Multi-cavity injection molding heated nozzle

An injection molding nozzle having a melt channel with a number of diagonal portions which branch to equally spaced outlets for multi-cavity molding. The nozzle has an integral electrical heating element with a forward portion which extends adjacent the forward face of the nozzle between the spaced outlets of the melt channel. The forward portion of the heating element is integrally brazed in channels in the forward face of the nozzle and has a number of radially extending arms. One of the arms extends outward midway between each two adjacent outlets. This provides additional heat to the melt near the outlets and ensures it is evenly balanced between the diagonal portions of the melt channel.

BACKGROUND OF THE INVENTION 
This invention relates generally to injection molding and more particularly 
to a nozzle for multi-cavity molding having superior heating adjacent the 
melt channel outlets. 
Multi-cavity injection molding is often provided by having a melt passage 
or channel branch in a heated manifold to several different nozzles. One 
example of this is shown in the applicants' U.S. Pat. No. 4,424,622 which 
issued Jan. 10, 1984. It is also known to provide for multi-cavity edge 
gating by having the melt passage or channel branch in the nozzle itself. 
This is shown in Gellert U.S. Pat. No. 4,344,750 which issued Aug. 17, 
1982. While these nozzles have an integral electrical heating element, 
they have the disadvantage that adequate balanced heat is not provided 
around the different branches and outlets of the melt passage. This has 
become a more serious problem with the increasing demand to mold more 
temperature critical materials. An attempt to overcome this problem is 
shown in Gellert U.S. Pat. No. 4,921,708 which issued May 1, 1990. It 
shows the nozzle having a number of spaced conductive probes, one aligned 
with each gate. After the melt flows centrally through the nozzle, it 
branches outward around each of the conductive probes and through the 
respective gate. However, this nozzle does not provide sufficient heat for 
all applications. Also, the large areas of liquid melt apply so much back 
pressure against the manifold that leakage can result at high pressure. 
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 nozzle for 
multi-gate molding having an integral heating element which provides more 
balanced heat adjacent each of the various melt channel outlets. 
To this end, in one of its aspects, the invention provides an injection 
molding nozzle to be seated in a well in a cavity plate, the nozzle having 
a rear end, a forward face, and a melt channel extending therethrough to 
convey melt from an inlet at the rear end towards a plurality of spaced 
gates extending through the cavity plate, the melt channel having a 
central portion and a plurality of diagonal portions, the central portion 
extending longitudinally from the rear end, and each of the diagonal 
portions branching diagonally outwards to an outlet, the outlets being 
equally spaced with each outlet leading to a respective one of said gates, 
the nozzle having an integral electrically insulated heating element, the 
heating element having a terminal adjacent the rear end of the nozzle and 
a spiral portion extending in the nozzle around at least part of the 
central portion of the melt channel, the improvement wherein the heating 
element has a forward portion extending adjacent the forward face of the 
nozzle transversely between the equally spaced outlets of the diagonal 
portions of the melt channel, the forward portion of the heating element 
extending in a predetermined configuration with a plurality of arms, one 
of said arms extending radially outward in a direction midway between each 
adjacent two of said outlets. 
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 portion of a multi-cavity 
injection molding system having integral heated nozzles 10 according to 
one embodiment of the invention. While the system shown has a steel 
manifold 12 to distribute melt to several nozzles 10, other systems may 
only have a single nozzle which itself distributes the melt to several 
different gates as described in more detail below. Each nozzle 10 extends 
into a well 14 in a steel cavity plate 16. While only a single cavity 
plate 16 is shown for ease of illustration, there may, of course, be 
various spacer, retainer or other types of plates or inserts depending 
upon the mold configuration. In this embodiment, each nozzle 10 has a 
circumferential insulation flange 18 which seats against a matching 
shoulder 20 in the well 14, and the well 14 is shaped to provide a desired 
insulative air space 22 between it and the heated nozzle 10. Each nozzle 
10 has a forward face 24 and a rear end 26 against which the melt 
distribution manifold 12 abuts. The manifold 12 has a cylindrical inlet 
portion 28 and an electrical heating element 30. The manifold 12 is 
mounted to extend between the cavity plate 16 and a steel back plate 32. 
