Patent Description:
This invention relates to lead acid battery grids and more particularly to a battery grid continuous casting shoe and machine.

Various machines for casting battery grids in a continuous manner have been developed, as e.g. described in <CIT>.

Some of these machines have a rotary cast iron drum with a mold cavity of a plurality of the desired battery grid pattern formed in a cylindrical peripheral surface of the drum and a shoe of a highly thermally conductive metal such as aluminum-bronze or steel is positioned in confronting and close fitting relationship with an arcuate segment of the drum. The shoe typically has a generally axially extending orifice slot opening onto the face of the drum. Typically, excess molten lead is supplied at a super atmospheric pressure to the orifice slot to fill the portion of the mold of the drum rotating past the slot to thereby continuously cast an elongated web or strip of connected successive battery grids. The excess molten lead is directed back to a lead pot of a furnace which melts the lead supplied to the orifice and maintains it in a molten condition in the pot.

Such a continuous casting machine and shoe is disclosed in <CIT> assigned to the applicant of this patent application. Prior art shoes for battery grid continuous casting machines are also disclosed in <CIT> and <CIT> assigned to the applicant of this application. This type of machine produces satisfactory battery grids when operated under carefully controlled conditions particularly if the temperatures of portions of the shoe and the drum are maintained within selected narrow ranges. However, various problems have occurred when attempting to consistently produce grids of the highest quality at a high speed or rate of production over a long period of continuous machine operation. When operating over a prolonged period of continuous production, some of the problems have been flashing of lead between the grooves of the drum mold and thus flashing on the wires of the grid, lack of complete filling of the drum mold grooves with molten lead and thus undersized grid wires and cold welded seams or junctions of the lug with adjacent wires of the cast grid (knitted or cold weld joints) as distinguished from a homogeneously fused joint of the lug with the adjacent wire portions of the cast grid. These knitted or cold formed joints produce grids with both poor structural quality and a significantly reduced current carrying capacity of the grid.

The present invention is claimed in independent claim <NUM> and preferred embodiments are set forth in dependent claims <NUM>-<NUM>. An inventive casting shoe for a battery grid continuous casting machine includes a body with a longitudinally elongate orifice slot opening into a face configured to confront a rotary drum with a mold cavity therein, a longitudinally elongate molten lead supply slot opening into the orifice slot and upstream of the face relative to the direction of flow of molten lead into the orifice slot, and a longitudinally elongate excess molten lead return slot separate from the supply slot and opening into the orifice slot downstream of the supply slot. In at least some implementations, the supply slot may be inclined downwardly relative to the direction of rotation of the drum past the orifice slot. In at least some implementations, the return slot from the orifice slot may be inclined downwardly relative to the direction of rotation of the drum past the orifice slot.

According to the invention, the body includes a molten lead supply passage communicating with the supply slot upstream of and at least substantially throughout the longitudinal extent of the supply slot. The supply passage may be configured to receive molten lead through an inlet and to discharge through an outlet excess molten lead not supplied to the orifice slot.

According to the invention, the body may include a molten lead return passage separate from the supply passage and communicating with the return slot downstream of and at least substantially throughout the longitudinal length of the return slot. The return passage has a molten lead inlet adjacent one end and be configured to receive excess molten lead from the return slot and to discharge it though an outlet adjacent the other end of the return passage. The return passage may be configured to receive molten lead through its inlet and to discharge such molten lead and excess molten lead from the return slot through the outlet of the return passage.

In at least some implementations, an axially elongate molten lead return supply tube may be received in the return passage with an outside diameter smaller than the inside diameter of the return passage and with a nozzle adjacent the molten lead outlet of the return passage. The return supply tube may have spaced apart outlet passages through the wall of the tube configured to discharge molten lead into the return passage.

The following detailed description of certain embodiments and best mode will be set forth with reference to the accompanying drawings, in which:.

