GB2055646A - Machine and method for continuously casting battery grids - Google Patents

Abstract

The machine has a rotary drum (24), the pattern of the battery grid cavity being recessed (44, 46) into the outer periphery thereof. An arcute shoe (40) is fixedly positioned against the drum in sliding contact with the outer peripheral surface thereof. The shoe has an internal passageway connected to an orifice slot (60) which extends to the periphery of the drum. The orifice slot is connected at one end to a source of molten lead under pressure and at its other end to a restricted outlet which maintains the molten lead in the orifice slot under pressure and controls the rate of flow of the molten lead through the orifice slot. <IMAGE>

Description

SPECIFICATION Machine and method for continuously casting battery grids This invention relates to a battery grid casting machine and method, and, more particularly, to a machine and method for casting battery grids in a continuous manner.

At the present time battery grids are normally cast individually in molds having separable mold sections, the grid pattern cavity being machined as shallow grooves in the opposed faces of the mold sections. The mold faces in which the grid cavity is machined are periodically coated with a thin layer of powdered cork or acetylene smoke which acts as an insulator to prevent the lead from chilling before all of the grooves defining the grid pattern are completely filled. The production of individual battery grids in this manner is a relatively slow process and requires a considerable amount of skill on the part of the operator.

In recent years attempts have been made to cast battery grids in a more rapid, continuous manner utilizing a rotary drum having the desired battery grid pattern cavity machined into the outer peripheral surface of the drum.

Such continuous casting machines have presented numerous problems, especially with respect to the difficulty in obtaining complete filling of the shallow grooves forming the grid cavity with molten lead while rotating the drum at a reasonably rapid rate. Because of this and other problems encountered, continuous casting of battery grids with such drums has not enjoyed wide commercial use at the present time.

The primary object of the present invention is to provide a machine and method for casting battery grids in a continuous manner which overcomes the problems heretofore encountered with such methods and machines.

More specifically, it is an object of this invention to provide a machine and method for continuously casting battery grids which utilize a rotary drum having the grid cavity machined in the outer peripheral surface thereof and in which complete and rapid filling of the grid cavity is assured by directing the lead thereto under substantial pressure and in an amount greatly in excess of that required to fill the grid cavity as the drum rotates.

The machine of the present invention includes a shoe having a smooth arcuate surface conforming closely to the outer cylindrical surface of the drum. The shoe is held in fixed position against the outer periphery of the drum while the drum is rotating so as to provide a smooth sliding engagement therewith. An internal passageway in the shoe extends to the surface of the drum and is connected to a source of molten lead under pressure and the outlet is restricted by suitable means to maintain the molten metal flowing through the passageway under superatmospheric pressure. This arrangement produces several desirable advantages discussed hereinafter.

Other objects, features and advantages of the present invention will become apparent from the following description and accompanying drawings, in which: Figure 1 is a vertical sectional view of a battery grid casting machine according to the present invention taken on a plane transverse to the axis of rotation of the casting drum; Figure 2 is a plan view of a portion of the continuous battery grid strip cast in the machine; Figure 3 is a sectional view taken along the line 3-3 in Fig. 1; Figure 4 is a sectional view generally along the line 4-4 in Fig. 3; Figure 4a is an enlarged view of a portion of the arrangement shown in Fig. 4; Figure 5 is an enlarged sectional view of a portion of the machine shown in Fig. 1; Figure 6 is a fragmentary sectional view taken along the line 6-6 in Fig. 5; Figure 7 is a sectional view of a modified form of shoe on the machine;; Figure 8 is a sectional view taken along the line 8-8 in Fig. 7; and Figure 9 is a fragmentary side elevational view, partly in section, of another modification of the machine.

Referring first to Figs. 1 and 3, the machine comprises a supporting frame 10 by means of which it is mounted on the supporting structure 1 2 of a heated lead pot 14. Frame 10 can be of any suitable construction and, in the arrangement shown, includes a pair of spaced channels 1 6 supported at their opposite ends for vertical adjustment on upright threaded rods 1 8. A pair of pillow blocks 20 on channels 1 6 support a shaft 22 to which a casting drum 24 is keyed. A suitable drive 26 is connected to shaft 22 for rotating drum 24 at the desired speed. in the arrangement shown in Fig. 1 drum 24 is rotated in a counterclockwise direction.

