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Threads for Extreme Heat

Contents

Types of Fibres and their Fire Resistance
Fire Resistance Standard for Various Thread Applications
Maximum Operating Temperature for Various Fibres
Comparing Aramids
Coats Products

Fire Resistant Thread and Zip Recommendations (page not yet created)

Types of Fibres and their Fire Resistance

Types of Fibres and their Fire Resistance
Material Flame Retardancy Ignition Temp
°C / °F
Cotton Combustible, ignites and burns 252 / 485
Polyester Combustible, burns slowly and may self-extinguish 421 / 790
Nylon Combustible, burns slowly and may self-extinguish 449 / 840
Meta Aramid Flame retardant self-extinguishing when removed from flame -
Para Aramid Flame retardant self-extinguishing when removed from flame -
Fibre Glass Flame retardant will not burn -
Quartz Flame retardant will not burn -
Ceramic Flame retardant will not burn -

Cotton threads, which continue to burn at relatively low temperatures, should be avoided at any time if there is a possibility of contact with fire. Standard polyester and nylon threads are combustible, but will burn slowly and may self-extinguish.

Fire resistant threads fall into three categories:

  1. Threads that do not burn
  2. Threads that burn in flame but self-extinguish when removed from flame
  3. Threads that burn, but burn slowly and may self-extinguish

Types of Sewing Thread and their Fire Resistance

Types of Sewing Thread and their Fire Resistance
Product Material Category Feature Standards
- Ceramic 1 Does not burn NFPA 701 / ASTM E84
- Quartz 1 Does not burn NFPA 701 / ASTM E84
Glasmo Tee Glass fibre 1 Does not burn NFPA 701 / ASTM E84
Firefly Meta Aramid 2 Burns in flame but self-extinguishes when removed NFPA / EN469
Protos Para Aramid 2 Burns in flame but self-extinguishes when removed NFPA
Flame Master Flame retardant 100% polyester corespun 3 Will not burn for short period, then burns slowly and may self-extinguish EN 15025
Epic RD 100% Polyester corespun 3 Burns slowly and may self-extinguish CFR 1615 / BS EN 14878:2007
Astra RD 100% Staple spun polyester 3 Burns slowly and may self-extinguish CFR 1615 / BS EN 14878:2007

Firefly industrial thread

Products in category 1 include; glass fibre (bonded and PTFE coated), high silica glass fibre (quartz), and ceramic. These products do not ignite and are therefore useful in end products where the possibility of fire is high e.g. blast furnaces, mattresses etc.

Products in category 2 include Kevlar® and Nomex®. Kevlar® is the brand name for a para-aramid, and Nomex® is the brand name for a meta-aramid; both are special types of nylon. Kevlar® is manufactured by Du Pont. Other para-aramids include Twaron® (Acordis) and Technora (Teijin). Nomex® is also made by Du Pont; other meta-aramids are Teijinconex (Teijin). These products will normally burn in flame but will immediately self extinguish on removal from the flame. They are therefore useful in end uses where the possibility of fire is high.

Products in category 2, while not as fire resistant as category 1, have much better sewing performance. They are also much softer making them a more suitable choice for protective clothing and upholstery.

Products in category 3 include Coats Epic RD and Coats Astra RD. These are combustible threads manufactured to minimize burning and promote self extinguishing after removal of flame. These products meet fire specifications (such as CFR1615 for children’s sleep-wear).

Fire resistant testing

There is no way to test thread itself for fire resistance; it must first be sewn into fabric. In conducting any test, it is best to use the exact fabric, thread, and seam construction to be used in the finished product.

Fire Resistance Standard for Various Thread Applications

Fire Resistance Standard for Various Thread Applications
Industry Standard
Uniform and Building Code Standards UBC 8-1 (42-2), 8-2(42-2), 26-1(17-2), 26-3(17-5)
Automotive FMVSS302
Aviation FAR 25.853, 25.855
General (Buildings, transport, interior furnishing, protective clothing) NFPA 701 Standard Methods of Fire Tests for Flame Propagation of Textiles and Films
ASTM E84 (Standard Test Method for Surface Burning Characteristics of Building Materials)
Children's Nightwear
(Pyjamas)
CFR 1615: Standard for the flammability of children's nightwear: sizes 0 through 6x (FF 3-71)
CFR 1616: Standard for the flammability of children's nightwear: sizes 7 through 14 (FF 5-74)
BS EN 14878:2007 (Nightwear Safety Regulations)
Protective Clothing EN 531 Protective clothing against industrial heat
EN 407 Protective gloves against thermal risks
EN 366 Protective clothing against heat and flame
Test method: Assessment of clothing materials and material assemblies exposed to a radiant heat source
EN 367 Protective clothing against heat and flame
Test method: Determination of the heat transmission on exposure to flame
EN 373 Protective clothing against heat and flame
Test method: Determination of the resistance of materials to molten metal splash
EN 469 Protective clothing - Requirements for fire fighter’s protective clothing
EN 533 Protective clothing - Protection against heat and flame - Limited flame spread materials and material assemblies

Heat resistant and fire resistant are two separate characteristics

However it is possible for a thread to be both fire resistant and heat resistant. In fact, many of the threads already mentioned as fire resistant are also heat resistant.

Flame Retardant and Protective Wear

In general synthetic sewing threads (e.g. nylon, polyester, Kevlar® & Nomex®) are all good resistors of heat. This means that heat will not pass through them as effectively as it may pass through a substance such as silver or copper. However, as temperature increases, some polymers (such as nylon and polyester) will melt and lose strength before other polymers (such as Nomex®). Their reaction to heat is inherent in their chemical make-up.

