Feeding Systems in Extrusion: The Key to Consistent Material Feed and High Product Quality

In extrusion technology, consistent material feed plays a central role. Especially during the feeding of the extruder, even small fluctuations or interruptions can lead to significant problems. These often manifest as pressure and output fluctuations, which affect the quality of the final product. For example, feed fluctuations can lead to irregular dimensions or, in the worst case, bubbles on the product's surface.
 

Effects of Insufficient Filling

A common problem in extrusion is called underfilling. This means that the feed screw in the extruder is not fully filled with material. In this case, air is drawn into the extruder, which later appears as air bubbles on the product's surface. These bubbles often appear like a string of pearls along the entire product.

Signs of underfilling include an incompletely filled feed hopper, with the screw flights remaining visible. The motor's power consumption also decreases while the output decreases. At the same time, the material outlet temperature significantly increases, which can lead to additional surface defects due to scorching.
 

Feeding Systems in the Extrusion Process for Rubber, Silicone, and Butyl

The extrusion process is a critical step in the manufacturing of rubber, silicone, and butyl products. The quality and efficiency of this process largely depend on the feeding system used. There are various systems specifically designed for different materials and requirements.

Below, we look at the most common feeding systems and their advantages:

1. Piston Feeder

The piston feeder is ideal for silicone extrusion. It operates on the principle of intermittent feed. A piston pushes the material into the extruder, ensuring a consistent and controlled material feed. This method is particularly suitable for high-viscosity and sticky materials that are more difficult to transport.

Advantages:

• Precise Control: Piston feeders allow for exact control of feed speed, which is essential for consistent product quality.
• Continuous Feed: They ensure a steady material flow, minimize downtime, and increase efficiency.
• Versatility: These systems can handle various silicone formulations with different flow properties.
• Closed System: Only the final transition from the feeder to the extruder is exposed.
• Adjustable Volume: Can be adjusted for shift or batch times in extrusion.

2. Strip Feed Device

The strip feed device is often used for feeding silicone and rubber compound in the form of strips or sheets. The material is fed into the extruder in uniform strips, where it is evenly processed. This type of feeding is particularly well suited for materials that are not very sticky and can be produced in 'endless' strip form.

Advantages:

• Efficient Material Use: Even feeding ensures optimal material utilization.
• Less Waste: Strip feed devices minimize both startup time and material loss, leading to cost savings.
• Synchronized Feeding: These systems adjust the feed speed to the production line, resulting in a more efficient overall process.
• Monitored Feeding: Optical and acoustic alerts are given to the operator in case of strip breakage, knots, or strip end.
• Adjustable Speeds: Speeds can be adjusted to prevent overloading the strip when pulling from the Wig-Wag.
• Maintenance Flexibility: Movable variant for better maintenance access to the extruder.
• Versatility: Both classic endless strips laid in the Wig-Wag and foiled strips can be fed into the extruder. 

The transfer foil is wound up space-efficiently and in a disposal-friendly manner.
 

3. Conical Screw Feeding Systems

Conical screw feeding systems are used for feeding pigs-shaped or granulated rubber, silicone, and butyl. The material is slowly and evenly transported into the extruder by a conically shaped feed screw. Its special shape allows for progressive shearing of the material, resulting in better mixing. This type of feeding is particularly suitable for materials with varying flow properties.

Advantages:

• Optimal Mixing: The conical shape ensures improved material homogeneity.
• Efficient for Low Bulk Density: The larger volume in the feed area is particularly suitable for materials with low bulk density.
• Adjustable Control: The radial gap can be adjusted to further optimize the mixing process.
• Increased Precision: These systems offer high stability and accuracy, ensuring consistent product quality.
   

Innovative Solutions from Rubicon

To meet the challenges in extrusion technology, rubicon offers state-of-the-art feeding systems designed for precision, efficiency, compliance, and safety. The systems are equipped with advanced sensors and control techniques that continuously monitor and adjust the material flow as needed, providing operators with the appropriate status information. This not only increases process safety but also improves product quality.

Examples of two of the systems mentioned are the rubicon-developed strip feed device SEV 120 and the piston feeder KF1/7000.

SEV 120

With the strip feed device, a feeding strip is drawn in and fed in a controlled manner to a subsequent extruder. The strip feed device is positioned in front of the extruder so that the support roller is above the feed hopper. The provided feeding strip is pulled between the drive and pressure rollers. Then, it is guided under a dancer and over the support roller to the extruder and drawn in there. The dancer monitors the slack of the feeding strip. The drawing cycles are regulated by the dancer. The speed of the drive roller can be adjusted by the operator.

KF1/7000

The cold-piston feeder is used for the production or shaping of unvulcanized strand products for feeding a silicone extruder. It is designed to be mounted on a silicone extruder. The piston press essentially consists of the base frame, the feeding tube, and the associated press drive.
 

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