A pair of support bars 28 is mounted on shaft 22 at opposite sides of drum 24 by means of pillow blocks 30. Each support bar 28 has one end thereof fixed to its adjacent channel 1 6 at a desired angle of inclination by a screw 32. A pair of laterally spaced guide bars 34 is mounted on support bars 28 by screws 36, 38 which enable the guide bars 34 to be adjusted toward and away from support bars 28. Between guide bars 34 there is mounted a shoe 40.

The desired pattern of the battery grid cavity 42 is machined in the smooth outer cylindrical surface of drum 24. This grid pattern comprises a plurality of circumferentially extending grooves 44 and a plurality of trans versely extending grooves 46. Grooves 44 are adapted to form the longitudinally extending wires 44a, 44b and the transverse grooves 46 are adapted to form the transverse wires 46a, 4627 of the finished grid shown in Fig. 2.

The wires 44b and 46b are normally wider than the wires 44a and 46a and form the outer framework of the finished grid. At one side of the grid the the groove 44 is enlarged to form the conventional solder lug 44e adja- cent one end of each grid. At each side thereof the grid cavity terminates inwardly from the side edges of drum 24 so that the laterally outer edge portions 48 of the drum 24 are in the form of smooth, continuous, cylindrical surfaces which lie in the same cylindrical surface as the areas of pads 48a bounded by grooves 44, 46. In the embodiment illustrated the drum 24 comprises a central web 50 with a cylindrical flange 52 extending around the periphery thereof. The grid cavity 42 is machined around the outer face of flange 52.

Shoe 40 is in the form of a block of metal having a smooth curved surface 54 which conforms closeiy to and which is in sliding engagement with the outer cylindrical surface portions 48, 48a of drum 24. A smooth sliding engagement between the curved surface 54 of shoe 40 and the outer peripheral surface of the drum 24 is obtained by the adjustment of screws 36, 38. In the embodiments illustrated in Figs. 1 to 6 and 9, shoe 40 has an inlet 56 at one side thereof and an outlet 58 at the opposite side thereof. An internal orifice slot 60 extending transversely across shoe 40 and open at the curved surface 54 thereof extends between inlet 56 and outlet 58. Orifice slot 60 is of smaller cross section than the inlet and the outlet and is connected thereto at its opposite ends by upwardly angled passageways 62.As shown in Fig. 6, the orifice slot 60 is co-extensive in a direction transversely of drum 24 with the grid cavity 42 therein. As shown in Fig. 3, a conduit 64 extends downwardly from inlet 56 into the molten lead in pot 1 4 and is connected with the outlet of a pump 66. A suitable drive shaft 68 extending upwardly from the pump is provided for driving the pump at the desired speed. A similar conduit 70 extends downwardly into the lead pot 14 from outlet 58 and discharges into the lead pot through a restricting valve 72, the amount of restriction provided by valve 72 being adjustable by control rod 74. Valve 72 allows adjustment of the rate of lead flow and back pressure in orifice slot 60.

The liquid level in lead pot 14 is designated by the broken line 76. It will be noted that the lower portion of drum 24 is spaced above the lead level 76 and that the shoe 40 is partially submerged within the lead in pot 14.

Shoe 40 is provided with a plurality of coolant passageways 78, each of which is located above the lead level 76. In the arrangement shown three such passageways 78 extend trnnsversely through shoe 40 downstream of orifice slot 60 and one such passageway 78 extends transversely through shoe 40 upstream of orifice slot 60. The upstream coolant passageway 78 is provided to prevent molten lead from flowing in a clockwise direction from orifice slot 60 and discharging from between the drum and the upstream end of shoe 40. The terms "upstream" and "downstream" are used with reference to the direction of rotation of drum 24. Passageways 78 are connected by suitable piping 80 for conducting coolant (such as water) through shoe 40. A thermocouple is also preferably located in shoe 40 within a thermocouple recess 82.

In operation drum 24 is rotated at a desired speed and pump 66 is operated to provide a continuous supply of molten lead alloy (for example, at 371 to 426"C (700-800"F)) to inlet 56. The interior of the drum flange 52 is preferably cooled by air nozzles 84 so that the casting surface of the drum will be maintained at a temperature (for exariple 204 to 260"C (400-500"F)) substantially below the solidification temperature of the alloy being cast.

