Abstract:
The invention relates to a device for receiving and transporting molded parts in order to especially permit the removal of plastic molded parts produced in injection molding machines from the cavities, and to permit the transport of the molded parts through a number of work stations, without the use of separate handling systems. According to the invention, circulating transfer frames are provided from which retaining elements project and reach into the cavity to closely abut the mold. The molded part is bonded to the retaining element during injection molding of the molded part and is thus fixed in the transfer frame for transport to additional work stations. The molded part is removed from the retaining elements at the end of the transport line. In a modification, the molded part is molded directly or via intermediate pieces onto a circulating rope or a chain conveyor, or on rods mounted on a rope.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a device for receiving and transporting molded parts made in cavities, in particular plastic molded parts, through a production line (processing line) with several work stations. Preferred field of application of the invention is the production of high-quality, flat plastic parts, in particular the production of plastic panes. 
     It is known from the prior art to use a so-called index plate for producing molded parts with several components in a work station of a machine for processing plastic material, whereby the index plate is used to transfer the molded parts between the individual cycles within this work station. The index plate is configured as transfer frame and includes retaining elements on which the molded part is initially formed on and transferred therewith. Removal of the molded parts is realized by moving the retaining elements away from the molded part which is then withdrawn by a separate handling system or falls out of the work station. In a two-cycle machine, the index plate turns from the first cycle to the second cycle by 180°, at several cycles with respectively shorter turns. In any event, the index plate with its retaining elements remains in this work station. 
     The invention is now based on the object to provide a device by which molded parts, in particular plastic molded parts, made in cavities, can be removed from the cavities and transported through several work stations. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the invention, the molded parts can travel through a production line with several work stations, without requiring contact with the molded part itself. This is especially of importance when manufacturing high-quality plastic panes because any adverse effect in quality or damage to the surface can be eliminated, when avoiding a contact therewith. In accordance with the invention, it is hereby proposed to use a transfer frame which travels through the production line and includes retaining elements on which the molded part in the cavity is formed. The transfer frame is then removed together with the molded part from the respective work station and can be further transported along the processing line. Hereby, it is necessary to provide the molds in the area of the retaining elements with recesses in correspondence to the contour of the retaining elements, so that the latter closely abut in a form-fitting manner the mating surfaces of the mold halves, when the mold is closed. Care should be taken that the retaining elements so project into the space between the mating surfaces as to realize a bond with the molded parts during production of the molded parts. 
     According to one embodiment of the invention, linear guides with respective guide rails may be provided for the transport of the transfer frame through the processing line. The transfer frames may be transported through the processing line on the guide rails in upright disposition or suspended disposition. As an alternative, the embodiments provide for gripper arms having grippers for moving the transfer frames. 
     The manufacture of flat plastic parts by means of an injection compression process with dipping peripheral dies requires measures to detach the molded parts from the fixed or the moving mold half. Accordingly, the linear guide in the area of the mold halves includes segments which are movable orthogonal to the partition plane of the mold halves. The segments may be configured, for example, as a compound table. For implementing a smoothest possible run of the transfer frame on the linear guide, the linear guide is implemented as ball-type linear guide. 
     The use of the invention for the preferred field of application requires the provision of retaining elements which can be attached to the edge of the pane and easily separated therefrom again. The retaining elements may have particularly configured pointed ends for engagement into the edge of the pane. In order to be movable away from the panes, the retaining elements are slidingly supported in the transfer frame and can be displaced therein by suitable means. 
     According to another aspect of the invention, transfer frames and retaining elements can be completely eliminated. Rather, a linear transport system, for example a transport rope, is used for receiving as well as transporting the molded parts. The transport rope thus assumes a dual function and replaces the transfer frame and the retaining elements. In this case, the transport system engages directly into the cavities, and the molds are provided in the area of the linear transport systems with recesses in correspondence to the cross section of the linear transport systems, so that the latter effect a form-fitting seal with the mating surfaces of the mold halves, when the mold is closed. According to a particularly advantageous embodiment, a rope is used which is embraced by the molded part, when being formed thereon, only to such an extent that its cross section is not completely embraced. The molded part can then easily be pushed off the rope. The use in the injection compression process, i.e. when using dipping peripheral dies, it is advantageous to provide one or more stroke elements by which the linear transport systems can be moved orthogonal to the transport direction in order to detach the molded parts from the fixed or the moving mold half. 
