Abstract:
A feeding device is provided for forwarding a pliable thermoplastic rod into a heated pressure chamber for extrusion through an outlet nozzle to effect thermoplastic welding. The device includes a block with a machined channel through the block including an arcuate inlet portion for receiving the pliable rod and a tubular outlet portion dimensioned to closely surround the rod to prevent buckling of the rod for ejecting the pliable rod under longitudinal force into the chamber. A rotatable drive disk has an outer serrated cylindrical surface engaging one side of the rod in the arcuate inlet portion so that the rod is pinched by a counteracting surface portion in the channel in opposition to the contacting portion of the disk whereby angular movement of the disk around the disk axis acts to forward the rod along its length along the channel. The disk sits in a slot cut in the block with the channel at the bottom of the slot with the same width as the slot.

Description:
This invention relates to an apparatus for forwarding a rod which is primarily but not exclusively designed for use in an arrangement for thermoplastic welding using high pressure injection. 
     BACKGROUND OF THE INVENTION 
     In U.S. Pat. No. 4,711,746 issued Dec. 8 th , 1987, the present inventor disclosed a device for forming a thermoplastic weld between two plastic parts in which a thermoplastic material is forced into a chamber and melted within the chamber so as to generate a molten plastic material under a pressure of at least 1000 psi and more preferably of the order of 2500 psi. The molten plastic is expelled through an orifice so that the molten plastic under pressure from the heating chamber is forced into the space between two plastic components to effect a weld therebetween. It will be appreciated that the pressure set forth above is orders of magnitude higher than the pressure necessary for a conventional simple glue gun in which a hot melt adhesive is expelled simply under low or zero pressure. 
     The thermoplastic welding system disclosed in the above patent has achieved considerable commercial success. However in order to successfully operate the device it is necessary to inject into the heating chamber a thin rod or wire of the thermoplastic material so that the pressure generated within the chamber is obtained by forcing the rod into the chamber with a longitudinal force which is sufficient to generate the required pressure. The thermoplastic material in rod form generally has a diameter of the order of one sixteenth to one quarter inch and more preferably of the order of one eighth inch. This relatively small diameter reduces the longitudinal force necessary on the rod to generate the required pressure but makes the rod more pliable and difficult to feed. 
     The original patent disclosed a technique for feeding the rod in which the rod passes between two feeding disks with the rod tangential to each of the disks and lying in a common plane with the disks. Each disk has a groove in its outer periphery so as to attempt to trap the cylindrical rod between the rollers. However in practice this arrangement was ineffective and was replaced by a reciprocating clamping arrangement which acted to feed or stuff the pliable rod into the tube leading to the chamber. This device using the reciprocating clamp arrangement has achieved commercial success, but the rod feed has remained a source of concern and potential problem in that it is relatively expensive, complex and prone to breakdown. 
     Attempts have been made to replace the reciprocating clamp of the commercial embodiment and one attempt is set forth in U.S. Pat. No. 5,971,212 of the present inventor which is issued Oct. 26 th , 1999. This device provides a friction block on one side of the rod which reciprocates back and forth so as to feed the rod forwardly along a channel. The use of the reciprocating drive arrangement however requires a component to prevent reverse movement of the rod when the reciprocating device reverses to commence a further feeding stroke. This device unfortunately has failed to overcome the above problems and has not been adopted. 
     SUMMARY OF THE INVENTION 
     It is one object of the present invention to provide an improved apparatus for driving a pliable rod longitudinally under sufficient force to generate significant pressure in the rod. 
