Abstract:
Apparatuses and methods of forming battery parts are disclosed herein. In one embodiment, a method of forming a battery part includes receiving a flowable material into a cavity, and reducing a volume of the cavity while a pin extending through at least a portion of the cavity remains at least generally stationary therein. The method further includes sealing the cavity by slidably engaging at least a portion of the pin with a recess in the piston proximate the end face of the piston.

Description:
CROSS REFERENCE TO RELATED APPLICATION(S) 
     The present application is a continuation of U.S. patent application Ser. No. 12/470,363, filed May 21, 2009, now U.S. Pat. No. 8,512,891, which is a continuation of U.S. patent application Ser. No. 11/709,365, filed Feb. 22, 2007, which is a continuation of U.S. patent application Ser. No. 11/058,625, filed Feb. 15, 2005, which is a divisional of U.S. patent application Ser. No. 10/683,042, filed Oct. 9, 2003, now U.S. Pat. No. 6,866,087, which is a divisional of U.S. patent application Ser. No. 10/112,999, filed Mar. 29, 2002, now U.S. Pat. No. 6,701,998. The disclosures of all the above-listed applications are incorporated herein by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     This invention relates generally to pressure casting and, more specifically to die casting of lead or lead alloy battery parts such as battery terminals to form a finished battery part while at the same time inhibiting the formation of cracks and tears during and after the solidification of the battery part through peripherally contracting the mold cavity volume by bringing an entire mold face toward a mold cavity to reduce the bounded surface volume of the mold cavity without disrupting the integrity of the faces of the mold part solidifying within the bounded surface volume. 
     BACKGROUND 
     Battery parts such as battery terminals, which are typically made of lead or a lead alloy, are usually cold formed in order to produce a battery terminal that is free of voids and cracks. If lead or lead alloy battery parts are pressure cast, air is left in the battery part cavity in the mold so that as the lead solidifies, the air bubbles prevent the battery part from cracking. That is, the air bubbles act as fillers so the lead remains distributed in a relatively uniform manner throughout the battery part. Unfortunately, air bubbles within the battery parts cause the battery parts to be rejects as the air bubbles can produce large voids in the battery part. In order to minimize the air bubbles in the battery part, a vacuum can be drawn in the battery part cavity mold; however, although the vacuum removes air from the mold and inhibits the forming of air bubbles in the battery part, the battery parts cast with a vacuum in the battery part cavity oftentimes solidify in an uneven manner producing battery parts with cracks or tears which make the battery parts unacceptable for use. 
     The process of pressure casting or die casting of battery parts wherein intensification of the battery part is used to form battery parts substantially free of cracks and tears is more fully described in my co-pending applications U.S. Ser. No. 09/170,247, filed Oct. 13, 1998, titled Apparatus for and Method of Casting Battery parts; U.S. Ser. No. 09/458,198 filed Dec. 10, 1999, now U.S. Pat. No. 6,564,853, titled Multiple Casting Apparatus and Method, and U.S. Ser. No. 09/321,776 filed May 27, 1999, now U.S. Pat. No. 6,405,786, titled Apparatus and Method of Forming Battery Parts which are herein incorporated by reference. 
     In one such embodiment, a battery part is cast which is substantially free of cracks and tears by pressure casting a lead alloy while a vacuum is being applied to the battery part cavity. At the moment when the lead in the battery part cavity reaches the liquid-to-solid transformation stage, the part is intensified by driving a piston into the mold cavity to rapidly reduce the volume of the mold for solidification. By precisely controlling the time of application of an external compression force to the molten lead in the battery part cavity, and consequently, the time at which the volume of the battery part cavity is reduced, one can force the molten lead or lead alloy in the flowable state into a smaller volume where the pressure on the battery part cavity is maintained. By maintaining the pressure on the battery part cavity during the solidification process by intensification (driving a piston into the lead), the battery part can be cast in a form that is substantially free of cracks and tears. 
     In another embodiment, the mold for forming the pressure cast battery part is sealed off while the molten lead is still in the molten state and before the molten lead can begin to solidify the supply of pressurized lead is shut off and at the same time the internal pressure of the molten lead is increased by driving a piston into the molten metal. This intensification process is suited for those applications where the entire mold can withstand the higher pressures. That is, when the liquid metal is in a molten state an increase in pressure of the molten lead throughout the mold and the maintaining of the increased pressure during solidification can produce a battery part free of tears and cracks. This process of intensification by driving a piston into the mold allows one to obtain greater molding pressure than is available with conventional pressure casting techniques. 
