GB2080723A - Battery container mould - Google Patents

Abstract

A mould is described for injection moulding battery containers which include a plurality of thin resilient ribs integral with and projecting at acute angles from the inside walls thereof into the cell compartment(s) to hold the electrochemical components of the battery therein. The core of the mould includes a mandrel 24 which defines the interior of a cell compartment. The mandrel has dovetail-like mortises 26 therein and complementary-shaped ejector bars 30 reciprocally slideable within the mortises between retracted and extended positions to facilitate stripping the container from the core. The rib-forming portions 32 of the mould cavity are formed in the side walls 88 of the ejector bars. The ejector bars travel with the container during at least part of the ejection cycle so as to free the ribs from the rib-forming cavities without untoward resistance or permanent deformation of the ribs. <IMAGE>

Description

SPECIFICATION Battery container mould This invention relates to moulds for injection mould ing battery containers, the walls of which have thin, resilient, integrally moulded ribs projecting at acute angles into the cell compartment(s) defined by the walls. The ribs deflect various amounts according to the thickness of the cell elements comprising the electrochemical components of the battery and serve to firmly retain the components in the contain er while cushioning them against vibration. While the invention is most particularly useful for mould ing multicell, lead-acid, automotive battery contain ers, it is also applicable to single cell and other types of batteries.

Automobile, lead-acid storage batteries have stan dardized outside dimensions in different size cate gories. The manufacturers thereof typically provide batteries with varying energy capacities in each size category. This is done by varying the number of positive and negative plates in each cell element of the battery. Varying the number of plates, however, varies the thickness of the cell element to be positioned and firmly retained in the cell compart ment(s) of the container. Lower energy batteries typically contain about nine plates per cell element while higher energy batteries can contain as high as sixteen plates per element. These elements typically vary in thickness from about 2.42 cm for the low energy batteries to about 4.24 cm for the high energy batteries, depending on the number of plates and the particular manufacturer's specifications.In most commercial batteries today, each cell element is spaced from the walls defining the cell compartment by relatively thick (e.g., ca 1.5 mm) ribs integrally moulded normal to the walls, which ribs engage the cell elements and hold them firmly in the center of the comartment. Larger ribs (i.e., in greater relief from the wall) are used for the thin cell elements and conversely smaller ribs for the thicker cell elements.

These ribs are simply formed by cutting slots into the solid cores of the mould.

To provide a variety of battery models, many battery manufacturers stock at least one case mould for each battery model and have to shut down their production lines to change over from one model to the next. Other manufacturers stock a lesser number of moulds, but provide additional inert spacers (e.g., extra separators) in each cell element to add thick ness to the cell elements having fewer plates. This approach, however, adds the extra cost of the spacer and frequently complicates the in-plant handling of the cell element particularly during insertion into the container.

At least one manufacturing moulds oversized ribs in a few standardized containers and then cuts the ribs back to the desired size depending on the thickness of the cell element destined for the particu lar container. This technique is disclosed in United States patent No. 4,041,603.

This approach requires a separate trimming oper ation and tools therefor.

Still other manufacturers have proposed moulding thin (ca. 0.6 mm) resilient ribs at angles to the container walls, which ribs deflect by an amount commensurate with the thickness of the cell element inserted in the cell compartment. However, moulding containers of this type is difficult if the ribs are to have any substantial size (i.e., height and extension).

In this regard, it is difficult, at best, to accurately machine thin angled, slots into a mould core with conventional tools without creating some undercuts and backdrafts; and to polish the surfaces of such slots sufficiently to reduce drag on the ribs during container ejection. Even when relatively smoothwalled slots are provided, the large area of ribforming mould surface relative to the thickness of the ribs creates such a resistance to stripping that the force required to free the ribs from the narrow slots often stretches and deforms the ribs. Occasionally, the ribs tear leaving portions thereof lodged in the slot which then necessitates shutdown and cleaning of the mould.Finally, experience has shown that such moulds require excessively long moulding cycle times: to ensure adequate filling of the thin, poorly-vented, rib-forming cavities at the beginning of the cycle; and to free the ribs from the cavity without distortion during container stripping at the end of the cycle.

