The results of wet spinning machines (i.e. the quality and performance of the final fibers) are influenced by multidimensional factors, involving the synergistic effects of raw material characteristics, process parameters, equipment design, environmental control, and post-treatment. The following analysis will be conducted from six core aspects:
1、 Preparation and Properties of Raw Liquid
1. Polymer and solvent system
-The molecular weight distribution, purity, and solubility of fibrous polymers directly affect the stability of spinning solution. For example, polyacrylonitrile (PAN) requires the selection of a suitable solvent (such as DMSO) and the formation of a homogeneous solution through a swelling dissolution process.
-The viscosity of the original solution needs to be controlled within a specific range (usually 100-500 Pa · s). If it is too high, it will cause difficulty in extrusion, and if it is too low, it will easily lead to wire breakage.
2. Pre spinning treatment
-The stock solution needs to be mixed, filtered (removing gel blocks and impurities) and deaerated to avoid blocking the spinneret hole or forming defects during spinning.
-In the production of viscose fibers, a maturation process is also required to regulate the spinnability of the original solution.
2、 Spinning process parameters
1. Design of spinneret head
-The nozzle diameter (usually 0.05-0.12mm), number of holes, and arrangement determine the fiber cross-sectional shape (such as circular, irregular) and linear density uniformity.
-The material is mostly made of platinum alloy or tantalum alloy, which is corrosion-resistant and ensures hole stability.
2. Extrusion and stretching control
-Spinning head stretch ratio: It is often negative or slightly positive in wet spinning to stabilize the forming process.
-Stretching tension: affects the orientation and crystallinity of molecular chains. Moderate stretching can enhance fiber strength, while excessive stretching can lead to fracture.
3、 Solidification bath conditions
1. Double diffusion kinetics
-The bidirectional diffusion rate of solvent and coagulant determines the fiber coagulation rate. Raising the temperature can accelerate diffusion, but it is necessary to balance the synchronicity of fiber surface hardening and internal solidification.
-The concentration gradient of the coagulation bath affects the phase separation behavior, for example, the PAN/DMSO system requires precise control of the DMSO/H ₂ O ratio to avoid microporous defects.
2. Fluid dynamics environment
-The flow rate and direction of the coagulation bath circulation affect the uniformity of mass transfer, and turbulence may cause fiber shaking or local stress concentration.
-The choice between deep bath method and shallow bath method affects the fiber contact time and stretching effect.
4、 Equipment structure and function
1. Accuracy of the spinneret system
-The combination of metering pump and candle filter ensures the quantitative delivery and high-pressure filtration of the raw material, and pressure fluctuations can cause uneven flow.
-The distance between the spinneret and the guide roller (spinning range) affects the stretching range, and a short spinning range is beneficial for high-speed winding but requires higher precision control.
2. Post processing integration
-The design of washing, drying, and oiling devices directly affects the removal rate of residual solvents and surface properties of fibers.
-The short fiber production line requires a continuous post-processing combination machine to ensure the stability of bundling and step-by-step processing.
5、 Environment and operating standards
1. Temperature and humidity control
-Temperature fluctuations in the workshop (recommended ± 1 ℃) can cause changes in the viscosity of the original solution, while excessive humidity can lead to abnormal performance of moisture absorbing fibers (such as adhesives).
-Cleanliness requirement: Suspended particles should be less than 5 μ m to prevent contamination of the nozzle or embedding into the fiber surface.
2. Standardization of operations
-Cleaning and anti clogging measures (such as ultrasonic descaling) of the nozzle after shutdown can prolong the service life of the equipment and reduce the rate of defective products.
-Regularly calibrate the speed of the metering pump and stretching roller to avoid cumulative errors that may cause fiber specification deviations.
6、 Post processing and optimization of finished products
1. Stretching and heat setting
-Multi stage stretching (usually 3-5 times) enhances orientation and significantly increases tensile strength through molecular chain rearrangement.
-The heat setting temperature should be lower than the melting point of the polymer to eliminate internal stress while maintaining dimensional stability.
2. Functional modification
-Adding nanoparticles or flame retardants to the original solution can endow fibers with antibacterial and anti-static properties.
-Surface coating treatment improves wear resistance and dye affinity.
The result of wet spinning machine is essentially a comprehensive embodiment of the trinity of "material process equipment". Enterprises need to optimize the related factors based on their product positioning (such as high water absorption for medical dressings and high temperature resistance for industrial filter materials) in order to achieve efficient and stable high-quality fiber production.