     In another embodiment, the cast battery part is subjected to at least a partial cold forming during the volume contraction step by rapidly driving a piston into the solidified cast battery part with sufficient force to cold form a portion of the lead in the battery part to thereby produce a battery part that is free of cracks and tears. This method of partial cold form intensification is more suitable for those battery parts where one does not want to subject the mold to excessively higher pressures than the die casting pressures. 
     In the present invention, a finished battery, which is die cast and substantially free of cracks and tears, is formed by extending a piston that first shutoffs the flow of molten lead into and out of the mold cavity. Further extension of the piston brings a piston face that forms a bounded end face of the mold part toward the other faces of the mold. Instead of driving a piston into the mold cavity to increase the pressure of the die cast battery part the entire mold face is brought toward the set of other mold faces to decrease the volume of the mold. Thus the shutoff and intensification are accomplished by a single stroke of an extendible piston carrying a mold face thereon. 
     By finished surface it is meant that the surface of the battery does not contain flashing or irregularities where the molten lead was supplied through a gate. That is, in die casting the runner that supplies lead to the mold is usually broken off when the battery part is removed from the mold thus leaving an unfinished surface. Since irregularities can create problems in electrical operation of the battery part it is desired to have a smooth finished surface over the entire battery part. As pointed out, such finished surfaces are usually obtained only with cold forming a battery part. The present invention provides such a finished surface without having to cold form the battery part. In addition, one can also increase the pressure sufficiently to inhibit voids and cracks in the battery part. 
     In the present invention a retractable piston has an impact surface or mold face that forms an entire side-to-side mold face or mold surface of the battery part thereby eliminating the formation of a local irregularity in the portion of the surface of the battery part that would occur if the piston penetrated a portion a mold face i.e. breaking the surface plane of the mold cavity. The use of a side-to-side or bounded mold face that does not break the surface plane of the mold cavity substantially eliminates the need to finish the battery part. That is, once the part is removed from the mold it is ready for use since the surface plane of the mold cavity has not been broken or penetrated by the moving end face. In addition, since the entire side-to-side surface of the battery part is impacted the precision timing of the intensification step is eliminated. That is, since the intensification pressure is applied on a side-to-side portion of the battery part cavity the lead can be in either the liquid, solid or mush state since the all the lead can be confined and squeezed within the cavity of the battery part mold cavity. 
     SUMMARY 
     An apparatus for pressure casting a battery part wherein a mold includes a set of faces to form a portion of a battery part mold cavity and an extendible piston having a battery part mold cavity face that extends in a side-to-side condition on the piston with the faces coacting to form a bounded battery part mold cavity. The piston includes sidewalls for shutting off the supply of molten lead to and from the mold cavity so that when the extendible piston is brought toward the battery part mold cavity the extendible piston first shuts off a further supply of molten metal to the battery part mold cavity as well as egress of metal from the battery part mold cavity to create a closed battery part mold cavity. The battery part mold cavity peripherally contracts as the face of the piston forms an entire bounded face of the battery part mold cavity. The peripheral contraction eliminates localized surface penetration of the face of a battery part as the peripheral surface of the cavity remains intact as it is decreased. The result is the battery part in the battery part mold cavity have non-disturbed faces when the battery part mold cavity is brought to a closed condition. If intensification is desired one maintains the pressure on the lead as it solidifies so that upon solidification the part is substantially free of tears and cracks as well as surface irregularities. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partial sectional view of the apparatus of the mold and extendible pistons for forming a battery part in an open condition; 
         FIG. 2  is partial sectional view of the apparatus of  FIG. 1  showing one of the extendible pistons extended to form part of an interior surface for a battery part and the other extendible piston in a retracted condition to allow molten lead to flow into the mold; 
         FIG. 3  is the partial sectional view of the apparatus of  FIG. 1  showing the extendible piston in an engaged condition that prevents further molten lead from flowing into the battery part cavity and at the same time intensifying the lead in the battery part cavity; 
         FIG. 4  shows an isolated view of the multiple mold surfaces that coact to form a battery part mold cavity wherein moving an end face of the mold cavity contracts the volume of the cavity; 
         FIG. 5  shows an isolated view of the mold faces with the mold cavity in an open condition to allow flow of molten lead therein; 
         FIG. 6  is an isolated view of the mold faces of  FIG. 5  with the end face in a sealing condition or closed mold condition; and 
         FIG. 7  is an isolated view of the mold faces of  FIG. 5  with the mold cavity in a contracted condition. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a partial sectional view of apparatus  10  for face intensification during die casting of battery parts. Apparatus  10  includes an upper first mold part  11  and a lower second mold part  12  that are held proximate each other by a member (not shown) to form a cavity  16  therein. The two parts are joined a parting surface  12   p  that extends between the two mold parts. 