The present invention comprises a mould for injection moulding thermoplastic battery containers having thin, inclined resilient ribs moulded on the compartment walls thereof to retain the electrochemical components of the battery. A preferred mould has a core-bearing portion which includes: a mandrel(s) for shaping the cell compartment(s); and means for stripping the container from the mandrel(s), wherein the stripping means includes a plurality of dovetail-shaped ejector bars reciprocally slideable within complementary shaped mortises in the mandrel(s). More specifically, the invention comprehends the rib-forming portions of the mould cavity being formed in the diverging walls of the dovetailed-shaped ejector bars and between the ejector bars and the diverging (i.e., from the exterior surface of the mandrel) walls of the complementaryshaped mortises.The ejector bar forms one side of the rib-forming cavity and the mortise wall forms the opposite side. The ejector bars and mortises are machined and polished separately before assembly.

Hence, their critical surfaces are more readily accessible to the appropriate tools and more accurate finishing is possible. The ejector bars assist in stripping the container from the mandrel(s) by concurrently pushing on the bottom of the container and the tops of the ribs to free the container from the mandrels without distortion of the ribs. Moreover, the ejector bars travel with the container during ejection at least until the ribs are nearly clear of the mortises in the mandrel(s). This travelling of the ejector bars with the ribs virtually eliminates any drag on the ribs resulting from any interfacial adherence between the ribs and the ejector bars while the ribs are still confined to the narrow rib-forming cavities.This travelling, coupled with the pushing on the top of the ribs appears to reduce the force required to free the ribs from the cavity and shift some of it away, from the base and roots of the ribs where heretobefore it was concentrated and resulted in rib deformation. The stripping means also includes a typical stripper plate for engaging the rim of the container and applying stripping force thereto. In a preferred embodiment, the stripper plate and ejector bars move (i.e., about 7.5-8.0 cm) together until the tops of the ribs are nearly clear from the end(s) of the mandrel (s). At that time, the direction of the ejector bars is reversed and the stripper plate then pushes the now unconfined ribs free of the ejector bars and ultimately the remainder of the mandrel(s).While the stripper plate completes the stripping of the container from the mandrel(s), the ejector bars return to their retracted position and are ready for the next moulding cycle. The ribforming cavity vents between the ejector bars and mortises thereby permitting a more rapid and complete filling thereof during injection.

The invention and how it may be performed are hereinafter particularly described with reference to the accompanying drawings, in which: Figure 1 illustrates a sectioned perspective view of a multicell battery container of the type moulded in a mould according to the present invention; Figure 2 illustrates a plan view of the battery container of Figure 1; Figure 3 illustrates a side elevational view of a core-bearing portion of a mould according to the present invention in the mould-open position (i.e., with the female portion of the mould displaced to the rear of the viewer); Figure 4 is a sectioned front elevational view of the core-bearing portion of the mould taken in the direction 4-4 of Figure 3, but in the mould-closed position (i.e., mated with the stationary/female portion of the mould);; Figure 5 is a sectioned bottom view of the core-bearing portion of the mould taken in the direction 5-5 of Figure 3, but in the mould-closed position (i.e., mated with the stationary/female portion of the mould); Figure 6 is a sectioned front elevational view of the core-bearing portion of the mould shown in Figure 4 (i.e., with the stationary/female portion of the mould displaced) early in the stripping cycle and showing the stripper plate in a partially forward position and the ejector bars in a fully forward position; Figure 7 is a sectioned front elevational view of the core-bearing portion of the mould shown in Figure 4 (i.e., with the stationary/female portion of the mould displaced) late in the stripping cycle and showing the stripper plate in a fully forward position and the ejector bars in a retracted position;; Figure 8 is an enlarged perspective illustration of a mandrel and associated ejector bars of the mould of Figure 3 in the retracted position; and Figure 9 is an enlarged perspective illustration of a mandrel and associated ejector bars of the mould of Figure 3 in the fully extended position.

