Hot runner valve gated system

A hot runner valve gated system comprising at least one nozzle housing adapted to be positioned in a manifold plate. The nozzle housing includes a gate orifice and a reciprocal valve stem positioned therein. The system also includes a mechanism for moving the valve stem for opening and closing the gate valve and is designed to maintain the mechanism for moving the valve stem in a substantially cooled state. The mechanism for moving stem is positioned coaxially relative to the nozzle housing.

BACKGROUND OF THE INVENTION 
This invention relates to hot runner valves, and more particularly, to hot 
runner valves designed for cooling the motive mechanism thereof during the 
operation of the valve. 
Hot runner systems can be categorized into two types with respect to the 
method of closing off the mold cavity injection gate. These types include 
a thermally closed gate and a mechanically closed gate. This invention 
relates to mechanical or valve gate closing mechanisms for use in 
multi-cavity or high cavitation molds and molding systems as well as 
single cavity molds. Typically, a valve gated actuating mechanism is a 
unitized device which is attached to a valve stem or other commonly known 
gate closing component. Accordingly, valve stem actuation devices 
typically consume a considerable amount of space within a mold platen. As 
a result of such large space consumption, molds are formed which are too 
large for typical injection molding machine, resulting in increased 
expense due to the necessity to use larger and more materials for 
producing a larger mold to accommodate the mechanism. 
Such a scenario typically arises when a valve gated hot runner system is 
desired for a multi-level or stack mold. Most valve gated actuation 
mechanisms assume a large space which would be better used for an opposing 
injection nozzle housing arrangement. Such is the case for typical 
mechanically actuated closed gate mechanisms and a typical thermally 
activated closed gate mechanisms. In comparing two such mechanisms, it is 
obvious that the mechanically closed gate is generally significantly 
larger than the thermally closed gate. Accordingly, it would be beneficial 
in the art to design a mechanically actuated closed gate system of a size 
comparable to thermally closed gate systems. 
German patent 1,133,880 shows a nozzle suitable for attachment to the end 
of an injection molding machine extruder. The actuating mechanism used to 
move the valve stem in reciprocating fashion is shown as an annular 
piston, where a pressurized fluid is employed as the motive force. As with 
all piston type actuators, it is necessary to provide resilient seals 
which serve to prevent pressure leak from the pressurized chambers on both 
sides of piston, so that maximum force is transferred to the piston. 
Additionally, pressurized fluid leakage can lead to, wasting energy or 
fluid substance; creating undesirable noise; fire hazards; and undesirable 
cooling effects on the hot melt conveying components adjacent to it. The 
resilient seals for this nozzle design must be of a very high temperature 
capability. 
Plastic conveying equipment, such as that described in the German patent, 
often needs to operate at temperatures well over 500.degree. F. Resilient 
seals which can survive in such an environment for desirable periods of 
time are either unavailable or require that a more complex, multiple-piece 
piston design be used. Additionally, such seals are prohibitively 
expensive and will not provide a 100% seal over extended periods of time. 
Although the German patent does not show or describe the method of piston 
sealing, it is presumed that it suffers from the sealing/leaking problems 
as discussed above. 
U.S. Pat. No. 4,082,226 shows another gate valve actuating mechanism. An 
annular piston of complex and bulky design is used, which includes many 
parts requiring high manufacturing expense and laborious assembly time. By 
necessity, the piston seals must withstand a very high temperature to 
provide prolonged service next to the hot medial portion of the nozzle. 
The very bulky piston design, because of its ratio of height to diameter, 
is prone to cocking and jamming should one of the piston posts 50 show 
resistance to slide due to sticking or friction. Also, as seen in FIG. 7 
of the patent, the valve stem 66 must hit the outlet bore 71 to stop 
travel of the stem. Such contact can lead to undesirable wear and possibly 
the damage of the bore and front nozzle portion. 
U.S. Pat. No. 4,443,178 shows a compact method of actuating a valve stem 
using a spring, as shown in FIG. 8. However, this method relies on plastic 
pressure to push the valve stem back and the spring pressure is not 
readily adjustable with respect to force or time desired of the stem to 
close the gate. A pressurized piston is far superior in its ability to 
readily vary stem force as well as permit actuation of the stem while 
pressure still exists in the system or delay closing of the stem even 
after pressure has been released. 
U.S. Pat. No. 4,832,593 shows a design similar to the aforementioned 
patent, but where the motive means, in this case an air piston, is not 
annular in shape. The piston is solid and is positioned on the center axis 
and directly behind the nozzle housing. Because the piston resides within 
the heated body used to convey plastic melt to the nozzle housing, it 
requires a cast iron piston ring as a sealing device to withstand the high 
temperatures. Such metal-on-metal dynamic seals inherently do not provide 
100% sealing efficiency and thereby are not capable of allowing maximum 
supply pressure to act on the piston face. Also, it can be seen from FIG. 
