Pressure screens and screen baskets are the key equipment in the pulping and papermaking process.
Their core function can be summarized as “impurity removal and fine selection,” that is, separating qualified fibers from impurities in the pulp under pressure.
For pressure screens, the slot width of the screen basket is one of the most critical parameters affecting their screening effect.
If the slot width is too wide, contaminants can easily pass into the accepts.
If the slot width of the screen basket is too narrow, it may reduce the processing capacity, increase energy consumption, and increase the risk of clogging.
Therefore, there is no unified standard for the selection of screen slots for pressure screens, but it needs to be determined comprehensively based on the screening section, slurry properties, and quality requirements.
The Core Principle of Pressure Screen Basket Slot Selection
The key to selecting the slot width for a pressure screen basket lies in considering its specific location (or function) in the production process to balance “slurry quality” and “production efficiency.”
Generally, the earlier a pressure screen is positioned in the process (such as coarse screens and grading screens), the more its function is focused on high throughput and impurity removal, and the wider the slits in the pressure screen basket.
The further back the pressure screen is located (such as the fine screen or pre-wire screen), the more its function focuses on the quality of the final paper, and the finer the screen slot on the pressure screen basket.
Recommended Range of Pressure Screen Basket Slot Width for Different Sections
Fiber Fractionation Pressure Screen Basket
It is used for separating long and short fibers, allowing different fibers to enter different process flows.
Pressure Screen Basket Slot Width Selection
There is no standardized pressure screen drum slot width for this type of equipment.
Adjustments should be made based on the target grading ratio of your production line.
A larger slot width allows longer fibers to pass through.
A smaller pressure screen basket slot width results in a higher retention rate of long fibers.
Our Advice
Many fiber grading screens use slotted pressure screen basket. This is because the slotted structure can create stronger microturbulence on the surface of the pressure screen basket, reducing fiber bridging and thus improving grading efficiency compared to the drilled one.
Coarse Screening Basket
Located in the pulping section, it is used for primary screening of pulp and removal of large-sized impurities from the pulp, protecting downstream equipment.
Pressure Screen Basket Slot Width Selection
Generally, wider slot widths are used here, typically in the range of 0.25-0.55 mm.
This is because the primary goal of coarse screening is to ensure production capacity and continuous operation, rather than achieving the highest possible slurry cleanliness.
Selecting a pressure screen basket with a wider slot width can reduce the risk of clogging and increase throughput.
Our Advice
The main goals at this stage are high output and impurity removal. Combining this with a cleaner can achieve better results in removing heavy impurities.
Fine Screening Basket
Used for pulp selection, further removing fine impurities and improving pulp quality, it is necessary to balance screening efficiency and pulp quality.
Pressure Screen Basket Slot Width Selection
Choose the pressure screen basket with a finer slot width, typically in the range of 0.15- 0.30 mm.
Our Advice
At this stage, fine-slotted pressure screen basket (e.g., 0.15- 0.25 mm) is often used to improve pulp quality.
Although their screening capacity is 30-50% lower than that of the drilled pressure screen baskets, they can ensure better pulp quality.
Pre-Wire Screen Basket
The final screening process before the paper machine directly affects the quality of the pulp on the wire and the final surface quality of the paper.
Pressure Screen Basket Slot Width Selection
Select the pressure screen drum with a finer slot width, 0.15- 0.25 mm is generally recommended.
Our Advice
The pre-wire screen focuses more on the uniformity and cleanliness of the pulp, so it usually uses a pressure screen basket with a finer slot width to reduce the entry of small impurities into the paper sheet.
Among them, the internal flow screen basket is a common choice, which can provide a stable, low-pulse, and high-quality slurry.
To ensure stable operation, you should also reasonably control the feed pressure (0.1-0.25MPa) and the pressure difference before and after the screen (0.01-0.05MPa) to avoid pressure screen basket blockage and reduced screening efficiency.
Other Pressure Screen Basket Slot Width Selection Affecting Factors
Types of slurry
Different fiber characteristics exist for chemical pulp, mechanical pulp, and waste paper pulp, requiring the selection of different appropriate pressure screen basket slot widths.
Fiber length
When you need to process the long-fiber pulp, a wider pressure screen basket slot width is required to prevent clogging.
Finished product quality requirements
The higher paper surface quality (such as high-grade cultural paper) you require, the finer the screen basket slot width should be.
There is no fixed standard for pressure screen basket slot width selection that applies to all operating conditions.
Instead, it is a process of continuous optimization between slurry cleanliness, processing capacity, operational stability, and energy consumption.