Profiled plate heaters for injection molding nozzles

Injection molding nozzle having electric plate heaters mounted thereon. Insulative air spaces are provided according to a predetermined size, shape and pattern between the outer surfaces of the nozzle and the abutting inner surface of each heater. This provides heat transfer from the heaters to the nozzle according to a desired profile along the melt flow passage through the nozzle, depending upon the system configuration and the application.

BACKGROUND OF THE INVENTION 
This invention relates generally to injection molding and more particularly 
to a nozzle having electric slab or plate heaters which provide heat 
according to a predetermined profile. 
Plate heaters are well known in the injection molding field, but recently 
most nozzles are made with a helical heating element extending around the 
central melt bore. For instance, the applicant's U.S. Pat. No. 4,795,337 
which issued Jan. 3, 1989 discloses a nozzle in which an electric heating 
element is integrally brazed in a spiral channel extending around the 
central melt bore. One of the advantages of helical heating elements over 
these previous plate heaters for nozzles has been that the heat can be 
distributed over the length of the nozzle according to a predetermined 
profile by spacing the coils of the heating element as required. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the invention to at least partially 
overcome the problems of the prior art by providing a nozzle with a plate 
heater which provides for distribution of heat transfer according to a 
desired profile. 
To this end, in one of its aspects, the invention provides an injection 
molding nozzle having an elongated injection molding heated nozzle having 
a central portion extending between a rear portion adjacent a rear end and 
a forward portion adjacent a forward end, and a melt bore extending 
therethrough from the rear end to the forward end, the improvement wherein 
the central portion of the nozzle has at least one outer face which 
receives an electric plate heater securely mounted thereagainst, the 
heater having an inner face which abuts against the outer face of the 
central portion of the nozzle, the inner face of the plate heater and the 
outer face of the central portion of the nozzle being shaped to define at 
least one insulative air space therebetween having a configuration to 
provide heat flow from the plate heater to the nozzle according to a 
predetermined profile. 
Further objects and advantages of the invention will appear from the 
following description, taken together with the accompanying drawings.

