MINING TYRES
operational downtime at the jobsite. It has a
more vertical sidewall that reduces the chance of
damage by 30%, dramatically extending the life
of the tyre over previous generation Bridgestone
V-Steel Smooth Tread MS. A more vertical shape
is less likely to catch stones, especially when the
vehicle is backing, reducing the risk of sidewall
cuts that tend to occur during loading.
In surface mining, the Bridgestone 46/90R57
VREV (V-Steel Rock Extra V-Operation) 57 in tyre
has been designed for heavy duty mining
applications. The tyre has increased heat and
wear resistance for users operating in severe
haulage applications to provide reliable
performance, increased efficiency and reduced
costs. Innovative buttress fins in the shoulder
use air flow from the rolling tire to force cooler
air into shoulder grooves and across the base of
the tyre to draw heat away, while parallelogram
blocks in the tyre’s tread pattern minimise wear
and tear. Together, these features contribute to a
10% increase in TKPH when compared to the
Bridgestone V-Steel Rock Premium Service
(VRPS) tyre.
Retreading trends
EM tyre retreading became something of a
growth industry during the late 2000s because of
the EM tyre supply crisis at that time. Mines were
prepared to do whatever was necessary to
reduce the requirement for new tyre purchases.
Tony Cutler argues that retreading is currently
seeing a resurgence as mine sites worldwide
once again experience a shortage of new EM
tyres. “Regional mining culture plays a big role in
regard to the retreading of tyres on large haul
trucks. Retreading is regarded as a significant
aspect of EM tyre life management in some
regions, such as areas of the US and South
America, either where it has evolved with the
mining industry as is the case particularly in the
US, or where it can be combined with on-site tyre
servicing to increase demand for it. In other
regions, notably Australia, EM tyre retreading
has traditionally been seen as a cottage-industry
and has not been as readily embraced as an
effective means of reducing mining tyre
operating cost.”
He adds that retreads are far more likely to be
successful in easy operating conditions – with
low operational TKPH, mild climate, excellent
roads, soft material, good operators and good
operating culture. Cooler ambient temperature,
easier underfoot conditions – especially coal –
and less demanding haul truck payload and
productivity targets in the US (and UK) favour
large tyre retreading in these countries compared
with other mining regions such as Australia and
Southern Africa.
There are two main processes used for
retreading EM tyres: One is Slick and Groove
16 International Mining | JULY 2018
(strip winding) – a continuous strip of uncured
rubber is wound onto the buffed casing of the
original tyre; the tyre is then cured in an
autoclave and the tread pattern is then grooved
into the tyre. The other is Pre-Cure – one or two
strips of pre-cured rubber (with the tread pattern
already moulded into the strips) is attached to
the buffed casing of the original tyre; the process
is fin ished using a special curing press but at
lower temperatures than used for the slick and
groove curing process. Most large EM tyre
retreading uses the Slick and Groove process.
Cutler states: “There are two main models of
the Slick & Groove retreading process –
retreading of effectively worn out tyres or
retreading of partially worn tyres in single or
multi-retread variations. To my mind, the
retreading of partially worn tyres is the better
technical option as it greatly improves the chance
of the retread operating until it wears out rather
than suffering a process-related premature
failure.”
Dan Allan at Kal Tire, one of the main players
in mining tyre retreading globally states:
“Customers in this part of the cycle have been
focused heavily on productivity improvements.
Since there was no shortage, tyre supply was not
a constraint. Now with potential bottlenecks
looming, it only makes sense that the supply
chain would be interested in ways to reduce the
need for new tyres where possible. We have seen
many customers looking at programs to use
retreading and repairing as a means to
supplement tyre supply and to help get more life
out of each casing. We inaugurated our OTR
retread plant in Chile in late 2016, and we
continue to see customer interest in our offerings
there. Additionally, we have broken ground on
our new facility in Mexico as we know customers
will benefit from retreading there. We continue to
develop business around our plant in Ghana as
well. Through our five international OTR
retreading locations, we are constantly looking
for ways to not only increase our productivity, but
to also work on new offerings as well to help
customers get more from their current tyre
investment. We are looking actively at new
technology to continue to push this
development.”
Mining tyre recycling
The traditional means of disposing of scrapped
EM tyres on mine sites has been to stack them in
piles, in old disused pits or at the bottom of
waste dumps, and to cover them with waste
material. Cutler states: “This is still done on
many mines around the world although there has
been an increasing trend over the past decade to
store them, uncovered, in tyre waste dumps on
open areas of the mining lease and assigning a
GPS coordinate linked to the serial number (and
hence full descriptive and life history details) of
each scrapped tyre to allow retrieval for whatever
purpose – including future recycling.”
But for the majority of mining regions of the
world there is no end-user charge (at present) for
scrapped tyres that are stored/disposed of
within the mining lease. However, if the tyres are
sent off-site, eg for repair or retread, and are
subsequently deemed unsuitable for
reconditioning and are factory-scrapped, then
unless the tyre is transported back to the mine
site for storage a substantial fee of up to many
hundreds of dollars will be charged for local
disposal.
Cutler ads: “Changes are afoot. Some
government authorities are charging disposal
fees linked to tyre sales, so that an entity –
usually the tyre manufacturer, first importer into
the region or tyre distributor – must pay
irrespective of where final disposal occurs, with
the charge being passed on to the end-user.
Burial of whole tyres – given that their displaced
volume is much greater than their solid volume –
is very inefficient and can lead to ground
subsidence and pollution problems. Solely
cutting tyres into sections does not solve this
issue. The end goal in the mind of most
government authorities is not just disposal, but
the complete recycling of all tyres – including
EM. While the recycling of passenger and road-
truck tyres is now commonplace, although still
not economical without either the incentive of a
government impost upon non-recycled tyres or a
recycler-imposed collection fee, this is certainly
not yet the case for EM tyres. The biggest
problem with EM tyres is cutting them into small
enough sections to facilitate the end-stage of the
recycling process – eg cement kiln or power
generator feed, pyrolysis, etc. The main problems
are the steel beads and radial steel casing and
belts which take a huge toll on shearing
equipment. A range of equipment is required to
reduce each tyre to an appropriate feed size for
end-stage treatment – a large EM tyre handler, a
grab crane, a de-beading machine, sectioning
machine and shredding machine. Until recently,
government authorities have hesitated in
imposing a tyre recycling regime on EM tyre
sellers or end users because many of these
machines were either not commercially available
or impractical to operate safely and effectively;
this is now changing.”
Brazil was the first country, in the late 2000s,
to legislate that all EM tyres must be properly
recycled – driven by health issues arising from
mosquitos breeding in water that collects in the
internal chamber of scrapped EM tyres. “This
encouraged engineering companies to design
and develop the EM capable de-
beading/sectioning/shearing machines that are
available in today’s market and has prompted