Hot channel injection moulding die

The hot channel die (1) is arranged within a casing (13) filled with oil. In the hollow space (15) filled with oil, baffles (17, 19) are installed which effect a current of the oil directed toward the two ends of the die (1). For this purpose, the heating element (23) is arranged on the underside of the casing (13). The discharge sleeve (117), which introduces the liquid plastic from the feeding screw, discharges into the hollow body (115), which is mounted in a recess in the hot runner plate (105) of a hot channel injection molding die. The distribution conduits (119), which are constructed as curved tubes, are installed on the discharge sleeve (117), and lead to the side wall (121), against which the rear ends of the injection nozzles lie. The hollow space (125) is filled with a heat-conducting medium, for example oil, which is heated by a heater (127) and uniformly circulated within the hollow space (125) by convention or motorized circulation. Baffles (131) optimize the circulation of the medium and its return guidance to the heater (127).

BACKGROUND OF THE INVENTION 
The present invention concerns a hot channel injection molding die 
including an injection die with a nozzle body having an injection channel, 
a heating jacket enclosed by a casing and surrounding the nozzle body, and 
an electrical element. The invention also concerns a hot channel injection 
molding die including a hot runner plate with a heater, wherein at least 
one distribution conduit in the hot runner plate conducts plastic material 
from a discharge sleeve to at least one injection nozzle. 
With the conventional hot channel injection molds, also called hot runner 
molds, liquid plastic fed by the feeding screw conveyors of the injection 
machine is conducted into a heated distribution block to the injection 
nozzles arranged at a distance from a side face of the same. The 
distribution conduits within the distribution block are usually created by 
bore holes lying at right angles to one another. The production of such a 
distribution block with distribution channels running at right angles to 
one another is very expensive, and despite expensive processing methods, 
sharp edges arise on the right angle intersections of the channels which, 
for one, can damage plastic material transported in them, and on which 
deposits can establish themselves. Furthermore, the heating of the known 
distribution blocks has only been unsatisfactorily worked out, since 
higher temperatures occur in channels situated respectively closer to the 
heating rods than in regions further removed. Moreover, the temperature 
profile in the individual channels is different. This can lead to local 
uncontrolled overheating of the plastic material, especially when the 
machine is shut down for a time during production interruptions. 
The same problems with reference to temperature profiles also occur in hot 
channel dies in injection molds. For their heating, electrical resistance 
wires are arranged around or in the nozzle (die) body. The resistance 
wires can be embedded in a carrier material substrate or be arranged 
directly on the surface of the nozzle body. The nozzle body is joined at 
the foot end in the injection mold with the heat channel distributor in a 
heat-conducting manner, and the hot channel plate is likewise joined at 
the outflow side with the base plate forming the cavity. Heat flows over 
these contact points from the hot channel distributor block into the 
nozzle body, and from the nozzle body into the hot channel plate, and on 
the base plate side heat flows from the heated nozzle to the cooled base 
plate. These inflows and outflows of heat have the effect that the nozzle 
is not evenly heated over its entire length. The temperature profile is, 
however, also not uniform in its radial extension. This non-homogeneous 
heat distribution can lead to the consequence that individual sections of 
the nozzle can damage the plastic material to be injected due to 
overheating, which leads to sacrifices in quality of the product generated 
by the plastic injection machine. 
SUMMARY OF THE INVENTION 
One object of the present invention is creating a hot channel die with a 
heater which generates a basically constant heat distribution or a uniform 
temperature profile over the entire nozzle body. 
An additional object of the present invention is creating a hot channel 
injection mold, especially a distribution block, which makes possible a 
sparing and residue-free transit of the liquid plastic to the hot channel 
nozzle, and with which a uniform heat supply to the distribution channels 
is moreover guaranteed. 
These objects are accomplished by a hot channel injection molding die with 
a hot channel nozzle having a heating jacket formed by a fluid in a hollow 
space lying between the nozzle body and its casing, with the heating 
element lying below the casing. For a hot channel injection molding die 
having a hot runner plate, the hot runner plate includes a box-shaped 
hollow body in whose hollow space at least one distribution conduit is led 
by a central distribution tube to at least one injection nozzle arranged 
at a distance, and the heater is arranged below the at least one 
distribution conduit. Advantageous configurations of the invention are 
defined hereinafter. 