DETAILED DESCRIPTION OF THE DRAWINGS 
Reference is first made to FIG. 1 which shows a nozzle 10 according to a 
preferred embodiment of the invention received in a well 12 in a cavity 
plate 14. The nozzle 10 is secured by bolts 16 to a manifold 18. The 
manifold 18 has a locating flange 20 which is seated against a 
circumferential shoulder 22 of the cavity plate 14 to provide an 
insulative air space 24 between the heated nozzle 10 and the cooled cavity 
plate 14. The locating flange is secured by a locating collar 26 which is 
fastened in place by bolts 28 which extend through a back plate 30 into 
the cavity plate 14. The nozzle 10 is also located laterally by a forward 
nose portion 32 being received in a matching cylindrical opening 34 
through the cavity plate 14. 
The nozzle 10 has a central bore 36 which extends into the nose portion 32 
to form a gate 38 leading to a cavity 40. An elongated valve member 42 is 
received in the central bore 36 with an enlarged forward end 44 which 
seats in the gate 38 in the retracted closed position. The valve member 42 
has a forward portion 46 which extends through the central bore 36 of the 
nozzle 10 and a rear portion 48 which extends into an opening 50 in the 
manifold 18. The forward portion 46 of the valve member 42 is smaller in 
diameter than the surrounding portion of the central bore 36 to provide a 
melt flow space 52 between them. A melt flow passage 54 extends to convey 
pressurized melt from a central inlet 56 in the manifold 18 to the gate 
38. The melt passage splits into two branches 58 which extend around the 
opening 50 in the manifold and join the space 52 around the valve member 
42 in the central bore 36. When the injection pressure of the melt forces 
the valve member 42 to the forward open position, melt flows through the 
gate 38 outwardly around the enlarged forward end 44 of the valve member 
42 into the cavity 40. 
In this embodiment, as seen in FIG. 2, the nozzle 10 is heated by two 
slab-shaped electric plate heaters 60 according to the invention which are 
described in more detail below. The plate heaters 60 are secured against 
diametric flat outer faces 62 of the central portion 64 of the nozzle 10. 
The manifold is heated by an electrical heating element 66 which is 
integrally cast into it. The cavity plate 14 is cooled by pumping cooling 
water through cooling conduits 68. In this large volume application, it is 
desirable to provide more cooling to the enlarged forward end 44 of the 
valve member 42 which extends to the cavity 40. Thus, a twisted partition 
70 is mounted in the hollow valve member 42, and a circulation of cooling 
water is provided between inlet and outlet pipes 72,74 which extend 
laterally from the rear portion 48 of the valve member 42 through lateral 
openings in the manifold 18. Thus, cooling water flows into the valve 
member 42 through the inlet pipe 72, forward along one side of the twisted 
partition 70 to the enlarged forward end 44 where it crosses over and 
flows rearwardly along the other side of the twisted partition and back 
out through outlet pipe 74. 
In this application, the valve member 42 is biased towards the retracted 
closed position by a pair of biasing mechanisms located on opposite sides 
of the opening 50 in the manifold 18. As described in detail in the 
applicant's Canadian patent application Ser. No. 587,417 filed Jan. 3, 
1989 entitled "Injection Molding System Having Offset Valve Pin Biasing 
Mechanisms" each mechanism includes a coiled compression spring 76 which 
is seated in the manifold 18 to pivot a lever member 78 which engages the 
valve member 42 through a split ring 80. 
Each slab-shaped plate heater 60 is cast of a copper alloy and has an 
electrically insulated heating element 82 extending from terminals 84. As 
seen in FIG. 4, each heater 60 has channels 86 machined in a flat inner 
face 88. When the heater 60 is fastened to one of the flat faces 62 of the 
nozzle 10 by bolts 90 which extend through holes 92, the channels 86 form 
insulative air spaces 94 between the inner face 88 of the heater and the 
outer face 62 of the nozzle. In this embodiment, the channels 86 are 
larger in the middle of the heater 60 because less heat is required in 
that area due to greater heat loss near the rear and forward ends 96,98 of 
the nozzle. However, the channels can be made in a variety of sizes, 
shapes and patterns to provide heat flow from the plate heater 60 to the 
nozzle 10 according to a predetermined profile along the central bore 36 
depending upon the system configuration and the application. Each plate 
heater 60 also has a curved outer surface 100 so that the central portion 
64 of the nozzle 10 with the heaters 60 in place has a generally 
cylindrical outer surface 102. In this embodiment, each of the plate 
heaters 60 has a cutout 104 to receive a screw 106 to hold a thermocouple 
108 in place in a hole 110. 
In use, the system is assembled as shown and electrical power is applied to 
the terminals 84 of the plate heaters 60 and the terminal (not shown) of 
the heating element 66 to heat the nozzle and manifold 14 to a 
predetermined operating temperature. Pressurized melt from a molding 
machine (not shown) is introduced into a melt passage 54 through the 
central inlet 56 according to a predetermined cycle. When injection 
pressure is applied, the force of the melt on the enlarged forward end 44 
of the valve member overcomes the spring force and drives the valve member 
42 forward to the open position. The melt then flows through the melt 
passage 54 and the gate 38 until the cavity 40 is filled. Injection 
pressure is held momentarily to pack and then released. When the injection 
pressure is released, the force of the springs 76 pivots the lever members 
78 and drives the valve member 42 to the retracted closed position in 
which the enlarged forward end 44 is seated in the matching gate 38. After 
a short cooling period, the mold is opened to eject the molded products. 
After ejection the mold is closed, injection pressure is reapplied which 
reopens the gate 38. This cycle is repeated continuously with a frequency 
dependent upon the size of the cavity and the type of material being 
molded. As it is well known, it is desirable that the melt remain at a 
constant temperature as it flows through the melt passage 54 until it 
reaches the gate 38. Using the plate heaters 60 which provide the 
insulative air spaces 94 greatly facilitates this in the nozzle 10 because 
the pattern or profile of heat flow to the nozzle can be designed to suit 
the requirements of the system. 
The embodiment of the invention shown in FIG. 5 is very similar except that 
channels 114 are provided in the outer faces 62 of the nozzle 10 rather 
than the inner faces 88 of the plate heaters 60. However, when the plate 
heaters 60 are mounted on the nozzle 10, insulative air spaces are formed 
between the faces according to the predetermined pattern. Otherwise, the 
description of this embodiment and its use are the same as that given 
above and need not be repeated. 
While the description of the nozzle 10 and the plate heaters 60 have been 
given with respect to preferred embodiments, it is not to be construed in 
a limiting sense. Variations and modifications will occur to those skilled 
in the art. For instance, it is apparent that the nozzle 10 and the plate 
heaters 60 can have different shapes and configurations depending upon the 
type of application, and that there can be a different number of heaters 
60. Reference is made to the appended claims for a definition of the 
invention.