Abstract:
A circular knitting machine has a circular knitting unit fitted with needles and an expander arranged under the circular knitting unit for tubular knit formed by the circular knitting unit. The expander is rotatably mounted on a central rod arranged coaxially to a knitting machine axis. A pivoting bearing is arranged on the central rod to allow limited swivel movements of the expander relative to the central rod.

Description:
CROSS-REFERENCE TO A RELATED APPLICATION 
     The invention described and claimed hereinbelow is also described in German Priority Document DE 10 2013 105941.4, filed on Jun. 7, 2013. The German Priority Document, the subject matter of which is incorporated herein by reference, provides the basis for a claim of priority of invention under 35 U.S.C. 119(a)-(d). 
     BACKGROUND OF THE INVENTION 
     The invention relates to a circular knitting machine with a circular knitting unit fitted with needles and an expander arranged under the circular knitting unit for the tubular knit formed by the circular knitting unit. The expander is rotatably mounted on a central rod arranged coaxially to a knitting machine central axis. 
     With the expander the tubular knit is formed into a double-layered web laid flat and is then withdrawn and wound up. In this process the knitted fabric exerts considerable forces on the expander. These forces are transferred to the central rod, which can thus result in fatigue fractures of the central rod. Moreover, the forces also can result in folding and ringing of the knitted fabric during winding, which makes further processing difficult. 
     To remedy this problem document DE 12 28 021 has proposed to suspend the expander on the machine on chains. However, this type of suspension of the expander can lead to a relatively substantial lateral displacement of the expander as a result of the forces exerted by the tubular knit. The lateral displacement makes it difficult to uniformly withdraw and wind up the web. 
     DE 24 43 067 describes an expander with articulated straps, which are connected to a rigid expander frame by a damper unit. The damper units absorb part of the forces exerted by the tubular knit. This solution, however, is structurally complicated. The damper units suffer fatigue over time and must be regularly replaced. 
     DE 31 12 181 also discloses expanders with different adjustment possibilities of individual expander parts relative to one another to enable forces exerted by the knitted fabric to be compensated. These solutions, however, also are very complicated structurally. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the shortcomings of known arts, such as those mentioned above. 
     To that end, the present invention provides a circular knitting machine with an expander, which absorbs forces generated by the tubular knit in a structurally simple manner. 
     In an embodiment, the invention provides a circular knitting machine with a circular knitting unit fitted with needles and an expander arranged under the circular knitting unit for the tubular knit (formed by the circular knitting unit). The expander is rotatably mounted on a central rod arranged coaxially to a knitting machine central axis. The expander has a pivoting bearing arranged on the central rod that allows limited swivel movements of the expander relative to the central rod. 
     As a result of the pivoting bearing, the expander can move out of the way of the forces exerted by the tubular knit by swivel movements relative to the central rod to relieve the load on the central rod. However, in contrast to the known chain suspension arrangements of expanders, lateral deflection of the expander does not occur and, therefore, the withdrawal and winding up of the web are not detrimentally affected. Ringing or folding in the web can likewise by avoided by the swiveling expander. 
     The pivoting bearing is preferably configured as a ball bearing, which allows a uniform movement of the expander in all spatial directions perpendicular to the direction of the longitudinal axis of the central rod. Alternatively, the pivoting bearing is configured as an elastic pivoting bearing. The elastic pivoting bearing is achieved by spring elements or other elastic coupling elements. These elastic bearing elements can absorb forces in the direction of the central rod. 
     In a first configuration, the expander is arranged rotatably on the central rod by the pivoting bearing, i.e., pivoting and rotating bearings for the expander are arranged in a unit in the region of the lower end of the central rod. 
     If, however, larger swivel radii of the expander are desired, then the central rod can be divided into an upper and a lower section and the pivoting bearing can be arranged between the upper and the lower section. The longer the lower section of the central rod is selected to be, the larger the possible swivel radius of the expander and thus the greater its ability to move out of the way of forces generated by the knitted fabric. 
