Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TITLE OF THE INVENTION
Zinc Based Material Wheel Balancing Weight
FIELD OF THE INVENTION
The present invention relates to a weight for attachment to the wheel of an
automobile for counterbalancing irregularities which would otherwise cause
unwanted and potentially dangerous vibrations of the wheel during rotation,
especially at high speeds. In particular, the invention relates to a wheel
balancing weight fabricated from a zinc basedl material, including a zinc
composite or a zinc alloy, having a very low lead content which exhibits
physical characteristics in terms of corrosion resistance and ductility
comparable to those of traditional lead alloy wheel balancing weights while
at the same time providing an environmentally friendly alternative to lead.
BACKGROUND OF THE INVENTION
In an automobile wheel assembly including a wheel rim, tire and air inlet
valve, there is a potential for a dynamic imbalance in weight to exist when
the wheel is rotated. Generally, in order to compensate for this imbalance,
the wheel is provided with a wheel balance weight.
The prior art reveals a variety of wheel balancing weights and attachment
assemblies for weights manufactured principally from an alloy of lead and
approximately 4% of antimony. Lead's physical attributes, including its high
molar mass, low melting temperature and the ease with which it can worked,
have led to it becoming the primary choice for wheel balancing weights.
Lead, however, is toxic and exposed lead can be released into the
environment due to leaching or other types of corrosion. As a number of
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countries, especially in Europe and Asia, are determined to reduce the
amount of lead which is released into the environment, alternative materials
have been investigated for the fabrication of wheel balancing weights.
The prior art reveals a number of alternative materials which have been
proposed and used for the construction of wheel balancing weights,
including steel (see, for example, U.S. Patent Nlo. 6,260,929) , ductile cast
iron (see, for example, U.S. Patent No. 6,250,721) and tin (see the PCT
application published under WO 99155924) as well as mixtures of a
thermoplastic resin mixed with tungsten powder (see the application for
European patent published under EP 1079141 A1) or an ultraviolet curing
resin mixed with glass beads (see the PCT application published under WO
99/00609).
However zinc has been rejected for use in wheel weights. For example, PCT
application published under WO 99/55924 reports attempts to use zinc for
the fabrication of wheel balancing weights. However, it is stated that zinc
corrodes easily, that its corrosion resistance can be further impacted
negatively by lead contamination, and that zinc lacks the ductility required
for the intended purpose. Also there was a perceived need that movement
to the production of a zinc wheel weight would required widespread
upgrades in order for existing facilities to fabricate wheel balancing weight
from zinc. For these reasons, the prior art teachEa away from the use of zinc
and its use has heretofore not been pursued.
SUMMARY OF THE INVENTION
The present invention addresses the above and other drawbacks by
providing a wheel balancing weight attached to the rim of a wheel for
balancing the wheel. The wheel balancing weight comprises a weight mass
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manufactured from a zinc composite or a zinc based material and a means
for attaching said weight mass to the rim. The zinc composite and zinc
based materials both have a very low lead content and substantially alleviate
the drawbacks associated with the use of lead or zinc having a high lead
content.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a side elevated view of a wheel weight in accordance with an
illustrative embodiment of the present invention;
Figure 2 is a cross-sectional view of a wheel weight in accordance with an
illustrative embodiment of the present invention mounted on the rim of a
wheel; and
Figure 3 is a cross-sectional view taken along 3-3 in Figure 1 of a wheel
weight in accordance with an illustrative embodiment of the present
invention.
DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS
The illustrative embodiments of according to they present invention will now
be described.
Referring now to Figure 1, there is illustrated a zinc based material wheel
balancing weight generally indicated by the numeral 10. The wheel
balancing weight 10 is comprised of a weight body 12 and a mounting clip
14 for attaching the weight body 12 to the flange of a wheel rim 16.
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Zinc based materials as used herein includes zinc alloys, where zinc is
mixed with other metals to produce an alloy having characteristics
comparable to those of lead. Zinc based materials also include zinc based
metals which, although not considered alloys in a conventional sense,
contain materials (other than lead) that have either been added deliberately
to the zinc or are not completely removed from 'the zinc during refining and
that effect the physical characteristics of the zinc metal such that the
characteristics are comparable to those of lead.
The weight body 12 is elongate and roughly oval shaped in cross section.
The upper edge 18 is slightly curved in order to match the curvature of the
wheel rim 16 against which the weight body 12 is snugly held by the
mounting clip 14 when in place. The ends 20 of t:he weight body are tapered
towards the upper edge 18. Additionally, the cross sectional area of the
weight body 12 diminishes as one moves from the centre of the weight body
12 towards the ends 20. This contributes a low aerodynamic profile to the
weight body 12 which in turn reduces the likelihood that wheel weight 10 will
attract dirt and other materials or that the wheel balancing weight 10 will be
dislodged, for example by the actions of a car wash or when the rim comes
into contact with foreign objects such as a curb stones or the like.
