CA1039169A

CA1039169A - Tyre protective chains

Info

Publication number: CA1039169A
Application number: CA271,392A
Authority: CA
Inventors: Hans O. Dohmeier
Original assignee: Dome Inventions Pty Ltd
Current assignee: Dome Inventions Pty Ltd
Priority date: 1976-02-16
Filing date: 1977-02-09
Publication date: 1978-09-26
Also published as: SE7701408L; JPS5299503A; IT1114102B; DE2706621A1; ZA76913B

Abstract

A B S T R A C T

A tire chain comprising tread links and connectors interconnecting the tread links to form a network of closed figures, the tread links and connectors being.
of different carbon steels whereby after heat treating each is hardened throughout its thickness with the tread links having a surface hardness in the range 46 to 54 Rockwell and the connectors having a core hardness in the range 15 to 35 Rockwell.

Description

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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1039~i9 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.

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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.

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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.
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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 _ 8 --10391~9 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.
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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 10391f~9 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.

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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

, 540VPN 50RC516VPN 48RC 429VPN 47RC 280VPN 26RC

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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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1.
A tyre protective chain comprising an open network of tread links forming a pattern of closed figures and arranged to be perpendicular to the surface of a tyre and connectors interconnect-ing the tread links at the corners of the closed figures and arranged to be parallel to the surface of a tyre, the connectors being loops that are threaded through perforations in the tread links and that are welded closed after being engaged with the tread links, characterised in that the tread links and connectors are of different carbon steels which have been heat treated after assembly of the chain to be hardened throughout their thicknesses, in 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 a core hardness of 15 to 35 Rockwell C-scale.

2.
A chain as claimed in claim 1 in which the tread links have a surface hardness of 48 to 52 Rockwell C-scale and the connectors have a core hardness of 25 to 34 Rockwell C-scale.

3.
A chain as claimed in claim 1 in which the tread links have a carbon content of between 0,45 and 0,65 weight percent.

4.
A chain as claimed in claim 1 in which the tread links have a carbon content of between 0,50 and 0,60 weight percent, 5.
A chain as claimed in claim 1 in which the connectors have a carbon content of between 0,20 and 0,45 weight percent.

6.
A chain as claimed in claim 1 in which the connectors have a carbon content of between 0,35 and 0,45 weight percent.

7.
A chain as claimed in claim 1 in which the tread links have a manganese content of between 0,70 and 1,00 weight percent.

8.
A chain as claimed in claim 1 in which the connectors have a manganese content of between 0,70 and 1,00 weight percent.

9.
A chain as claimed in claim 1 in which the tread links have a work-hardening property and in which in service they develop a surface hardness in the range of 53 to 58 Rockwell C-scale.