Injection molding with shooting pots

A multi-cavity mold in combination with a hot runner system wherein the hot runner system includes metering means individual to each mold cavity for feeding precisely measured quantities of thermoplastic material to each cavity.

FIELD OF THE INVENTION 
The invention relates to precise control of injection molding compound 
being introduced to a multi-cavity mold. More specifically the invention 
relates to a control or metering apparatus and a metering method that is 
individual to each cavity. 
The invention also relates to adjustment of the metering or control unit on 
an individual cavity basis. For example, where a single source of one 
resin is being supplied simultaneously to a plurality of mold cavities 
provision is made to adjust the flow of molding compound to one cavity, 
individually, without disturbing the meter setting in the remaining 
cavities. 
BACKGROUND OF THE INVENTION 
The use of control units such as shooting pots to introduce thermoplastic 
resin into single cavity molds is well known. In such arrangements a 
primary resin source feeds the reservoir of a shooting pot and the 
shooting pot, in turn, is operated to feed a measured or metered quantity 
of compound into a single cavity mold to form large items such as buckets, 
trash containers and like receptacles. 
In contrast, the present invention is directed to the concept of supplying 
thermoplastic molding compound to a multi-cavity mold there the cavities 
of the mold are fed by a hot runner system where the hot runner system 
includes hooting pots (metering means or control units) which are 
individual to each cavity. That is, conduits that lead from the hot runner 
system to feed the respective mold cavities each contain a shooting pot or 
metering means for controlling precisely the introduction of a single shot 
of compound to a mating cavity on an individual or cavity by cavity basis. 
The hot runner system is supplied or fed with thermoplastic material from a 
primary source usually in the form of an extruder or similar device in 
well known fashion. 
For purposes of claiming the present invention, the shooting pots are 
referred to as metering means or as secondary compound advancing units. 
It is a primary feature of the present invention to provide a hot runner 
system cooperating with a multi-cavity mold where the hot runner system 
includes metering means individual to each mold cavity. 
It is a further feature of the invention to provide metering means in the 
hot runner system which are operable to feed precisely measured quantities 
of compound to each cavity. 
It is a further feature of the invention to provide metering means 
individual to each cavity where the metering means are adjustable to 
change volume, for example, on a cavity by cavity basis. That is, each 
metering means may be adjusted individually without disabling the setting, 
function and operation of the other metering means in the hot runner 
system. 
A further feature of the invention is the treatment of a multi-cavity mold 
and a hot runner system as a unitary assembly. 
A still further feature of the invention is the provision of a novel 
process for feeding, metering and adjusting the introduction of 
thermoplastic compound into individual cavities of a multi-cavity mold by 
incorporating the feeding, metering and adjusting steps into a hot runner 
system. 
An arrangement embracing certain features of the present invention may 
comprise, in combination, a multi-cavity mold and a hot runner system, 
supply means incorporated in the hot runner system for feeding measured 
quantities of thermoplastic compound to each said mold cavity on an 
individual cavity basis. 
A method embracing certain other features of the present invention may 
comprise the steps of providing a mold having a plurality of cavities, 
providing a hot runner system for feeding said cavities, connecting the 
hot runner system to each cavity by means of compound conduits individual 
to each cavity and placing metering means in each said cavity conduit for 
controlling the introduction of compound to each cavity on an individual 
cavity basis. 
Other feature and advantages of the present invention will become more 
apparent from an examination of the succeeding specification when read in 
conjunction with the a pended drawings in which;

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
In FIG. 1 an assembly A within the dashed lines includes a multi-cavity 
mold M in combination with a hot runner system S with an external primary 
thermoplastic compound feed unit defining an extruder. Mold cavities 11, 
12, 13 and 14 are connected individually to the hot runner system by 
compound conduits 16, 17, 18 and 19, respectively. 
The reference numerals 21, 22, 23 and 24 represent valves controlling the 
introduction of compound into reservoirs 26, 27, 28 and 29 of metering 
means or shooting pots 31, 32, 33 and 34. 
Each valve is connected to manifold 35 by compound conduits 36, 37, 38 and 
39 and the manifold is, in turn, supplied thermoplastic compound by a 
primary unit defining, in this embodiment of the invention, an extruder 
via conduit 40. 
The metering means, in the disclosed embodiment, defines a piston-cylinder 
assembly where the stroke of each piston 41, 42, 43 and 44 is adjustable 
individually to change the volume of the reservoirs 26, 27, 28 and 29 
(cylinder portion) to facilitate feeding (metering) precise quantities of 
compound to the mold cavities on a cavity by cavity basis. 
Referring to FIG. 2 details of a single metering means within the hot 
runner system will be described recognizing that each metering means 
within the hot runner system is of the same structure and operation. 
Extruder B feeds thermoplastic compound through channels 53 and 54 of hot 
runner manifold block 51 and through valve 56 to charge reservoir 58 of 
metering means or shooting pot 59 in the manner described in said 
copending application Ser. No. 869,269 now U.S. Pat. No. 4,717,324. 
As described further in the copending '269 application, when the reservoir 
58 is fully charged with a precise amount of compound (corresponding to 
the volume of the reservoir) the valve 56 is closed and the nozzle stem 83 
is opened. Next, the piston 61 is advanced until it bottoms at the point 
indicated by the reference numeral 100 advancing compound through conduit 
63 and nozzle passage 84 into a mating mold cavity. 
In this manner a precisely measured quantity of compound is advanced from 
the hot runner system to a mating mold cavity such as cavity 11 (FIG. 1). 
After the measured charge of compound has been introduced into the mold 
cavity the stem 83 is moved to the closed position, valve 56 is opened and 
the reservoir is recharged by extruder B as described in said copending 
application SN 869,269 now U.S. Pat. No. 4,717,324. 
During this occurrence the piston 61 is displaced by incoming compound 
until it contacts adjustable stop ST. 
The stop ST is adjustable axially of the piston 61 to change the stroke of 
the piston 61 which, in turn, controls the volume of the reservoir. In 
this fashion, metering of compound is controlled precisely and 
individually from mold cavity to mold cavity. 
As stated previously, the stroke of each piston 41 through 44 FIG. 1 is 
adjustable individually to change the volume of its mating reservoir 
without disturbing the setting (stroke) of the other pistons in a given 
plural piston configuration within a hot runner system. 
It is to be understood that the invention is not limited to the 
illustrations described and shown herein, which are deemed to be merely 
illustrative of the best modes of carrying out the invention, and which 
are susceptible of modification of form, size, arrangement of parts and 
details of operation. The invention rather is intended to encompass all 
such modifications which are within its spirit and scope as defined by the 
claims.