The structure and principle of pulp beater

First, the slurry tank

The pulp tank of a paper machine pulp beater generally adopts a reinforced concrete structure. Simple grout tanks can also be constructed with bricks and cement. In order to make the pulp circulate well in the tank, reduce the friction of the pulp, and keep the pulp clean, the inner wall of the tank should be polished or lined with tiles.

For the pulp beaters currently in use, the size of the size tank is 3-12m3, the length of the size tank is generally 3.5-1.5 times the diameter of the flying knife roll, and the length-to-width ratio of the size tank is generally 1.5-1.8.

The shape of the slurry tank has a great influence on the flow and mixing of the pulp. At present, the upper knife roller of a relatively complete pulp beater has a triangular downward slope, so that after the pulp passes through the mountain-shaped part, the pulp inside the trough is interchanged with the pulp outside, which is conducive to even beating; in addition, the two ends of the partition wall are made particularly plump. It conforms to the characteristics of the fluid, promotes the pulp to mix well when turning, is consistent with the flow rate, and is also conducive to uniform beating.

In order to make the pulp easy to circulate, the bottom of the pulp tank of the pulp beater has a certain slope. However, the slope should not be too large, otherwise the slurry will cause dead slurry at the front and corners of the tank. The suitable slope is generally 7%-8%, and sometimes up to 13% for higher-concentration slurry.

Second, the flying knife roller

1. Roller

The flying knife roller is also called the beating roller, and its structure has two types: drum type and disc type. Now, the fly-knife roller generally adopts the back-to-disk structure. It consists of 2-4 roulettes, spindles, etc. The disc of the roulette is processed into grooves. Then insert the pin iron, the flying blade is inlaid with hardwood in the gap with the pin iron, and the two ends of the flying blade are fixed with rings.

The speed of the disc of the flying knife roll directly affects the process performance of the pulp beater, and its size depends on the process conditions. The linear speed of the flying knife roll of general pulp beating machine is 7-8m/s, and that of pulping machine is 10-12m/s. After the flying knife roll is replaced with a new flying knife, it is usually necessary to put a part of the wood in the pulp beater, put some sand near the flying knife roll, and start the pulp beater to sharpen the knife so that the flying knife and the bottom knife are in full contact. Before it can be put into production.

2. Flying knife

The flying blade is installed on the circumferential surface of the knife roll. The new surface of the flying blade is generally rectangular, the blade is straight, and there are U-shaped notches at both ends; there are also some flying blades with a bevel on the back.

The length of the flying blade is alternated with the width of the roller surface, and the height is usually 100-120mm. The thickness of the flying blade is determined according to the process requirements of beating, usually 6-12mm. A thin knife should be used to beat free pulp, and a thick knife should be used to beat sticky pulp. In order to cut the fiber effectively when making high free pulp, the thickness of the knife can be as small as 1-3mm. But when determining the thickness of the knife, the strength of the knife must also be considered. The space surrounded by the two flying knives and the hard water block is called the slot. The geometrical dimensions such as the distance and depth of the knife groove have a certain influence on the beating effect. When the depth of the knife groove is constant, the distance between the blades is larger, and the amount of pulp entering the knife groove is larger, which can increase the flow rate of the pulp; but if the distance between the blades is too large, the amount of pulp entering the groove exceeds the beating time, which will affect The quality of pulp also consumes power. Generally, when the beating is mainly based on cutting and splitting fibers, under certain conditions of the width of the sipe, the depth of the sipe is too small, the pulp will wear the hardwood faster and increase the power consumption; if the depth of the sipe is too large, That is to say, if the flying blade extends a long distance, it is difficult for the hardwood to firmly fix the flying blade. The blade will vibrate during beating, and the pulp attached to the deep part of the sipe will fall off in the pulp flow after drying, which will affect the quality of the pulp. . The depth of the knife groove is generally 40-50mm.

The number of flying blades is related to blade thickness, blade tip width and knife roll diameter.

