Note: Descriptions are shown in the official language in which they were submitted.
1 0 3 ~ jg
THIS invention relates to tyre protective cl~ains o~ the type
comprising an open network of links forming closed figures
and connectors interconnocting the lin~s at the corners of the
figures. The linl;s form the wea)in~ or tread members of the chain.
In a popular form of tyre protective chain for heavy-duty earth-
moving vehicles each link is an elongate plate having a closed
longitudinal slot or a pair of perforations fGrmed in it. Each
connector is forme~ fro~ a rod that is bent into a loop. The
connectors are threaded through the perforations in the links
before being closed by a bridging member or by welding.
The links and connectors are heat treated to ensure they each
have the required hardnesses. The treating may be done before
assembly of the chain. In the event of welded connectors this
~akes welding difficult and frequently results in hairline cracks
developir,~ ,n the cGr,r.ectors because of localised st)esses set
up during welding and subsequent cooling. Non-welded connectors
do not have this problem, but they do have the disadvantage that
the strength of the chain and the density of the net are limited.
Alternatively, the heat treating may be done after the chain has
been assembled. This overcomes the disadvantages of heat treating
before assembly for welded connectors. However, when identical
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steels are used for the linl~s and connectors the required hardnesses
cannot be obtained. Up till now us;n~ the same steel for the wearing
links and the connectors the hardness of the links and connectors
is made to be a maximum of about ~2 to 44 Rockwell C-~cale. This
has been found to be the upper limit for the connoctors whicil sti11
develop cracks in use and is considerably below that required for
a lon~ service life for the links. If carbon or tool steel is
used for the links and a mild steel for the connectors, then the
connectors can be welded and the chain heat treated after assembly
for a uniform through hardening of the links and a re-carburised
surface zone for the connectors (U.S. patent 3 943 990 Rie~er).
This, howeYer, has the disadvantage that the chain has a limited
life in that, once the carburised zone of the connectors has worn
away and the mild steel of the connector exposed, then the connector
deteriorates rapidly.
Rieger U.S. patent 3 943 990 considered using tool steel for the
links and connectors, but discarded this because the connectors
were not weldable and open and closed links had to be used. Such
a chain of open and closed links was not acceptable to him for the
reasons set out above.
It is an object of the invention to provide a tyre protective
chain which satisfactorily resolves the problems of conventional
protective chains.
.
Acc'ording to the inyention there i$ provi~led a tyre protective chain
cor,lprising cln open net\rork of tread l'inks fori~ling closed figures
and arranged to be perpcndicular to the surface of a tyre anci
connectors interconnec~ing ~he ~Jearing links at the ccrners of
the closed figures and url^allged to be parallel to the surface
of a tyre, the connectors being loops that are threaded througi
perforations in the tread lin~s- and that are welded closed
after being engaged with the ~learing links, characterised in that
the tread links and connectors are of different carbon steels and which
have been heat treated after assembly 'of tlle cha'in to ~e hardened through-
out their thicknes'ses, ir, that each connector is a loop having
ends which lap each other and which are welded together, and in
that the tread links have a surface hardness of 46 to 54 Rockwell
C-scale and the connectors have a core hardness of about 15 to 40 Rockwell
C-scale.
The hardnesses in the ranqes specified by the inyenticn will ensure
a long service life for both the links and the connectors. A more
preferred range is 25 to 3~ Rockwell C-sca'le for the core of the
connectors and 48 to 52 Rockwell C-scale for the surface of the links.
The invention is further discussed with reference to the accompanying
drawinys, in which:-
Fi~ure 1 shows a portion of a tyre protective chain according to the
invention;
Figure 2 shows a variant of connector for the chain of the invention;
and
Figure 3 shows another variant of connector for the chain of the
invention.
~ 0391~i9
Figure 1 sno~Js a number of wearin~ or tread lin~s 10 forlning latlerns of
closed figures and connector~ 12 interconnecting the ~Yearing linl~s
10 at the corners of the figures. Four wearirlg links 10 are
threaded on to eacl~ connector 12.
