Driven ring-type non-return valve for injection molding

A non-return valve for an injection molding machine is provided which includes a conventional tip member threaded into the end of a plasticating screw and carrying therewith an annular valve seat member. An annular check ring receives the tip member. Tang protuberances axially extend from the check ring to rotably engage the retainer end of the tip member. This causes the check ring to couple with the tip member during screw rotation to minimize valve wear while permitting the check ring to axially move relative to the tip member for effecting valve closure by pressure differentials in the normal manner. A ramp surface is provided on the tang protuberances which engages a drive surface on the retainer end of the tip/stud member upon reverse rotation of the screw through a predetermined rotational angle or for a set time to positively close the valve prior to injection.

This invention relates generally to the art of injection molding and more 
particularly to non-return valves used in injection molding machines. 
The invention is particularly applicable to and will be described with 
specific reference to a ring-type non-return or anti-backflow valve. 
However, the invention in a broader sense relates to an arrangement 
achieving accurate control of shot size while improving injection 
efficiency of the injection molding machine. 
BACKGROUND 
Conventional injection molding machines of the type to which this invention 
relates include a reciprocating, auger-type plasticating feed screw 
mounted in a heated barrel for conveying and plasticizing or transforming 
into a molten state pelletized or granular thermal plastic materials which 
are fed into the barrel and advanced while being heated to a molten state 
by the auger type screw to the front end of the barrel whereat a 
controlled outlet provides fluid communication with a mold. The screw 
rotates and retracts as the molding material fills the bore space in the 
barrel between screw end and closed nozzle opening. When a predetermined 
quantity of molding material is collected in the barrel ahead of the 
screw, screw rotation is stopped and the screw is forcefully advanced, 
axially, towards the open outlet. By advancing the feed screw forward 
towards the nozzle outlet in the barrel, the molding material or shot 
ahead of the screw is forced or injected from the barrel through the 
nozzle and into the mold. After injection, screw rotation again starts and 
the molding material is again collected ahead of the screw in the barrel 
bore to force the screw to axially retract as pressure builds. The molding 
sequence is automated and operator variable vis-avis computer commands 
setting microprocessor controls. Specifically, it is conventionally known 
practice to control screw rotation and barrel temperature to deposit a 
predetermined shot in the barrel bore ahead of the screw. It is 
conventionally known practice to sense shot pressure, screw travel, etc., 
and control the ram injection pressure (variable or constant) and the rate 
of flow of molding material into the mold (variable or constant) as well 
as pressure (ram and mold) control after injection. 
In order to insure that the shot is delivered to the mold during the 
injection stroke, non-return or antibackflow valves mounted to the front 
of the screw have long been used in the prior art. Such non-return valves 
are one-way check valves which are typically classified as either a ball 
check type valve or a sliding ring-type valve. The present invention 
relates to sliding ring valves. 
Ring type valves typically comprise a tip/stud member having a threaded 
rear end for attachment to the front of the screw and a retainer nose at 
its opposite end with a rod or stud portion interconnecting the retainer 
nose with the threaded end. Attached to the rod portion is a valve seat 
generally adjacent the threaded end. An annular, axially slidable, check 
ring fits over the rod portion and is sized to fit closely within the 
barrel. When the valve is assembled, the check ring is free to axially 
move until one of its ends contacts the retainer end or its opposite end 
contacts the valve seat affixed to the tip/stud member. When the screw 
rotates, flow of the molding material advanced by screw rotation axially 
slides the check ring into contact with the nose-retainer end and material 
flows past the open valve seat and then between the ring and stud into the 
barrel bore. During injection, the shot develops pressure against the 
check ring adjacent the retainer end and moves the check ring to close 
against the valve seat. Numerous modifications have been made to ring-type 
valves to enhance or improve their operation. 
One such modification, somewhat pertinent to the present invention, may be 
described as a driven ring valve and is known in the art. For example, 
Japan Steel Company and Mallard Machine Company offer such valves. In this 
type of valve, the forward end of the check ring and the rearward end of 
the retainer nose are in essence serrated so that rotation of the tip/stud 
member drives or causes the check ring to rotate. The check ring is still 
free to axially cycle between the retainer nose and valve seat for opening 
and closing the valve. Because the check ring and tip/stud member rotate 
together, wear between retainer nose and check ring is virtually 
eliminated. 
In spite of the developments made in microprocessor controls and computer 
programming now employed to precisely control flow rates, injection speed, 
shot size, etc., it has been concluded that control variations necessary 
in precision molding have not been achieved because of inherent variation 
in shot size. The problem is generally defined in the April, 1987 issue of 
Plastics Technology at pages 91-95. Secondary valving to improve shut-off 
operation of the valve is disclosed in the Nov. 1, 1986 issue of English 
publication Plastics and Rubber Weekly. The same type of a concept is 
disclosed in assignee's prior U.S. Pat. No. 3,319,299. Simply put, shot 
size injected into the mold is determined by valve closure and valve 
closure in ring-type valves is dependent upon unequal pressure build-up 
acting against the check ring. Slight variations in material, temperature, 
viscosity, etc., inherently affect valve closure making impossible 
consistent, repeatable shot size. In certain molding applications, shot 
sizes less than 1% in variation must be constantly produced. A valve 
relying solely on pressure differentials to move a fixed distance cannot, 
inherently, produce consistent closures at the accuracy desired for 
certain molding applications. 