Thus, the molten lead directed into the orifice slot 60 through inlet 56 from pump 66 is quickly chilled as it comes into contact with the surfaces 48, 48a and the grooves 44, 46 on the outer surface of drum 24. Since the drum is rotating in a counterclockwise direction, the lead which tends to solidify on the surfaces 48, 48a is scraped off of these surfaces by the downstream edge 86 of orifice slot 60 and tends to accumulate along this edge. However, since the molten lead directed through the orifice slot 60 by pump 66 is far in excess of that required to fill the adjacent portion of the rotating cavity, the continuous stream of lead flowing through orifice slot 60 is maintained at a relatively high temperature sufficient to melt, break-up or remove the solidified lead scraped from the surface of the drum. This rapid and continuous flow of high temperature molten lead through the orifice slot 60 thus prevents the solidified lead from building up along the edge 86 and thereby prevents clogging of the orifice slot 60. In addition, since valve 72 provides a restriction for the free flow of lead back to the lead pot through outlet 58, the lead in orifice slot 60 is maintained at a desirably high, superatmospheric pressure. This pressure is sufficient to continuously feed and force molten lead into the portions of grooves 44, 46 that have rotated upwardly past orifice slot 60. This assures a final and complete filling of the grooves 44, 46 even if the grooves have voids therein after they rotate past the orifice slot 60.Thus, the combination of the excessive lead flow and the superatmospheric pressure on the lead being directed into the grid cavity assures complete filling of the succes sive portions of the grid cavity while still maintaining a very rapid chill within the grooves. The rapid chill results in a very fine and uniform grain structure in the lead alloy.

This very fine grain structure is excellent in cast battery grids because of its resistance to corrosion.

As the filled portions of grooves 44, 46 rotate upwardly in a counterclockwise direction they advance along the portion of shoe 40 cooled by the coolant passageways 78 on the downstream side of orifice slot 60. Thus, the temperature of the lead in these grooves is progressively lowered such that, as it emerges from the downstream end of the shoe, the lead has solidified into a continuous strip having the battery grid pattern. The strip S is preferably stripped from the top side of the drum so that it will have cooled to a sufficiently low temperature to assume a sufficiently rigid condition to permit easy handling. The grid strip is cooled substantially after it emerges from between the shoe and drum by the nozzles 84 which direct streams of air against the interior and exterior surfaces of flange 52 as these surfaces rotate past the shoe and before the grid is stripped therefrom.Thereafter, strip S is advanced to a die (not illustrated) which shears it into individual battery grids.

In a typical machine according to the present invention the drum has a diameter of about 45.7 cm (18 inches,) a width of about 8.2 cm (3-1/4 inches) and is rotated at about 20 R.P.M. to produce a lineal speed of 28.6m (94 feet) per minute. The battery grids are cast from a lead alloy containing about .09% Ca and .3% Sn and have a length of (13.2 cm 5-1/2 inches), a width of 5 cm (2 inches) and a thickness of 0.89 cm (.035 inches). Each grid weighs about 18 grams and the grid strip weighs about 0.124 kg/m (.085 pounds per foot). At a lineal speed of 28.6m (94 feet) per minute the grid strip uses about 3.6kg (8 pounds) of alloy per minute.

Pump 66 has a capacity of about 20.4kg (45 pounds) per minute and can be operated at full capacity or its inlet can be adjusted so that the pump delivers somewhat less than its full capacity depending upon the setting of restrictor valve 72. The shoe 40 has a length of about 10.2 cms (4 inches) and a width of about 8.25 cm (3-1/4 inches). The orifice slot 60 has a width of about 0.95 cm (3/8 inches) a depth of about 0.8cm (5/16 inches) and is located about 2.54cm (1 inch) from the upstream end of the shoe.

The lead pot is heated to a temperature of between 396 to 426"C (750t to 800"F).

With cooling water at about 216C (70"F). and the air nozzles as shown, the temperature of the shoe stabilizes at about 301"C (575'F) and at the outer surface of the drum at about 232at (450to) While these relative dimensions and other parameters are given by way of example and are not critical, several basic considerations are important. For example, it is very important to maintain a close sliding fit between the curved surface 54 of the shoe 40 and the outer preipheral surface of the drum.Since the temperature of the shoe differs substantially from the temperature of the drum and since the temperatures of each vary somewhat at different sections thereof, the length of shoe 40 should be maintained at a minimum consistent with relatively fast solidification of the grid strip in order to assure close sliding contact between them. Furthermore, a longer shoe requires the application of a greater clamping force to the drum to obtain the proper close fit therebetween and results in excessive friction. A relatively narrow orifice slot is also desirable to prevent the temperature of the drum from becoming excessively high at the section thereof contacting the shoe.Furthermore, it is important that the upstream end of the shoe and the portion of the drum in contact therewith be maintained at temperatures sufficiently low to prevent the pressurized molten lead from leaking out therebetween. The amount of molten lead delivered by the pump must be sufficiently in excess of the amount required to fill the grid cavity to maintain the temperature of the lead in the orifice slot sufficiently high to melt and wash away the lead that solidifies against the outer smooth surface portions of the drum. In addition, the pressure on the molten lead in the orifice slot must be sufficiently high to force the lead up into any voids or past any lead blockages that might occur in the cavity grooves 44, 46 as they rotate upwardly past the orifice slot.