     Located partially in mold part  11  is a first extendible cylindrical piston  14  which is axially slideable into mold part  11 . Piston  14  includes a cylindrical surface  14   a  for slidingly engaging cylindrical surface  11   a  in mold part  11  to prevent molten lead from flowing therepast. The end of piston  14  includes a hemispherical recess  14   c  and an annular impact surface  12   e  there around with the annular impact surface  12   e  located in a single plane. Extendible piston  14  slidingly engages the sidewall  11   a  of mold part  11  to allow for axial insertion thereof to bring the impact surface  12   e  downward to become a portion of the battery part cavity surfaces formed by the sidewalls of cavity  16 . That is, the impact surface  12   e  forms an entire end or side-to-side top surface to the battery part cavity  16  thereby preventing formation of local irregularities in the end surface of a battery part cast since the entire end face  12   e  can be brought inward to form the battery part mold cavity. 
     Extending downward into mold part  11  is a first runner or gate  17  terminating in a mouth  17   a  and a second runner  18  or vent terminating in a mouth  18   a . Runner  17  is connected to a supply of molten lead (not shown) and vent  18  connects to a vent valve  18  to allow air to escape from the mold cavity. Located around the mold part  11  is a heater  20  for maintaining the temperature of the upper portion of mold part  11  sufficiently hot to maintain the lead in runners  17  and  18  in a molten state during the intensification and casting of a battery part. 
     Located beneath mold part  12  is a cylindrical pin  13  that extends through cavity  16  and into a cylindrical sleeve  15  in piston  14 . Pin  13  has a cylindrical surface  13  that slidingly engages cylindrical sleeve  15  to maintain a sliding relationship between piston  14  and pin  13 . 
       FIG. 2  is a partial sectional view of the apparatus of  FIG. 1  showing the pin  13  extended upward into battery part cavity  16  to form part of an interior surface for a battery part. The top extendible piston  14  is in a retracted condition to allow molten lead to flow into the mold cavity  16  through the runners  17  and excess lead and air to evacuate through runner  18 , as indicated by the arrows. Thus as evident by  FIG. 2  the molten lead flows around the extendible piston  13  into the annular battery part cavity  16 . Note, at this point end annular surface  12   e  forms no part of the contiguous boundary wall of the battery part cavity  16 . That is the mold cavity is in an open condition so that molten lead can flow into cavity  16  thought gate  17 . 
     While the present battery part cavity is shown with an annular shaped battery part cavity one can use the present process without a pin  13  to obtain a non-annular shaped battery part. 
       FIG. 3  is the partial sectional view of the apparatus of  FIG. 1  showing the extendible piston  14  in an engaged or closed condition that prevents further molten lead from flowing into or out of the battery part cavity  16  and at the same time in a condition that one can intensify the lead in the battery part cavity  16  to inhibit the formation of tears and cracks. In the position shown, the sidewalk  14   a  of piston  14  close off the mouths  17   a  and  18   a  to prevent further molten lead from flowing into or out of battery part cavity  16 . Molten lead  30  is shown in battery part cavity  16  as well as in runners  17  and  18 . 
     During the extension of member  14  excess molten lead in chamber  31  is forced backward or backwashed into runners  17  and  18  until the end of extendible piston covers the mouths  17   a  and  18   a  of the runners  17  and  18 . This ensures that the mold cavity is filled with molten lead. At this point battery part cavity  16  becomes closed as no lead can leave the battery part cavity. Further downward pressure on extendible piston  14  brings end face  12   e  downward decreasing the volume of the battery part cavity without penetration of a surface. By maintaining the pressure one intensifies the cast part by increasing the internal pressure of the lead in the battery part cavity  16  sufficiently high so that when the lead solidifies the part is substantially free of tears and cracks. Thus, the intensification process of the present method comprises creating an abrupt increase in the internal pressure of the lead in a mold cavity to a level which is sufficient to reduce the size of trapped air bubbles therein by bringing an entire face of the battery part mold cavity toward the other mold faces so that when the battery part solidifies the battery part is substantially free of cracks and tears. 
