Do You Know The Component of Paper Machine Doctor Blade

The doctor blade in a paper machine generally consists of a doctor blade seat, doctor blade holder, pressure/lifting device, swinging device, doctor blade, etc., as well as auxiliary components such as bearings and shaft necks.

Considerations for Doctor Blade Seat

The hardness of the doctor blade holder must be rigorously calculated, designed, and produced. This structure requires the ability to support the blade holder and blade in the appropriate position. The blade holder used in the wet section must be coated with high-quality stainless steel or directly made of stainless steel to prevent corrosion. For the blade holder used in the dryer section, a painted carbon steel structure is sufficient.

At the same time, it is necessary to design the cross-section of the doctor blade seat according to different paper machine widths. For a complex triangular or four corner section welding, any angle must ensure that the overall deviation is not greater than 12mm. The blade seat also includes different structures depending on the usage position, such as the blades used for turning rollers and some press rollers. Shovel, white water collection tray, and pipeline are also the main components.

What is the Function of a Doctor Blade Holder? What are Its Common Types?

The doctor blade holder is a part that keeps the blade blade in its operating position. The blade holder must have a suitable design to allow the blade to be easily and quickly inserted and moved, and to secure the blade in place. There are many types of blade racks, two of which are commonly used. One type is the fix doctor blade holder , which cannot automatically adjust when the contact surface changes after being fixed. The second type is a flexible or self-adjusting doctor blade holder. When the position of the blade seat changes or the pressure changes, this structure can be automatically adjusted. The trachea is filled with hydraulic or compressed air. The trachea provides sufficient flexibility to vary according to the surface in contact.

Common Types of Doctor Blades

The doctor blade is a part that comes into contact with the surface of the roller and functions as a blade. The material of the doctor blade can be many different types of metals (such as steel, copper, stainless steel, etc.) and non-metallic materials (high-density polyethylene, glass fiber, carbon fiber, etc.). The type of each material is determined according to the required hardness of the doctor blade and the material on the surface of the roller. Commonly used doctor blades types include: carbon fiber doctor blade, glass fiber doctor blade, epoxy resin doctor blade, HDPE doctor blade, and phosphor bronze doctor blade, etc.

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Axle Neck

The journal is a device that connects the blade seat to the bearing, located on the operating and transmission sides of the paper machine. The design of the shaft neck not only needs to bear the weight of the blade seat, but also the force when the blade swings. The positioning of the shaft neck is very important. A doctor blade should exert a force of no less than 9-13kgf/m2 on the roller under its own gravity without applying any external force. Due to this reason, it is quite difficult to move the position of the doctor blade, and if it is a fix doctor blade frame, changing the pressure of the blade requires redesigning the shaft neck.

Bearing

The bearing of the doctor blade is supported by the journal to keep the blade in place. Bearing design is very diverse, so choosing the right bearing is important. Choosing the right bearing depends on factors such as whether the blades is fixed or swinging, whether it is used in wet or dry areas, or in high-temperature environments.

Pressure/Lifting Device

This mechanical device is used for the pressurization and lifting of doctor blade, and there are several different ways according to the different types of doctor blade frames, ranging from a simple gravity cam pressurization and lifting device to a complex system implemented through cylinders. This pressure/lifting device is only used in conjunction with a fix doctor blade frame. The self-adjusting doctor blade holder requires the blade seat to be strictly fixed by bolts or cylinders during operation. If this cannot be guaranteed, the effect of the mechanical pressurization device cannot be achieved. Changing the blade pressurization pressure can be achieved by adjusting the air tube pressurization pressure.

Swing Device

The most common doctor blade swinging device is a combination of a motor and a reducer using a cam to achieve swinging action. The purpose of the blade swinging device is to move the blade seat forward at a fixed speed. Compared to the roller surface, this is a cutting action that helps the doctor blade remove contaminants from the roller.

Similarly, the doctor blade will wear out when used on the surface of a high-speed roller, and through continuous swinging, it will remove some small paper particles that cause wear on the blade edge.