Where are automotive sewing threads used?
From the airbag to the steering wheel to the seat belt - textiles in various forms are important components of the vehicle interior. The sewing thread plays an outstanding role for these textiles, which fulfill a wide range of functions in terms of safety, functionality and design.
Automotive interior systems
Processing leather and textiles in the automotive industry places highest requirements onto materials and production processes. It is important to achieve the best possible production efficiency, and very high standards are required to ensure the trouble-free use of the components throughout the automobile's entire lifetime. The sewing thread must fulfil these requirements, too. In car interior, there are two main application fields, seating and interior systems.
Seating systems include seat covers, headrest covers and side bolsters. The thread is important, not only for creating a functional joining seam, but also as a visual enhancement to the vehicle.
Seat comfort is as important as appealing decorative seams. Both criteria can only be fulfilled ideally using high quality sewing threads and the correct processing parameters. A speciality in seat cover manufacturing is the side-airbag deployment seam.
Processing of seat and headrest covers
In almost all cases, seat and headrest covers are processed with continuous filament threads. Other sewing thread types are normally not applied due to the high requirements on the sewing
thread performance during processing and in later usage of the component.
Requirements and characteristics
Polyester threads, such as Serafil offer very good lightfastness, universal possibilities for automotive colour design and can also fulfil all automotive requirements in the mechanical characteristics.
A very precise processing is enabled due to the very consistent performance profile of Serafil, whose substantial characteristic is the excellent gliding ability of the thread. Especially with
challenging decorative seam patterns on seat middle parts, outstanding seam results featuring high process stability can be achieved. Strongfil+, the polyamide sewing thread has advantages, especially due to its very good mechanical product characteristics. The lightfastness and dying ability is good, related to the raw material in comparison to polyester, it is however limited.
Serafil, as well as Strongfil+, are both suitable for seat cover manufacturing, whereas the different polymer characteristics have to be considered during seat development.
Interior systems are e.g. dashboard, armrest, console, door panel and gear shaft cover. The thread is used for safe functional seams, decorative seams as well as a tearing thread for dashboard deployment seams.
Processing of interior systems
Only continuous filament threads are recommended when stitching interior trim. Other thread types are unsuitable due to the high thread performance required during manufacture, and the durability required from the finished component.
Requirements and characteristics
Perfect decorative seams are essential in interior trim. Very often, contrast threads are used. Every stitch is visible and must be perfect. This can be reliably achieved by using AMANN's high quality sewing threads in combination with ideal sewing parameters. The excellent gliding ability, balanced twist ratio and very good off-winding characteristics of Serafil and Strongfil+ are the basis for a trouble-free sewing operation at high process stability and low scrap rate.
Polyester threads are the best choice for decorative seams on interior parts. Serafil stands out for application in highly UV-exposed areas due to its very good UV-resistance. Very precise processing is enabled due to the very consistent performance profile of Serafil, especially on very thin sewing materials as used for interior trim parts. Substantial characteristic is the excellent gliding ability of the thread
Safety-critical systems in automobiles
Safety systems such as airbags, seat belts, but also steering wheels place the highest demands on the functionality and quality of the individual materials and components - and that over the entire service life of the vehicle. Even under the most extreme climatic conditions, the functionality of all safety systems for occupant protection must be available without restriction. Depending on the application, there are very strict specifications for the technological performance profile of the sewing threads.
Airbags are standard safety features in automobiles. Driver, passenger, side or curtain-airbag, they all must prove function. In case of an accident, it can be a matter of life or death. Thus,
highest requirements are set on the production: processing problems such as thread breakage, seam irregularities or material damage lead to scrap. A barcode identification secures the
documentation of the entire production process and allows monitoring and storing of all relevant processing parameters. For production, there are specific requirements based on quality management systems, such as IATF 16949. The sewing threads in use are subject to strict and extensive specifications defined by the OEM or Tiers. The approval process for serial deliveries includes highly elaborate procedures and testing.
Processing of airbags
Mainly multifilament threads made of polyester are used due to the variety of the polyester belts. The sewing thread fineness depends on the required seam strength and is usually exactly specified by specifications. Sewing threads on tickets 8–15 are common practice. With a maximum tensile force of approx. 22,500 cN z. B. Serafil 8 in seam patterns with a suitable number of stitches can achieve a seam tensile strength of approx. 71,300 cN / cm. There are predominantly black threads used. B. Serafil 8 jet black. These products combine very high strength with very good light fastness.
Due to the extremely tight webbing and the high needle sizes, there is intense friction between the needle and the material. The result is high needle temperatures that harbor the risk of thermal material damage to the sewing thread and material. Equipping the sewing threads with the appropriate finishing is one of the key factors here. The finish has a cooling effect on the one hand, and on the other hand it guarantees that the thread slides evenly through the thread guide elements. A fully automated process can thus be ensured without thread abrasion. This means a significant processing advantage over bonded threads, in which the intense friction causes the bond to separate and contaminate the machines. Frequent cleaning intervals are the result. Furthermore, the deposits of the bonding in the rapier area can interfere with the functionality of important bobbin thread monitoring systems, which is a major disadvantage in belt sewing systems with a high degree of automation. A reduction in sewing speed and additional needle cooling are also required for difficult applications. Regular needle replacement is important due to the high stress on the needle, because a damaged needle can cause material damage and many rejects. Changing the needle at the beginning of each shift is recommended.
Safety belts are an essential safety feature in automobiles. The lifetime of a car is around 15 years. At least for this period of time, faultless functioning must be guaranteed. The thread as the joining element, as well as its correct processing determine the system's durability. The strength of the thread in combination with the chosen seam pattern and the number of stitches defines the strength of seam.
Processing of Safety belts
Mainly continuous filament threads made of polyester are used due to material purity to polyester belts. The linear density of thread complies with the requested seam strength and is generally indicated in exact specifications. Standard tickets are 8 –15. With a thread strength of 22,500 cN, Serafil 8 can achieve a seam break strength of approx. 71,300 cn/cm in seam patterns with an appropriate number of stitches. Mainly spun-dyed black threads are in use, e.g. Serafil 8 spun-dyed black. These products combine very high strength with very good colourfastness characteristics.
Due to the extremely densely woven belt webbings and the high needle sizes, the friction between needle and material is immense. The result is a high needle temperature, bearing the risk of thermal damage to both material and thread. The thread finish with an appropriate lubrication is one of the key factors. The lubrication has a cooling effect and also ensures a smooth gliding of the thread through the thread guiding elements. A fully automated process can be ensured without any thread deposit. This is a significant processing advantage over bonded threads. Due to excessive friction, the bonding comes off and soils the machines. Frequent cleaning intervals are the result. Further, due to the deposit in the hook area, important automatic bobbin thread control systems cannot work completely, which is a big disadvantage with seat belt assembly lines with high level of
automatisation. Sewing speed reduction and needle air cooling devices are additionally required with demanding applications. A regular needle change is fundamental as a damaged needle can cause material damage and plenty of scrap parts. A needle change at the beginning of every shift is recommended.
The AMANN Group is a globally active manufacturer of industrial, sewing and embroidery threads and smart yarns. The company's headquarters are located in Bönnigheim in Baden-Württemberg. From universal sewing thread to high-tech special thread, AMANN offers a wide range for a variety of applications. As a car expert, AMANN knows how to combine design and functionality with the demanding technical requirements of the automotive industry.
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