Abstract:
A device for producing a thin-walled elongate body from thermoplastic material includes a removable sleeve ( 25 ) and a bush ( 33 ), the casing of the removable sleeve ( 25 ) and the bore ( 31 ) in the bush ( 33 ) are arranged eccentrically with respect to the axis of symmetry of the core and, by rotation relative to one another, a displacement of the core can be achieved both in terms of magnitude and also in relation to a deflection angle.

Description:
BACKGROUND 
     The field of the invention is a device for producing a thin-walled elongate body, such as a pipette or a tip. 
     When producing thin-walled elongate bodies, such as particularly pipettes or tips, the problem arises that no rotary symmetrical parts are produced due to off-setting and tolerances in the tool. This means that during automatic pipetting the outlet opening for the liquid to be pipetted is not located at the predetermined position. Such unsymmetric pipettes may lead to problems and/or they represent rejects. 
     SUMMARY 
     An objective of the present invention comprises to provide a device, which allows the production of thin-walled elongate bodies, with their wall thicknesses being constant, i.e. after the production their tip is located on the geometric axis of symmetry of the body. Another objective of the invention comprises to embody the device such that deviations determined can be corrected in a simple fashion directly at the injection molding tool. 
     This objective is attained in a device according to the invention. Advantageous embodiments of the device are described below. 
     This is achieved by the eccentric embodiment of the eccentric bush and the removable sleeve engaging each other such that the position of the core can be aligned by a simple rotary motion of one of the two elements. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Based on an illustrated exemplary embodiment the invention is explained in greater detail. It shows: 
         FIG. 1  is a perspective view of a thin-walled elongate body based on a pipette, 
         FIG. 2  is a cross-sectional view through an injection tool for a pipette, 
         FIG. 3  is a perspective view of the core of the tool, 
         FIG. 4  is a perspective view of a removable sleeve, 
         FIG. 5   a  is a perspective view of a bush, 
         FIG. 5   b  is a view of a bush seen from a different angle, 
         FIG. 6  is a detail of the first mold halves—ejection side, and 
         FIG. 7  is a perspective view of a fastening plate. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In  FIG. 1 , a pipette is marked with the reference character  1  as an example for a thin-walled elongate body. It is embodied conically tapering at the right side, i.e. as a hollow, acute-angled frustum  3 . The front end shows a diameter of 0.75 mm, for example, and an outlet opening  5  of 0.45 mm. In other words the wall thickness (thickness of the wall) amounts to only 0.15 mm. At the left side, a flange  7  is discernible at the frustum  3 , which is intended to connect the pipette  1  to and/or with a pipetting device. Instead of a conically extending pipette  1 , of course a body with a cylindrical sleeve can also be used. 
       FIG. 2  shows at the left side details of a first mold half (ejection side) of the injection mold  9 , mold half  9  for short, and on the right side the second mold half (nozzle side) of the injection mold  11 , mold half  11  for short. The second mold half  11  includes a matrix  13 , which forms the exterior contour of the pipette  1 , i.e. of the work piece. 
     The first mold half  9  (left) carries the core  15 , which forms the interior contour of the pipette  1  and comprises several parts. The molding part, i.e. the core  15 , is shown in  FIG. 3  in an enlarged fashion. At the top it comprises a tip  45  and subsequently an acute frustum  17 , which forms the interior space of the acutely tapering area of the pipette  1 . Here, a cylindrical or conical section  19  follows, which forms the rear section of the pipette  1 . The section  21  located at the bottom in  FIG. 3  ends in a flange  23 , by which the core  15  is fastened at the first mold half  9  of the tool  9 . The core  15  is surrounded by a removable sleeve  25 . 
     The removable sleeve  25  comprises an axially symmetrical bore  27 , with its diameter exhibiting a diameter in the rear part which is greater than the exterior diameter of the core  15 . In the front part, the bore  27  extends conically and essentially contacts the core  15  at the rear at the conical section  18 . The core  15  is consequently connected on the one side by the flange  23  at the section  21  with the mold half  9  and at its conical section at the rear  18  via the removable sleeve  25  without any play. The casing  29  of the removable sleeve  25  is not embodied axially symmetrical but exhibits eccentricity, which for example may amount to 0.08 mm. The eccentricity comprises the cylindrical section of the removable sleeve  25  as well as the conically progressing section. 
