Abstract:
Link chain with improved wear resistance as well as method of manufacturing such a link chain. For manufacturing of a link chain, several chain links ( 39; 40 ) comprising link pins ( 41 ) or plates provided with coatings being applied by means of a PVD process are assembled. The coatings consist of hard material layers and/or slide material layers. It is possible that no PVD coating is provided on a transition zone ( 1   a   ; 4 ) of elements ( 41; 42 ) used for the manufacturing of the chain links predetermined for connection with another element ( 42; 41 ).

Description:
PRIORITY  
       [0001]     This application claims priority from German Patent Application No. DE 10 2005 011 705.8, which was filed on Mar. 11, 2005, and is incorporated herein by reference in its entirety.  
       TECHNICAL FIELD  
       [0002]     The invention concerns a link chain in which chain links are connected to each other via pins.  
       BACKGROUND  
       [0003]     Link chains are disclosed in DE 198 36 374 C1, in DE 100 33 726 C1 and in DE 1 752 557 A1. In addition, DE 203 04 437 U1 shows a link chain where the inside of an aperture is provided with a coating in order to receive a stud bolt.  
         [0004]     U.S. Pat. No. 6,666,013 B2 discloses a chain where at least a portion of the chain, for example a surface, is coated with DLC (diamond-like carbon) with preferably metal particles being formed in the DLC hard material layer. The disadvantage of such a coating is that the DLC layer has to be applied by means of a CVD process where the amorphous carbon for the DLC layer is deposited from a chemical gaseous phase out of hydrocarbon ions reacting with fixed carbon. In this process, however, hydrogen is formed, so that it cannot be excluded that the hydrogen released by the hydrocarbon ions in the CVD process may cause a hydrogen embrittlement in the chain material. Moreover, such a CVD process requires a compact and expensive process and plant engineering and has therefore, not proven itself successful in practice for the finishing of chain links.  
       SUMMARY  
       [0005]     It is the aim of the invention to further improve durability of the known link chains and reduce their noise development and to use a coating process and/or coating sequence for it which protect the elements of a link chain against hydrogen embrittlement.  
         [0006]     This is solved by the subject matter of the independent claims. Advantageous further developments result from the dependent claims.  
         [0007]     According to the invention, an element of a link chain, especially a pin, a sleeve, a plate or a roller and in the area of its surface includes a coating of at least a hard material layer with at least a material from the group AlN, AlON, CrN, CrCN, CrC, WC, WCN, TiN, TiBN, TiCN, TiC, TiAlN, ZrN, VC, cubic boron nitride or boron carbide suitable to be used in a PVD process. Thickness D of the PVD coating from a hard material layer is preferably 1 μm≦D≦10 μm with the hard material layer having one or several layers. Moreover, it may have variable stoichiometry.  
         [0008]     Such a coating presents the advantage that the risk of a hydrogen embrittlement is excluded, since the non-coated element neither comes into contact with water as in electroplating or laminating nor with hydrogen ions as in the CVD process. Moreover, a hard material coating with such a material has the advantage of high affinity to CrNi steel thus reducing the risk of chip off or abrading of the coating from the coated element of a link chain which fact is connected to high service life. Finally, with a thickness D of 1 μm≦D≦10 μm excellent fit and tolerances as well as high wear resistance for the coated surfaces of the elements are produced.  
         [0009]     In a preferred embodiment of the invention, further hard material layers in combination with a fundamental coating, preferably out of CrN, can be placed onto the element. This includes in particular nitride, carbide and/or carbonitride hard material layers. A CrN coating has an excellent affinity to the basis material of the elements of a link chain and can be used cost-effectively in a PVD coating process.  
         [0010]     The term PVD process (abbreviation for physical vapour deposition) designates all methods of physical deposition of thin layers via the vapour phase).  
         [0011]     In this process, the basic material for the layers is converted into the vapour phase in high-vacuum via the physical actions of vaporization (with arc, with ion beam or electron beam) or cathode sputtering and subsequently precipitated again on a suitable substrate. The layer thicknesses produced vary between 1 μm and 15 μm maximum.  
         [0012]     The wear protection layers on the elements of a link chain under discussion here can be deposited with all three of the above mentioned PVD processes on computer-controlled coating plants.  
         [0013]     In a typical embodiment of the invention, these are nitride hard material layers, i.e. compounds from the transition metals titanium or chromium with nitrogen. But also non-nitride hard material layers such as for example tungsten carbide are possible as additional hard material layers. Extended properties are furnished by hard material layers containing aluminum and carbon in addition.  
