WO2005046963A1

WO2005046963A1 - Circular slit-type breaker plate assembly for use in extruder

Info

Publication number: WO2005046963A1
Application number: PCT/KR2004/002849
Authority: WO
Inventors: Dae-Hee Cho
Original assignee: Lg Cable Ltd.
Priority date: 2003-11-12
Filing date: 2004-11-05
Publication date: 2005-05-26
Also published as: CN1871111A; KR20050045648A; KR100571149B1

Abstract

Disclosed herein is a circular slit-type breaker plate assembly for use in an extruder. The breaker plate assembly comprises a housing having an inner diameter tapered toward an exit side, and a breaker plate installed in the housing. The breaker plate is perforated with a center hole, and a plurality of circular arc-shaped slits are concentrically formed around the center hole such that they are symmetrical in all directions, thereby being capable of preventing oxidation and discoloration of resin caused by an extended residence time of the resin during long-term extrusion, and of restricting the passage of impurities through the periphery of a screen mesh, resulting in an improved quality of products.

Description

Description CIRCULAR SLIT-TYPE BREAKER PLATE ASSEMBLY FOR USE IN EXTRUDER Technical Field

[1] The present invention relates to a circular slit-type breaker plate assembly for use in an extruder, and more particularly to a circular slit-type breaker plate assembly for use in an extruder which can prevent oxidation and discoloration of resin caused by an extended residence time of the resin during long-term extrusion, and can restrict the passage of impurities through the periphery of a screen mesh, resulting in an improved quality of products.

[2] Background Art

[3] In general, screw-type extruders are designed in such a fashion that resin, supplied therein, is nixed and molten by means of a screw while passing through the interior of a barrel, and then the molten resin is returned from a tip end of the barrel to an adaptor. In this case, in order to remove impurities contained in the resin, between the screw and an extrusion head is installed a screen mesh, and in turn, the screen mesh is supported by a breaker plate. Such a screen mesh and breaker plate also serve to maintain the pressure of the resin within a constant range, essentially required to endow molded products with uniformity.

[4] In relation with the breaker plate, particularly, it is essential that the resin passes through the breaker plate with a uniform flow rate. In order to prevent early bridging and carbonation and to maintain uniform residence time of the resin, conventionally, various breaker plates as shown in Figs. 1 and 2 have been developed and used.

[5] Among the various breaker plates, a conventional hole-type breaker plate 40, as shown in Fig. 1, is integrally formed with a coupling portion of a screen mesh (not shown), and a plurality of holes 41 are formed at the breaker plate 40 in the arrangement of a plurality of concentric circles. This arrangement means that the holes 41 exist even around the periphery of a screen mesh. The holes 41 located around the periphery of the screen mesh, however, cannot successfully filter the impurities contained in the resin. Further, due to a pressure drop at an inlet side of the breaker plate 40, there is a problem of flow-rate deflection between the resin entered along the edge of the breaker plate 40 and the resin entered through the center of the breaker plate 40. [6] Fig. 2 shows a conventional slit-type breaker plate 50, which is the most widely used breaker plate. The slit-type breaker plate 50 is designed in such a fashion that the size of slits 51 is longer in the center of the breaker plate 50 in order to equalize the flow of fluid. Further, in the case of the slit-type breaker plate 50, inlet and outlet sides of the respective slits 51 are tapered, such that distances between the adjacent slits 51 are nininized at the inlet and outlet sides. In this case, a housing 55, for use in the coupling of a screen mesh (not shown), is separately formed with the screen mesh. Such a slit-type breaker plate 50, however, has a problem in that a flow rate of molten resin at the edge of the breaker plate is lower than that at the center of the breaker plate, resulting in flow-rate deflection of the molten resin.

[7] That is, both the hole-type and slit-type breaker plates, more or less produce low- rate regions at the center and edge thereof, respectively, and thus increased flow resistance and residence time of the resin, resulting in carbonation and discoloration of the resin.

