Abstract:
An injection molding apparatus for manufacturing dental floss holders has at least one strand of dental floss from a supply spool extended through the space between mating mold pieces and thereafter to a take-up device. From each injection stage of the molding cycle a rack of connected dental floss holders is produced. Tension of the floss is maintained from the upstream supply spool by a first tensioning device through the mold to the downstream end by the take-up device. During each injection cycle the take-up device engages another rack of molded parts and moves it to a downstream position where it is severed from the strand of floss while it maintains the tension in the floss upstream of the severed rack. This is achieved by the take-up device engaging at least two successive racks downstream of the mold and using the rack closest to the mold to maintain tension.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention is in the field of apparatus and methods for manufacturing dental floss holders with high volume injection molding machines which draw one or more continuous strands of dental floss from a supply to and through the mold so that the floss is molded in situ into the dental floss holders which are ejected while still attached to the floss extending both upstream and downstream of the mold. Typically, a multi-cavity mold is used with each strand of floss in the mold spanning a plurality of cavities. This invention further concerns improved efficiency in processing the molded flossers, securing the floss therein and packaging same. 
     2. Relevant Prior Art 
     
       
         
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Patent No. 
                 Inventor 
                 Date 
               
               
                   
                   
               
             
             
               
                   
                 4,006,750 
                 I. S. Chodorow 
                 02/08/77 
               
               
                   
                 4,016,892 
                 I. S. Chodorow 
                 02/08/77 
               
               
                   
                 D 244,376 
                 I. S. Chodorow 
                 05/ /77 
               
               
                   
                 D 250,214 
                 I. S. Chodorow 
                 11/07/78 
               
               
                   
                 5,086,792 
                 I. S. Chodorow 
                 02/11/92 
               
               
                   
                   
               
             
          
         
       