         [0014]     In another embodiment of the invention, a slide material layer is placed. As slide material layers, for example Sn, Pb, In, their alloys or MoS, WS, polytetrafluor ethylene are provided. For this purpose, initially the hard material layer is deposited on the element of the link chain by means of the PVD process and subsequently the slide material layer is placed onto the hard material layer. This presents the advantage that the material of the link chain element is protected by a “dry” PVD coating process such that subsequently even by eventual slide material layers applied by electroplating, hydrogen embrittlement is excluded since the element surfaces are protected by the hard material layer being applied by a “dry” process.  
         [0015]     A hard material and slide material layer combination represents the advantage that the hard material layer directly on the surface of the element concerned provides long service lives for the link chain with the softer slide material layer being provided for good sliding properties. Such elements provide good internal frictional properties of the link chain, especially during running-up times such as in motor testing after motor assembly, when motor oil lubrication has not yet been build up. In this connection a layer thickness preferably in the range of 0.2 μm≦d≦20 μm is already sufficient. This PVD coating of a thickness of only a few μm or even less with a slide material layer of a soft metal such as Sn, Pb, In or a polymer such as for example polytetrafluor ethylene (PTFE) or lubricating varnish can provide this effect. When the soft slide material layer with good sliding properties is worn off, the motor oil assumes this task with the underlying hard material layer guaranteeing a good service life of the link chain.  
         [0016]     According to the invention, the pin may be formed as a solid pin and/or link pin, as a sleeve, as a hollow pin or as a bushing. Likewise the plate can be formed as an external plate, as an internal plate, as a guide plate, as a link plate or as a transport plate.  
         [0017]     The invention has also been realized in a link chain having elements such as plates, pins, sleeves or rollers with at least one PVD coated element being provided.  
         [0018]     Also chains may be contemplated such as those disclosed in DE 203 04 437 U1 with the internal chain link having no hollow pin and/or sleeve. It is provided by a single widened internal plate. In such a chain, preferably the link pin and the outside of the internal plate receive a hard material layer by means of a PVD process.  
         [0019]     The invention includes link chains with such chain links as well as pairs of such link chains and one or more chain wheels on which the link chain is running.  
         [0020]     For contact with a link chain, a chain wheel according to the invention in the area of sprockets comprises at least a coating with a material suitable for use in a PVD process.  
         [0021]     The invention proceeds from the findings that wear resistance of state of the art link chains can be improved particularly well, if on the pin outside of a chain link, which normally connects two or more plates with each other, a uniform thin layer of a hard material is applied which can be deposited by means of a PVD process (Plasma Vapour Deposition).  
         [0022]     Suitable materials are here apart from the CrN basic coating, hard material layers such as, for example, TiN, TiCN, TiAlN. As slide material layers preferably soft metals or their alloys, such as for example Sn, Pb or In or MoS and WS, or polymers such as polytetrafluor ethylene (PTFE), or PTFE derivatives are applied on top of these hard material layers.  
         [0023]     For running-in of a link chain, the PVD coating with a material such as polytetrafluor ethylene (PTFE) has proven successful, which has excellent sliding properties but only a short service life. The invention is not limited to the materials mentioned above.  
         [0024]     Layers produced with the PVD process are particularly remarkable due to the fact that their surface roughness does not considerably deteriorate that of the coated surface. Especially CrN layers can easily be smoothed by finishing with mechanical methods.  
         [0025]     Among the materials mentioned above, CrN has turned out to be favorable for use with link chains because it is durable, easily to be applied and induces a long link chain service life which is attributed to little layer thickness variations after application.  
         [0026]     According to the invention, also the entire element of a link chain or its outer element easily accessible by a PVD process can be provided with the wear protection layer and/or the inventive coating.  
         [0027]     Advantageously, the PVD layer is provided within a transition zone between pin and plate. This is particularly beneficial to chain links where the pins are received and retained in the plates by means of a press fit. This is attributed to the fact that manufacturing tolerances in the event of thin material layers applied according to the invention can be kept so small in a simple and economical way that the preloads caused by the joining of plate and pin are far smaller than is the case, for example when chromising chain link elements. Chromising of metals, for example, is described in U.S. Pat. No. 4,670,172.  
         [0028]     Contrary to chain elements chromised wet-chemically by means of dipping or spraying methods in accordance with the state of the art, professionally manufactured and finished PVD coated chain elements are characterized by a surface roughness which is lower by approximately a factor  10 .  