The shoe 88 shown in Figs. 7 and 8 differs only slightly from shoe 40 previously described. In shoe 88 two molten lead passageways 90, 92 extend transversely through the shoe. At one end these passageways are plugged. At the opposite end one of these passageways is connected to an inlet pipe extending from pump 66 and the other passageway is connected to an outlet pipe extending to the restriction valve 72. At the curved surface 94 of the shoe 88 an orifice slot 96 similar to orifice slot 60 is machined. However, orifice slot 96 is closed at its opposite ends. A plurality of two sets of oppositely inclined passageways 98, 100 extend, respectively, from passageways 90, 92 to the orifice slot 96.Thus, referring to Fig. 8 and assuming that passageway 90 is the inlet passageway and passageway 92 is the outlet passageway, the molten lead is directed as a continuous stream which flows upwardly through the inclined passageways 98 into the orifice slot 96 and then downwardly from orifice slot 96 into the discharge passageway 92 and back to the lead pot through the restriction valve 72. It will be observed that, whether the lead passageways through the shoe are formed in the manner illustrated in Figs. 1 through 6 or in the manner illustrated in Figs.

7 and 8, the orifice slot is connected in series relation with the inlet and the outlet of the lead recirculation path. Thus, the hot molten lead continuously recirculates throughout the entire length of the orifice slot. This constant flow of molten lead at high temperature and superatmospheric pressure prevents excessive chilling and lead build up on the localized surfaces of the drum against which the molten lead is directed. It also insures that the solidified lead scraped off the drum by the downstream edge of the orifice slot will be melted, broken up or otherwise removed to prevent clogging of the orifice slot and imcomplete filling of the grooves forming the battery grid cavity.

The arrangement shown in Fig. 9 differs from that shown in Fig. 1 in that the shoe 40a is located at the top side of drum 24 rather than at the bottom side thereof. When the shoe is located so that it is not partially submerged in the molten lead in pot 14, the temperature thereof is maintained at the relatively high value required by means of auxiliary heaters 102. In other respects the construction and operation of the modification shown in Fig. 9 are substantially the same as in the embodiments previously described.

In each of the embodiments illustrated it will be noted that the drum is located out of contact with the molten lead in the lead pot.

This is desirable not only from the standpoint of maintaining the drum at a desirably low temperature to produce rapid solidication, but also because, if the drum is wetted by the lead bath, oxides and other contaminants form, collect or build up on the outer peripheral surface of the drum. It will also be noted that the lead flows between the lead pot and the orifice slot in the completely closed path.

This substantially completely eliminates the tendency for the formation and entrainment of oxide films and particles in the molten metal being cast.

Claims (11)

1. A machine for continuously casting battery grids comprising a rotary drum having a cylindrical outer surface, means for rotating the drum in one direction at a predetermined speed, said outer surface having a cavity recessed therein which conforms to the desired battery grid pattern, a fixedly supported shoe having an arcuate surface thereon extending around a relatively short arcuate segment of the outer cylindrical surface of the drum in close fitting sliding relation, said shoe having a passageway therein for molten lead, a portion of said passageway comprising an orifice slot extending directly to and transversely of said arcuate surface and communicating with a segment of the peripheral surface of the drum across substantially the full width of the grid cavity, a pot for molten lead, means for directing molten lead from said pot to said passageway in an amount substantially in excess of that required to progressively fill the grid cavity as the drum rotates past the orifice slot, means for directing the excess lead from the passageway back to the lead pot, means for maintaining the molten lead in the orifice slot at superatmospheric pressure to insure complete filling of the grid cavity, means for maintaining the outer peripheral surface of the drum at a temperature sufficiently below the melting temperature of the lead so that a portion of the lead tends to solidify against the periphery of the rotating drum within the circumferential extent of the orifice slot, the downstream side of the orifice slot being defined by a transversely extending edge adapted to scrape the solidified lead from the outermost surface of the drum and means for causing the molten lead to flow through the orifice slot at a sufficiently high velocity to at least partially remelt and wash away the lead accumulating at said downstream edge of the slot for return to the lead pot.

