CA1122000A - Methods and apparatus for the rapid consolidation of moist porous webs - Google Patents
Methods and apparatus for the rapid consolidation of moist porous websInfo
- Publication number
- CA1122000A CA1122000A CA000324280A CA324280A CA1122000A CA 1122000 A CA1122000 A CA 1122000A CA 000324280 A CA000324280 A CA 000324280A CA 324280 A CA324280 A CA 324280A CA 1122000 A CA1122000 A CA 1122000A
- Authority
- CA
- Canada
- Prior art keywords
- roll
- web
- nip
- heated
- rolls
- 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
- D21F3/00—Press section of machines for making continuous webs of paper
- D21F3/02—Wet presses
- D21F3/0281—Wet presses in combination with a dryer roll
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
- D21F5/00—Dryer section of machines for making continuous webs of paper
- D21F5/02—Drying on cylinders
- D21F5/022—Heating the cylinders
- D21F5/025—Heating the cylinders using combustion gases
Abstract
ABSTRACT OF THE DISCLOSURE
A moist, porous web is consolidated and dried by running it through the nip between two rotatable rolls, the surface of one of which is heated as it approaches the nip. One side of the web is in direct contact with the surface of the heated roll and the other side faces a permeable surface. The rolls are pressed together under high pressure to transfer heat from the heated roll to the web compressed therebetween to dry the same. The roll sur-face may be heated by hot gases from a fuel combustion burner or by a liquid medium. The dried and consolidated web may be removed from the heated roll by doctoring or it may be conveyed from the nip between the rolls to apparatus for processing it further.
A moist, porous web is consolidated and dried by running it through the nip between two rotatable rolls, the surface of one of which is heated as it approaches the nip. One side of the web is in direct contact with the surface of the heated roll and the other side faces a permeable surface. The rolls are pressed together under high pressure to transfer heat from the heated roll to the web compressed therebetween to dry the same. The roll sur-face may be heated by hot gases from a fuel combustion burner or by a liquid medium. The dried and consolidated web may be removed from the heated roll by doctoring or it may be conveyed from the nip between the rolls to apparatus for processing it further.
Description
~ 1 ~ 2 S~CIFIC~TI0~
- Background of the Invention The present invention relates to the consolida-tion of porous, moist webs by pressing and drying, and more particularly to new and improved methods and apparatus for consolidating thin fibrous webs, especially soft papers such as toilet and facial tissues, paper towels, and thin printing papers, for example, although it is not limited to:such applications.
J Moist pa~er webs are commonly dried by pressing them against heated rolls For ex~mple, in drying with a so-called Yankee d-yer, the web is firmly pressed against a steam heated cylinder of large diameter, which must have considerable thic~ness to withstand the lnternal pressure and external load. Usually, a dryer or ventilating hood surrounds part of the cylinder periphery to assist in dry-ing the web. In order to meet the high capacity demands of modern tissue macnines, cylinders of very large diameter have been used, yet more than 60% of the drying energy comes 1 6 ~
~ ' from the hoo~. S~c:~ mac:~inery is large, costly to build and operate, and oceu?ies considerable space in ~he plant.
Multic~ der machines have also been used in which the web is ^irs. pressed between rolls, together with one or two 'elts ~n~ ~ossi~ly accompanying wires. The web is usually ta'.~en ihrough two to four press nips in order to remove as much ~a_er as possible by mechanical means before final consolida~on is e~fected by drying with heat. This is done by ~ressi-~ he web against steam heated cylinders by web tensionin- or with the aid of a felt or wire adjusted to apply a very l~sht load. Drying then takes place partly while the web is beir!g heàted on the cylinders and partly by evaporation of wa_er rrom the web in the open and preferably ventilated dra.is be~l~een the cylinders. The contact pressure between the web and ~he cylinders, however, must be kept very low iL damage to '_h2 web is to be avoided, and this limits the heat trans~er from the cylinders to the web. Multi-cylin2er machines are therefore very large and long in rela-tion to the produc.ion capacity allowed by the dryer section.
- It has also been proposed to dry a web of wet fibrous material b.y running it over externally heated rollers to genera~e a vapor layer on which the web floats, as disclosed in Ca~adian patent No. 1,013,316. Since the web does noL come into direct contact with the heated roller, heat transfer bet;Jeen the web and the rollers is limited.
S~-;Fary of the Invention It is an object of the invention, accordingly, to provide new and i ?roved methods and apparatus for consolidating 23~36 ~ 22~0 and drying moist po-o~s webs that are free from the above-noted deficiencies o^ tne prior art.
According to the invention, drying of a web is effected by trans.erring heat very rapidly directly to the web under high pressure, insteacl of conducting it through the cylinder shell to the web. More specifically, heat is supplied to the outer surface of a roll and the heated sur-face is then presse~ under high pressure against the moist web to be consolica,ed. The heat energy is stored at a high temperature in a ,hin surface layer of the roll or cylinder, from which it can be extracted very quickly. Moreover, the heat transfer to ~he we~ takes place substantially in a press nip where essen,ially only fibers and water are present and in particularly close contact with the heated roll sur-face, so that e~ce?tionally high rates of heat transfer can _~ be obtained.
Complex steam supply and condensate drainage facili-ties are not required and the roll can be constructed very simply and ruggedly or material having suitable thermal properties. Also, the roll surface may be made permeable in any known manner so that any expressed water and gener-ated steam can escape.
By applyin~ relatively high press loads, very high power densities can be used without causing the web to come loose from the heated roll. In fact, the temperatures and power densities used for the heated roll are so high as to cause a very rapid, violent and almost explosive generation of steam to ta;e pl~ce at the interEace between the roll and the moist s~eb. The steam thus formed tends to pass straight throush the -~eb, carrying with it any free water remaining in the ca~iLies between the fibers of the web.