     According to the present invention there is provided an apparatus for forwarding a pliable rod comprising: 
     a housing; 
     a channel through the housing including an inlet portion for receiving the pliable rod and an outlet portion for ejecting the pliable rod under longitudinal force; 
     at least the outlet portion forming a tubular closed surface surrounding the rod and dimensioned to closely surround the rod to prevent buckling of the rod when forwarded under longitudinal force into the outlet portion; 
     a drive disk rotatable about an axis of the disk for forwarding the rod from the inlet portion into the outlet portion, the disk having an outer cylindrical surface surrounding the axis for engaging one side of the rod; 
     the disk and the channel being arranged such that the channel lies in a radial plane of the axis of the disk; 
     the disk and the channel being arranged such that a contact portion of the outer cylindrical surface extends along and defines one side of the channel; 
     and a counteracting surface portion in the channel in opposition to the contacting portion of the disk arranged such that the rod in the channel is pinched between the contacting portion of the disk and the counteracting surface portion whereby angular movement of the disk around the disk axis acts to forward the rod along its length along the channel. 
     The term disk as used herein is not intended to imply any particular structure of the member except that it has an axis and a peripheral surface around which the surface rotates. Normally the disk will be relatively narrow so that its diameter is greater than its width and its width is relatively small to match that of the rod, but these dimensions are not essential to the invention. 
     Preferably the counteracting surface portion is formed by a stationary surface of the channel. However in alternative arrangements, the counteracting surface may be formed on another member inserted into the channel and even may be another similar opposing disk. 
     Preferably the counteracting surface portion of the channel is arcuate so as to lie on a circle surrounding the disk axis so that the rod is pinched by the surface of the disk and the arcuate surface portion as it is carried around the arcuate surface portion by movement of the disk. This ensures that the disk has contact over an extended arc preferably as much as 90 degrees to provide enough grip to ensure driving without slip. 
     Preferably the housing includes a slot therein for receiving at least a part of the disk, the slot having two parallel sides each lying closely adjacent a respective side of the disk such that the outer cylindrical surface of the disk projects into the slot, the channel being arranged at the slot adjacent the outer cylindrical surface of the disk. 
     Preferably the channel has a width substantially equal to the width of the slot so as to have sides contiguous with the sides of the slot. Thus the disk which closely matches the shape of the slot has a width matching that of the channel which is approximately equal to the width of the rod. 
     Preferably the disk has transverse, angularly spaced serrated edges thereon for engaging the rod and driving the rod. 
     Preferably the tubular closed surface forming the outlet portion commences at a position immediately adjacent the outer cylindrical surface of the disk such that the rod as it leaves the outer surface of the disk forwarded thereby immediately enters the tubular closed surface and is confined thereby to prevent buckling under the longitudinal forces on the rod. 
     Preferably the outlet portion is tangential to the outer surface of the disk. 
     Preferably the channel and the tubular portion are integrally and contiguously formed in an integral structure forming the housing. 
     Preferably the inlet portion of the channel has one side thereof defined by the outer surface of the disk. 
     Preferably the counteracting surface portion extends around an angle of the order of 90 degrees of the disk. 
     Preferably the outlet portion of the channel is connected to a chamber into which the rod is fed under the longitudinal force, the chamber having a heating element for effecting melting of the rod such that the melted rod in the chamber is under a pressure from the forwarding of the rod and wherein there is provided a discharge nozzle connected to the chamber for receiving the melted rod therefrom through which the melted rod is forced by the pressure for effecting a thermoplastic welding action. However the rod forwarding device disclosed herein can be used for other end uses and the thermoplastic welding technique disclosed herein is only one example. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings, which illustrate an exemplary embodiment of the present invention: 
     FIG. 1 is a vertical cross sectional view of the apparatus according to the present invention. 
     FIG. 2 is a top plan view of the drive block only of the apparatus of FIG.  1 . 
     FIG. 3 is a front elevational view of the drive block only of the apparatus of FIG.  1 . 
     FIG. 4 is a top plan view of the apparatus of FIG. 1 with the heating chamber and extrusion nozzle omitted. 
     FIG. 5 is a cross sectional view along the lines of  5 — 5  of FIG. 1 on an enlarged scale. 
