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MIL-C-52128C
3.10 Feeder. The vibrating grizzly shall be fed by a feeder not less than 3 feet wide by not
less than 8 feet long. The feeder shall receive quarry run rock to include individual rocks
weighing not less than 1000 pounds dumped from power shovels without, breakage of parts,
damage to feeder or components, or reduced production. If an apron type feeder is furnished, the
feeder shall have overlapping steel pans or flights mounted on not less than three hardened alloy
steel roller chains supported on a series of load-carrying rollers or rails. The chain shall conform
to ANSI B29.1. The maximum design load shall not exceed 15 percent of the minimum ultimate
tensile strength of the chain. All bearings on the feeder shall be fitted with grease fittings. The
feeder shall be equipped with a 10-hp electric motor conforming to 3.8.2. A receiving hopper
not less than 8 feet wide and not less than 9 feet long shall be mounted on the feeder. The feeder
hopper shall be provided with side plate extensions over the vibrating grizzly so as to deliver
material from the feeder to the vibrating grizzly without spillage. The hopper shall be fabricated
from steel plate conforming to ASTM A242 having a thickness of not less than 3/4-inch with no
liners required. To provide roller chain tension, a take-up adjustment consisting of two Acme
thread arrangements (one per side), with threads conforming to ASNI B1.5, shall be provided at
the tail shaft.
3.11 Grizzly. The crusher shall be equipped with live type grizzly not less than 3 feet wide
and not less than 5 feet long, having two level or sloping decks and equipped with bypass chutes.
The grizzly shall be provided with a 10-hp electric motor conforming to 3.8.2. The top deck
shall consist of heavy duty, high-carbon-steel bars or rails extending the full length of the
grizzly. The bars or rails shall withstand the discharge of heavy abrasive rock from the feeder
and shall be spaced to permit passing 2-inch-minus rock onto the lower deck. The second deck
shall be equipped with a 3 by 5 foot, 3/4-inch slotted screen cloth to screen off one size and
discharge the oversize onto the end discharge conveyor belt. A hopper shall be provided below
the second deck. The hopper shall contain a flop gate or means of bypassing material either from
the hopper to the end discharge conveyor; or into a discharge chute or side delivery conveyor as
specified in 3.13.12. When a discharge chute is furnished, it shall be provided with means for
diverting materials to either side of the crusher and shall provide ground clearance for the
receiving hopper of a portable conveyor.
3.11.1 Screen activating mechanism. Any screen activating mechanism subject to material
from the deck or decks striking on the mechanism shall be equipped with a replaceable,
protective cover.
3.11.1.1 Shaft bearings. All shaft bearings shall be double-row, selfalining, antifriction type.
All bearings exposed to dust shall be provided with labyrinth-type grease and dust seals which
will prevent dust from entering the bearings. The drive shaft and bearings shall withstand the
loads imposed under any operating condition specified herein.
3.11.2 Woven wire screen cloth. Screen cloth shall conform to MS39127.
3.11.2.1 Material. All screen cloth shall be made of crimping grade, oil-tempered wire
conforming to NSGA Circular No.80, table 3, grade B, carbon range 0.55 to 0.70, drawn and
hardened as specified.
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