         [0029]     On the contrary, for a known chromised link pin, the diameter may vary in the joining area by up to 20 μm. If on the other side the plate aperture for accommodation of the link pin is now at the lower limit of the manufacturing tolerance, a very thick link pin is joined with a very narrow plate aperture resulting in great preloads. In the event of additional load on the link chain produced with it, precisely the weakest link, namely the plate, is loaded in addition in the joining location which may lead to tearing in this preloaded location.  
         [0030]     As a side effect a very precise chain pitch results which is just by such an amount more precise that individual elongations are considerably reduced when the link chain is unwound on a chain drive. Already very little improvement with respect to an admissible variation of the chain pitch will result in a distinct improvement of wear resistance.  
         [0031]     When the thin PVD coating is provided on the remaining surface of the pin joining the two plates and especially on its functional surfaces, the service life of the link chain according to the invention is even further improved. This is attributed to the fact that the surface of such pins particularly in the area of such functional surfaces frequently comes into contact with other areas of the chain drive. If during such a contact, wear is reduced, as is the case by the inventive provision of a hard material layer or a combination out of a slide material layer and a very hard surface, the uniform chain pitch is maintained over an especially long operational life of the link chain delaying its failure even further beyond the operational life of the chain.  
         [0032]     According to the invention, the hard surface coating can in that case be provided on the external surface of a hollow pin which is also designated as a sleeve or bushing according to the state of the art. Such hollow pins are used for connection of the internal plates of an internal chain link. A sleeve and/or hollow pin can be wound, sintered or extruded and subsequently be shot blasted as an option. When a combination of slide material layer and hard material layer is provided on the outer surface of such a hollow pin, such a combined layer in the area of the press fit results in a reliable joining of the hollow pin with the plate aperture of the internal plate. Rollers are often still located on such hollow pins adapted to rotate on the hollow pin by forming a slide bearing surface. Such rollers are used especially when a roller chain is supposed to run on a gearwheel which reduces wear even further. In that case the roller may be provided on its inside with an inventive layer out of a hard material which is then sliding on the outside of the pin and/or hollow pin with combined layer attributed to it. This results in an improvement of the friction pairing between roller and hollow pin on which the roller is rotating which contributes to improvement of the link chain service life. But the roller may also be coated on its outside with a combination of a slide layer and a hard material which would then be gentle on or save the teeth of a driving means engaging into the chain.  
         [0033]     The sleeve may be coated not only on its external surface but also on the internal surface, if a hollow pin and/or sleeve is provided. Such hollow pins and/or sleeves are provided for the manufacture of internal chain links for the internal links of a plate link chain. This is particularly advantageous, if these internal chain links with solid pin and external plates are assembled into link chains. In that case the solid pin slides inside the hollow pin and with provision of an inventive thin hard material layer a small tolerance of the fit can be provided between hollow pin and/or sleeve and solid pin. Due to the particularly hard formation of the contiguous surfaces moreover very little wear occurs thus increasing the link chain service life.  
         [0034]     Coating of the hollow pin and/or sleeve inside represents a technological challenge. With an elongated hole diameter of the hollow pin varying between 2 and 5 mm and a length of several centimetres, not always a uniform coating results. Due to the difficulties connected to the coating of the hollow pin inside by means of a PVD process, it is therefore preferred with the hollow pin/solid pin pair to coat the solid pin outside according to the invention.  
         [0035]     Advantageously, the inventive coating is performed selectively in certain locations of the chain elements. Contrary to other processes such as, for example, chromising, the PVD process, especially for chain elements, offers the possibility of excluding certain areas from coating, if desired.  
         [0036]     Thus, it may be advantageous not to provide an additional coating in a transition zone between pin and plate. The manufacturing tolerances after manufacture of the pins are maintained there despite coating of the remaining surface areas of the pins which modifies surface roughness and diameter. Detrimental preloads in the area of the plate aperture are thus avoided.  
         [0037]     Masking of the pins can be made such that after manufacture they are pressed into one dead hole each with their ends which is provided, for example, in a flexible, heat resistant material. It is also possible to put a magnetic plate on the object, for example, if the face of a pin or a sleeve is supposed to be masked. Subsequently the pins are PVD coated, removed and integrated into the link chain manufacturing process. Handling may be made by a robot or an automatic pick-and-place machine.  
         [0038]     Apart from the steps specified above, coating of the inverted tooth type chain may be provided as well.  