     
     3. Background 
     Disposable dental floss holders, also called “flossers”, have become popular alternatives to using traditional long strands of dental floss wrapped about the user&#39;s fingers. These flossers are now produced in great numbers; however, because each of these devices is quite small and is discarded usually after one or a few uses, it can command only a small sale price. Consequently, a manufacturer must produce huge volumes in the millions in order to be economically profitable. Under these circumstances improved efficiency of manufacture is a most significant aspect for economic viability. 
     In this high volume manufacture there are many problems including properly positioning the floss in the mold, securing the floss in the holders, minimizing breakage of the continuous strand(s) of floss extending from the floss supply to the point of severing molded flossers from the supply floss, selecting suitable plastic for the handle for the floss with regard to molding temperatures, strength and fraying, and post-molding operations of breaking the holders from the central runner, separating the flossers from each other, securing the floss ends in the handles and finally packaging the holders with efficient mass production techniques. 
     The present invention concerns a number of problem areas in the manufacturing and packaging process. The first is minimizing breakage of the floss supply lines during molding while maintaining proper predetermined tension in the floss so that the floss in each finished flosser will be relatively straight and taut. 
     In known high volume injection molding machines for producing dental floss holders, an objective is to maintain the floss in tension while it is drawn into the mold, during molding, and subsequently as quickly as possible to move the ejected aggregate of molded flossers (“shot”) out of the mold and to move the next segment of floss into the mold. Also, the shot transported downstream must be severed from the successively molded shots, all the while trying to maintain proper tension in the floss which traverses the mold. 
     In the above described procedure there are persistent serious problems. When the floss is not properly tensioned in the mold the resulting flossers may have sloppy slack floss, or worse, the floss may be positioned incorrectly in the mold and become damaged. If the floss breaks anywhere between the supply at the upstream end and the severing point at the downstream end, the entire machinery has to be stopped, cleaned up, and new floss fed through the stages and tension re-established. 
     Such “down time”, if frequent, obviously will greatly diminish efficiency and possibly render the entire process unprofitable. For injection cycles as fast as four to six per minute, for example, breakage of the floss or non-constant tension is recognized as a major problem. The present invention provides a novel apparatus and technique for overcoming this problem. 
     After the injection molded “shots” or racks of, for example, twenty flossers attached to a central runner are produced, the high efficiency mass production must be maintained during the stages of severing the flossers from the central plastic runner and from each other and securing the floss ends in the holder. The present invention provides new apparatus and techniques for improving this efficiency also. 
     SUMMARY OF THE NEW INVENTION 
     The new invention is an apparatus ancillary to an injection molding machine, operable with a supply of one or more a continuous strands of dental floss, a supply of injection-moldable plastic, and a multi-cavity mold having mating parts moveable between open and closed positions, with said dental floss extending from said supply between the faces of and through and out of said mold. The molding machine in operation produces a shot of a plurality of dental floss holders molded in situ onto said floss every injection cycle, where every two adjacent shots comprises a set with one of said set being the downstream shot and the other the upstream shot until the upstream shot becomes the downstream shot of the next adjacent shot. This molding machine apparatus further includes (a) first tension means constantly applying a force to said floss upstream of said mold and in the upstream direction, (b) take-off means downstream of said mold engaged to said floss and maintaining tension in the downstream direction by intermittently pulling said floss in said downstream direction, after each injection and ejection phase and holding said floss from moving without pulling in any direction during said injection and ejection stage, and (c) severing means for severing the downstream shot from the upstream shot of each of said sets received by said take-off means while said upstream shot remains engaged to said take-off means and maintains said tension in said floss downstream of said mold. 
     The second principal phase of this high speed—high volume production process invention concerns taking the molded shots as seen in FIG. 9, each shot containing a plurality of dental floss holders still joined to a central runner, feeder runner and gate and joined to each other via the continuous strand of floss, and proceeding with the steps of separating the individual flossers from the central runner and from each other, securing the floss ends to the holder simultaneously with severing the floss joining adjacent flossers, and finally packaging the flossers either individually or in groups. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic elevation view of the new invention. 
     FIG. 2 is a top plan view of FIG.  1 . 
     FIG. 3 is a perspective view of the apparatus of FIG.  1 . 
     FIG. 4 is a fragmentary schematic view of a mold and the strand of floss traversing the cavities therein. 