     At the front of the removable sleeve  25  an eccentric bush is provided, called bush  33  for short, with its bore  31  being embodied congruent in reference to the casing  29  of the removable sleeve  25 . The bore  31  of the bush  33  is also embodied eccentric in reference to the casing surface  35  of the bush  33 , i.e. the casing surface  35  is located symmetrically in reference to the axis of symmetry of the bush  3 ; the bore  31  is eccentrically in reference to the axis of symmetry A. 
     The bush  33  is supported in an axial fashion with its rear end  39 , embodied as a flange, on a circumferential flange-like web  37  of the removable sleeve  25 . The cylindrical base  30  of the removable sleeve  25  can be inserted into the first mold half  9  in a cylindrical receiving bore  32 . The removable sleeve  25  and the bush  33  are engaged on each other and protected from rotation in reference to each other by a fastening plate  41 , on which the mold half  9  rests. The fastening plate  41  is held by at least one screw  43 . 
     By the eccentric embodiment of the casing  29  on the removable sleeve  25  and the eccentric embodiment of the bore  31  in the bush  33 , by a mutual rotation of the removable sleeve  25  and the bush  33 , the position of the core  15  can be determined in a radial displacement, radially displaced by a predetermined range and simultaneously here the angular displacement. In other words, the conical area at the rear  18  of the core  15  is displaced from the axis of symmetry A by the removable sleeve  25  and the bush  33 . 
     Markings  49  are provided on the surface  47  of the flange-like web  37  at the removable sleeve  25 , e.g., in the form of bumps or grooves. These markings  49  may be provided with numbers in order to allow identification. As an alternative to the bumps, bores may also be provided as markers, penetrating partially or entirely. Further, on the periphery of the circumferential web  37  at “0” a marking  51  is inserted or applied. Another marking  52  is applied at the widest position of the facial area. A marking  53  is also inserted or applied at the bush  33  ( FIG. 5 ) on the top of the flange-like rear end  39 . Between the key areas  57  of the bush  33  another marking  50  is applied. It is arranged with the marking  53  at the bush  33  in an alignment. Another marking  54  is applied at the widest point of the facial end. Further, at the bottom a pin  55  is inserted, intended and suitable to engage and/or latch in the markings  49  at the removable sleeve  25  in order to determine the adjusted angular rotary position between the removable sleeve  25  and the bush  33 . Further, an option is provided at the bush  33  to attach an open-end wrench. For this purpose, at the perimeter key flanges  57  are provided similar to a hex nut. 
       FIGS. 6 and 7  show perspective illustrations of the fastening plate  41  ( FIG. 7 ) as well as the mold plate (ejection side)  59 . Receiving bores  61  are formed in the mold plate  49 , into which the removable sleeves  25  can be inserted axially. Scales from +180° to −180° are respectively engraved at the edges  63  of the accepting bores  61 . These scales  65  serve to position the removable sleeve  25  during the assembly and to fixate it in a new position upon correction thereof. 
     Holes  67  are in turn embodied on the fastening plate  41  ( FIG. 7 ) aligned to the receiving bores  61  of the molding plate  59  and also markings of +/−180° are applied on its periphery. 
     During the assembly of the core  15  in the mold halves  9  the removable sleeve  25  and the bush  33  are assembled in each other such that the core  15  is subjected to a displacement/deflection known from experience. However, if it is now detected that either the amount of the displacement of the injection molded parts, here the pipette  1 , deviates from the target value and/or its angular position from the target value, in an open injection mold (mold halves  9  and  11  spaced apart as in  FIG. 2 ) the screw  43  can be released and the fastening plate  41  can be disassembled and the mutual position of the removable sleeve  25  and the bush  33  as well as the angular position of the two elements  25 ,  33  can be adjusted in reference to the molding plate AS  59 . The adjustment can occur based on a table deducted from experiments. Such a readjustment of a core  15  can be performed within a few minutes and it is not required for the injection mold to be disassembled from the injection molding machine, here.