Hot runner system having a block-shaped casing

A hot runner system (10) for injection molding which includes a block-shaped casing (12) with a bore (14) for facewise insertion of at least one cartridge-like unit (16) having a material flow tube (32) enclosed by a heating device (38), and by a thermoconductive casting (V), and opposite flow transfer openings (35, 36), there are radial supports (40) protruding over the outer diameter (D) of the cast body (30) with an engaging face that is recessed relative to the bore (14) and serves for form-fit to nozzles (11), further units (16), additional flow tubes (32), etc. the supporting element for the cast body (30) being symmetrically arranged in either axial direction to form hollow compartments, including thin spiders (49), ribs (50), supporting segments (51) and tube-type studs (68), axial abutting members (18, 19) providing for tight closure of the hot runner system (10).

Conventional runner systems comprise distributor or manifold blocks with 
built-in heating cartridges or tubular heating elements whose thermal 
insulation relative to the casing and/or to the injection molding unit is 
often insufficient. Consequently, heating the runner block necessitates 
rather large power input and quite long heating-up time. In addition, 
cleaning may be difficult in particular with interior heating systems. 
A runner system in accordance with U.S. Pat. No. 3,091,812 comprises a 
heated material-supply tube encompassed by a T-shaped conductive tube 
engaging the tool block inside. The T-tube is welded at its ends to a 
steel plate which is not insulated relative to the supply tube, resulting 
in plenty of heat dissipation and correspondingly large energy loss. 
Moreover, there is an uncontrolled influence on the tool temperature. The 
unit is not suited or ill-equipped for cleaning which must be done by the 
factory with particular mechanical and chemical efforts; if production is 
to continue, a replacement unit is indispensable during maintenance 
activities. 
In a similar hot runner system according to U.S. Pat. No. 3,520,026, the 
entire runner block must be heated, too, so that a steep decrease of 
temperature is inevitable at the plastics material transfer points. Forces 
due to the very high processing pressure must be steered around the block, 
increasing the design expenditures. 
Another hot runner system as disclosed in EP 0 274 005 includes an 
independent unit comprising a plastics material supply tube as well as a 
heating device encompassed by a concentric sleeve. The unit is generally 
cylindrical and adapted for facewise insertion into or dismantling out of 
the associated casing relative to which it is thermally insulated by one 
or more separating means, A resistor band of special shape or a mains 
supply heating coil is used for electrical heating designed to dissipate 
less heat to the inner portions of the plastics material tube than to its 
ends. The sleeve has air gaps for thermal insulation underneath supporting 
rings. Outer insulating spaces adjacent to the casing are filled with 
solidified plastics during operation. It would be desirable to cut the 
expenditures required for both manufacture and assembly of the structure. 
OBJECTS OF THE INVENTION 
In order to satisfy the existing need for an advance, the invention aims at 
improving a hit runner system as mentioned above and more particularly a 
distributing or manifold system therefor such that is can be manufactured 
more economically and that its mechanical and thermal properties be 
considerably enhanced in a simple manner. 
It is a special objective of the invention to create means for minimum heat 
transfer to the casing and for a high standard of electrical safety of the 
hot runner system. 
Another object of the invention is to provide economical and convenient 
means for assembling, maintaining and cleaning the hot runner system. 
Moreover, economical operation is to be warranted so that time and energy 
consumption be reduced as far as possible. 
SUMMARY OF THE INVENTION 
In a hot runner system that comprises a block-shaped manifold casing with 
at least one bore for facewise insertion of a cartridge-type unit having a 
material flow tube enclosed by a heating device, e.g. by an electric coil 
or a resistor band, and by a thermoconductive casting, the invention 
provides thin web-like spacers for supporting the cast body and/or the 
flow tube within the bore, and further provides radial supports which 
have, recessed relative to the bore, an engaging face each form-fit to 
other components such as nozzles, further units, additional flow tube, 
etc. 
Thus the cast body is a component part that can easily be introduced into 
the casing bore and be fixed therein, under thermal separation, for 
convenient heating and distribution of the plastics material processed. 
The engaging faces of each radial support permit tight connection of 
further components with minimum heat dissipation towards the cooler 
casing. Owing to good thermal insulation, identical thermal conditions are 
warranted at each flow transfer opening so that a well-balanced 
temperature profile is achieved. 
SPECIALIZATION OF THE INVENTION 
Preferably the engaging faces of the radial supports are plane to 
facilitate tight attachment of any further component. Axially extended 
radial segments arranged diametrically opposite to each radial support 
will reliably receive the pressure of recoil during operation. 