    
    
     DETAILED DESCRIPTION 
     The apparatus comprises a device  10  for forwarding a pliable rod  11  of a thermoplastic material so that the rod can be forced into a chamber  12  where the longitudinal force on the rod generates a pressure within the chamber. The chamber is heated by a heating element  13  so that the thermoplastic material of the rod is melted within the chamber so as to form a mass of the thermoplastic material under the pressure generated by the longitudinal force on the rod. The chamber is connected to an outlet nozzle  14  to which the molten thermoplastic material from the chamber is ejected under the pressure within the chamber so as to effect thermoplastic welding as described in the above patents. The chamber, the heating element and the nozzle are shown only schematically since these are readily available to one skilled in the arts from the above patents and from products manufactured and sold in accordance with the above patents. 
     The rod feeding device  10  comprises a block  16  and a drive disk  17 . The drive disk  17  is mounted on a hub  18  attached to a shaft  19  for rotation of the disk about the axis  20  of the shaft. The shaft  19  is carried in bearing blocks  21  and  22  carried on suitable support elements  23  and  24  each attached or carried on a respective side of the main block  16 . Suitable arrangements of the bearing blocks and the supports therefor are again well known to one skilled in the arts so that further detail is not necessary here. The hub  18  maintains the disk  17  fixed in a radial plane of the axis  20 . 
     Disk  17  includes two side surfaces  25  and  26  which are parallel and lie in radial planes of the axis  20 . The disk further includes an outer surface  27  lying generally on a cylinder surrounding the axis  20  so that the peripheral surface has a constant radius from the axis  20  around its full extent. The peripheral surface is serrated with teeth  28  defining an apex  29  formed by two side surfaces  30  and  31 . The apex  29  thus forms a leading edge which tends to bite into the rod and forward the rod when the disk is rotated in the clockwise direction D. The shaft  19  is driven in rotation in the direction D by a drive  32 . 
     The block  16  has a slot  35  machined into the block from a top surface  36  of the block so as to receive the lower half of the disk  17 . The slot  35  has side walls  37  and  37 A which are spaced by the width of the peripheral surface  27  so that the sides of the disk lie closely adjacent or in sliding contact with the sides of the slot. 
     The top surface  36  is recessed across its width to form a receptacle  38  in the shape of a semi-cylindrical cut out portion which crosses the slot  35  and forms a receptacle for the requires the receptacle  38  to allow one half of the disk including one half of the hub to be received within the block The shaft  19  projects outwardly to each side of the receptacle  38  as shown in FIG.  4 . 
     As best shown in FIG. 5, the peripheral surface  27  and particularly the leading edge  29  and the trailing recess  29 A are straight and parallel to the axis  20 . However these may also be concave to better grasp the convex outer surface of the rod. 
     The slot  35  has a bottom surface generally following the peripheral surface  27 . Thus a first portion of the slot indicated at  40  lies immediately adjacent the peripheral surface  27  so that the leading edges  29  pass immediately adjacent the first portion  40  of the bottom of the slot. Thus the first portion  40  is arcuate and has a radius which is constant spaced from the axis twenty. 
     A second portion of the slot is arranged to be deeper than the first portion  40  and thus defines a channel at the bottom of the slot and surrounding one part of the disk  17 . The portion of the slot forming the channel is indicated at  41  and commences at the surface  36  and an inlet  42  of the channel and terminates at an edge  43  at the bottom of the portion  40 . This portion  41  thus defines a first portion of a channel commencing at the inlet  42  with the second portion of the channel defined by a bore  44  commencing at the edge  43  and extending from the first portion  41  of the channel through to an exit  45  of the bore at an end wall  46  of the block which is attached to the chamber  12 . The exit  45  of the bore thus defines an exit mouth for the channel through which the rod is forced by the drive motion of the disk. 
     The bore  44  is cylindrical with a generally circular cross section closely matching the diameter of the rod  11 . A small clearance may be provided around the outside of the rod within the bore  44  so as to prevent jamming of the rod within the bore. However the bore  44  is dimensioned to prevent buckling of the rod and a longitudinal forces from the disk prior to the rod being forced into the chamber  12 . 
     The portion  41  of the channel is thus formed integrally with the slot and in effect forms an outer portion of the slot. As shown in FIG. 5, the bottom of the slot is circular in cross section as indicated at  49  so as to match the cylindrical cross section of the rod thus allowing the rod to slide over the bottom surface of the slot within the channel. 