In the drawings, <FIG> illustrate a battery grid continuous casting machine <NUM> with a battery grid casting drum <NUM> journaled for rotation in bearing assembly <NUM> carried by a frame <NUM>. In use the drum is driven for rotation in the direction indicated by arrow <NUM> in <FIG> by an electric motor <NUM> which may be a variable speed electric motor. A mold cavity <NUM> with a desired predetermined battery grid pattern is machined in an outer peripheral cylindrical surface <NUM> of the drum. Typically, the mold cavity may have a whole number of a plurality of the predetermined desired grid pattern in the cylindrical surface of the drum. In use molten lead may be supplied through a shoe <NUM> into a confronting portion of the mold cavity <NUM> of the rotating drum to form a continuous strip or web <NUM> of connected battery grids which are removed from the drum downstream of the shoe such as by passing around a roller <NUM> downstream of the shoe.

Molten lead at a super atmospheric pressure may be supplied to the shoe by a pump <NUM> from a lead melting pot <NUM> of a furnace <NUM>. The pump may be driven by a variable speed electric motor <NUM> the speed of which may be varied and controlled to select, vary as needed and control the super atmospheric pressure and/or flow rate at which molten lead is supplied to the shoe. Excess molten lead may be returned from the shoe to the lead pot <NUM>.

As shown in <FIG>, the cast web <NUM> may have a plurality of connected battery grids <NUM> typically of the same longitudinal web length A and web transverse width B and each with a connector lug <NUM>. As shown in <FIG>, the web may be separated into separate individual grids <NUM>. The web and thus each grid <NUM> may have generally longitudinally extending and laterally spaced apart grid wires <NUM> and generally laterally or transversally extending and longitudinally spaced apart grid wires <NUM>. The web and thus each grid may include longitudinally extending wires <NUM> and <NUM> which in an individual grid may be top and bottom frame wires respectively and laterally or transversely extending wires <NUM> and <NUM> which in an individual grid may be end or side frame wires. In the web the lateral wires <NUM> and <NUM> may have a longitudinal width at least twice that of the intermediate lateral wires <NUM> so that when severed and separated into individual grids the end wires <NUM>' and <NUM>' may desirably have a width equal to or greater than the immediate lateral wires <NUM>. The top and bottom longitudinal wires <NUM> and <NUM> may have a greater width and/or depth than the intermediate longitudinal wires <NUM>. A peripheral frame <NUM> of each grid formed by the interconnected wires <NUM>, <NUM>, <NUM>', and <NUM>' may provide each grid with sufficient structural strength to be readily further processed and assembled into a battery.

As shown in <FIG>, the mold cavity <NUM> in the drum may have circumferentially continuous and axially spaced apart grooves in its cylindrical peripheral surface which form the cast longitudinal wires <NUM>, <NUM>, and <NUM> of the web and after severing the individual longitudinal grid wires. The mold cavity <NUM> may also have generally axially extending and circumferentially spaced apart grooves in its cylindrical surface which form the lateral wires <NUM>, <NUM>, and <NUM> of the cast web and after severing of each individual grid <NUM>. The mold cavity <NUM> in the cylindrical surface of the drum will also have an appropriate recess for casting a lug <NUM> as part of each grid <NUM> of the web of continuous grids. Typically, each grid of the as cast web will have essentially the same longitudinal length A and transverse width B and after separation from the web each individual grid will have substantially the same length A and width B.

Skilled persons understand and know that the intermediate lateral wires <NUM> may be arranged in other patterns in which they are not substantially perpendicular to the longitudinal wires <NUM> and the intermediate lateral wires <NUM> may extend at an angle with respect to the bottom and top wires <NUM> and <NUM> and may be inclined to extend toward the lug <NUM>.

Skilled persons know how to design and construct a variety of continuous casting machines and drums with a suitable mold cavity for continuously casting a web of a wide variety of a plurality of connected grids and thus the construction of machine <NUM>, rotary drum <NUM>, and furnace <NUM> will not be further described herein. One continuous casting machine is disclosed in <CIT> which is incorporated herein in its entirety by reference.