1 that the nozzle body is necessarily much larger in diameter than the 
nozzle itself and the axial length of the nozzle and nozzle body together 
is extended, due to the internal space required to provide the piston 
assembly. 
All of the above cited patents are not adaptable for use inside an 
injection mold frame, especially in a mold where molding cavity spacing is 
dense, so as to maximize production output from the molding tool. Nor do 
they permit the design of a multi-level or stack mold with a minimum mold 
open distance, compatible with standard injection machines. Also, the 
prior art does not disclose an appropriate piston assembly design or 
piston seal which overcomes leaking, wear or attrition in a very hot 
environment. 
There exists, therefore, a need in the injection molding art for a 
mechanically actuated valve gated system which is self-cooling and space 
efficient. 
SUMMARY OF THE INVENTION 
The primary object of this invention is to provide a space efficient 
mechanically actuated valve gated system. 
Another object of this invention is to provide a mechanically actuated 
valve gated system which is self-cooling so as to reduce wear of heat 
sensitive parts. 
Yet another object of this invention is to provide a mechanically actuated 
valve gated system which functions to alleviate weld lines. 
Still another object of this invention is to provide a mechanically 
actuated self-cooling valve gated system having a motive means coaxially 
positioned relative the nozzle housing for acquiring a space efficient 
design. 
And still another object of this invention is to provide a valve gated 
system which is particularly useful for stack mold arrangements due to the 
space efficient design thereof. 
The foregoing objects are obtained by the inventive hot runner valve gated 
system of the present invention which comprises at least one nozzle 
housing adapted to be positioned in a manifold plate. The nozzle housing 
includes a gate orifice and a reciprocal valve stem positioned therein. 
The system also includes means for moving the valve stem for opening and 
closing the gate valve and is designed to maintain the means for moving 
the valve stem in a substantially cooled state. The means for moving the 
valve stem is preferably positioned coaxially relative to the nozzle 
housing. 
In one embodiment of the invention, the piston is substantially cylindrical 
having a wall with an inner diameter adjacent the nozzle housing. The wall 
includes an opening therein adapted to engage a stop for terminating the 
piston stroke. In the same embodiment, and during the opening of the valve 
system, the piston stroke is of a distance which substantially removes the 
valve stem from the flow path of the molding material such that weld lines 
are not formed. This embodiment also includes means for creating a seal 
between the piston and the manifold plate, wherein the means for cooling 
is also adapted to cool the means for creating a seal. 
The details of the present invention are set out in the following 
description and drawings wherein like reference characters depict like 
elements.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings in detail, there is shown in FIG. 1 an 
overhead cross-sectional view of the hot runner gate valve system of the 
present invention, designated generally as 10. The valve gated system 10 
generally includes a valve stem 12, a sleeve 13, a cylindrical piston 14 
and a nozzle housing 16. System 10 is adapted to be positioned within a 
mold plate, as mold manifold plate 18, sandwiched between manifold backup 
plate 20 and mold plate 22. 
Mold manifold plate 18 includes a bore 24 therein for receiving valve gated 
system 10 of the present invention. Bore 24 has a diameter for slidably 
engaging the outer surface of cylindrical piston 14. The inner surface of 
cylindrical piston 14 slidably engages the outer surface of cylindrical 
sleeve 13, and nozzle housing 16 is positioned coaxially within sleeve 13. 
Nozzle housing 16 extends outwardly from surface 26 of mold manifold plate 
18 adjacent mold plate 22, extending partially into mold plate 22. 
Referring to FIGS. 1 and 2, nozzle housing 16 is essentially an elongated 
rod shaped member having a base portion 23 adapted to be fastened inside 
mold manifold plate 18. Nozzle housing 16 includes at least one channel 
28, preferably two as shown in FIG. 2, extending therethrough and in 
communication with melt flow channel 30 located in hot runner manifold 31. 
Channel 28 extends substantially the length of nozzle housing 16 and 
converges with channel 32, which runs longitudinally in nozzle housing 16, 
and guides valve stem 12. Channel 28 and valve stem channel 32 converge 
toward the end of nozzle 16 adjacent mold plate 22. With valve stem 12 in 
the closed position as shown in FIG. 1, the end of valve stem 12 blocks 
the flow of molding material through channel 28 and into valve stem 
channel 32. However, with valve stem 12 in the retracted position as shown 
in FIG. 3, molding material is allowed to flow through channel 28 into 
valve stem channel 32 which also leads into mold plate 22. Upon closing 
the valve, valve stem channel 32 extends to a position relatively close to 
injection gate orifice 33, thereby assuring a true center location of the 
valve stem in the gate and avoiding undue wear caused by valve stem 
bending or flexing during the closing of the valve stem. 
