Patent Publication Number: US-4732558-A

Title: Injection mold with end core locks and extended side core locks for forming a partitioned container

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of my co-pending U.S. Patent Application, Ser. No. 823,528, filed Jan. 29, 1986, now U.S. Pat. No. 4,676,731. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention is in the field of injection molding and associated tools. In E. W. Mold &amp; Tool Company, Inc.&#39;s two prior U.S. Pat. Nos. 3,473,197 and 3,816,047, there was disclosed an injection mold assembly for forming a thin walled multi-partitioned container, such as a battery case. The male portion of the mold included a plurality of upstanding cores spaced apart to form the battery case interior partition walls. Movement of the cores during the high pressure injection step was controlled by means of a plurality of wedge shaped members extendable along the longitudinal axis of the battery case between the ends of adjacent cores holding the cores apart. Use of such wedge shape members resulted in the formation of ridges within the case along the interior surface of the bottom wall of the case. The two aforementioned patents further disclose locking members abuttable against the two opposite ends of the array of cores in a direction perpendicular to the longitudinal axis of the battery case preventing the cores from moving outwardly. 
     Additional locking members have been designed to further control movement of the array of cores. In E. W. Mold &amp; Tool Company, Inc.&#39;s U.S. Pat. Nos. 4,278,417 and 4,576,568, there are disclosed differenet types of locking fingers moveably mounted on one core and extendable against an adjacent core. In U.S. Pat. No. 4,278,417, the interior locks mounted to the cores are provided in conjunction with locking members abutting the opposite ends of the array of cores without the wedge shaped members being provided which extend between cores. In the aforementioned U.S. Patent Application, the wedge shaped members extendable between the cores are disclosed along with the end locking members. Further, in U.S. Pat. No. 4,481,161, there is disclosed a pressure stabilized injection mold which includes the wedge shaped members extendable between cores along with the end locking members abuttable against the array of cores. Last, in the U.S. Pat. No. 3,509,603 issued to Halsall, et al. and No. 4,570,897 issued to Von Holdt there is disclosed springs for moving the cams surrounding the formed product. 
     Changes to the design of the thin walled compartment, such as a battery case, have been instituted requiring new and improved injection molds. With the decrease in size of vehicles, less space has been allocated to receive a compartment such as a battery case. Thus, it is desired to shorten the height of the battery case necessitating resting the interior cells of the battery directly against the top surface of the bottom wall of the case. It is therefore necessary to provide a completely flat top surface of the bottom wall eliminating any ridges which previously were formed by the wedged shaped members extending between the mold cores. At the same time due to the reduced thickness of the cores, it is also desirable to eliminate any interior locking members mounted on one core and extending against an adjacent core. Disclosed in my co-pending U.S. patent application Ser. No. 823,528 is an injection mold having an array of cores which not only includes locking members positioned against the two opposite ends of the array of cores, but which further includes: in combination therewith, a plurality of wedge-shaped locking members extendable from the side of and between the cores in a direction perpendicular to the longitudinal axis of the battery case. 
     It is also desirable to provide a battery case having an exterior hold down flange. Such a flange is formed immediately adjacent the bottom wall of the battery case and also adjacent the locking members extending between the cores. As such, the formation of the outwardly extending flanges interferes with the normal retraction of the locking members and the opening of the mold for the removal of the formed case. Disclosed in my aforementioned patent application is a mold having side locking members which are moveable to allow proper opening of the mold without interference with the hold down flanges. 
     With the decrease of battery size the spaced apart cores forming the male portion of the mold tend to bow. In order to further increase the stability of the array of cores, I have herein disclosed positioning the side locks downwardly from the bottom wall 212 of the formed container at an approximate location one-third the length of the container. The side locks are actuated by horizontal extending actuating means and in an alternate embodiment vertically extending actuating means allowing the device to fit within either a short or a narrow work space. Further, the actuating means are arranged to absorb only a portion of the outward pressures applied by the side locks thereby increasing the pressure resistance of the mold. 
     SUMMARY OF THE INVENTION 
     One embodimnt of the present invention is a separable mold assembly for injection molding a plastic container having compartments separated by thin walls comprising a male mold with a longitudinal axis, an end axis, and a side axis, said longitudinal axis, said end axis, and said side axis being perpendicular to each other, said male mold including deep longitudinal slots extending transversely thereacross parallel to said longitudinal axis and said side axis forming a plurality of upstanding cores parallel to said longitudinal axis to form said compartments separated by said thin walls, a female mold mounted adjacent said male mold but spaced therefrom to form said container therebetween, injector means mounted to said female mold and aligned relative to said cores to inject plastic material under pressure into said slots and between said female mold and said male mold, end locking means engageable with the outermost cores of said male mold in a direction parallel to said end axis to limit outward movement of said cores during injection of plastic between said male mold and said female mold, and, a plurality of wedge shaped fingers movable from a position outward of said cores to a position in said slots in a direction parallel to said side axis limiting relative motion between said cores, said wedge shaped fingers located at a position along said longitudinal axis of approximately one-third the length of said cores. 