The mounting clip 14, which is inserted into i:he weight body 12 during
casting (see Figure 3), extends above the upper edge 18 of the weight body
12 where it divides into a pair of clip fingers 2:?. The clip fingers 22 wrap
around the flange of the wheel rim 16 and in this manner the wheel rim 16 is
securely gripped between the weight body 12 and the pair of clip fingers 22.
The mounting clip 14 is typically fabricated from carbon steel, although a
variety of steels are potentially useable, includling carbon steel, stainless
steel, tool steel, spring steel, etc.. In order to reduce the effects of
galvanic
corrosion which arise when two dissimilar metals are brought into contact in
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the presence of an electrolyte, the steel clips are preferably coated with an
alloy rich in zinc. Note that, although in the present illustrative embodiment
the mounting clip 14 is shown with two clip fingers 22, in another
embodiment (not shown) a single clip finger for wrapping around the flange
5 of the wheel rim 16 could be provided for.
The weight body 12 is manufactured from a c<~st zinc alloy comprised of
pure zinc with a content of less than 0.006% by weight of lead alloyed with
about 4% by weight of aluminium and 0.04% by weight of magnesium, the
alloy once cast also known as Zamak 3. Although a variety of zinc based
materials such as zinc alloys, including those .with the usualltrade names
Zamak 2, Zamak 5, Zamak 7, ZA-8, ZA-12 and ZA-27, are also potential
metals for use in manufacturing the weight body 12 of the wheel balancing
weight 10, the alloy Zamak 3 provides a number' of attributes which make it
preferable for wheel balancing applications.
Firstly, in many cases existing technology previously used for the fabrication
of lead wheel balancing weights can be used to manufacture wheel
balancing weights from Zamak 3 with minor modifications.
Additionally, although zinc alloys tend to loose a greater percentage of their
weight due to corrosion than do similar lead weights, this loss is negligible.
In this regard, two test wheel balancing weights fabricated from Zamak 3
zinc alloy and two test wheel balancing weights fabricated from lead alloy.
The weights were painted with a thermoset polyester base powder coating
containing about 3% aluminum, although a paint containing up to about 5%
zinc could also be used.
The weights were then attached to steel rims and subject to an accelerated
corrosion test according to ASTM B117. This test involved exposing the
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wheel balancing weight/steel rim assemblies to a salt spray at warm
temperatures for 100 hours, then cleaning the wheel balance weights
according to ASTM G1 to remove any corrosion. Additionally, the painted
surfaces of weights Lead #2 and Zinc #2 were :.cored with a metal scraper
to accelerate corrosion of the underlying metal alloys. The results of the
test
are tabled following:
Weight Mass Mass Difference Loss
#
(Before) (After) (% weight)
Lead #1 32.1668 32.1308 0.036 0.11
Lead #2 32.9438 32.9008 0.043 0.13
Zinc #1 19.471 g 19.3308 0.141 0.72
Zinc #2 21.3488 21.1308 0.218 1.02
As is apparent from the results, Zamak 3 zinc alloy tends to loose a greater
percentage of their weight due to corrosion ithan does the lead alloy.
However, the test resulted in a loss due to corrosion on the zinc alloy of
typically under 1 %, which is still within acceptable limits for the use as a
wheel balancing weight.
In any case, the effects of corrosion can be readily reduced by the
application of a suitable coating such as paint. For example, coating the
outer surfaces of the weight body 12 with a corrosion resistance paint, in
particular paint rich in metallic powders of alumiinium, zinc or other metals
which have an electronegativity similar to the zinc used to fabricate the
weight body 12, provide good protection from the effects of corrosion. A
paint which is rich in aluminium provides the added benefit of matching the
appearance of an aluminium rim, and therefore in some cases can be used
to enhance the aesthetic appearance of the wheel balancing weight 10.
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Furthermore, although zinc alloys invariably have a tensile strength and
hardness greater than that of lead, Zamak 3 is somewhat ductile and allows
the cast weight portion of the wheel balancing weight to some degree to be
moulded (typically by hammering) to the shape oif the wheel rim to which it is
being attached. This is important given the variety of diameters of wheels to
which the wheel balancing weight might potentially be fastened, even when
the intended use of the wheel balancing weight is for a limited range of
applications (for example, in the automotive sector, even though a wheel
radius of fifteen (15) inches is quite common, wheels of fourteen (14)
inches, sixteen (16) inches and up to nineteen (119) inches for use with high
performance tires are not uncommon) Therefore the wheel weights can be
cast to fit a widely used diameter of wheel, forexample a wheel radius of
fifteen (15) inches, and then the weight portion adapted by hammering to fit
other wheel sizes.
