Composition and function of scraper in paper machine

The doctor blade in a paper machine is generally composed of a doctor blade seat, a doctor blade holder, a pressurizing/lifting device, an oscillating device, a doctor blade, etc., as well as ancillary parts such as bearings and journals.

1. Scraper seat

The hardness of the scraper holder must be calculated, designed and produced very strictly. This structure requires that the scraper holder and the blade can be supported in the proper position. The scraper holder used in the wet end must be plated with high quality stainless steel or directly made of stainless steel to prevent corrosion. , For the scraper holder used in the dryer section, the painted carbon steel construction is sufficient.

At the same time, it is also necessary to design the cross section of the scraper 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 scraper holder also includes different structures depending on the position of use, such as scrapers used in steering rolls, some of the press rolls, shovels, white water collection trays and pipes are also the main components.

2. Scraper holder

The doctor blade holder is the part that keeps the doctor blade in its operating position. The doctor blade holder must be designed to allow easy and rapid insertion and movement of the blade and to hold the doctor blade in place. There are many types of scrapers, two of which are commonly used. One is a rigid tool holder, which cannot be automatically adjusted when the contact surface changes after being fixed. The second type is the flexible or self-adjusting tool holder. This structure can be automatically adjusted when the position of the scraper seat changes or the pressing pressure changes. The air pipes are filled by hydraulic or compressed air action. The trachea provides sufficient flexibility to vary according to the surface contacted.

3. Scraper blade

The doctor blade is the part that is in contact with the surface of the roller and performs the function of the doctor blade. The material of the scraper blade can be many different kinds of metals (such as steel, copper, stainless steel, etc.) and non-metallic materials (high-density polyethylene, glass fiber, carbon fiber, etc.), and the type of each material is different according to the required hardness of the scraper. It is formulated according to the application site and the material of the roller surface.

4. Journal

The journal is the device where the scraper seat is connected with the bearing, which is located on the operation side and the transmission side of the paper machine. The journal is designed not only to bear the weight of the scraper seat, but also to withstand the force of the scraper when it swings. The positioning of the journal is very important, a scraper, in the absence of any external force, the force added to the roller under its own gravity should be no less than 9-13kgf/m2. For this reason, it is difficult to move the blade position, and, in the case of a rigid blade holder, changing the pressing pressure of the blade requires a redesign of the journal.

5. Bearing

The scraper's bearings are journalled to keep the scraper in place. Bearing designs are very diverse, so it is important to choose the right bearing, which depends on whether the scraper is fixed or oscillating, in wet or dry applications, or in high temperature environments, etc.

6. Pressurizing/lifting device

This mechanical device is used to pressurize and lift the scraper in several different ways, depending on the type of scraper frame, from a simple gravity cam pressurized lifting device to a complex system implemented by air cylinders, etc. This pressing/lifting device is only intended for use in conjunction with rigid doctor blades. The self-adjusting scraper holder requires the scraper seat to be strictly fixed by bolts or cylinders during operation. If this cannot be guaranteed, the effect brought by the mechanical pressure device will not be achieved. The pressure of the scraper can be changed by adjusting the pressure of the air bag. pressure to achieve.

7. Swing device

The most common scraper swinging device is a motor combined with a reducer to use a cam to achieve swinging action. The purpose of the scraper oscillating device is to move the scraper block forward at a fixed rate. This is a severing action relative to the roll face, helping the doctor blade to remove contamination from the roll.

Similarly, the paper machine blade will wear when used on the surface of the roller running at high speed, and will remove some fine paper wool and particles that wear the blade through continuous oscillation.