GB2088772A

GB2088772A - Manufacture of helical turbulence-inducing members

Info

Publication number: GB2088772A
Application number: GB8134760A
Authority: GB
Original assignee: MIHAMA Manufacturing; MIHAMA Manufacturing CO Ltd; Kato Hatsujo Inc
Current assignee: MIHAMA Manufacturing; Piolax Inc; MIHAMA Manufacturing CO Ltd
Priority date: 1980-11-21
Filing date: 1981-11-18
Publication date: 1982-06-16
Also published as: FR2494626A1; IT8125217A0; DE3145887A1; FR2494626B1; DE3145887C2; IT1142059B

Abstract

An extruder 20 has an outlet 26 fitted with a rotary nozzle 34 formed with a slit orifice to extrude a flat plastics strip which emerges downwardly. In operation the nozzle is rotatingly driven, so as to twist the strip into a helical configuration which is cooled and solidified by a water bath 42 where it passes around the guide rollers 44 and 46. The twisted strip is advanced by a drawing device 48 and wound on a reel 52. When cut into lengths the twisted strip forms turbulence-inducing members for insertion into e.g. domestic radiators. The member may be extruded from a nozzle slit comprising a single diametral arm, or a plurality of radial arms (36). <IMAGE>

Description

SPECIFICATION Manufacture of turbulence-inducing members This invention relates to the manufacture of members for inducing turbulence in a line of fluid, referred to subsequently as turbulenceinducing members. Such members may be inserted in lengths in fluid flow paths in a heat exchanger such as a domestic radiator so as to enhance the effect of heat radiation or heat absorption of the heat exchanger.

There have been previous proposals for turbulence-inducing members made from a thin metallic ribbon, which are each formed into two wave-formed strips in different phases by press working and so forth. These members have been inserted in lengths into fluid flow paths in a heat exchanger such as a radiator so as to stir up the fluid and thus to enhance the effect of heat radiation or absorption. However, these metallic members have disadvantages in that when they are rolled around a reel, the ridges of the wave-formed strips are crushed so as to entangle the strips and since the lengths into which the metallic members are cut are kept bent in the form of an arc when on the reel, the bent portions must be manually straightened one by one when inserting the members into the fluid paths in a heat exchanger, thereby entailing much time and labour.Moreover, since the members are made of a metal, the weight of the heat exchanger is increased.

According to the invention turbulence-inducing members are made of synthetic resin by a process in which the heated resin is extruded through a slit in a rotary nozzle so that the extruded resin is rotated around its central axis and thereby automatically given helical twist, after which the extruded resin is cooled and solidified by passage through water. Not only are the members thus formed much lighter than metallic members, but also they overcome the various disadvantages just referred to.

Apparatus for the manufacture of turbulence-inducing members in accordance with the invention comprises an extruder having a rotary nozzle formed with an extrusion slit and rotatably fitted to the outlet of the extruder, means for rotating the nozzle to cause molten resin extruded through the slit to be rotated around its central axis, a water vessel for receiving the extruded resin and cooling and solidifying it, and a drawing device for drawing the cooled and solidified resin through the water vessel.

The invention will now be described in more detail, with reference to the accompanying drawings, in which: Figure 1 is a perspective view illustrating a conventional turbulence-inducing member; Figure 2 is a cross sectional view showing lengths of the member of Fig. 1 used in a radiator; Figure 3 is a schematic view illustrating one embodiment of the apparatus for the manufacture of plastics turbulence-inducing members according to the present invention; Figure 4 is a cross sectional view showing a portion of a nozzle used in the apparatus of Fig. 3; Figure 5 is a schematic view illustrating a device for cutting the plastics turbulence-inducing members manufactured by the apparatus of Fig. 3 into lengths of a given size;; Figures 6 (A and B), 7 (A and B) and 8 (A and B) show respectively different shapes of slit and perspective views of the corresponding turbulence-inducing members obtained by use of the respective slits; and Figure 9 is a schematic view illustrating another embodiment of apparatus according to the present invention.

