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Clutch Shatter Blankets

Ed Bateman's Clutch Blanket

This article presupposes your Puller is fitted with a Steel Flywheel. If not then please read the Steel Flywheels article first!

Why do we cover the clutch?

Very simply safety; not only yours but that of the spectators and Track Officials. All the major (sorry, no pun intended) Tractor Pulling Association and Club Rules in the UK make Clutch protection a mandatory requirement for all classes of Puller.

Blanket v Shielding

It may seem odd to start an article about Clutch Blankets by comparing them with shielding but please bear with me, all will become plain...

If you have used 10 mm steel shielding around the flywheel and clutch and there is a catastrophic failure, the steel prevents the fragments flying out sideways towards the spectators and track crew BUT it cannot stop the bits from bouncing around within the shielding! It is inevitable that a few will ping off at an angle and guess what will stop them. Various parts of your anatomy which just happen to be in the vicinity of the clutch housing... If your Puller is something like a Fordson Major you can add a perforated fuel tank to the rest of your woes, unless of course the underside of the tank is shielded.

To put things into even starker relief, at 4,000 rpm the outer edge of a 13" clutch has a linear velocity of 69.1150 m/s, 248.814 km/h or 154.6059 mph which takes some stopping!

For 'Farm Class' Puller limited to 2,700 rpm the linear velocity is 46.6527 m/s, 167.94972 km/h or 104.3591 mph.

Another drawback with using shielding is that you may well have to remove some or all of it if you want the get at the Bellhousing bolts for clutch maintenance, repair or inspection.

Clifton & Holland Clutch Blankets

The Clutch Shatter Blanket, or more properly Ballistic Blanket doesn't deflect the flying fragments but rather catches them, absorbs the energy and contains the debris. Safe spectators, Track Marshall's and best of all, from your point of view, a safe driver!

No contest...

What is Kevlar?

At the heart of the Clutch Blanket is an incredibly strong fabric called Kevlar. Kevlar is the registered trademark for a para-aramid synthetic fibre ([-CO-C6H4-CO-NH-C6H4-NH-]n), related to other aramids such as Nomex and Technora. Developed by Stephanie Kwolek at DuPont in 1965, this high-strength material was first commercially used in the early 1970s as a replacement for steel in racing tires.

Bullet and Kevlar fabricTypically it is spun into ropes or fabric sheets that can be used as such or as an ingredient in composite material components. Currently, Kevlar has many applications, ranging from bicycle tires and racing sails to body armour because of its high tensile strength-to-weight ratio; by this measure it is 5 times stronger than steel.

It is also used to make modern drumheads that withstand high impact. When used as a woven material, it is suitable for mooring lines and other underwater applications.

Molecular structure of Kevlar

A similar fibre called Twaron with roughly the same chemical structure was developed by Akzo in the 1970s; commercial production started in 1986, and Twaron is now manufactured by Teijin.

Several grades of Kevlar are available: -

Kevlar K-29 - in industrial applications, such as cables, asbestos replacement, brake linings, and body/vehicle armour.
Kevlar K49 - high modulus used in cable and rope products.
Kevlar K100 - coloured version of Kevlar
Kevlar K119 - higher-elongation, flexible and more fatigue resistant
Kevlar K129 - higher tenacity for ballistic applications
Kevlar AP - 15% higher tensile strength than K-29
Kevlar XP - lighter weight resin and KM2 plus fibre combination
Kevlar KM2 - enhanced ballistic resistance for armour applications

The ultraviolet component of sunlight degrades and decomposes Kevlar, a problem known as UV degradation, and so it is rarely used outdoors without protection against sunlight.

Kevlar - 50 years strong

When Kevlar is spun, the resulting fibre has a tensile strength of about 3,620 MPa, and a relative density of 1.44. The polymer owes its high strength to the many inter-chain bonds. These inter-molecular hydrogen bonds form between the carbonyl groups and NH centres.

Additional strength is derived from aromatic stacking interactions between adjacent strands. These interactions have a greater influence on Kevlar than the van der Waals interactions and chain length that typically influence the properties of other synthetic polymers and fibres such as Dyneema.

The presence of salts and certain other impurities, especially calcium, could interfere with the strand interactions and care is taken to avoid inclusion in its production. Kevlar's structure consists of relatively rigid molecules which tend to form mostly planar sheet-like structures rather like silk protein.

