Fire Safety for Magnesium Processing and Finishing Operations

1. NADCA North American Die Casting Association Fire Safety for Magnesium Processing and Finishing Operations Unit 4

2. Enabling Objectives • After completing this section of the course students should be able to: • Discuss magnesium melting and casting operations and the precaution for carrying out these operations safely. Explain procedures for fire and explosion prevention for melting and casting, heat treating, machining and finishing, dust collection, cleaning procedures, electrical equipment, personal protective equipment, spark producing operations, grinding wheels, stamping and drawing, fugitive dust, vacuums, storage and fire prevention

3. Magnesium!

4. Magnesium Melting & Casting • Buildings non-combustible • Melt rooms access to fire control • Floors free of moisture & standing water • Storage below magnesium no depressions where H2O could accumulate Pouring magnesium castings

5. Magnesium Melting & Casting • Solid metals thoroughly dried by pre-heating > 250°F or higher if impurities are present • Fuel supply lines to melt pots remote shutoffs Ovens for preheating ingots

6. Magnesium Melting & Casting • Turnings, powders etc. can ignite at lower temperatures than the solid metal and should be avoided • Keep solid magnesium free of dust, grindings and swarf

7. Magnesium Melting & Casting • Concrete always contains water! • Contact with molten magnesium and concrete will cause a violent explosion!

8. Magnesium Melting & Casting • Keep the furnace and the surrounding area free of moisture and iron oxide in the event of a runout Area around the furnace is kept clean and dry

9. Magnesium Melting & Casting • Molten magnesium systems to have 110% secondary containment of largest expected failure • Install barriers or shields to prevent contact with incompatible materials • Iron scale and magnesium possible thermite reaction

10. Magnesium Melting & Casting • Crucible interiors and covers free of iron oxide scale to avoid thermite reaction • Inspect crucibles and melting pots regularly! • Use of protective atmospheres can cause formation of iron scale above

11. Crucible Maintenance • Repair or discard damaged crucibles • Preheat ladles, skimmers & sludge pans and molds • Vigilant for avoiding spilling magnesium

12. Crucible Maintenance • FR clothing & no pockets or cuffs • Foundry boots • Safety glasses and faceshields when handling molten magnesium Shields over metatarsals

13. Magnesium Melting & Casting • Practice Quiz • 1. Where the melting of magnesium takes place: • A. There should be no standing water on the floor. • B. There should be no depressions under the magnesium where water could collect. • C. Buildings should be non-combustible construction. • D. All of the above

14. Magnesium Melting & Casting • Practice Quiz • 2. Concrete always contains water, therefore contact with molten magnesium and concrete will likely cause: • A. A housekeeping problem • B. A violent explosion • C. A minor nuisance • D. None of the above

15. Magnesium Melting & Casting • Practice Quiz • 3. Damaged crucibles can create a safety hazard, crucibles should therefore: • A. Be inspected for damage regularly • B. If damaged, be discarded or repaired • C. Used until there is a definite problem • D. Only choices A & B above.

16. Magnesium Melting & Casting • Practice Quiz • 1. Where the melting of magnesium takes place: • A. There should be no standing water on the floor. • B. There should be no depressions under the magnesium where water could collect. • C. Buildings should be non-combustible construction. • D. All of the above

17. Magnesium Melting & Casting • Practice Quiz • 2. Concrete always contains water, therefore contact with molten magnesium and concrete will likely cause: • A. A housekeeping problem • B. A violent explosion • C. A minor nuisance • D. None of the above

18. Magnesium Melting & Casting • Practice Quiz • 3. Damaged crucibles can create a safety hazard, crucibles should therefore: • A. Be inspected for damage regularly • B. If damaged, be discarded or repaired • C. Used until there is a definite problem • D. Only choices A & B above.