Apart from variation in shot size, it is to be appreciated that, in 
accordance with conventional practice, some movement of the ram or screw 
during the injection stroke must occur before pressure at the front of the 
check ring develops sufficient force to close the conventional check ring 
valve. During injection forward movement, a portion of the shot material 
travels past the check ring into the barrel where it remains until the 
next injection stroke. The injection efficiency of injection molding 
machines operated in the conventional manner with conventional check rings 
must always be less than theoretical. The loss of shot material is, of 
course, dependent upon a number of factors and is not limited only to the 
density of the material. Tests conducted on an injection molding machine 
having a maximum shot capacity of 38 ounces demonstrated that when the 
machine was operated at 19 ounces (one half machine capacity), the loss of 
shot which occurred during the time the valve closed was about 2.8%. 
However, many times machines are operated at a shot capacity of only 5% to 
10% of maximum capacity. At a shot size indicative of 5% of the machine's 
shot capacity, the loss of shot to close the valve rises to 28.5% of the 
shot volume initially accumulated ahead of the check ring valve. The prior 
art has recognized the throughput loss attributed to valve closing which 
also results in shot variation. Conventional techniques used with 
conventional check ring non-return valves have included a pullback 
technique where, prior to the injection stroke, the screw is axially 
pulled backwards a slight distance within the barrel. It has been found 
that use of the pull-back technique makes the check ring more responsive 
to valve closure upon initiation of the injection stroke with the result 
that throughput is increased. However, the pull-back technique can cause 
"splay" on the molded plastic parts causing the parts to be defective. 
Thus, application of pull-back can be limited and is dependent upon mold 
design or application. 
SUMMARY OF THE INVENTION 
Accordingly, it is a principal object of the present invention to provide 
an improved, non-return valve and/or method for operating same which 
permits consistent shot sizes to be injected into a mold. 
This object along with other features of the invention is achieved in a 
non-return valve assembly for an injection molding machine having a 
plasticating screw disposed within the barrel and rotatable in either 
direction. The valve includes a tip/stud member having a rearward end 
adapted to be removably affixed to the forward end of the plasticating 
screw, a configured forward retainer end and an intermediate rod-like 
portion between the retainer and rearward ends. An annular check valve 
seat member adjacent the rearward end is adapted to be fixed to the 
forward end of the plasticating screw when the rearward end of the 
tip/stud member is affixed to the plasticating screw. An annular check 
ring concentrically receives the rod portion of the tip/stud member and is 
adapted to axially and radially move relative to the rod portion between 
the retainer and rearward end of the tip/stud member. The check ring has a 
valve seat formed on its rearward end and a forward end defined by a 
forward annular edge surface. A cam mechanism associated with the forward 
annular edge surface of the check ring member and the retainer end 
positively forces, through contact between the check ring and retainer 
end, the check ring valve seat to sealingly close against the annular 
valve seat member when the plasticating screw rotates in a direction 
opposite to that whereat molding material flows from the screw through the 
check ring whereby a consistent, repeatably formed shot of molding 
material is formed in the barrel prior to injection. 
In accordance with another aspect of the invention, a drive coupling 
mechanism associated with the retainer end of the tip/stud member and the 
check ring is provided for rotating the check ring with the tip/stud 
member when molding material flows from the plasticating screw through the 
check ring past the retainer end upon rotation of the plasticating screw 
in a shot forming direction whereby valve wear between retainer end and 
check ring is minimized. More specifically, the retainer end has a flange 
edge surface radially extending outwardly from the rod portion and 
generally flat profile surfaces in the shape of an arrowhead extending 
from the laterally spaced ends of the flange edge surface. The check ring 
has a pair of diametrically opposed tangs axially protruding from the 
forward annular edge surface, each tang having a contact surface at one 
side thereof axially extending a distance greater than the movement of the 
check ring relative to the rod portion and the contact edge surface of one 
tang is circumferentially spaced from the contact edge surface of the 
other tang a distance at least equal to the distance the flange edge 
surface extends between the profile surfaces. Thus, the drive coupling 
mechanism includes the contact edge surfaces of the tangs and the profile 
surfaces of the retainer end in contact with one another when the tip/stud 
member rotates in a shot forming direction whereby the check ring rotates 
with said tip/stud member in a radially and axially separable manner. 
In accordance with yet another specific feature of the invention, the 
camming mechanism includes an annular cam ramp surface adjacent the tang's 
contact edge and extending about the check ring's forward annular edge for 
a fixed arcuate distance from the tang's contact edge to an entry edge. 
The entry edge is generally adjacent the annular edge surface of the check 
ring so that the cam ramp surface increasingly axially protrudes from the 
check ring as it extends from the entry edge to the contact edge and the 
flange surface of the retainer end contacts the ramp surface of the tang 
upon reverse rotation of the screw to positively seal the valve seat 
against the annular check valve seat member. 