     The depth of the channel at the bottom of the slot is arranged so that the spacing between the leading edges  29  and the bottom of the slot  49  as indicated by the dimension L is slightly less than the diameter D of the rod. 
     The width of the slot is equal to the width of the channel so that the side walls  37  and  38  of the slot smoothly converge into the bottom surface  49  of the slot at the channel. Similarly the width of the disk  17  is substantially equal to the width of the slot and therefore the width of the disk is substantially equal to the diameter of the rod. Slight clearances in the dimensions may be provided so that the disk is slightly increased in width and thus the channel at the bottom of the slot is slightly greater than the diameter of the rod so as to prevent jamming when the rod is compressed by its engagement with the leading edges of the serrations on the peripheral surface of the disk. 
     The bottom surface  49  of the slot at the channel is arcuate with a constant distance from the axis  20  from the inlet  42  to the edge  43 . 
     As shown in the embodiment the arcuate channel portion  41  from the inlet  42  to the edge  43  extends over approximately 90 degrees of arc. The bore  44  is arranged so that it is substantially tangential to the disk and smoothly joins with the channel portion  41  so that the surface  49  is contiguous with a bottom surface  50  of the bore. 
     The inlet  42  is slightly chamfered as indicated at  42 A so that the surface of the chamfered section is spaced from the edges  29  by the diameter of the rod thus allowing the rod to be inserted through the chamfered section into the first channel portion to be engaged by the edges  29 . 
     In operation, therefore, when the rod end is inserted into the first channel portion, the leading edges  29  bite into the adjacent part of the periphery of the rod due to its pliable nature and act to carry the rod in a sweeping action around the arcuate surface  49  and to insert the pliable rod into the bore  44  where it is striped from the disk by the edge  43 . The disk is driven with sufficient force to inject the rod through the bore  44  into the chamber with sufficient longitudinal force on the rod to generate a pressure within the chamber of at least 1000 psi and preferably of the order of 2500 psi. The arcuate engagement of the rod with the plurality of leading edges  29  around the portion  41  is sufficient to provide a driving force along the longitudinal length of the rod as the rod is swept over the surface  49 . 
     While the channel portion  41  is formed with a width equal to the width of the slot, it is possible that the channel may be narrower than the slot and thus narrower than the disk and formed as a counter bore section at the bottom of the slot. It is preferable that the channel has a width equal to the width of the rod. 
     The surface  49  is preferably a half circle so as to match the outside surface of the rod which is cylindrical but this is not essential and it is possible that the bottom surface of the channel may be flat and parallel to the edges  29  so the channel is in effect rectangular. Similarly the slot  44  may also be rectangular with its side surfaces generally tangential to the outside cylindrical surface of the rod. 
     The angle around which the rod engages the disk is as shown of the order of 90 degrees but this angle may be increased or decreased in order to increase or decrease as necessary the length of contact with the rod. At a minimum, the rod may indeed simply be tangential to the disk so that it is engaged only by a few of the edges  29 . However it is preferred that some length of the first channel portion  41  is arcuate around the disk in order to increase the number of edges  29  in engagement with the rod. 
     In the embodiment shown, the peripheral surface  27  of the disk co-operates with a stationary surface at the bottom of the slot defined by the channel portion  41  this is of course the simplest arrangement available since the surface  49  is simply formed by machining a stationary block. However in order to reduce friction, it is possible that moving surfaces provided by one or more rollers may form in effect the surface  49  for co-operating with the peripheral surface of the disk in the driving action. 
     The bore  44  commences immediately at the disk at the edge  43  and is not spaced away from the disk so that the rod when it is under pressure has no free space between the end of the first channel portion and the bore in which it can buckle under the longitudinal force. 
     While one embodiment of the present invention has been described in the foregoing, it is to be understood that other embodiments are possible within the scope of the invention. The invention is to be considered limited solely by the scope of the appended claims.