[8] In addition, although not shown in the drawings, a circular slit-type breaker plate, similar to the present invention, is disclosed in Japanese Patent Laid-Open Publication No. 1995-214640 (published on August 15, 1995). The disclosed conventional circular slit-type breaker plate is designed in such a fashion that upper and lower circular slits have the same length as the inner diameter of an adaptor. Such a breaker plate is applicable to the extrusion of planar products, such as films, but is unsuitable for the extrusion of cylindrical bulks. Further, in order to couple a screen mesh, the circular slit-type breaker plate has to be squeezed using a separate ring. In this case, the ring tends to produce an additional gap, causing accumulation of a material in the gap.

[9] Disclosure of Invention Technical Problem

[10] Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a circular slit-type breaker plate assembly for use in an extruder which can prevent oxidation and discoloration of resin caused by an extended residence time of the resin during long-term extrusion, and can restrict the passage of impurities through the periphery of a screen mesh, resulting in an improved quality of products.

[11] Technical Solution [12] In accordance with the present invention, the above and other objects can be accomplished by the provision of a circular slit-type breaker plate assembly for use in an extruder comprising: a housing having an inner diameter tapered toward an exit side; a breaker plate installed in the housing and having a plurality of circular arc-shaped slits defining one or more concentric circles about the center of the breaker plate, such that at least two circular arc-shaped slits are arranged on one of the concentric circles, the slits of the same circle being symmetrically arranged in all directions; and a screen mesh installed in the housing and supported by the breaker plate.

[13] Preferably, the breaker plate may further have a center hole perforated therethrough.

[14] Preferably, all the slits may define an opening ratio of 50 to 80% on the basis of the total area of the breaker plate.

[15] Preferably, the total number of the slits may be from 4 to 24.

[16] Preferably, inlets and outlets of the slits and the center hole may be tapered by an angle ranging from 40 to 80 degrees.

[17] Preferably, the slits may take the form of circular arches arranged to define three concentric circles about the center of the breaker plate; the slits primarily adjacent to the center of the breaker plate taking the form of elongated circular arcs having an angle ranging from 40 to 45 degrees; the slits secondarily adjacent to the center of the breaker plate taking the form of elongated circular arcs having an angle ranging from 62 to 68 degrees, and the slits thirdly adjacent to the center of the breaker plate taking the form of elongated circular arcs having an angle ranging from 70 to 75 degrees.

[18] Preferably, the housing may be internally formed with an annular protrusion coming into contact with the edge of the breaker plate, such that some of the slits corresponding to a periphery of the screen mesh are intercepted by the protrusion.

[19] Advantageous Effects

[20] In this way, according to the present invention, through the use of the circular slit- type breaker plate assembly for an extruder, it is possible to prevent oxidation and discoloration of resin caused by an extended residence time of the resin during long-term extrusion, and to restrict the passage of impurities through the periphery of a screen mesh, resulting in an improved quality of products

[21] Brief Description of the Drawings [22] The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

[23] Fig. 1 is a partially cut-away side sectional view and a front view, respectively, il lustrating a conventional hole-type breaker plate;

[24] Fig. 2 is a front view and a perspective view, respectively, illustrating a conventional slit-type breaker plate;

[25] Fig. 3 is a sectional view illustrating an exploded state of a breaker plate assembly in accordance with the present invention;

[26] Fig. 4 is a front view of a breaker plate constituting the breaker plate assembly in accordance with the present invention;

[27] Figs. 5 - 8 are graphs showing the result of a monitoring of the detected content of oxidized carbon impurities.

[28] Best Mode for Carrying Out the Invention

[29] Now, a preferred embodiment of the present invention will be explained with reference to the accompanying drawings. The present embodiment is proposed only for the purpose of explanation, rather than to limit the scope of the present invention. Some parts in the embodiment are substantially the same as those in the prior art and are thus denoted by the same reference numerals and terms.

[30] Fig. 3 is a sectional view illustrating an exploded state of a breaker plate assembly in accordance with the present invention. Fig. 4 is a front view of a breaker plate constituting the breaker plate assembly in accordance with the present invention.