Finally, referring now to Figure 2, a wheel balance weight 10 is typically
installed by first determining the position and mass of the weight necessary
to counter any unbalance. In this regard, unbalance can arise due to
irregularities in the wheel rim 16, irregularities in the tire 24 (for
example,
due to uneven wear) or the addition of an air inlet valve 26. A wheel balance
weight 10 of the requisite mass is then attached to the flange of the wheel
rim 16. Referring now to Figure 3, the method of installation typically
comprises hammering the mounting clip 14 over the flange of the wheel rim
16 such that the flange of the wheel rim 16 is gripped between the clip finger
22 and the inside surface 28 of the weight portion 12. Further hammering of
the outer surface 30 of the weight portion 12 ;>erves to drive the weight
portion 12 onto the rim surface 32, thereby providing a snug and secure fit
as well as adapting to some degree the shape of l:he weight portion 12 to the
curvature of the rim surface 32. The snug fit of the weight body 12 to the
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wheel rim 16 also provides some added protection against the ingress of
water and dirt which can loosen the wheel weight 10.
It is apparent, therefore, that the weight portion 12 of the wheel balance
weight 10 must be able to bear the impact of a hammer (not shown) and be
flexible to some degree without breaking in order to accommodate a variety
of different wheel diameters. Given their relatively low tensile strength and
hardness, lead alloys are well adapted to deforming under impact and
absorbing shock. In order to assess the suitalbility of zinc alloys in this
regard, a comparative impact test according to ,ASTM E23 was performed
on a series of wheel balance weights wherein the weight portion was
manufactured from Zamak 3 zinc alloy or lead alloy. The results of the
comparison are tabled following:
Weight Region ResistanceWeight Region Resistance
# #
Foot/Lbs Foot/Lbs
Zinc #1 Ends 9.8 Lead #1 Ends 6.2
Zinc #2 Ends 7.5 Lead #2 Ends 9.2
Zinc #3 Ends 5.2 Lead #3 Ends 8.0
Zinc #4 Ends 5.8 Lead #4 Ends 8.4
Zinc #5 Ends 6.4 Lead #5 Ends 7.8
Zinc #6 Ends 3.3 Lead #6 Ends 9.8
Mean 6.3 Mean 8.2
Variance 2.2 Variance 1.2
Weight Region ResistanceWeight Region Resistance
# #
Foot/Lbs FootlLbs
Zinc #7 Clip 3.7 Lead #7 Clip 4.3
Zinc #8 Clip 3.1 Lead #8 Clip 4.6
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Zinc #9 Clip 6.1 Lead #9 Clip 3.8
Zinc #10 Clip 8.6 Lead #10 Clip 3.5
Zinc #11 Clip 5.8 Lead #11 Clip 5.2
Mean 5.5 Mean 4.3
Variance 2.2 Variance 0.7
In the above tables, "Ends" indicates that the impact was in the region away
from the centre portion of the wheel balancing weight towards the ends 20
and "Clip" indicates that the impact was in the region towards the centre
portion of the wheel balancing weight over the portion where the mounting
clip 14 is inserted.
Test results revealed that the Zamak 3 zinc alloy absorbed impact in a
manner comparable to the lead alloy. Therefore, notwithstanding its greater
tensile strength and hardness, Zamak 3 zinc alloy is generally suited for use
in the manufacture of wheel balancing weights.
Although the weight portion 12 of the wheel balancing weight 10 is
illustratively cast from a zinc alloy, the weight potion 12 could also be cast
from pure zinc or manufactured from a composite including pure zinc or zinc
alloy powder combined with a suitable polymeric or silicate binder.
Illustratively, the pure zinc or zinc alloy powder -would be mixed with the
binder and injected into a mould along with the metal mounting clip 14. Once
the binder has cured and of sufficient hardness the wheel balancing weight
10 is removed from the mould and on the flange of the wheel rim 16 in a
conventional manner as previously described. The pure zinc or zinc alloy
powder would constitute about 80% to 90% by weight of the weight portion
12 of the wheel balance weight 10 with 10% to 20% by weight of a suitable
binder. In the case of pure zinc powder, which lacks the ductile attributes of
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a zinc alloy powder, selection of a suitable binder will include one which
provides ductility to the weight mass.
The mounting clip 14 used in the above illustrative embodiment is imbedded
5 in the weight portion 12 of the wheel balancing weight 10 during casting of
the zinc alloy or curing of the adhesive binder. However, it is within the
scope of the present to attach the mounting clip 14 to the weight portion 12
of the wheel balancing weight 10 either by means of an appropriate
adhesive, such as a double sided tape, or by provision of grooves or other
10 openings (not shown) in the weight portion 12 into which the mounting clip
14 is inserted.
Additionally, the weight portion 12 of the wheel balancing weight 10 can also
be attached to the wheel rim 16 via an adhesive without provision of a
mounting clip 14, for example by means of a double sided adhesive tape
(not shown). Typically, such wheel balancing weights are relatively flat in
cross section and are attached not to the flange of the wheel rim 16 but to
an inner surface of the rim, thereby reducing the likelihood that the wheel
balancing weight 10 is dislodged due to the centrifugal forces exerted on the
wheel balancing weight 10 during wheel rotation. In this regard, those
adhesives which are currently used for attaching lead alloy wheel balancing
weights would be appropriate for attaching zinc alloy wheel balancing
weights.
Although the present invention has been described hereinabove by way of
an illustrative embodiment thereof, this embodiment can be modified at will,
within the scope of the present invention, without departing from the spirit
and nature of the subject of the present invention.
