Injection molding valve gated system

This invention relates to an improved valve gated injection molding system in which the heated nozzle has a nose portion which extends through a cylindrical opening in the cavity plate to the cavity. The valve gate extends through the nose portion and is tapered so that the forward face of the nose portion can be machined to a predetermined length to provide a gate of a particular size. This has the advantage of improving heat transfer to the gate area and reducing the accuracy required of the moldmaker in that both the valve pin and the matching seat in the gate are provided by the manufacturer. Furthermore, each size of nozzle can be adapted for several different gate sizes which reduces manufacturing and inventory costs.

BACKGROUND OF THE INVENTION 
This invention relates to valve gated injection molding and more 
particularly to an improved system in which the heated nozzle has a nose 
portion which extends through an opening in the cavity plate directly to 
the cavity and itself forms the gate in which the tip end of the valve pin 
seats to control the flow of melt to the cavity. 
As is well known in the art, this type of injection molding sytem has an 
insulative air space extending between the heated nozzle and the cooled 
cavity plate. In many early applications, this space was allowed to fill 
with melt which partially solidified and acted as an insulator. However, 
this has the disadvantage that it is difficult, if not impossible, to 
clear the previous material on colour and/or material changes, and 
furthermore for some materials additional heat is required in the gate 
area to ensure satisfactory seating of the valve pin in the gate. 
Thus, in order to overcome these problems, the applicant provided a hollow 
cylindrical nozzle seal formed of titanium as described in the applicant's 
U.S. Pat. No. 4,043,740 which issued Aug. 23, 1977. This seal is seated in 
both the nozzle and cavity plate to bridge the air space around the gate. 
More recently, as described in the applicant's U.S. Pat. No. 4,286,941 
which issued Sept. 1, 1981, a titanium nozzle seal has been provided which 
extends through an opening in the cavity plate right into the cavity to 
provide even more heat in the gate area adjacent the cavity. While these 
previous systems have been very successful, they have the disadvantages 
that a particular unit has to be used for a particular gate size and the 
moldmaker has to be very precise in making the gate the correct size and 
the correct angle. 
In a more recent application relating to a different aspect of sprue 
gating, the applicant discloses in Canadian patent application Ser. No. 
370,734 filed Feb. 12, 1981 entitled "Heated Nozzle Bushing with Fixed 
Spiral Blade", a heated nozzle or nozzle bushing with a portion which 
extends through the cavity plate to the cavity. However, this structure 
was necessary to extend the spiral blade right to the cavity, and there is 
no suggestion it could be transposed to a valve gated system requiring a 
gate to seat the valve pin in. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to at least partially 
overcome the disadvantages of the prior art by providing a valve gated 
system in which the heated nozzle has a nose portion which is received in 
an opening in the cavity plate which is easy to make. In one of its 
aspects, the nozzle can be adapted for a particular gate size by machining 
off a portion of the nose portion. 
To this end, in one of its aspects, the invention provides a valve gated 
injection molding system having a heated nozzle seated in a cooled cavity 
plate, an elongated valve pin which reciprocates in the heated nozzle 
between open and closed positions, a melt passage which extends through a 
bore in the heated nozzle around the valve pin and conveys hot pressurized 
melt from a molding machine to a gate leading to a cavity which is 
partially defined on one side by a face of the cavity plate, the valve pin 
having a driven end and a tip end which seats in the gate in the closed 
position, and valve pin actuating mechanism which engages the driven end 
of the valve pin to drive it between the open and closed positions, 
including the improvement wherein the heated nozzle has a nose portion 
with a forward face, the nose portion being tightly seated in an opening 
in the cavity plate to the cavity, the nose portion extending through the 
opening to a position wherein the forward face of the nozzle portion is in 
substantial alignment with said face of the cavity plate to define said 
one side of the cavity, the nose portion having the gate therein extending 
from the bore to the cavity. 
In another of its aspects, the nose portion of the heated nozzle is formed 
with at least a portion of the gate tapered to decrease in size away from 
the bore, whereby a predetermined portion of the nose portion may be 
machined off prior to assembly to increase the minimum size of the gate at 
the forward face of the nose portion to a particular cross-sectional area 
and to reduce the length of the nose portion. 
