Plasticizing assembly for use in an injection molding machine

The strokes performed in the direction of the injection axis by a valve-actuating cylinder disposed near the rear portion of the plasticizing cylinder are transformed by a motion-deflecting lever into opening and closing movements of the valve needle. The motion-deflecting lever is disposed within the protective skeleton, which surrounds the plasticizing cylinder. The lever is pivoted to the skeleton by a supporting pivot assembly. The valve needle extends rearwardly to a location which is radially aligned with the feed screw when it is in its foremost position. The valve needle extends in a needle-guiding bore, which is formed in the plasticizing cylinder and has a relatively wide rear portion having an open rear end at a location which is radially aligned with the back flow valve when the feed screw is in its foremost position. Owing to that design the assembly by which movement is effected by the valve-actuating cylinder in the direction of the injection axis and transmitted to the valve needle, which is inclined relative to the injection axis, can be manufactured at much lower cost.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a plasticizing assembly for use in an injection 
molding machine, which plasticizing assembly comprises a plasticizing 
cylinder comprising a nozzle section, a cylinder section, and clamping 
means holding said nozzle section and cylinder section together in axial 
alignment, also comprises heating means for plasticizing plastic material 
in said cylinder section, a feed screw, which is operable to rotate for 
feeding plastic material being plasticized in said cylinder section toward 
said nozzle section and to perform an axial stroke for injecting 
plasticized plastic material from said nozzle section, and a back flow 
valve for preventing a back flow of plastic material during said stroke, 
which plasticizing assembly also comprises a carrier block, in which said 
cylinder section is mounted near its rear end. 
wherein a skeleton is provided, which surrounds said cylinder section 
between said carrier block and the location of the foremost position of 
said back flow valve and comprises skeleton elements for protecting and 
supporting said plasticizing cylinder, inclusive of said heating means, 
wherein said nozzle section is formed with a nozzle orifice for discharging 
said plasticized plastic material along a predetermined injection axis and 
with a needle-guiding bore, which communicates with said nozzle orifice 
and is inclined relative to said injection axis, and a valve needle for 
opening and closing said nozzle orifice is longitudinally slidably mounted 
in said bore, 
wherein said plasticizing assembly comprises a valve-actuating cylinder, 
which is disposed adjacent to said carrier block and operable in a 
direction that is parallel to said injection axis to displace said valve 
needle in said bore to open and close said nozzle orifice, and a 
force-transmitting linkage, which operatively connects said 
valve-actuating cylinder to said valve needle and comprises a rear link, 
which is parallel to said injection axis and connected to said 
valve-actuating cylinder, a forward link, which is parallel to said bore 
and connected to said valve needle, and a motion-deflecting lever, which 
on spaced apart axes is pivoted to a supporting structure and to said 
links and is arranged to transform a longitudinal movement imparted to 
said rear link by said actuating cylinder to a longitudinal movement of 
said forward link and said valve needle in the direction of said bore. 
2. Description of the Prior Art 
In a plasticizing assembly of that kind which is known from U.S. Pat. No. 
4,886,439 the plasticizing cylinder is surrounded by a skeleton, which 
extends axially along an intermediate length portion of the plasticizing 
cylinder. 
The basic structure of that skeleton has specifically been disclosed in 
FIG. 5 of U.S. Pat. No. 4,863,362 and its description and that disclosure 
is incorporated herein by reference. 
In plasticizing assemblies of the kind described first hereinbefore the 
plasticizing cylinder is detachably mounted in a bore of the carrying 
block and the valve-actuating cylinder is disposed adjacent to the carrier 
block and adapted to be uncoupled from the force-transmitting linkage so 
that the valveactuating cylinder may be left in the injecting unit when 
the plasticizing cylinder is to be replaced. The motion-deflecting lever 
is pivoted to the nozzle section or to the cylinder section so that the 
motion-deflecting lever and its pivots will be subjected to extremely high 
temperatures during the injection molding operation and said lever and 
pivots must be made of heat-resisting castings having finished surfaces. 
