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MAINTENANCE FREE AUTOMOTIVE BATTERY GRID CASTING
(Using Lead-Calcium Alloys)
IMPORTANT FEATURES TO CONSIDER WHEN CASTING CALCIUM LEAD ALLOYS
- Control Drossing
- Control Calcium Loss
- Control Casting Temperatures
- Careful Handling of Grids
- Provide Suitable System of Equipment Layout
- Antimony and Calcium Alloys Must Not Be Mixed
CONTROL CASTING TEMPERATURES
Because of the different melting and solidifying temperatures (as noted below) the Ca alloy must be poured at a higher temperature, and the mold temperature must be kept higher to keep it from solidifying before the cast is complete.
5% Sb Lead Alloy |
.1 Ca - 1.0 Sn Lead Alloy |
Solid at approx. 480°F (249°C) |
Solid at approx. 619°F (326.1°C) |
Melts at approx. 540°F (282°C) |
Melts at approx. 620°F (326.7°C) |
Heat Controls Are Important
Furnace temperatures should be (approximately 750°F / 399°C).
Ladle pouring temperature is controlled (approx. 900°F / 482°C) and ladle is covered and gas shielded to reduce drossing.
Molds are heated with four electric heaters top and bottom (two on each half) with mold temperatures about 400°F (204°C).
With higher mold temperatures cooling oil is used in the C.C.S. re-circulating cooling system instead of water for gate cooling at 300°F (149°
C) to 350°
F (177°
C). Center cooling must also be used.
Four grid ejectors are used in the gate, four in the middle and four at the bottom.
Trim foot locators are strengthened.
Cork allowance is usually a little higher.
CONTROL OF LEAD CALCIUM ALLOY
Control Drossing |
By keeping agitation to a minimum. |
Recommendations |
Shielded low RPM pump. No open flow from dispense system.
Shielded dispense ladle.
Gravity feed system.
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Control Calcium Losses |
Re-melting scrap (.02% to .03% calcium loss). Adding pigs (.01% to .02% calcium loss).
Surface loss (.005% to .01% calcium loss in 8 hours).
Solidifying and re-melting furnace (.033% calcium loss). |
Recommendations |
Return the scrap to the furnace. Add pre-alloyed pigs, to hold constant level.
Dross the pot at constant intervals (once each shift).
Add calcium rich alloy at constant intervals as determined below.
Check calcium level in pot at constant intervals as described below.
Establish a routine program of control.
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EXAMPLE Basis of |
Three machines to one 7500# Furnace. Casting speed of 15/minute. Average weight of double grid including gate, etc., equals .6 lbs.
Amount of lead cast per hour = 15 x .6 lbs. x 3 machines x 60 minutes = 1620#.
Average scrap weight is established at 150g per panel.
Average scrap returned to furnace per hour equals  x 15/minute x 3 machines x 60 minutes =
900#/hr.
Average grid weight per panel is established at 120g.
Average grid metal to be replaced in pot equals
 x 15 minute x 3 machines x 60 minute =720#/hr.
Fill lead pot, heat to 780°F., hand stir and dross surface. Check calcium level and add calcium rich alloy until pot checks .1 calcium
When operating estimated calcium loss will be as follows:
Pot  = .045 lbs. loss.
Re-melt scrap 900 lbs. x .0002 = .225 lbs. loss.
Figure no loss from pigs since they are usually above .10 Calcium . Total estimated loss = .270 lbs. Calcium/Hr.
Therefore start by counting the number of pigs added to pot. For each 7 pigs of 100 lbs. each you have added 700 lbs. of lead and can expect the calcium loss to be approximately .27 lbs.
Therefore add one 25 lbs. pig of calcium rich (25 x .01 = .25 lbs. calcium) for each 7 pigs added. Check pot every 4 hours and adjust calcium rich pigs up or down (one each 6 pigs or one each 8 pigs) to suit. Once control is established check pot each 8 hours. If any change is made in procedure, such as changing number of times drossed per shift or large amounts of grids re-melted or pot is solidified, the calcium loss will change and the pot should be re-checked and re-alloyed. |
CAREFUL HANDLING OF GRIDS
The grids as they are ejected from the mold are soft and must be handled gently and reliably until they have achieved a short term age hardening. (2 to 3 days)
The grid handling system incorporates a gentle transfer from the mold through feed rollers, that flatten, and with air cooling pipes, cools and blows off lead drips that may be adhering to the grid.
The patented die entry plate in addition to gently and accurately transferring the grid to the trim die is water cooled.
The trim die is cooled top and bottom and is designed to precisely trim the still soft grid.
The transfer mechanism to the hardened and chrome plated stacker rails completes the precision, gentle handling system.
From the stacker rails, the cooled grids have hardened sufficiently for removal to subsequent operations.
SUITABLE SYSTEM OF EQUIPMENT LAYOUT
Grid Casting Machines, may be set up to lead melting furnaces in many combinations to suit particular production requirements.
Examples of Production
One man can run 2 machines (including the furnace).
Production should be 18 to 20,000 grids per shift.
One man can run 3 machines (not including furnace).
Production should be 25 to 30,000 grids per shift.
One man can run 4 machines under some circumstances (not including furnace).
Examples of Layouts
With trim scrap returned to the furnace (preferred) or re-melted in a separate furnace.
With furnace elevated for gravity feed or on the floor for pump feed.
With 1, 2, 3, or more grid casters set up to one furnace.
See Illustrations Attached
With Wirtz equipment designed to recognize and control the important features of Lead-Calcium alloys, and suitable equipment layouts, high casting rates can be realized, with corresponding competitive costs with other alloys.
Wirtz Manufacturing Company can supply complete casting systems, provide technical assistance for installation, start up and operator training.
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