     In the embodiment shown the annular end  12   e  of the extendible piston  14  is driven to an adjoining condition at the corner line of the cavity of the battery part cavity surface  16  in mold part  11 . By having the impact surface  12   e  form the entire bounded top surface of the battery part cavity one eliminates the formation of irregularities in the finished battery parts since the top surface of the battery part cavity remains a continuous surface. 
       FIG. 3  shows that the battery part cavity is formed of multiple surfaces or faces some of which are formed by the extendible piston and others that are formed by the mold parts. That is, the battery part cavity has an interior surface  12   d  formed by piston  13 . Mold part  12  includes annular mold part surface  12   b  and lateral mold part surface  12   a . Mold part  11  includes the lateral mold part surface  12   c  with impact surface  12   e  defining the final surface portion of the battery part. 
     As can be seen pin  13  slidingly mates with the cylindrical recess  14   c  in piston  14  thus ensuring that both pin  13  and piston  14  are in axial alignment and that the interior surface of the cast part is centrally positioned within the battery cavity  16 . 
     With the present apparatus and method one eliminates any runner marks as well as intensification marks on the finished battery part since the battery part is contiguously defined by the coactions of the extendible pistons and the battery part molds. In addition, the alignment of the extendible pistons allows for an on-the-go formation of the battery cavity. 
     In the present process, the method of die casting a finished battery part while minimizing cracks and voids in the battery part includes the steps of forming a mold  11 ,  12  with the mold defining a plurality of faces  12   a ,  12   b ,  12   c    12   f  for a first portion of a battery part mold cavity  16 . One forming a gate passage  17  that fluidly connects to the first portion of the battery part mold cavity  16  when the mold is in a pouring condition. A moveable member or piston  14  includes a portion  12   e  defining a further face of the battery part mold cavity  16  with the plurality of faces  12   a ,  12   b ,  12   c    12   f  and the further face  12   e  defined a surface bounded mold cavity when the moveable member is in a closed condition as illustrated in  FIG. 3 . By pouring a lead containing metal in a fluid state into the gate  17  of the mold when the mold cavity  16  is in an open condition as illustrated in  FIG. 2  allows molten lead to flow into the mold cavity  16 . By allowing the lead containing metal to fill the first portion of the battery part mold cavity  16  of volume V1 ( FIG. 4 ); and then driving the moveable member  14  toward the first portion, the battery mold part one closes off the gate passageway  17  and the vent passage  18 . One continues to drive the movable member  14  toward the first portion of the battery mold part cavity  16  until the further face  12   e  forms the final surface to close the mold cavity  16 . By applying pressure to member  14  one can increase the internal pressure of the lead in the mold increases sufficiently to force lead into any solidification voids formed in the battery part. Next, one allows the battery part to solidify under pressure. Once the battery part is solidified, one can remove the mold from the battery part to produce a finished battery part. 
     The method of forming a finished battery part can be obtained by pouring a lead containing metal in a liquid state into an open battery cavity  16  defined by a first set of faces in a battery part mold and allowing the lead containing metal to solidify around the first set of faces in the battery part mold and then driving a member having a portion defining a completion face  12   e  toward open battery cavity  16  until the completion face  12   e  and the first set of faces coact to form a closed surface for the battery cavity. By maintaining pressure on the battery part therein during solidification of the metal in a liquid state it forces molten lead to flow into any solidification voids formed during solidification phase of the molten lead in the battery part cavity. 
       FIG. 4  illustrates the set of faces for forming the die cast battery part. For ease in comprehension the mold parts have been left out with exception of the faces that form the mold cavity. That is the set of mold faces comprises a cylindrical interior face  12   c , a lower end face  12   b , a lower side face  12   a , an upper side face  12   c , a cylindrical end face  12   f  and a top end face  12   e . These set of faces form the boundary surfaces for defining the battery part which is die cast with the present invention. The surfaces defined by the set of faces have a volume designated by V 1 . It is within the volume V 1  that the finished battery part would solidify into a battery part with minimum cracks and tears. 