As illustrated in Fig. 1, a conventional turbulence-inducing member 10 is made from a thin metallic ribbon and shaped into two wave-formed strips in different phases by press working or the like.

Twenty to thirty lengths of the member 10 are inserted, as illustrated in Fig. 2, into flow paths 1 4 for hot water in a radiator 12 to stir up the hot water, thereby enhancing the conduction efficiency of heat to fins 16 and improving the effect of heat radiation.

However, these metallic turbulence-inducing members 10 entail disadvantages in that when they are rolled around a reel, the ridges of the wave-formed strips thereof are crushed, thereby entangling the strips. Moreover, since the lengths into which the turbulence-inducing members are cut have arc-like bent portions, the bent portions must be re-formed manually one by one when inserting the members into the fluid flow paths 14, thereby requiring very troublesome work and much time and labour, and since the members are made of metal, the weight of a radiator 12 is considerably increased.

Under these circumstances, there has been a strong demand for turbulence-inducing members capable of overcoming these disadvantages.

Referring now to Figs. 3 to 8, a synthetic resin is melted by heat in an extruder 20 and extruded from the outlet thereof, the extruder having a supply hopper 22, a feed screw 24 and a die head 26. The die head 26 is provided with a downwardly extending passage 30 for guiding the molten resin from the extruder 20 in a vertical direction within a cylindrical portion 32 which protrudes downwardly. The lower end of the passage 30 is obstructed by a cap-shaped rotary nozzle 34 which is rotatably attached to the outer periphery of the cylindrical portion 32. A slit 36 is formed in the end of the nozzle 34 and communicates with the passage 30 of the cylindrical portion 32. The slit may be formed as a straight opening or a number of openings radially from the centre, as illustrated in Figs.

6(A), 7(A) and 8(A).

The rotary nozzle 34 is rotated at a variable speed by a driving chain (not shown) connected to a variable speed driving device (also not shown) and engaging with teeth 38 formed on the circumference of the nozzle. A water vessel 42 having a depth of about one metre is disposed below the leading end of the rotary nozzle 34 and is filled with water for the purpose of cooling the resin extruded from the slit 36.

The distance between the surface of the water in the water vessel 42 and the under side of the nozzle 34 can be adjusted, e.g. by providing the water vessel 42 wit inlet and discharge valves, or by disposing the water vessel 42 on a supporting base capable of vertical adjustment.

A roller 44 is disposed near the bottom of the water vessel 42 opposite the leading end of the nozzle 34, and a guide roller 46 is disposed at the other end, near the top of the vessel 42.

A drawing device 48 provided with a pair of opposed feed rollers 50a and SOb serves to draw the resin from the water vessel at the same speed as that of the extruder 20 and to guide the resin between the feed rollers to be wound up on a takeup reei 52.

In operation, resin particles are introduced into the hopper 22 and melted by heat in the extruder 20. The molten resin is forwarded to the passage 30 by means of the screw 24 and subsequently extruded downwardly from the slit 36 of the rotating nozzle 34. Since the molten resin tends to hang down vertically under its own weight, the nozzle 34 is preferably arranged vertically. The resin is then guided to the interior of the water vessel 42, led to the lower surface of the roller 44, then to the upper surface of the guide roller 46 rotating in the reverse direction, gripped between the feed rollers 50a and SOb of the drawing device 48 and wound around the take-up reel 52.

in the process just described, the resin is guided to the interior of the water vessel 42 while it is rotated around its vertical axis by the action of the rotary nozzle 3rye. The resin meets with resistance both from the water in the water vessel and of the part of the resin which has been cooled and solidified and held against rotation in contact with the lower surface of the roller 44.Between the leading end of the nozzle 34 and the surface of the water, the resin is automatically twisted, then cooled and solidified in the waster vessel and subsequently drawn continuously by the draJv- ing device 48. Turbulen#e-inducing members 60 of a given length may be obtained by forwarding the extruded strip drawn from the drawing device 48 towards a feeder 54 capable of continuously feeding the strip to a cutter 56 for cutting to the given length as illustrated in Fig. 5, or they may be introduced directly into the fluid flow paths in the heat exchanger via a supply mechanism (not shown) having a suitable guide passage.

