Two-Layer Forming Fabric for Paper Machine Dewatering
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Solution Overview
Problem
Current forming fabrics for paper machines face challenges in achieving a balance between fiber support and dewatering performance, resulting in paper webs with high moisture content and low strength, which can lead to paper breaks and inefficiencies in downstream processing.
Innovation Solution
A forming fabric design with a specific thread distribution and structure, including two longitudinal thread layers with high-strength plastic threads and strategically placed transverse threads, optimizing the fiber support index (FSI) and air permeability to minimize fiber loss and enhance paper web strength and dryness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the longitudinal thread fill level is increased to improve fiber support, then the fiber support index improves, but the air permeability and dewatering performance deteriorate
Solution Approach 1:
The fabric is divided into two separate longitudinal thread layers (machine-side and paper-side) with different thread counts and configurations. This segmentation allows each layer to be optimized independently - the paper-side layer provides higher fiber support while the machine-side layer maintains open structure for drainage, resolving the contradiction between support and dewatering
Solution Approach 2:
Different regions of the fabric have different thread densities and structures. The paper-side longitudinal thread layer has a higher thread count (50-70 threads/10cm) compared to the machine-side layer (30-50 threads/10cm), creating local quality variations that simultaneously achieve good fiber support on the paper side while maintaining high permeability on the machine side for efficient dewatering
2Strength
If high-strength plastic threads are used to reduce thread diameter, then the longitudinal strength improves, but the fabric openness and permeability may be compromised
Solution Approach 1:
The fabric uses composite material construction with high-strength plastic monofilaments (such as polyamide or polyester) that have exceptional strength-to-diameter ratios. This allows the use of thinner threads (0.05-0.15mm) that maintain high longitudinal strength while creating more open fabric structures with better permeability, as the reduced thread diameter compensates for the lower fill level
3Productivity
If the thread diameter is reduced to increase fabric openness, then the air permeability improves, but the fiber support capability deteriorates
Solution Approach 1:
The invention optimizes multiple parameters simultaneously: thread diameter (0.05-0.15mm), thread count (30-70 threads/10cm), and fabric construction (two-layer structure with specific weave patterns). These parameter changes work together to achieve the target FSI of 180-220 and air permeability of 5000-12000 m³/m²/h, where the specific combination of thin threads with optimized spacing and weave structure maintains both permeability and support capability
Data Source
AI summary
The screen (1) has longitudinal threads (4, 5) divided in the ratio of number of threads in a longitudinal thread layer (3) on a machine side and a thread layer (2) on a paper side. Binding cross threads (10, 11) are bound in the thread layers (2, 3). Fiber support index (FSI) of the screen ranges between 230 to 250, and rectangular shaped flow-through openings are formed on the paper side. Diameter of the threads in the longitudinal thread layer on the machine side ranges between 0.15 to 0.25 millimeter. A part of the threads consists of polyethylene terephthalate (PET) material. Air permeability of the screen ranges between 5700 to 10600 meter cube or meter square/hour. The total fill degree of the longitudinal threads is 85 percent.