19. Magnesium Heat Treating • sulfur dioxide (SO2) • sulfur hexafluoride with carbon dioxide (SF6/CO2) • helium (He) • argon (Ar) • Poses fire risks! • In furnaces > 750°F use a special atmosphere inside the furnace to retard the ignition of magnesium • Procedure needed to check for furnace hot spots, check prior to the heat and at regular intervals

20. Magnesium Heat Treating • Combustion safety controls • One set maintains operating temperature • High set control to shut fuel or power if max op temp is exceeded even by a small amount!

21. Magnesium Heat Treating • Only clean parts free of swarf & turnings placed in furnace! • No combustible or aluminum separators or any other Al in furnace load of Mg • Furnaces for Mg cleaned as necessary to remove any accumulation of iron oxide scale

22. Magnesium Heat Treating • When heat treating it is critical to identify Al containing Mg alloys • Aluminum and magnesium can form a eutectic alloy which can cause furnace fires! • Same effect if Al contact Mg at elevated temperatures • Use alloy manufacturer heat treating specifications

23. Magnesium Heat Treating • Ensure magnesium alloys are never immersed into salts used for aluminum • Mg in nitrate salt baths may cause an explosion! • Mg and Al parts easily distinguished • Magnesium and aluminum together forms an alloy which has a lower melting and auto-ignition temperature of either parent metal + =

24. Magnesium Heat Treating Practice Quiz 1. Heat treating of magnesium: A. Poses potential fire risks B. Should be done using a special atmosphere that retards ignition of magnesium C. Include procedures to check the furnace for undesirable hot spots. D. All of the above

25. Magnesium Heat Treating • Practice Quiz • 2. A second set of temperature controls on magnesium heat treating furnaces is needed because: • A. The first set of controls may fail. • B. To shut down the furnace if the maximum operating temperature is exceeded. • C. For convenience and to speed heating treating.

26. Magnesium Heat Treating • Practice Quiz • 3. Nitrate salt baths if used for magnesium: • A. Will likely cause an explosion. • B. Is the preferred solution. • C. Is sometimes use to reduce processing time.

27. Magnesium Heat Treating • Practice Quiz • 1. Heat treating of magnesium: • A. Poses potential fire risks • B. Should be done using a special atmosphere that retards ignition of magnesium • C. Include procedures to check the furnace for undesirable hot spots. • D. All of the above

28. Magnesium Heat Treating • Practice Quiz • 2. A second set of temperature controls on magnesium heat treating furnaces is needed because: • A. The first set of controls may fail. • B. To shut down the furnace if the maximum operating temperature is exceeded. • C. For convenience and to speed heating treating.

29. Magnesium Heat Treating • Practice Quiz • 3. Nitrate salt baths if used for magnesium: • A. Will likely cause an explosion. • B. Is the preferred solution. • C. Is sometimes use to reduce processing time.

30. Machining, Finishing & Fabricating Magnesium • Cutting tools must not ride on the metal without cutting – frictional heat can ignite the fines! • Back the tool off as soon as the cut is finished • Cutting tools kept sharp, ground with sufficient clearance • Drilling holes > 5X diameter of drill, use high helix bits (45°) to prevent packing

31. Machining, Finishing & Fabricating Magnesium • Use only high flash tapping fluid • Don’t use water, water soluble oils and oils > 0.2% fatty acids (hydrogen gas hazard) • Use water-oil emulsion fluids that inhibit hydrogen gas formation

32. Machining, Finishing & Fabricating Magnesium • Machines provided with pan to catch turnings and chips • Pan designed to be pulled out quickly in case of fire • Pan arranged so fire can be quickly extinguished

33. Machining, Finishing & Fabricating Magnesium • Machine to keep chip size large • Maintain good housekeeping around magnesium machining operations • Remove chips regularly • Avoid accumulation of more than 3 lbs of chips • Chips stored in covered containers

34. Magnesium Machining & Finishing • Practice Quiz • 1. Machine magnesium so as to keep the size of chips generated: • A. A consistent size. • B. Large. • C. Small to reduce scrap volume.