The material of the flying blade can be carbon steel, stainless steel, phosphor blue steel and basalt. Which one to choose can be determined according to the type of beating and the purpose of the slurry. The flying blades of general pulp beaters are made of steel (Brinell hardness 230-250 degrees). When the pulp is required to be free of iron ions, green steel blades are required; for corrosion resistance and wear resistance, stainless steel blades can be used; for high-viscosity beating, stone blades can be used. The most commonly used stone blade is basalt, with 15-20mm deep grooves engraved on the knife surface, and the distance between the ridges is 30-40mm.

Basalt has a large porosity, rough surface, like many tiny blades, suitable for longitudinal tearing and pressure staining of fibers. It is mostly used in beating equipment for the production of tissue paper and other paper types; and because it is a non-metallic material, it is suitable Used for beating capacitor paper. The power consumption of the basalt flying knife during beating is about 20% larger than that of the metal blade, but the beating time can be shortened.

Third, the bottom knife

The bedknife of the early paper machine pulp beater was located directly below the fly knife roll to obtain a larger specific pressure. Most of the bottom knives of pulp beaters are now installed on the mountain-shaped part. In this way, the pulp in the sipe will not be thrown to the mountain-shaped part prematurely, which is conducive to making full use of the kinetic energy of the flying knife roller to push the pulp, ensuring that the pulp obtains a higher circulation speed, and preventing the vortex and reflow of the industry, which reduces the beating. kinetic energy.

According to the number of blades, the bedknife can be divided into 1-3 groups for assembly. Each group has 15-20 blades. In each set of bottom blades, the blades are inlaid with hardwood and then clamped with bolts. The arc of the bedknife should match the circumference of the blade. The installed bedknife is placed in a cast iron bedknife box, and then secured with a wedge iron. Since the bedknife is easy to wear and must be replaced frequently, the bedknife box installed in the mountain-shaped part can be taken out from the side of the outer wall of the slurry tank during maintenance.

The arrangement of the bedknife blades is mostly obliquely formed in a herringbone shape, which can prevent the flying knife from being embedded in the gap of the bedknife; at the same time, it can form a scissors-like shearing effect with the flying knife, which is conducive to beating. The oblique angle of the oblique bedknife is usually 5°-7°.

The thickness of the metal bottom knife blade is about 2-3mm smaller than the thickness of the flying knife. The reason why the bottom blade is thinner than the flying blade is to reduce the root grinding speed of the flying blade, because the bottom blade is easier to replace than the flying blade. In the bottom knife set, the first and second bottom blades should be thicker to withstand the impact of the pulp. The interval between the blades of the bedknife is mostly equal to or slightly larger than the thickness of the blade by 1-2mm, and some are 1 times larger than the thickness of the blade. If the interval is too small, it is easy to be blocked by the pulp and reduce the beating efficiency.

Fourth, the adjustment mechanism

During the beating process, the clearance between the fly knife roll and the bedknife, the shape and size of the knife, and the specific pressure of the fly knife roll on the slurry all directly affect the quality of beating, so the gap and specific pressure should be adjustable. Usually the gap and specific pressure adjustment devices are designed together to become a complete mechanism.

(1) Gap adjustment device: 2, 3, 4, 5, 8, and 7 in the figure constitute the flying knife roll lifting system to adjust the gap. The lifting device is to lift the screw rod through the hand wheel (or sprocket), worm and nut. One end of the screw is hinged with one end of the arm supporting the bearing of the flying knife roller. In this way, when turning the hand wheel into a sprocket, the flying knife roller can be raised and lowered.

(2) Pressure regulating device: 9, 6, 8, 7 constitute a pressure regulating system. The two systems are connected together by a pin 8. When the slurry passes through the gap between the fly knife roll and the bottom knife seat of the pulp beater, the slurry flow has to withstand the pressure from the fly knife roll. During beating, not only the gap between the fly knife roll and the bedknife seat can be adjusted, but also the pressure (that is, the pressure exerted by the fly knife roll on the bedknife) on the slurry flow through this gap can also be adjusted. Always adapt to the beating requirements under different process conditions.

The pressure regulating device can be used to control the pressure between the bedknife and the flying knife roll by adjusting the water pressure, and it can also be adjusted by air pressure. However, most paper machine pulp beaters use the principle of lever to adjust the pressure.

The weight W of the counterweight reduces the force of the knife roller on the bedknife through the lever.