         [0039]     According to the invention, one or several plates of a link chain may also be provided with a thin coating out of hard material on their external surface. This is particularly advantageous, when the plate is formed such that it comes into contact with other components. Thus, for example, inverted tooth type chains may be contemplated, the teeth of which are provided with the uniformly thin hard material layers according to the invention which improves service life of the teeth considerably. For coating of the plates, these are threaded through their eyes and onto two rods so that they sit tight to each other. The package of plates thus created is then coated on its still visible outer surface by means of the PVD process with a hard material layer comprising CrN. Subsequently the plates are removed from the rods and integrated into the link chain manufacturing process. Handling may be made by a robot or an automatic pick-and-place machine.  
         [0040]     It may also be advantageous to carry out plate coating such that the holes for receiving the link chain pins are provided with a thin hard material layer in the area forming the pairing or the articulation with the pin.  
         [0041]     The invention has already been realized in a chain link which serves to manufacture a chain. Likewise the invention comprises a chain with such improved chain links as well as a pairing of a chain and driving means such as for example a chain wheel.  
         [0042]     It is the objective of the novel chain pairing to improve wear resistance without degrading service life, cost or other marginal conditions. The chain pairing according to the invention is used in the following link-articulated chains such as for example sleeve type chains, inverted tooth type chains and leaf chains.  
         [0043]     Instead of a chain pairing with thermochemically heat treated pins and sleeves in the form of surface carbonitrided sleeves and chromised pins, elements are used having a hard material layer and/or slide material layer combination deposited by means of a PVD process. Thus problems are reduced which have resulted from constantly increasing requirements on the chain in the motor. Service life, which is limited by wear in the chain link, is increased.  
         [0044]     The present invention proposes a chain pairing of the type described permitting permanent use in the motor despite increasing requirements and which can simultaneously be manufactured in a continuous process.  
         [0045]     The invention employs a novel heat treatment combination of the pin and the plates. An alloyed or unalloyed steel is used as a basic material which should have a surface hardness varying between 650 and 960 HV 5 and simultaneously have a core hardness between 350 and 650 HV 5.  
         [0046]     Dependent on the steel grade used, these requirements can be fulfilled by hardening and tempering, surface nitriding or carbonitriding. A so-called white layer may be formed in the process without impairing the effect of the invention.  
         [0047]     The increased wear resistance within the chain pairing is for example achieved by a subsequent CrN coating of the pin or the sleeve. The CrN coating is carried out in a PVD process in a temperature range varying between 200 and 450° C. within 3 to 8 hours.  
         [0048]     Layer thickness can be varied as a function of the two parameters of time and temperature. For an optimum wear protection layer for link-articulated chains, a layer thickness of 1 μm to approx. 5 μm is aimed at, if necessary, also slightly above this value. In case of a layer thickness far beyond this value, it often happens that the hard material layer deposited by means of the PVD process chips off. With layer thicknesses below 1 μm the desired effect is generally not achieved.  
         [0049]     If the required surface hardness of the steel is achieved by surface nitriding or carbonitriding, nitriding without white layer is advantageous. A white layer up to approx. 2 μm, however, can be tolerated.  
         [0050]     Chain wear can be improved by up to 90% compared with State of the Art.  
         [0051]     Apart from a clear wear reduction, the possibility of continuous production of the elements, for example of the chain pins, has to be emphasized. Contrary to current production with a plurality of individual process steps, the pins can be produced continuously in the new chain pairing. Studies show that the pairing specified above of novel pin and existing sleeve exhibit optimum wear properties in the motor.  
         [0052]     The invention provides a parts pairing in link-articulated chains, which due to the employment of hard material layers deposited by means of a PVD process, exhibits a minimum of wear in the motor, since the hard material layers produced by this process minimize the coefficient of friction. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0053]     The invention is illustrated more in detail in the figures below by means of an exemplary embodiment.  
         [0054]      FIG. 1  shows a perspective and partly sectional view of a link chain according to the invention;  
         [0055]      FIG. 2  shows a side view of an inverted tooth-type chain link according to the invention; and  
         [0056]      FIG. 3  shows a link pin according to the invention during PVC coating. 
     
    
     DETAILED DESCRIPTION  
       [0057]      FIG. 1  is a perspective and partly sectional view of a link chain according to the invention.  
         [0058]     The link chain  1  is divided into a number of internal chain links  39  which are connected to each other via a number of external chain links  49 . Each internal chain link  39  has two internal plates  32  which are connected to each other via one sleeve  33  each, which is also called bushing or articulated sleeve. Sometimes, but not very often, the sleeve  33  is also called hollow pin. For connection, each internal plate  32  has two internal plate holes  3  into which the sleeve  33  is inserted with its edge portions by forming a press fit. The internal plate holes  3  are also called internal plate eye. On the outside of the sleeves  33 , one roller  40  each is located, adapted to rotate on the sleeve  33 .  