     It is an object of the present invention to provide a new and improved injection mold for the formation of battery cases. 
     Yet a further object of the present invention is to provide an injection mold assembly for forming a thin walled multi-partitioned battery case having exterior hold down flanges. 
     In addition, it is an object of the present invention to provide an injection mold having extended length side locks for removably extending between adjacent cores of the male portion of the mold. 
     Related objects and advantages of the present invention will be apparent from the following description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a fragmentary perspective view of a plurality of upright cores provided on the male portion of an injection mold. 
     FIG. 2 is a reduced fragmentary cross-sectional view taken along the line 2--2 of FIG. 4 and viewed in the direction of the arrows showing a top view of the male mold. 
     FIG. 3 is a fragmentary cross-sectional view taken along the line 3--3 of FIG. 2 and viewed in the direction of the arrows with the male mold of FIG. 1 shown inserted into the female mold. 
     FIG. 4 is a fragmentary cross-sectional view taken along the line 4--4 of FIG. 2 and viewed in the direction of the arrows with the male mold and female mold shown in the closed position. 
     FIG. 5 is the same view as FIG. 4 only showing an alternate embodiment of the mold in the open position for forming a battery case having hold down flanges. 
     FIG. 6 is the same view as FIG. 5 only showing the mold in a closed position and showing the preferred embodiment of the mold having extended length, horizontally actuated side locks. 
     FIG. 7 is a fragmentary cross sectional view taken along the line 7--7 of FIG. 6 and viewed in the direction of the arrows. 
     FIG. 8 is the same view as FIG. 6 showing an alternative embodiment of the mold having extended length, vertically actuated side lock. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates. 
     Referring now more particularly to FIGS. 1, 2 and 3, there is shown an alternate embodiment of mold assembly 40 which includes a male mold 20 sized to fit slidably into the female mold 32 and being spaced therefrom in order to form a four sided container such as a battery case. The container has a bottom wall integrally connected to a pair of end walls 11, 12, a pair of side walls and five separate interior partitioned walls. Thus, the container includes six separate compartments into which electrical cells may be inserted. The male mold 20 has six separate cores 21-26 to form the six compartments in the battery case. The array of cores 21-26 have a longitudinal axis 35 (FIG. 4) extending centrally through the male mold. The cores are spaced apart forming slots 27-31 to form the five partitions. The distal ends of the cores are smooth and flat as is the facing surface of cap 62 (FIG. 2) to form the smooth and flat bottom wall of the formed container. 
     The six cores 21-26 of mold 20 have bottom ends fixedly mounted in cantilever fashion to a base. The top distal ends of the six cores are spaced apart forming the slots 27-31 for forming the five partitions separating the six separate compartments. Slots 27-31 terminate at location 41 forming the upper edge portion of each partition wall. Each core is in contact with an adjacent core from location 41 to the base 33 forming a rigid bottom portion of the male mold, whereas the top distal ends when not positioned within the female mold are moveable when large sideways pressure is exerted thereon. 
     Female mold 32 includes a pair of cavity end cams 43 slidably mounted in plate 64 that will slide atop wear plates 135 in turn mounted atop stripper plates 51. Cams 43 are moveable inwardly in the direction of arrows 52 and 53 until they are slightly spaced apart from the cores forming gaps 54 and 55 in which the end walls 11 and 12 of the container are formed. Female mold 32 further includes end locking members 56 and 57 fixedly mounted, respectively, to the extendable piston rods of hydraulic cylinders 58 and 59 which move the side locking members inwardly in the direction of arrows 60 and 61 to engage the outermost surface of the top distal ends of cores 21 and 26 preventing outward movement of the cores. The end cams 43 as well as the end locking members 56 and 57 are disclosed in my U.S. Pat. No. 3,473,197, which is herewith incorporated by reference and operate in the same manner. 
     Female mold 32 further includes a cavity insert 62 fixedly mounted by conventional fastening devices 63 to plate 64. A plurality of injectors 100-105 (FIGS. 2 and 3) are mounted, to plate 68 in turn secured to plate 64. The injectors are positioned over the center of each core and have a top end fixedly secured by threaded bushings 83 to plate 68. The bottom end 84 of each injector opens over the center line of the top of the core to allow plastic material to be injected into the mold. The injectors are in fluid communication with a source of pressurized plastic melt via passage 90 extending through plate 68 thereby insuring that each injector applies the same pressure to the mold assembly. 
