Understanding Puncturesafe, and a basic guide
to tyre sealants by Graham Ames - Puncturesafe UK.
(This article was published in the BMW
Club magazine after a request from the editor)
With the
recent popularity of Puncturesafe, and with so much lack of knowledge about
our product, I have been asked to write an article about how Puncturesafe
functions inside a tyre. I will also give a little guidance as to what to
look for when choosing a puncture preventative, whether for high or low
speed use. Sealants in general have been around since the early sixties.
Whilst they were primarily manufactured for the low speed markets such as
construction, and agricultural use, many people attempted to inject them
into their car and motorcycle tyres resulting in problems that were costly
and sometimes dangerous. This was fuelled by unscrupulous manufacturers who
saw a quick profit. You can still see these companies today advertising
their products suitable for high speed. Inexpensive sealants manufactured
for low speed use have a very basic carrier liquid, very similar to
wallpaper paste that contain large chunks of rubber that will bridge a large
punctured hole. They are intended to create a temporary plug in an off road
tyre, to enable the operator to continue with the use of the vehicle/machine
until a tyre fitter is able to make a repair at the end of the day. They
cost pennies to manufacture and are sold to farmers and builders, who put
them into their tractor and JCB tyres in huge quantities. These sealants
contain a high amount of water and slop around at the bottom of the tyre, so
when they are installed in a high speed tyre (over 20mph) they are extremely
hazardous, and many rust wheel rims and corrode alloys. The worst that can
happen is that large rubber chunks can log jam in a large punctured hole
that has secondary damage, and because rubber will stay slippery when wet,
the seal can fail with high speed. Even the many sealants that also contain
fibres are useless because they usually contain the wrong type of fibre that
ball up in a high speed tyre. The inexpensive and inferior polymers in these
products will also separate and dry up due to heat after 500 to 2,000 miles.
With these sealants, once separation begins, there is no recovery. Another
problem that is inherent in many sealants is their inability to disperse
throughout the inner tyre. They readily flow to the bottom of the tyre,
almost like water. The fast rotating tyre forces the sealant into a narrow
band against the outermost portion of the tyre's inner surface, causing the
sealant to remain in the centre portion of the tread area, allowing no
protection elsewhere. Consequently, porosity and bead leaks continue to
exist giving rise to under-inflation. Because under inflation makes tyres
run hotter and wear faster, they become subject to punctures and road hazard
damage. Hot rubber simply has less resistance to cuts and punctures.
Although an uneven road surface will cause this type of sealant to splash
around, the outwards centrifugal forces will always pull the product back to
the centre of the tread area. Any punctures that these products seal in a
high speed tyre is usually short lived with failure of the seal inevitable
within a month or two due to extreme heat and polymer shrinkage in the
puncture.
So, what type
of product do you need that will work effectively in a high speed tyre, and
will be 100% safe? We at Puncturesafe endeavoured to formulate a polymer gel
that would stay liquid up to speeds of 150 mph, and that would only seal a
hole that was recovering in size from a puncture because secondary damage
had not occurred to the cords, or rubber had not been lost as a result of
that puncturing object, which is usual with objects like glass and screws.
We managed to formulate a thixotropic liquid gel of over 20 polymers, all
working together to withstand extremes of heat and stress forces. Most
importantly we developed a combination of special fibres and very small, low
density rubber particles that work with the polymer gel to create a safety
product of outstanding abilities. An effective sealant for high speed will
be thixotropic and in a gel form. Thixotropic describes a compound of a
framework of one kind of particle, which supports other particles within the
substance, and is semi solid or gel like. When a force is applied, the bonds
between the particles in the suspension become weaker, and the substance
loses some of its structure. It then behaves more like a liquid and the
viscosity decreases as the sheer force increases, returning to the gel state
upon standing. Puncturesafe's thixotropic sealant gel is manufactured by a
secret proprietary process, not mixed like a cake recipe. Good sealants
should not be ethylene glycol based and contain a combination of fibres,
particulates, pigments, adhesion agents, rust/corrosion inhibitors, thixotropes, viscosity control agents and PH retainers, which all come
together to form an air-impervious plug in the event of a puncture. The plug
should maintain flexibility because of plasticising additives, so it flexes
with the tyre and positively remains in place sealing the puncture. Though
thixotropic, such formulas regain their fluidity due to kinetic energy from
tyre revolution. Adhesion agents should be added to hold the sealant in
place after the vehicle hasIn depthstopped. An effective sealing compound remains
in a thixotropic gel state and will resist flowing to the bottom of the tyre
by actually clinging to the entire inner surface, stretching as the
centrifugal forces increase, acting as a thermal conductor, transferring
heat from areas of higher temperature, to areas of lower temperature. This
thixotropic state allows the compound to stretch as sheer forces increase
and revert back to its original viscosity as the sheer forces diminish, and
also prevents the centrifugal force from separating the various polymers.
