Abstract:
A rolling body of a moving carriage cage for drawer guides has an internal core part and a separate casing part surrounding the core part. The core part is preferably composed of a first plastic, and the casing part is preferably composed of a second plastic. The plastics of the core part and of the casing part have different indentation hardnesses.

Description:
BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The invention concerns a rolling body of a carriage cage for drawer guides. The invention further concerns a carriage cage for a drawer guide having such rolling bodies as well as a drawer guide having a carriage cage and an article of furniture having a drawer guide. 
     (2) State of the Prior Art 
     Rolling bodies of that kind serve essentially for the transmission of kinetic energy between mostly metallic drawer rails. Those rolling bodies are supported rotatably in a carriage cage arranged between rails and in the closed condition of the drawer have to partially carry the static loading and upon movement guarantee that the drawer is pushed in and pulled out of the body of an article of furniture as easily and without problem as possible. 
     Rolling bodies in a carriage cage are to be found for example in WO 2008/046118 A2. A disadvantage with those one-piece rolling bodies for carriage cages is that they wear relatively quickly, they are flattened off under a static loading between metallic drawer rails and often have spalling phenomena which are due to the manufacturing process. 
     SUMMARY OF THE INVENTION 
     Therefore the object of the invention is to provide rolling bodies which are improved over the state of the art or an improved carriage cage. In particular the invention seeks to provide that the strength of the rolling bodies is increased, the flattening tendency is reduced, load support is improved and nonetheless there is a certain elasticity in the rolling body and a reduction in wear. 
     That is achieved for a rolling body and a carriage cage in that the rolling body has an inwardly disposed core portion and a separate casing portion surrounding the core portion. That two-part configuration of the rolling body according to the invention makes it possible to prevent the spalling phenomena which occur with the hitherto usual one-part manufacture as the individual components can now be more easily produced in a shrinkage-free and shrink hole-free fashion. In addition there is the possibility of the individual components, core portion and casing portion being designed to suit the specific factors involved in the carriage cage. 
     Accordingly, in a preferred embodiment of the invention, it is provided that the core portion and the casing portion comprise mutually different materials like plastic and steel. In that way the loading can be ideally transmitted by the materials of the rolling bodies without causing unnecessary wear. 
     Alternatively, it is also possible for the core portion and the casing portion to comprise the same but separately provided plastic. Preferably however it can be provided that the core portion and the casing portion comprise different types of plastic, depending on the respective loading and the magnitude of the flattening tendency. 
     Particularly preferable for that purpose, it can be provided that the plastics of the core portion and the casing portion have different ball indentation hardnesses. Those rolling body components which involve different ball indentation hardnesses provide for a substantial improvement in the properties of the carriage overall and implement a drawer guide which is more easily movable and suffers less wear in comparison with the state of the art. 