The good conductivity of fluid situated in the intermediate space between 
the nozzle and a casing enclosing the nozzle body or the partition in the 
distributor block makes possible an optimal, even distribution of the heat 
supplied by the heating element under the nozzle or the distribution 
conduits. The fluid which is more strongly heated locally by the heating 
element can be conducted by convection around the nozzle body or the 
distribution conduits, and especially into the contact regions with the 
hot channel plates and with the base plate. 
An especially optimal distribution of the quantity of heat supplied along 
the nozzle or the distribution conduits can be realized by guide means. 
These run in a preferred embodiment from the middle region of the nozzle 
toward its two ends and steer the fluid stream into the heat outflow 
zones. The heating element can be mounted on the casing from the outside 
and consequently be replaced without trouble in the event of a defect. 
The essentially constant temperature over the entire nozzle length in a 
narrow temperature range makes possible the processing of 
temperature-sensitive plastics. The casting losses arising in a cold 
channel process can therewith be completely avoided. 
The distribution block is hollow and filled with a fluid heating medium, 
which uniformly surrounds the kink-free curved distribution tubes arranged 
therein. The heater is installed in the base area below the distribution 
tubes and effects a circulation of the heating medium generated by 
convection around the distribution tubes. Suitably arranged guide means 
increase the circulation and produce an absolutely uniform heating of the 
distribution tubes and the liquid plastic conducted therein. The 
distribution tubes can be manufactured with optimal bending radii (as they 
are mounted running freely through the hollow space), and if desired, 
their length can be constructed identically for all tubes independent of 
the distance of the entry point of the plastic into the channel block. 
This yields an absolutely equal residence time of the plastic within the 
distribution tubes.

DETAILED DESCRIPTION OF THE INVENTION 
The entirety of a hot channel nozzle, designated with reference numeral 1, 
has a tube-shaped nozzle body 3 with a central boring which forms the 
injection channel 5 and is aligned at the entry side in region A with a 
boring 7 in the hot channel plate 2. The injection channel 5 ends in 
region B, but tapers there before the cavity 9. The cavity 9 is located in 
the so-called base plate 11, also called the insertion plate. The nozzle 
body 3 is enclosed over almost its entire length by a casing 13 forming a 
hollow space 15. Within the hollow space are contained two guide means 17 
and 19 which embrace the nozzle body 3. The peripheries of the two guide 
means 17 and 19 preferably lie against the interior of the casing 13. The 
total hollow space 15 is filled with a fluid, for example with oil. The 
latter is poured in through a bore hole 21. Another heat-conducting liquid 
or a gas could be poured in as an alternative to oil. 
Below the casing 13 a heating element 23 is arranged. This lies completely 
on the surface of the casing 13. 
From the representation in FIG. 3 the position of the two baffles 17 and 19 
within the indicated casing 13 can be seen in perspective. 
FIG. 2 shows the profile of the temperature T over the entire length of the 
nozzle body 3 and further partial areas at both ends in the hot channel 
plate 2 and in the base plate 11. 
As an alternative to the casing 13 represented as a cylinder in the 
Figures, a conically shaped casing could also be used in order to support 
the heat transport appropriately. 
As an alternative to the elliptically configured baffles 17 and 19, beads 
(20) can be applied to the casing 13, which project into the hollow space 
15 and assume the function of the baffles 17 and 19. These embodiments are 
represented in FIG. 1A. 
In the following, the functioning of the heating of the hot channel nozzle 
1 will first be explained. The heat generated by the heating element 23 
proceeds from below through the jacket of the casing 13 to the oil in the 
space 15. This is heated and rises upwardly on both sides from the deepest 
spot in the region area of the crest S. The rise does not, however, take 
place vertically, but the two baffles 17 and 19 cause the heated rising 
oil to be deflected to the ends of the nozzle body. In these regions A, B, 
the nozzle body 3 is strongly heated or cooled as a consequence of heat 
inflow and outflow in adjacent regions. The oil arriving there evens out 
the temperature differences and is deflected, in order then to be reheated 
in the region of the lower crest S over the heat source, namely the 
heating element 23. It can begin its journey through the space 15 again. 
