ROCK CIRCUIT

FIBRE CIRCUIT

DRY ROCK
STORAGE

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—— GROUP 4
7
GROUP 4
Ld :
GROUP 3
RETURN
LEGEND ——
|. BELT CONVEYOR il ea a BAGGING
2. SCREEN 3 FIBRE STORAGE
3, CONE CRUSHER
4. FIBERIZER TAILINGS
5. CYCLONE
6. DEDUSTER O
7. FAN OPENER
8. BIN
9. FAN GROUP 5
10. DUST COLL. TYPICAL FLOW LINE
ASBESTOS FIBRE

FIGURE 6 — Typical flowsheet for asbestos fibre at Cassiar.

claim tunnel, which runs the full length of the dry-
rock storage. These drawpoints discharge onto vari-
able-speed belt feeders, which feed the reclaim belt. .

Milling Circuit (Fig. 6)

The reclaim belt from dry-rock storage discharges
into two rotary distributors, each of which feed three
horizontal gyratory double-deck Hall screens. These
primary mill screens are fitted with a two-mesh top
deck screen and an 18-mesh screen on the bottom deck.
The first fibre is lifted from the top deck at the dis-
charge end by air through an aspirating hood (Fig. 7)
and is conveyed through ducting to a 7-ft-diameter
cyclone. This first aspiration is designed to pick up
all of the released fibre, thus preventing damage by
further crushing. To ensure aspiration of all the fibre,
a certain amount of rock is necessarily lifted at the
same time and this rock is eliminated in subsequent
screening and aspiration stages.

The cyclone collector is designed to separate the
fibre from the air by means of centrifugal action. The
fibre drops through the cone of the cyclone and is dis-
charged through a six-bladed rotary airlock. The air
and dust are vented through the central core of the
cyclone to a_fan which discharges to a fabric dust
filter. The cyclone is not designed to be highly effi-
cient, as it also acts as a fibre cleaner, removing some
of the finer dust, thus improving the fibre quality
during the air-conveying cycle.

The oversize rock from the primary screens is
crushed in two 3-ft short-head cone crushers in paral-
lel. The cone crusher product is elevated to four addi-
tional screens in closed circuit with the crushers. These
screens are also fitted with a two-mesh screen panel

FIGURE 7—Primary mill screens with aspirating hoods.

and the aspirated fibre from these screens is conveyed
to similar cyclones in the initial fibre circuit. The
fibre lifted from the two-mesh screen decks is directed
to the group three or spinning fibre cleaning circuit.

The middle size of both the primary and secondary
screens discharges onto six screens fitted with a top
screen deck of four mesh. Aspiration from these

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