     FIG. 5 is a schematic view of the supply drum of floss and magnetic clutch combination. 
     FIG. 6 is a schematic view of a take-off wheel and floss severing element. 
     FIG. 7 is a schematic view showing the time and power coordinated elements, namely the floss supply tension, mold cycle, take-off wheel and burn phase. 
     FIG. 8 is a schematic circuit diagram showing the operation of this invention. 
     FIG. 9 is a fragmentary plan view showing a typical shot containing dental floss holders attached to a central runner. 
     FIG. 10 is a detail view of a multi-cavity mold. 
     FIG. 11 is a perspective schematic view of a break-off fixture. 
     FIG. 12 is a top plan view of the break-off fixture of FIG. 11 with a shot of flossers positioned thereon. 
     FIG. 13A is a front elevation view of the fixture of FIG. 11 with a transfer bar attached. 
     FIG. 13B is a side elevation view of FIG.  13 A. 
     FIG. 14A is a perspective view of a flame shield fixture. 
     FIG. 14B is a fragmentary top plan view of the break-off fixture of FIG. 12 coupled to the flame shield fixture of  14 A. 
     FIG. 14C is a fragmentary and enlarged view of FIG.  14 B. 
     FIG. 14D is a fragmentary and enlarged top plan view of a finished flosser. 
     FIG. 15A is an end elevation view of the break-off fixture and transfer bar of FIG.  13 B. 
     FIGS. 15B-15D are elevation views of the inversion of the structure of FIG.  15 A. 
     FIG. 16 is a side elevation view of an assembly fixture coupled to the transfer bar. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The injection molding machine and techniques of the new invention are illustrated in the drawings as described below. FIGS. 1-3 show schematically a basic injection molding machine as known in the prior art with a base  10 , ejector housing  12  and mating housing  14 , a two piece multi-cavity mold  15 ,  16 . Raw plastic for the injection cycle is fed through inlet  18 , the preferred plastic for the dental floss holders manufactured by this machine being polypropylene or polystyrene. The multi-cavity mold  15 ,  16  as seen in greater detail in FIG. 4 has cavities for the central runner  17   a , feeder runners  17   b , gates  17   c  and the principal flosser cavities  17   d.    
     A supply of floss  20  is fed from spool (or cylinder or drum)  21  that rotates about central spindle  22 . The wound floss  23  is a continuous strand of multifilamented ultra high molecular weight polyolefin, nylon or PTFE which reels off the drum  21  in a downstream direction indicated by arrow  25 . Support rollers  26   a ,  26   b  guide and support the floss until it is directed to and through the mold  15 ,  16 . 
     In the injection molding cycle, following injection and cooling, the mold opens and the shot or rack  27 A of twenty injection molded flossers is ejected while they are still attached to and essentially suspended by the floss  24 A above it (in the downstream direction) and floss  24   b  below it (in the upstream direction). More particularly the segment of floss  24   a  separates the shot  27 A being ejected from the shot  27  previously ejected and moved upward when fresh floss was moved into space  17  between mating parts  15 ,  16  of the open mold. Above shot  27  are prior ejected shots  28  and  29  now engaged and pulled by the take-off mechanism  30  which is followed by the severing stage  40  and the discharge chute  50 . 
     In the operation of this machine each time the molds  15 ,  16  opens and a shot is ejected, the take-off mechanism  40  pulls the floss and shots carried thereon one incremental distance corresponding to the length of one shot plus the length of floss between two adjacent shots. A brake mechanism  36  in or associated with the take-off drive  34  then stops and holds this new position where the floss and shots have been moved one unit of distance. A central timing control mechanism (not shown) then causes the mold to close, capturing a new segment or segments of floss to begin the next injection cycle. 
     A principal objective of this invention is to maintain a level of tension in the floss that extends through the open mold and upstream and downstream thereof 
     (a) so that the floss when molded in situ into the floss holders will be generally uniformly taut and properly aligned within the mold, and 
     (b) so that during the axial movement of the floss during the various phases of the molding cycle, excess tension will not develop causing breakage of the floss, and insufficient tension will not develop causing misalignment and/or tangling. Any of these problems causes an extremely costly shut-down of the entire apparatus until the interruption is cleared and restarted. 
     To achieve this constant but somewhat flexible level of tension in the floss, without stopping the process even while the most downstream shot is severed from the others for further processing, the new invention utilizes a new take-off structure in combination with magnetic clutch tensioning at the upstream supply end. 
     FIG. 5 shows schematically a known magnetic clutch  20  operable or incorporated with the cylindrical supply drum  21  carrying one or more continuous strands of floss  23 . Spindle  22  is rotated clockwise per arrow C, from a known drive ( 20 A seen in FIG.  3 ), and drum  21  is rotated counter clockwise per arrow B due to the pull on floss  24  in said downstream direction indicated by arrow  25 . 