     The molds shown in the drawings as compared to prior art molds do not include wedge shaped locking members which project between adjacent cores in a direction of the longitudinal axis of the cores. Instead, the locking members extend perpendicular to the longitudinal axis of the array of cores and between cores at the front and back of the array, as well as abut the opposite ends of the array. Thus, a pair of end locking members 56 and 57 (FIG. 3) are shown in their retracted position. In their forward position they would be abutting the opposite ends of the array of cores at a location adjacent the bottom wall of the formed battery case. Likewise, two separate groups of five side locking members extend between the cores and contact the cores on the opposite sides thereof corresponding to the front and rear walls of the formed battery case immediately adjacent the bottom wall of the case. That is, a first group 128 and second group 129 (FIG. 4) of side locking members are slidably mounted to the mold assembly to engage the opposite sides of the array of cores. Group 128 will now be described, it being understood that a similar description applies to group 129. Group 128 includes five separate locking members 130 through 134 (FIG. 2 with each locking member having a pointed distal end extending between two adjacent cores at a location slightly apart from the top ends of the cores. Thus, member 130 has a pointed distal end 135 extendable into a complementary shaped groove formed in the adjacent sides of cores 21 and 22. Likewise, the remaining four locking members 131 through 134 have pointed distal ends which extend between adjacent cores to insure the cores are spaced apart during the injection molding process. Locking members 130 through 134 have proximal ends fixedly mouned to a transverse member 136 in turn slidably mounted to the distal end 137 of piston rod 138 associated with cylinder 139. Operation of cylinder 139 causes the locking members 130 through 134 to engage and disengage the array of cores. Likewise, the five locking members associated with group 129 are associated with a separate cylinder motor operable to move the locking members into engagement and out of engagement with the opposite side of the array of cores. 
     Cavity cam 140 (FIG. 4) is slidably mounted in plate 64 that will slide atop wear plates 141 in turn fixedly secured to stripper plate 51. Cavity cam 140 is moveable inwardly until it is slightly spaced apart from the cores forming gaps in which the side walls of the container are formed. A pair of helical springs 142 are each mounted within cavities 143 provided in each cam 140. Springs 142 include a longitudinal axis extending centrally therethrough which is arranged at an acute angle 36 with respect to the longitudinal axis 35 of the array of cores. A rod 144 is threadedly mounted to the cam and is centrally positioned within the cavity and positioned within the helical spring. Threaded rod 144 has a sufficiently smaller length than the cavity to not abut plate 64 whereas the top end of each helical spring contacts the bottom surface of plate 64. Rod 144 limits movement of the helical spring in case of breakage thereof. As the array of cores 21 through 26 are moved away from cap 62, cams 140 as well as the end cams 43 move apart from the cap 62. Helical springs 142 extend at an approximate angle of 15 degrees relative to the longitudinal axis 35 of the array of cores thereby forcing cams 140 outwardly. The movement of cams 140 has a component parallel to the longitudinal axis of the array of cores and also a lateral component perpendicular to the longitudinal axis. FIG. 4 depicts the cams 140 and side locking members 128 and 129 in the most inward position during the injection of plastic. 
     Cam 140 includes an indented end 145 complementarily receiving transverse member 136. Once the melt is injected into the mold under high injection pressure, i.e. 16,000 psi, and before it is allowed to solidify, the cylinders are operated to disengage the end and side locking members from the array of cores allowing the plastic melt to flow under low injection pressure, i.e. 6000 psi, into the spaces occupied by the locking members. Then the plastic is solidified. Thus, transverse members 136 are moved outwardly in indentations 145 a sufficient distance to move the groups 128 and 129 of side locking members outwardly thereby also allowing th cams to move both longitudinally and laterally with respect to the array of cores without interfering with transverse members 136. 
