MIL-DTL-68G
SOCIETY FOR PROTECTIVE COATINGS (SSPC)
SSPC SP 10
- Near-White Metal Blast Cleaning
(Copies of this document are available from www.sspc.org or from the Society for Protective Coatings, 40 24th
Street, 6th Floor, Pittsburgh, PA 15222-4643.)
2.4 Order of precedence. Unless otherwise noted herein or in the contract, in the event of a conflict between
the text of this document and the reference cited herein, the text of this document takes precedence. Nothing in
this document, however, supersedes applicable laws and regulations unless a specific exemption has been
obtained.
3.
REQUIREMENTS
3.1 First article. When specified in the contract or purchase order, a sample shall be subjected to first
article inspection (see 4.2 and 6.3).
3.2
Material. Cast iron shall not be used.
3.2.1 Class 1 magnetic fans. When class 1 fans are specified (see 6.2.1), the parts may be constructed of
paramagnetic materials.
3.2.2 Class 2 nonmagnetic fans. When class 2 fans are specified (see 6.2.1), parts, except the magnetic
circuit, shall be of nonmagnetic material. Nonmagnetic material is defined as material which has a maximum
permeability of less than 2.0 after fabrication.
3.3 Blades. Fans shall have at least three blades of diameters as applicable, which shall be corrosion
resisting metal, polished and lacquered, or of a metal treated in accordance with MIL-E-917 to resist corrosion
and finished to match frame, base, and guard; or of a plastic conforming to MIL-P-81390. Fan blades shall be of
such design that normal cleaning will not result in their being bent out of alignment.
3.4 Guard. The guard shall be corrosion-resisting steel , polished and lacquered, or of a metal treated in
accordance with MIL-E-917 to resist corrosion and finished to match the frame and base. The guard shall
enclose the entire blade (perimeter, and front and back sides) such that a 1-2-inch sphere shall be rejected at all
points of the guard except that, for 8-inch diameter blades, sufficient opening may be left in the rear of the guard
to permit entrance of the fan blade. Where the guard is constructed with wire, the wire shall be not smaller than
0.0915 inch diameter (number 13 gage, steel wire gage). Where wire is used as supporting ribs for the guard,
the wire shall be not smaller than 0.1350 inch diameter (number 10 gage, steel wire gage). For 12-inch diameter
blades, the guard may be constructed as two parts, but the two parts shall be firmly attached together such as to
remain together under HI shock conditions and shall be readily disassembled to permit cleaning or removal of the
blades. The guard shall adequately protect personnel from injury and shall not become distorted or vibrate
excessively under normal operating conditions. The guard shall be securely fastened to the motor by screws or
other means to permit ready removal.
3.5
Motor.
3.5.1 Bearings. Bearings may be ball or sleeve type. The bearings and bearing housing shall be so
designed as to prevent dripping or throwing of the lubricant and to permit relubrication of the bearing without any
disassembly of the fan.
3.5.2 Temperature rise. The temperature rise of the motor, when measured by a thermometer in contact
with the windings, shall not exceed 40° C (Celsius) and, when measured by change in resistance, shall not
exceed 50° C.
3.5.3 A.c. motors. The design shall be such that commutators, collector rings, or automatic starting
devices shall not be used.
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