DIE FOR MOLDING HONEYCOMB STRUCTURES

Abstract: The die for moulding honeycomb structures has a main body with an inlet surface which is perforated by numbers of independent feed passages in matrix format to admit the raw material to be extrusion-moulded. The complimentary die mask has an outlet surface with moulding grooves corresponding to the inlet surface feed passages. The tops of through bores which provide intercommunication for the feed passages are of semi-circular cross-section while their lower portions are cone-shaped, narrowing to the dia. of the moulding grooves.

Description: This invention relates to a die for molding lattice structures, and in particular relates to a die for extrusion molding lattice structures using plastic materials that exhibit a water-releasing phenomenon when pressurized and thereby a deterioration their ability to flow. Various methods for forming lattice structures have been proposed up to now. However, the lattice structures used as catalysts, whose core length is exceedingly longer than the core cross section, have normally been formed by extrusion molding using dies. Accordingly, it is safe to say that the shapes and structures of the dies constitute very important factors for obtaining lattice structures. Generally speaking, the die used for extrusion molding is arranged to form a lattice molding groove in the outlet surface of raw material, and further to form a supply passage that is opposite to the intersecting portion of said molding groove in the raw material inlet surface opposite to said outlet surface and has a depth penetrating to the bottom of said molding groove. When carrying out extrusion molding by the use of the thus constructed die, if the plastic material to be extrusion molded is not arranged to pass through the lattice molding groove at a substantially uniform speed, there are caused defects such as distortion of the resulting lattice structure, blur inside the partition wall, partial vanishing of the lattice (which is called "hanging" hereinafter) and the like. Accordingly, in order that the plastic materials to be extrusion molded may be extruded at uniform speed from every portion of the molding groove, there have been proposed various methods designed to form a through hole along the lattice at the place connecting the supply passage with the molding groove of the die. The typical die of this sort has been disclosed in Japanese Published Utility Model Gazette No. 3780/1982 Specification, which is shown as the prior art in Fig. 1. In this drawing, the reference numeral 21 stands for a die, wherein a lattice molding groove 22 is formed in its outlet surface 23; plural and independent supply passages 25 are formed in a raw material inlet surface 24 opposite thereto, said passages being opposite to the intersecting portion of said molding groove 22 and extending toward the outlet surface 23; and a large number of independent circular holes 26, whose diameter is larger than the groove thickness, penetrate from the side of the die along the rear end of the molding groove 22 in the manner of crossing each other. In Japanese Laid Open Patent Gazette No. 178712/1982 Specification, furthermore, there is disclosed a die for molding a lattice structure characterized by that in order to prevent the hanging phenomenon of the lattice structure to be obtained, the through hole of the die takes the form of an oblong or a rectangle whose long diameter/short diameter ratio is 1.2-5 and further the short diameter of the through hole/width of the lattice cut-in groove ratio is arranged to be in the range of 1.2-10. In Japanese Published Patent Gazette No. 164/1986 Specification, still further, there is disclosed a die characterized by that a guide groove corresponding to the through hole is formed, the cross-sectional opening area of said guide groove is larger than that of a molding groove, and further a resistance portion guide groove is formed corresponding to a supply passage portion. However, these usually proposed dies (apparatus) for molding lattice structures can not necessarily obtain moldings that satisfy the extrusion molding ability, the properties of obtained lattice structures such, for instance, as distortion, hanging and mechanical strength, and the properties such as cracking and the like occurring at the time of drying and calcining, depending upon the properties of plastic materials to be extrusion molded. Especially when extrusion molding a lattice structure raw material consisting mainly of titanium oxide and/or silica-alumina and a fibrous substance-containing plastic material that exhibits a water-releasing phenomenon when pressurized and hence a deterioration in its fluidity, it was difficult for the usual molding dies to maintain a good molding ability because masses caused by a partial water-releasing phenomenon within the through hole block up part of the molding groove, the fibrous substance clings to part of the molding groove to thereby form a non-flowing section, the resulting lattice structure is subject to hanging, and the extruding pressure increases gradually in course of molding. German Specification DE 3 622 695 A discloses a die for molding a lattice structure possessing a mutually communicating molding groove having a sectional shape corresponding to that of a lattice core and having a predetermined depth from the outlet surface of the die to the inlet surface of the die, and plural mutually independent supply passages that are opposite to intersecting portions and/or acute side portions of said molding groove and have a predetermined depth from the inlet surface of the die to the outlet surface of the die, wherein a through hole for communicating mutually adjacent