     An alternate design of the battery case is shown in FIG. 5. Battery case 150 includes a pair of outwardly projecting hold down brackets 151 and 152 integrally joined to the case immediately adjacent the bottom wall thereof. Normally, such brackets 151 and 152 would contact both groups 128 and 129 of the side locking members as the mold is opened. The mold as closed is shown in my U.S. patent application, Ser. No. 823,528 and in FIG. 5 thereof which is herewith incorporated by reference. Each side locking finger is provided with a recess 175 which cooperates with a second recess 176 formed in cap 62 to properl form the hold down brackets 151 and 152. Both groups 128 and 129 of side locking members shown in FIG. 4 move only laterally with respect to the array of cores and do not move along the longitudinal axis of the cores apart from cap 62. Thus, in order to produce brackets 151 and 152, both transverse members 136 of the FIG. 5 embodiment are removably engaged with the distal ends 137 of piston rods 138. That is, transverse member 136 (FIG. 5) includes a slot 153 which slidably receives the enlarged distal end 137. The FIG. 5 transverse member 136 also includes an aperture 154 through which piston rod 138 projects with the aperture 154 and slot 153 forming a stop surface 155 for engaging the rear surface 156 of enlarged head 15 allowing the piston rod to withdraw the transverse member when positiond therein. In all other respects, the mold assembly shown in FIG. 5 is identical with that previously described and shown in FIG. 4 with the additional exception that the side walls of the array of cores are indented at location 157 to complementarily receive similarly configured cams providing an indented side wall in the battery case. 
     In order to operate the mold assembly shown in FIG. 5, the melt is injected into the mold under high injection pressure, i.e. 16,000 psi, and before it is allowed to solidify, the cylinders are operated to disengage the end and side locking members from the array of cores allowing the plastic melt to flow under low injection pressure, i.e. 6000 psi, into the spaces occupied by the locking members. Then the plastic is solidified. The array of cores are then moved apart from cap 62. The helical springs within the cams force the cams to move laterally and longitudinally away from cap 62 with the transverse members 136 eventually disengaging the enlarged distal end 137 of the piston rods. 
     The outwardly extending side locking fingers arranged in groups 128 and 129 are retractable by the power cylinders only a distance slightly greater than the thickness of the case formed between the molds. Thus, in the embodiment of FIG. 4, the side locking fingers separate from the side cavity cams 140 as the cams move along the longitudinal axis of the cores away from cap 62. 
     The temperature of the melt injected into the mold assembly depends upon the type of plastic utilized. Typically the temperature of the polyolefin melt is 500° F. with the pressure exerted on the melt being between 1,500 psi to 20,000 psi. In the typical embodiment, the pressure is maintained on the melt for 6 seconds allowing the melt to flow uniformly between the molds and between the cores. Typically, the side locking fingers and end locking members remain in contact with the cores for a period of approximately 2 seconds. This time period starts with the high pressure injection stage, and concludes when the pressure is dropped to the low, or pack stage. A typical cycle for producing a battery case has a Vduration of 35 seconds with the first 6 seconds reserved for the injection of the plastic (2 seconds for high, and 4 seconds for low), the next 22 seconds reserved for the cooling of the melt, with the remaining 7 seconds reserved for opening of the mold assembly, ejection of the container and reclosing of the mold assembly for the formation of the next container. 
     The preferred design of the battery case is shown in FIGS. 6-8. Battery case 200 includes a pair of outwardly projection hold down brackets 201 and 202 integrally joined to the case immediately adjacent the bottom wall thereof. The cap 199 of the mold is identical to the cap shown in FIG. 5 and includes recesses 203 and 204 to cooperatively form with recesses formed in the top distal ends of side cams 205 and 206 the battery hold down clampss 201 and 202. 
     Side cams 205 and 206 slide outwardly and downwardly from cap 199 as the mold is opened. The side cams slidably ride upon wear plates 20 in turn fixedly secured to stripper plate 208. Side cams 205 and 206 are moved inwardly until they are slightly spaced apart from the cores 209 cantileveredly mounted and movable downwardly from cap 199 as the mold is opened. Helical springs identical to springs 142 (FIG. 4) are each mounted within cams 205 and 206 and are operable to force the cams outwardly as the cams are moved downwardly apart from the cap to facilitate removal of the formed container. 
     In order to increase the stability of the array of cores 209 and prevent any possible bowing of adjacent cores, the side locks are located downwardly from wall 212 at an approximate location of at least one-third the length or height of the battery case from the bottom wall 212 of the case toward the open top edge 213 of the formed case. A single recess forming member 214 fixedly secured to side cam 206 by conventional fastening devices 215 is provided adjacent cap 199 with an identical recess forming member fixedly secured to side cam 205. Member 214 extends into a recess formed on core 209 but is spaced from the core. Member 214 extends from location 216 to location 217 (FIG. 7) thereby forming a recess extending substantially across the width of the cores and forming an indentation in the side wall of the formed container 200. Side cams 205 and 206 include a plurality of horizontally extending slots to slidably receive the wedge shaped side locks with members 214 being located above the wedge shaped side locks but fixedly secured to the side cams. Immediately beneath member 214 are a plurality of locking members 218 through 222 each having an inner distal end 223 projecting between adjacent cores and preventing relative motion between cores. The proximal ends 224 of the locking members 218 through 222 have heads formed thereon held captive by five separate slots 225 formed in carrier 226. In the preferred embodiment shown in FIG. 7, a conventional hydraulic cylinder 227 is fixedly mounted to the mold and has an extendable piston rod 228 held captive within slot 229 provided in carrier 226. The hydraulic cylinder and piston rod extend horizontally away from the mold. 