     The present invention is suitable for single component injection as well as, in particular, for multi-component injection of plastic molded parts. The invention is usable in horizontal as well as vertical injection molding machines or injection compression machines. Especially suitable is the invention for the production of also large-area, flat plastic parts with extreme, optical surface properties. Moreover, the invention permits the use of a small mold opening space which can be kept more easily under clean air conditions. Therefore, it is possible to easily operate at clean air conditions. Furthermore, the invention provides for a high degree of freedom with respect to the constructive configuration of the plastic parts because random components can be attached by injection onto the main plastic part, either completely or partially and one-sided or two-sided, or fully one-sided (overlay). Moreover, the device according to the invention permits the use of short cycles. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     Exemplified embodiments of the invention will now be described in more detail with reference to FIGS. 1 to  10   b,  in which: 
     FIG. 1 shows a cross section (left) and a side view (right) of a second embodiment of the invention in the area of a work station with bottom guide rail and upright transfer frame; 
     FIG. 2 shows a cross section (left) and a side view (right) of a first embodiment of the invention in the area of a work station with overhead guide rail and suspended transfer frame; 
     FIG. 3 is a plan view of a work station with open (left) and closed (right) mold; 
     FIG. 4 shows a work station for simultaneous manufacture of two panes with two components with two overhead guide rails and suspended transfer frame; 
     FIG. 5 is a detailed illustration (in cross section) of a suspended or upright transfer frame; 
     FIGS. 6 a  to  6   h  show various embodiments of the retaining element; 
     FIG. 7 shows a transfer frame with integrated piston and cylinder unit for the retaining element; 
     FIG. 8 shows a further embodiment of the invention with a transport rope for receiving and transporting the molded parts; 
     FIGS. 9 a  to  9   b  show details of the bond of a plastic pane upon the transport rope; 
     FIGS. 10 a  and  10   b  show a side view (FIG. 10 a ) and a cross sectional view (FIG. 10 b ) of an attachment of the pane to the transport rope by means of a transport hook. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The following exemplified embodiments relate to the production of plastic panes, as used, for example, as side window panes for passenger cars. The invention is, however, not limited thereto, but is generally applicable for the production and processing of molded parts made in cavities. 
     FIG. 1 shows a plastic processing machine with a moving and a fixed mold clamping platen which are guided along four rods  4  arranged on a machine frame  3 . Mold halves  5  and  6  are disposed on the mold clamping platens  1 ,  2  and form a cavity, when closed for introduction of plasticized plastic material and compressing to a pane  7 . Provided in the mold halves are recesses for snug fit engagement of the retaining elements  8  so as to effect a form-fitting seal with the mating surfaces of the mold halves, when the mold is closed. The retaining elements  8  are mounted in a transfer frame  9  which remains outside the mold contour, when the mold halves are closed. Upon its manufacture, the pane is formed on the retaining elements  8  and can subsequently be withdrawn with the transfer frame  9  from the work station for transport to further work stations. The movement of the transfer frame is implemented via a guide rail  10  having a T-shaped recess for engagement of the T-shaped foot piece  11  of the transfer frame  9 . In order to manufacture a pane  1 , an empty transfer frame  9  is initially readied in an entry station  12  with its retaining elements  8 , and—after the preceding transfer frame has left the work station—pushed onto the segment  13  which can be moved orthogonal to the transport direction on a rail  14 . The segment  13  with the transfer frame  9  travels to the moving mold clamping platen  1  and is accurately positioned there in place. This is important in particular when using dipping peripheral dies to insure a clean interlocking of core and female mold member. Subsequently, the moving mold clamping platen with the core and the cavity-engaging retaining elements  8  (thus also with the transfer frame  9 ) are moved in the direction of the fixed mold clamping platen  2 . As soon as the cavity is closed, plasticized plastic material can be introduced and a compression stroke can be executed. After conclusion of the injection compression process and sufficient solidifying of the pane  1 , the mold is opened and the guide rail segment  13  with the transfer frame  9 , on which the pane  7  is now attached via the retaining elements  8 , are moved in alignment between the entry station  12  and the exit station  15 . The transfer frame  9  with the pane  7  can now leave this work station and be transferred to further work stations, for example, for spray-coating further components or for a surface treatment of the pane. Displacement of the transfer frame  9  may be implemented by hydraulic and/or pneumatic piston and cylinder units which push the empty transfer frame  9 , positioned at the entry station  12 , into the work station, and, at the same time, move the preceding transfer frame with the finished pane  7  out of this work station. Hereby, the transfer frames  9  are provided with foot pieces  11  of sufficient length, or with respectively long intermediate pieces. 