An important embodiment features radial supports which are thermoresistive 
for insulation relative to the thermoconductive parts including the 
casting so that from the latter, too, only minimum heat will be disspated 
to the casing. The excellent performance will even be promoted by equal 
number of identical supports associated to each flow transfer point 
whereby well-defined constant thermal conditions are established 
throughout the system, in particular if these radial supports or further 
ones are arranged symmetrically to the flow transfer openings and if 
identical heating means are provided on either side of the flow inlet. 
As to practical design, it is advantageous to provide axially spaced 
spiders for radially supporting the flow tube, e.g. by way of at least 
three narrow spokes in a star or cross configuration comprising a hub that 
is integral with or rigidly connected to the flow tube. Such supports are 
preferably thermoresistant. They have few and very small engaging faces 
through which heat may dissipate, and they provide wide gaps for 
comfortably lodging longitudinal bridges of the heating device that are 
thermoconductively fixed in the cast body. 
Radial studs may be secured to the flow tube e.g. by a set screw or by 
welding for easy mounting of the flow tube or the cast body, respectively. 
Another mode of setting the flow tube is the use of externally engaging 
bolts, resting screws or the like, whereby later adjustment is 
facilitated. The invention also contemplates embodiments wherein the flow 
tube is fixed without clamping at its ends. Moreover, a plurality of flow 
outlets may be equipped with a fitting bush each for attaching a nozzle, 
said bush preferably having two bevels for close packing of adjacent 
nozzles.

DESCRIPTION 
As seen in FIG. 1, a hot runner system designated as a whole by 10 includes 
a casing 12 having a bore 14 for receiving a cartridge-like unit 16. 
Abutting members 18 close the unit 16 on either axial end in the casing 12 
the top of which comprises means for supplying plastics material fed 
through the system for injection out of nozzles 11 arranged below. 
The cartridge-like unit 16 includes a cast body 30 with a flow tube 32 
carrying an insulating layer 39 and a heating coil 38. Between the latter 
and an outer protective tube, an electrical insulation (not shown for 
reasons of clarity) may be provided. 
A thermoconductive casting V, e.g. of or including aluminium, serves to 
positively bond the component parts at the outside. The flow tube 32 
comprises a main runner 34 as well as flow transfer openings 36. At inlet 
point 35, the plastics material to be processed will enter the runner 34 
form where it will be discharged through at least two flow outlets 36. The 
directions of material flow are designated by M in FIG. 1. 
The flow tube 32 includes collar-type radial supports 40 (see FIGS. 2 and 
5) in the region of the flow transfer points 36 (FIGS. 1 and 4) for full 
contact to joining faces of further components such as nozzles, branching 
elements, etc. Opposite to every radial support 40, there is a 
counteracting thin supporting segment 51 that preferably extends over some 
axial length. In addition, the cast body 30 comprises spiders 49 of star 
or cross configuration as well as ribs 50 having peripheral gaps so that 
they form narrow spokes (FIGS. 3 and 6). These further radial supports 49, 
50, 51 snugly engage bore 14 from within. Due to their extremely small 
engaging faces because of their narrow shapes and also to the 
thermoresistive material used, which may be titanium, aluminium oxide 
ceramics or the like, very little heat is dissipated to the casing 12. 
Another inherent advantage of this design is the allowance for thermal 
expansion or shrinkage between the hot flow tube 32 and the casing 12 
which remains rather cool during operation. 
Outer hollows or clearances 52 are present between the individual supports 
49, 50 for enhancing the thermal insulation of the cartridge-type unit 16 
towards the casing 12. Owing to the close fit of the radial supports 40 
and their engaging faces, these hollows 52 will remain free of processed 
plastics. 
The gorges of the spiders 49 are adapted to receive longitudinal bridges 48 
of the heating coil 38, namely connecting leads, and are also filled with 
the thermoconductive casting V for promoting heat transfer between the 
various portions of the heating coil 38 (see FIGS. 3 and 6). 
The casing 12 is closed at either face end by abutting members 18 (FIG. 1) 
or by a terminal ring 19 (FIG. 4). The main runner 34 is axially closed at 
either end by a deflecting plug 56 one of which (the righthand one in 
FIGS. 1 and 4) may contain a thermo-probe 60 held in a feed-in plug 58. 
Adjacent thereto, connectors 62 to the heating coil 38 can be easily 
attached. The cast body 30 is positioned relative to the material supply 
means (FIG. 1) by a central gripping bolt 37, preferably also with thermal 
insulation. 