In accordance with another aspect of the invention, an injection molding 
machine includes a cylindrical barrel having an outlet opening at one end 
thereof for injecting molding material into a mold, a plasticating screw 
disposed within the barrel, a hopper for feeding a molding material to the 
barrel, a reversible motor for rotating the screw, an injection mechanism 
for axially moving the screw within the barrel, a control mechanism for 
controlling the motor and injection mechanisms and a non-return valve 
affixed to the screw between the barrel opening and the screw. The 
improvement includes the valve having a tip/stud member with a forward 
retainer end, a rearward end affixed to the screw so that the tip member 
rotates with the screw and an intermediate rod-shaped portion between the 
ends. A valve seat member is provided adjacent the rearward end of the tip 
member. A check ring member concentrically receives the rod portion of the 
tip/stud member and is radially and axially movable between the forward 
end of the tip member and the valve seat member. A coupling mechanism on 
the check ring and the forward end of the tip/stud member rotationally 
couples the check ring with the tip/stud member when the motor mechanism 
rotates the screw in a first direction whereby molding material is 
deposited in the barrel in front of the non-return valve while axially 
driving the check ring into sealing engagement with the valve seat member 
upon reversing the direction of the screw's rotation. More specifically, 
the coupling mechanism includes a drive mechanism for permitting the check 
ring to axially move relative to the rod portion of the tip/stud member to 
seat against the retainer end and to move away therefrom. The coupling 
mechanism also includes a cam mechanism effective to mechanically move the 
check ring into sealing contact with the valve seat member upon reversal 
of rotational direction of the screw, and the screw motor is operative to 
drive the screw in the first rotational direction and reverse the 
rotational direction and the control means is effective to control the 
reverse rotation at predetermined angular increments either through direct 
angular measurements or through a timed period of reverse rotation or by 
measuring motor torque developed, etc. 
In accordance with yet another aspect of the invention, a process is 
provided for injecting consistent, repeatable shot sizes of molding 
material from an injection molding machine into a mold. The injection 
machine has an auger type plasticating screw axially and rotatably movable 
within a barrel and an anti-backflow valve attached to the forward end of 
the screw. The process includes the sequential steps of: a) rotating the 
screw in a material accumulating direction until a predetermined amount of 
molding material has been accumulated in the barrel ahead of the 
antibackflow valve; b) rotating the screw in the opposite direction of 
rotation while holding the axial position fixed to close the anti-backflow 
valve thus establishing a precise quantity of material or shot size in the 
barrel ahead of the anti-backflow valve; and c) axially moving the screw 
in the barrel to inject the precise shot of molding material in the barrel 
ahead of the anti-backflow valve into the mold. 
In accordance with a still further aspect of the invention, there is 
provided a method or process for operating an injection molding machine 
having a conventional check ring, anti-backflow valve or a driven ring 
anti-backflow valve in which after a predetermined shot size is 
accumulated ahead of the check ring upon rotation of the screw in the 
conventional manner, the screw rotation is reversed for a predetermined 
time period or degree of angular rotation prior to the injection stroke 
whereby the pressure distribution on the check ring is changed so that a 
more responsive valve action is achieved. 
It is an object of the invention to provide a non-return valve, or a 
non-return valve in combination with an injection molding machine or an 
injection molding machine which permits the formation of consistently 
repeatable shot sizes which are injected into the mold. 
It is yet another object of the invention to provide a non-return valve or 
a non-return valve in combination with an injection molding machine or an 
injection molding machine or a method for operating an injection molding 
machine in which a positive anti-backflow valve closure is achieved to 
produce consistently repeatable, accurately controlled shot sizes which 
can be injected into a mold. 
In accordance with the principal objects stated above, it is still yet 
another object of the invention to provide a non-return valve arrangement 
in which throughput of the injection molding machine is improved by 
minimizing loss of shot size. 
It is yet another separate object of the invention to provide a driven ring 
anti-backflow valve for use in an injection molding machine which is open 
in design to provide improved unrestricted material flow through the 
valve. 
It is yet another object of the invention to provide a driven ring 
anti-backflow valve which utilizes a coupling connection whereby the ring 
remains free to axially and radially shift relative to the tip/stud member 
to avoid excessive barrel wear. 
It is still yet another object of the invention to provide a multi-purpose 
driven ring anti-backflow valve which can be actuated to a closed position 
either by pressure differential in a conventional manner or by being 
mechanically driven to a positively closed position. 
It is still yet another object of the invention to provide a control 
process for operating an injection molding machine to insure that shot 
sizes are consistently and reliably produced for precision molding of 
certain articles. 
It is still another object of the invention to provide an anti-backflow 
valve with improved wear characteristics. 
Still yet another object of the invention is the utilization of reverse 
screw rotation with or without fixed axial screw position for improving 
valve closure response and injection molding machine throughput for any 
check ring non-return valve in general and more specifically for the open 
flow, driven check ring non-return valve disclosed herein which is not 
mechanically driven to a closed position. 