Actuation of valve stem 12 in a reciprocating manner for opening and 
closing the flow path of the molding material from channel 28 into valve 
stem channel 32 is accomplished via the sliding movement of piston 14 
against sleeve 13. Piston 14 is set into motion by the use of pressurized 
air directed into ports 34 and 36 which extend through mold manifold plate 
18 in fluid communication with the outer surface of cylindrical piston 14. 
An annular space 38 is located between bore 24 and sleeve 13 for the 
movement therein of piston 14. However, in order to direct the fluid 
against the outer surface of the piston, the piston is necessarily not 
entirely cylindrical in shape. 
The piston is essentially annular in shape, including a first and second 
wall thickness wherein the first wall thickness at the ends of piston 14 
is substantially half the width of the annular space 38 and at the middle 
portion of piston 14, the wall is substantially equivalent in width to the 
annular space such that the central portion slidably engages bore 24. The 
differing widths form walls 39a and 39b on which the fluid or air can be 
directed. Accordingly, when pressurized air is directed into ports 34 and 
36, the air is directed into the annular space not occupied by piston 14. 
In order to place the valve gated system in the closed position as shown 
in FIG. 1, air is directed into port 34 against wall 39a and in order to 
place the valve gated system in the open position as shown in FIG. 3, air 
is directed into port 36 against valve 39b. 
Because the piston is of annular design, it cannot achieve the same force 
as a solid piston under equal air pressures, for a given outside diameter. 
Consequently, to achieve an equivalent force, the air pressure must be 
increased. Alternatively, the outside diameter of the annular piston can 
be increased in size to provide the equivalent force under the same air 
pressures used for solid pistons. Such an increase in diameter will not 
cause the piston to become prohibitively large or space consuming, 
typically requiring an increase in outside diameter of only approximately 
one third the diameter of a solid piston. In comparison to the prior art 
of the assembly of the present invention, as a whole, remains 
substantially more compact. 
Piston 14 also includes a series of seals 40a and 40b, and 42a and 42b, 
wherein seals 40a and 40b are positioned between the outer surface of 
piston 14 and bore 24 and seals 42a and 42b are positioned between the 
inner surface of piston 14 and sleeve 13. The seals function to allow 
pressure build-up in annular space 38 on each end of piston 14 for moving 
the same through the annular space for opening and closing the valve gated 
system. Due to the construction of sleeve 13 and other cooling features 
discussed below, seals 40a and 40b and seals 42a and 42b can be typical 
O-ring seals, not requiring special materials for withstanding high 
temperatures. 
Valve stem 12 is reciprocated through nozzle housing 16 via a mechanical 
attachment between piston 14 and valve stem 12. That is, a cross bar 44 
extends from piston 14 inwardly through an opening 46 in sleeve 13 and 
into a cavity 48 in nozzle housing 16. Upon the movement of piston 14 
through annular space 38, cross bar 44 is also moved through opening 46 
and cavity 48 and due to the connection of bar 44 with valve stem 12, 
valve stem 12 is moved with the movement of piston 14. Within cavity 48, a 
cap 50 is attached to cross bar 44 and is adapted to engage a back wall 52 
(See FIG. 1) upon a complete opening stroke of the piston, as shown in 
FIG. 3. Referring back to FIG. 1, piston 14 is limited to a stroke of a 
"A" which is essentially the size of opening 46 and the length of the 
space between cap 50 and back wall 52. Stroke "A" is designed at a 
distance such that valve stem 12 is moved substantially out of the flow 
stream of channel or channels 28 so that a weld seam is avoided. 
Sleeve 13, coaxially positioned relative to nozzle housing 16, functions to 
guide piston 14 adjacent nozzle housing 16 and also functions to align 
nozzle housing 16 centrally within bore 24 through mold manifold plate 18. 
Preferably, sleeve 13 is formed from a material having low thermal 
conductivity properties, such as ceramic. By using a material of low 
thermal conductivity, heat generated in nozzle housing 16 of system 10 can 
be maintained confined to the nozzle housing area. That is, because the 
material comprising the sleeve will not conduct heat well, heat is not 
transferred from nozzle housing 16 to the outside area which includes 
piston 14, seals 40 and 42, and annular space 38. Because of this property 
of sleeve 13, seals 40 and 42, as discussed above, can be constructed from 
a material which does not have to be substantially heat resistant. 
By constructing sleeve 13 from a material having low thermal conductivity, 
the piston seals 40 and 42 will operate at lower temperatures and perform 
over a longer period of time. A temperature drop of 50.degree. F. may be 
sufficient to allow the seal to operate for such an extended period. To 
achieve this drop, the sleeve is constructed from materials such as, for 
example, ceramic or titanium alloy. These materials possess a thermal 
conductivity of much less than 10 BTU/ft hr F..degree., typical of steels 
generally used, thereby reducing the temperature of the seals to suitable 
values. 