     In order to illustrate the volume of the battery part mold cavity V 2  in the unreduced state dashed lines have been included to illustrate the position of the gate  17  for supplying molten lead to the cavity as well as the vent  18  for discharging air and excess lead. The annular surface identified as  12   e  identifies the position of the mold when the mold is in an open condition and the annular surface  12   e  identified the boundary of the mold cavity  16  in closed condition but not yet in a pressurized condition. V identifies the contracted volume 1 . Thus the end annular face  12   e  can be brought downward to decrease the first volume V 2  of the battery part cavity by forcing the annular mold face  12   e  toward the battery part cavity  16  while the molten lead in the battery part cavity is at least partially in an unsolidified state. By maintaining the battery part cavity  16  in a decreased volume during a solidification of a battery part one inhibits the formation of cracks and tears in a die cast battery part. 
     Thus the method of die casting a battery part comprises injecting a lead containing metal in a molten state into an open battery part cavity  16  which is partially defined by a mold  11  and  12 . By closing the battery part cavity  16  by bringing a member  14  with a finished mold face  12   e  toward the open battery part cavity  16  partially defined by the mold  11  and  12  one shuts off the passage ways  17  and  18  to create a closed battery part cavity  16  to thereby prevent further lead containing metal in a molten state from entering or leaving the closed battery part cavity  16 . By increasing the pressure of the lead in the closed battery part cavity  16  one can force lead that is in a molten state in the battery part cavity into any solidification voids in lead in the closed battery part cavity  16  to thereby inhibit the formation of tears and cracks in the battery part. 
     The present method can include the step of maintaining the mold faces at a temperature below the solidification temperature of the molten lead to cause peripheral surface solidification. By allowing peripheral surface solidification to occur before the volume contraction occurs one can force the molten lead into voids and cracks in the peripheral surface solidification thereby inhibiting the formation of solidification voids in the die cast part. 
     Thus with the present process one can form an unfinished die cast battery part with the die cast battery part having a set of bounded faces with each of said set of bounded faces adjoining each other to defining a closed surface for the battery part. Each of faces  12   a ,  12   b ,  12   c ,  12   f  and  12   e  are characterized by having a continuous bounded surface free of surface imperfections so that a battery part formed within the cavity is also free of surface imperfection when the die cast battery part is removed from a die cast mold. 
       FIG. 5 ,  FIG. 6  and  FIG. 7  illustrate the various conditions of the cavity during the process of solidification. 
       FIG. 5  shows the mold in the open condition with the set of mold faces  12   a ,  12   b ,  12   c    12   d  and  12   f  forming the lower battery part mold cavity. This state is referred to as an open mold cavity since molten lead can enter the mold cavity through the open annular top of mold cavity  16 . In this condition the mold part cavity  16  can be filled with molten metal. 
       FIG. 6  shows the mold in the closed condition with the set of mold faces  12   a ,  12   b ,  12   c    12   d  and  12   f  forming the lower battery part mold cavity and annular face  12   e  forming the top face of mold cavity  16 . This state is referred to as a closed mold cavity since molten lead cannot enter or leave the mold cavity  16 . In this condition the mold part cavity  16  forms a bounded or confined region for the molten metal. Note in this condition the downward movement of piston  14  has sealed off both the inlet and outlet to the mold cavity  16 . Extending laterally outward is a cavity closing line SL that identifies the point wherein the sidewalls of piston  14  close off both the inlet and outlet for metal to the cavity  16 . 
       FIG. 7  shows the next phase wherein piston  14  has been extended beyond the cavity closing line S L  a distance x. Note, the entire face  12   e  has been moved toward the mold cavity  16  to decrease the volume of the mold cavity  16 . This is the contracted condition wherein the pressure of the molten lead has been increased sufficiently so that it inhibits the formation of tears and cracks in the solidified metal.  FIG. 7  illustrates that the entire face  12   e  moves downward along sidewall  12   f  to not only reduce the volume of cavity  16  but to reduce the peripheral surface area of the faces forming the cavity  16 . In addition, since the entire face  12   e  moves toward the cavity  16  to contract the volume of the cavity the solidifying battery part surfaces are not disturbed. This results in a die cast product that, when removed from the mold, has a finished surface condition, thus eliminating the need for an extra step of finishing the product.