Figures 1 and 2 illustrate perspective and plan views respectively of thermoplastic multicell battery containers 2 injection moulded from moulds made in accordance with the present invention. The invention, however, is equally applicable to single cell containers as well. End walls 4, side walls 6 and bottom wall 8 define the container 2, while internal I partitions 10 divide the container 2 into a plurality of individual cell compartments l2#Theeteotro#hernic- ally active components of the battery lie., plates, separators, and connectors) are inserted into each of the compartments 12 through the open top {l.e., as defined by a rim 16) of the container and are appropriately electrically connecteci to schietha .desired battery voltage. Thin, flexible ribs 14 are integrally moulded with the intercept partitions 10 and end walls 4 are disposed at an angle (e.g., about 60 ) thereto. The ribs 14 have thais baees 13 at , the bottom 8 and their roots 15 at the N."rtitions 10 arid walls 4.The ribs 14 deflect commensurate# with components of varying thicknesses and serve to space the components from the compartoent watis and cushion them against damage due to vibration.

Mould description Figures 3-5 illustrate various views of the principal structural elements of a mould acccvreting to the present invention. Figure 3 views the cone-bearing portion 18 of the mould head-on in the mould-open position with the.female or statio nay portion of the mould to the rear of the viewer. press, the mouLd halves would move apart horizonta#ilyand separate along a vertical parting line.Figures 4 and Ei, on the other hand, are views in the mould-closed position showing the core-bearing portion 18 with thesta- tionary/female portion 74 of the mould in place and ready to receive the melt (e.g-., polyprnpylena)~ - The core-bearing portion 18 of the mould Includes a stationary backplate 20, a core 22 and means for stripping the container 2 from tile core 22. The core 22 comprises a plurality of mandrels 24 sized to the - compartments 12. The mandrels 2Ainctude a plural ity of pairs of dovetail-shaped (e.g., trapezoidal) mortises 26 formed in the moulding surfaces 28 thereof.The mortises 26 of each pair of arranged back-to-back such that the ribs 14 formed therein wall lie directly opposite each other in e battery comr partment 12. Moreover, the mortises in one mandrel lie directly opposite the mortisas1n#the next adjacent mandrel(s) so that the ribs 14 formed theteln till lie directly opposite each other on opposite sides of the partition 10 formed between such ribs. A plurality of complementary-shaped ejector bars 30 each fit within the respective mortises 26 and are adapted-to reciprocate therein as will be discussed herejnaftet.

Recesses 32 (see Figures 8 and 91 inthe diverging faces 88 of the ejector bars 30 define the rib-fonriir5g cavities. The ejector bars 30 are joined to a pedestal 34 located in a groove 47 in an el tor sotuatir plate 40. The pedestal has a tenon portions 36 adap;bd to be slideably received in a mating opening-38 in the ejector actuating plate 40. A flange 42 on the pedestal 34 is spaced apart from the actuating plate 40 by a gap 44. Bolts 43 are slideably received in openings 45 in the ejector plate 40 and retain the pedestal 34 in the groove 47-ia-the plate b-#itare such as to permit relative moveni#-ntbetweenTha pedestal 34 and plate 40 to a~or lai;e shrinkage as .

will be discussed hereinaFte-ss The ejector actuator plate hrdraufl--c-c#iin#- cylinder 48 @@@@@@@@at@@@@ Cylinder rods 50 from the cylinders 46 slideably pass through openings 52 in the ejector plate 40 and adjustably attach to the stationary backplate 20 as illustrated (Figure 4). Posts 51 are anchored to the plate 20 and serve to guide the ejector plate 40 during stripping.

The mandrels 24 are held tightly together, and to the core-bearing portion 18, by means of stationary mounting plates 54 and 56. In this regard, the roots or bases 58 of the mandrels 24 flare outwardly and are mated with a complementary-shaped opening 60 in the forward mounting plate 54. The rearward mounting plate 56 is then bolted to forward plate 54 and the mandrels wedged tightly together. The stationary mounting plates 54 and 56 are rigidly affixed to pillars 62 and rails 64 which in turn are rigidly affixed to the stationary backplate 20 and serve to space the plates 54-56 from the backplate 20. The ejector bars 30 extend from the pedestal 34 through an opening 57 in the rearward mounting plate 56 and thence through the mandrels 24.