During the processing of certain molding materials or plastics through the 
hot runner valve gated system 10 of the instant invention, minute amounts 
of plastic processing byproducts may make their up the valve stem channel 
32. For such a case, a drainage channel 54 has been provided which leads 
to a free air space such as the one between hot runner manifold 31 and 
mold manifold plate 18. At this space, the byproducts have ample room to 
collect before requiring a periodic clean out. In addition, the byproducts 
are prevented from progressing further up the valve stem bore and impeding 
the operation of piston 14 and bar 44. 
An advantageous application of the system 10, described above, is shown in 
FIG. 4 for use with a stack mold design. The simplicity of this design in 
comparison to the prior art discussed above can be readily appreciated by 
reviewing the figures of the present invention. The savings in space 
offered by the compact design of the system of the instant invention 
allows a stack mold to fit into tight capacities, allowing greater 
flexibility and efficiency on the production floor of the molder. Also, 
because of the reduction in distance between opposing cavity gate orifices 
33 for stack molds, the novel design allows closer spacing of the molding 
cavities as compared to the prior art. The cavities may be spaced at a 
pitch slightly greater than the overall diameter of the nozzle housing 
assembly itself. 
Another embodiment of the invention is shown in FIG. 5, wherein the means 
for maintaining the means for reciprocating in a cooled state include 
cooling channels. The cooling channels are placed between the mold 
manifold plate and sleeve 213. Accordingly, at various points along the 
length of nozzle housing 216, a coolant is introduced into a port 271 
through a channel 272 and into an annular space 238 between mold manifold 
plate 218 and sleeve 213. The fluid is removed from the other side of 
nozzle housing 216 through channel 274. In this manner, a more direct 
cooling of seals 276 can be achieved. 
In the embodiments described above in FIGS. 1-5, the system is preferably 
installed into mold or manifold plate 18 from the front, i.e., the side 
defined by front surface 26. That is, the nozzle assembly can be inserted 
from surface 26 of manifold plate 18. This feature provides for easier 
maintenance when required, as plates 18 and 20 do not have to be separated 
for access or removal of the nozzle assembly from the rear surface. 
Accordingly, with this design, the manifold can remain between the mold 
plates and not be disassembled. 
In operation, and in order to move the gate valve system from the closed 
position in FIG. 1 to the open position in FIG. 3, pressurized air is 
introduced into port 36 against wall 39b of piston 14. The pressurized air 
functions to move the piston 14 through the annular space 38 until cap 50 
collides with the wall 52 of cavity 48 in nozzle housing 16. At this 
point, valve stem 12 is retracted from gate orifice 33, as shown in FIG. 3 
and molding material can be introduced through channel or channels 28 and 
into the end of valve stem channel 32. Accordingly, the molding material 
is directed into valve gate orifice 33 and into the mold. Because the 
molding material must flow smoothly through channel or channels 28 nozzle 
housing 16 is heated for maintaining viscosity. 
Sleeve 13, constructed from the low thermal conductivity material, 
functions to confine that heat produced in nozzle housing 16 to the area 
surrounding nozzle housing 16 and does not conduct the heat outwardly to 
piston 14. Accordingly, seals 42a and 42b do not become warmed by the heat 
and have a longer life span. In addition, special and expensive seals 
which can withstand high temperatures do not have to be used. If along 
with using sleeve 13, the embodiment of FIG. 5 is used, wherein coolant is 
passed through cooling channels, the coolant is circulated through the 
channels during and prior to the introduction of the molding material into 
the nozzle housing for maintaining the piston and seals at a relatively 
cool temperature. 
The primary advantage of this invention is that a space efficient 
mechanically actuated valve gated system is provided. Another advantage of 
this invention is that a mechanically actuated valve gated system is 
provided which is designed for being self-cooling so as to reduce wear of 
heat sensitive parts. Yet another advantage of this invention is that a 
mechanically actuated valve gated system is provided which functions to 
alleviate weld lines. Yet another advantage of this invention is that a 
mechanically actuated valve gated system is provided having a motive means 
coaxially positioned with the nozzle housing for acquiring a space 
efficient design. And still another advantage of this invention is that a 
valve gated system is provided which is particularly useful for stack mold 
arrangements due to the space efficient design of the system. 
It is apparent that there has been provided in accordance with this 
invention a improved gate valve which fully satisfies the objects, means, 
and advantages set forth hereinbefore. While the invention has been 
described in combination with specific embodiments thereof, it is evident 
that many alternatives, modifications, and variations will be apparent to 
those skilled in the art in light of the foregoing description. 
Accordingly, it is intended to embrace all such alternatives, 
modifications, and variations as fall within the spirit and broad scope of 
the appended claims.