Because the valve needle is rather short, the motion-deflecting lever and 
its pivots must be made with small manufacturing tolerances. For this 
reason the pivoting of the lever to the nozzle section or cylinder section 
involves relatively high manufacturing costs, particularly as regards the 
provision of pivot bearings for mounting the pivots of the 
motion-deflecting lever in the nozzle section or cylinder section. 
In the known plasticizing cylinder the inclination of the needle-guiding 
bore relative to the injection axis is rather large, for various reasons, 
and amounts to about 30.degree.. As a result, the intersection between the 
inclined bore and the axially extending nozzle orifice is relatively short 
so that the closing of the nozzle orifice will be facilitated. Besides, a 
large inclination is required in view of the adjacent clamping ring, the 
forward end of the cylinder section and the adjacent heating element. 
These adjacent parts would render the mounting of the valve needle in a 
bore haivng a smaller angle of inclination extremely difficult. 
SUMMARY OF THE INVENTION 
It is an object of the invention so to design a plasticizing assembly which 
is of the kind described first hereinbefore that the means for 
transforming the movement of the valve-actuating cylinder in a direction 
that is parallel to the injection axis to a movement of the valve needle 
at an acute angle to said axis can be manufactured at lower cost. 
That object is accomplished in accordance with the invention in that the 
motion-deflecting lever is pivoted to said skeleton within the latter by 
supporting pivot means which with respect to said injection axis are 
radially spaced from said heating means, said valve needle extends 
laterally of said feed screw when it is in its foremost position, said 
needle-guiding bore has a relatively wide rear portion and a relatively 
narrow forward portion opening into said nozzle orifice, said rear portion 
has an open rear end at a location which is radially aligned with said 
back flow valve when said feed screw is in its foremost position, and said 
valve needle extends rearwardly from said open rear end to a location 
which is radially aligned with said feed screw when it is in its foremost 
position. 
The supporting pivot means are so arranged within the skeleton that the 
radial distance between said supporting pivot means and said heating means 
is smaller than the radial distance between the skeleton elements 
supporting said supporting pivot means and said heating means so that 
mechanical actions from the outside will affect the skeleton but will not 
affect the motion-deflecting lever. 
In the plasticizing assembly in accordance with the invention the 
motion-deflecting lever and its pivots are disposed outside the region 
which is strongly heated by the adjacent heating means and the 
motion-deflecting lever is virtually incorporated in the skeleton 
associated with the plasticizing cylinder so that the motion-deflecting 
lever and its pivots can be so designed that they can be manufactured at 
lower cost. 
The motion-deflecting lever may be offset and just as its pivots may be 
made with relatively large manufacturing tolerances. For instance, the 
motion-deflecting lever may be composed of bent metal strips. It may 
preferably be pivoted to horizontal track bars of the skeleton, which bars 
are required in any case for supporting the plasticizing cylinder during 
its periodic axial movements. 
To close and open the nozzle orifice, the pivots by which the rear and 
forward links of the force-transmitting linkage are pivoted to the 
motion-deflecting lever are constrained to move along an arc of a circle 
so that the forward link and the rear portion of the valve needle will 
then be subjected to a bending stress. But that bending stresses can be 
minimized if the motion-deflecting lever is spaced a large distance from 
the nozzle orifice. 
Finally, the valve needle and the forward link are accommodated in the body 
of the plasticizing cylinder and in the skeleton to such a large extent 
that damage to the valve needle and the forward link will virtually be 
precluded. 
In a preferred embodiment the angle between the needle-guiding bore and the 
injection axis is less than 25.degree., the valve needle extends through a 
clamping ring, which is included in the clamping means and disposed at the 
parting line between the nozzle section and the cylinder section, and the 
rear end of the relatively wide rear portion of the needle-guiding bore is 
disposed adjacent to the sealing plane defined by said back flow valve in 
said plasticizing cylinder. Behind the needle-guiding bore the valve 
needle may extend in recesses, which are formed in heating elements, which 
consist of cast shell sections, and said recesses may constitute a passage 
which adjoins said rear portion of the needle-guiding bore. In such an 
embodiment the inclination of the valve needle may be very small because 
the valve needle extends through the clamping ring of the clamping means 
and the rear end of the needle-guiding bore is formed in the cylinder 
section adjacent to the sealing plane of the back flow valve and behind 
said rear end of the bore the valve needle extends in recesses of a cast 
heating element. 
