Heated injection molding nozzle with alternate thermocouple bores

A heated injection molding nozzle having a melt channel which branches outwardly to several spaced edge gates. The nozzle has alternate thermocouple element receiving bores spaced longitudinally along a temperature gradient extending between the heating element and the front end of the nozzle. The nozzle facilitates the temperature control of materials having different thermal characteristics. When molding an amorphous material, a temperature somewhat lower than the prescribed operating temperature is desirable so the thermocouple element is mounted in the rearward bore closer to the heating element. If it is critical to maintain the temperature of the melt near the prescribed operating temperature for a material such as a crystalline material, the thermocouple element is received in the forward bore further along the temperature gradient from the heating element.

BACKGROUND OF THE INVENTION 
This invention relates generally to injection molding and more particularly 
to a heated nozzle for edge gating having alternate bores to receive a 
thermocouple element to monitor the operating temperature. 
It is well known to monitor the operating temperature by mounting a 
thermocouple element in a bore extending inwardly near the front end of a 
heated nozzle. Examples are shown in the applicants' U.S. Pat. Nos. 
4,768,283 which issued Sep. 6, 1988, 4,981,431 which issued Jan. 1, 1991, 
and the applicants' Canadian Patent application Ser. No. 2,101,480 filed 
Jul. 28, 1993 entitled "Injection Molding Nozzle which Retains a 
Thermocouple Element." U.S. Pat. No. 4,981,431 shows an edge gated 
configuration with the thermocouple element bore extending inwardly 
between the front end of the heating element and the seals extending to 
the gates. While these previous configurations are satisfactory for many 
applications, there is a problem that there is a temperature gradient near 
the front end of the nozzle due to heat loss to the surrounding cooled 
mold. This is particularly true for edge gating where the front end of the 
heating element must be spaced far enough from the front end of the nozzle 
to leave room for the outwardly extending seals. Thus, the accuracy of the 
measurement of the operating temperature is very dependent upon where the 
thermocouple element receiving bore is located between the heating element 
and the front end of the nozzle. The temperature measured by the 
thermocouple element relative to a temperature setpoint determines how 
much heat is provided by the heating elements. Thus, erroneous measurement 
of the operating temperature results in various problems dependent upon 
the type of material or melt being processed. For instance, if a 
crystalline material with a narrow temperature window or span between the 
melting point and processing temperature is being processed and the 
thermocouple element receiving bore is very close to the heating element, 
the temperature setpoint has to be well above the operating temperature 
prescribed for the material to provide sufficient heat to avoid the melt 
in the melt passage near the gates dropping below the solidification 
temperature. Conversely, if an amorphous material is being processed and 
the thermocouple element receiving bore is closer to the front end of the 
nozzle, the temperature setpoint can be well below the operating 
temperature prescribed for the material to avoid melt degradation, 
stringing and slower cycle time due to excessive melt temperatures. This 
problem of erroneous temperature measurement due to heat loss is 
exacerbated by the fact that the melt itself generally is a considerably 
better insulator if it is amorphous rather than crystalline. While an 
operator can compensate for this problem by adjusting the temperature 
setpoint higher or lower than the prescribed operating temperature 
dependent upon the type of material and location of the thermocouple 
element receiving bore, this has been found to be very confusing due to 
the fact that a material can only be processed with a temperature setpoint 
which is outside of the recommended processing temperature range for that 
material. 
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 heated nozzle 
having alternate locations for the thermocouple element depending upon the 
characteristics of the material to be processed. 
To this end, in one of its aspects, the invention provides an elongated 
injection molding nozzle having an outer surface, a rear end, a front end, 
a melt channel extending therethrough, and a heating element, the melt 
channel having a central portion extending forwardly from an inlet at the 
rear end and a plurality of radial portions branching outwardly from the 
central portion to convey melt to a plurality of edge gates spaced around 
the outer surface in a common plane a first predetermined distance 
rearwardly from the front end of the nozzle, the heating element extending 
around the central portion of the melt channel and being spaced a second 
predetermined distance rearwardly from the front end of the nozzle, having 
the improvement wherein first and second thermocouple element receiving 
bores extend inwardly from the outer surface into the nozzle between the 
heating element and the front end of the nozzle, the first and second 
thermocouple element receiving bores being spaced longitudinally a third 
predetermined distance apart, whereby one of the first and second 
thermocouple element receiving bores is selected to receive a thermocouple 
element therein to monitor the operating temperature, the one of the first 
and second thermocouple element receiving bores selected to receive the 
thermocouple element being predetermined by the characteristics of the 
material to be processed. 