These objects and other features of the present invention will become 
apparent from the following description of the invention taken together 
with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings wherein the showings are for the purpose of 
illustrating a preferred embodiment of the invention only and not for the 
purpose of limiting the same, there is shown in schematic form in FIG. 1 
an injection molding machine 10 preferably of the type which injects 
plastic or a plastic type material into a mold but which, in concept, can 
also be used for die casting of metals and other material which upon 
application of heat assume fluidic characteristics, all such material 
hereinafter referred to as molding material. Injection molding machine 10 
includes an axially extending barrel 12 which has an outlet 13 at its 
forward end which can be viewed as an orifice. In practice, a nozzle 15 is 
secured to outlet 13 and nozzle 15 has a passageway 16 communicating with 
a sprue 18 for feeding molding material to a mold cavity 19. Mold cavity 
19 is formed from two halves of a mold 21, 22 which are brought together 
and held together in a timed sequence by means of a hydraulically actuated 
clamp (not shown). Molding material is disposed at an inlet end 24 of 
barrel 12 by means of a conventional feed hopper 25. Electrical band 
heaters 26 are provided for heating barrel 12 in a precise arrangement by 
a control mechanism (not shown). 
Disposed within barrel 12 is an axially extending plasticating screw 28. 
Plasticating screw 28 has helically shaped threads or flights 29 extending 
from its stem to the barrel for conveyance of molding material from inlet 
24 to outlet 13 in an auger-type manner. Affixed to the forward end of 
screw 28 is an anti-backflow or non-return valve 30. Non-return valve 30 
includes an annular check ring 31 which axially moves within barrel 12 to 
admit or prevent flow of molding material through non-return valve 30 to 
the forward end of barrel 12. For terminology purposes herein, the space 
within barrel 12 ahead of non-return valve 30 through to and including 
barrel outlet 13 which space contains a shot of molding material (which 
may be varied or variable) will be defined as shot space 34. 
Screw 28 is rotated by a motor 35 through a suitable gear train 36, 37. As 
the plasticized molding material is conveyed by rotation of screw 28 
towards barrel outlet 13, the volume of molding material at the forward 
end of barrel 13 increases resulting in an increase in shot space 34 and 
screw 28 is axially displaced toward the right, as viewed in FIG. 1 away 
from nozzle 15 in which a shut-off valve (not shown) is disposed. 
The rearmost end 39 of screw 28 includes a piston 40 which is slidably 
received within a cylinder 41. A variable displacement pump 42 is in fluid 
communication with the back face of piston 40 through a conduit 43 and 
maintains a back pressure on the molding material. 
As thus far defined, molding material in a softened, plasticated state 
passes from screw flights 29 through non-return valve 30 into shot space 
34 while screw 28 is rotated by motor 35. When a desired quantity of 
molding material has been collected in shot space 34, which is normally 
referred to as "shot", rotation of screw 28 is stopped. In the normal 
conventional operation of injection molding machine 10, high pressure 
fluid from pump 42 is then delivered through conduit 43 against piston 40 
while the nozzle shutoff valve (not shown) is opened and piston 40 causes 
screw 28 to move toward the left as viewed in FIG. 1 thus causing the shot 
in shot space 34 to pass through outlet 13, passageway 16, sprue 18 and 
into mold cavity 19. Pressure is maintained on the molding material within 
mold cavity 19 until the mold has cooled the molding material to a 
solidified state. At that time, the nozzle shut-off valve (not shown) is 
closed and screw rotation is again started and the cycle is again repeated 
to provide successive molded parts. 
Within the injection molding art, programmable controls have been developed 
which, assuming a consistently reliable non-return valve 30, will 
accurately collect a predetermined quantity of shot and then inject the 
shot at precisely controlled rates into mold cavity 19 which rates may 
vary during the injection cycle. A conceptually conventional control 
arrangement used to regulate shot size and flow rate is schematically 
illustrated in FIG. 1. The arrangement includes a conventional position 
indicating device 46 associated with screw 28 which generates an 
electrical feedback signal on electrical line 47. Similarly, a pressure 
transducer 49 associated with shot space 34 so as to measure the pressure 
of the molding material within shot space 34 generates an electrical 
feedback pressure signal on line 50. A programmable master controller 52 
such as a computer generates a pre-programmed electrical signal on line 53 
which controls motor 35 and this signal is compared to the electrical 
position indicating signal on line 47 and the pressure signal on line 50 
in a conventional, closed loop motor feedback circuit 54 which in turn 
develops a signal that controls motor 35. Similarly, master controller 52 
generates a pre-programmed signal for controlling pump 42 which during the 
injection cycle is compared to position indicating signal on line 47 and 
pressure signal on line 50 and a conventional pump, closed loop feedback 
circuit 57 develops a signal inputted on line 58 to control pump 42. This 
control arrangement permits an accurate quantity of shot to be collected 
in shot space 34 and a controlled injection of the molding material during 
the injection stroke. As is well known in the injection molding art, 
precision molding requires that the shot size consistently vary less than 
1% and that the rate at which the shot is injected into mold cavity 19, 
may be varied during the time of the injection cycle to produce molded 
parts having desired physical characteristics. Physical characteristics 
could include molded parts which do not have flow lines through thin 
sections of the part which can typically occur when the mold is designed 
so that the thin sections of the finished part feed thick sections of the 
molded part. 
For purposes of the subject invention, it should or will be clear that 
motor 35 is of the reversing type, and it is also to be understood that 
axial position indicator 46 can sense degrees of screw 28 rotation and 
develop a feedback signal to control reverse rotation of screw 28. It 
should also be apparent that computer 52 alternatively can function as a 
simple timer to control reverse rotation. The actual circuits by which any 
of the control functions described are believed conventional are readily 
available to those skilled in the art and thus are not shown or described 
in detail herein. The circuitry per se does not form part of the present 
invention. It is believed sufficient to simply note that reverse rotation 
of screw 28 can be accurately controlled by either measurement of shaft 
rotation or timing shaft rotation or combination thereof. 