The cavity plate 16 and the back plate 32 are cooled by pumping cooling 
water through cooling conduits 34. A ring 36 is seated between the 
manifold 12 and the cavity plate 16 to accurately locate the manifold 12 
in place. Double insulative and resilient spacer members 38 are located 
between the manifold 12 and the back plate 32 by pins 40. The back plate 
32 is secured in position by retaining bolts 42 which extend into the 
cavity plate 16. The back plate 32 applies a force through the spacer 
members 38 and the heated manifold 12 which holds the nozzles 10 securely 
in position. Thus, the heated melt distribution manifold 10 is securely 
located in a position which provides an insulative air space 44 between it 
and the adjacent cooled cavity plate 16 and back plate 12. As is well 
known, this provides considerable thermal separation by minimizing actual 
steel to steel contact between the heated and cooled components of the 
mold. 
A melt passage 46 extends from a common inlet 48 in the inlet portion 28 of 
the manifold 12 and branches outwardly to each nozzle 10 where it extends 
through a melt channel 50. The melt channel 50 of each nozzle 10 has a 
central portion 52 and several diagonal portions 54. The central portion 
52 extends longitudinally from an inlet 56 at the rear end 26, and the 
diagonal portions 54 branch diagonally outward from the central portion 52 
to spaced outlets 58. In this embodiment the outlets 58 are equally spaced 
around the forward face 24 of the nozzle 10 and each leads to a gate 60 
which extends through the cavity plate 16 to one of the cavities 62. Each 
diagonal portion 54 of the melt channel 50 through the nozzle 10 has an 
enlarged seat 64 to securely receive a torpedo 66 and a hollow cylindrical 
seal 68. As seen in the applicants' U.S. Pat. No. 5,028,227 which issued 
Jul. 2, 1991, each torpedo 66 has an outer ring 70 and several spaced fins 
72 which taper to a pointed tip 74 which is aligned with one of the gates 
60. Each nozzle 10 has a locating pin 76 which extends into an opening 78 
in the cavity plate 16 where it is secured by a cam 80 to ensure the 
alignment of the pointed tips 74 of the torpedoes 66 with the respective 
gates 60 is accurately maintained. Each seal 68 slip fits into one of the 
seats 64 to hold one of the torpedoes 66 in place and abuts against a 
circular seat 82 extending around one of the gates 60 in the cavity plate 
16 to prevent leakage of pressurized melt into the insulative air space 
22. Each seal 68 has a circular removal flange 84 which provides 
additional hoop strength and facilitates it being pried out of the seat 64 
with an appropriate tool for replacement of the torpedo 66. 
Each nozzle 10 is heated by an integral electrically insulated heating 
element 86, and reference is now also made to FIG. 3 in describing how it 
is made. The heating element 86 has a nickel-chrome resistance wire 88 
extending through a refractory powder 90 such as magnesium oxide in a 
steel casing 92. It is integrally brazed in the nozzle 10 and has a spiral 
portion 94 which extends around the central portion 52 of the melt channel 
50 to an external electrical terminal 96. The terminal 96 is made of a 
number of components as described in Gellert U.S. Pat. No. 4,837,925 which 
issued Jun. 13, 1989 to provide a threaded connection for a lead 98 from 
an external power source (not shown). The heating element 86 also has a 
forward portion 100 which extends in a predetermined configuration 
transversely adjacent the forward face 24 of the nozzle 10. In this 
embodiment, the melt channel 50 has four outlets 58 which are equally 
spaced around the forward face 24 of the nozzle 10. A length of heating 
element 86 is cut to have a diagonal forward end 102 to expose the 
internal resistance wire 88. It is then prebent adjacent its forward end 
102 into the predetermined configuration to form the forward portion 100. 