<FIG> illustrates the shoe <NUM> for dispensing molten lead into a cavity of a rotating drum for continuously casting a web of a plurality of connected grids. As shown in <FIG> this shoe may have a body <NUM> with a generally arcuate front face <NUM> with an axially elongate orifice slot <NUM> therein which may confront a rotating drum (such as drum <NUM>) and may extend axially or longitudinally generally parallel to the axis of rotation of the drum. The longitudinal length of the orifice slot <NUM> may extend across the entire axial width of the mold cavity <NUM> including the lug portion of the mold cavity. In use, excess molten lead may be supplied to the orifice slot <NUM> through a longitudinally extending supply slot <NUM> which may open into an upper recessed portion of the orifice slot <NUM> and may extend longitudinally substantially the whole longitudinal length of the orifice slot. Desirably the supply slot is inclined downwardly relative to the direction of rotation of the drum past the orifice slot to facilitate flow of both molten lead into the portion of the mold cavity passing the slot and the return of excess molten lead from the orifice slot. As shown in <FIG>, the supply slot <NUM> may be inclined downwardly (relative to the direction of rotation of the drum) at an acute included angle Ø relative to a radius R of the drum extended through the arcuate center of the orifice slot <NUM> in the range of about <NUM>° to <NUM>°, desirably <NUM>° to <NUM>° and preferably about <NUM>°.

As shown in <FIG>, the upstream end of this supply slot <NUM> opens into a molten lead supply passage <NUM> which may extend axially throughout the length of the shoe body <NUM> and communicate with an inlet connector <NUM> at one end of the body and an outlet connector <NUM> at the other end of the body. Generally, radially outward of the supply passage, an arcuate isolator slot <NUM> may extend generally axially throughout the body to decrease the thermal transfer of heat from molten lead in the supply passage to the body of the shoe.

In use, more molten lead is supplied through the supply slot <NUM> to the orifice slot <NUM> then is dispensed into the mold cavity <NUM> of the rotating drum and the excess molten lead is returned from the orifice slot through a return slot <NUM> which communicates with the recess of the orifice slot downstream of the supply slot <NUM> and is inclined downwardly away from the orifice slot <NUM> relative to the direction of rotation of the drum. As shown in <FIG> the return slot <NUM> may be inclined downwardly away from the orifice slot <NUM> at an acute included angle β relative to an extension of the radius R of the drum through the arcuate center of the orifice slot <NUM> that may be in the range <NUM>° to <NUM>°, desirably <NUM>° to <NUM>° and preferably about <NUM>°. This return slot is longitudinally elongate and desirably may extend the entire longitudinal length of the recess of the orifice slot <NUM>. The minimum cross sectional area of the return slot <NUM> may be on the order of four to ten times greater than the minimum cross sectional area of the supply slot <NUM>, desirably six to eight times greater than that of the supply slot, and preferably about seven times greater than that of the supply slot.

The downstream end of the return slot <NUM> may communicate with and open into a return passage <NUM> extending generally axially through the body of the shoe and communicating at one end with a molten lead inlet connector <NUM> and at the other end with a molten lead outlet connector <NUM>. An arcuate isolator slot <NUM> generally radially outward of the return passage may extend through the body <NUM> of the shoe to reduce heat transfer from molten lead in the return passage and the return slot to the shoe body.

When casting a continuous web of battery grids, molten lead dispensed from the orifice slot <NUM> into the circumferential grooves of the drum mold cavity <NUM> tends to flow upstream counter to direction of rotation of the drum. Therefore, to inhibit this upstream flow, as shown in <FIG> and <FIG> the shoe has a series of axially spaced apart ribs <NUM>, <NUM> extending circumferentially upstream from the upper edge of the orifice slot and projecting radially outwardly from the arcuate face <NUM> of the shoe with each rib in cross section configured to be closely received in an associated circumferential groove of the mold cavity <NUM> in which one of the longitudinal grid wires is cast. As shown in <FIG>, the ribs <NUM> received in the cavity grooves in which the intermediate longitudinal wires <NUM> are cast may be smaller in or otherwise have a different cross sectional area than that of the ribs <NUM> (<FIG>) received in the circumferential grooves in the mold cavity in which the top and bottom longitudinal wires <NUM>, <NUM> of the grid are cast. Typically, a top wire <NUM> of a grid and its associated rib <NUM> may have a larger cross sectional area than that of a bottom wire <NUM> and its associated rib. The exterior surfaces of each rib <NUM>, <NUM> may be designed and constructed to have a slight clearance with the corresponding surface of its associated groove of the mold cavity <NUM> of about <NUM> to <NUM> thousands of an inch.

