CA1144795A - Twin wire web former (adaption) - Google Patents
Twin wire web former (adaption)Info
- Publication number
- CA1144795A CA1144795A CA000350147A CA350147A CA1144795A CA 1144795 A CA1144795 A CA 1144795A CA 000350147 A CA000350147 A CA 000350147A CA 350147 A CA350147 A CA 350147A CA 1144795 A CA1144795 A CA 1144795A
- Authority
- CA
- Canada
- Prior art keywords
- roll
- fourdrinier
- band
- wire
- forming
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
- D21F9/00—Complete machines for making continuous webs of paper
- D21F9/003—Complete machines for making continuous webs of paper of the twin-wire type
Landscapes
- Paper (AREA)
Abstract
TWIN WIRE WEB FORMER (ADAPTION) ABSTRACT OF THE DISCLOSURE
A fourdrinier paper machine is convertible to a twin wire web forming operation by the addition of a module carrying the second wire, and limited adaptation of the original machine. The composite machine provides a planar stock deposition zone, a convergent throat section where the wires are positioned in converging relation, having suction boxes or foils in supporting and dewatering relation beneath the throat section. The module includes a first forming roll, over which both of the wires are guided, and a second subsequent roll on which the two wires are reverse wrapped, followed by one or more spaced apart guide rolls to substantially align both the wires with the plane of the original fourdrinier wire.
A suction box section is located beneath this portion of the lower wire, for passage thereon to the couch roll, and separation therefrom of the upper wire on its return path.
A fourdrinier paper machine is convertible to a twin wire web forming operation by the addition of a module carrying the second wire, and limited adaptation of the original machine. The composite machine provides a planar stock deposition zone, a convergent throat section where the wires are positioned in converging relation, having suction boxes or foils in supporting and dewatering relation beneath the throat section. The module includes a first forming roll, over which both of the wires are guided, and a second subsequent roll on which the two wires are reverse wrapped, followed by one or more spaced apart guide rolls to substantially align both the wires with the plane of the original fourdrinier wire.
A suction box section is located beneath this portion of the lower wire, for passage thereon to the couch roll, and separation therefrom of the upper wire on its return path.
Description
TWIN WIRE WEB FORMER ~(ADAPTION) This invention is directed to a web forming machine such as a paper machine, and in particular to a twin wire machine or providing two sided web formationO
Significant advances in web formation have taken place over the past three decades, with the advent of twin wire forming, wherein a web is formed between a pair of wires so as to provide two sided formation.
Historically, from the earlier work at St. Anne's Boaxd 10 Mill by R.J. Thomas and others, as evidenced in Canadian Patent No. 583,482 - September 15, 1959 which comprised in essence a second wire run superimposed on a fourdrinier machine, the twin wire arrangements progressed to special purpose machines such as that of David Webster, and of 15 R.M.A.T. de Montigny (U.S. Patent No. 2,995,186), and the later Papriformer (T.M.) machine of de Montigny et al Canadian Patent No. 731,383, April 5, 1966.
Another twin wire machine embodying certain characteristics was the "centrifugal dewatering" twin 20 wire concept of C.A. Lee (U.S. Patent No. 3,150,037 -September 22, 1964). These special purpose machines diverged from the planar aspect of the old fourdrinier machines to a convoluted wrap arrangement.
Considering the characteristics of twin wire 25 machines, as compared with web forming on a fourdrinier, the length of the formation zone is significantly shortenedf the strength and characteristics of the product are enhanced by two sided formation, and machine speed :,, ~
.
' ~ :
'7~5 can be significantly increased with consequent enhancement of productivity.
The gains afforded by adoption of the special purpose formers are offset by high costs, and loss of production time while a mill is converted from conventional fourdrinier operation.
The present invention provides an alternative solution which permits the upgrading of an existing fourdrinier machine to twin wire forming while minimizing both conversion CQStS and production time losses during changeover; and makes the provision for a modular unit for integration with the existing machine elements, to facilitate easy, rapid erection while permitting upgrading of the facility. This imparts the inherent advantages of twin wire formation generally and particularly through a potential increase in speed of operation together with the provision of an improved, "two sided" product.
