Which parts of pulping system of papermaking machinery belong to wearing parts?

In the pulping system of paper-making machinery, the wearing parts refer to the parts that need to be replaced regularly due to long-term exposure to friction, impact, corrosion, high temperature or high pressure, resulting in high wear, aging or damage frequency. The loss of these parts directly affects the pulping efficiency and slurry quality. The following are the main vulnerable parts and specific parts in the pulping system:

I. Wearable parts in raw material pretreatment stage

This stage mainly deals with raw materials such as wood, straw, waste paper, etc., and the parts have to bear severe mechanical impact and friction.

Chipper components:

Blade: it is worn continuously when cutting raw materials, especially when dealing with hard wood or raw materials containing impurities, and the cutting edge is easy to become dull or crack.

Bottom cutter (fixed cutter): cooperate with the blade to cut, and long-term contact with raw materials will lead to surface wear, which will affect the cutting accuracy.

Feed roller bushing/rubber layer: the rubber layer is easy to age and crack and the metal bushing is easy to wear due to friction and extrusion when conveying raw materials.

Components of pulper (for waste paper or fiber raw materials):

Rotor blade: high-speed rotating and stirring slurry rubs against fibers and impurities (such as sandstone and metal sheet), resulting in blade edge wear or deformation.

Sieve plate (inside the pulper): filter coarse impurities in the pulp, and the holes are easy to be worn and enlarged, or blocked or scratched by hard objects.

Agitator blades: When stirring at low speed, they are in long-term contact with the slurry, and the materials (such as cast iron and stainless steel) are easily corroded or worn.

Second, the vulnerable parts in the pulping and cooking stage

In cooking (chemical pulping) or mechanical pulping (such as disc milling pulping), parts are subjected to high temperature, chemical corrosion or high-intensity grinding.

Related components of digester (chemical pulping):

Heating pipe: steam is introduced to heat the slurry, and the inner wall is easy to scale (calcium and magnesium deposition) or be corroded by cooking liquid (such as caustic soda and sulfite), which leads to the decrease or leakage of heat transfer efficiency.

Shaft seal of agitator: Under high temperature and high pressure, shaft seal (mechanical seal or packing seal) is prone to aging and failure, resulting in leakage of cooking liquid.

Disc refiner (refiner) core components:

Grinding disc: it is the key wearing part of mechanical pulping. Two grinding discs rotate relatively at high speed to grind fibers, and the surface tooth profile is gradually worn due to friction, which affects the effect of fiber cutting and filament separation (materials are mostly high chromium cast iron and stainless steel, which need to be recast or resurfaced after wear).

Grinding shaft bearing: it supports high-speed rotating grinding shaft and bears radial and axial loads. After long-term operation, lubrication failure or ball wear will lead to abnormal sound or vibration.

Sealing element (end of grinding disc shaft): prevent slurry from leaking. Rubber or PTFE sealing elements are prone to aging and cracking due to high temperature and chemical substances (such as bleach) in the slurry.

Iii. Wearable parts in washing and screening stage

At this stage, the waste liquid is removed by washing, and impurities are screened and separated. The parts should be resistant to slurry scouring and chemical corrosion.

Washing equipment components:

Filter cloth/filter screen of vacuum pulp washer: the water and waste liquid in the pulp are filtered, and the fiber residue will block the filter holes, resulting in fabric fiber breakage and hole enlargement due to long-term friction (the material is mostly polyester or nylon, which needs to be replaced regularly).

Rubber layer of press roll: When squeezing and dewatering, the rubber layer rubs against wet pulp, which is prone to local wear, bulging or aging and hardening, affecting dewatering efficiency.

Screening equipment parts:

Screen drum (pressure screen, vibrating screen):

Round-hole screen drum/slit screen drum: When the slurry passes through the screen hole, fibers and impurities continuously rub the screen surface, leading to the expansion of screen hole wear (especially when dealing with slurry containing sand particles) or being scratched by hard impurities (such as metal wires).

Rotor (inside the pressure screen): high-speed rotation produces negative pressure, which pushes the slurry through the screen drum. The gap between the rotor edge and the screen drum is small, and it is easy to be deformed due to friction, wear or collision.

Vibrating screen spring/damping pad: it supports the vibration of the screen body. Long-term high-frequency vibration leads to the elastic attenuation of the spring and the aging and cracking of the damping pad (rubber material).

Iv. Wearable parts in bleaching stage

Strong corrosive chemicals such as chlorine and hydrogen peroxide are used in the bleaching process, and the parts are vulnerable to corrosion and erosion.

Bleaching tower agitator components:

Stirring blades: When contacting with the pulp containing bleach, metal blades (such as stainless steel) are easy to be corroded, and the surface is pitted or thinned; Plastic blades (such as PVC) are prone to brittle fracture due to aging.

Lining (inner wall of bleaching tower): Rubber, glass fiber or ceramic tile lining is used to prevent corrosion. After long-term use, the lining is easy to fall off and crack, resulting in corrosion of the tower body.

Pump components (such as centrifugal pump):

Impeller: when conveying pulp containing bleach, the surface of impeller is corroded by chemicals and washed by particles, and the blades are easy to wear and puncture.

Mechanical seal: contact with corrosive medium, the sealing surface is easy to be eroded, leading to leakage.

Five, transportation and pump wearing parts

Pumps and conveyors are widely used in pulping system to transport slurry and waste liquid, and the components are subject to wear and corrosion.

Slurry pump/centrifugal pump:

Impeller and pump casing: Friction with high-concentration slurry (containing fibers and impurities) makes metal materials (such as cast iron and high-chromium steel) easy to wear, especially the impeller inlet and the inner wall of pump casing.

Bushing: protect the pump shaft from wear. Long-term contact with slurry will lead to surface wear and out-of-tolerance size of the bushing.

Screw conveyor:

Spiral blade: when pushing raw materials or slurry, the edge of the blade rubs against the material, which is easy to wear, thin or deform (especially when conveying materials containing hard impurities).

Liner (conveyor trough): In contact with spiral blades and materials, liner (such as wear-resistant cast iron and polymer materials) is easy to be worn and needs to be replaced regularly.

summary

The loss of vulnerable parts in pulping system is mainly related to four factors: friction, corrosion, impact and high temperature, among which grinding plate, blade, impeller, sieve plate and seal are the most frequently replaced parts. In actual production, it is necessary to regularly check the status of wearing parts according to the characteristics of raw materials (such as impurity content of waste paper and wood hardness) and operating parameters (such as speed and temperature) and replace them in time to avoid downtime losses. Choosing wear-resistant and corrosion-resistant materials (such as high chromium alloy, duplex stainless steel and ceramic coating) can prolong the life of wearing parts and reduce maintenance costs.