Kevlar on a roll Hybrid plain weave Kevlar

Kevlar maintains its strength and resilience down to cryogenic temperatures (−196 °C); in fact, it is slightly stronger at low temperatures. At higher temperatures the tensile strength is immediately reduced by about 10–20%, and after some hours the strength progressively reduces further. For example at 160 °C (320 °F) about 10% reduction in strength occurs after 500 hours. At 260 °C (500 °F) 50% strength reduction occurs after 70 hours.

How is the Clutch Blanket constructed?

Inside the protective sheath there are multiple layers of Kevlar laid at angles to each other in order to maximise strength and resilience. The number and lay of the layers is a closely guarded secret. Yes, I have asked a number of the manufacturers but they point blank refused to tell me (now there's a surprise). Probably the only sure way to find out would be to take one to pieces which is probably not the best idea in the world.

The outer 'wrapper' has four main purposes: -

Why does it have an 'expiry' date?

Although Kevlar is remarkably strong, UV light, acids, heat and mechanical abrasion will cause degradation which will seriously impair its strength and a its ability to act as a ballistic blanket.

Manufacturers of Clutch Blankets have no control over how the product is used and cared for after it leaves their premises. To ensure the product is still able to perform as specified despite misuse, they are given a five year life span. In the case of Holland Blankets this can be extended (see below).

What will damage my Clutch Blanket?

How do I look after my Clutch Blanket?

One of the best ways of looking after is in not to leave it on the Puller parked out in the open throughout the year for a start!

Before you do any work on the Puller take the Blanket off and lay it out flat in a safe place and that doesn't mean chucking it on the workshop floor. A Blanket soaked in oil and diesel is neither use nor ornament and don't even think of putting it in the washing machine!

Please use your common sense. The Blanket represents a not inconsiderable financial investment and is your guarantee in terms of not only your but also everyone around you's safety so treat it with the respect it deserves.

ETPC approved suppliers

Belport, Belgium No contact details found
Clifton Canvas Developments Ltd., UK http://www.cliftoncanvas.co.uk/
Holland Blankets, Netherlands http://www.whisperinggiant.nl/safety-blankets.html
Security Race Products, USA http://securityrace.com/containment-devices/
Stroud Safety http://www.stroudsafety.com/EngineContainment.html

NB

These are personal notes based on my experiences in dealing, or rather trying, to deal with the ETPC approved suppliers. The latter two are US-based which means you will have to pay not only shipping cost's but import duty as well.

I can find no contact details for Belport so unless you know how to contact them, then forget it...

Clifton Canvas is the obvious choice for us in the UK. James Tolfrey and Jon Cole are the two people you need to talk to and the shipping costs will be less however they have never re-certified blankets but have made subjective views that the blanket had not visually degraded in its life.

They tell me that this is all you could do without destructive testing of the blanket. Because they are made at different times and all treated differently by different customers it’s not possible to batch test them as would be the case with body armour.

Holland Blankets products are warranted for five (5) years BUT, if you return the Blanket back to them after the 5-years, they will examine it with a microscope (well, not literally) and if all is well, will re-warranty the Blanket for another 5-years! So for the (nominal) cost of the recertification, you're good to go for a full 10-years. If you require any further information, click here to open their on-line contact form.

Click here to download the Holland Blankets Shatter Blanket Application Form as a PDF.

UK Clutch Inspectors

If you need to have your clutch inspected and are a member of a Pulling Association or Club this should be your first port of call...

All of these are ETPC approved and are members of the BTPA, which is the ruling body for Competition Tractor Pulling in the UK.

Aberdeenshire David Gall david@drgtechnology.co.uk
Buckinghamshire Peter Clarke declarke3@btconnect.com
Cumbria
David Todd doggtodd@gmail.com
Lancashire John Eccles simplyredpuller@btinternet.com

Acknowledgements

Paul Tucker (ETPC Technical Committee) has been an invaluable source of information and advice. He used to keep all the BTPA records for Clutch Blankets and has a very close working relationship with Clifton Canvas.

Patrick Wever of Holland Blankets and the Argos Oil Whispering Giant Team who supplied much of the 'nitty-gritty' information for the article.

James Tolfrey of Clifton Canvas Developments Ltd. who supplied the missing information regarding the care of blankets and what will damage them.

Sources

https://en.wikipedia.org/wiki/Kevlar

http://www.dupont.co.uk/products-and-services/fabrics-fibers-nonwovens/fibers/brands/kevlar.html

http://www.explainthatstuff.com/kevlar.html

Clifton Canvas Developments Ltd. (James Tolfrey and Jon Cole)

Holland Blankets (Patrick Wever and Bas Liefting)

ETPC

 

Related Links Flywheels - Steel v Cast (UKTP)
  Kevlar - Wikipedia
  Linear to angular speed Calculator