It will be further understood that the position of the module, in its relation downstream, relative to the breast roll, is not a fixed factor, but would be determined in accordance with relevant factors such as machine speed and stock feed. Furthermore, because o:E
the modular nature of the module, and the manner of its mounting by intermediate stools upon the structure of the original fourdrinier, it is possible to comparatively readily relocate the module along the fourdrinier, in order to modify its action relative to the other elements corporating therewith.
The terms "wire" and "band", encompass fourdrinier wires, "wires" o synthetic fabrics, and felts of various types on which a web can be formed.
The present invention thus provides in a paper machine for forming a web on a first moving endless band, having a source for depositing stock on the band the improvement comprising a second endless band, a forming roll to receive the first and second bands in wrappiny relation about a portion of the periphery of the forming roll, a second roll spaced from the first roll to receive the first and second bands in reversed wrapping relation about the second roll, and at least one guide roll located within the loop of the second band to guide the bands in a predetermined direction prior to separation of the band from the web and the other band.
In co-ordinating the modular unit containing the ~orming roll, the second rolII guide rolls, the second wire etc. with the existing fourdrinier structure, suitable provision is made for wire support means, such as foils, located beneath the main fourdrinier or first ~ire in the convergence zone and defining, in combination with the second wi.re, the throat into which the stock layer travels, whereby the geometry of the throat is dynamically stabilized in conjunction with the breast roll by means of which the second wire is guided to the throat, i.n relation to the amount of the stock material present therein at any gi~en time. Again, at the point of divergence of the two wires, the provision of suction boxes beneath the first wire provides separation of the formed web from the offgoing second wire, which follows a return path.
In carrying out the invention there is provided a method of modifying a fourdrinier machine, including the steps of locating a forming roll to carry a second wire in converging relation with the wire of the fourdrinier, passing the fourdrinier wire and the second wire in wrapping relation about a portion of the periphery of the forming roll, providing a second dewatering roll downstream of the forming roll, passing the two wires in wrapping relation about a portion of the periphery of the second roll, and separating the two wires while retaining the formed web on the fourdrinier wire. The method includes the further steps of ,.. , ~,~,.~9~t~S
supporting the fourdrinier wire and the second wire at the zone of convergence, and dewateri~g the wires.
Certain embo~iments of the invention are described, reference being made to the accompanying drawings wherein Figure 1 represents a schematic cross-sectional elevation of a first embodiment of the paper machine, and Figure 2 is a similar drawing of a second embodiment, each embodi-ment incorporating its respective twin wire module in accordance with the present invention.
The drawings are not intended to represent scale of the components nor of their relative positions in terms of downstream location.
Referring to Figure 1, the arrangement 10 comprises a fourdrinier section 12 having a module 14 in superposed co-operating relation thereover. A headbox 16 provides a stock supply under desired conditions of directionl velocity and volume to the for~ard reach 18 of the fourdrinier wire 20.
The module 14 has a forming roll 24, a second roll 26 spaced therefrom, guide rolls 28 and a breast roll 29 over which the second wire 30 is trained.
The zone of convergence 32, between wire 20 and wire 30 forms a throat, bounded beneath ~he wire 20 by a suction box 34 having foil portions thereon in wire supporting relation.
The lower wire 20 and upper wire 30 are trained for two sided stock dewatering around the open surface forming roll 24, which may be a vacuum forming roll, as is well known in the art, or a grooved roll with, or without a mesh sleeve thereover.
The wires 20, 30 are reverse wrapped about roll 26, so that the top wire 30 of the module is outermost.
Guide rolls 28 align the off-going wires 20, 30, as they leave the second roll 26, with the couch roll 38 of the fourdrinier. A series of suction boxes 40 are provided beneath the wire 20, underlying the point of divergence ~4~79S
of wire 30 which commences the return path of wire 30~
whereby the web is held in contact with the bot~om wire 20, for passage to the couch roll 3~.
Referring to Figure 2, -the arrangement 110 comprises a fourdrinier section 112 having a module 11~ in superimposed co-operating relation thereover. A headbox 116 supplies stock material under controlled volume-direction-velocity conditions ~o the forward reach 118 of the fourdrinier wire 120. This forward reach 118 is repositioned upwardly by repositioning the breast roll.