[31] Referring to Figs. 3 and 4, the circular slit-type breaker plate assembly of the present invention comprises a housing 30 having an inner diameter tapered toward an exit side thereof, and a breaker plate 10 installed in the housing 30. The breaker plate 10 is centrally perforated with a circular center hole 11, and a plurality of circular arc- shaped slits 12 are concentrically formed around the center hole 11. The circular arc- shaped slits 12 are symmetrical in all directions.

[32] The breaker plate assembly of the present invention further comprises a screen mesh 20, which is installed in the housing 30 such that it can be supported by the breaker plate 10 installed in the housing 30. As stated above, the breaker plate 10 is centrally perforated with the center hole 11, and 4 to 24 of the circular arc-shaped slits 12 are symmetrically arranged in all directions around the center hole 11, thereby minimizing residence of molten resin. In this case, if the total number of the slits 12 exceeds 25, the slits 12 define a structure similar to that of the conventional hole-type breaker plate, increasing the possibility of flow-rate deflection. On the contrary, if the number of the slits 12 is below 4, it may disadvantageously generate accumulation of the molten resin between the slits 12.

[33] Explaining the arrangement of the slits 12 in more detail, the slits 12 take the form of circular arcs arranged to define at least three concentric circles around the center hole 11 perforated in the center of the breaker plate 10. In the present embodiment, the slits 12 primarily adjacent to the center hole 11 take the form of elongated circular arcs having an angle (Al) ranging from 40 to 45 degrees, the slits 12 secondarily adjacent to the center hole 11 take the form of elongated circular arcs having an angle (A2) ranging from 62 to 68 degrees, and the slits 12 thirdly adjacent to the center hole 11 take the form of elongated circular arcs having an angle (A3) ranging from 70 to 75 degrees.

[34] In this case, preferably, curvature radius of the respective slits 12 (Rl, R2, R3) is within the range of 4 to 6mm.

[35] Further, it is preferable that all the slits 12 define an opening ratio of 50 to 80% on the basis of the total area of the breaker plate 10. That is, if the opening ratio is below 50%, it raises extrusion pressure, and causes a heat generation problem. On the contrary, if the opening ratio exceeds 80%, it fails to maintain an appropriate extrusion pressure, thereby making it impossible to uniformly nix the molten resin, and disadvantageously causing oxidation due to a lowered extrusion velocity.

[36] The breaker plate 10 is made of a material chemically non-reactive at a high temperature, and is applicable to the extrusion of all kinds of plastic materials, which contain polyolefin as a basic resin component. Further, an inlet 12a and an outlet 12b of the respective slits 12 and an inlet and an outlet of the center hole 11 are tapered by an angle (α) ranging from 40 to 80 degrees (See. Fig. 3), such that the flow rate of the molten resin increases at wall surfaces of the slits 12, thereby preventing the molten resin from being accumulated and oxidized between the slits 12.

[37] In this case, the breaker plate 10 is preferably formed to have a thickness of 15 to 23mm so as not to affect flow-ability of the molten resin while securing a sufficient support force for the screen mesh 20.

[38] The housing 30 is internally formed with an annular protrusion 31 such that the annular protrusion 31 comes into close contact with the edge of the breaker plate 10. Such an annular protrusion 31 serves to intercept some of the slits 12 corresponding to the periphery of the screen mesh 20, thereby preventing the molten resin from flowing through the slits 12.

[39] Now, the operation and effects of the breaker plate assembly of the present invention configured as stated above will be explained.

[40] First, in the breaker plate assembly, the circular arc-shaped slits 12 are symm etrically arranged in all directions, so as not to generate flow-rate deflection of the molten resin, thereby being capable of preventing oxidation and discoloration caused by the residence of the molten resin.

[41] Further, since the edge of the breaker plate 10 corresponding to the periphery of the screen mesh 20 is intercepted by the annular protrusion 31 of the housing 30, there is no risk of impurities, entered through the periphery of the screen mesh 20, being nixed and extruded along with the molten resin.

[42] In addition to the above-described effects, as a result of the opening ratio of 50 to 80%, the breaker plate is effective in preventing an increase in extrusion pressure and heat generation, and in maintaining the extrusion pressure at an appropriate level, thereby allowing the molten resin to be uniformly nixed, and preventing accumulation of the molten resin.

