T.O. 1-1A-9
c.
Machine the metal dry whenever possible, avoiding fine feeds and keeping speeds below 500-700 surface feet
per minute during turning and boring. If a coolant is definitely required use a mineral oil.
d.
Keep work areas clean.
e. Store magnesium chips in clean, plainly labeled covered, non-combustible containers where they will remain
dry. Do not allow chips to accumulate on machines or operator's clothing. Machinists should not wear texture or fuzzy
clothing and chips and sawdust not be allowed to accumulate in cuffs or pockets.
f.
Do not permit tools to rub on the work after a cut has been made.
g.
Keep an adequate supply of a recommended magnesium fir extinguisher within reach of the operators. If chips
should become ignited, extinguish them as follow:
WARNING
Water or any of the common liquid or foam type extinguishers will intensify magnesium chip
fire and may cause an explosion and shall not be used.
(1)
Cover with a layer of G-1 or Met-L-X powder. Clean, dry unrusted cast iron chips, graphite powder clean
dry sand, talc and pitch may also be use
(2)
Actively burning fires on combustible surfaces should be covered with a 1/2 inch layer or more of
extinguishing powder; then the entire mass shoveled into a iron container or onto a piece of iron plate. Alternately a one
or two inch layer of powder can be spread o the floor or surface nearby and the burning metal transferred to it, then add
more powder as required.
(3)
High cutting speeds, extremely fine feeds, dull chipped or improperly designed tools, tool dwell on work
after feed is stopped, tool rub, or tool hitting a steel or iron insert increase the chances of chip ignition. Keeping the
cutting speed below 700 feet per minute will greatly reduce the fire possibilities even with dull or poorly designed tool
and fine feeds.
4-22. GRINDING AND POLISHING SAFETY PRACTICES . During grinding and polishing operations a proper dust
collection system must be used. Figure 4-1 illustrates acceptable type collectors. The dust produced during grinding
and polishing of magnesium must be removed immediately from the working area with a properly designed wet type
dust collection system. Proper systems precipitate the magnesium dust by a heavy spray of water and must be so
designed that dust or sludge cannot accumulate and dry out to a flammable state . Small collectors as shown in Figure
1A, serving one or two grinders are the best. The grinder to collector ducts should be short and straight. The self
opening vents illustrated prevent hydrogen collection during shutdown. The grinder's power supply air exhaust blower
and liquid level controller should be electrically water connected so cessation or failure of the dust collector operation
will shut the grinder off. In addition a suitable device should be installed in the system that will insure the collector
system is in full operation and has changed the air in the duct, etc., several times before the grinder begins running.
Dry type filter collectors or central collector system which carry the dust through long dry ducts should not be used for
magnesium. The collector portrayed in Figure 4-1B is used with booth type portable grinding and polishing where the
dust passes through the grate with the air being circulated into a liquid spray which removes the dust. Design the booth
to catch all the dust possible. On individual grinders for small scale work, as shown in Figure 4-1C, the hood design
and the oil pan combine to afford a satisfactory dust collection. Any dust escaping the hood should be kept swept up
and properly disposed of.
4-23. The following specific safety rules pertain to the grinding and polishing of magnesium:
a.
Magnesium grinding should be done on equipment set aside and labeled for that purpose. Do not grind sparking
material on these grinders unless the magnesium dust has been completely removed from the equipment system. In
addition, the grinding wheel or belt must be replaced prior to grinding of any other metal.
b.
If chrome pickled magnesium is to be ground, sparks may result. Therefore, dust and air-dust mixtures must not
be allowed to accumulate within spark range.
c.
Maintain adequate supplies of plainly labeled approved fire extinguishing powder and suitable dispensing tools
readily available to operators. Fire control is the same as detailed in paragraph 4-21 for machine chips.
d.
Keep dust from accumulating on surrounding floors, benches, windows, etc. If such accumulation is evident the
collector system is not operating properly and must be checked and repaired. Periodically and no less than once a
month, completely clean the entire collector systems. Inspect and clean the grinder to collector ducts daily or move
frequently if the volume of collection is high.
4-14