supply passages is provided at a place forming part of each partition wall between supply passages and connecting with said molding groove; the sectional shape of said through hole taking the combined shape of a trapezoid with the molding groove width as a top side and with the supply passage diameter as a maximum base side and a semicircle having a diameter corresponding to the base side of said trapezoid. The object of this invention is to provide a die for molding a lattice structure suitable for extrusion molding a plastic material containing a fibrous substance that exhibits a water-releasing phenomenon when pressurized and hence a deterioration in its ability to flow. According to the present invention there is provided a die possessing a mutually communicating molding groove having a sectional shape corresponding to that of a lattice core and having a predetermined depth from the outlet surface of the die to the inlet surface of the die, and plural mutually independent supply passages that are opposite to intersecting portions and/or acute side portions of said molding groove and have a predetermined depth from the inlet surface of the die to the outlet surface of the die, wherein a through hole for communicating mutually adjacent supply passages is provided at a place forming part of each partition wall between supply passages and connecting with said molding groove; the sectional shape of said through hole taking the combined shape of a trapezoid with the molding groove width as a top side and with the supply passage diameter as a maximum base side and a semicircle having a diameter corresponding to the base side of said trapezoid; characterised in that an angle ϑ formed by extension lines of oblique sides formed by joining both mutually corresponding ends of the top side and the base of said trapezoid is less than 60 degrees; a ratio of the sectional area (A) of the through hole to the sectional area (B) of the molding groove is in the range of 1.5-3.0; and a length extending from the outlet to the inlet of the molding groove is in the range of 5-10 times as long as the molding groove width. This die for molding lattice structures is suitable for extrusion molding plastic materials that exhibit a water-releasing phenomenon when pressurized and hence a deterioration in their ability to flow such, for instance, as materials consisting mainly of titanium oxide and/or silica-alumina, plastic materials containing fibrous substances, plastic materials containing zeolite substances and the like. For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Fig.1 is a longitudinal front view of the usual typical embodiment of the die of the sort discussed above, Fig.2 is a plan view of the molding die according to this invention, Fig. 3 is an enlarged longitudinal front view of the die according to this invention, Fig. 4 is an enlarged view of the portion encircled by the chain line IV in Fig.2, and Fig. 5 is a view taken in the direction of the arrows along the line V-V of Fig.4 In order to explain this invention in more detail, this invention will be explained with reference to Figs. 2-5 hereinafter. The reference numeral 1 denotes a square die. Like the conventional die shown in Fig. 1, this die is provided with a lattice molding groove 2 on its outlet surface 3, and is also provided with plural independent supply passages 5 on its opposite inlet surface 4 for raw materials, that are opposite to intersecting portions 9 of the molding groove 2 and extend towards the outlet surface 3. These supply passages 5 may be disposed opposite acute side portions 9a in place of the intersecting portions 9. A through hole 6 for communicating adjacent supply passages 5 mutually is provided at a place forming part of each partition wall 8 between supply passages 5 and connection with the molding groove 2. This through hole 6 has a sectional shape combined of a trapezoid 11, 12, 13, 14 with a side joining between rear ends 11, 12 of the molding groove 2 as a top side and with a side joining between front ends 13, 14 of the supply passage 5 as a maximum base side and a semicircular having a diameter corresponding to the base side 13-14 of said trapezoid. Herein an angle ϑ formed by extension lines of oblique sides 11-13 and 12-14 formed by joining both mutually corresponding ends of the top side 11-12 and the base side 13-14 of the trapezoid 11, 12, 13, 14 is less than 60 degrees, and a ratio of the sectional area (A) of the through hole 6 to the sectional area (B) of the molding groove 2 is in the range of 1.5-3.0. Further, said die 1 is provided on the outer periphery of the outlet surface 3 of a die body 7 with a die mask 10 whose portion corresponding to the through hole 6 is projected on the through hole side. In Fig. 3, the reference numeral 10a indicates the projecting portion of the die mask 10. The thus prepared moldings such, for instance, as lattice structures used as catalysts, in particular lattice structures consisting mainly of titanium oxide and the like used as denitrifying catalysts, involve the problem that especially when said structure has an aperture of more than 150 mm □ and a length more than 350 mm, its mechanical strength weakenes. In order to hold the strength of lattice structures, therefore, it is customary that fibrous substances such, for instance, as glass fiber, asbestos, silicon nitride and the like should be added to the raw plastic materials, and then extrusion molded. However, there is an indication that these fibrous substances have a bad influence upon the extrusion molding ability, and as the amounts of fibrous substances are increased and the extruding pressure is raised, the plastic materials represent water-releasing