     A coupling arrangement with the pivoting bearing can be arranged between the two central rod sections to connect the sections to one another. This coupling arrangement has a holding element and a fastening element, for example, which are connected to one another by spacer screws. In this case, the holding element is connected to one of the sections of the central rod, e.g., the upper section, and the fastening element is connected to the other section. The pivoting bearing is arranged on the fastening element in this case. Moreover, the spacing between the two central rod sections can be adjusted by the spacer screws. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features and advantages of the invention will become apparent from the description of embodiments that follows, with reference to the attached figures, wherein: 
         FIG. 1  presents a perspective view of an expander with divided central rod, configured according to the invention; 
         FIG. 2  presents an enlarged detail view of the connection region of the central rod sections of the expander of  FIG. 1 ; 
         FIG. 3  presents an exploded drawing of a pivoting bearing on the central rod of the expander of  FIG. 1 ; 
         FIG. 4  presents a perspective view of a second connection region of the central rod sections of an expander; and 
         FIG. 5  presents a perspective view of a third connection region of the central rod sections of an expander. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following is a detailed description of example embodiments of the invention depicted in the accompanying drawings. The example embodiments are presented in such detail as to clearly communicate the invention and are designed to make such embodiments obvious to a person of ordinary skill in the art. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention, as defined by the appended claims. 
       FIG. 1  shows an expander  10  formed according to the invention with two trapezoidal straps  11 ,  12 , which are connected to one another at a base  16 . The trapezoidal straps are held at an angle α relative to one another by means of struts  13 ,  14 , as shown. The length of the base  16  is adjustable and thus adaptable to a diameter of the tubular knit. 
     The base  16  is connected by a strap  17  and a rotating bearing  18  to a lower section  20 . 1  of a central rod  20 . The central rod  20  is fastened to a machine frame of the circular knitting machine. The central rod  20  is oriented coaxially to a central axis of the circular knitting machine in this case. 
     A coupling unit  21  and a pivoting bearing  22 , as shown in  FIGS. 2 and 3 , respectively, are arranged between the lower section  20 . 1  of the central rod  20  and an upper section  20 . 2  of the central rod  20 . As result of the pivoting bearing  22 , the expander  10  can pivot in relation to the central rod  20  and thus move out of the way of forces that are exerted on it by the tubular knit (not shown) generated by the circular knitting machine. These forces are thus not transferred to the central rod  20 . The central rod  20  is thus subject to a significant relief of load as a result of the pivoting bearing  22 . Moreover, the flat double-layered web generated from the tubular knit by the expander  10  can be withdrawn and wound up free from tension as a result of the limited pivoting ability of the expander  10 . 
     Coupling unit  21  is shown in  FIG. 2  with a holding element  23  that is connectable to the upper section  20 . 2  of the central rod  20  and, is connected to a ring-shaped fastening element  25  by spacer screws  24 . A pivoting bearing  22  and the lower section  20 . 1  of the central rod  20  are fastened to the underside of the fastening element  25 . 
     Pivoting bearing  22  ( FIG. 3 ) consists of a bearing shell  26 , which is screwed to the fastening element  25 , a ball  27  and a spacer ring  28 . The ball  27  is hollow so that the upper end of the lower central rod section  20 . 1  is passed through it. The length of the lower central rod section  20 . 1  determines the swivel radius of the expander  10 . 
       FIG. 4  shows a further embodiment of a pivoting bearing  122 , which is arranged between two central rod sections  20 . 1  and  20 . 2  of the expander and is configured as an elastic joint. The upper central rod section  20 . 2  is fastened to a holding element  123 , whereas the lower central rod section  20 . 1  is arranged on a fastening element  125 . The holding element  123  and the fastening element  125  are connected to one another by an elastic element  30 . The elastic element  30  forms the pivoting bearing  122  and can be made, for example, from rubber, polyurethane or another plastic. 
       FIG. 5  shows a further elastic pivoting bearing  222 , which is formed from four spring elements  31  arranged between a holding element  223 , on which the upper central rod section  20 . 2  is fastened, and a fastening element for the lower central rod section  20 . 1 . 
     Elastic element  30  and the spring elements  31  of the pivoting bearings  122  and  222  allow a limited swivel movement between the central rod sections  20 . 1  and  20 . 2  and thus, also of an expander  10  ( FIG. 1 ) that is fastened to the lower central rod section  20 . 1 . 
     As will be evident to persons skilled in the art, the foregoing detailed description and figures are presented as examples of the invention, and that variations are contemplated that do not depart from the fair scope of the teachings and descriptions set forth in this disclosure. The foregoing is not intended to limit what has been invented, except to the extent that the following claims so limit that.