The module 114 provides the second dewatering roll 126, guide rolls 128 and a breast roll 129, over which the second wire 130 is trained.
The zone of converyence 132, between wires 120 and 130 forms a throat, bounded beneath by the wire 120 and having foils thereunder, in wire supporting relation or the segments of a suction box 134.
The lower wire 120 and the upper wire 130 are trained around an upper portion of the periphery of the forming roll 124 in downward wrapping relation and formin~ the apex of the throat region thereon. The wires 120, and 130 are subsequently reverse wrapped around a lower portion of the periphery of the second roll 126, such that the resulting wire path is substantially serpentine in profile view, having wire 120 outermost.
Guide rolls 128 align the off-going wires 120, 130, as they leave the second roll 126, with the couch roll 138 o~ the fourdrinier and the plane described by roll and the appropriate surfaces of the suction or flat boxes 40~ these boxes being deployed in wire supporting relation under wire 120. A series of suction boxes 140 specifically deployed beneath wire 120, and underlying the point of divergence of wires 120 and 130, further function to hold the web in contact wi~h bottom wire 120 for delivery to the couch roll 138.
Refering now to both drawings, by their , 7~5 appropriate ~eference numerals, the illustrated extent of the modules 14, 114, is not intended to be proportionate to its size, relative to the fourdrinier section 12, 112, and in all probability there is a significant run of the wire 20, 120, downstream from the return run of wire 30, 130.
In operation, the stock deposited on the lower wire 20, 120, commences downward drainage and felting onto the wire 20, 120, before entry into the throat 32, 132. In the throat 32, 132, the top wire 30, 130, contacts the stock layer and commences formation against the top wire 30, 130. Passage of the wires in mutual reacting and compressive relation with the stock about the forming roll 24, 124, produces dewatering through both wires under pressure generated by the tension force of the outermost wire 20, 130, which is reapplied as the wires reverse about roll 26, 126, wi-th the wire 30, 120 to the outside. Various save-alls 39, 139, are provided within the loop of the wire 30, 130, to receive water expressed through the wire 30, 130. Water passing - through the upper reach of the lower wire 20, 120, is deflected downwardly into a saveall within the wire loop.
The presently disclosed modular arrangement 1~, 114, may be erected as a unit and moved into position astraddle the fourdrinier section 12, 112. There then remains the need to restring a new, lower fouxdrinier wire and to modify or install the disclosed suction boxes 34, 40, 134, 140. Such a changeover is normally effected with an up-rating of the headbox and the drive of the machine, with modLfication to the drier section to match the increased capacity of the machine, due to the higher speed. In the event that production quantity up rating is not required, it is generally possible to retain the original drive, substantially unmodified, as the longer wire of the modified forming section passes over significantly fewer suction boxes, flat boxes, 47~S
foils or the like, With consequent reduction in wire drag, and enhanced wire li$e. The second wire is normally driven by contact with the longer wire.
.~, ~
Significant advances in web formation have taken place over the past three decades, with the advent of twin wire forming, wherein a web is formed between a pair of wires so as to provide two sided formation.
Historically, from the earlier work at St. Anne's Boaxd 10 Mill by R.J. Thomas and others, as evidenced in Canadian Patent No. 583,482 - September 15, 1959 which comprised in essence a second wire run superimposed on a fourdrinier machine, the twin wire arrangements progressed to special purpose machines such as that of David Webster, and of 15 R.M.A.T. de Montigny (U.S. Patent No. 2,995,186), and the later Papriformer (T.M.) machine of de Montigny et al Canadian Patent No. 731,383, April 5, 1966.
Another twin wire machine embodying certain characteristics was the "centrifugal dewatering" twin 20 wire concept of C.A. Lee (U.S. Patent No. 3,150,037 -September 22, 1964). These special purpose machines diverged from the planar aspect of the old fourdrinier machines to a convoluted wrap arrangement.
Considering the characteristics of twin wire 25 machines, as compared with web forming on a fourdrinier, the length of the formation zone is significantly shortenedf the strength and characteristics of the product are enhanced by two sided formation, and machine speed :,, ~
.
' ~ :
'7~5 can be significantly increased with consequent enhancement of productivity.