As shown in <FIG>, the orifice slot <NUM> and the associated portions of the supply and return slots <NUM>, <NUM> extend generally axially or longitudinally significantly beyond or outboard of the mold cavity <NUM> groove forming the top frame wires <NUM> to extend across and desirably slightly beyond the axial extent of the recesses of the mold cavity forming the lug <NUM> of the battery grids of the continuous web. It has been empirically determined that the construction, arrangement and orientation of the orifice, supply and return slots <NUM>, <NUM>, <NUM> improves the casting and integrity of each lug <NUM> and the homogeneity of its merging into and attachment with the associated frame wire <NUM> of the cast grids and significantly decreases if not essentially eliminates any cold welding and seams between them. This is believed to be due to significantly less upfill or upflow of molten lead relative to the direction of rotation the drum as the initial portion of the mold cavity recess forming the cast lug <NUM> moves downwardly into registration with this portion of the orifice slot <NUM> and the molten lead entering this recess remains in a molten condition for a sufficient period of time to result in a flowing together and homogeneous casting of the lug with the adjoining frame wire as this wire is being cast and solidifies throughout the longitudinal and lateral extent of the attachment and merging of the lug into this frame wire. Regardless of any theoretical explanation, it has been empirically determined that improvement of this cast lug and lug wire interface occurs even though the temperature of the molten lead supplied to the shoe is at a lower temperature than that of prior art shoes.

The minimum cross sectional flow area of the orifice slot <NUM> through the confronting face is significantly greater than the minimum cross sectional flow area of the supply slot <NUM> and in some implementations may be in the ratio or range of <NUM>:<NUM> to <NUM>:<NUM> and desirably in the ratio range of <NUM>:<NUM> to <NUM>:<NUM>. In one practical implementation the orifice slot has a width of <NUM> of an inch, the supply slot has a width of <NUM> of an inch and each has a longitudinal length of <NUM> inches. In at least some implementations, a minimum cross sectional flow area of the orifice slot <NUM> may be substantially equal to or greater than the minimum cross sectional flow area of the return slot <NUM> and may be in the ratio or range of <NUM>:<NUM> to <NUM>:<NUM> and desirably in the ratio or range of <NUM>:<NUM> to <NUM>:<NUM>. In one practical implementation the orifice slot <NUM> has a width of <NUM> of an inch, the return slot <NUM> has a width of <NUM> of an inch and each has a longitudinal length of <NUM> inches. In at least some implementations, the minimum cross sectional flow area of the return slot <NUM> is substantially greater than the minimum cross sectional flow area of the supply slot <NUM> and may be in the ratio or range of <NUM>:<NUM> to <NUM>:<NUM> and desirably <NUM>:<NUM> to <NUM>:<NUM>. In one practical implementation the return slot <NUM> has a width of <NUM> of an inch, the supply slot has a width of <NUM> of an inch and each has a longitudinal length of <NUM> inches. In at least some implementations a shoe may be used in a continuous casting machine to produce a web of a plurality of continuously cast grids each having for example a longitudinal length A of <NUM> and a nominal transverse width B of <NUM>, a thickness of <NUM>, and weighing about <NUM> grams of a lead alloy.

The orifice slot <NUM> and associated separate supply and return slots <NUM>,<NUM> extending longitudinally or axially across the mold cavity <NUM> of the drum has the significant practical advantages of providing longer periods of continuous casting of webs of connected battery grids without having to clean out and remove dross, solidified lead particles and other contaminants from the shoe, the ability to continuously cast webs at a lower molten lead temperature and lower shoe temperature, a significantly increased maximum production rate, improved grain structure of the lead of the cast grids, significantly improved lug structure and integrity of the cast grids, improved control of the continuous casting process, and improved castability of lead alloys particularly lead alloys commonly used in lead acid battery grids including lead antimony alloys. As used in this description and the claims, the terms lead, molten lead and cast lead include without limitation both essentially pure metallic lead and a wide variety of lead alloys including without limitation lead alloys with one or more of calcium, antimony, selenium, copper, tin, aluminum, silver, arsenic, barium, bismuth, etcetera.

