Apparatus for Forming Threaded Molded Article

The present invention resides in an apparatus for forming a threaded, molded plastic article, as plastic closures, and particularly for removing said article from the mold.

The art of injection molding plastic closures is well known in the industry. Dependant upon the design of the plastic closure, including the thread type and number of complete threads, it may be ejected from the mold in a variety of ways. If the plastic material being molded is flexible or resilient it may be stripped by a commonly known stripper ring pushing the article off the core. The molded part must be solidified enough not to be folded over onto itself during ejection but sufficiently elastic to return to essentially its original molded shape after the threads have been stretched over the core. If the molded material does not possess the appropriate characteristics of flexibility for this most economical and simple method of ejection, the article will be damaged or may not return to its original shape and size. Similarly, a very defined or deep thread profile may be inherently prone to stripping damage. Also, the part may have other delicate or fragile features such as a commonly known tamper evident ring, which could be damaged even if an otherwise acceptable plastic is being injection molded.

For such situations where the molded part will be too rigid or fragile to simply push off the core, a collapsible core could be used such as the type shown in U.S. Pat. No. 4,130,264. This patent shows a plurality of thread forming segments situated around the periphery of the core which move on tracks to collapse the core inwardly, so that the molded article can easily be pushed off.

In the case of molding a cap having an integral tamper evident ring, an alternative method is shown in U.S. Pat. No. 4,155,698. Here the first female portion of the cavity which surrounds the threaded portion of the closure is removed from the molded closure, while a second female portion adjacent the tamper evident ring stays in place. The core is then retracted while the closure stretches elastically over it. This is possible because the closure device is held fast by the second female portion in the region of the tamper evident ring. The part can then be ejected by a core pin pushing on the inside of the closure or cap, as the inward elastic yielding of the fragile tamper evident ring is permitted.

When molding a plastic resin which is too rigid to be stripped from the threaded portion of the cavity, without permanent deformation of the molded article, one may use a method as shown in U.S. Pat. No. 4,652,227. In this patent, an unscrewing chuck is used to come over the molded part once the female portion of the cavity is removed. The chuck grasps the outer feature of the closure, then rotates the closure as it moves slidably backward to facilitate the axial movement of the unscrewing closure. The patent also teaches that the unscrewing function can be accomplished, separately and simultaneously, outside of the molding area so as not to delay the injection molding of more closures. This method has the advantage of a simpler mold design which requires no moving parts for ejection of the article; however, the unscrewing system can become quite complicated and costly as it is virtually a machine unto itself.

Another method of unscrewing is accomplished by first separation of the mold halves (opening the mold), then rotating the core portion of the mold cavity while a stripper ring or bottom forming portion of the cavity moves slidably forward in timed relationship with the axial movement of the closure, until the closure is clear of the core portion and allowed to fall free from the molding area. The stripper ring will often employ protruding features, such as teeth or notches, which will keep the molded article from turning in the direction of the rotating core. The stripper ring may be moved forward by a sliding cam attachment that is linked to the rotation drive of the core, thereby ejecting the closure from the core.

This approach carries with it various disadvantages and short-comings. If the core rotation and stripper ring plate movement are directly linked to a motive means which in turn is not directly linked to the mold closing means, there is the likelihood of collision damage should the mold closing means complete its task before the stripper ring return means. To eliminate this possibility, the stripper ring return means must be completed in sequence before the mold closing begins. These non-simultaneous movements can undesirably add one or two seconds to the entire mold cycle time.

A further disadvantage of the system is found in the molded article cooling time required.

For example, if water cooling is desired in the core portion to hasten solidification of the injected plastic, it is necessary to employ rotary water seals around the core to prevent water leaks. These seals will wear out with time due to rotational friction and must be replaced before the imminent leak occurs. In addition, the cores typically have a small drive gear (to maintain overall compactness) which restricts the water channel size in the core. A further disadvantage is evidenced in that the core portion is long and slender and as such, it is prone to wobble as it rotates, causing premature wear on the mating stripper ring surface. This causes a gap between the normally shut-off surfaces between the stripper ring and the core and allows the plastic melt to squeeze into the space (commonly known as "flashing" of the part). Costly repairs and down-time are the result of this occurrence. Of course, gear wear is also to be expected as the rack is used to drive the core rotation for the ejecting of the article as well as for the reregistering of the rack into its original position, ready for the next ejection stroke. Still a further disadvantage includes the excessive overall length of the core assembly, which incurs higher material costs and manufacturing difficulty, as well as limiting the number of available injection molding machines with sufficient clamp stroke to accept the overall mold shutheight. This has been found to be especially true for multi-level or stack molds.

It is, therefore, the principal object of the present invention to provide an improved apparatus for forming a threaded, molded article, as a plastic closure and particularly for removing said article from the mold.

It is a further object of the present invention to provide an improved apparatus as aforesaid which is compact and durable and is capable of more rapid production without undue wear.

It is a still further object of the present invention to provide an apparatus as aforesaid which permits a mold core cooling channel of maximum size.

Further objects and advantages of the present invention will appear hereinbelow.

In accordance with the present invention, the foregoing objects and advantages are readily obtained.

The apparatus of the present invention comprises:

a female mold having a mold surface for the formation of the outer surface of a molded, plastic article;

a mold core having an external core surface cooperating with the female mold to form a mold cavity therebetween in the mold closed position, said mold core being so constructed to form a threaded inner surface of said molded article in the mold closed position;

means for injecting plastic material into said mold cavity;

means for relatively moving the female mold to a position spaced from the mold core to space the female mold from the molded article and form a mold open position;

a movable, rotatable stripper ring fitted over the external core surface having a rearward and forward position and being in contacting relationship with the threaded article in the mold open position; and

means to rotate and axially move the stripper ring from the rearward to forward position thereof and thereby remove the threaded article from the mold core by rotating same.

The article may have a smooth external surface or axially oriented features such as ribs or serrations and the means for relatively moving the female mold is operative to move same away from the mold core and article thereon. Also, the molded article is preferably a threaded closure or cap with a flat, shaped or open upper portion and a side wall or skirt portion thereof depending therefrom, wherein the rotatable stripper ring forms a part of the mold cavity between the core and upper portion in the mold closed position, as for example, contacting the base of the skirt in the mold closed position.

The mold core is advantageously stationary and includes cooling channels therein with means for introducing a cooling medium into the cooling channels. Because the mold core is stationary, the cooling channel may be of maximum size. Also, the water seals which may be required are static and not prone to leakage.

The apparatus includes driving means connected to the stripper ring for rotational driving of the stripper ring. The driving means preferably includes a rack which drives a pinion which in turn drives the stripper ring, and means to reciprocate the rack, whereby the stripper ring moves to axially relative to the core and is rotated from the rearward to forward position thereof to remove the article from the core and is returned to the rearward position. Advantageously, the driving means includes a clutch operative to prevent rotational movement of the stripper ring when the driving means is returned to the rearward position. Additionally, the motive means for axial movement of the stripper ring provides that should the mold close before the stripper ring is moved independently to its rearward position, there is submission to the force without damage to mold components. The motive force for the stripper ring axial movement in this case is a spring pneumatic piston or other such means which provides motive energy that can be overcome without damage.

Preferably, one rack is engagable with multiple pinions and one pinion is engagable with multiple stripper rings.

The present invention may also be used to obtain a closure with a tamper ring.

Additional features and advantages of the present invention will appear hereinbelow.

The present invention will be more readily understandable from a consideration of the following exemplificative drawings, wherein:

FIG. 1 is a sectional view of a core and mold assembly in the mold closed position;

FIG. 2 is a front view of a 32 mold cavity layout using the assembly of FIG. 1;

FIG. 3 is a view similar to FIG. 1 in the mold open position;

FIGS. 4A, 4B and 4C are side views of the layout of FIG. 2 in different stages of operation;

FIGS. 5 and 6 are partial sectional views of alternate embodiments; and

FIGS. 7 and 8 are enlarged detail views of the piston arrangement for moving the front and rear bearing plates.

FIG. 1 shows an apparatus of the present invention comprising a mold cavity assembly 1 in the mold closed position including mold core 10 cooperating with female mold 11 to form a mold cavity 12 therebetween, with female mold 11 having a mold surface 13 for the formation of the outer surface of molded plastic article 14 formed in mold cavity 12. Mold core 10 has a grooved surface 16 adjacent mold cavity 12 in the mold closed position for the formation of a threaded inner surface 18 on molded article 14. Naturally, the particular threaded design may vary depending on requirements.

Molded article 14 may be a threaded closure or cap with a flat, shaped or open upper portion 20 and depending skirt portion 22.

Mold core 10 is an elongated hollow core with an external core surface 24 having cooling channels 26 therein supplied by cooling inlet means 28 in fixed core plate 39 for introducing a cooling fluid, as water, into the cooling channels so that the mold core and molded article may be rapidly cooled. A static O-ring type water seal 30 may surround the cooling passages. Because the mold core is stationary, its design features permit a cooling channel or channels of maximum size for greatest efficiency in the solidification of the plastic product. Furthermore, the seal 30 is static and not prone to wear or leak.

Injection means 32 are provided for injecting molten plastic material into mold cavity 12, as an injection nozzle fed from a source of molten plastic (not shown) for the formation of molded article 14 in the mold cavity. Motive means 34, shown schematically in FIG. 1, are provided for moving mold 11 towards and away from mold core 10 to respectively form the mold closed (FIG. 1) position and mold open (FIG. 3) position. As shown in FIG. 1, the molded article 14 desirably has a smooth external surface but may also have axial serrations or the like so that the motive means 34 is operative to move mold 11 axially, in a straight line, towards and away from mold core 10.

Annular stripper ring 36 is fitted over the external core surface 24 and is retained between the front bearing plate 38 and rear bearing plate 40 by sandwiching the flange portion 42 of stripper ring 36 in front bearing plate recess 44 using wear plates 46. Centering alignment of stripper ring 36 is provided by needle bearings 48 placed on opposite ends of the stripper ring. The stripper ring also has gear teeth 50 which are used for rotational driving of the stripper ring. The gear teeth are preferably located midway between the needle bearings for best support.

Pinion 52 is fitted in the front 38 and rear 40 bearing plates using thrust bearings 54 and needle bearings 56. Pinion gear 58, which engages stripper ring gear 50, is fitted with clutch 60. The pinion gear and clutch are fitted over the pinion into engagement with the stripper ring gear. The rear portion of pinion 52 also has a gear tooth configuration 62 or a separate gear mounted on the pinion which is engaged with a gear rack 64 used to initiate rotation of the stripper ring 36, as shown by arrow B in FIG. 3 and to move stripper ring 36 to its forward position as shown in FIG. 3, and as shown by arrow A in FIG. 1 to move stripper ring 36 to its rearward position as shown in FIG. 1. Front and rear bearing plates 38 and 40, respectively, adjoin fixed core plate 39 in the mold closed position shown in FIG. 1 and are spaced therefrom by space 90 in the mold open position shown in FIG. 3.

FIG. 2 shows a front view of a representative mold cavity assembly 66 using the assembly of FIG. 1 wherein rack 64 is placed vertically through the mold cavity assembly 66 engagable with multiple pinions 52, which in turn are engagable with four stripper rings 36 each. It is naturally possible to vary this arrangement based on particular requirements, for example, the pinion can engage only one or two or more stripper rings, based on the size variables of the molded article, pinion, stripper ring and mold layout. Other means known in the art may be used to rotate the pinions or stripper rings. Racks 64 are reciprocated by hydraulic cylinder 68 or other desired means, which is fastened at its base to the top of the mold. The rack 64 and cylinder rod 70 are attached in assembly using cross member 72. Also, attached to cross member 72 is cam 74. FIG. 2 shows the cylinder rod 70 in the retracted position with the racks pulled down. Movement of the cam 74 and rack 64 together provide the correct timing of forward and rotational motion for the given molded article 14 and thread pitch thereof.

In operation, once the plastic has been injected and solidified, as shown in FIG. 1, the mold opens via motive means 34 to move female mold 11 away from mold core 10, the mold assembly 1 is in the mold open position and the molded article 14 remains on the core. As shown in FIG. 1, stripper ring 36 preferably forms a part of the base of mold cavity 12 in the mold closed position and contacts the base of the skirt 22 of molded article 14. Alternatively, as shown in FIG. 5, stripper ring 36 may form a part of the side of mold cavity 12 and contact the side of skirt 22 of molded article 14. The stripper ring removes the article by inward pressure thereon due to the angular configuration of the forward portion of the stripper ring adjacent the molded article, alternatively assisted by air pressure. A further alternate embodiment is shown in FIG. 6 wherein molded article 14A includes an upper portion 20A with an outer flange portion 21o In this embodiment, stripper ring 36 forms a part of mold cavity 12A adjacent flange portion 21 and removes the molded article 14A by pressure on the flange portion 21. Core 10 may optionally include core sleeve 10A which facilitates manufacturing of the core section.

FIGS. 4A, 4B and 4C show side views of the layout of FIG. 2 in various stages of operation. The rack 64, cam 74 (both associated with hydraulic cylinder 68) and fixed pneumatic piston 82 (see FIGS. 2 and 4 and the enlarged detail views of FIGS. 7 and 8) are then activated simultaneously to turn the pinion 62 and stripper ring 36 and advance the stripper ring forward at a predetermined rate governed by the angle of cam face 84 as it slides against cam follower 83. The effect of pneumatic piston 82 is to hold cam face 84 in contact with cam follower 83. Cam follower 83 is fixed to the rear bearing plate 40 as shown in FIG. 4. This action serves to unscrew article 14 from mold core 10. FIG. 3 shows stripper ring 36 in its forward position with article 14 released from core 10 by rotation thereof in the direction of arrow C. The stripper ring and mold can now be returned to their mold closed position independent of the rack and cam assembly as shown in FIG. 4, saving time in the operation. If the pneumatic piston 82 has not been energized to move the stripper ring back before the mold closes, no damage will occur due to the compressive spring nature of the pneumatic piston 82. As the rack-cam assembly moves back to its home position, clutch 60 allows the stripper ring to remain stationary without rotation thereof and without the resultant wear between gear teeth or mold shut-off surfaces 76, 78.

The operation and detail of piston 82 and cam 74 will be described below. Since the stripper ring 36 is supported and held between bearing plates 38 and 40, it is necessary to move these two plates away from core plate 39 in timed relationship with the rotation of the stripper ring 36 to eject the molded article. To achieve this, air pressure is supplied to first face 81 of fixed piston 82 in the direction of arrow X into chamber 81A which adjoins first face 81, see FIG. 8. The air pressure in the direction of arrow X acts on bearing plates 38 and 40 and moves plates 38 and 40 away from fixed core plate 39 enlarging chamber 81A as shown in FIG. 8. However, the movement is restricted by face 84 of cam 74 which is associated with plate 39 and face 85 of cam follower 83 which is associated with plate 40. As cam 74 moves upwardly in the direction of arrow Y as shown in FIGS. 4A, 4B and 4C, inclined face 84 of cam 74 permits separation of plates 38 and 40 from plate 39 as shown in FIG. 8 with space 90 between these plates. The angle of cam face 84 and cam follower face 85 is designed such that the vertical distance moved by rack 64 (and consequently cam 74) to produce exactly one rotation of stripper ring 36, will also permit a horizontal movement of cam follower 83 and therefore to stripper ring 36 equal to the pitch of the thread on the molded part 14. At the end of the stroke, the parts will have fallen off and the mold is ready for closing. Air pressure is then switched to second face 86 of piston 82 in the direction of arrow Z into chamber 86A urging plates 38 and 40 towards plate 39 as shown in FIG. 7 by enlarging chamber 86A and moving plates 38 and 40 in the opposite direction shown in FIGS. 4A and 4B. This can be done when the mold is closing as the cam and cam follower faces are not restricted from separating and are independent in this direction of motion. Therefore, it is not necessary to wait for cam 74 to return to the original position. This should be contrasted to the usual method of using a cam to push the plate mechanically forward by wedging itself between two plates. Of course, in that device, it would be mandatory to wait for the cam (wedge) to be repositioned to allow the return of plate 38 and 40 for the closing operation of the mold to commence. Rollers 87 are used to provide back-up support for the cams.

It is to be understood that the invention is not limited to the illustrations described and shown herein, which are deemed to be merely illustrative of the best modes of carrying out the invention, and which are susceptible of modification of form, size, arrangement of parts and details of operation. The invention rather is intended to encompass all such modifications which are within its spirit and scope as defined by the claims.