Each ~earing lin~ 10 is an elonsate plate formod ~ith two slot
shaped perforations 14 for receiving a connector 12 therethrollg'il.
The perforations 1~ are positioned towards one side of the
longitudinal axis of the wearing link so as to provide a large
amount of material which may wear away before the wearing link
becomes unservicable.
The perforations 14 may be replaced by a single slot. In another
form the wearing plate may be replaced by rings. These forms are
not shown as they are well known to persons versed in the art.
Each connector 12 is for~ed from a steel rod and includes an open
ring portion 16 with li~,bs 18 extending radially outwardly from
the ring and lapping each other. In practice, after wearing links
10 have been threaded on to the connector, the connector is closed
by welding the limbs 18 to each other along their lapped portions.
In the draw;ng the connectors to one side of the line A-A are shown
as being deposition welded and to the other side of the line A-A
are shown as being resistance welded.
..
Figure 2 shows a variant of connector 22 in which there is a ring
portion and the ends of the ring overlap one another,in the curvature
- of the ring portion, one of the limbs being bent out of the general plane
of the ring.
1 0 3 ~3 ~ 3
In Figure 3 is shown a c~nnector 32 ~imilar t~ that o~ Figure
2, but in which the ~nds of t!~e ring overiap each othcr and both
are in the general plane of the ring. In practice this connector
has one portion of the ring bent with a s~aller radius than the
remainder.
The connectors 22,32 are closed using deposition cr resistance
welding.
The connectors 12, 22, 32 each have lapping limbs or ends and
the welding is performed along the length of the lapped portions This
permits a reliable welding of carbon steel which has been found to be
impracticable previously. ~lith the connectors 12, the we1ded
portion is outside the ring portion. With the connectors 22, 32
the welded portion is inside the ring, but the amount of material
is doubled and the weld is extensive.
An example of a tyre chain which has been tried with success had
the following compositions of carbon steel:
~' ' ' .
~Jearing Links lO:A carbon-steel sold in South Africa by Union
.
Steel Corporation of South Africa Limited (USC0) under the trade
reference E N 45 and having the following composition, tiie
percentages being content by weight:-
.. . . .
10391~9
Carbon 0,50 -0,60%
Silicon 1,50 -2,00~
Manganese 0,70 -1,00%
Sulphur 0,50'~ approx.
Phosphorous 0,50X approx.
Connectors ~2,22,32: lligh-tensile carbon steels sold in South
Africa by USC0 under the trade reference E N 8 and E N 5 A,
the percenta~es being content by weight:-
E N 5A or E N 8
Carbon 0,25 - 0,30% 0,35 - 0,45%
Silicon 0,05 - 0,35% 0,05 - 0,35X
Manganese 0,70 - 0,90% 0,60 - 1,00~
Sulphur 0,60% approx. 0,60% approx.
Phosphorous 0,60% approx. 0,60% approx
In practice the cha;n is made as follows.
Firstly the links and connectors are formed and then
assembled on a table, three, four or five links being
threaded on to each connector to arrive at the desired
pattern and mesh opening size. The overlapping.ends of
the connectors are then squeezed against each other,
tack welded and then welded by deposition welding. Alter-
natively resistance welding may be used in which event
the jaws through which the welding current is passed
are also used to squeeze the ends toyether.
10;~
The asscn;~led chain is then heat treated in the followirlg
steps. The reference to a "salt bath" refers to a carbon-
nitrogen salt sotd under the Trade Name "C-carbon-80" and
hav ng a hinh boiling point.
1) The chain is heated and retained in a salt bath at 8~0C
for 42 hours. This carburises the surfaces of the chain
elements to a depth of 8mm.
2) The chain is air cooled to room temperature.
3) The chain is annealed to 700C.
4) The chain is re-heated to 450C.
5) The chain is again soaked in a salt bath at 840C for a
time calculated at 0 7 minutes/mm thickness.