     In contrast to FIG. 1, the embodiment according to FIG. 2 shows suspended transfer frames  9  which are shifted along an overhead guide rail  10 . Therefore, the pane  7  is molded onto the retaining elements  8  and the transfer frame  9  in suspended state. In this case, the guide rail  10  has a T-shaped cross section  16 , and the transfer frame  9  includes a complementary T-shaped recess for engagement of the T-piece of the guide rail. The mode of operation and the movement of the transfer frames correspondents to the exemplified embodiment of FIG.  1 . 
     FIG. 3 shows a top view of the work station, with the movable segment  13  of the guide rail  10  positioned at the core, when the mold is opened (left illustration) and closed (right illustration). In the left illustration, the movable segment  13  is shifted from the entry station  12  and the exit station  15  in the direction of the moving mold clamping platen. When the mold is closed (right illustration), the segment  13  is in alignment with the entry station  12  and the exit station  15 . This, however, is not necessarily required, i.e. the entry station  12  and the exit station  13  may also be positioned differently as the segment  13  is randomly movable between the moving and the fixed mold clamping platens. 
     FIG. 4 shows a work station for the simultaneous production of two panes by means of a multi-component injection compression process. Two guide rails  10  are arranged above one another for the suspended transport of the transfer frames  9  with the panes  7  molded onto the retaining elements  8 , and extend across through the machine frame  3 . In order to realize a clean and parallel travel of the mold clamping platens toward one another, four synchronizing devices  17  are provided which measure in their sphere the respective distance of the mold clamping platens from one another and readjust accordingly in response to the measuring result transmitted by an evaluating unit. For movement of the transfer frame  9  between the mold clamping platens, the segments  13  of the guide rail  10  are supported for movement orthogonal to the transport direction. Like in the exemplified embodiments according to FIGS. 1 to  3 , the transfer frames  9  are also in this case in ready position at the entry station  12  when empty and shifted into the space between the mold halves, when the mold is open. After completing the pane, an empty transfer frame  9  is pushed ahead, the transfer frame  9 , charged with the pane  7 , is forced out of the work station to leave the first work station at the exit station  15 . Through a further cycle pulse (pushing ahead of empty transfer frames  9 ), the charged transfer frames  9  are pushed further along the guide rails  10  and reach at a later time a next work station. 
     FIG. 5 shows a cross section of a suspended transfer frame  9  which depends from a guide rail  10  with a T-shaped guide element  16 . In this case, the transfer frame  9  includes a complementary T-shaped recess. The guide rail  10  is configured in the area of the mold clamping platens as carrier plate for the transfer frame and is connected to a piston and cylinder unit  18 , so that a stroke in the direction of the arrow  19  can be executed, so that the pane  7  can be detached from the moving mold clamping platen  1  or the core  5 . Subsequently, the transfer frame  9  returns with the pane  7  on the movable segment  13 , not shown here, to the starting position and is ejected by pushing ahead an empty transfer frame  9  from the work station. For better understanding, the retaining elements  8  have not been shown here. They may be positioned, for example, outside of the plane of projection. FIG. 5 represents essentially a detailed view of the right illustration of FIG.  2 . 
