering blade with airknife coating systems enables more precise control over the thickness of the applied coating film. For processes such as short dwell coating and fountain coating, a metering doctor blade capable of directly applying and regulating the coating quantity serves as a viable and effective option. Furthermore, for high end coating applications, metering doctor blades featuring extremely thin profiles constitute an excellent choice.

Creping Doctor Blade

Dry Creping Doctor Blade

Used for the creping of household papers such as toilet paper and napkins.

During production, the creping blade allows for precise control over the creping effect, thereby determining the paper's softness and absorbency. In this process, the blade's angle, pressure, material composition, and vibration parameters constitute the core elements of the creping technique.

Wet Creping Doctor Blade

Used for label paper, wallpaper, specialty creped papers, and packaging paper.

Since wet creping is performed while the paper web retains a high moisture content, the doctor blade operates in a significantly wetter environment, necessitating superior resistance to corrosion and hydrolysis. Furthermore, this higher moisture level requires the blade's cutting edge to engage the paper web with a gentler, softer action.

Stabilizing Doctor Blade

Stabilizing blades are typically used in the drying and press sections of paper machines. These doctor blades help prevent problems caused by high speed operation and high pressure conditions during the drying and pressing processes, such as paper web fluttering, drifting, breakage, and wrinkling, thereby ensuring smooth and stable web running.

Particular Doctor Blade

Guide Doctor Blade

Used to guide, control, and stabilize the movement of scraped off materials (such as water, slurry, and fibers) as well as the running path of the paper web, preventing contamination spread and back splashing, thereby avoiding secondary contamination.

Sealing Doctor Blade

Used to form a stable seal between the roller surface and the scraper, preventing leaks of liquids, air, slurry, or vacuum.

Choose a special precision grade stainless steel belt with a flexible blade edge that is typically straight, continuous, and notch free. The sealing doctor blade is designed to ensure even pressure distribution through flexible contact, thereby minimizing potential leak points

Anti Stripping Doctor Blade

The anti stripping blade is used to prevent the paper web from prematurely detaching from the roll surface during operation due to air suction, centrifugal force, or airflow turbulence. This type of blade is widely used in high speed paper machines, tissue paper production, and coating equipment, helping to reduce issues such as paper breaks, paper drift, and paper wrinkles caused by premature web detachment.

By the Shape & Structure of Doctor Blade

Straight Doctor Blade

The blade is linear in shape and characterized by a simple structure and low cost. It is the most widely used type.

Curved Doctor Blade

The blade of this doctor blade is curved, allowing it to conform more closely to the roller surface and ensuring a more even and stable distribution of pressure, thereby improving the blade’s cleaning performance. It helps reduce paper defects caused by blade marks and vibration, making it particularly suitable for wide web and high speed machines.

Tooth Type Doctor Blade

This type of blade features regular serrations, grooves, or an interrupted pattern.

The tooth type blade is primarily used to break up liquid films, separate fluids, and reduce continuous water streams, thereby preventing the formation of water marks and streaks on the paper.

In addition, the doctor blade can create pressure relief gaps on high speed rollers, improving drainage and reducing airflow turbulence.