Non-return valve 30 of the present invention is a three-piece valve 
assembly which includes a tip member hereinafter referred to as tip/stud 
member 60 shown in FIGS. 2-4, a check ring 31 shown in FIGS. 5 and 6, and 
an annular valve seat member 62 shown in FIGS. 8a, 8b, 9a and 9b. 
Referring now to FIGS. 2-4, tip/stud member 60 has a rearward end 64, a 
retainer forward end 65 and a rod portion 66 extending between rearward 
end 64 and retainer end 65. Rod portion 66 has a first cylindrical seat 
surface 68 adjacent rearward end 64 which abuts against a larger second 
cylindrical seat surface 69. As will be shortly explained, first and 
second cylindrical seat surfaces 68, 69 function to retain annular valve 
seat member 62 relative to screw 28. Rod portion 66 then includes a 
transition surface 71 which as best shown in FIGS. 3 and 4 is cylindrical 
adjacent second cylindrical seat surface 69 and tapers along transition 
line 72 into the rectilinear configuration of retainer end 65. The 
configuration of retainer end 65 includes a drive cam surface 75 which has 
a discrete width and which radially extends outwardly from transition 
surface 71 a fixed distance. Extending axially forwardly from each edge of 
drive cam surface 75 is a profile bearing surface 76, 77 there being two 
such profile surfaces, one extending from each edge of cam surface 75. 
Each profile bearing surface 76, 77 is a generally flat surface and is 
shaped in an arrowhead configuration with the tip of the arrowhead at the 
foremost forward edge of retainer end 65. 
In the preferred embodiment, drive cam surface 75 and check ring surface 88 
are each segments of a helical type barrel cam surface. Surface 75 is of 
sufficient area to reduce contact stress between surfaces 75 and 88 below 
that which would cause surface wear when surfaces 75 and 88 are in sliding 
contact relationship during valve closure with reverse rotation of screw. 
As will be explained in further detail hereafter, drive cam surface 75 
will axially displace check ring 31 upon reverse rotation of screw 28. 
Those skilled in the art will appreciate that check ring 31 is free to 
float in barrel 12 and what prevents check ring 31 from rotating in the 
direction of screw 12 when screw rotation is reversed is the viscous shear 
characteristics of the plastic film between the ID of barrel 12 and the OD 
of check ring 31. The viscous shear characteristics of the plastic acting 
over the entire OD surface area of check ring 31 thus provides a 
"retarding torque" resisting reverse rotation of check ring 31. When drive 
cam surface 75 contacts check ring 31, the "retarding torque" will be 
reduced by the value of the frictional force generated between drive cam 
surface 75 and check ring 31. If the frictional force between surfaces 75 
and 88 becomes great enough to reduce the "retarding torque" to zero, 
check ring 31 will rotate in the reverse direction of screw 12 and prevent 
valve closure. However, it is within the scope of the present invention to 
reduce the frictional force developed by contact between drive cam surface 
75 and surface 88 of check ring 31 by modifying the drive cam surface 75 
to include cylindrical cam rollers. Cylindrical rollers positioned on 
drive cam surface 75 (not shown) produce only rolling friction which would 
not develop significant forces acting in opposition to the retarding 
torque. Specifically, this modification would constitute the preferred 
embodiment of the invention where plastic material exhibits low value of 
retarding torque at normal operational settings. 
Referring next to FIGS. 5 and 6, check ring 31 is an annular ring having a 
forward annular edge surface 80 and a rearward annular edge surface 81. 
Rearward annular edge surface 81 could either be frusto-conical or ring 
shaped in configuration. The outside diameter of check ring 31 is sized 
closely to fit within barrel 30 in accordance with conventional practice 
so that molding material does not flow between ring OD and the barrel. The 
inside diameter of check ring 31 is larger than the diameter of second 
cylindrical surface 69 so that it can slide thereover but less than the 
outermost radial distance of cam surface 75 so that forward edge 80 of 
check ring 31 cannot slide past retainer end 65. Axially protruding from 
annular forward edge 80 is a pair of protuberances or tangs 83, 84 which 
are diametrically opposed to one another. Each tang 83, 84 has an axially 
extending contact edge surface 86 which extends axially forwardly from 
forward annular edge 80 a distance not less than, and preferably slightly 
greater than, the axial distance which check ring 31 can travel relative 
to tip/stud member 60. Each tang 83, 84 circumferentially extends about 
forward annular surface 80 a fixed arcuate distance defined as that 
distance extending between contact edge surface 86 and an entry edge line 
87. In the preferred embodiment of check ring 31 shown in FIGS. 5 and 6, 
entry edge 87 is coincident with forward annular edge surface 80. Thus, 
the face of each tang includes a cam ramp surface 88 which is arcuate as 
best shown in FIG. 6 and which extends over a circumferential portion of 
each tang 83, 84 from leading edge 87 until terminating in a flat surface 
89 which extends to and terminates adjacent to contact edge surface 86. 