In a preferred embodiment the skeleton comprises flat vertical skeleton 
elements formed with circular apertures, through which the cylinder 
section extends, said flat skeleton elements are provided with flanges, to 
which track bars are secured, which are included in the skeleton and are 
disposed in a horizontal plane which includes the injection axis, the 
supporting pivot means of the motion-deflecting lever are supported on the 
inside of said track bars and the motion-deflecting lever is pivoted to 
the forward link by a pivot disposed in a plane which is approximately at 
right angles to the forward link. That embodiment permits the skeleton to 
be manufactured at particularly low cost and ensures that the bending 
stresses in the forward link and the valve needle will be minimized. 
In a preferred embodiment the skeleton comprises a protective shell, which 
surrounds and is secured to internal skeleton elements and surrounds also 
the motion-deflecting lever, which is made from two sheet metal blanks, 
and the forward link of the force-transmitting linkage. In that embodiment 
any damage to the valve needle, the forward link and the motion-deflecting 
lever by external force actions, particularly during a replacement of the 
plasticizing cylinder and its transportation to and from storage, are 
almost precluded. This is of special significance for injection molding 
machines used in countries which are not highly industrially developed. 
In a preferred embodiment the forward link of the linkage consists of a rod 
and a tapped sleeve, by which the rod is joined to the valve needle, each 
of the sections of the motion-deflecting lever which have been made from 
sheet metal blanks has a vertical top portion, a horizontal intermediate 
portion and a forwardly inclined vertical bottom portion, the rear link is 
pivoted to the top end of the bottom portions and the forward link is 
pivoted to the bottom end of the bottom portions. That embodiment permits 
a manufacture of the forward link and of the motion-deflecting lever at 
particularly low cost. 
In a preferred embodiment, the cylinder section consists of forward and 
rear cylindrical subsections and a tapped sleeve connecting said 
subsections, the parting line between said subsections is axially spaced 
from the protective shell by a distance which equals the distance of the 
parting line between the nozzle section and the cylinder section in an 
assembly in which the cylinder section is integral, and each of the 
forward link of the linkage and the feed screw has a length which is 
sufficient in view of the provision of the forward subsection. The 
distance from the supporting pivot means to the nozzle orifice may be 
approximately one-third of the total length of the plasticizing cylinder 
if the plasticizing cylinder is integral and may be increased by the 
length of the forward subsection of a two-part plasticizing cylinder. In 
that case the plasticizing cylinder has a much larger length and can be 
converted with a very small amount of work to a plasticizing cylinder 
having a normal length. As a result, a plasticizing assembly for both 
alternatives can be provided at very low manufacturing costs because it is 
sufficient in manufacture and storage to provide in addition to the 
standard parts only a forward subsection for the cylinder section, a 
longer rod as the forward link of the linkage, and a longer feed screw. 
The connecting portions at the forward and rear ends of the forward 
subsection and of the longer rod correspond to the adjacent connecting 
portions of the nozzle section and of the normal-length cylinder section 
and of the normal-length rod. 
In a preferred embodiment the cylinder section has a forward portion which 
is enlarged in inside diameter and surrounds the nozzle section in part of 
its length and the nozzle section extends rearwardly to a location which 
is radially aligned with the forward end of the feed screw when it is in 
its rearmost position. In that case the rear end of the nozzle section is 
disposed in the cylinder section at a location which when the feed screw 
is in its rearmost position is disposed behind the sealing plane of the 
back flow valve, i.e., in a region which is under a relatively low 
pressure, whereas that space which is disposed in front of the sealing 
plane and will be subjected to extremely high pressures during the 
injection stroke is completely surrounded by the nozzle section.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Illustrative embodiments of the invention will now be described more in 
detail with reference to the drawings. 
