Oxide and Grid Processing » Grid Production and Parts Casting

Grid production machine
Grid production machine

Grid production and parts casting involves book casting, continuous casting, and strip casting. In all of these processes, lead pigs are melted down and the molten lead is poured into molds or continuously cast into grids, strips, or parts. Expanded metal grid production involves mechanical operations on the cast strip and is not a source of airborne lead dust or oxide. The major source of lead exposure in this process is from lead fumes and lead oxide which can become easily airborne.

Figure 1. Lead pot enclosure

Potential Sources of Exposure

  • Drossing the lead pot may increase lead exposure.

  • High levels of lead fumes are generated when a flame is put in contact with lead, such as when cutting out frozen pots.

  • Settled lead dust on surfaces and equipment may become airborne due to exhaust from fuel-powered fork-lifts or vehicular traffic.

  • High exposure to lead fumes can occur when the pig is loaded into the lead pot.

  • Airborne lead dust can migrate from other areas of the plant depending on the plant layout.

  • Separator boards may become contaminated by using lead contaminated pallets that have not been cleaned after being returned from the pasting line.

  • Dust may become airborne as a result of using a rotary sander for cleaning molds.

  • Oxide that has collected on the dross ladle may become airborne while cleaning or storing it in an area outside the hood.

Figure 2. Continuous grid casting machine

Possible Engineering Controls

  • Develop a system to minimize the formation of dross.

  • Place a local exhaust ventilation on the lead melting pot and the dross pot (Figures 1, 2, and 3).
  • Dross with a ladle with holes in it to allow lead to drain back into the pot.

  • Install Laminar Flow (Supplied Air) Islands at the drossing station if exposures exceed the PEL.

  • Provide local slot ventilation or a ventilated torch for cutting out frozen pots.
  • Suspend plastic curtains to separate the casting areas from the traffic areas.

  • Isolate the lead pots from casting operations.

Figure 3. Ventilated and automated lead pot

Possible Work Practice Controls

  • Handle dross carefully within a ventilated enclosure.

  • Keep the doors closed on the dross cabinets when drossing into the containers.

  • Keep the dross covered where air turbulence may cause powdery dross to become airborne.

  • Cool waste drums under exhaust ventilation.

  • Enclose cooled waste drums with a plastic bag prior to storage (Figure 3).

  • Do not add sawdust to the dross.

  • Keep dross from calcium and antimonial alloys separate and dry since arsine and stibine gases could be emitted.

  • Slide pigs into the casting pots, where feasible.

  • Use a long-handled push rod or mechanical system to feed the pigs into the pot.

  • Use separate pallets for grid storage and pasted plate storage (Figure 4).

  • Provide adequate PPE, change of clothes, and shower rooms (see OSHA Lead Requirements for PPE, Housekeeping, and Hygiene Facilities).

  • Maintenance:
    • Ensure ventilation is working properly.

    • Use electric powered fork lifts.

    • Use an automatic conveyance system.

    • Avoid using a rotary sander to clean molds.

  • Housekeeping:
    • Use dust suppression techniques, such as, using dust suppression compounds or vacuuming.

    • Keep the floor areas and work surfaces around the lead pots and lead storage areas free of oxide dust.

    • Scrape metal splashes with a shovel or long-handled scraper.

Figure 4. Waste drum under exhaust ventilation
Figure 5. Lead-contaminated separator boards