phenomenon and hence deterioration in their ability to flow. Further, the fibrous substances added to the plastic materials stick to part of the molding groove, thereby resulting in non-flowing spots. The conventional dies were not necessarily satisfactory for extruison molding the plastic materials as aforesaid into lattice structures. This invention, that has the through hole 6 of the die 1 shaped as aforesaid, can decrease the non-flowing spots within the die and the degree of sticking of fibrous substances even when using the above mentioned plastic materials that are liable to cause a water-releasing phenomenon, which will be clarified by each example referred to afterwards. In this example, in case the angle ϑ of the through hole 6 is more than 60 degrees, the non-flowing spots of the plastic material are easily caused, whereby the extruding pressure is raised, and the resulting lattice structure is liable to hanging at a high rate. In case the angle ϑ is reduced too much, contrarily, there is a tendency that the flow rate within the molding groove 2 toward the acute side is reduced and thus the function of the molding groove as the through hole is hampered. Therefore, it is preferable that the angle ϑ of the through hole 6 is in the range of 60-45 degrees. In order to allow the plastic material to pass through the lattice molding groove 2 at a uniform rate, the ratio of the sectional area (A) of the through hole 6 to the sectional area (B) of the molding groove 2 is in the range of 1.5-3.0. In case the said sectional area ratio is less than 1.5, there is a tendency that the flow rate of the plastic material in the direction of the acute side portion 9a of the molding groove 2 (which will be called "horizontal direction" hereinafter) is reduced, and the flow rate from the acute side portion 9a becomes slow as compared with the crossing portion 9 of the molding groove 2. In case the above mentioned sectional area ratio is larger than 3.0, contrarily, there is caused a tendency opposite to the above mentioned one with undesirable results that the flow rate in the horizontal direction is increased and the passing velocity from the outer peripheral portion of the die is increased. Compared with the case of extrusion molding the fibrous substance-free plastic material, when extrusion molding the plastic material that represents the water-releasing phenomenon as aforesaid, the molding pressure plays an important role in holding a good molding ability. The molding pressure, although being dependent upon the properties of the plastic materials, is largely influenced by the die. Cosequently, the extrusion molding pressure can be held low for a long period of time by limiting the length extending from the outlet surface 3 to the inlet (a point of contact with the through hole 6) of the molding groove 2 of said die 1 within 5-10 times the width of the molding groove 2. In the case of extrusion molding the lattice structure like the above mentioned denitrifying catalyst, it is desirable also from the view point of the pore volume affecting the catalytic activity to carry out the extrusion molding under the pressure of 2.5 Kg/cm² or less, because the extrusion molding under the high pressure decreases the macro pore volume. According to the die 1 of this invention, furthermore, the die mask 10 is provided on the side of the through hole 6 with a projection 10a for the purpose of controlling the extruding velocity from the outer periphery of the outlet surface 3. Examples of this invention will be shown hereinafter. Example 1 A plastic material (X) suitable for extrusion molding was prepared by adding glass fiber, clay component, polyethylene oxide and water to titanium oxide powder and mingling same. Said die 1 was set in a two-stage single shaft type vacuum extruder for use. Said die 1 was designed to have a through hole 6 whose angle ϑ is 60 degrees, a core with an aperture 161 mm □ and 20 x 20, the width of molding groove 2 of 1.4 mm, the ratio of the sectional area (A) of the through hole 6 to the sectional area (B) of the molding groove 2 of 2.7, and the ratio of the length of the molding groove 2 to the width of the molding groove 2 of 5.1. By using the die 1 like this, said plastic material (X) was extrusion molded into a lattice honeycomb structure having an aperture of 161 mm □ and a length of 1 m. 50m-continuous extrusion molding was conducted while holding the extrusion molding pressure within the range of 16-17 Kg/cm². The obtained 50 pieces of lattice structures were dried and calcined. The structures were found to be of good quality, namely free from hanging, cracking and distortion. Example 2 The plastic material (X) used in Example 1 was extrusion molded by using exactly same die used in Example 1 except that the angle ϑ of the through hole 6 was changed into 60 degrees, the ratio of the sectional area (A) of the through hole 6 to the sectional area (B) of the molding groove 2 was changed into 2.7, and the ratio of the length of the molding groove 2 to the width of the molding groove 2 was changed into 7.3. 50m-continuous extrusion molding was conducted while holding the extrusion molding pressure within the range of 17-18 Kg/cm². The obtained 50 pieces of lattice structures were dried and calcined. These structures were found to be of good quality, namely free from hanging, cracking and distortion. Example 3 The plastic material (X) used in Example 1 was extrusion molded by using exactly same die used in Example 1 except that the angle ϑ of the through hole 6 was changed into 60 degrees, the ratio of the sectional area (A) of the through hole 6 to the sectional area (B) of the molding groove 2 was changed into 2.7, and the ratio of the length of the molding groove 2 to the width of the molding groove 2 was changed into 10. 