Referring next to FIGS. 7, 8a, 8b, 9a and 9b, non-return valve 30 is shown 
in its assembled, unsectioned configuration but in FIGS. 8a, 8b, 9a, and 
9b, for reference purposes, non-return valve 31 is inserted into barrel 12 
and screw 28 which are shown sectioned. Further, non-return valve assembly 
30 in FIGS. 8a, 8b, 9a and 9b, is split into halves along its axially 
extending centerline 44 to better show the open and closed positions of 
check ring 31. Further, FIGS. 7, 8a, 8b, 9a and 9b show, for purposes of 
illustration and to indicate the invention has patentable features without 
mechanically driving check ring 31 into a closed position, tangs 83, 84 
which do not have cam ramp surfaces 88. 
Annular valve seat member 62 is shown with a frustoconical valve seat 
surface 91 which is adapted to mate with a similar frusto-conical valve 
seat surface 92 formed in check ring 31. Annular valve seat 62 has a first 
inside cylindrical surface 94 adjacent its rearward end of a diameter 
substantially equal to first cylindrical surface 68 on tip/stud member 60 
so as to tightly fit thereabout. Annular valve seat 62 also has a second 
internal cylindrical surface area 95 adjacent its front end which is 
adapted to tightly fit against second cylindrical surface 69 of tip/stud 
member 60. 
Non-return valve 30 is assembled by sliding check ring 31 over rod portion 
66 of tip/stud member 60 and then sliding annular valve seat 62 over 
rearward end 64 of tip/stud member 60. For drawing purposes and ease of 
explanation, rearward end 64 is shown as threaded in a conventional 
manner. A wrench grabbing flat profile surfaces 76, 77 rotates rearward 
end 64 of tip/stud member 60 into threaded engagement with a centrally 
threaded opening 97 in screw 28 and as tip/stud member 60 is threaded into 
screw bore 97, annular valve seat 62 is forced over first and second 
cylindrical surfaces 68, 69 of tip/stud member 66 until annular valve seat 
62 is compressed between an axial end face 98 of screw 28 and a radially 
extending flange formed between first and second cylindrical surfaces 68, 
69 of tip/stud member 60. As will be shortly explained because screw 28 
will rotate, clockwise and counterclockwise, in accordance with the 
teachings of the invention, provisions can be made to the connection 
between rearward end 64 and threaded opening 97 to prevent unscrewing (or 
loosening) of non-return valve 30. For example, tip/stud member 60 can be 
tightened to a minimum torque level which will be sufficient to prevent 
unscrewing of rearward end 64. Other conventional mechanisms can be used. 
For example, a flat on the threaded end of rearward end 64 could be 
provided and a threaded cross bore provided in screw 28 so that a set 
screw in the bore will seat against the flat to prevent rotation of 
tip/stud member 60. Alternatively, a lock washer can be provided. Other 
mechanisms preventing loosening of tip/stud member 60 which permitting 
removable attachment of rearward end 64 from screw 28 will suggest 
themselves to those skilled in the art. 
As thus assembled, tip/stud member 60 and annular valve seat 62 are affixed 
to screw 28 so that both members axially move and rotate with screw 28. 
Check ring 31 rotates with tip/stud member 60 in the drive or molding 
material feed direction of rotation of screw 28 indicated by arrow 100 in 
the drawings because of contact between contact surface 86 and profile 
surface 76 for first tang 83 and contact between contact surface 86 and 
second profile surface 77 for second tang 84. While check ring 31 rotates 
with tip/stud member 60 in the molding material feed direction, check ring 
31 is free to axially move within rod portion 66 of tip/stud member 60. 
More specifically, check ring 31 can axially move between the position 
shown in FIGS. 8a and 9a whereat valve seat surfaces 91, 92 contact one 
another to the position shown in FIGS. 8b and 9b whereat forward leading 
annular edge surface 80 of check ring 31 contacts drive cam surface 75 of 
tip/stud member 60. The movement is possible because tang contact surfaces 
86 can slide relative to side profile surfaces 76, 77. Further, check ring 
31 can assume to the extent permissible within barrel 12 attitudinal 
angular relationships relative to longitudinal centerline 44. Thus, check 
ring 31 is a freely floating member capable of moving axially and radially 
and as described thus far and with reference to the check ring 
configuration shown in FIG. 7 will rotate with tip/stud member 60. (As an 
aside, it should also be noted that retainer end 65 could be modified to 
have a plurality of flange surfaces 75 and a plurality of opposed tangs 
83, 84 and the coupling will still work. While a plurality of driving 
connections could be employed, it is preferred that only two tangs 83, 84 
be used as described from a material flow consideration.) In connection 
with the driven rotation of check ring 31, it should be noted that the 
axial distance or protrusion depth of contact surface 86 as in to FIGS. 8a 
and 8b relative to FIGS. 9a and 9b is longer than the axial travel limits 
of check ring 31 within rod portion 66 of tip/stud member 60 thus assuring 
driving engagement. As thus far described, wear between retainer end 65 
and check ring 31 in non-return valve 31 is eliminated because relative 
rotation between the members has been eliminated. Wear resulting from the 
axial sliding motion between tangs 84, 85 and profile surfaces 76, not 
significant because non-return valve 31 does not axial cycle at a 
frequency rate anywhere approaching the relative rotational motion of 
prior art non-return ring valves. What is happening is that the normal 
valve wear between retainer end 65 and check ring 31 in prior art 
non-return valves has been transferred in the design of the present 
invention to relative rotation between check ring 31 and barrel 12. 