<FIG> illustrates an optional addition to the shoe <NUM> of a return passage molten lead return tube <NUM> which improves the return of excess lead from the orifice slot <NUM> through the return slot <NUM>. In use, molten lead is supplied to the return passage <NUM> through this return tube which when received in the return passage may dispense molten lead through both a series of longitudinally spaced apart holes or apertures <NUM> through its side wall as shown in <FIG> and/or through a restricted orifice <NUM> in the downstream end of the tube. As shown in <FIG>, the holes <NUM> in the side wall <NUM> of the tube may have a cylindrical bore <NUM> which merges into a frustoconical opening <NUM> outwardly through the wall.

The end of the tube <NUM> with the restricted orifice <NUM> may be disposed near the outlet end of the return passage <NUM> and in use is believed to provide a nozzle which with the return passage <NUM> forms an eductor or jet pump <NUM> which decreases the pressure of the molten lead in the orifice slot and increases the flow rate at which excess molten lead may be removed from the recess of the orifice slot <NUM> through the return slot <NUM>. Regardless of any theoretical explanation, the use of this return tube improves the casting of the lugs <NUM> and the adjoining portion of the wires <NUM> and permits a higher flow rate of excess molten lead through the shoe which is believed to permit the supply of molten lead to the orifice slot <NUM> at a lower temperature and thus molten lead in the mold cavity <NUM> solidifies in less time which enables a higher or faster production rate of cast webs of continuous grids. In some applications this may permit molten lead to be supplied to the supply passage <NUM> at a temperature in the range of <NUM> to <NUM> above the solidification temperature of the lead and enable the maximum production rate of cast webs to be increased by <NUM>% to <NUM>% greater than that achieved with prior art shoes of continuous casting machines. This also improves the integrity of the cast lug <NUM> and the metallurgical grain structure of the cast grids.

Claim 1:
For a battery grid continuous casting machine (<NUM>) with a rotary drum (<NUM>) with a mold cavity (<NUM>) therein, a casting shoe (<NUM>) comprising:
a body (<NUM>) with a face (<NUM>) configured to confront the rotary drum (<NUM>) and extending generally axially over at least the axial extent of the mold cavity (<NUM>) of the rotary drum (<NUM>);
a longitudinally elongate orifice slot (<NUM>) in the body (<NUM>) and opening into the confronting face (<NUM>) of the body (<NUM>) and extending longitudinally across the generally axial extent of the mold cavity (<NUM>);
a longitudinally elongate molten lead supply slot (<NUM>) opening into the orifice slot (<NUM>) along at least substantially the longitudinal extent of the orifice slot (<NUM>) and upstream of the confronting face (<NUM>) relative to the direction of flow of molten lead through the supply slot (<NUM>) and into the orifice slot (<NUM>);
a molten lead supply passage (<NUM>) in the body (<NUM>) and communicating with the supply slot (<NUM>) upstream of the orifice slot (<NUM>) and at least substantially throughout the longitudinal extent of the supply slot (<NUM>), the supply passage (<NUM>) having an inlet (<NUM>) adjacent one of its ends and an outlet (<NUM>) adjacent the other of its ends;
a longitudinally elongate excess molten lead return slot (<NUM>) separate from the supply slot (<NUM>) and opening into the orifice slot (<NUM>) downstream of the supply slot (<NUM>) and extending along at least substantially the longitudinal extent of the orifice slot (<NUM>); and
a return passage (<NUM>) in the body (<NUM>) separate from a supply passage (<NUM>), communicating with the return slot (<NUM>) downstream of the orifice slot (<NUM>) and at least substantially throughout the longitudinal length of the return slot (<NUM>), the return passage (<NUM>) having a molten lead inlet (<NUM>) adjacent one of its ends, a molten lead outlet (<NUM>) adjacent the other of its ends, and being configured to receive excess molten lead from the return slot (<NUM>) downstream of the orifice slot (<NUM>) and to discharge such excess molten lead from the return slot (<NUM>) through the outlet (<NUM>) of the return passage (<NUM>);
wherein the ratio of a minimum cross-sectional flow area of the orifice slot (<NUM>) through the confronting face (<NUM>) to a minimum cross-sectional flow area of the supply slot (<NUM>) into the orifice slot recess is in the range of <NUM>:<NUM> to <NUM>:<NUM>.