2. A machine as called for in claim 1 wherein said means for maintaining the lead in the orifice slot at superatmospheric pressure comprises flow restricting means for preventing free flow of the lead from the orifice slot back to the lead pot.

3. A machine as called for in claim 1 or 2 wherein both the drum and the shoe are located such as to be out of physical contact with the lead in the lead pot and means for maintaining the shoe at a selected elevated temperature to maintain the lead in the orifice slot at casting temperature and means maintaining the peripheral surface of the rotating drum at a sufficient low temperature to promote complete solidification of the lead in the portion of the grid cavity extending between the downstream edge of the orifice slot and the downstream end of the shoe.

4. A machine is called for in claim 1, 2 or 3 wherein said passageway has an inlet and an outlet connected in series relation with said orifice slot to assure a continuous flow of molten lead throughout the length of the orifice slot.

5. A machine as called for in any of the claims 1 to 4 wherein the orifice slot extends transversely of the shoe at a location closer to the upstream end of the shoe than the downstream end of the shoe.

6. A machine as called for in claim 5 including means for cooling the upstream end portion of the shoe to prevent egress of lead from between the drum and the upstream end of the shoe and means for cooling the downstream end portion of the shoe to a greater extent than the upstream end portion of the shoe.

7. A machine as called for in any of claims 1 to 6 wherein said passageway has an inlet and an outlet located on opposite sides of said orifice slot and spaced radially outwardly therefrom, said inlet being connected to the orifice slot by a radially inwardly inclined passageway section and said outlet being connected to the orifice slot by a radially outwardly inclined passageway section so that the molten lead flows into the orifice slot in a direction towards the periphery of the drum and flows out of the orifice slot in a direction away from the periphery of the drum.

8. A method of continuously casting battery grids around a rotating cylindrical drum having a grid cavity recessed into the outer peripheral surface thereof by directing molten lead from a lead pot to successive segments of the peripheral surface of the rotating drum through an orifice slot in a fixed shoe having a relatively short, circumferentially extending, curved surface conforming to and positioned against the periphery of the drum in close sliding engagement, said slot extending transversely across substantially the entire width of the grid cavity directly adjacent the periphery of the drum, which method includes the steps of continuously directing molten lead through said shoe to said orifice slot and into the portion of the grid cavity rotating past the slot in an amount substantially in excess of that required to fill said portion of the cavity; maintaining the lead in said slot at superatmospheric pressure to ensure complete filling of the grid cavity; controlling the temperature of the drum so that a portion of the lead tends to solidify against the periphery of the rotating drum within the circumferential extent of the orifice slot; causing the downstream edge of the slot to scrape the solidified lead from the outermost surface of the drum; causing the excess molten lead to flow back to the lead pot; and directing the molten lead through the slot at a sufficiently high velocity to at least partially remelt and wash away the lead accumulating at the downstream edge of the slot.

9. The method called for in claim 8 wherein said lead in said slot is maintained at superatmospheric pressure by restricting the free flow thereof back to the lead pot.

10. The method called for in claim 8 or 9 including the step of cooling the drum to a sufficient low temperature to ensure rapid and complete solidification of the battery grid as it emerges from the downstream end of the shoe.

11. The method called for in claim 8, 9 or 10 wherein the drum and shoe are maintained out of physical contact with the lead in the lead pot.

1 2. The method called for in claim 11 wherein the orifice slot is located circumferentially between the upstream and the downstream ends of the shoe, the method including the step of cooling the shoe on both the upstream and the downstream side of the orifice slot, the shoe being cooled on the downstream side of the orifice slot to a greater extent than on the upstream side thereof.

1 3. A machine for continuously casting battery grids, substantially as hereinbefore described with reference to Figs. 1 to 6 or to Figs. 7 and 8 or to Fig. 9 of the accompanying drawings.

1 4. A method for continuously casting battery grids, substantially as hereinbefore described with reference to Figs. 1 to 6 or to Figs. 7 and 8 or to Fig. 9 of the accompanying drawings.

1 5. A battery grid whenever produced by the machine as claimed in any of claims 1 to 7 and 1 3 or by the method as claimed in any of claims 8 to 12 and 14.