SPOT – Spin Pattern Optimization Tool: Smart Optimization of Spinneret Hole Patterns

The Problem: Uneven Distribution of Quench Air – Why Conventional Hole Patterns Limit Fiber Quality

In typical dry/wet spinning systems, quench air flows radially from the inside of the ring spinneret to the outside, thereby cooling and solidifying the freshly extruded fibers. However, conventional, uniformly arranged hole patterns give rise to well-known aerodynamic problems:

• Wake effects accumulate: Each fiber creates a slipstream, thereby partially shielding the fibers behind it from the incoming air.
• Fibers in the outer rows receive insufficient quench air: As the slipstream effect increases, significantly less process air reaches the outer areas than the inner ones.
• Fiber properties vary: Uneven cooling leads to variations in fiber diameter, crystallization, mechanical strength, dyeability, and other quality-critical parameters.
• The risk of fiber breaks increases: Breaks typically occur in the outer rows, as these are often insufficiently cooled and moisture tends to accumulate there more heavily. This leads to corresponding production downtime and material waste.

These effects usually remain hidden during the design phase of the spinneret and are difficult to diagnose during operation. The problem is further exacerbated as the number of holes increases – a direct consequence of the industry trend towards higher throughput and finer filaments.

The Solution: CFD-Based Optimization of the Hole Pattern Using Spot

SPOT brings together two core capabilities of our department »Flow Processes«:

• High-fidelity CFD simulations of the quench airflow through the fiber bundle, which resolve the wake interactions between individual filaments in detail.
  
• Mathematical optimization based on our in-house software for shape optimization cashocs.

For nearly three decades, we have been modeling, simulating, and optimizing fiber spinning processes. In doing so, we have:

• built up in-depth expertise in fiber aerodynamics and the physics of spinning processes – from melt spinning and spunbond processes to solution spinning and glass wool production
• developed our own simulation tools (VISPI, FIDYST, MESHFREE, SPOT, cashocs) and validated them in collaboration with industry partners
• established long-term partnerships with leading textile machinery manufacturers and fiber producers worldwide
• award-winning research – including the Joseph von Fraunhofer Prize 2024 for our MESHFREE simulation software
• built an interdisciplinary team that combines CFD expertise, mathematical optimization, and deep domain knowledge in textile production.

We don’t just deliver black-box results. Instead, we work closely with your team of engineers, gain a deep understanding of your specific process, validate the simulation using your production data, and develop solutions that can be directly implemented in your production environment.

Exploiting Periodicity to Reduce Computational Cost

Simulating a ring spinneret with tens of thousands of holes is computationally intensive and costly. SPOT specifically leverages the periodicity of the ring geometry: Instead of simulating the entire nozzle, we analyze a representative section. This allows us to drastically reduce computational effort without sacrificing accuracy. We then apply the optimized pattern to the full spinneret.

Cascading Structures for Uniform Airflow

Rather than a regular pattern, SPOT relies on cascading structures. Strategically offset hole arrangements create aerodynamic »lanes« through the fiber bundle. This allows the quench air to penetrate deeply into the structure and reach every row of fibers at sufficient speed. The key principle: No fiber lies directly in the wake of an upstream filament in front of it.

Results: Measurably Better Fiber Quality

We have demonstrated the effectiveness of SPOT in an industrial setup: a ring spinneret with a PCD of 500 mm, consisting of 31 concentric rings, each with 2,149 holes – for a total of 66,619 fibers. This setup shows clear improvements:

Air reaches all fibers more evenly, significantly reducing the risk of fiber breaks. The fibers that previously received the least airflow – precisely those that pose the greatest quality risk in conventional designs – benefit the most. At the same time, SPOT reduces the variation in fiber properties across the entire spinneret, thereby ensuring:

• more consistent fiber diameters across all holes
• more uniform crystallization and mechanical properties
• fewer fiber breaks
• less unplanned production downtime

We achieve these effects purely through the new arrangement of the spinneret holes – process parameters and materials remain unchanged.

In addition, SPOT also helps save energy: As the air supply for all fibers is optimized and increased, less quench air is required for the spinning process. This directly reduces energy consumption and, consequently, process costs.

Industrial Applications of SPOT – Customizable to Your Process

We have demonstrated the potential of spin pattern optimization using SPOT for a dry/wet spinning process involving solution-spun fibers (e.g., Lyocell, acrylic, PAN-based carbon fiber precursors, aramid). The underlying methodology has a wide range of applications:

• ring spinnerets with radial quench air (inside-out or outside-in)
• round or rectangular spinnerets with a directed quench air flow
• high-density spinnerets with thousands to tens of thousands of holes
• various fiber types: cellulose-based, PAN, aramid, and other solution-spun fibers
• melt spinning processes where quench air uniformity is critical

SPOT can be fully customized to match your spinneret geometry, hole count, and process parameters – from air velocity and temperature to fiber draw and polymer viscosity. Please feel free to contact us.

How Spot Complements Our Vispi Software Solution

SPOT and VISPI are seamlessly integrated and were developed by the same research team:

Together, these two tools cover the entire digital engineering workflow –from spinneret design to final fiber properties. In this way, they eliminate the need for complex physical prototypes and costly test runs.

How to Get Started With Our Software Solutions

We offer SPOT and VISPI as a closely integrated, collaborative service – tailored precisely to your spinneret geometry and process conditions. A typical project proceeds as follows:

• Specifications – You provide your spinneret geometry, process parameters, and quality targets.
• Simulation – We create a CFD model of your process, validate it using your data, and use VISPI to simulate the status quo of your spinning process.
• Optimization – SPOT calculates the optimal hole pattern for your objectives.
• Delivery – You receive the optimized hole coordinates, a detailed analysis of air distribution, and specific recommendations for implementation.

Depending on the complexity of your configuration, results can be delivered within a couple of weeks.