Further objects and advantages of the invention will appear from the 
following description taken together with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Reference is first made to FIG. 1 which shows one heated nozzle 10 of a 
multi-cavity hydraulically actuated valve gated injection molding system 
seated in a steel cavity plate 12 with a cavity 14 extending between the 
cavity plate 12 and a movable mold platen 16. A manifold 18 positioned by 
locating ring 20 extends between the heated nozzle 10 and cavity plate 12 
and a back plate 22. The heated nozzle 10 is formed generally of a 
corrosion and abrasion resistant metal such as steel, but has an electric 
heating element 24 cast into an inner portion 26 formed of a highly 
thermally conductive metal such as copper to more rapidly disperse the 
heat to the steel. The heated nozzle 10 has a central bore 28 which 
receives an elongated valve pin 30 having a driven end 32 and a tip end 
34. The driven end 32 of the valve pin 30 is engaged by hydraulically 
driven actuating mechanism which is seated in the back plate 22 and 
reciprocates the valve pin longitudinally between the open position shown 
and a closed position in which the tip end 34 is seated in a gate 36 
leading to the cavity 14. 
The actuating mechanism includes a piston 38 which reciprocates in a 
cylinder 40 seated in a bore in the back plate 22. The cylinder 40 is 
secured in position by bolts 42 extending through a flanged portion 44. 
The cylinder is sealed by a cap 46 which is screwed into the cylinder 40 
and tightened by a forked wrench (not shown) which has pins that fit into 
the small holes 48 in the top of the cap 46. The valve pin 30 extends 
through a hole in the piston 38 and is secured to it by a plug 50 which is 
tightened against the driven end 32 of the piston by inserting a hexagonal 
wrench (not shown) into a socket 52. The piston 38 has an O-ring 54 which 
provides a seal between it and the cylinder, and a high temperature seal 
is provided around the neck 56 of the piston 38 by a V-shaped flexible 
ring 58 which is held in position by an expansion washer 60 seated in a 
groove. An abutment sleeve 62 is located between the piston 38 and the cap 
46 so that the extent of travel of the piston 38 and the valve pin 30 in 
the open position can be adjusted by changing the height of the abutment 
sleeve 62. As described in more detail in the applicant's U.S. patent 
application Ser. No. 485,024 filed Apr. 14, 1983 entitled "Hydraulically 
Actuated Injection Molding System with Alternate Hydraulic Connections", 
the piston is driven according to a predetermined cycle by the application 
of pressurized hydraulic fluid through ducts 64,66 leading to the cylinder 
40 on opposite sides of the piston 38. 
A melt passage 68 branches out from a recessed inlet 70 through the 
manifold 18 and extends around the valve pin 30 through the bore 28 in the 
heated nozzle 10 to the gate 36. The melt passage 68 joins the bore 28 in 
a stainless steel bushing seal 72 which is seated in the nozzle 10. As 
described in the applicant's U.S. Pat. No. 4,026,518 which issued May 31, 
1977, the bushing seal prevents leakage of the pressurized melt along the 
reciprocating valve pin 30. 
The cavity plate 12 and back plate 22 are cooled in a conventional manner 
by cooling channels 74. As described above, the nozzle 10 is heated by the 
insulated electrical element 24 which is cast into it and receives power 
through terminals 76 (only one shown) to maintain the melt flowing through 
the melt passage 68 within the necessary temperature range. The heated 
nozzle 10 is seated in the cavity plate 12 on an insulation bushing 78 
which provides an insulative air space 80 between the hot nozzle and the 
cool cavity plate. Similarly, the locating ring 20 separates the hot 
manifold 18 from the cool cavity plate to ensure the insulative air space 
80 continues between them. As may be seen, a second insulative air space 
82 extends between the cool back plate 22 and the hot manifold 18. 
As mentioned above, in the past, the gate to the cavity has extended 
through the cavity plate itself and the air space 80 between the heated 
nozzle 10 and the cavity plate 12 has been bridged by a cylindrical 
titanium nozzle seal extending around the gate. As may be seen, according 
to the present invention, the heated nozzle 10 has a cylindrical shaped 
nose portion 84 through which the gate 36 extends to the cavity 14. The 
nose portion 84 is securely seated in a cylindrical opening 86 through the 
cavity plate 12 and has a forward face 88 which, at working temperature, 
is in alignment with the face 90 of the cavity plate 12 which partially 
defines the cavity 14. In addition to sealing off the air space 80 from 
the pressurized melt, this arrangment has the advantage for critical 
temperature materials such as polyester and also very high and sharp 
melting point materials that a more uniform temperature is provided right 
into the cavity. In other words, improved heat transfer is provided to the 
gate area and it is not necessary to overheat the melt in the area of the 
heating element 24 to avoid too low a temperature adjacent the cavity. As 
compared with the great majority of polymers which have a gradual 
softening curve, there is a variety of heat and shear sensitive polymers 
with high and sharp melting points where it is desirable to have a gate 
temperature that is somewhat below the melting point of the polymer, 
without the temperature of the melt at any other point in the system 
rising to more than about 20.degree. C. above its melting point. For these 
mostly crystalline polymers, a simple means of adjusting gate temperature 
without separate heating means is important. 