     In general in the case of rollers which are not of the general kind set forth herein (see AT 317 473, DE 41 08 884 A1, DE 41 04 271 A1, DE 26 02 979, DE 24 61 341 and DE 39 22 716 A1), there is admittedly a two-part structure, but these cannot be used in any way in carriage cages due to their size and their manner of mounting. In addition those large rollers which are known from the state of the art do not have a core portion which does not have any spindle and which is substantially in the form of a solid cylinder and for that reason also inter alia they cannot be used in carriage cages. In addition those rollers of a different general kind are always part of a drawer guide, as individual, highly loaded rollers, whereas the rolling bodies according to the invention are mostly arranged in conjunction with a plurality of rolling bodies in the carriage cage. Accordingly, changes in the nature thereof (two-part configuration) act in a quite different fashion on the running and extension characteristics of a drawer, as for example the flattening tendencies and load support are distributed to many rolling bodies in the composite assembly. 
     As according to a preferred embodiment of this invention the core portion is substantially in the form of a solid cylinder, it is possible to achieve a substantial improvement in quality insofar as in particular the core portion is produced in the form of a compact plastic portion without an opening or a hole having to be left free for a spindle pin—which is necessary in the state of the art of a different general kind. In the state of the art of the different general kind, the core portions are always in the form of hollow cylinders and not in the form of solid cylinders and for that reason in a preferred rolling body of this invention the core portion extends from the radially inwardly disposed surface of the casing portion (that is to say within the casing portion), to the notional axis of the rolling body. That compact nature of the core portion provides in particular for better stability of the overall rolling body as the compact core portion is exposed to fewer crushing and squashing effects or can better carry them than an annular core portion which has a stability-reducing axial opening. 
     In a preferred embodiment of this invention it can be provided that the core portion has a higher ball indentation hardness than the casing portion, wherein the first plastic has a ball indentation hardness above 125 N/mm 2 , preferably above 140 N/mm 2 , and the second plastic has a ball indentation hardness below 105 N/mm 2 , preferably below 90 N/mm 2 . With such a rolling body which is so-to-speak internally hard and externally soft, the casing can remain substantially non-reinforced, while in the case of the reinforced core the properties that are useful are that there is a reduction in wear, an increase in strength, and a reduction in creep of the plastic in the closed condition under a static loading. 
     In an alternative embodiment of the present invention it can be provided that the casing portion has a higher ball indentation hardness than the core portion, wherein the second plastic has a ball indentation hardness above 125 N/mm 2 , preferably above 140 N/mm 2 , and the first plastic has a ball indentation hardness below 105 N/mm 2 , preferably below 90 N/mm 2 . With such a rolling body having a reinforced casing portion and a relatively soft core (externally hard, internally soft), there are the positive properties of a substantial reduction in flattening, load support in respect of the casing and an increase in the elasticity of the rolling body. 
     For the different types of plastic it can preferably be provided that one of the plastics is polyoxymethylene (POM) with a ball indentation hardness of between 150 and 170 N/mm 2  and one of the plastics is a polyamide, preferably PA6, with a ball indentation hardness of between 65 and 80 N/mm 2 . Thus those two types of plastic can be used in the carriage cage at different locations depending on the respective purpose of use and kind of loading on the rolling body. 
     Additional differences which form important criteria for use of those plastics as rolling bodies are listed hereinafter: 
     