     FIG. 6 a  shows a cross section of a first embodiment of the bond of the pane  7  to the retaining elements  8 . A pointed end  20  is hereby provided which includes an elongate cross section (FIG. 6 b ) or a cylindrical cross section (FIG. 6 c ). FIGS. 6 b  and  6   c  shows sectional views, taken along the line A—A in FIG. 6 a.    
     FIGS. 6 d  to  6   f  illustrate a second embodiment of the retaining elements  8  which include a pointed end  20  with a U-shaped recess which is penetrated by the plasticized plastic material, so that the finished pane  7  is embraced by the pointed end  20  of the retaining element  8 . To prevent a lateral slipping of the pane, a centering groove  21  or a centering ridge  22  may be provided in the U shaped recess of the pointed end  20  (FIGS. 6 e  and  6   f ). 
     FIGS. 6 g  and  6   h  show a further embodiment of the retaining element  8  in which a pin  23  is embedded in the end of the retaining element  8  and embraced by the pane  7 . FIG. 6 g  further shows that the mold halves  5  and  6  are provided in the area of the retaining element  8  with recesses and closely bear upon one another when being closed, so that plastic material is prevented from escaping the cavity. 
     According to FIG. 7, the retaining element  8  includes a head piece  24  which assumes the function of a piston and is accommodated in a cylinder  25 , thereby forming a piston and cylinder unit  24 ,  25  by which the retaining element  8  is movable in the transfer frame and detachable from the pane  7 , for example, to withdraw the finished part  7  from the transfer frame  9  at the end of the production line. 
     An alternative embodiment of the device according to the invention is illustrated in FIG.  8  and includes a transport rope  26  which is guided over two deflection pulleys  27  and  28 , with one of the deflection pulleys including a drive. The lower part of the transport rope  26  is guided through the mold which is thereby provided with recesses of a cross section corresponding to the cross section of the transport rope  26 . When the mold halves are closed, the transport rope  26  extends within the cavity and effects a form-fitting seal with the mating surfaces of the mold halves. When injecting the plasticized plastic material at closed cavity and compressing the pane, the pane  1  becomes attached via the sprue  29 , comprised of a cylindrical manifold  30  and a film gate  31 . After molding the pane  7  onto the transport rope  26 , the mold halves open, and the pane  1  can be detached from one of both mold halves. The transport rope travels then with the attached molded part to the two-cycle injection process in the first work station. Subsequently, the transport rope  26  is moved further by an increment in order to position again an empty segment of the transport rope in the first cavity. By simply circulating the transport rope  26 , the panes  7  can be fed to further work stations and finally removed at a withdrawal station  33 . For example, a hard silicate layer can be applied in a coating machine on the pane  7 . Curing of the pane  1  with the silicate coat is realized in a following drying station  35 . 
     FIG. 9 a  shows, on an enlarged scale, a pane  7  molded onto the transport rope  26 , so that the sprue  29 , comprised of manifold  30  and a film gate  31 , is clearly recognizable. FIG. 9 b  shows a cross section, taken along the line B—B. As can be seen from the Figure, the sprue element  36 , projecting out from the sprue  29 , embraces the transport rope  26  by slightly more than a half, so that a secure seat of the sprue element  36  and thus a good fit of the pane  7  is ensured, on the one hand. On the other hand, this configuration realizes that the entire molded part can easily be pushed away downwards and detached from the transport rope  26  at the withdrawal station  33 . 
     FIGS. 10 a  and  10   b  show a variation of the device according to the invention with transport rope. Provisions are made here for transport hooks  37  which embrace the transport rope  26  from above and on which the sprue is attached. The transport rope  26  with the transport hook  37  are guided over rolling elements  38 . The number of transport hooks  37  or sprue elements  36  depends on the weight of the pane  7  after the last work station.