The gains afforded by adoption of the special purpose formers are offset by high costs, and loss of production time while a mill is converted from conventional fourdrinier operation.
The present invention provides an alternative solution which permits the upgrading of an existing fourdrinier machine to twin wire forming while minimizing both conversion CQStS and production time losses during changeover; and makes the provision for a modular unit for integration with the existing machine elements, to facilitate easy, rapid erection while permitting upgrading of the facility. This imparts the inherent advantages of twin wire formation generally and particularly through a potential increase in speed of operation together with the provision of an improved, "two sided" product.
It will be further understood that the position of the module, in its relation downstream, relative to the breast roll, is not a fixed factor, but would be determined in accordance with relevant factors such as machine speed and stock feed. Furthermore, because o:E
the modular nature of the module, and the manner of its mounting by intermediate stools upon the structure of the original fourdrinier, it is possible to comparatively readily relocate the module along the fourdrinier, in order to modify its action relative to the other elements corporating therewith.
The terms "wire" and "band", encompass fourdrinier wires, "wires" o synthetic fabrics, and felts of various types on which a web can be formed.
The present invention thus provides in a paper machine for forming a web on a first moving endless band, having a source for depositing stock on the band the improvement comprising a second endless band, a forming roll to receive the first and second bands in wrappiny relation about a portion of the periphery of the forming roll, a second roll spaced from the first roll to receive the first and second bands in reversed wrapping relation about the second roll, and at least one guide roll located within the loop of the second band to guide the bands in a predetermined direction prior to separation of the band from the web and the other band.
In co-ordinating the modular unit containing the ~orming roll, the second rolII guide rolls, the second wire etc. with the existing fourdrinier structure, suitable provision is made for wire support means, such as foils, located beneath the main fourdrinier or first ~ire in the convergence zone and defining, in combination with the second wi.re, the throat into which the stock layer travels, whereby the geometry of the throat is dynamically stabilized in conjunction with the breast roll by means of which the second wire is guided to the throat, i.n relation to the amount of the stock material present therein at any gi~en time. Again, at the point of divergence of the two wires, the provision of suction boxes beneath the first wire provides separation of the formed web from the offgoing second wire, which follows a return path.
In carrying out the invention there is provided a method of modifying a fourdrinier machine, including the steps of locating a forming roll to carry a second wire in converging relation with the wire of the fourdrinier, passing the fourdrinier wire and the second wire in wrapping relation about a portion of the periphery of the forming roll, providing a second dewatering roll downstream of the forming roll, passing the two wires in wrapping relation about a portion of the periphery of the second roll, and separating the two wires while retaining the formed web on the fourdrinier wire. The method includes the further steps of ,.. , ~,~,.~9~t~S
supporting the fourdrinier wire and the second wire at the zone of convergence, and dewateri~g the wires.
Certain embo~iments of the invention are described, reference being made to the accompanying drawings wherein Figure 1 represents a schematic cross-sectional elevation of a first embodiment of the paper machine, and Figure 2 is a similar drawing of a second embodiment, each embodi-ment incorporating its respective twin wire module in accordance with the present invention.
The drawings are not intended to represent scale of the components nor of their relative positions in terms of downstream location.
Referring to Figure 1, the arrangement 10 comprises a fourdrinier section 12 having a module 14 in superposed co-operating relation thereover. A headbox 16 provides a stock supply under desired conditions of directionl velocity and volume to the for~ard reach 18 of the fourdrinier wire 20.
The module 14 has a forming roll 24, a second roll 26 spaced therefrom, guide rolls 28 and a breast roll 29 over which the second wire 30 is trained.
The zone of convergence 32, between wire 20 and wire 30 forms a throat, bounded beneath ~he wire 20 by a suction box 34 having foil portions thereon in wire supporting relation.
The lower wire 20 and upper wire 30 are trained for two sided stock dewatering around the open surface forming roll 24, which may be a vacuum forming roll, as is well known in the art, or a grooved roll with, or without a mesh sleeve thereover.
The wires 20, 30 are reverse wrapped about roll 26, so that the top wire 30 of the module is outermost.