         [0059]     In an alternative embodiment (not shown), no rollers  40  are located on the outside of the sleeves  33 . In that case the sleeve  33  is sometimes called running sleeve, because it is running directly on the chain wheel.  
         [0060]     The internal plates  32  are arranged mainly parallel to each other.  
         [0061]     Two external plates  42  each and two link pins  41  each, arranged in external plate holes  4 , connect two adjacent internal chain links  39 . The external plate holes  4  are also called external plate eye. The link pin  41  is also called solid pin, rivet, chain rivet, stud bolt or hinge pin. Two external plates  42  each, with link pins  41  accommodated in the external plates, form an external chain link  40  each. The internal chain links  39  are also called internal plate chain links and the external chain links  40  are also called external plate chain links.  
         [0062]     One link pin  41  each is located in one external plate hole  4  each by defining a press fit. The link pins  41  illustrated in  FIG. 1  exhibit an entire hard material layer out of CrN with a layer thickness of approx. 2.5μ which has been deposited by means of a PVD process.  
         [0063]     For assembly of the link chain  1  reference is made to DE 198 36 374 C1, DE 1 752 557 A1 and DE 100 33 726 C1. The invention may be realized with any assembly method.  
         [0064]     During manufacture of the individual elements of the link chain  1  from  FIG. 1  and during its assembly, care is taken that the internal pitch Pi, which results from the centre distance of symmetry axes of adjacent link pins  41  in an internal chain link  39 , is as uniform as possible over the entire chain length. Likewise care is taken that the external pitch Pa, which results from the centre distance of symmetry axes of adjacent link pins  41  in an external chain link  40 , is as uniform as possible over the entire chain length. To that extent reference is made to DE 203 05 741 01, which among others describes the correlation between internal pitch Pi, external pitch Pa and noise development.  
         [0065]      FIG. 2  is a side view of a chain link  39 ′ which in major parts corresponds to the internal chain link  39  from  FIG. 1 . Same parts have the same reference numerals, equivalent parts are identified by a prime attached to the reference numeral.  
         [0066]     The internal plates  32 ′ are provided here with sprocket portions  35  projecting towards the bottom which engage into a gearwheel (not shown). The internal chain link  39 ′, instead of the internal chain link  39 , is assembled into a link chain together with the external chain links  40  from  FIG. 1 . A plate provided with a sprocket portion  35  is also called sprocket plate.  
         [0067]     In another embodiment (not shown), the external plates  42  from  FIG. 1  are provided with sprocket portions which correspond to the sprocket portions  35  of the internal chain link  39 ′ from  FIG. 2 .  
         [0068]     For application, manufacture and assembly reference is made to DE 203 04 437 U1.  
         [0069]      FIG. 3  illustrates how a coating is applied selectively in certain locations.  
         [0070]     In a subsequent transition zone La between link pin  41  and external plate  42 , no hard material coating is provided as an option. The manufacturing tolerances after production of the link pins  41  are maintained there despite a coating of the remaining surface areas li of the link pins  41  altering surface roughness and diameter. Detrimental preloads in the area of the plate hole  4  are thus avoided.  
         [0071]     For masking of the link pins  41 , after manufacture they are pressed into one dead hole  51  each with their ends which is provided in a masking holder  50  manufactured out of a flexible, heat resistant material such as for example PTFE. Subsequently the pins are coated by means of a PVD process in a PVD chamber (not shown) with a hard material layer out of CrN, removed and integrated into the link chain  1  production process. Layer thickness is controlled in this process via adjustment of coating time and coating temperature.  
         [0072]     If a magnetic plate attachment (not shown) is provided for masking, masking of faces and transition zones is simplified. It is also possible to mask only one pin end and turn it after coating.  
         [0073]     In this process, the basic material for the hard coating out of CrN is converted into the vapour phase in high-vacuum via the physical actions of vaporization (with arc, with ion beam or electron beam) or cathode sputtering and subsequently precipitated again on the unmasked link pins  41 . The layer thickness produced on the unmasked link pins  41  in this process vary between 1 μm and approx. 5 μm.  
         [0074]     Handling is done by a robot (not shown) or by an automatic pick-and-place machine.  
       LIST OF REFERENCE NUMERALS  
       [0000]    
       
           1  link chain  
           3  internal plate hole  
           4  external plate hole  
           32  internal plate  
           33  sleeve  
           35  sprocket portion  
           39  internal chain link  
           40  roller and/or external chain link  
           41  link pin  
           42  external plate  
           50  masking holder  
           51  dead hole