Basic Functionality of a Down-Draw Unit in Creating Nonwoven Fabric via the Spunbond Process

The spunbond (Nonwoven) fabric sector has made tremendous progress in recent years due primarily to development in the methods used to make these fabrics. Within the entire production sequence, the down-draw unit is one of the most important components as it lengthens and thins the many continuous filaments of spunbonded material. Therefore, the ability for producers and suppliers to comprehend and apply the principles governing the operation of down-draw units are critically necessary in improving the quality of the fabric and productivity of the entire process.

Definition of Down-Draw Unit

The down-draw unit is a piece of specialized equipment used during the production of spunbonded (nonwoven) fabrics. The main purpose of the down-draw unit is to take the melted spunbond polymer filaments that have just been extruded through the spinneret and lengthen and thin them into individual strands that will subsequently be used to manufacture the finished fabric. The down-draw unit performs its function as a part of an integrated system in collaboration with other units such as extruder, quencher, and laydown.

How the Down-Draw Unit Works

The primary purpose of a down-draw unit is to elongate and thin out (thin) the polymer filaments after they have been melted and extruded through the spinnerets. The following describes how the down-draw unit works in the production of spunbond nonwoven fabrics:

• Polymer Melting: Polymer resin is heated until it melts and forced through an extruder (spinneret) to obtain long strands called 'filaments'.
• Quenching Process: After exiting the spinneret, the filaments are cooled and hardened using an air-quenching method prior to entering the down-draw unit (the stretching process).
• Stretching with Air Streams: The filaments are drawn (stretched) using ultra-high-velocity (high-speed) air streams, or in some methodologies, called a "slot draw unit," over the entire length as they pass through the down-draw unit.
• Diameter Refinement: The controlled manner in which the filaments are stretched reduces their diameter significantly, resulting in the same diameter of each filament produced for a very fine filament.
• Fabric Formation: Once the filament has attained the desired diameter, the filament is laid onto a conveyor or collector drum to form one continuous layer of fabric.

The down-draw unit uses a precise mechanism and precise process control to ensure filaments produced have the tensile strength and uniformity desired for production of spunbond nonwoven fabric.

How Does the Down-Draw Unit Produce Fine Filaments?

The down-draw unit produces fine filaments because of its unique design and process control. The down-draw unit utilizes high-velocity air streams and precise temperature control to allow the polymer material to be stretched without adversely affecting the integrity of the polymer material. Moreover, the speed of these stretching forces can be changed to create different sized filaments, giving each process a lot of flexibility, depending on what the end development will be.

The Advantages of Utilizing A Down-Draw Unit

By bringing a down-draw unit into spunbond production, manufacturers benefit in several ways:

• Filament Quality: The ability to control stretching allows for filament diameters and strength that are consistent.
• Increased Production Rates: Operating at higher speeds results in shorter production cycles.
• Customizable: The down-draw unit can be tuned to produce a variety of filament diameters and fabric properties focusing on meeting customer requests.
• Energy Efficient: New down-draw unit designs utilize features that optimize energy usage reducing production costs.

Spunbond Nonwoven Fabric Applications Made From Down-Draw Units

Spunbond nonwoven fabrics are used across numerous industries, including agriculture, health care, hygiene, and construction. The light weight and durability of spunbond nonwovens make them a good choice for such products as face masks, medical gowns, roof underlayments, and crop coverings. With the accuracy provided by the down-draw unit, manufacturers can easily satisfy the requirements found in these diverse applications.

FAQ: Frequently Asked Questions About Down-Draw Units And Their Function

Q: What process does a down-draw unit use to produce fine filaments?

A: A down-draw unit produces fine filaments through the use of high-pressure air streams to pull the filaments. By controlling the air flow speed and temperature, it will produce filaments that are uniform and fine diameter while maintaining material integrity.

Q: What is the difference between a down-draw unit and a slot draw unit?

A: Both types of draw units use filament attenuation as their principal. A slot draw unit simply refers to a type of down-draw unit that produces filament attenuation through the use of narrow slots to control air flow and can be considered a specialized type of draw unit.

Q: Do down-draw units work with other types of polymers?

A: The down-draw unit is designed to work with many different types of polymers and can be used to produce many different types of nonwoven fabrics.

Maximizing Performance From The Down-Draw Unit

The down-draw unit operates at its highest level of performance when it is properly maintained, calibrated, and monitored while in operation. Upgrading to newer down-draw units with automated controls will improve the efficiency and adjustability of the unit even further, helping to meet the needs of today’s high volume production of spunbond nonwoven fabrics.

Manufacturers are encouraged to invest in R&D and experiment with filament properties in order to create new materials which can be produced in larger volumes for specific niche markets as a competitive means of staying in business.

With knowledge and experience of the proper operation of the down-draw unit, manufacturers should have a high degree of success in producing high quality spunbond nonwoven that meet customers’ specifications and conform to industry standards.

Summary

The down-draw unit, used in the production of spunbond nonwoven fabrics, is a critical piece of equipment for converting polymers into fine, uniform filaments. Understanding how the down-draw unit functions will provide significant benefits for both manufacturers wishing to increase their throughput and buyers looking for high quality spunbond nonwoven fabric. The continuing advancement of technology used in down-draw units has enabled these pieces of equipment to achieve improved levels of performance and quality, resulting in spunbond nonwoven fabrics that can be produced at levels that meet the requirements of all industries.