50m-continuous extrusion molding was conducted while holding the extrusion molding pressure within the range of 21-22 Kg/cm². The resulting lattice structures were dried and calcined. These structures were found to be of good quality, namely free from hanging, cracking and distortion. Example 4 The plastic material (X) used in Example 1 was extrusion molded by using exactly same die as used in Example 1 except that the angle ϑ of the through hole 6 was changed into 60 degrees, the ratio of the sectional area (A) of the through hole 6 to the sectional area (B) of the molding groove 2 was changed into 1.6, and the ratio of the length of the molding groove 2 to the width of the molding groove 2 was changed into 7.3. 50m-continuous extrusion molding was conducted while holding the extrusion molding pressure within the range of 16-17 Kg/cm². The resulting lattice structures were found to be of good quality, namely free from hanging, cracking and distortion. Comparative Examples against said Examples will be enumerated hereinafter. Comparative Example 1. The plastic material (X) of Example 1 was extrusion molded by using a die 21 designed to have a circular through hole 26, the ratio of the sectional area (A) of said through hole 26 to the sectional area (B) of a molding groove 22 of 3.1, the ratio of the length of the molding groove 22 to the width of the molding groove 22 of 7.3, a core with an aperture 161 mm □ and 20 x 20 and a molding groove width of 1.4 mm as in Fig. 1. The extrusion molding pressure used was initially 21 Kg/cm², but said pressure mounted up to 26 Kg/cm² at the point of time when 10m-continuous extrusion molding had been completed. Thus, the extrusion molding was discontinued. Partial hanging phenomena were observed in 7 pieces of 10 pieces of obtained lattice structures. Comparative Example 2 The plastic material (X) of Example 1 was extrusion molded by using exactly same die as used in Example 1 except that the angle of the through hole 6 was changed into 80 degrees, the ratio of the sectional area (A) of the through hole 6 to the sectional area (B) of the molding groove 2 was changed into 2.5, and the ratio of the length of the molding groove 2 to the width of the molding groove 2 was changed into 10.9. 15m-continuous molding was conducted holding the extrusion molding pressures within the range of 23-27 Kg/air. The resulting 15 pieces of lattice structures were dried and calcined. Partial hanging phenoma were observed in 3 pieces thereof. Comparative Example 3 The plastic material (X) of Example 1 was extrusion molded by using exactly same die 1 as used in Example 1 except that the angle of the through hole 6 was changed into 60 degrees, the ratio of the sectional area (A) of the through hole 6 to the sectional area (B) of the molding groove 2 was changed into 3.3, the ratio of the length of the molding groove 24 to the width of the molding groove 24 was changed into 7.3, and a normal die mask was used lacking the projection 10a. 10m-continuous molding was conducted holding the extrusion molding pressure within the range of 18-21 Kg/cm². Referring to the molding state, it was observed that since the outer peripheral portion of the die was extruded at a very high speed, the outer peripheral portion of the thus obtained lattice structure was thickened. When this lattice structure was dried, there was observed partial cracking therein. This invention as aforesaid is available for molding of catalysts or carriers, molding of lattice-structured dry kneading agents or adsorbents, molding of organic fiber-containing ceramics and the like.

Claims: A die possessing a mutually communicating molding groove (2) having a sectional shape corresponding to that of a lattice core and having a predetermined depth from the outlet surface (3) of the die to the inlet surface (4) of the die, and plural mutually independent supply passages (5) that are opposite to intersecting portions (9) and/or acute side portions (9a) of said molding groove and have a predetermined depth from the inlet surface of the die to the outlet surface of the die, wherein a through hole (6) for communicating mutually adjacent supply passages is provided at a place forming part of each partition wall between supply passages and connecting with said molding groove; the sectional shape of said through hole taking the combined shape of a trapezoid (11,12,13,14) with the molding groove width as a top side (11-12) and with the supply passage diameter as a maximum base side (13-14) and a semicircle having a diameter corresponding to the base side of said trapezoid; characterized in that an angle (ϑ) formed by extension lines of oblique sides (11-13) formed by joining both mutually corresponding ends of the top side (11-12) and the base (13-14) of said trapezoid is less than 60 degrees; a ratio of the sectional area (A) of the through hole (6) to the sectional area (B) of the molding groove (2) is in the range of 1.5-3.0; and a length extending from the outlet to the inlet of the molding groove is in the range of 5-10 times as long as the molding groove width. A die as claimed in claim 1, wherein a die mask (10) is provided on the outer periphery of the outlet surface (3) of the die, the portion corresponding to the through hole (6) of the die mask projecting on the through hole side.

Inventors: FUKUDA, MORIO 178, SHIOYA, HANADA, MASAYUKI 7-38, HATAKEDA 1-CHOME, INUTSUKA, HIDEO 13038-2, MIMASAKA-KOU, OGATA, KATSUYA 3335-10, SHIKU
Applicants: CATALYSTS & CHEMICALS INDUSTRIES CO., LTD., IWAO JIKI KOGYO CO., LTD.
Application year: 1986
Main classification: B29C47
IPC codes: B29C47, B28B3, B01J35