       
         
               
               
               
             
               
               
               
             
           
               
                   
                   
               
               
                   
                 POM 
                 PA6 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 E-modulus 
                 2800-3200 N/mm 2   
                 1400-3200 N/mm 2   
               
               
                 Density 
                 1.41-1.43 g/cm 3   
                 1.13-1.14 g/cm 3   
               
               
                 Elongation at break 
                 45-70% 
                 40-150% 
               
               
                 Breaking strain or yield stress 
                 70-80 N/mm 2   
                 45-65 N/mm 2   
               
               
                   
               
             
          
         
       
     
     The ball indentation hardness (also referred to as the ball impression hardness) substantially determines the visco-elastic deformation component of the plastics. If during hardness testing of the plastic an indentation body used in the testing process is relieved of load the elastic component of the deformation goes back instantly and the visco-elastic component then goes back gradually. Therefore the indentation body is loaded over a certain period of time during hardness measurement on plastics and then under load the total elastic and visco-elastic indentation depth is measured. A ball indentation test which can be used for determining those parameters should be based on DIN EN ISO 2039-1. 
     In a preferred embodiment of the invention it can be provided that the rolling body is produced in a two-component injection molding process. The spalling effects which have hitherto often occurred can be avoided by that manufacturing process as upon injection molding of the two components they remain substantially shrinkage-free and shrink hole-free, wherein those shrinkage phenomena otherwise subsequently cause those spalling effects. Due to the casing portion being shrunk on to the core portion an intimate join is also achieved between the two component parts of the rolling body. The possibility should not be ruled out that, for example, the core portion itself is produced in such a preferred two-component injection molding process. Alternatively, the possibility should also not be ruled out that the two plastic components are extruded and cut to length for a given rolling body width after the extrusion operation. As a further alternative the two components of the rolling body can also be assembled only upon fitment of the carriage cage in the drawer guide. 
     To achieve rotatability and guidance for the rolling bodies in the carriage cage by virtue of the rolling bodies not having any spindle member, it can preferably be provided that the rolling body has two ends, wherein raised guide portions or guide recesses are provided in the ends, and wherein the raised guide portions or guide recesses project away from the rolling body or extend into the rolling body in the direction of the axis, less than 20%, preferably less than 10%, of the width of the rolling body. 
     As the rolling bodies according to the invention generally also have to carry very high loads during the movement of the drawer, it is preferably provided that the width of the rolling body can be greater than the diameter thereof. In that case the ratio of the width of the rolling body to the diameter of the rolling body can be between 1.01 to 1 and 1.8 to 1, preferably between 1.05 to 1 and 1.35 to 1. Alternatively, the possibility should not be ruled out that the width of the rolling body is less than the diameter thereof. That can be appropriate in particular when two or more such rolling bodies are arranged in coaxially successive relationship in the carriage cage. 
     Preferred dimensions of a rolling body according to the invention have the diameter of the rolling body between 1 and 8 mm, preferably between 3.5 and 6.5 mm, and the thickness of the casing portion transversely to the axis of the rolling body between 0.1 and 2.5 mm, preferably between 0.2 and 0.5 mm. 
     A preferred embodiment of this invention can provide that a reinforcing layer of glass fiber is arranged in the rolling body. In addition, the possibility should not be ruled out that, in spite of the advantages already set forth for a core portion in the form of a solid cylinder, nonetheless a narrow spindle or shaft portion is provided in the rolling body. 
     In a preferred embodiment of a carriage cage according to the invention it can be provided that all rolling bodies rotatably supported in the carriage cage have a core portion comprising a first plastic and a casing portion comprising a second plastic, wherein the plastics of the core portion and the casing portion are of different ball indentation hardnesses. Depending on the respective location of use and load range, the individual rolling bodies may have mutually different plastics with different ball indentation hardnesses or different types of plastic. Generally the same preferred variants also apply to the carriage cage, as to the rolling body. 
     It can further preferably be provided that raised guide portions or guide recesses are provided at the ends in the rolling bodies and that the carriage cage has a housing with receiving spaces for the rolling bodies, wherein the housing has in the receiving spaces holding depressions or holding projections at which the rolling bodies are rotatably supported and held by way of the raised guide portions or guide recesses. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further details and advantages of the present invention are described more fully hereinafter by means of the specific description with reference to the embodiments and by way of examples illustrated in the drawings, in which: 
         FIG. 1  shows a longitudinal section through a roller according to the state of the art, 
         FIG. 2  shows a longitudinal section through a rolling body according to the invention, 