The pitch between the adjacent helical con solutions of the turbulence-inducing member can be determined independently or interdependently by the extrusion speed of the resin, the rotation speed of the nozzle 34 and the distance between the leading end of the nozzle and the surface of the water in the water vessel 42. When a turbulence-inducing member having a half pitch is desired, for example, the rotation speed of the nozzle 34 may be doubled.

Rilelical turbulence-inducing members of the configurations shown in Figs. 6(B), 7(B) and 8(B) can be obtained by forming the slit in the shapes shown in Figs. 6(A), 7(A) and 8(A) respectively.

The use of the apparatus just described makes it possible very simply to manufacture turbulence-inducing members having a precise and uniform outside diameter and convolutions of precise and uniform thickness and pitch, and has the advantages that since the rate of working can be increased, production is also increased and production costs are reduced. Since the turbulence-inducing members are made of a synthetic resin, the heat exchanger is lightened and the members are easily held straight after cutting even after winding around a take-up reel. Consequently any troublesome manual operation for re-forming the bent portions of the turbulence-inducing members is not required and the time and labour for the insertion of the members into the fluid paths are considerably decreased.

A second embodiment of apparatus according to the invention will now be described with reference to Fig. 9 identical or similar components being denoted by the same numerals as those of the first embodiment. In Fig. 9 an extruder 20 comprises a hopper 22, a die head 26 and a cap-shaped rotary nozzle 64 fitted into the side of the die head 26 and having a structure similar to that of the nozzle 34.

The shape of the slit in the leading end of the rotary nozzle 64 is not illustrated, but it may be composed of a straight opening or radial openings similar to those illustrated in Figs. 6(A), 7(A) and 8(A).

The resin melted by heat within the extruder 20 is extruded in a substantially horizontal direction while being rotated around its central axis. Instead of being horizontal, the direction in which the resin is extruded may be slightly inclined.

A cooling vessel 82 containing water is disposed in the neighbourhood of the leading end of the nozzle 64. The vessel is closed at the top and divided into a first cooling cham ber 86 on the side of the nozzle 64 and a second cooling chamber 88 separated from the first by a partition wall 84. Apertures 90, 92 and 94 formed respectively in the side walls and the partition wall 84 of the cooling vessel have diameters slightly larger than the diameter of the extruded resin and are all aligned with the slit of the nozzle 64 in the horizontal direction. The resin extruded from the slit thus enters the first cooling chamber 86 through the aperture 90, then enters the second cooling chamber 88 through the aperture 94 and subsequently leaves the cooling vessel 82 through the aperture 92.

A pipe 100 has one end connected to a suction pump (not shown) and the other end extending through the second cooling chamber 88 to a point higher than the apertures 90, 92 and 94 so as to open into the space between the closed upper surface of the second cooling chamber and the surface of the water in the second cooling chamber 88. A water supply pipe 102 is connected to the top of the first cooling chamber 86.

The resin discharged from the aperture 92 of the second cooling chamber 88 is gripped between pairs of rollers 50a and 50b and drawn by a drawing device 48 at a speed equal to the extrusion speed and rolled around a take-up reel 52.

In operation the resin melted by heat within the extruding machine 20 is extruded from the slit of the rotary nozzle 64 in a substantially horizontal direction while being rotated around its central axis by the rotation of the nozzle 64, cooled and solidified within the cooling vessel 82 by its successive passage through the apertures 90, 94 and 92, drawn by the drawing device 48 and rolled around the reel 52.

The resin is automatically helically twisted by its own rotation around its central axis between the leading end of the nozzle 64 and the interior of the first cooling chamber 86 while it is supported by the portion of the resin which has been cooled within the cooling vessel 82, and then stops rotation at the drawing device 48. The helical shape may be determined by appropriate choice of the shape of the slit as in the first embodiment (Figs. 6, 7 and 8).