A stripper plate 66 lies adjacent the forward mounting plate 54 and, in conjunction with the ejector bars 30, serves to strip the container 2 from the mandrels 24 following moulding. The stripper plate 66 includes a cross-shaped recess 68 for mating with the stationary/female portion 74 of the mould as illustrated in Figures 4 and 5. The stripper plate 66 is bolted (see Figure 5) to cylinder rods 69 of hydraulic cylinders 70 which are, in turn, bolted to the backplate 20. Four pilot posts 72 (see Figures 3, 6 and 7) are anchored to the forward stationary mounting plate 54 and serve both to guide the stripper plate 66 and to register the core-bearing portion 18 of the mould with the stationary/female portion 74 during mould closing.

Four coordinating posts 73 are anchored to the ejector plate 40 by means of mounting plates 75. The coordinating posts 73 extend slideably through openings in the mounting plates 54-56 into contacting engagement with the backside of the stripper plate 66 and serve to maintain the spacing between the plates 40 and 66 during ejection.

The stationary/female portion of the mould 74 is shown in Figure 4 and 5 only, and comprises a main body 76 having a hollow 78 therein. In customary fashion, four cam doors 80 appropriately slide and fit within the hollow 78 to define a container-shaped mould cavity 82 therewith. Upon opening of the mould a spring 84, acting in concert with appropriate linkages (not shown), causes the cam doors 80 to slide along surfaces 86 and thereby move laterally away from the core 22 to release the outside of the container 2 from the mould. Upon closing, the cam doors 80 slide back into the position shown in Figures 4 and 5. Appropriate means (not shown) are provided to inject plastic material into the cavity 82.

Such stationary portions of the mould are well known in the art and require no further description.

Mould operation Figure 6 and 7 show the location of the principal structural elements of the core-bearing portion 18 of the mould at different stages in the containerstripping cycle. After the injected thermoplastic material has solidified in the mould cavity 82, the core-bearing portion 18 of the mould separates from the stationary/female portion 74 and carries with it the container 2 shrunk tightly about the core 22. At this stage, the several moving parts of the corebearing portion 18 of the mould are substantially in the position shown in Figure 4. After the cores 22 have cleared the stationary/female portion 74 of the mould, hydraulic cylinders 70 are energized and the stripper plate 66 advances slightly (i.e., about 0.050"0.125" (1.27 mm - 3.18 mm)) to engage the rim 16 of the container 2 which has receded slightly from the face of the stripper plate 66 due to shrinkage.This moves the stripper plate 66 slightly away from the forward mounting plate 54 and the ends of the coordinating posts 73. Hydraulic cylinders 46 are then energized to advance the ejector actuating plate 40 until the coordinting posts 73 again engage the backside of the stripper plate 66. At this time, the bolts 43 slide in their openings and the gap 44 between the actuating plate 40 and the pedestal 34 is closed. The gap 44 is set to match the amount of shrinkage occurring at the rim 16, and hence, prevents the ejector bars 30 from puncturing holes in the bottom of the container 2 before the stripper plate 66 can start to push the container 2 off the core 22. After these initial short moves, the stripper plate 66, ejector plate 40, pedestal 34 and ejector bars 30 move forward together to push the container 2 off the mandrels 24 as best shown in Figure 6.The coordinating posts 73 hold the relative positions of the stripper and ejector plates 66 and 40 respectively and thereby prevent ejector plate 40 from overtaking stripper plate 66 and causing the ejectors 30 to puncture the bottom of the container 2.

When the ejectors 30 have advanced to the point (i.e., about 3"-3 1/2" (76.2 mm - 88.9 mm)) where the ribs 14 are substantially clear of the mandrels 24, the action of cylinders 46 is reversed as well as the direction of the ejector plate 40. When the ejector plate 40 reverses, the bolts 43 slide in their openings 45 until their heads engage the backside of the ejector plate 40 and pull the pedestal 34 back and retract the ejector bars 30 into the mandrels 24 (see Figure 7). While the ejector bars 30 are retracting into the mandrels 24, the stripper plate 66 continues its forward movement to push the container 2 free from the mandrels 24 (see Figure 7). Thereafter, the stripper plate 66 reverses direction and returns to the position shown in Figure 4, the mould is closed and the moulding cycle is repeated.