         FIG. 3  shows a longitudinal section through a rolling body with guide recess, 
         FIG. 4  shows a longitudinal section through a rolling body with raised guide portion, 
         FIG. 5  shows a perspective view of a rolling body, 
         FIG. 6  shows a cross-section through the rolling body, 
         FIG. 7  shows an exploded view of a carriage cage, 
         FIG. 8  shows a carriage cage with fitted rolling bodies, 
         FIG. 9  shows a carriage cage and  FIG. 9A  shows a section A-A of  FIG. 9 , 
         FIG. 10  shows a carriage cage and  FIG. 10A  shows a section B-B of  FIG. 10 , 
         FIG. 11  shows a rolling body and  FIG. 11A  shows a section C-C of  FIG. 11 , 
         FIG. 12  shows an exploded view of a drawer guide, 
         FIG. 13  shows an assembled drawer guide, and 
         FIG. 14  shows an article of furniture with drawers guided on drawer guides. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a relatively large roller  31  (of about 1.5 cm in diameter) in accordance with the state of the art, as can serve for example as a single guide roller for a drawer rail in a body rail. In that respect it is already known for a casing portion  35  and a core portion  34  to be made from different plastics. What is complicated and expensive in those rollers  31  according to the state of the art is inter alia that a spindle opening  33  always has to be provided for a spindle pin  32 , by way of which the roller is rollably mounted for example on the drawer rail. 
     In comparison,  FIG. 2  shows how an embodiment of a rolling body  1  according to the invention has a compact, spindle-less core portion  4  in the form of a solid cylinder which comprises a casing portion  5  which differs from the core portion  4  and which is of a different ball indentation hardness. The preferred two-component injection molding manner of manufacture of such a rolling body  1  (and/or only the core portion  4 ) affords a substantial increase in quality as there are no shrinkage holes or cavities (air inclusions). In that respect, for example, an inner core portion  4  of a diameter d of between about 1.5 and 4 mm can be injected in a first step. Then in a second step the inner core portion  4  has an outer core portion  4  of the same material injected therearound, to give an overall diameter of between about 3 and 7 mm. That provides for an increase in the service life and an increase in the strength of the two-component core portion  4  and/or the two-component rolling body  1 . The thickness of the core portion  4  in comparison with the casing portion  5  can vary considerably in comparison with the embodiment in  FIG. 2 . What is essential for functionality is that the width b of the rolling body  1 , measured in the direction of the axis x, is greater than the diameter d of the rolling body  1 . 
       FIGS. 3 and 4  show mutually alternative embodiments of a rolling body  1 , wherein on the one hand a guide recess  8  with a recess depth a can serve as part of a holding or guide device for the rolling body  1  on a carriage cage  2 , while on the other hand, in a correspondingly reversed configuration, a raised guide portion  7  of a raised height dimension a can be provided on the rolling body  1 . The line X shown in  FIGS. 3 and 4  designates the axis about which the rolling body  1  rotates, and an axle shaft unitary with the core portion  4  is made of the material of the core portion  4 . 
       FIG. 5  shows a perspective view of a rolling body  1 , wherein provided in the region of the core portion  4  is a guide recess  8  surrounded by a substantially circular raised guide portion  7 . That raised guide portion  7  has inclined flanks, which makes it easier for the rolling body  1  to be introduced into a receiving space  10  which is provided in a carriage cage  2  and which has a holding projection  12  (see e.g.  FIG. 7 ). 
       FIG. 6  shows a cross-section through a rolling body  1 , wherein the casing portion thickness c can preferably be between 0.1 and 0.7 mm. 
       FIG. 7  shows an exploded view of a carriage cage  2  which as essential parts has a housing  9  which preferably comprises plastic and is injection molded, and a plurality of rolling bodies  1 . Provided in the housing  9  at various locations are receiving spaces  10  for the rolling bodies  1 , wherein projecting into those receiving spaces  10  are holding projections  12  by way of which the rolling bodies  1  are held by way of the recesses  8 . In that respect those holding projections  12  substantially only serve to prevent the rolling bodies  1 , which are only loosely introduced into the receiving spaces  10 , from falling out upon assembly of the drawer guide. Carriage dampers  16  can be arranged at the ends of the carriage cage  2 . The rolling bodies  1  are arranged in the receiving spaces  10  in  FIG. 8 . 
       FIG. 9  shows a side view of a carriage cage  2  and  FIG. 9A  a section A-A, wherein it is possible to see how a plurality of rolling bodies  1  are held in the housing  9  of the carriage cage  2  by way of holding projections  12  or guide recesses  8 , respectively.  FIG. 10  shows a plan view of the carriage cage  2  and  FIG. 10A  a section B-B.  FIG. 11  shows a view on to the end  6  of a rolling body  1 , wherein  FIG. 11A  is a section C-C which shows the two-component nature (core portion  4  and casing portion  5 ) of the rolling body  1 . 
       FIG. 12  is an exploded view showing the essential component parts of the drawer guide  3  comprising a rail member  13  in the form of a body rail, a rail member  14  in the form of a central rail, a drawer rail  17  and a carriage cage  2  with rolling bodies  1  that is arranged between the body rail  13  and the central rail  14 . The drawer guide  3  can also have an ejection device  19 , a retraction device  18  and various further elements  20 . The component parts of  FIG. 12  are shown in the assembled condition in  FIG. 13 . 
     Finally,  FIG. 14  shows an article of furniture  15  comprising a plurality of drawers  21  which can be moved in and out in a furniture body  22  by way of drawer guides  3  according to the invention.