minutor chamber. Because of the guards 64 and 66 no
scrap can be thrown up from the comminutor chamber
by the rotor 32. As the ground plastic passes through
the screen 34 it is directly delivered through conduit 48
to the hopper 50 adjacent the extrusion cylinder inlet 5
port. Because of the positioning of the discharge end
52 of the conduit 48 adjacent the port, the regrind is
used on the next cycle of injection along with virgin
material surrounding the conduit 48 in the hopper 50.
This assures immediate, and therefore proportional, feed 1Q
back of regrind into the molding machine.
The control means 70 then actuates the return of the
metering drum to the original position with the mouth
62 thereof facing upwardly to receive the next dose of
The comminutor rotor 32 and blower 44 operate continuously.
It should be noted that because of the rapid rotation of the rotor 32 there is some danger that some scrap could escape from the comminutor chamber. It is important 2o that there be no escape because such "fly-back" of hard plastic in the mold cavity, could, on the next cycle cause virtual destruction of the mold. The avoidance of such an occurrence is a primary objective of this invention. Further, the amount of scrap delivered to the hopper 50 25 for each cycle must be uniform. To avoid the escape of such "fly-back" the metering drum 36 serves as a guard over the upper end of the comminuting chamber irrespective of whether the drum 36 is facing up or down.
The tube 48 may be vented near the end 52 so that the 30 blast of air coming therefrom will not overly disturb the plastic in the hopper 50.
Fail safe means connecting the shielding drum drive 38 and the press may be provided whereby an alarm is actuated if after a given time after the drum starts to rotate from its upward-facing position, it does not reach its downward-facing position. This could signal, for instance, the failure of motor 38.
It should be understood that while the embodiment shown is preferred, variations of the invention are possible. For instance, it would be possible to time the operation of the metering drum 36 so that it delivers plastic scrap to the comminutor chamber at some time other than as the press is closing. It is an essential of the invention, however, that the shelding means avoid "fly-back" and deliver a uniform dose of scrap to the comminuting chamber once each press cycle.
The present invention may thus be embodied in other specific forms without departing from the spirit or central attributes thereof and, accordingly, reference should be made to the appended claims rather than the foregoing specification as indicating the scope of the invention.
X. For an injection molding machine having a twopiece mold, means adapted to open and close the mold, and a feed port for introduction of plastic to be plasticized; a scrap grinder comprising:
(a) a rotary comminutor having an inlet opening at its upper end,
(b) a drum housing mounted over and having its lower end communicating with the inlet of said comminutor and terminating upwardly in a mouth,
(c) a shielding drum mounted in said housing between the month and the comminutor inlet for rotation about a horizontal axis, said drum having a
pocket therein for the receipt of plastic scrap while the pocket is at a first station where it faces upwardly in the mouth, the pocket adapted to discharge such scrap into the comminutor when the pocket is at a second station where it is facing downward toward the comminutor,
(d) means to rotate the drum to move the pocket from the first station to the second station and to the first station again, and
(e) conveyor means adapted to convey comminuted scrap from the comminutor to the feed port of the injection molding machine.
2. A scrap grinder as described in claim 1 wherein the means to rotate the drum moves the pocket from the first station to the second station while said means adapted to open and close the mold is closing the mold.
3. A scrap grinder as described in claim 1 wherein the means to rotate the drum moves the pocket from the second station to the first station so that the pocket is at the first station during part of the time that the mold is open.
4. A scrap grinder as described in claim 1 wherein means are provided to actuate a signal if by a given time after the drum is actuated from its first station it does not reach its second station.
5. Scrap grinding apparatus comprising conduit means for receiving plastic scrap discharged from separable molds of an injection molding machine, comminuting means for grinding said plastic scrap and coupled with said conduit means, conveying means for feeding ground scrap from said comminuting means to the inlet of an injection cylinder, and gating means interposed between said conduit means and said comminuting means for dispensing scrap to said comminuting means at predeter
35 mined intervals while constantly blockading and preventing any return therefrom of any particles of hardened scrap or dust to the molds through said conduit means whereby fly-back is avoided.
6. The apparatus of claim 5 wherein said gating means 40 is rotary.
7. The apparatus of claim 6 including a pocket in said gating means normally disposed in an upright position for receiving scrap from said conduit, and means for rotating said gating means through 180° so as to invert said
45 pocket and discharge the contents thereof into said comminution means.
8. The apparatus of claim 7 including means for actuating a signal when said means for rotating does not invert said pocket from a receiving to a discharging position
50 within a predetermined period of time.
9. The apparatus of claim 5 wherein said conduit means comprises a closed channel.
10. The apparatus of claim 9 wherein said conveying means is pneumatic.
UNITED STATES PATENTS
2,531,524 11/1950 Nichols etal.
60 2,995,775 8/1961 Schnitzius et al.
3,000,055 9/1961 Schlicksupp.
WILBUR L. McBAY, Primary Examiner.
U.S. CI. X.R.