Guide rolls 28 align the off-going wires 20, 30, as they leave the second roll 26, with the couch roll 38 of the fourdrinier. A series of suction boxes 40 are provided beneath the wire 20, underlying the point of divergence ~4~79S
of wire 30 which commences the return path of wire 30~
whereby the web is held in contact with the bot~om wire 20, for passage to the couch roll 3~.
Referring to Figure 2, -the arrangement 110 comprises a fourdrinier section 112 having a module 11~ in superimposed co-operating relation thereover. A headbox 116 supplies stock material under controlled volume-direction-velocity conditions ~o the forward reach 118 of the fourdrinier wire 120. This forward reach 118 is repositioned upwardly by repositioning the breast roll.
The module 114 provides the second dewatering roll 126, guide rolls 128 and a breast roll 129, over which the second wire 130 is trained.
The zone of converyence 132, between wires 120 and 130 forms a throat, bounded beneath by the wire 120 and having foils thereunder, in wire supporting relation or the segments of a suction box 134.
The lower wire 120 and the upper wire 130 are trained around an upper portion of the periphery of the forming roll 124 in downward wrapping relation and formin~ the apex of the throat region thereon. The wires 120, and 130 are subsequently reverse wrapped around a lower portion of the periphery of the second roll 126, such that the resulting wire path is substantially serpentine in profile view, having wire 120 outermost.
Guide rolls 128 align the off-going wires 120, 130, as they leave the second roll 126, with the couch roll 138 o~ the fourdrinier and the plane described by roll and the appropriate surfaces of the suction or flat boxes 40~ these boxes being deployed in wire supporting relation under wire 120. A series of suction boxes 140 specifically deployed beneath wire 120, and underlying the point of divergence of wires 120 and 130, further function to hold the web in contact wi~h bottom wire 120 for delivery to the couch roll 138.
Refering now to both drawings, by their , 7~5 appropriate ~eference numerals, the illustrated extent of the modules 14, 114, is not intended to be proportionate to its size, relative to the fourdrinier section 12, 112, and in all probability there is a significant run of the wire 20, 120, downstream from the return run of wire 30, 130.
In operation, the stock deposited on the lower wire 20, 120, commences downward drainage and felting onto the wire 20, 120, before entry into the throat 32, 132. In the throat 32, 132, the top wire 30, 130, contacts the stock layer and commences formation against the top wire 30, 130. Passage of the wires in mutual reacting and compressive relation with the stock about the forming roll 24, 124, produces dewatering through both wires under pressure generated by the tension force of the outermost wire 20, 130, which is reapplied as the wires reverse about roll 26, 126, wi-th the wire 30, 120 to the outside. Various save-alls 39, 139, are provided within the loop of the wire 30, 130, to receive water expressed through the wire 30, 130. Water passing - through the upper reach of the lower wire 20, 120, is deflected downwardly into a saveall within the wire loop.
The presently disclosed modular arrangement 1~, 114, may be erected as a unit and moved into position astraddle the fourdrinier section 12, 112. There then remains the need to restring a new, lower fouxdrinier wire and to modify or install the disclosed suction boxes 34, 40, 134, 140. Such a changeover is normally effected with an up-rating of the headbox and the drive of the machine, with modLfication to the drier section to match the increased capacity of the machine, due to the higher speed. In the event that production quantity up rating is not required, it is generally possible to retain the original drive, substantially unmodified, as the longer wire of the modified forming section passes over significantly fewer suction boxes, flat boxes, 47~S
foils or the like, With consequent reduction in wire drag, and enhanced wire li$e. The second wire is normally driven by contact with the longer wire.
.~, ~
Claims (7)
1. A modified fourdrinier machine having a breast roll and a couch roll in combination with:
a first forming roll and a second forming roll both located intermediately of said breast roll and said couch roll and an elongated endless fourdrinier foraminous forming band wrapping said forming rolls and said breast and couch rolls, said first forming roll being spaced from said breast roll to provide an exposed forward reach of said fourdrinier band between said breast and first forming roll, a second endless foraminous band overlying said fourdrinier band, guide rolls for supporting said second band, said second band wrapping said first and second forming rolls in serpentine fashion, means to deposit a layer of stock on an upper surface of said forward reach of said endless fourdrinier band, extending between said breast roll and said first forming roll, said second band and said rolls being arranged so that said layer of stock and said bands traverse around said forming rolls in sandwich relationship with said stock between said bands, said first roll having an open surface to permit two-way drainage under the effects of band tension and centrifugal force;
said bands passing around said second roll in a reverse wrap relationship relative to said first roll to provide outward de-watering away from said second roll.