In addition, as will now be described with particular reference to FIG. 2, 
this structure enables the nozzle manufacturer to supply a single size of 
nozzle which may be readily adapted by the customer's moldmaker to the 
necessary gate size for a particular application. FIG. 2 shows the nose 
portion 84 and the valve pin tip end 34 as they are supplied by the 
manufacturer prior to installation. The moldmaker then machines the nose 
portion to a particular length corresponding to one of the dotted lines 
shown in FIG. 2 which provides the gate with a selected minimum size at 
the forward face 88 due to the fact that the gate 36 is tapered in the 
area. The manufacturer provides the moldmaker with a chart showing the 
nozzle length to which the nose portion must be machined to provide 
minimum gate diameters of say 1.5 mm, 2.0 mm, 2.5 mm or 3.0 mm. Of course, 
the tip end 34 of the valve pin 30 must similarly be machined to a 
selected length to correspond to the minimum gate diameter as indicated by 
the dotted lines in FIG. 2. The tip end 34 of the valve pin 30 is tapered 
to match the taper of the gate 36 to provide a tight seal in the closed 
position. As will be appreciated, both of these are formed by the 
manufacturer and the gate is normally lapped to provide a good match. 
Thus, the moldmaker has the much easier task of providing cylindrical 
opening 86 through the cavity plate rather than forming a tapered gate of 
a particular size to match a particular valve pin. 
In use, the moldmaker machines the nose portions 84 of the nozzles and the 
tip ends 34 of the valve pins 30 to provide gates of a particular size, 
and the system is assembled as shown in FIG. 1. The cylindrical opening 86 
in the cavity plate 12 is made to receive the nose portion 84 of the 
nozzle 10 when it is cool so that it expands to provide a tight press fit 
when the nozzle is heated to operating temperature. The amount of heat in 
the gate area may also be increased by the moldmaker reducing the length 
of contact H between the cooled cavity plate 12 and the nose portion 84 of 
the heated nozzle 10. This will depend upon the material to be molded; for 
instance H might be about 2 mm for nylon and about 4 mm for PVC or ABS. It 
is, of course, necessary that the insulation bushing 78 be machined to 
provide for substantial alignment of the forward face 88 of the nose 
portion 84 with the adjacent cavity face 90 of the cavity plate after heat 
expansion at operating temperature. Similarly, the height of the locating 
ring 20 is adjusted to accurately position the manifold 18 against the 
nozzle 10. 
Electrical power is then applied to the terminals 76 of the heating element 
24 to heat the nozzle 10 up to operating temperature. Pressurized melt 
from the molding machine is then introduced into the melt passage 68 and 
controlled hydraulic pressure is applied to the actuating mechanism 
according to a predetermined cycle in a conventional manner. After 
sufficient melt has been injected to fill the cavity 14 and the high 
injection pressure held for a short period to pack, the hydraulic pressure 
is applied to reciprocate the valve pin 30 and piston 38 to the closed 
position in which the valve pin tip end 34 is seated in the gate 36. The 
melt pressure is then reduced and the position held for a cooling period 
before the mold is opened for ejection. After the mold is closed again, 
hydraulic pressure is applied to reciprocate the valve pin 30 to the open 
position and the high injection pressure is reapplied. The forward face 88 
of the nose portion 84 and the adjacent face 90 of the cavity plate 12 
form one side of the cavity 14, and therefore it is important that the fit 
between them be tight to provide the desired temperature in the gate, 
minimize the witness line on the product, as well as, of course, to avoid 
leakage. 
Reference is now made to FIG. 3 which shows an alternate embodiment of the 
invnetion in which the nose portion 84 of the heated nozzle 10 has a 
somewhat different configuration. In this embodiment, the nose portion 84 
is undercut to provide it with a cylindrical shaped head portion 92 
extending from a reduced diameter neck portion 94 to the forward face 88. 
This extends the air space 80 down around the reduced neck portion 94 and 
reduces heat loss to the cavity plate 12 and also enhance heat transfer to 
the gate area. Thus, this undercut configuration may be used in addition 
to or instead of increasing height H for materials where less heat is 
required or can be tolerated at the forward face 88. Otherwise, the 
structure and operation of this embodiment of the invention is the same as 
that described above, and the description need not be repeated. 
Although the description of this invention has been given with respect to 
particular embodiments, it is not to be construed in a limiting sense. 
Variations and modifications will occur to those skilled in the art. For 
instance, different types of nozzles and/or actuating mechanisms could be 
used within the scope of the invention. For a definition of the invention, 
reference is made to the attached claims.