35. Magnesium Machining & Finishing • Practice Quiz • 2. Tapping fluids for magnesium must be approved for use with magnesium and: • A. Prevent the formation of explosive hydrogen gas. • B. Have a very low flash point. • C. Have a high concentration of fatty acids.

36. Magnesium Machining & Finishing • Practice Quiz • 3. Machines that produce chips and turnings should be provided with a catch pan that: • A. Will catch the chips and turnings. • B. Can be removed quickly in case of fire. • C. Is arranged so the fire can be put out quickly. • D. All of the above.

37. Magnesium Machining & Finishing • Practice Quiz • 1. Machine magnesium so as to keep the size of chips generated: • A. A consistent size. • B. Large. • C. Small to reduce scrap volume.

38. Magnesium Machining & Finishing • Practice Quiz • 2. Tapping fluids for magnesium must be approved for use with magnesium and: • A. Prevent the formation of explosive hydrogen gas. • B. Have a very low flash point. • C. Have a high concentration of fatty acids.

39. Magnesium Machining & Finishing • Practice Quiz • 3. Machines that produce chips and turnings should be provided with a catch pan that: • A. Will catch the chips and turnings. • B. Can be removed quickly in case of fire. • C. Is arranged so the fire can be put out quickly. • D. All of the above.

40. Dust Collection for Magnesium Operations • Machines fitted with enclosures or hoods to capture dust produced • Use wet-type collectors or cyclone collector located outdoors • Do not use bag-type collectors for magnesium

41. Wet-Type Collectors • Any hydrogen generated from contact with water must be properly vented • Remove sludge from the tank if the collector will be inoperable for longer than a day • Use a secondary blower to ensure venting of the sludge tank whenever the main exhaust is not on

42. Wet-Type Collectors • Use good collector housekeeping! • Sludge build up in the collection tank should not exceed 1/20 of the tank capacity • Remove sludge whenever the collector will be shut down for extended periods greater that a day. • Wet collectors must be dedicated to the collection of magnesium type materials only • Aluminum especially containing copper is incompatible

43. Cyclone Dust Collectors • Locate collectors outdoors! • Vent exhaust outside to a safe location • Do not recycle air back into the building

44. Dust Collection for Magnesium Operations • All components of the dust collector should be conductive and the system should be bonded and grounded • Ensure no water can leak into the collector

45. Dust Collection for Magnesium Operations • Separate the collector from the machines that feed it with duct that is at least 15 feet long • Explosion venting can be used on cyclone dust collectors • Vent away from personnel and other equipment

46. Cyclone Dust Collection for Magnesium Operations • Air movement should be such to keep the concentration of magnesium dust below ¼ of the minimum explosive concentration for machines feeding a cyclone dust collection system • Fast air movement helps keep concentration of dust at safe levels …FAST!! KEEP AIR MOVEMENT

47. Cyclone Dust Collection for Magnesium Operations • Keep duct tubes as short as possible • Eliminate any unnecessary bends in ductwork • No dead end section or unused caps where dust can accumulate • Interlocked equipment power supply with exhaust blower Explosion venting in short duct run

48. Dust Collectors • Practice Quiz • 1. Wet dust collectors must be. • A. Vented to prevent the accumulation of hydrogen gas. • B. Located outdoors. • C. Fitted with duct runs that incorporate bends.

49. Dust Collectors • Practice Quiz • 2. Insufficient air movement in a dust collection system could cause: • A. A high concentration of dust that approaches the minimum explosive concentration. • B. Helps keep the concentration of dust below ¼ of the explosive range. • C. Will prevent dust from collecting in ducts.

50. Dust Collectors • Practice Quiz • 3. For cyclone dust collectors: • A. Keep the duct runs as short as possible. • B. Eliminate unnecessary bends in the ductwork. • C. Eliminate dead ends and unused caps. • D. Interlock the collector to the machines that feed into it. • E. All of the above.