The oil, which is situated between the two baffles 17 and 19, is also 
heated strongly enough there to rise upwardly, and brings about an 
essentially even distribution of the heat along the upper-lying jacket 
surface of the nozzle body 3. Experiments have shown that a nearly 
constant temperature profile, being within a few degrees Celsius in 
accordance with FIG. 2, results with a hot channel nozzle outfitted in 
accordance with FIG. 1. It is apparent from this curve that in region A 
the temperature is highest, namely because the hot channel distributor 2 
is likewise heated to keep the plastic material liquid in the boring hole 
7. The temperature T remains almost constant until near the end at the 
base plate side of the nozzle 3, and ranges even in a band of a few 
degrees Celsius. Only in the region of the transition to the cooled base 
plate 11 does the temperature fall below the mean value. It remains 
nonetheless within an optimal processing range for the plastic material. A 
temperature spike, which can lead to damaging the material, is 
successfully avoided. 
The embodiment described in FIGS. 1, 2, and 3 depicts two baffles 17, 19. 
Obviously, with a longer nozzle, a modified baffle configuration could 
find application. Equally obvious would be such a configuration with a 
single baffle 17, in the event that the nozzle is very short. 
In FIG. 4, a hot channel injection molding die is visible, which includes 
three mold blocks, namely the base plate 103, the hot runner plate 105 and 
a cover plate 107. Four injection nozzles 109 are installed in the base 
plate 103, which lie vertically directly above one another. In the cover 
plate 107, a discharge sleeve 117 is mounted in which the outlet opening 
for the liquified plastic material is situated, which for example can be 
conveyed to the hot channel injection molding die 101 by a screw conveyor 
and introduced into this. The hot runner plate 105 has a recess 113, in 
which a hollow body 115 is installed in the embodiments represented. In 
the hollow body 115, or in the recess 113, a discharge sleeve 117 is 
mounted for introducing the liquid plastic mass. From this the liquid 
plastic is distributed to the injection nozzles 109 by distribution 
conduits 119. The distribution conduits 119 end in the side wall 121 of 
the hollow body 115 and are tightly connected with the latter, for example 
hard soldered, welded or the like. The tube-shaped distribution conduits 
119 have curved regions 123 between the connection point A with the 
discharge sleeve 117 and their ends in the wall 121, the bending radius of 
which has the largest possible value permitted by the space relationship. 
The two conduits 119 leading to the injection nozzles 109 lying uppermost 
and undermost in FIGS. 4 and 5 have a course with a 90.degree. bend lying 
in a plane. The two other distribution conduits 119, which lead to the two 
injection nozzles 109 lying inbetween, emerge first horizontally from the 
discharge sleeve 117 and lead in a three-dimensional course to the 
injection nozzles 109 (see especially FIG. 5). 
In the hollow space 125 of the hollow body 115 or below it, a further heat 
source, for example a heating cartridge 127, is inserted. Preferably, the 
heating cartridge 127 lies protected in a tube 129, which is open on both 
ends and permits changing the heat cartridge 127 without having to open 
the hollow body 115. This is completely filled with a heat-conducting 
medium, for example a liquid, such as oil, or a gas. The medium surrounds 
the distribution conduits 119 situated in the hollow space 125, and the 
discharge sleeve 117 as well. 
In the following, the functioning of the heating of the distribution 
conduits 119 in the hot runner plate 105 is explained. The heat generated 
in the interior of the hollow body 115 by the heater below the 
distribution conduits 119 is transferred to the heat-conducting medium, 
and begins a circulation by convection and therewith uniform coverage of 
all surfaces of the distribution conduits 119 lying in the heat-conducting 
medium. The circulation of the medium effects a balanced heat transfer 
from the medium to the distribution conduits 119 and the plastic material 
conducted therein. A local overheating, for example in the region of the 
distribution tube 119 lying closest to the heater 127, is ruled out. As an 
alternative to the circulation of the medium by convection, a circulation 
can take place with a pump in very large molds (no illustration). 
In a further advantageous configuration in accordance with FIGS. 6 and 7, 
baffles 131 are installed in the hollow space 125 of the hollow body 115 
laterally of the distribution conduits 119. The baffles 131 conduct the 
medium heated by the heater 127 upward within a narrow channel 133 along 
the distribution conduits lying one above the other and allow the medium 
thereby cooled above, and for this reason specifically heavier, to sink 
downward outside the baffles 131, where it is warmed again at the heater 
127. In order to keep the vertical narrow channel 133 formed by the 
baffles 131 as narrow as possible, the looped-shaped segments of the 
distribution conduits 119 penetrate the baffles 131.