     A magnetic field is established between the spindle  22  and the drum  21  whereby rotation of the spindle in the direction opposite of the drum rotation tends to restrain the drum rotation and thus apply a tension on floss  24  in the upstream direction. This magnetic field is easily adjustable by means not shown to establish a specific or range of tension level applied to said floss. In this particular embodiment two separate strands of floss  24 ,  24 A are unwinding from (reeling off) the supply drum  21  which is schematically representative of two separate spools or perns, since the mold of this embodiment is designed to receive two strands simultaneously. Typically the magnetic field will be set to apply a tension of about 10 pounds on the strands of floss. Because this force is applied by a magnetic field, it operates as a flexible force which is self-adjustable should the force on the floss become greater or smaller. 
     At the downstream end of the system are the take-off mechanism  30  and the severing station  40 . Successive shots  27 A,  27 ,  28  and  29  form a belt. As seen in FIGS. 1-3 shot  27 A will be ejected from the mold, shot  27  has just been ejected and moved downstream toward the take-off wheel  30 A, shot  28  has engaged side  28 S of the wheel, shot  29  has engaged side  29 S of the wheel and shot  31  is being severed from shot  29 . 
     The take-off wheel  30 A in FIGS. 1-3 and  6  has six equal surfaces about its outer periphery, thus defining hexagonal sides. The wheel is rotatable about a central axis  33  and is operated by a drive and control means  34 ,  36  which rotates the wheel in intermittent incremental steps of 60° each (⅙ of a revolution) and thus stops the wheel for the time period of the next injection cycle during which time the floss is captured in the mold and does not move axially. With each opening of the mold and ejection of the shot, the wheel  30 A moves another 60° pulling the belt of shots one additional step downstream (and onto the wheel). 
     Should an unusually high tension develop in the upstream direction, the drive-brake-clutch arrangement  34 ,  36  for the wheel will release at about one hundred pounds to avoid breakage of the floss. Then the problem causing the excessive tension can be rectified and the system returned to normal operation. 
     Each of said six peripheral edge surfaces of wheel  30 A has a shot-engagement means  41  formed as fingers projecting generally radially outward and adapted to hook beneath the bottom flossers in each shot as the shot comes to overlie said edge surface. By this engagement these fingers serve to apply a pulling force on the belt of shots extending upstream of the shot just engaged. 
     Further rotation of another 60° positions shot  29  at the top of the wheel while the next shot downstream becomes engaged by the next set of fingers of the next surface of the wheel. This engagement of each shot corresponding to  28  onto side  28 A of the wheel is adequate to maintain the tension in the floss upstream of this engagement, such that the earlier engaged shot may be severed without affecting the tension maintained by shot  28  or its equivalent. 
     Consequently, at any time after the wheel  30 A engages a new shot, the previously engaged shot could be severed. For this, the wheel could have six, or four or three or even two sides or engagement surfaces; however, the quantity of six forming a hexagon was chosen because of numerous practical benefits. With six sides, one side first receiving a shot can be easily aligned with the belt of shots emerging from the mold to readily receive same without changing its orientation. The shot essentially falls onto the wheel surface  28 A and engagement by the fingers  41  is automatic. The next two 60° moves of the wheel reorient the shot to be severed into a suitable position to be dropped onto chute  50  which may be inclined to a receiving container  50 B or may contain a conveyor belt  61  for transporting the severed shots to the next station. Two more 60° rotational movements of the wheel brings the now-exposed or empty side surface back into position to pick-up the next shot on the belt of shots. 
     The severing stage can be done in many ways including without limitation cutting and burning. In this embodiment a heat element  42  that burns the floss is positioned closely adjacent and upstream of said fingers  41  positioned just below the lowest of the flossers of the shot. At the appropriate time, namely, for example, when a set of adjacent downstream and upstream shots,  31 ,  29 , respectively, are at the top of the wheel, and a further upstream shot is securely engaged to said wheel surface, the heat element is energized, thus severing shot  31  from shot  29 , 
     (a) without interrupting the maintenance of tension by the upstream shot  28 , and 
     (b) without altering or disturbing the structure or arrangement of flossers of the severed shot  31 . The severed shot  31  then falls downward to the chute  50  or conveyor  50 A where it is directed to the next stage. 
     The entire system has a central electronic control not shown to assure that the take-off wheel rotates each 60° step only after the mold is opened and the shot ejected, thus freeing the belt of shots and the entire proceeding (upstream) floss to move axially, subject only to the restraining force of the magnetic tensioning at the supply end and other normal frictional forces. Obviously, the timing control with drive/brake  34 ,  36  also stops the rotation after the 60° movement and holds this position until the injection, cooling and ejection phase is again completed. In this embodiment the cycle time is about 12 seconds between ejections. With a 20 cavity mold and a machine operating continuously, the production rate can be up to 144,000 per 24-hour day or 50.4 million per 50-week year. Such quantities cannot even be approached if the injection molding apparatus is continually stopped due to broken or tangled strands of floss. The present invention is highly effective in minimizing such problems. 