Also this thixotropic state is what protects the polymer gel, allowing the
sealant to last beyond the life of the tyre. In the event of a puncture the
sealant is squeezed into the hole assisted by air pressure and capillary
action, and as the puncture rolls off the load point, leaves the fibres,
particulates and polymers in the hole to cure. Repeated rotation of the tyre
under normal load deposits more fibres etc, until the seal becomes extremely
tight. Fibres, unlike rubber are very coarse surface, and once they have
keyed and intertwined together in a hole that is shrinking and has recovered
in size, they become very strong and are permanent. Our combination blend of
small rubber particles and special fibre is extremely safe, compared with
chunky rubber when they seal a hole, as they will not bridge a large gap. If
cords are cut or rubber has been lost in a puncture, then fibres will slowly
bleed out of the hole giving a controlled deflation. Our fibre blend will
only stay in place where there is a good thickness of rubber, which is why
you will get a controlled deflation with a puncture to the much thinner
sidewall. It is the ability of our special blend of fibres, to distinguish
what is safe to seal, and what is not, that gave rise to our marketing
slogan “Puncturesafe is a clever thinking product”. Any legitimate sealant
manufacturer shouldn't make the claim that a high speed tyre will never go
flat with its sealant installed, otherwise this raises the question of
safety.
Sealant
manufacturers don’t put the same fibres as we do into their sealants because
we have them specially made for us, and the rubber we use is a very low
density, so as it does not cause a balance problem. Heavy high density
rubber which I frequently see in competitors products will not stay
suspended within the liquid, but with speed, will press hard against the
tyre casing causing vibration, and because of this they will also not find
the hole in a punctured tyre quickly. We mix specially manufactured
butyl rubber particles that inner tubes are made of with our fibres, rather
than chopped up old rubber tyres that we see others do.
80%
of punctures are straightforward with nails cleanly penetrating between the
cords causing little damage. If a good sealant is present, then the
lubrication from the sealant will usually help expel the nail sooner rather
than later, helping to avoid secondary damage. When the nail is expelled;
the puncture recovers to a tiny hole less than a half mm in diameter, and if
a good sealant is present within the tyre, it will positively seal the hole
safely. If the puncturing object is at a bad angle and left in for any
length of time, secondary damage may occur, so when the object is removed
you should get a controlled and slow deflation. Glass and screws are
notorious for causing this type of damage by cutting the cords and gouging
tyre rubber away leaving a cavity, which is not usually seen by the naked
eye. In this instance a good reputable sealant will slowly and safely let
the tyre down in a controlled manner, and sometimes halt the air loss at
about 10 to 15psi, which could allow the driver to remove the vehicle from a
possible dangerous location. With the correct amount of sealant installed,
tyre balance will not be upset in a well balanced wheel. With a bad sealant
fitted to an unbalanced or out of round tyre you will get an effect of
hydronomics (motion of fluids). An out of balance wheel rotates
eccentrically, causing a dislocation of mass toward the centre of gravity,
but away from the geometric centre of the wheel, producing vibration. In a
well balanced tyre, thixotropic sealant gels containing adhesion agents can
dampen the occasional shudder or vibration because they are distributed by
centrifugal force to the centre of gravity, causing the geometric centre and
the centre of gravity to become aligned.