a first forming roll and a second forming roll both located intermediately of said breast roll and said couch roll and an elongated endless fourdrinier foraminous forming band wrapping said forming rolls and said breast and couch rolls, said first forming roll being spaced from said breast roll to provide an exposed forward reach of said fourdrinier band between said breast and first forming roll, a second endless foraminous band overlying said fourdrinier band, guide rolls for supporting said second band, said second band wrapping said first and second forming rolls in serpentine fashion, means to deposit a layer of stock on an upper surface of said forward reach of said endless fourdrinier band, extending between said breast roll and said first forming roll, said second band and said rolls being arranged so that said layer of stock and said bands traverse around said forming rolls in sandwich relationship with said stock between said bands, said first roll having an open surface to permit two-way drainage under the effects of band tension and centrifugal force;
said bands passing around said second roll in a reverse wrap relationship relative to said first roll to provide outward de-watering away from said second roll.
2. A modified fourdrinier as defined in claim 1, wherein said first roll is within the loop of said second band and said second roll is within the loop of said fourdrinier band.
3. A modified fourdrinier as defined in Claim 1 wherein said first roll is within the loop of said fourdrinier band and said second roll is within the loop of said second band.
4. The modified fourdrinier as defined in claims 1, 2 or 3 further comprising directing roll means for directing said fourdrinier band into substantially horizontal alignment with the upper surface of said couch roll thereby to provide a substantially horizontal stretch of the fourdrinier band between said directing roll and said couch roll.
5. A modified fourdrinier as defined in claims 1, 2 or 3 wherein said second forming roll is a solid roll and dewatering at said second roll is substantially solely away from said second roll.
6. A modified fourdrinier as defined in claims 1, 2 or 3 wherein said sandwich relationship is formed at said first forming roll.
7. The method of modifying a fourdrinier machine having a first wire band, to provide twin wire web forming capability including the steps of locating a second endless wire band above the fourdrinier, positioning a first forming roll having an open surface within the loop of one of the wire bands and a second roll adjacent thereto within the loop of the other of said wire bands, said first forming roll providing two-way dewatering of stock deposited on said first band by extracting water through both said bands under the effects of band tension and centrifugal force, and arranging said bands to pass in reverse wrapping relation about said second roll, relative to said first roll to at least provide outward dewatering relative to said second roll.
Priority Applications (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000350147A CA1144795A (en) | 1980-04-18 | 1980-04-18 | Twin wire web former (adaption) |
| JP5514181A JPS56159391A (en) | 1980-04-18 | 1981-04-14 | Twin wire type strip material forming apparatus |
| IT21216/81A IT1135733B (en) | 1980-04-18 | 1981-04-16 | TWIN PAPER TAPE FORMER |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000350147A CA1144795A (en) | 1980-04-18 | 1980-04-18 | Twin wire web former (adaption) |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1144795A true CA1144795A (en) | 1983-04-19 |
Family
ID=4116734
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000350147A Expired CA1144795A (en) | 1980-04-18 | 1980-04-18 | Twin wire web former (adaption) |
Country Status (3)
| Country | Link |
|---|---|
| JP (1) | JPS56159391A (en) |
| CA (1) | CA1144795A (en) |
| IT (1) | IT1135733B (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FI75375C (en) * | 1982-03-02 | 1988-06-09 | Valmet Oy | Path forming lot for paper machine. |
-
1980
- 1980-04-18 CA CA000350147A patent/CA1144795A/en not_active Expired
-
1981
- 1981-04-14 JP JP5514181A patent/JPS56159391A/en active Pending
- 1981-04-16 IT IT21216/81A patent/IT1135733B/en active
Also Published As
| Publication number | Publication date |
|---|---|
| IT8121216A0 (en) | 1981-04-16 |
| IT1135733B (en) | 1986-08-27 |
| JPS56159391A (en) | 1981-12-08 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |