Abstract:
A reduced flash molding process and apparatus useful for a variety of parts, especially flat plastic panels, reduces trimming time, regrind waste, increases production speeds, reduces energy consumption, and reduces part weight. The reduction in flash is made possible by providing side members which close before molding material reaches them. Flash still occurs at the ends of the mold, but is eliminated from the sides. Because the parison can be more carefully managed during molding, the mold can be placed closer to the parison extrusion die, thereby reducing parison swell and sag and permitting more accurate filling of all areas within the mold geometry.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS, IF ANY 
     None 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to the art of molding articles and more particularly to the elimination of flash during molding. In its most preferred embodiment, the present invention relates to a molding process and apparatus for flat panels which reduces flash by employing movable side plates which close prior to complete parison formation, blowing and mold closure. 
     2. Description of the Prior Art 
     Blow molding of plastic parts, such as flat panels used in outdoor sheds, tops for coolers and numerous other products has been accomplished by employing a mold which includes two mold halves. In one traditional molding process, a parison, or tube of hot plastic material is extruded downwardly between the mold halves. As the mold begins to close, the bottom of the parison is pinched closed to allow the plastic material to be blown to fill the mold cavity. In traditional molds the parison exceeds the dimensions of the mold at the time of final mold closure creating flash. Once heat is removed from the plastic, such as by the use of cooling water flowing through the mold halves, the part is removed, trimmed and further processed for its end use application. 
     While this blow molding process has been successfully used for many years, trimming is time consuming, labor intensive and therefore expensive. Moreover, a trim line is created around the part which may not yield a desirable appearance. In addition, a greater amount of material must be processed than would be necessary if the flash could be eliminated. Since the material itself is made by heating a plastic starting material to a molten condition, energy is wasted for that portion of the molded product which must be trimmed away. In addition, the part weight is typically higher using traditional molding than would be necessary if the flash were not produced, and the cycle time for a complete molding operation is high. Furthermore, the flash removal process can be relatively dangerous, and the elimination of the manual step of cutting plastic from a part could reduce lost time injuries, workers&#39; compensation claims and the like. The development of a reduced flash molding process which is adaptable to a wide variety of articles, including flat panels, would represent a significant advance in this art. 
     FEATURES AND SUMMARY OF THE INVENTION 
     The present invention features a reduced flash molding process and apparatus which eliminates at least a part of the post molding trimming operation by addressing the source of the flash in the mold. 
     Another feature of the present invention is a reduced flash molding process and apparatus which eliminates excess flash along at least the sides of the molded article, reducing production cost and cycle time. 
     A different feature of the present invention is to provide a reduced flash molding process and apparatus which allows a part to be made using less material, thereby reducing part weight and reducing energy costs. 
     A still further feature of the present invention is to provide a reduced flash molding process and apparatus in which overall cycle time is reduced. 
     A still further feature of the present invention is to provide a reduced flash molding process and apparatus in which the mold can be placed closer to the plastic extrusion die, yielding greater control during parison formation and handling during the molding operation. 
     Yet another feature of the present invention is to provide a reduced flash molding process and apparatus which may be used for molding techniques other than blow molding of plastic parts, e.g. in glass molding, vacuum forming and the like. 
     How the foregoing features of the invention are accomplished individually, and in various combinations, will be described in detail in the following description of the preferred embodiment, taken in conjunction with the drawings. Generally, however, the reduced flash molding process and apparatus of the present invention includes the use of members at the sides of the mold which are closed before or while a parison is extruded (when using blow molding), following which the mold closes around the parison. While the mold closes, the parison is blocked by the side members which prevents any of the molding material from extending outside of the mold where the side members are located, and flash is formed only at the top and the bottom of the mold. Following formation of the part, trimming of only the top and bottom is required. Certain features are also provided by placing the extrusion die nearer the mold to improve parison management. As the parison begins to be extruded from the die, and since the extrusion gap is relatively small, parison swell can be enhanced to ensure better material distribution. As parison shooting progresses, the die gap itself is increased to give the parison sufficient strength to hold its own weight, and when the parison is fully extruded, the diameter at the die itself is smaller than the diameter at the bottom. Following prepinching, which can be done closer to the mold using the present invention, the parison is enlarged, such as by blowing air into it, so that the parison extends to and contacts the side members, which in turn prevent any material escape and allow a more uniform pre-blow inflation. The reduced flash molding process and apparatus of the present invention also permit the use of less material due to parison control at the top of the mold. Other ways in which the features of the invention may be individually or collectively accomplished will become apparent to those skilled in the art after they have read this specification. Such other ways are deemed to fall within the scope of the present invention if they fall within the scope of the claims which follow. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     In the following FIGURES, like reference numerals are used to indicate like components, and 
     FIG. 1 is a schematic, perspective illustration of a reduced flash molding system with the mold in the open or preclose position; 
     FIG. 1A is schematic, perspective illustration of a traditional molding system with the mold in the open or preclose position; 
     FIG. 2 is a schematic, perspective illustration of the reduced flash molding system shown in FIG. 1, with the mold partially closed; 
     FIG. 2A is a schematic, perspective illustration of the traditional molding system shown in FIG. 1A, with the mold partially closed; 
     FIG. 3 is a schematic, perspective illustration of the reduced flash molding system shown in FIG. 1 with the mold closed; 
     FIG. 3A is a schematic, perspective illustration of the traditional molding system shown in FIG. 1A, with the mold closed; 
     FIG. 4 is a schematic, perspective illustration showing a portion of the molding system shown in FIG. 1 and a molded part; 
     FIG. 4A is a schematic, perspective illustration of a portion of the traditional molding system shown in FIG. 1A and a molded part; 
     FIG. 5A is a perspective view of the two major components for a mold for a flat panel employing movable side members; 
     FIG. 5B is a side view of the components of FIG. 5A located together with the side members touching and the mold halves spaced apart; 
     FIG. 6 is a side-by-side schematic comparison illustrating the beginning of a molding operation using the reduced flash system of the present invention and a traditional molding system; 
     FIG. 7 is a side-by-side schematic comparison of the reduced flash molding system of the present invention and a traditional molding system, with the parison shoot in progress; 
     FIG. 8 is a side-by-side schematic comparison of the reduced flash molding system of the present invention and a traditional molding system, with the parison shown after it has reached the required length; 
     FIG. 9 is a side-by-side schematic comparison of the reduced flash molding system of the present invention and a traditional molding system, at a prepinch stage; 
     FIG. 10 is a side-by-side schematic comparison of the reduced flash molding system of the present invention and a traditional molding system, with final mold closure and parison rupture; 
     FIG. 11 is a side-by-side schematic comparison of the reduced flash molding system of the present invention and a traditional molding system, with the flash illustrated after the molding of a part has been completed; 
     FIGS. 12A-12C are schematic top views of three stages of a molding operation wherein the side members are integral with the mold components; 
     FIGS. 13A-13C are schematic top views showing the three stages of a molding operation wherein the side members are fixed; 
     FIG. 13D is a schematic top view similar to FIGS. 13A-13C, except that one of the side members is pivotable; and 
     FIG. 13E is a schematic top view similar to FIGS. 13A-13C, except that one of the side members is slidable. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Before beginning the detailed description of the preferred embodiment, several general comments can be made about the applicability and the scope of the present invention. First, while the illustrations deal with the blow molding of flat panels, such as the types of panels used to make cooler chest tops or wall panels for modular outdoor storage sheds and the like, the principles of the invention have wide applicability with regard to the overall dimensions, shapes and types of products which can be advantageously produced using the new reduced flash system. Accordingly, the invention is not to be limited to flat panels (such as the ones illustrated or otherwise), and the invention has applicability to other types of molding than blow molding where the elimination of flash is desirable. The invention could be readily adapted to glass molding or vacuum forming processes, for example. 
     Second, schematic illustrations are used for most of the FIGURES, it being well within the ordinary skill of one familiar with the plastic molding art to construct extrusion dies, prepinching and mold manipulation systems for the desired final product. Cylinders are typically used for movement of the side members, and such cylinders may be hydraulic or pneumatic. Alternatively, they can be replaced by other systems, such as gears and the like, for moving the side members into and out of position as required. Moreover, while all the illustrations show a vertical parison shot into a space having vertical side walls and an open top and bottom, the process could be used with inclined molds and side members which have open ends. 
     Third, the particular rectangular product shown in the illustrations, and the use of two pairs of side members is again for purposes of illustration, rather than limitation, and other configurations of molded products will benefit from the use of a single or more than two pairs of side members for the elimination of flash. The principles of the present invention could be readily adapted by those skilled in this art, once a basic understanding of its principles has been achieved by reading the present specification and reviewing the drawings provided herewith. 
     Fourth, the illustrations show the side members being fully extended before mold closure begins, but this is not required, as long as full extension (closure) occurs before the parison reaches the location in the mold where the side members reside. In other words, mold closure can be initiated while the side members are being extended toward one another. In addition, a single side member could be used to define the space, rather than a side member comprising two plates having contact faces, and the side member(s) could be separately supported or could be attached to mold components and move therewith. 
     Fifth, the illustrated prepinch mechanism and location can be variously embodied. For example, it could be located above the mold to seal the parison at the beginning of the parison shoot, while other techniques have a prepinch device mounted directly to the bottom of the mold and can be separately energized or be part of the mold itself. The present method of this invention is readily adaptable to all such techniques, as well as systems where no separate prepinch is used at all. 
     Sixth, while a round parison is shown in the FIGURES, non-round parison extension dies can be used, e.g. oval or square. 
     Seventh, while top shooting of the parison is shown in the FIGURES, shooting from the bottom and pulling of the parison in an upward direction may also be used within the scope of the invention. 
     Proceeding now to a description of the preferred embodiment, FIG. 1 illustrates in schematic fashion the reduced flash molding system  10  according to the present invention. Reduced flash molding system  10  includes first and second mold halves  12  and  14 , a first pair of side members  16 ,  18  and a second pair of side members  20 ,  22 . In FIG. 1, the mold halves  12  and  14  are spaced apart from one another and a generally cylindrically shaped parison  25  is shown schematically located therebetween. 
     FIG. 1A shows a traditional molding system  30  including first and second mold halves  32 ,  34  and a parison  35  located therebetween. In the illustration of FIG. 1A, a mold recess  37  is shown in mold half  34 , a compatible recess is located in mold half  32 , but it is not visible in this illustration. In this case, the folded part to be prepared is a generally rectangular, flat panel. 
     FIG. 2 shows the reduced flash molding system  10  at a stage where mold halves  12  and  14  have started to approach one another, squeezing the parison  25  so that portions thereof contact, but do not penetrate the joint between the respective pairs of side elements  16 ,  18  and  20 ,  22 . 
     FIG. 2A shows a similar configuration for the traditional molding system  30 , with parison  35  being squeezed into a generally oval configuration. 
     FIG. 3 differs from FIGS. 1 and 2 in that the mold halves  12  and  14  are closed. Similarly, and by comparison, FIG. 3A illustrates the traditional molding system  30  with the two mold halves  32 ,  34  closed. 
     Some of the most significant differences in the reduced flash molding system  10  compared to the traditional molding system  30  are illustrated in FIGS. 4 and 4A. In FIG. 4, the forward mold half  12  is not shown and a molded part  27  is shown adjacent the remaining components. Part  27  includes flash  28 ,  29  at the top and bottom respectively of part  27 . In contrast, a part  38  is shown in FIG. 4A totally surrounded by flash  39 . From this very simplified description, it will be readily appreciated that the amount of flash which must be removed, as well as the amount of time it will take to remove it, is substantially greater using the traditional molding system  30 . Moreover, a flash trim line will be present on all edges of part  38 , but will only be present at the top and bottom of part  27 . 
     FIGS. 5A and 5B illustrate how the various parts of a reduced flash molding system  40 , according to the present invention, may be constructed. In particular, FIGS. 5A and 5B shows the mold halves  41  and  42  and side members  43 ,  44  and  45 ,  46 . The mold and side member closure components are not included for purposes of simplifying the drawings. FIG. 5B shows the two components of FIG. 5A together as they would appear before parison shooting. 
     FIG. 6 is a side schematic illustration showing, side-by-side, the reduced flash molding system  10  of the present invention and the traditional molding system  30 . In the process shown in FIGS. 6-11 the moving side members  18  and  22  are used, but only the ends thereof are shown. Only the mold halves  14  and  34  are shown in these FIGURES. In addition, the extrusion dies  70  and  70 A are included. It can be noted from FIG. 6 that die  70  is located closer to mold half  14  than die  70 A is to mold half  34 . As will become apparent from the description of this and subsequent FIGURES, the location can be closer because of the ability to more closely manage the parison during shooting and mold closure. The parison formation begins at the stage illustrated in FIG. 6, the parisons being illustrated at  72  and  72 A. At this stage in the molding sequence, the die gaps of the extrusion dies  70  and  70 A are quite small causing the greatest possible amount of parison swell. 
     As parison shooting continues, and as illustrated in FIG. 7, the weight of the molten plastic will cause a sag of the parison to begin, causing a phenomenon known as “neck down”. The neck down overcomes the swell, and decreases the overall diameter of the parison. To offset this effect, it is conventional practice to increase the die gap to give the parison enough material strength to be able to support its own weight. The increase in the die gap also reduces parison swelling at this stage. 
     As parison formation continues, and as illustrated in FIG. 8, by the time the parison reaches the required length the diameter of the parison at the die is substantially smaller at the top than it is at the bottom. In both the reduced flash process of the present invention and in traditional molding, the parison formation is continued until the lower portion of the parison extends below the bottom of the mold. 
     The prepinch processing step is illustrated in FIG.  9 . Its purpose is to seal the bottom of the parison to allow the now closed system to be expanded by introducing air thereto. After prepinch to seal the parison and pre-blow inflation, the parison begins to fill the mold cavity. Initially, the pre-blow will enlarge the lower portion of the parison, causing it to exceed the cavity dimensions in a traditional mold as is shown at area  75 A. With the reduced flash molding process  10  of the present invention, the side members will stop the parison from inflating past the cavity side, as is illustrated by the straight line  75  in this FIGURE. Accordingly, a more uniform pre-blow inflation is made possible, using less pre-blow air. The prepinch mechanism is schematically illustrated at  73  and  73 A. These devices, in and of themselves, are conventional in the blow molding art and do not form part of the present invention. They may be simple plates moved between open and closed positions by pneumatic or hydraulic cylinders or other mechanisms. 
     By the time the mold closes further, and as illustrated in FIG. 10, ballooning of the parison occurs at it contacts the mold. The ballooning will cause an excess enlargement above and below the mold as illustrated at  77  and  77 A (at the top) and  79  and  79 A (at the bottom). Eventually, when the mold is closed or very nearly closed, the enlargements will rupture (see reference number  80 ), and deflation of the parison balloon will occur. Complete mold closure and inflation of the parison within the mold must take place before the deflation and collapse of the parison occurs. It will be noted in FIG. 10 that the parison has completely filled the reduced flash mold along its sides from the top to the bottom, while mold filling is more irregular using the traditional molding process. 
     Finally, the results of the molding operation are observed in the schematic of FIG.  11 . It will be noted first that the amount of flash resulting from a traditional mold system  30  is shown on the right side of this FIGURE, with diagonal lining. The flash occurs around the entire molded article, requiring a substantial amount of trimming and labor to create the desired rectangular flat panel. On the other hand, with the reduced flash molding system  10  of the present invention, flash exists only at the top and the bottom, and no converting operations such as trimming are required elsewhere. 
     These illustrations point out the importance of being able to control the distance from the die to the mold, which is typically determined by the amount of parison width required to fill the top geometry&#39;s of the mold. By managing the pre-blow inflation and using greater swell in the reduced flash molding system  10 , less distance is required between the die and much more precise parison sizing for a particular molded article can be accomplished. It is also noted in the FIGURES that the prepinch mechanism  73  is located closer to the bottom of the mold than is possible using the traditional molding system  30 . 
     FIGS. 12A-12C illustrate, in a top view, an alternate embodiment wherein the side members are combined with the mold elements. In these FIGURES,  90  and  91  represent mold press platens, while two L-shaped molds are illustrated at  93 ,  94 . Legs  96 - 97  of the molds  93 ,  94 . Legs  96 - 97  of the molds  93 ,  94  act as the side members as best seen in FIG. 12B where the schematic parison  99  is also shown. FIGS. 12C shows the molded part  100 . Another embodiment of the invention would include fixed side members which are paralleled to one another and spaced by a distance sufficient to accommodate the moving mold parts. If it were desirable to remove a molded part from the side, one or both of the side members could be mounted for pivotable rotation to facilitate the part removal step. 
     This embodiment is described in FIGS. 13A-13E which show in top schematic form a pair of moving mold components  110 ,  112 . In FIGS. 13A-13C, the side members  114 ,  116  are fixed and the parison  120  is illustrated in FIGS. 13B and 13C. In FIG. 13D, side member  116  is replaced by a pivoting side member  122  to permit part removal, and in FIG. 13E, the side member  116  is replaced by a sliding side member  124  to also permit sideways part removal. 
     While the reduced flash molding process and apparatus of the present invention have been illustrated in schematic form from an overview standpoint and from the standpoint of parison management, those skilled in this art will readily appreciate how the reduced flash molding concept can be adapted to a wide variety of molded article shapes and to different molding techniques. Accordingly, the present invention is to be limited, not by the illustrations or description above, but solely by the scope of the claims which follow.