Many threads will resist high temperatures and continue to function well in the seam, e.g. aramids, co-polyimide (P84™), glass fibre (bonded and PTFE-coated), quartz, and ceramic. These products remain functional (in the case of ceramic or quartz) up to temperatures in excess of 2000°F (see Table 4).

Nylon and polyester are thermoplastic and start to soften well below their melting point. This means that nylon and polyester seams will begin to weaken around 350°F, while aramid seams will remain as at room temperature, even in excess of 500°F.

As shown in Table 4, the trade-off for better heat resistance is sewing performance.

Maximum Operating Temperature for Various Fibres

Maximum Operating Temperature for Various Fibres
Material Max. Operating Limit °C / °F Constant Operating Limit °C / °F Sewing Ability
Quartz 1093 / 2000 1093 / 2000 Slow speeds, fibres may break
Ceramic 1371 / 2500 1371 / 2500 Slow speeds, fibres may break
Glass Fibre 538 / 1000 538 / 1000 Breaks easily. PTFE coating used for difficult operations
P84® Polyimide Fibres 260 / 500 260 / 500 Good
Meta Aramid e.g. Nomex® 371 / 700 204 / 400 Good
Para Aramid e.g. Kevlar® 427 / 800 204 / 400 Good
Nylon 177 / 350 121 / 250 Excellent
Polyester 177 / 350 121 / 250 Excellent

Heat resistant - temperatures

The Coats Technology Centre is experimenting with nylon threads for automotive applications. High amounts of copper in these threads will act as a heat sink and improve the thread's resistance to heat, for instance in the deployment of an airbag.

Bullet-proof Vests

Nowadays, bullet-proof vest manufacturers use Kevlar®. This allows for lighter-weight, more wearable body armour. There are other materials available for soft-body armour that are cheaper than Kevlar®, but which require a trade-off in weight, comfort and/or bulk.

To understand how Kevlar® works, imagine several wooden sticks. You can break them one at a time with your fist. However, if these sticks are bundled, none can be broken. When Kevlar® is woven into cloth and layered; a bullet encounters many threads at once. The denser the weave (the more threads per unit area), the more bullet resistant it is.

A small bullet fired at Kevlar® encounters fewer threads than a large bullet. A fast small bullet (with the same total energy of a large slow bullet) will penetrate body armour to a greater extent. A .357magnum fired from a revolver is therefore easier to stop than a .22 magnum from a rifle.

Additionally, harder bullets do not deform as much on impact, and penetrate to a greater extent than soft ones. A deformed bullet will encounter more Kevlar® and is more likely to be defeated.

Aramid Threads

There are two main aramid threads - para-aramids (e.g., Kevlar®), and meta-aramids (e.g., Nomex®). While both products are widely used for heat and fire resistance, they have slightly different properties in terms of thread performance.

The table below describes these products' advantages and disadvantages.

Comparing Aramids

Comparing Aramids
Material Advantages Disadvantages
Meta Aramid Flame and heat retardant
Sewing performance and physical properties similar to nylon
Good UV resistance
Lower tenacity than nylon
Much lower than para aramid
Cost
Para Aramid Flame and heat retardant
Low stretch
Very high tenacity
Poor UV resistance
Poor abrasion resistance
Low loop strength
Low stretch can sometimes be a disadvantage
Cost

Aramids come in a number of forms:

  • Continuous filament -- generally the heavier the yarn, the lower the cost, e.g., 138 (1500/1) bonded aramid is significantly lower in cost than a 138 (400/4) bonded aramid
  • Spun staple
  • Stretch broken - a hybrid form consisting of six-inch length staples, which have been made by stretching and breaking continuous filament Kevlar®, and then spinning these staples together.

Glass Fibre Thread

As well as having excellent heat resistance, glass fibre (particularly the PTFE-coated form) has excellent chemical resistance. This makes it especially suitable for high-temperature filtration. Glass fibre thread also has a high tensile strength. The trade-off for excellent heat resistance is brittleness and difficult sewability. Finishes, such as PTFE, improve the sewing performance.

Table of Products

Table of Products
Coats Brand Material Product End Use
Protos Steel Steel Kevlar® coated special steel High temperature insulation up to 1093°C / 2000°F
Helios Steel Cotton or Kevlar® coated stainless steel Ducting
- Ceramic Lubricated Filtration, ducting
Glasmo Tee Glass Fibre Bonded Filtration, blast furnaces, mattress, ducting
Glasmo PTFE Glass Fibre PTFE Coated Filtration, blast furnaces, mattress, ducting
Firefly Metaspun Meta Aramid e.g. Nomex® Staple spun or stretch broken Protective clothing
Firefly Metafil Meta Aramid e.g. Nomex® Bonded continuous filament Filtration, airbags, upholstery, protective gloves / footwear, electrical motors
Firefly Paraspun Para Aramid e.g. Kevlar® Staple spun or stretch broken Airbags, gauntlets, bullet proof vests
Firefly PF Para Aramid e.g. Kevlar® Bonded continuous filament Airbags
HTF P84® Polyimide Fibres Bonded continuous filament Filtration
Epic RD 100% Polyester corespun Lubricated Children's nightwear
Astra RD 100% Staple spun polyester Lubricated Children's nightwear

Coats Helios industrial thread