Since the air present in the cooling vessel 82 is removed by the suction pipe 100, the space between the top of the cooling vessel and the surface of the water is at all times kept under negative pressure and the position of the surface of the water in the cooling vessel is level with the upper end surface of the suction pipe 100 which is higher than the level of the apertures 90 and 92, with the result that the resin passed through the apertures 90, 94 and 92 is under water and is sufficiently cooled.

Since the negative pressure under which the aforementioned space is kept is higher than the positive pressure exerted by the water in the regions of the apertures 90 and 92, little water flows out of the cooling vessel through the apertures 90 and 92. Any excess water from the pipe 102 overflows into the suction pipe 100 and air entering the cooling vessel 82 through the apertures 90 and 92 is removed by the suction pipe, so that the aforementioned space is kept at all times under negative pressure which is higher in numerical value than the aforementioned water pressure.

Since the side wall of the first cooling chamber 86 on the side of the nozzle 64 can be made thin because the internal water pressure is decreased by the negative pressure, the gap between the leading end of the nozzle 64 and the water in the first cooling chamber can be made short, and thus avoid any possible deformation of the resin which might otherwise occur in the gap due to the leakage of the molten resin. Further, since little of the water in the first cooling chamber flows out of the chamber through the aperture 90 the extrusion of the resin is not obstructed.

The pitch between the adjacent helical convolutions of the turbulence-inducing members can be determined by the resin extrusion speed, the rotation speed of the nozzle 64, the distance between the leading end of the nozzle 64 and the cooling vessel 82.

The magnitude of the negative pressure varies with pulsations of the suction pump (not shown) leading to the possibility of vibration of the water within the cooling vessel 82.

The existence of the partition wall 84 effectively prevents such vibration and, as a result, the deformation of the resin within the cooling vessel can be avoided. The partition wall is not essential, however, and may be omitted by using a suction pump producing relatively little pulsation.

When the resin is extruded substantially horizontally and then cooled, solidified and drawn horizontally as just described, the results are the same as in the first embodiment.

Further, the second embodiment excludes a possibility of inconvenience due to possible reversal of the direction of the resin within the cooling vessel in the first embodiment, and thus leads to increased efficiency in manufacture.

The invention is, of course, not limited to the described embodiments and various modifications can be made. For example, the resin may be extruded from the nozzle at a relative speed different from the speed of rotation of the nozzle, while it is rotated around its central axis.

Claims

1. A method of manufacturing turbulenceinducing members from a synthetic resin in which the heated resin is extruded through a slit in a rotary nozzle so that the extruded resin is rotated around its central axis thereby automatically given helical twist, after which the extruded resin is cooled and solidified by passage through water.

2. A method according to claim 1 wherein the molten resin is extruded substantially vertically downwardly while being rotated around its central axis.

3. A method according to claim 1 wherein the molten resin is extruded substantially horizontally from the slit while being rotated around its central axis.

4. Apparatus for the manufacture of turbulence-inducing members from a synthetic resin, which comprises an extruder, a rotary nozzle formed with an extrusion slit and rotatably fitted to the outlet of the extruder, means for rotating the nozzle to cause molten resin extruded through the slit to be rotated around its central axis, a water vessel for receiving the extruded resin and cooling and solidifying it and a drawing device for drawing the cooled and solidified resin through the water vessel.

5. Apparatus according to claim 4, in which the rotary nozzle is arranged to extrude the resin substantially vertically downwardly and the water vessel is disposed below the nozzle to receive the extruded resin.

6. Apparatus according to claim 4 in which the rotary nozzle is arranged to extrude the resin substantially horizontally and the water vessel is connected to a water supply and is provided in its side walls with apertures of a diameter slightly larger than the outside diameter of the resin extruded from the rotary nozzle and aligned with each other and with the nozzle to thereby allow the extruded resin to pass substantially horizontally through the apertures, the water vessel being tightly closed at the top and having a suction pipe of which one end is connected to a suction pump and the other end open to the interior of the water vessel at a higher level than the level of the apertures.