However, this wear is now spread out over an area defined by the outer 
circumference of check ring 31 multiplied by its axial length and because 
this wear area has been tremendously increased when compared to wear area 
between retainer end and check ring of prior art valves, wear is not a 
significant problem. Further, for wear to occur, there must be both 
relative motion and a force acting on the parts in contact. Since the ring 
floats radially, the radial force of the ring on the barrel is reduced to 
substantially the weight of ring alone compared to the entire weight of 
the screw and valve as in the case of a ball check type valve. Therefore, 
wear between check ring and barrel is not a significant factor. Check ring 
31 may also be heat treated to a lower hardness than that of barrel screw 
12 to prevent barrel wear. 
Another significant feature of the invention as thus far described is the 
open flow area present in non-return valve 31 when compared to other prior 
art ring type non-return valves and this open area permits unimpeded 
passage of various molding materials through non-return valve 31. As best 
shown in FIG. 7, the flow area in the end view shown extends from the 
inner diameter of check ring 31 to profile surface 77 on one side and from 
the inner diameter of check ring 31 to the side profile surface 76 on the 
other side. 
The invention has been described thus far without reference to cam ramp 
surfaces 88 because non-return valve 30 can be used as disclosed in a 
conventional injection molding machine without reference to bi-directional 
screw rotation while still possessing advantages over prior art non-return 
valves and even over other check ring driven prior art valves. This 
results because of the drive configuration and the configuration of 
retainer end 65 of tip/stud member 60. Thus, when non-return valve is to 
cycle between open and closed position by virtue of molding material 
pressure differentials, non-return valve 30 is more responsive than prior 
art non-return valves. This occurs because more surface area of the 
annular front end face 80 of check ring 31 is exposed to the shot in shot 
space 34. In non-return valve 30 of the present invention, the area of 
forward annular edge surface 80 of check ring 31 when covered by the 
overlying area of drive cam surface 75 nevertheless is significantly 
greater than prior art valves meaning that the valve 30 of the present 
invention is less unbalanced and thus faster to move axially in accordance 
with pressure buildup in the shot in the injecting portion of the cycle. 
Since the valve is more responsive, this means that a more accurate 
quantity of shot can be regulated in shot space 34 by pressure 
differential. As thus far described, non-return valve 30 with the tang 
configuration which simply includes contact edge surface 86 operates as a 
conventional non-return valve but is improved in that wear is minimized 
between check ring 31 and retainer end 65 of tip/stud member 60. In 
addition, non-return valve 30 has a significantly large open flow area for 
handling a wide variety of plasticized molding materials which could 
otherwise be adversely affected by minimal flow rates in prior art 
non-return valves. Finally, non-return valve 30 is better balanced and 
more responsive to pressure differentials for quick opening and closing 
actions. 
When check ring 31 is provided with a cam ramp surface 88 shown in the 
preferred embodiment of the check ring of FIGS. 5 and 6, a significant 
advance in the control of shot size and anti-backflow art is made 
possible. As noted above, screw 28 rotates in a first direction whereat 
molding material is advanced through flights 29 to accumulate in barrel 
bore 44. At that time, screw rotation is stopped, the shut-off valve in 
the nozzle (not shown) is opened and piston 40 actuated to inject molding 
material into mold cavity 19. With the conventional control circuit shown 
in FIG. 1, it is possible to reverse the rotational direction of shaft 28 
through a predetermined fixed and controlled arcuate angle which equates 
to the axial distance which drive cam surface 75 rides up or axially 
displaces ramp surface 88 to positively drive valve seat 92 into contact 
with valve seat 91. This reverse rotation occurs prior to opening the 
shut-off valve and starting the injection stroke by piston 40. Preferably, 
the axial position of screw 28 is stationary or fixed within barrel 12 
while the screw's rotation is reversed. This can be accomplished by 
blocking oil flow to and from cylinder 41. Thus, shot material lost is 
only that volume displaced by axial movement of check ring 31 which for 
all intents and purposes is negligible. This means that throughput for 
non-return valve 30 with cam ramp surface 88 is very close to theoretical, 
especially when it is considered that the axial position of screw 28 does 
not shift. 
Positively and mechanically forcing check ring 31 to close prior to 
injection prevents varying loss of molding material through non-return 
valve 31 during the start of the injection stroke. That is, inconsistent 
closure of a valve operated by pressure differential alone is known to 
occur for any number of reasons such as pellets not completely plasticized 
or abrasive materials such as fiberglass strands, etc. This is prevented 
in the preferred embodiment. Not only is variation in shot weight 
controlled, but also and importantly, throughput of the injection molding 
machine is improved. Shot is not lost during the initial forward motion of 
screw 28 on the injection step as in conventional check ring non-return 
valves. Because the axial position of screw 28 does not change prior to 
injection, efficiencies close to theoretical values can be achieved. 
