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IN VIEW OF THE SEVERAL LEAD ALLOYS BEING USED OR CONSIDERED FOR BATTERY GRID CASTING, THE FOLLOWING GENERAL INFORMATION MAY BE OF INTEREST.
Approximate operating temperatures for some example lead alloys.
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Calcium Alloys |
Antimony Alloys |
| Lead Pot |
Pb-Ca-Sn
°F750/800
°C399/428 |
Pb-Ca-Al
°F900/950
°C482/510 |
Pb-4.5% Sb
°F750
°C399 |
Pb-2.75% Sb
Pb-1.8% Sb
°F850/900
°C454/482 |
| Feedline |
°F900/950
°C482/510 |
°F900/950
°C482/510 |
°F900
°C482 |
°F900/950
°C482/510 |
| Ladle |
°F900/1000
°C482/538 |
°F900/1000
°C482/538 |
°F900/950
°C482/510 |
°F900/1000
°C482/538 |
| Mold-Gate |
°F390/440
°C199/227 |
°F310/340
°C154/171 |
°F300/330
°C149/171 |
°F300/340
°C149/171 |
| Upper Zone |
°F400/450
°C204/232 |
Not Required |
Not Required |
Not Required |
| Lower Zone |
°F400/450
°C204/232 |
°F380/400
°C193/204 |
°F340/380
°C171/193 |
°F380/400
°C193/204 |
| Mold Coolant |
Oil |
Water |
Water |
Water |
NOTES ON CASTING Pb-Ca-Sn
More mold knockout pins are required to eject the softer grid out of the mold.
The grid wire shape and size varies by customer requirements.
More cork is generally required because of the higher temperatures the mold is operated at. We recommend Wirtz W-10, X500 or combination of both for improved insulating and adhesion characteristics under the higher temperature conditions.
Grid production expected from Wirtz casters operating with lead calcium is in the vicinity of 30,000 grids per operator per shift on a three machine set up.
Oil rather than water cooling of the mold is necessary because of the higher mold temperatures.
Cork or mold life varies greatly with the multitude of operational conditions. Generally with Wirtz Mold Coat materials cork life can be up to 8 hours between complete corking, with touch ups each 2 to 3 hours of operation.
Essentially the same operating speeds can be maintained when casting lead calcium as lead antimony on Wirtz casting machines.
Heating and cooling of the mold is generally more critical.
Proper mold venting is essential for calcium casting.
GENERAL NOTES
Practical casting speeds for the alloys listed above are approximately 14 to 18 panels per minute. As the antimony content is decreased, grid cracks are less of a problem, allowing potentially faster casting speeds. However, with less antimony the grids get softer and require more delicate handling through the casting operations.
With proper equipment and casting procedures, all the noted alloys can be cast at approximately the same production rates. However, as the antimony is decreased, casting procedures are more critical and require better discipline.
As antimony is decreased the specific gravity of an alloy increases. Therefore if different alloys are cast in the same grid mold, the grid weights will increase slightly unless a change is made in the mold to compensate (such as more cork in the wires). Grid weights for calcium alloys compared to antimony and low antimony alloys are approximately the same depending on grid design.
As antimony is decreased the casting temperatures of the lead, mold and mold coolant will increase become more critical. Mold venting is more critical as antimony is decreased.
Usually low antimony alloys (1.8% or 2.75%) can be run on molds designed for 4-1/2% antimony. Generally molds designed for 4-1/2% antimony can not be run on calcium.
MOLD COATING
As the amount of antimony is decreased corking technique is more critical and the amount of cork allowance also increases. Essentially the corking procedure can be the same for all alloys, with variations in the amount of cork necessary and the type of cork being used.
CASTING STRONTIUM LEAD ALLOYS
Strontium alloys have better castability and are not as soft coming out of the mold compared to calcium alloys. They have less tendency to dross and are more stable than calcium alloys (normally do not require alloy additions to the melting pot).
However, strontium must be kept above 900°F (482°C) at all times during casting. Special design lead pumps are required when using this alloy.
RECENT CHANGES IN WIRTZ GRID CASTING
New Style Electric Feedlines - eliminate hot and cold spots in the lines and provide easier maintenance.
Improved Lead Valve -less susceptible to dross problems and plugging.
Improved Lead Pumps - to meet the requirements of higher operating temperatures and corrosive alloys.
Improved Grid Handling - through the grid casting operation transfer and trim die. Addition of die exit roller assembly.
New Industrial Calcium Caster - for industrial negative grids: actual production casting rates of "18 plus" casts per minute on grids - 180 thick x 17" long, are being achieved. (Approximately 6,000 trimmed grids per 8 hour shift per machine). Casting temperatures are about the same as for automotive calcium grid casting, but ladle temperatures are lower, approximately 800°/850°F (428°/454°C).
Improved Grid Mold Technology - for better castability and ejection of softer alloys.
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