In the embodiment of FIG. 1, the electric coil 38 is designed for mains 
supply, e.g with a tension of 220 volts. By contrast, the design of FIG. 4 
is destined for low-voltage operation in that the heating wire 48 extends 
longitudinally, i.e. in an axial direction A, and in that the flow tube 32 
carries an electrical insulation layer 39 (schematically indicated). An 
alternative is the use of resistive bands or straps which, in a peripheral 
development view, may be meandering. The low-voltage heating elements are 
preferably non-insulated when applied to the insulating layer 39 of the 
flow tube 32, with subsequent electrical insulation prior to overcasting 
by the thermoconductive compound. 
FIGS. 7 and 8 show one end of a principally similar hot runner system 
having a cartridge-type unit 16 fitted into bore 14 of casing 12, the flow 
tube 32 including in the direction towards abutting member 18 a shoulder 
57 for the deflecting plug 56. A stud or pin 68 which may be tube-shaped 
and is thermo-insulated relative to the casting V serves for radial 
support of the flow tube 32, bearing onto the interior of bore 14. It will 
be evident from FIGS. 7 and 8 that a pair of such studs 68 may be provided 
on either side of nozzle 11 and another stud 68 opposite thereto so that a 
total of five tube-type radial supports is arranged at angles of 
120.degree. between them. They grab the flow transfer point 36 
symmetrically and are preferably made of a low thermoconductivity material 
such as chrome-nickel steel. Alternatively, a set screw 69 may be employed 
in order to support and position the flow tube 32 at an intermediate 
point, expediently with an insulating ring 74. It will be noted that these 
pins or studs--whether solid or tube-like--as well as further supports may 
be offset both radially and axially, in particular in symmetrical 
arrangements. 
In the embodiment of FIGS. 9 to 11, nozzles 11 (one of which is indicated) 
are joined to the flow transfer point 36 by means of a fitting bush 67 
each that may comprise two bevels 72 for close packing of neighboring hot 
runner components such as further nozzles. Tapped holes 71 serve to 
receive screws 70 for fixing the fitting bushes 67 within casing 
12--preferably in its cold condition--so that the cast body 30 is exactly 
positioned in bore 14. Thus allowance is made for thermal expansion or 
shrinkage between the flow tube 32 and the fitting bush 67 without 
detriment to the sealing. A strong radial support 65 for cast body 30 is 
located opposite to the flow outlet 36. As an additional seal, the fitting 
bush 67 may comprise a ring groove 73 holding a metal 0-ring at the face 
directly engaging the flow tube 32 (FIGS. 9 and 10). 
It will be realized that the invention permits numerous deviations from the 
preceding description. However, a preferred hot runner system (10) for 
injection molding comprises a block-shaped manifold casing (12) having at 
least one bore (14) for facewise insertion of a cartridge-like unit (16) 
containing a material flow tube (32) enclosed by a heating device (38), 
e.g. an electric coil, and by a thermoconductive casting (V). Opposite 
flow transfer openings (35, 36), there are radial supports (40) protruding 
over the outer diameter (D) of the cast body (30) with an engaging face 
that is recessed relative to the bore (14), may be plane and serves for 
form-fit to other components such as nozzles (11), further units (16), 
additional flow tubes (32), etc. Supporting elements for the cast body 
(30) are symmetrically arranged in either axial direction to form hollow 
compartments; they include thermoresistant thin spiders (49), ribs (50), 
supporting segments (51) and preferably tube-type studs (68). Axial 
abutting members (18, 19) provide for tight closure of the hot runner 
system (10). 
Essential advantages of the invention are due to the novel and clear-cut 
design that warrants identical thermal conditions in operation at every 
flow transfer point 35, 36. On either side thereof, the same number of 
coil windings or the same arrangement of identical heating devices 38 can 
be accommodated. It should also be noted that the inner hot runner tube 32 
enclosing the main runner 34 need not have clamped ends. Moreover, the 
symmetrical design is especially advantageous in that the hot runner 
distributing system is in full hydraulical balance whereby series arrays 
can be closely packed in a comparatively small volume, using a basically 
similar structure with a flow tube 32 of larger inner diameter which 
offers space for two or more main runners 34. 
While preferred embodiments have been illustrated and explained 
hereinabove, it should be understood that many variations and 
modifications will be apparent to one skilled in the art without departing 
from the principles of the invention which, therefore, is not to be 
construed as being limited to the specific forms described.