Figures 8 and 9 are enlarged perspective illustrations of typical mandrels 24 and ejector bars 30 are made in accordance with the present invention.

Figure 8 shows the ejector bars 30 in their retracted or moulding position. In this position, the recess 32 which is machined into the diverging faces 88 of the ejector bars 30 forms a rib-forming cavity with the corresponding walls 90 of the complementaryshaped mortises 26. The walls 90 of the mortises 26 diverge from the surface 28 of the mandrel 24 at an angle which is substantially the same as the acute angle that the ribs 14 bear to the partitions 10 in the finished container 2.

The present invention provides a commercially practical mould for injection moulding a thermoplas tic battery container having thin, inclined, resilient, retainer ribs projecting into cell compartment(s) of the container which mould can be readily machined and polished as well as operated at commercially practical moulding cycle times and all without stretching, tearing or otherwise substantially de forming the ribs while stripping the container from the mould.

Claims (6)

1. A mould for injection moulding a battery container having bottom, side and end walls defin ing a compartment for housing electrochemical components of said battery, said container having a plurality of thin, resilient ribs integral with and projecting at acute angles from said end walls into said compartment for holding said electrochemical components substantially centrally of said compart ment said mould including female and core-bearing portions coacting in a mould-closed position to define a mould cavity corresponding to said contain er, said core-bearing portion including a mandrel having an exterior surface for shaping the internal surface of said compartment and means for strip ping said container from said mandrel, said stripping means including: a plurality of mortises in said mandrel each mortise being defined in part by at least one side wall angling inwardly from said mandrel surface at substantially said acute angle; substantially complementary-shaped ejector bars each one reciprocally slideable within a respective one of said mortises, said ejector bars each being defined in part by at least one face juxtaposed said mortise side wall and being adapted for movement between an extended, container-release, position and a retracted, container-moulding, position; a recess in said face of each bar defining a rib-forming cavity between said ejector bar and said associated mortise wall while said ejector bar is in said retracted position; and means for moving said ejector bars between said retracted and extended positions such that said ejector bars travel with said ribs to free said ribs from said rib-forming cavities at the time said container is stripped from said mandrel.

2. A mould for injection moulding a battery container according to claim 1, in which the contain er has bottom, side and end walls and at least one partition parallel to said end walls and dividing said container into at least two compartments for hous ing electrochemical components of said battery, said container having a plurality of thin, resilient ribs integral with and projecting at actute angles from said partition and end walls into said compartments for holding said electrochemical components sub stantiallycentrally of said compartments; said core bearing portion includes a plurality of mandrels each having an exterior surface for shaping the internal surface of an associated compartment; and said stripping means includes: a plurality of dovetaii-like mortises, each mortise being defined in part by opposing side walls diverging from said surface at substantially said acute angle; and each of said ejector bars is defined in part by opposing faces juxtaposed said mortise side walls, a recess in each of said faces defining a rib-forming cavity between said ejector bar and and associated mortise side wall while said ejector bar is in said retracted position.

3. A mould for injection moulding a battery container according to claim 1 or 2, in which said container has a top rim and said stripping means includes first and second means for pushing upon said container at said top rim and bottom wall respectively to release it from the mandrel, said first means being a stripping plate and said second means including said ejector bars.

4. A mould for injection moulding a battery container according to claim 3, in which there are means for coordinating the movement of said ejector bars and said stripping plate during stripping to prevent said ejector bars from over-taking said stripping plate and puncturing the bottom of said container; said ejector bars being in the retracted position for forming said rib-forming cavities during moulding and thereafter travelling wfth said ribs to said extended position to free said ribs from said rib-forming cavities without untoward resistance or permanent deformation of the ribs,#

5. A mould for injection moulding a battery container according to any one of the preceding claims, in which earth mandrel includes at least two pairs of dovetail-like mortises, each pair comprising mortises arranged back to back on opposite sides of said mandrel.

6. A mould for injection moulding a battery container substantially as hereinbefore particularly described and as shown in Figure 3 to 9 of the accompanying drawings.