In accordance with the general concept of the invention, it is not 
necessary that the reverse rotation of the screw be driven through a 
precise rotational angle, although the invention would work if the motor 
rotation was reversely driven through a measured rotational angle. It is 
sufficient if only the reverse rotation time of motor 35 is measured and 
motor rotation stopped upon time out of a preset timer to assure valve 
closure. Any conventional timer can be employed. With respect to the 
schematic of FIG. 1, the timer could be set and controlled by master 
controller 52. Also, if desired, cam ramp surface 68 can be provided with 
an axially protruding stop at the point where valve closure in the annular 
check ring member 62 occurs. 
Referring now to FIG. 10, there is schematically shown a conventional, 
check ring non-return valve or alternatively the driven check ring 
non-return valve 30 of the present invention without the cam ramp surfaces 
88, i.e. the valve shown in FIG. 7. The non-return valve 30 is mounted to 
a screw 28 disposed within a barrel 12 and screw 28, for discussion 
purposes, is shown as a barrier screw which has a barrier portion 110 well 
known to those skilled in the art. A bi-directional rotation is imported 
to screw 28 through a conventional control arrangement such as that 
illustrated in FIG. 1. Importantly, for this embodiment of the invention, 
the ram pressure controlled through feedback controller 52 is regulated to 
maintain screw 28 in a fixed, axial position during reverse rotation. 
Check ring 31 is shown cross-sectioned in FIG. 10 in its open, shot 
accumulating position which occurs when screw 28 rotates in the direction 
of the reference arrow A. FIG. 10a shows diagrammatically the pressure 
profile developed along screw 28 for a given point of operation. The solid 
line 111 in FIG. 10a illustrates what the pressure distribution would be 
just at the end of the shot accumulating stroke prior to start of 
injection in accordance with conventional, standard molding practice, i.e. 
at completion of screw rotation in direction A. Pressure at line 1, 
P.sub.1, is the pressure which exists at the front of check ring 31. 
Pressure at line 2, P.sub.2, is the pressure which exists at the rear of 
check ring 31. Pressure at line 3, P.sub.3, is the pressure at the forward 
end of barrier 110 while pressure at line 4, P.sub.4, is the pressure at 
the rearward end of barrier 110. Barrier 110, by trapping plastic over 
that portion of screw 28 between lines 2 and 3, thus aggravates or causes 
a back pressure contributing to higher values of P.sub.2. 
Pressure graph line 111 thus shows that because P.sub.2 is greater than 
P.sub.1, non-return valve 30 is pressure balanced into an open, shot 
accumulating position. In any pressure operated valve, the valve will not 
and cannot close until P.sub.1 is made greater than P.sub.2. Thus, prior 
to the injection stroke, the non-return valve 20 is pressure biased in the 
wrong direction. Thus, the valve does not close right away and plastic 
material is "lost" from the shot and shot size varies. 
Heretofore, increasing P.sub.1 to be greater than P.sub.2 was accomplished 
in one of two ways or a combination thereof. In performing the standard 
injection forward stroke to fill the mold (i.e., the injection stroke), 
two things happen to permit the valve to close. Plastic or molding 
material flows from screw area between lines or points 2-3 over barrier 
110 between lines or point positions 3-4 so that P.sub.2 goes down and at 
the same time, resistance to flow of the plastic or molding material into 
the mold causes P.sub.1 to increase. When P.sub.1 becomes greater than 
P.sub.2, non-return valve 30 closes. A second way to change the pressure 
distribution is the standard pull back technique where screw 28 is axially 
retracted into barrel 12 (towards the right in FIG. 10) a short axial 
distance. As noted above, there are drawbacks resulting from the axial 
shift of screw 28 relating to the molded product, i.e splay. However, when 
pullback occurs and just prior to the injection stroke, the pressure 
distribution along the screw and valve would approach or assume the 
configuration shown by dotted line 115. 
In accordance with one of the concepts of the present invention, rotating 
screw 28 in the reverse direction, that is in the direction of arrow B, 
can be viewed as "pumping" plastic material in the reverse direction from 
area between lines 2-3 over barrier portion defined by lines 3-4 so that 
P.sub.2 will drop down immediately. The pressure distribution will assume 
the general shape indicated by dotted line 115 in FIG. 10a and non-return 
valve 30 will closely immediately upon start of the forward injection 
stroke. It is to be appreciated that reverse rotation of the screw 28 is 
only through a small angle and further the axial position of screw 28 in 
barrel 12 remains stationary so that shot volume remains constant. 
Importantly, limitations on the use of the conventional pullback technique 
which relate to product quality are not present in the invention. Thus, 
reverse rotation of screw 28 in combination with cam ramp surface 88 
permits a positive, mechanically driven shut-off of non-return valve 30. 
However, reverse rotation of screw 28 in combination with any pressure 
operated non-return valve will permit the valve to be more responsive 
because of pressure unloading behind the valve prior to the injection 
stroke. 
The invention has been described with reference to a preferred embodiment. 
Obviously, modifications and alterations will occur to those skilled in 
the art upon reading and understanding of the invention disclosed herein. 
For example, a protuberance could be applied to retainer end 65 of 
tip/stud member 60 and a groove formed in annular end face 80. 
Alternatively, a pin or pin with roller or a flight could extend from 
retainer end 65 and fit within grooves formed on the inside of check ring 
31. More than two tangs could be used. It is intended to include all such 
modifications insofar as they come within the scope of the present 
invention.