Further objects and advantages of the invention will appear from the 
following description taken together with the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION 
Reference is first made to FIGS. 1 and 2 which show a portion of a 
multi-cavity injection molding system or apparatus having a melt 
distribution manifold 10 interconnecting several heated nozzles 12 in a 
mold 14. While the mold 14 usually has a greater number of plates 
depending upon the application, in this case only a cavity plate 16 and a 
back plate 18 which are secured together by bolts 20 are shown for ease of 
illustration. The melt distribution manifold 10 is heated by an integral 
electrical heating element 22 and the mold 14 is cooled by pumping cooling 
water through cooling conduits 24. The melt distribution manifold 10 is 
mounted between the cavity plate 16 and the back plate 18 by a central 
locating ring 26 and insulative and resilient spacer members 28 which 
provide an insulative air space 30 between the heated manifold 10 and the 
surrounding cooled mold 14. 
In this embodiment, each steel nozzle 12 has a rear collar portion 32 
adjacent a rear end 34 and a front portion 36 which extends forwardly from 
the rear collar portion 32 to a front end 38. The front portion 36 has a 
generally cylindrical outer surface 40 which is smaller in diameter than 
the rear collar portion 32. The nozzle 12 is heated by an electrical 
heating element 42 which is integrally brazed in the nozzle 12 with a 
spiral portion 44 and an external terminal 46 to provide connection to 
leads 48 from an external power source (not shown). Each nozzle 12 is 
seated in a well 50 in the cavity plate 16 by a cylindrical insulating and 
locating flange 52 which extends forwardly from the rear collar portion 32 
to sit on a circular shoulder 54 in the well 50. This provides an 
insulative air space 56 between the outer surface 40 of the front portion 
36 of the heated nozzle 12 and the surrounding generally cylindrical inner 
surface 58 of the well 50 in the cooled mold 14. The nozzles 12 are 
securely retained in the wells 50 with their rear ends 34 abutting against 
the front face 60 of the manifold 10 by bolts 62 which extend from the 
manifold 10 into the cavity plate 16. 
A melt passage 64 extends from a central inlet 66 in a cylindrical inlet 
portion 68 of the manifold 10 and branches outwardly in the manifold 10 
into alignment with a melt channel 70 in each of the heated nozzles 12. 
The melt channel 70 in each of the heated nozzles 12 has a central portion 
72 extending forwardly from the rear end 34 and a number of radial 
portions 74 extending outwardly from the central portion 72. Each of the 
radial portions 74 of the melt channel 70 extends outwardly through an 
edge gate seal 76 to an edge gate 78 leading to one of the cavities 80. 
Each edge gate seal 76 is screwed into a threaded seat 82 extending 
inwardly from the cylindrical outer surface 40 of the nozzle 12 and 
extends outwardly across the insulative air space 56 into contact with the 
inner surface 58 of the well 50. The type of edge gate seal 76 seen in 
FIGS. 1 and 2 has an outer face 84 which contacts the inner surface 58 of 
the well 50 immediately around the edge gate 78 leading to the cavity 80. 
There are a number of aligned edge gate seals 76, edge gates 78, and 
cavities 80 equally spaced around the cylindrical outer surface 40 of the 
nozzle 12. The edge gates 78 extend around the nozzle 12 in a common plane 
86 spaced a predetermined distance A rearwardly from the front end 38 of 
the nozzle 12 (FIG. 2). 
The spiral portion 44 of the heating element 42 extends around the central 
portion 66 of the melt passage 64 and is spaced a predetermined distance B 
rearwardly from the front end 38 of the nozzle 12 to leave sufficient room 
for the edge gate seals 76. Each nozzle 12 has two thermocouple element 
receiving bores 88, 90 extending inwardly from the cylindrical outer 
surface 40 between the spiral portion 44 of the heating element 42 and the 
front end 38 of the nozzle 12. As seen in FIG. 1, in this embodiment the 
thermocouple element receiving bores 88, 90 are aligned between two 
adjacent edge gate seals 76. Also, the thermocouple element receiving 
bores 88, 90 are shown extending radially inward, but in alternate 
embodiments they can extend diagonally and do not have to be 
longitudinally aligned with each other. As clearly seen in FIG. 2, the 
thermocouple element receiving bores 88, 90 are longitudinally spaced a 
predetermined distance C apart, and in this embodiment are equally spaced 
longitudinally on opposite sides of the common plane 86 through the edge 
gates 78. The nozzle 12 has a hollow thermocouple element tube 92 which 
extends through the rear collar portion 32 and along the inside of the 
insulating and locating flange 52. A thermocouple element 94 extends 
through the thermocouple element tube 92 and the insulative air space 56 
around the nozzle 12 and is bent into the forward thermocouple element 
receiving bore 90 where it is securely retained in place by a high 
temperature wire 96 wrapped around the outer surface 40 of the nozzle 12. 
