CA1097472A

CA1097472A - Electrically heated nozzle and method of making the same

Info

Publication number: CA1097472A
Application number: CA269,237A
Authority: CA
Inventors: Walter R. Crandell
Original assignee: FAST HEAT ELEMENT MANUFACTURING COMPANY Inc
Current assignee: FAST HEAT ELEMENT MANUFACTURING COMPANY Inc
Priority date: 1976-07-16
Filing date: 1977-01-06
Publication date: 1981-03-17
Also published as: IT1077365B; DE2716950A1; GB1590692A; GB1590691A

Abstract

Abstract of the Disclosure An electrically heated nozzle device for plastic molding or die casting equipment having a novel casing with an integral heater core, and means to seal the casing for retaining the heater core in place and to electrically insulate the electrical heating element from the casing and prevent loss of thermal transmitting packing contained in the casing, which is structured to receive the heater core in the area close to its passage for carrying molten material to be molded or cast in a forming cavity, and which may be shaped. The casing may also include a probe for a thermocouple or a ther-mocouple well for sensing temperature: and the method includes the steps of arranging an unsheathed electric heating element in a bore formed in the nozzle casing in proximity to its molding material orifice, filling the bore with heat transmitting electrical insulation embedding an electric heating element, compacting the insulation about the heating element and in the bore to eliminate air voids, and sealing the bore. The method may also include the steps of assembling in the nozzle casing a body of relatively flexible green ceramic par-ticles impregnated in heat dissipatable material and embedding a resistance wire heating element in the body, heating the assembly to bake out the heat dissipatable material and embedding a resistance wire heating element in the body, heating the assembly to bake out the heat dissipatable material and sinter the ceramic particles together, and compacting the assembly to eliminate air voids therein and between the casing and said assembly.
Also disclosed herein is a heater body embodying modi-fied features of the invention.

Description

7~2 ELECTRICALLY HEATED ~OZZLE AND l~ETHOD OF
_KI~G ~HE SAME
Backqro nd and Summary of the Invention This invention relates to improvements in electri-cally heated nozzles, including torpedos, spreaders and heater bodies, for plastic molding or die casting equip-ment, and to the method of making same. Such devices may be inserted into the orifice of the sprue fitting of the equipment to maintain the temperature of the mat--erial flowing therethrough during ejection into a mold or die. The nozzle includes an integral internal heater body comprised of an insulated heater coil, which may have at its ends frangible ceramic spacer discs for holding the heater body axial:Ly spaced from the walls o~ its metal casing. The resistance wire is connected to leads that extend through l~oles in the discs and project out of the as~embly for connection with a source 1 of electric current. The space in~ide the casing, not occupied by heater coil and leads, is filled and packed ; with magnesium oxide powder or similar heat transfer or ceramic material, such as aluminum oxide or boron nitride, to maintain a high heat transfer between the coil and casing and to provide electrical insulation between the coil and casing. One end of the casing may be tapered so that the bushing can function as a valve needle in the flow orifice.
By using an asse~bly of relatively flexible strips of green ceramic particles impregnated in heat dissipat- -able material in place of insulation powders and winding resistance wire on the strips, and -then he~ting the as-se~bly to bake out the heat dissipatable material and sinter the ceramic particles together, the asse~bly may _ I--a7~L7%

be fabricated into an integral unit to conform to any surface to be heated with the heater wires e~bedded in ceramic insulation.
By selectively using a co~bination of the green ceramic heat dissipatable material in conjunction with insulation powder, the heater coil e~oedded therein, and then baking out the heat dissipatable material and sintering the ceramic particles together, the asssmbly may be fabricated in a shorter time with varied heat insulation and heat transmission but good electrical insulation characteristics, as to direct heat to the moldin~ orifice and away from other parts of the nozzle.
~ he heater-casing assembly must be compressed to eliminate air voids, usually by swaging or rolling, which compacts the magnesium oxide powder or ceramic insulation material firmly between the heater body and casing to insure that all voids in the casing are filled.
The heated nozzle assembly is forrned as an integral unit, thus affording optimum heat transfer characteristics be-tween the heating core and casing. The open end o thenozzle casing may be rolled over suitable removable fiber and nylon discs placed at the related end of the heater bore to prevent slippage or loss of heater components during assembly and swaging of the device.
Objects of the _nvention It is therefore an object of the invention to pro-vide a unitary heated nozzle of the character referred to.
Another object is to provide a heated nozzle of the character referred to with novel means to close the open end of its casing to retain the heater element in place therein.

a7~7~

Another object is to provide a heated nozzle of such character that the heater element therein terminates closely adjacent to its flow channel and the shaped end of its casing to insure uniform heating of the entire flow area of the nozzlein which it is encased.
Another object is to provide a compressed heater assembly integral with and in a nozzle device of a given minimum size capable of producing high operating temperatures.
Another object is to provide an integral heated nozzle device with-out air voids therein.
Another object is to provide compacted insulation in and unitary with a heated nozzle which may be varied as to direct maximum heat to its flow passage.
Another object is to provide a heated nozzle of such a character which is not difficult or expensive to manufacture and which is very efficient in its use and increases heater life substantially over the life of conven-tional cartridge heaters inserted in a molding orifice nozzle, and a nozzle unit which is easy to replace when no longer serviceable.
Other objects and advantages of the invention will become apparent with reference to the following description and the accompanying drawings.
According to one aspect of the present invention, there is provided the method of making an in-tegral heated torpedo for a molding nozzle which comprises winding a wire resistor upon a core having an opening therein extending the length thereof, extending a lead wire through said opening, connecting the end of said wire resistor to said lead wire~ placing a ceramic spacer at each end of said core, inserting the core and spacers un-sheathed into a casing open at one end and comprising a torpedo body filling the casing with heat transfer electrical insulation material to fill all `
voids in said casing between said core and spacers and said casing placing an insulated washer in the open end of the casing, swaging the casing to reduce the diameter thereof and to pack the insulation material tightly around the core and in all gaps in the casing, and shaping the closed end of the casing.

~7~7Z

According to another aspect of the present invention, there is provided in a heated nozzle assembly having a metal body, and a heater within and integral with said body, said heater comprising an agglomerated sandwich of ceramic layers having a winding of electrical resistance wire embedded therein, and electrical lead wires attached to the ends oE said resistance wire for connecting said winding to a source of current.
The invention will now be described in greater detail with refer-ence to the accompanying drawings:
Pigure 1 is a fragmentary sectional view of an insulated runner system incorporating an illustrative embodiment of the novel improved heated nozzle.
Figure 2 is an elevational view of a heater element.
Figure 3 is a central sectional view of the torpedo casing Eor the nozzle.

.

-3a-7d~7;:
Figure 4 is an enlarged fragmentary cantral ssction-al view of the heater-casing assembly for the torpedo be-fore sealing the insert end thereof and before compression of the casing.
Figure 5 is a diametrical s~ctional view of the torpedo heater-casing assembly taken on line S - 5 of Figure 4.
Figure 6 is an axial sectional view of the completed heated torpedo device for a molding nozzle.
Figure 7 is an end view of a modified torpedo made according to the invention and having multiple heater elements therein.
Figure 8 is a sectional view along the axis of the nozzle of a die casting machine, taken on line 8 - 8 of Figure 7.
Figure 9 is an axial sec!tional view of a modified form of heated nozzle.
Figure 10 i8 an enlarged fragmentary diametrical sectional view of the heated nozzle shown in Figure 9.
Figure 11 is an enlarged fragmentary sectional ; view of a modified heated nozzle.
Description of a Preferr d Embodiment Referring to the exemplary disclosure in the accom-panying drawings, and particularly to Figure 1, the elec-trically heated torpedo device 10 is of a type that is mounted in the molding head 11 of a plastic injection molding machine in a manner that enables it to function as a needle valve or nozzle for the injection orifice 12 leading from the runner 13. The heated torpedo device may include an externally flanged fitting or collar 14 which is seated on a shoulder 15 formed in a stationary plate 16. A threaded cap plug 17 may retain the torpedo : . - . . ~

~10~7~7Z
device in place.
Specifically, the heated torpedo device 10 is fabri-cated from a cylindrical metal casing 18 ~ses Figure 3) having an axial bore 19 which extends substantially the length of the casing and terminates short of one end thereof. The other or open end of said casing has a reduced diameter flange 21 surrounding its open end.
This casing receives therein an unsheathed heating ele-ment 22.
As best shown in Figures 2 and ~, the heating element 22 com~rises a resistance wire 23 which is wound tightly upon a ceramic core 24 which is of a dia~eter les~ than the diameter of the bore 19 in the casing, but shorter in length. The core has two holes extending from end to end which receive lead pins or wires 25 pro-jecting beyond the ends of the core, as shown. One end of the wound resistance wire 23 is ~ecured electrically to one of the leads, whereas the other end of said resis-tance wire is ~onnected electrically to the other of the leads.
Arranged at each end of the core, with the leads 25 extending therethrough, is a thin frangible ceramic spac-er 26, also slightly smaller in diameter than the diameter of the bore 19. With this heating element assembly inserted into the bore 19, as best shown in Figure ~, heat transmitting material such as magnesium oxide powder 27 or similar material is placed in the space between the heating element 22 and the casing 18, whereupon a mica or lava washer 28 and a nylon washer 29, having holes there~
in to permit passage of leads 25, are fitted into the open end of bore 19 firmly against one another and against the related end of the heating element 22.

7~
The assembly is vibrated to pack the magnesium o~ide powder -tightly within the casing, as to fill all air voids within the assambly, and the casing flange 21 is then spun, or rolled over into the nylon washer 29.
The nylon wash~r may be removed to provide a flat end after swaging, as best shown in Figure 6. This proced-ure tightly locks the heating element 22 and the magnes-ium oxide powder 27 within the casing.
The assembly o~ ths metal casing 18 and heating element 22 is then swaged, so as to reduce the diameter of the casing and -to compress the packed magnesium oxide powder 27 into all voids within the bore 19. This pro-vidas an effective heat transfe.r contact between the heating element 22 and the casing 18, and insures uni-form heating of the casing and electrically insulates the heating element from the casing. The closed casing end may be tapered, as at 3.1, or otherwis2 shaped, pre-ferably by milling, thus providing a surfaca to regulate the flow of material through the runner orifice 12. The construction also insures the location of the heating element 22 very close to the body end 31 and effective to heat the flow of material, and on the whole permitq lowest internal operating temperatures with th0 applica- -tion of highest watt density. Temperatures can be con~
trolled ~ a thermocouple, in which case the lead 32 may by embedded in the magnesium oxide powder. or a thermo-couple well may be utilized with the thermocouple probe slipped therein.
The flanged fitting or collar 14 is than welded to the metal casing and the extending ends of the lead wires .. `?
25 are encased in caramic sleeves 33 and laid in a radial trough 34 formed in the collar. Said wires are then con-~ ~ 7 ~7A3 nected to suitable wires leading to a source of electric current.
Description_of a Modified Preferred Embodiment In the Figures 7 and 8 disclosure, the heated nozzle is of a t~pe having threa heating elements 22 spaced a-bout the central flow orifice 35, and the heater cores 24 are encased in the bores or wells 19 and integral with the nozzle body 10, as disclosed hereinabove with respect to the single heater torpado. Such a structure is particularly useful in a nozzle for a die casting machine.

Description of a Second Modified Preferred Embodiment The Figures 9 and 10 dis~losure is concerned with a modified form of noæzle wherein a strip 37 o~ material having organically bound green ceramic particles is wound upon a core A, preferably steel, and resistance wire 36 is wound upon the material 37, and a second layer 38 is wound upon the resistan~e wire 36. A metal tube B is telescoped over the wire wound ceramic material, and the entire assembly is compressed together, as by swaging or rolling, to bring the materials into intimate contact with one another, after which the assembly is heated to bake out the binders and sinter the ceramic particles into a unitary mass em~edding therein the heater wire 36O
A second compression operation, as by swaging, may be performed after the baking step, to further increase the density of the ceramic insulation, which further en-hances heat transfer characteristics by furthar eliminat-ing small voids in the asssmbly ~hich may have resulted during carbonization of the heat dissipatable material a7472 and sintering of the ceramic particles.
The strips 37 and 38 before baking each comprise a layer body of "green" ceramic particles pressad and rolled to a high density, and bonded together with vap-orizable binder material, which may be organic in nature, to a desired thickness. The cer~mic particles are typi-cally powdered ceramic materials such as particles of al-uminum oxide or boron nitride. The bindars are typically rubber, varnish, glyptal or the like. These bonded "green" or unbaked ceramic particles units conventional-ly are used in the ~abrication of ceramic underlayment for printed circuits, the end product, when baked out or carbonized, being referred to as "ceramic substrata", but in their green state before baking they are pliable ; and bendable. ~nen baked, the ceramic particles are sin-tered and agglomerate into a ceramic mass.
After the assembly is compressed into a unitary mass, the asse~bly may be machined to a selected con~iguration, as to thread the core A or metal tube B. The core A may comprise rod stoc~, in which case the core may be drilled to provide an annular channel 50 and shaped to provide a discharge orifice 51 for molten material. Leads 52 may be attached to the ends of the resistance wire 36, and heat resistant cement 53 or other suitable material may be used to seal the lead connections and peripheral space between the core A and metal tube B.

Descxiption of a Third Modifled _eferred Embodiment ~ r In the Figure 11 embodiment, resistance wire 36 is wound on the layer 37 of green ceramic substrate, in the same manner as shown in Figures 9 and 10, but, instead of the application of a second substrate layer, the met-, .

47~

al tube B is slipped loosely over the assembly and the void between the tube and wire wound ceramic substrate is packed and filled with insulating powder 55 in the mannar described in the Figure 1 - 7 disclosure.
Preferably, the powder 55 is vibrated into packed position, and a lava disc 56 may be installed in the end recess 57 of the spaca between the core and tube to seal the ends, whereupon the assembly is baked to burn out the binders in the manner described. A plastic bushing 58 may be inserted into the recess to hold the alements in position, whereupon the assembly is swaged to elimi-nate air gaps therein and the plastic bu~qhings may be trimmed from the ends and the unit machined in the man-ner describ2d with reference to the Figures 9 and 10 disclosure Other_Modificcltions As shown in Figure 10, Zl hypodermic needle type thermocouple well 60 may be installed in tha nozzle f or reading the temperature, preferably by ~orming a groove 61 in the outer wall of the core A.
When baking out the ceramic substrate layers 37 and 38, the baking temperature should be below the melting point of the metal core and tube covering, pre-ferably in an oxygen atmosphere, as to vaporize and car-bonize the binder~ and oxidiæe the carbon, which is vented from the assembl~ in the form of carbon dioxide.-As a result of this process, the ceramic material agglo~
merates into an integral heat conducting and electrically insulating mass.
Fabrication time is significantly reduced where the nozzle is made according to the Figure 11 disclosure as - tha baking step is time con~uming, and the insulation 7~

powder requires no such baking. Also the use of different insula-tion materials as shown in Figure 11 permits the sub-strate layer 37 to be fabricated from material of good electric insulating properties, but high heat conductive characteristics, and the powder layer 55 may have high electric insulating prop-erties and high heat insulating characteristics, so that the heat is directed to the flow channel within core A and the outer wall of metal tube B is of a lesser temperature.
Applicant has tested conventional heater structures to the structure shown in Figures 1 through 8 and has concluded from these tests that integral heated nozzles and torpedos pro-vide far superior even distribution of heat from body to tip than conventional assemblies, to provide superior control of plastic fluidity in the main sprue area and gate area without 'freeze-up' or degradation of plastic, during inJection molding processes.
It was also observed that the integr~l hea-ted tor-pedo and nozzle units eliminate fit problems, voids and air gaps typical of conventional torpedo type and nozzle assemblies, provide longer heater life and allow higher wattage value. The same efficiencies are provided in the modified structures disclosed herein.
Although I have described preferred embodiments of the invention in considerable detail, it will be understood that the description thereof is intended to be illustrative rather than restrictive, as details of the structure and the steps of the method may be mod-ified or changed without departing from the spirit or scope of the invention. Accordingly, I do not desire ~C397~
to be restricted to the exact construction and ste~s of the method described and shown.

.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. The method of making an integral heated torpedo for a molding nozzle which comprises winding a wire resistor upon a core having an opening therein extending the length thereof, extending a lead wire through said opening, connecting the end of said wire resistor to said lead wire, placing a ceramic spacer at each end of said core, inserting the core and spacers unsheathed into a casing open at one end and comprising a torpedo body, filling the casing with heat transfer electrical insulation material to fill all voids in said casing between said core and spacers and said casing, plac-ing an insulated washer in the open end of the casing, swaging the casing to reduce the diameter thereof and to pack the insulation material tightly around the core and in all gaps in the casing, and shaping the closed end of the casing.

2. The method recited in claim 1, with the addition of flanging the casing to lock the washer therein.

3. The method recited in claim 1, with the addition of placing a plastic washer between the insulated washer and the related open end of the casing, and removing the plastic washer after swaging.

4. The method recited in claim 1, with the addition of mounting a flanged collar at the open end of said casing.

5. The method recited in claim 1, with the addition of vibrating the filled casing before swaging to pack down the insulating material.

6. The method recited in claim 1, with the addition of inserting a thermocouple element into the casing before the casing is filled with insulating material.

7. In a heated nozzle assembly having a metal body, and a heater within and integral with said body, said heater comprising an agglomerated sandwich of ceramic layers having a winding of electrical resistance wire embedded therein, and electrical lead wires attached to the ends of said resistance wire for connecting said winding to a source of current.

8. The heated nozzle recited in claim 7, wherein said agglomerated sandwich comprises an inner layer of ceramic insulator material having said wire wound therearound, and outer layers of ceramic insulator material overlying both faces of said wire wound layer.

9. The heated nozzle recited in claim 7, wherein a layer of heat insulating material encloses said sandwich.

10. The heated nozzle recited in claim 7, wherein the metal body has a passage for transmission of molten material therein.

11. The heated nozzle recited in claim 10, wherein said sandwich conforms and is in proximity to said passage for heating of material flowing therethrough.

12. The heated nozzle recited in claim 7, wherein the sandwich of layers is comprised of aligned sheets of ceramic particles bonded together by a vaporizable binder, and is adapted to agglomerate into a unitary mass of agglomerated ceramic material upon application of sufficient heat to vaporize said binder.