GB2126521A

GB2126521A - Cartridge heater for a hot-runner injection distributor

Info

Publication number: GB2126521A
Application number: GB08321804A
Authority: GB
Inventors: Riccardo Ravaglia
Original assignee: ROTFIL Srl
Current assignee: ROTFIL Srl
Priority date: 1982-09-03
Filing date: 1983-08-12
Publication date: 1984-03-28
Also published as: ES274307Y; FR2532583B3; FR2532583A1; ES274307U; GB2126521B; IT8253648V0; GB8321804D0; DE8324409U1

Abstract

The cartridge heater (1) comprises a single main part (2) forming an outer casing for both the heating-injection unit (1) and the resistive wire (3) inside. <IMAGE>

Description

SPECIFICATION Cartridge heating-injection unit for a hotrunner injection distributor The present invention relates to a cartridge heating-injection unit for a hot-runner injection distributor, specially designed for making multiple micro molds.

It is generally known that, on hot-runner injection distributors, the plastic material to be injected into the mold is kept fluid by cartridge heaters as it flows through the various runners to the injection nozzle by which it is injected into the mold cavity. Inside the injection nozzle runners, provision is made for injectors designed to feed the plastic material to the injection nozzle which is fitted inside with cartridge heaters. The heat generated by the cartridge heater inside is transmitted to the injector and, with it, to the surrounding plastic material which is thus kept fluid.

This design, however, is not without drawbacks: heat dispersion between the cartridge heater and injector is such that, to obtain sufficient heat outside the injector for keeping the plastic material fluid, a relatively powerful cartridge heater involving relatively high energy consumption is required.

What is more, the overall size of the injectors with the cartridge heaters inside is relatively bulky so that, when making multiple molds, there is a limit to how far the centre distance between the injection runners can be reduced. The molds are therefore relatively bulky and require the use of relatively powerful press machinery.

The aim of the present invention is to provide a cartridge heating-injection unit for a hot-runner injection distributor designed to overcome the aforementioned drawbacks.

Other aims and advantages of the present invention will become clear from the following description.

With these aims in view, the present invention relates to a cartridge heating-injection unit for a hot-runner injection distributor, characterised by the fact that it consists of a single main part forming an outer casing for both the said heating-injection unit and the resistive wire inside.

The invention will now be described in detail with reference to the attached drawings, provided by way of non-limiting examples, in which: Figure 1 shows a side view of a heatinginection unit according to the present invention; Figures 2, 3 and 4 show side cross sections of subsequent arrangements of the Fig. 1 heating-injection unit; Figure 5 shows a slight variation of the Fig.

1 heating-injection unit; Figure 6 shows a top view of a hot-runner injection distributor with a number of Fig. 1 heating-injection units; Figure 7 shows a side cross section along line VII-VII of the Fig. injection distributor; Figure 8 shows a side cross section along line VIII-VIII of the Fig. 7 injection distributor.

With reference to Figs. 1 and 4, number 1 indicates a heating-injection unit according to the present invention, consisting of a single cylindrical outer piece (2) made of metal, preferably stainless metal or treatable steel, which forms an outer casing for both the heating-injection unit (1) and an internal resistive wire (3) wound in a spiral and preferably made of nickel-chromium.

The bottom end (4) of wire 3 fits into an axial hole on the tapered end (5) of main part 2 and is welded to the pointed end (6). The top end (7) of wire 3 is wound round and welded to the bottom (8) of rod 10 which projects from the top of main part 2 and is threaded at the top.

The outer surface of main part 2 is machined with a vertical groove (12), whereas the top is wider in diameter with two ringshaped grooves (13) spaced apart and perpendicular to the axis of main part 2.

With reference to Figs. 2 and 3, heatinginjection unit 1 is made as follows.

Cylindrical main part 2 (Fig. 2) has a hole (15) at the top which communicates at the bottom with a shallow hole in which is fitted and welded the bottom end (4) of wire 3 which is wound in a spiral and fitted inside hole 15 and to rod 10 at the top.

Hole 15 (Fig. 3) is then filled with insulating powder (1 7), preferably magnesium oxide, and main part 2 machined, preferably drawn, to reduce its diameter (Fig. 4). By doing so, insulating material 17 is compressed and the wall thickness of main part 2 reduced to a few millimetres (preferably 3 to 5), that is, sufficient to allow for subsequent machining of vertical groove 12, the centre and bottom of main part 2, smaller in diameter than the top, ring-shaped grooves 13 in the said top section and tapered bottom end 5 with point 6.

Number 20 in Figs. 6 to 8 indicates a hotrunner injection distributor with a number of heating-injection units. The said injection distributor (20) is made to an essentially known design in the shape of a parallelepipedon with a number of liquid plastic feed runners, i.e. a vertical plastic inlet runner (22) which communicates at the bottom with a horizontal runner (23) from which branch off perpendicularly and horizontally on both sides respective pairs of horizontal runners (24, 25) each of which pairs communicates with respective horizontal and perpendicular runners 26 and 27. From each side of runners 26 and 27 slope off downwards four runners (29) which come out into vertical-axis cylindrical chambers (30) each of which containing a heating-injection unit (1).

Each of chambers 30 communicates at the top with a smaller diameter coaxial chamber (3) which communicates at the top with hole 32.

Each heating-injection unit (1) is housed with the centre inside chamber 30 and vertical groove 12 facing runner 29, whereas the top with grooves 13 is forced inside chamber 31 so as to rest against the top circular lip (34) of the said chamber 31.

Rod 10 comes out at the top through hole 32 and is fitted at the top with a bus bar (38) made of conducting material, preferably copper. The four rods (10) of heating-injection units 1 on the same side of runners 26 and 27 are connected by a single bus bar (38), making a total of 4. Each bus bar (38) has four holes, one each for rods 10 which are fixed by pairs of nuts (40) screwed on to rod 10, one on top of and one underneath bus bar 38. The ends of the four bus bars (38) on the same side are connected together by a perpendicular bus bar (41), bolts (42) and nuts (43). One of the said bus bars (38) has a section (45) for connection to a terminal (not shown but preferably comprising a nut and bolt) for supplying heating injection units 1 with electricity.

The bottom parts of main parts 2 on heating-injection units 1 are each housed in a larger diameter chamber (50) inside a mold (51), the said chamber having a tapered end (53) on the tapered end (5) of main part 2, the said end terminating in a nozzle (55) communicating with a molding cavity (56) fitted inside with a counter-mold (57) which determines the shape of the part to be molded. Two known types of cartridge heaters (60) are fitted in the known way inside the main part of injection distributor 20, over and parallel to runners 26 and 27.

Operation of the heating-injection unit (1) covered by the present invention needs little explanation. When section 45 of bus bar 38 is supplied by a positive pole and the mass of injection distributor 20 by a negative pole, thermal energy is generated by resistive wire 3 which is transmitted to main part 2 and from there to the plastic material coming from runners 29, so that the plastic material is kept fluid inside chambers 30 and 50, right up to the injection nozzle (55) and molding cavity (56). Groove 12 facilitates flow of the plastic material to nozzle 55.

The heating-injection unit (1) covered by the present invention therefore provides for numerous advantages. Firstly, efficient transmission of thermal energy from resistive wire 3 to the plastic material surrounding main part 2 provides for relatively low power consumption. Secondly, the fact that the heating-injection unit (1) consists of a single main part (2), forming an outer casing for both the heating-injection unit (1) and resistive wire (3) inside, provides for highly compact overall size which, in turn, provides for close spacing of nozzles 55 and molding cavities 56 which is particularly suitable for making multicavity (56) micro molds (51). Consequently, highly compact molds (51) can be made requiring very low clamping pressure and which can be used on machines with very low injection capacities.

The fact that main part 2 on heating-injection unit 1 is only a few millimetres thick enables all the necessary machining to be carried out with no need for an additional outer part.

The fact that electricity is supplied over a single cable connected to one of bus bars 38 provides for an extremely straightforward, reliable, safe, strong electrical system with no need for separate supply cables for each heater. To those skilled in the art it will be clear that changes can be made to the unit described by way of a non-limiting example without, however, departing from the scope of the present invention.

For example (Fig. 5), heating-injection unit 1 may be combined with a known type of thermocouple (60) placed inside main part 2 or alongside and simply secured inside the top of main part 2 so as to indicate when the required temperature is reached. Alternatively, the said thermocouple (60) may be fitted to only a few of the heating-injection units (1) on an injection distributor (20) for controlling electricity supply.

Claims

1. A cartridge heating-injection unit for a hot-runner injection distributor, wherein the heating-injection unit consists of a single main part forming an outer casing for both the heating-injection unit and a resistive wire inside.

2. A heating-injection unit according to claim 1, wherein the wall of said single main part is 3 to 5 millimetres thick.

3. A heating-injection unit according to claim 1 or 2, wherein said single main part is essentially cylindrical in shape.

4. A heating-injection unit according to any one of the precvious claims, wherein said outer casing is drawn to reduce its diameter.

5. A heating-injection unit according to any one of the previous claims, wherein said single main part is made of metal.

6. A heating-injection unit according to any one of the previous claims, wherein the outer surface of said casing is machined.

7. A heating-injection unit according to claim 6, wherein the outer surface of said casing has a groove to facilitate flow of the plastic material towards the pointed end of the heating-injection unit.

8. A heating-injection unit according to any one of the previous claims, wherein one end of the resistive wire inside is connected to a threaded rod projecting from one end of said casing.

9. A heating-injection unit according to claim 8, wherein the other end of the resistive wire inside is connected to said casing.

10. A heating-injection unit according to any one of the previous claims, wherein the unit comprises a thermocouple connected to said casing.

11. A hot-runner injection distributor comprising a number of heating-injection units according to any one of the previous claims.

12. A distributor according to claim 11 and either of claims 8 and 9, wherein said threaded rods of the heating-injection units are connected to one another by electrical connecting means and the latter are connected to a single electricity supply cable.

13. A distributor according to claim 12, wherein said electrical connecting means comprise a number of bus bars connected to one another and to said threaded rods.

14. A distributor according to any one of claims 11 to 13, wherein recesses are provided inside for corresponding machined surfaces for positioning said heating-injection units.

15. A cartridge heating-injection unit for a hot-runner injection distributor, substantially as hereinbefore described with reference to the accompanying drawings.

16. A hot-runner injection distributor substantially as hereinbefore described with reference to the accompanying drawings.