In use, the injection molding system or apparatus is assembled as shown in 
FIGS. 1 and 2. Although only a single nozzle 12 is shown for ease of 
illustration, the melt passage 64 normally branches in the manifold 10 to 
several nozzles 12, and the melt channel 70 in each nozzle 12 normally 
branches to four edge gates 78 so there is a large number of cavities 80 
depending upon the application. Electrical power is applied to the heating 
element 22 in the manifold 10 and to the heating elements 42 in the 
nozzles 12 to heat them to a predetermined operating temperature. 
Pressurized melt is applied from a molding machine (not shown) to the 
central inlet 66 of the melt passage 64 according to a predetermined 
cycle. The melt flows through the melt distribution manifold 10, nozzles 
12, and edge gates 78 into the cavities 80. After the cavities 80 are 
filled and a suitable packing and cooling period has expired, the 
injection pressure is released and the melt conveying system is 
decompressed to avoid possible stringing through the open gates 78. The 
mold 14 is then opened to eject the molded products. After ejection, the 
mold 14 is closed and the cycle is repeated continuously with a cycle time 
dependent upon the size of the cavities 80 and the type of material being 
molded. As can be seen, the thermocouple element 94 extends forwardly 
through the thermocouple tube 92 and the insulative air space 56 between 
the outer surface 40 of the front portion 36 of the nozzle 12 and the 
surrounding inner surface 58 of the well 50 and into the forward bore 90. 
This bore 90 is forward of the plane 86 on which the edge gates 78 are 
located and is relatively close to the front end 38 of the nozzle 12. 
Thus, there is considerably more temperature loss at the forward bore 90 
than at the rearward bore 88 so the temperature measured by the 
thermocouple element 94 is less than the temperature of the melt in the 
central portion 72 of the melt channel 70. This forward location of the 
thermocouple element 94 is suitable for crystalline or other materials 
which have a narrow temperature window or span between the melting point 
and processing temperature and therefore cannot be injected at a melt 
temperature below the prescribed operating temperature. As mentioned 
above, in this arrangement the outer faces 84 of the edge gate seals 76 
abut against the inner surface 58 of the well 50 around the edge gates 78 
which provides more heat near the gates 78 to avoid the melt temperature 
dropping below the solidification temperature. 
Reference is now made to FIG. 3 which shows the same nozzle 12 as described 
above with the thermocouple element 94 received in the rearward bore 88 
rather than the forward bore 90. As this bore 88 is rearward of the plane 
86 on which the edge gates 78 are located, there is very little 
temperature loss so the temperature measured by the thermocouple element 
94 is very close to the operating temperature of the melt in the central 
portion 72 of the melt channel 70. There is some temperature loss as the 
melt flows outwardly through the radial portions 74 of the melt channel so 
this rearward location of the thermocouple element 94 is suitable for 
amorphous or other materials which can be injected at a melt temperature 
somewhat below their prescribed operating temperature. As seen in FIG. 3, 
the edge gate seals 76 are of a different type to reduce heat loss to the 
cooled cavity plate 16. Each seal 76 has a space 98 between its outer face 
100 and the inner surface 58 of the well 50. This space 98 is surrounded 
by a circular flange 102 which abuts against the inner surface 58 of the 
well 50. In use, the space 98 fills with melt which partially solidifies 
to provide thermal insulation around the gate 78. 
This nozzle having two longitudinally spaced thermocouple element bores 88, 
90 allows one of them to be selected to receive the thermocouple element 
94 to correspond to the thermal characteristics of the material to be 
processed. If a material such as an amorphous material can be processed at 
a temperature somewhat lower than the prescribed temperature, it is 
desirable to do so to reduce degradation and cycle time. Thus, the 
thermocouple element receiving bore 88 closer to the heating element 42 
should be selected to take advantage of the temperature gradient due to 
heat loss to the cooled mold. On the other hand, the same nozzles 12 can 
be used by selecting the forward thermocouple element receiving bore 90 
further from the heating element 42 to process material such as 
crystalline materials which have a rapid solidification speed and are more 
critical to maintain near their prescribed operating temperature. 
While the description of the injection molding nozzle according to the 
invention has been given with respect to a preferred embodiment, it will 
be evident that various other 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.