The following features are common to the embodiment shown in FIGS. 1 to 5 
and the modifications shown in FIGS. 6 and 7: The plasticizing cylinder 
comprises a nozzle section 12; 112; 212 provided with a shield 33 and a 
cylinder section 11; 111; 211. The nozzle section and the cylinder section 
are held together in axial alignment by clamping means which comprise a 
tapped clamping ring 26 and screws 26a. The internal screw threads of the 
clamping ring 26 are in threaded engagement with external screw threads on 
the cylinder section 11 or 111 or 211. The clamping ring 26 extends 
axially beyond the rear end of the nozzle section. The protruding portion 
of the clamping ring is formed with tapped bores, which contain screws 
26a, which in the illustrated embodiment include an angle with the 
injection axis a--a. The edges at the free ends of the screws 26a bear on 
abutment surfaces of the nozzle section 12 or 112 or 212 so that the 
screws can be rotated to axially force the nozzle section and the cylinder 
section against one another. The plasticizing cylinder is intended for use 
in an injection molding machine and contains a feed screw 31, which is 
operable to rotate for feeding the plastic material being plasticized 
toward the nozzle section and to axially advance for injecting the 
plasticized plastic material. During the axial advance of the feed screw, 
a back flow valve 32 at the forward end of the feed screw 31 prevents a 
back flow of the plastic material. The rear portion of the plasticizing 
cylinder is detachably mounted in a carrier block 10. A skeleton is 
provided, which surrounds that length portion of the plasticizing cylinder 
which extends between the plane at which the back flow valve 32 is 
disposed in its foremost position and the carrier block 10. The skeleton 
comprises internal skeleton elements 29, track bars 18, an upper sheet 
metal shell section 15 and a lower sheet metal shell section 15a. They 
serve as supporting means and protect the plasticizing cylinder and the 
heating elements 27 associated with it against mechanical actions from the 
outside. The plasticizing cylinder is provided with a valve needle 13, 
which serves to open and close the nozzle orifice 12a and extends in the 
nozzle section 12; 112; 212 and in the cylinder section 11; 111; 211 in a 
bore, which extends at an angle of inclination .alpha. (FIGS. 4, 6) to the 
injection axis a--a. The valve needle 13 is operable by a hydraulic 
valve-actuating cylinder 14 (FIG. 1), which is provided adjacent to the 
carrier block 10. By means of a force-transmitting linkage, the strokes 
performed by the valve-actuating cylinder 14 in a direction which is 
parallel to the injection axis a--a are transformed to movements of the 
valve needle 13 at an inclination to the injection axis. A 
motion-deflecting lever 17 is pivoted by means of supporting pivots 24 to 
track bars 18 of the skeleton at a radial distance r from the heating 
elements 27 (FIG. 5). The linkage comprises the lever 17, a forward link 
b--b, which extends at an angle .alpha. to the injection axis a--a, and a 
rear link c--c, which is approximately parallel to the injection axis 
a--a, and said links are pivoted to the motion-deflecting lever 17 by 
pivots 25 and 25a, respectively. The motion-deflecting lever 17 is 
disposed within the skeleton and the supporting pivots 24 are mounted in 
track bars 18 of the skeleton. The valve needle 13 extends laterally of a 
length portion of the feed screw 31 when the latter is in its foremost 
position. At a location which is radially aligned with the back flow valve 
32 the valve needle 13 extends of the needle-guiding bore, which has a 
relatively wide rear portion 12b, 11a. Stated differently, these portions 
have, as seen, for example, in FIG. 2, a diameter appreciably larger than 
the diameter of the valve 13, so that between bore and needle a clearance 
is defined which allows for a lateral excursion (bending) of the valve 
needle 13 in the bore. In the embodiments shown by way of example the 
valve needle 13 extends through the clamping ring 26 at an angle of 
inclination .alpha. which is less than 25.degree.. The relatively wide 
rear portion 12b, 11a of the nozzle-guiding bore opens on the outside 
surface of the cylinder section 11; 111; 211 at a location which lies 
approximately in the sealing plane d--d of the back flow valve 32 when the 
feed screw 31 is in its foremost position. The heating elements 27 consist 
of cast shell sections, which are arranged in pairs to form axially 
adjoining heating cuffs, which consist of resistance heaters. The foremost 
heating cuff of the cylinder section 11, 111, 211 is formed with a passage 
27b, which adjoins the rear end of the needle-guiding bore and through 
which the valve needle 13 extends. The passage 27b is constituted by 
recesses formed in the shell sections of the foremost heating cuff as they 
are cast. 