[43] Hereinafter, the circular slit-type breaker plate according to the present invention will be compared with the conventional hole-type and slit-type breaker plates on the basis of the content of oxidized carbon corresponding to the output of continuous extrusion.

[44] The figs. 5 - 7 show the results of a monitoring of the detected content of oxidized carbon impurities, having a size of more than 30 micrometers, by making use of an impurity-detecting device. Here, the detected content of the impurities corresponds to the output of continuous extrusion.

[45] As shown in Fig. 5, the detected content of the oxidized carbon impurities is 25EA/L when the output is 21,000kg in an embodiment of the present invention,.

[46] In consideration of the fact that it is conventionally acceptable up to a linit value of 30EA/L, it will be understood that an embodiment of the present invention can continuously perform extrusion even after the output exceeds 21,000kg.

[47] On the contrary, in cases of the conventional hole-type breaker plate (Fig. 6 - Comparative Embodiment 1) and the conventional slit-type breaker plate (Fig. 7 - Comparative Embodiment 2), the detected content of the oxidized carbon impurities reaches 65EA/L and 40EA/L, respectively, when the output is only 18,000kg. Such results far exceed the linit value of 30EA/L, and thus in the case of the conventional breaker plates, additional continuous extrusion is impossible. [48] The Fig. 8shows the results of the monitoring of the detected content of the oxidized carbon impurities per hour by making use of an impurity-detecting device. Here, the impurities have a size of more than 70 micrometers.

[49] In this case, the άrαilar slit-type breaker plate according to the embodiment of the present invention has a value of 1 to 2EA/H, the conventional slit-type breaker plate has a value of 15EA/HR and the conventional hole-type breaker plate has a value of 35EA/HR.

[50] As can be seen from the above results, when the circular slit-type breaker plate of the present invention is used, the impurity-filtering ability of the screen mesh can be improved, compared to the prior art.

[51] Industrial Applicability

[52] As apparent from the above description, the present invention provides a circular slit-type breaker plate assembly for use in an extruder which can prevent oxidation and discoloration of resin caused by an extended residence time of the resin during long- term extrusion, and can restrict the passage of impurities through the periphery of a screen mesh, resulting in an improved quality of products.

[53] Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

[1] A circular slit-type breaker plate assembly for use in an extruder comprising: a housing having an inner diameter tapered toward an exit side; a breaker plate installed in the housing and having a plurality of circular arc- shaped slits defining one or more concentric circles around the center of the breaker plate, such that at least two άrαilar arc-shaped slits are arranged on one of the concentric circles, the slits of the same circle being symmetrically arranged in all directions; and a screen mesh installed in the housing and supported by the breaker plate.

[2] The assembly as set forth in claim 1, wherein the breaker plate further has a center hole perforated therethrough.

[3] The assembly as set forth in claim 1, wherein all the slits define an opening ratio of 50 to 80% on the basis of the total area of the breaker plate.

[4] The assembly as set forth in claim 1, wherein the total number of the slits ranges from 4 to 24.

[5] The assembly as set forth in claim 1 or 2, wherein inlets and outlets of the slits and the center hole are tapered by an angle ranging from 40 to 80 degrees.

[6] The assembly as set forth in claim 1, wherein the slits take the form of άrαilar arches arranged to define three concentric circles about the center of the breaker plate, the slits primarily adjacent to the center of the breaker plate taking the form of elongated circular arcs having an angle of 40 to 45 degrees, the slits secondarily adjacent to the center of the breaker plate taking the form of elongated circular arcs having an angle ranging from 62 to 68 degrees, and the slits thirdly adjacent to the center of the breaker plate taking the form of elongated circular arcs having an angle ranging from 70 to 75 degrees.

[7] The assembly as set forth in claim 1, wherein the housing is internally formed with an annular protrusion coning into contact with the edge of the breaker plate, such that some of the slits corresponding to a periphery of the screen mesh are intercepted by the protrusion.