.
6) The chain is quenched in oil.
7) Finally the chain is re-tempered so that the links of
EN 4~ steel have a hardness of 52-54 Rockwell C-scale
- and the connectors of EN 8 have a hardness of 25 to
34 Rockwell C-scale.
The steels mentioned above have a "work-hardening" property
so that in use it has ben found that the hardness of the
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links and connectors increase by about 5-10% which has
been found to be ideal for good wearing consistant with
reliability.
The heat treatm~nt described above is by way o-F example
only. Other treat~nts llave been tried with a degree of
success. For example one treatment involves heating
the chain in an oven at abcut 850C and then passiny a
carbon-nitrogen gas into the oven for 4 to 5 hours quench
ing in oil~and then tempering the chain to obtain the
required hardness.
.
An important advantage of the chain of the invention is
that both the conneciors and the links are each
hardened througho~ their thickness. This means
that wearing of the chain and rubbing of the links and
- 15 connectors against one another will cause a gradual deterior-
ation of the chain in service. This must be seen in contrast
- to chains having hardened carbon steel links and mild steel
surface-carburized connectors; such chains experience
rapid failure once the carburized surface of the connectors
- 20 have worn away i.e. the mild steel connectors break.
_g
~LO 3~
The exa~)les given above are of preferred steel alloys.
Ho~ever stecls which have the following carbon contents may
be used the heat treatnent being adjusted accordingly.
(i) wearing links ; carbon 0 45 to 0 65 % by weigllt
(ii) connectors ; carbcn 0 25 to 0 ~5 % by weight.
Tests and performance results obtained by the applicant
have found that for optin~um performance the relative
hardness should be maintajned wit11in the ranges specified
in the claims. In particular it has been found that for
the wearing links the surface hardness should not go above
60 Rockwell with work hardening otherwise the links will
crack. Lower hardnesses may be used but then the service
life of the links decreases. For the connectors the range
of hardnesses is more flexible and is usually dependent on
the application of the chain If the chain is merely ~Yrapped
around the surface of a tyre then hardnesses in the upper
range may be used as the connectors exper~ence some abrasion
and have to withstand twistjng of the links about their
lon5itudinal axis when the links come into contact with the
ground surface. If the chain is at least part~ally embedded
in the tread of a tyre e.g. see U.S. patent 3 722 566
Dohmeier then the connectors may have hardness in the
l~ower range. In has been found that the links perform
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e~ce11~ntly if th,e~ hd~e har~nesses in the rclnge 53
to 58 Ro~k~!ell ~-scale as a result o~ wor'c-h~rdening.
Analysis of chains ;~hich have per~orm~d successfully have
shown tha~ the links have a rela~ively flat hardness
'profile or gradient, i.e. change in hardness from the
core to the surface, while the connectors have a large
profile or gradierlt. For this reason it has bken found
to be effective to specify the surface har~ness of the l~nks
and the core hardness of the connectors, the latter
because it is the total and not merely the surface
hardness of the conn~ctor h~hich determines its successful-
ness.
.
The follol~ling table gives analysis of five successful chains.
The term RC refers to Rock~ell C-scale and the term VPN
refers to the corresponding Vickers hardness test result
WEhRING LINK CONNECTOR
- surf~ce core sur'face core
494VPN 49RC494VPN 49RC 41~VPN 49RC 306VPN 34RC
516VPN 502C494VPN 49RC 509VPN 46RC 268VPN 25RC
, 540VPN 50RC516VPN 48RC 429VPN 47RC 280VPN 26RC
473VPN 50RC473VPN 50RC 353VPN 49RC 313VPN 31RC
516VPN 52RC494VPN 52RC 391VPN 50RC 321VPN 28RC
103~1~9
The ~icrostructure of all the samples ~las similar and
consisted oF fine ~artensite in the case of the ~;earing links,
and in the case of the connectors tempered martensite,
pearlite a~d ferrite.
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