As seen in FIG. 3, in this embodiment, the forward portion 100 is made 
with two layers 104 and four radially extending arms 106. The forward 
portion 100 is then inserted into matching grooves 108 machined in the 
forward face 24 of the nozzle 10. Thus, the forward portion 100 of the 
heating element 86 extends between the four outlets 58 of the melt channel 
50 with each arm 106 extending midway between each adjacent two of the 
outlets 58. This provides more heat adjacent the melt channel outlets 58 
and the heat provided is evenly balanced between the outlets 58. The 
nozzle 10 has an outer surface 110 with a tapered portion 112. The heating 
element 86 is inserted to extend from the forward portion 100 through a 
longitudinal bore 114 in the nozzle 10 and is then wound in a spiral 
groove 115 which extends around the outer surface 110 of the nozzle to 
form the spiral portion 94 of the heating element 86. A hollow filler tube 
(not shown) is mounted where the grooves 108 cross on the forward face 24 
of the nozzle 10 to receive a nickel alloy. The nozzles 10 are then loaded 
in batches into a vacuum furnace. As the furnace is gradually heated to 
the melting temperature of the nickel alloy, it is evacuated to a 
relatively high vacuum to remove substantially all of the oxygen. Well 
before the melting point of the nickel alloy is reached, the vacuum is 
reduced by partially backfilling with an inert gas such as argon or 
nitrogen. When the nickel alloy melts, it flows by capillary action down 
to integrally braze the heating element 86 in the grooves 108, 112, and 
the other parts of the nozzle 10 are also integrally brazed together. This 
brazing in the vacuum furnace provides a metallurgical bonding of the 
nickel alloy to the steel which improves the efficiency of the heat 
transfer from the heating element 86. Of course, the nickel alloy contacts 
and fuses the resistance wire 88 at the diagonal forward end 102 which 
electrically grounds the heating element 86. Each nozzle 10 is also 
provided with a longitudinally extending thermocouple bore 116 to 
removably receive a thermocouple wire 118 to monitor the operating 
temperature adjacent the outlets 58 of the melt channel 50. 
In use, the injection molding system is assembled as shown in FIG. 1. 
Electrical power is applied to the heating element 30 in the manifold 12 
and to the heating elements 86 in the nozzles 10 to heat them to a 
predetermined operating temperature. Pressurized melt from a molding 
machine (not shown) is then injected into the melt passage 46 through the 
common inlet 48 according to a predetermined cycle in a conventional 
manner. In this embodiment, the pressurized melt branches first in the 
manifold 12 and then in each nozzle 10 to the gates 60 to fill the 
cavities 62. After the cavities 62 are filled, injection pressure is held 
momentarily to pack and then released. After a short cooling period, the 
mold is opened to eject the molded products. After ejection, the mold is 
closed and injection pressure is reapplied to refill the cavities 62. This 
cycle is continuously repeated with a frequency dependent on the size and 
shape of the cavities and the type of material being molded. The branching 
of the diagonal portions 54 of the melt channel 50 in each nozzle 10 and 
the location of the forward portion 100 of the heating element 86 between 
the outlets 58 provides additional heat to the melt near the outlets 58 
and ensures that it is evenly balanced between the various diagonal 
portions 54. 
Reference is now made to FIG. 4 to describe a second embodiment of the 
invention. As most of the elements of this embodiment are the same as 
those of the first embodiment described above, elements common to both 
embodiments are described and illustrated using the same reference 
numerals. In this embodiment, the nozzle 10 has a slightly different shape 
with a beveled surface 120 extending around adjacent the forward face 24. 
The diagonal portions 54 of the melt channel 50 branch outwardly from the 
central portion 52 to the outlets 58 which are equally spaced around the 
beveled surface 120. In this embodiment, the seals are provided by gate 
inserts 122 which are seated in the seats 64 around each of the outlets 
58. As shown, each gate insert 122 has a gate 60 which extends on an angle 
to provide for multi-cavity edge gating. The bore 110 extends on a slight 
angle and the forward portion 100 of the heating element 86 has somewhat 
different dimensions than in the first embodiment. The seat 64 and the 
gate insert 122 are threaded and the gate insert 122 has a hexagonal 
portion 124 for tightening it into place. Otherwise the description and 
operation of this embodiment is the same as that given above and need not 
be repeated. 
While the description of the nozzles 10 has been given with respect to 
preferred embodiments, it will be evident that various modifications are 
possible without departing from the scope of the invention as understood 
by those skilled in the art and as defined in the following claims.