The flat vertical skeleton elements 29, 29' are provided with flanges 29a, 
29a', to which additional internal skeleton elements consisting of track 
bars 18 are secured, which lie in a horizontal plane e--e (FIG. 5), which 
extends through the injection axis a--a. The supporting pivots 24 for the 
motion-deflecting lever 17 are mounted on the inside of said bars 18. The 
supporting pivots 24 and the forward pivots 25 lie in a plane k--k, which 
is approximately at right angles to the forward link b--b of the 
force-transmitting linkage. The skeleton also comprises a protective 
shell, which surrounds the internal skeleton elements 29, 29' and 
comprises an upper sheet metal shell section 15 and a lower sheet metal 
shell section 15a. The two sheet metal shell sections 15 and 15a have 
longitudinal edges, which are contiguous to adjacent surfaces of the track 
bars 18. The forward link b--b of the force-transmitting linkage comprises 
a rod 21 and a tapped sleeve 22 by which the rod 21 is joined to the valve 
needle 13. The motion-deflecting lever 17 comprises two sections made from 
sheet metal blanks. Each of said sections has a vertical top portion 17a 
formed with a bearing bore 17a', a horizontal intermediate portion 17b and 
a forwardly inclined vertical bottom portion 17c formed with two bearing 
bores 17c', as is particularly apparent from FIG. 3. The rear link c--c of 
the rod 28 of the force-transmitting linkage is pivoted to the lever 17 by 
pivots 25a extending through bearing bores 17c' near the top end of each 
bottom portion 17c. The inclined forward link b--b of the linkage is 
pivoted to the lever 17 by forward pivots 25 extending through bearing 
bores 17' near the bottom end of each bottom portion 17c. The pivots 25, 
25a are secured to the bottom portions 17c of the lever 17 by means of 
screws 19, washers 19a and nuts 19b. The screws 19 extend through the 
tubular pivot pins 25 and 25a. 
In the modification illustrated in FIG. 6 the cylinder section comprises 
two sub-sections, namely, a rear cylindrical subsection 111 and a forward 
cylindrical subsection 111', which are axially aligned and held together 
by a clamping ring 26'and screws 26a which act like the clamping means 26, 
26a of the embodiment shown in FIGS. 1 to 5. The parting line between the 
rear cylindrical subsection 111 and the forward cylindrical subsection 
111' is axially spaced from the sheet metal shell sections 15, 15a by a 
distance m--m (FIG. 6), which equals the distance from the parting line 
between the nozzle section 12 and the cylinder section 11 to the 
protective shell in the embodiment shown in FIGS. 1 to 5. The forward link 
b--b of the rod 121 of the force-transmitting linkage and the feed screw 
31 may be longer to the extent which is necessary because the length of 
the plasticizing cylinder has been increased by the provision of the 
forward cylindrical subsection 111'. In a practical embodiment of the kind 
shown in FIGS. 1 to 5, the distance y from the transverse vertical plane 
containing the supporting pivots 24 to the transverse vertical plane 
containing the nozzle orifice 12a is about one-third of the total length 
of the plasticizing cylinder. If the plasticizing cylinder comprises also 
the forward subsection 111' (FIG. 6), that distance will be increased by 
the length of the forward subsection 111'. 
In the embodiment shown in FIG. 7 the cylinder section 211 comprises a 
forward portion 211a, which has a relatively large inside diameter and 
surrounds the rear portion of the nozzle section 212. The nozzle section 
212 extends rearwardly to a plane in which the forward end of the feed 
screw 31 is disposed when it is in its rearmost position. As a result, the 
rear end face 34 of the nozzle section 212 regardless of the axial 
position of the feed screw is disposed on the rear of a space which will 
be subjected to an extremely high pressure during the injection of the 
plasticized plastic material into the mold.