     Slots 225 are arranged at angle 230 with respect to the longitudinal axis 231 of piston rod 228 which is parallel to the side 232 of core 209. Likewise, the headed proximal ends 224 of the locking members 218 through 222 are arranged at the same angle 230 with respect to longitudinal axis 231 with the size of each headed proximal end 224 being less than the length of each slot 225. Thus, extension of piston rod 228 along axis 231 results in inward movement of the locking members 218 through 222 forcing distal ends 223 to wedge between adjacent cores. Likewise, retraction of piston rod 228 results in carrier 226 moving toward hydraulic cylinder 227 and the withdrawal of the locking members 218 through 222 from core 209. Each slot 225 includes an hole 233 elongated in the direction of axis 231 through which the locking members 218 through 222 extend allowing the carrier 226 to move relative to the mold. Increased locking strength is provided by arranging the headed proximal ends at angle 230 since the outward plastic ejection pressure applied to distal ends 223 along the longitudinal axis of each locking member 218 through 222 is not applied directly along the axis 231. Instead, only a portion or component of the ejection pressure is applied to hydraulic cylinder 227 facilitating the use of a smaller cylinder while maintaining the force of the locking members against the core. 
     It should be understood that although five such locking members 218 through 222 have been described and illustrated for the right hand side of the mold depicted in FIGS. 6 and 7, that an identical set of five locking members are provided for the left hand side of the mold. The left hand side of the mold shown in the drawing has been shown through the mold in a different area to illustrate the construction of the side cam between and above the additional members. 
     End locking members 240 and 243 are provided which are identical to end locking members 56 and 57 (FIG. 3) with the inner distal ends 241 of the end locking members engaging the outermost cores and preventing outward movement thereof. End locking members 240 and 243 are slidably mounted to the mold and are extended against the core and retracted by means of hydraulic cylinders 42 fixedly secured to the mold. 
     When operating the mold,the core is moved upwardly towards the cap with the side cams moving upwardly and inwardly being spaced apart from the core a sufficient distance to form the container therebetween. The end locking members 240 and 243 are forced against the outermost cores with the side locking members also being forced at the same time wedgingly between the cores. Alternatively, the side locking members may be moved between the cores slightly before the end locking members engage the cores. The mold is then filled with plastic with the two sets of side locking members being retracted from the opposite sides of the core by means of movement of carriers 226. Additional plastic is injected into the mold filling the spaces voided by the removal of distal ends 223 with the plastic then cooling and the mold subsequently being opened. A plurality of cross slots 270 (FIG. 6) extend transversely across each core allowing plastic flow between the spaces separating adjacent cores. 
     An alternate embodiment of the mold utilized to produce container 200 is depicted in FIG. 8. Mold 250 is identical to all portions of the mold shown in FIGS. 6 and 7 with the exception that the side locking members are moved by means of a vertically extending hydraulic cylinder in lieu of the horizontally extending hydraulic cylinder 228. Thus, a first set of five side locking members are slidably mounted to side cam 252 and a second set of five side locking members are slidably mounted to side cam 251. The side locking members 253 have inner distal ends 254 which wedgingly project between adjacent cores whereas the headed cap proximal ends 255 are fixedly held captively carrier 261 slidably mounted to the vertically extending extension 270 fixedly secured to piston rod 257 of hydraulic cylinder 258. Carrier 261 includes a vertically extending slot 272 arranged at angle 271 relative to longitudinal axis 259 of piston rod 257. Likewise, the bottom end 273 extends at angle 271 and is slidably received by slot 272. Thus, vertical movement of extension 270 results in inward or outward movement of the wedge shaped fingers. The hydraulic cylinder is fixedly mounted to the mold and is operable to vertically move piston rod 257 along a vertically exending axis 259. Thus, the outward pressure generated against distal ends 254 by the plastic ejection pressure will be applied along a horizontal axis extending through the side locking members with only the vertical component thereof being applied along axis 259 to thereby only slightly urge the piston rod into the hydraulic cylinder. Thus, superior locking characteristics are observed as to the prior art. In all other regards, mold 250 is identical to the mold previously described and shown in FIGS. 6 and 7. Carriers 261 and 226 are slidably connected at all times to piston rods 257 and 228, respectively. 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiments have been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.