Granulation chamber for plastics materials

A granulation chamber for plastics materials comprises a top portion effective to be rotated symmetrically about a vertical axis and having a downwardly divergent concave shape, an opening located at the center of the top portion and engaged by an extruder head associated with a star arrangement of granulating knives to be rotated in a horizontal plane intersecting the top portion and a frusto-conical hopper-like bottom portion coupled with the top portion and converging downwardly into a discharge outlet.

BACKGROUND OF THE INVENTION 
This invention relates to a granulation chamber for plastics materials, 
wherein the plastics material is extruded from an extruder head and 
granulated by means of a rotary star or spider arrangement of knives which 
is connected frontally to the extruder head. 
Known are granulating chambers which comprise a hollow space of cylindrical 
shape, the top base whereof carries an extrusion head for the product to 
be granulated. Said head comprises an extrusion plate having orifices 
wherethrough the product, in a "spaghetti" form, is caused to emerge 
vertically continuously. A plurality of rotary knives arranged in a star 
or spider configuration are caused to shave the plate and cut into 
granules the product which is projected by centrifugal force against the 
walls of the granulating chamber. With certain products, the inner wall of 
the chamber is wet with a film of water which is effective to cool down 
the granules and prevent them from sticking to the wall. 
In order to improve the output of such apparatus, one endeavors to increase 
the cutting rate as far as possible. However, above a certain speed range 
(above about 800 rpm's) the granules tend to rebound against the chamber 
walls and interfere with the successively formed granules, thus resulting 
in a mutual sticking condition. 
SUMMARY OF THE INVENTION 
This invention sets out to obviate the cited drawback, that is to provide a 
chamber wherein the granules are prevented from sticking to one another 
even at high operational speeds or rates. 
This aim is achieved by a granulation chamber for plastics materials, 
wherein the plastics material is extruded from an extruder head and 
granulated by a rotating star arrangement of knives, frontally associated 
with said head, characterized in that it comprises a top portion effective 
to be rotated symmetrically about a vertical axis and having a downwardly 
divergent concave shape, an opening located at the center of said portion 
and engaged by said extruder head, thereby the star of knives is rotated 
in a horizontal plane intersecting said top portion, there being also 
provided a frusto-conical bottom portion coupled with said top portion and 
converging downwardly into a discharge outlet.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In the drawing FIGURE, the granulating chamber is generally indicated at 1. 
The chamber comprises a top or upper portion or cover 2 and a bottom or 
lower portion or hopper 3, which portions are provided with respective 
peripheral flanges 4,5 for their mutual fastening by means of screws. The 
cover 2 and hopper 3 are rotated symmetrically about a vertical axis A. 
More specifically, the hopper 3 has a substantially frusto-conical shape 
which converges downwards, with the wall thereof forming a substantially 
45.degree. angle with the axis A, the cover 2 is concave or hollow toward 
the interior of the chamber 1 and merges with the top of the hopper 3 to 
define complementary therewith a substantially parabola-like contour 
having an axis B which forms a 60.degree. angle with the axis A of the 
granulating chamber. 
The chamber is suspended through tie rods 6,7 from a stationary frame, not 
shown in the drawing. The tie rods 7 are suitably hinged to allow a 
certain tilting movement of the chamber with respect to the axis A. The 
hopper 3 has a bottom outlet 3a for discharging the granulated product. 
Externally to said outlet, there is welded a bracket 8 wherein a screw 10 
is engaged which also engages a second bracket 9 rigid with a container 11 
located under the discharge outlet 3a. The container has an inclined 
bottom for the removal of the product and water. 
The cover or lid 2 has at the center a circular opening 12 bordered by a 
rim 12a, in which opening there engages an extrusion head 13 with an 
extrusion outlet 13a and a cutting assembly including a star arrangement 
of knives 14 which rotates about the axis A. The rotation plane of the 
knives 14 intersects the cover close to the rim 12a. Around the opening 
12, there is formed an annular space 15 which is connected to a cooling 
water supply. The space 15 is formed from a tubular element 16 which is 
welded externally to the cover, whereon a ring-like plate 17 is welded. To 
the inner edge of the plate 17, there is welded a collar 18 which extends 
into the opening 12 and has an outer flange 19 which defines, together 
with the edge 12a of the cover, a flattened annular mouth adapted for 
forming a film of water directed against the chamber wall. With the 
opposite faces of the plate 17 and rim 12a of the cover, there are rigidly 
connected respective annular ridges 20,21 which form a labyrinth adapted 
to allow the building up of a certain pressure within the space 15, for a 
uniform distribution of the water. 
As may be seen, the shape of the chamber prevents the granules of the 
product from rebounding towards the axis A, after being cut by the knives 
14 and thrown outwardly, and thereby prevents them from sticking to other 
granules which have been cut in the meantime. In addition thereto, the 
inclination of the cover encourages a radially diverging flow of the 
granules, thereby any mutual contact is prevented as much as possible.