     The second principal phase of this high speed—high volume production process invention concerns taking the molded shots as seen in FIG. 9, each shot  55  containing a plurality of dental floss holders  56  still joined to a central runner  57 , feeder runner  58  and gate  59  and joined to each other via the continuous strand of floss  65 , and proceeding with the steps of separating the individual flossers from the central runner and from each other, securing the floss ends to the holder simultaneously with severing the floss joining adjacent flossers, and finally packaging the flossers either individually or in groups. 
     FIG. 11 shows a break-off fixture  60  having a base  61  and a plurality of ten posts  62  tapered slightly from the bottom up and terminating in an axial aperture  63 . As seen in FIG. 12 these posts are spaced apart a distance D the same as said flossers  64  are spaced in the shot of FIG. 9, and the base diameter width W of each post corresponds to the space between the pair of arms of each flosser. The base depth d of each post is essentially the same as the distance in each flosser from the floss to the yoke or arch joining the two arms. 
     After the shot is engaged on the fixture, the central runner  57 , feeder runners  58  and gates  59  are broken off manually from the alignment of floss holders, with the remaining sub-assembly of holders joined only by the common strand of floss  65 . This sub-assembly is positioned to overlie fixture  71  with the posts  62  protruding through the spaces between the pairs of arms respectively of the ten flossers. The floss  65  runs through the arms of adjacent flossers and extends as floss segments  66  (See FIG. 14 c ) between each two adjacent flossers. A multitude of shots is similarly stacked on the fixture. 
     Next, as seen in FIGS. 11A,  14 A and  14 B, a transfer bar  67  with downward pins  68  is positioned essentially upside down with pins  68  loosely inserted into the apertures  63 . Each transfer bar  67  has pins exactly corresponding to the ten posts  62  of the break-off fixture  60 . The transfer bar sits in this position while the next burning phase occurs, however, the transfer bar could as well be utilized later, and its purpose will be explained later. 
     Next, as seen in FIGS. 14 a ,  14   b  the break-off fixture  60  loaded with flossers is placed onto a flame shield fixture  69  having a base  70 , end guides  71 A to receive and exactly position ends  71  of the break-off fixture so that the floss segments  66  will be directly adjacent the rectangular apertures  73  between each two adjacent vertical shields  74  as seen in FIGS. 14A-C. 
     As seen in FIG. 14 c , a blue flame  75  of propane gas is directed from top to bottom or bottom to top through each of said apertures  73  of approximately {fraction (3/16)} inches in width to burn floss segments  66 , thereby separating each all adjacent flossers. The flame melts the floss and cause the exposed ends of each multi-filament strand of ultra high molecular weight polyethylene floss to coalesce as seen in FIG. 14D into beads  76 , each typically having a diameter greater than the original filament diameter. Consequently, the exposed end of the floss external of the arm of the flosser is greater in diameter than the original strand and thus greater in diameter than the aperture in the flosser arm through which the floss extends, and thus cannot be pulled through this aperture. Thus, the floss ends are secured from being pulled through the arms and out of the finished flosser  77 , unless such excessive force is applied to break the floss or the floss holder. 
     The flame shields are made of steel or any flame resistant material that can tolerate this flame temperature for the few seconds or less it takes to burn the floss by directing the flame through the aperture. Obviously, the shields protect the plastic of the floss holder from being damaged or destroyed. 
     From this burning phase the flossers are severed from each other but still positioned closely adjacent to each other as they are still each straddling a post  63  of the break-off fixture coupled to the flame shield fixture. The next step is to separate the break-off fixture from the flame shield fixture and then to invert the break-off base  71 , (with the transfer bar  67 ) (see FIGS. 13A,  13 B) still loosely attached. The inversion is shown in FIGS. 15A-15D whereby the finished flossers each slide from a post  62  of the break-off base  71  onto a stem  68  of the transfer bar  67 . 
     Now the slim and light-weight transfer bar and its stems hold the stacks of finished flossers which can be easily transported (and maintained in alignment) to a wall-mounted packaging fixture  78 , as seen in FIG. 16, where brackets  79  receive the transfer bar  67 . From this position and orientation the stems  67  extend generally horizontally and from them groups of flossers can be readily removed for subsequent packaging. 
     By using these break-off, flame shield and packaging fixtures the high-speed, high-volume process can be maintained. The flame shield fixture in particular allows three operations-in-one, namely, severing floss while protecting the holders from the flame and heat, fixing and securing the floss ends from pulling out of the holder, and setting-up the flossers for transfer. 
     Within the scope and spirit of this invention as defined by the claims, many variations are possible. The floss supply and magnetic tension mechanism may have alterations or substitutes; a great variety of injection molding machines may benefit from and use this invention; the take-off mechanism and the severing station, whether separate or combined may take many forms, in fact the take-off mechanism may even be a non-rotary device where successive shots are engaged, held and released within the concept of this invention.