Thus, the heat 'rans^~r between the steam and remaining fibers and water in 'he ~eb is very effective and cools the s'eam so effec.iv21~ that practically all of its heat _~ energy is transferred to the web and the water remaining therein.
While the roll surface can be heated in many different ways, this can most readily be done in an exist-ing p per machine by direct heating of the roll surface with liquid, pulverized, or gaseous fuel, preferably gas or oil. Direct firing with gas enables very great power densities to be achieved simply and inexpensively. Simple burners can be used to attain powers of up to 1 ~lW/m2, i.e.
twen,y to thirty times higher than power densities achiev-able with a modern Yan~ee dryer. It is not possible, however, to achieve a lOO~ transfer of the heat in the gases of combustion, even with the use of special blowingdevices and burbulence-generating elements near the roll sur-face.
Nearly lOO~ utilization of the heat supplied iseffecLed, according to the invention, by conveying the web, adhered to a felt or wire or a combination thereof, to a suction roll ~;hich constitutes the porous roll in the press nip. A hood is disposed around the co.~bustion chamber such _~_ ~2~0 23836 i that all of the ho_ cas ge~erated, eYcept for a minimum air surplus or de'ici., is dra~n through the fibrous web into the suction roll. In this fashion, practically the entire quantity of heat re~aining in the combustion gases S is utilized for heat-ng and, to some extent, for drying the paper web. Accordingly, almost the entire heat quan-tity supplied is utilized in the consolidation process without losses.
Descri~tion o~ RePresentative Embodiments For a better understanding of the invention, reference is made .o .he following detailed description taken in conjunction ~ith the accompanying drawings, in which:
-Figure 1 is a schematic showing of apparatus constructed according to the invention for consolidating a porous, moist ~7eb or fibrous material;
-Figure 2 sho-~s schematically a modification of the apparatus sno-~m in Figure 1 in which the web runs downwardly out of the press nip;
-20 -Figure 3 illustrates schematically another embodiment in which the roll is heated by a liquid medium;
and -Figure 4 is a schematic showing of another embodiment in ~hich the heated roll is perforated.
In Figure 1, a heated roll 1 and a suction roll
- Background of the Invention The present invention relates to the consolida-tion of porous, moist webs by pressing and drying, and more particularly to new and improved methods and apparatus for consolidating thin fibrous webs, especially soft papers such as toilet and facial tissues, paper towels, and thin printing papers, for example, although it is not limited to:such applications.
J Moist pa~er webs are commonly dried by pressing them against heated rolls For ex~mple, in drying with a so-called Yankee d-yer, the web is firmly pressed against a steam heated cylinder of large diameter, which must have considerable thic~ness to withstand the lnternal pressure and external load. Usually, a dryer or ventilating hood surrounds part of the cylinder periphery to assist in dry-ing the web. In order to meet the high capacity demands of modern tissue macnines, cylinders of very large diameter have been used, yet more than 60% of the drying energy comes 1 6 ~
~ ' from the hoo~. S~c:~ mac:~inery is large, costly to build and operate, and oceu?ies considerable space in ~he plant.
Multic~ der machines have also been used in which the web is ^irs. pressed between rolls, together with one or two 'elts ~n~ ~ossi~ly accompanying wires. The web is usually ta'.~en ihrough two to four press nips in order to remove as much ~a_er as possible by mechanical means before final consolida~on is e~fected by drying with heat. This is done by ~ressi-~ he web against steam heated cylinders by web tensionin- or with the aid of a felt or wire adjusted to apply a very l~sht load. Drying then takes place partly while the web is beir!g heàted on the cylinders and partly by evaporation of wa_er rrom the web in the open and preferably ventilated dra.is be~l~een the cylinders. The contact pressure between the web and ~he cylinders, however, must be kept very low iL damage to '_h2 web is to be avoided, and this limits the heat trans~er from the cylinders to the web. Multi-cylin2er machines are therefore very large and long in rela-tion to the produc.ion capacity allowed by the dryer section.
- It has also been proposed to dry a web of wet fibrous material b.y running it over externally heated rollers to genera~e a vapor layer on which the web floats, as disclosed in Ca~adian patent No. 1,013,316. Since the web does noL come into direct contact with the heated roller, heat transfer bet;Jeen the web and the rollers is limited.
S~-;Fary of the Invention It is an object of the invention, accordingly, to provide new and i ?roved methods and apparatus for consolidating 23~36 ~ 22~0 and drying moist po-o~s webs that are free from the above-noted deficiencies o^ tne prior art.
According to the invention, drying of a web is effected by trans.erring heat very rapidly directly to the web under high pressure, insteacl of conducting it through the cylinder shell to the web. More specifically, heat is supplied to the outer surface of a roll and the heated sur-face is then presse~ under high pressure against the moist web to be consolica,ed. The heat energy is stored at a high temperature in a ,hin surface layer of the roll or cylinder, from which it can be extracted very quickly. Moreover, the heat transfer to ~he we~ takes place substantially in a press nip where essen,ially only fibers and water are present and in particularly close contact with the heated roll sur-face, so that e~ce?tionally high rates of heat transfer can _~ be obtained.
Complex steam supply and condensate drainage facili-ties are not required and the roll can be constructed very simply and ruggedly or material having suitable thermal properties. Also, the roll surface may be made permeable in any known manner so that any expressed water and gener-ated steam can escape.
By applyin~ relatively high press loads, very high power densities can be used without causing the web to come loose from the heated roll. In fact, the temperatures and power densities used for the heated roll are so high as to cause a very rapid, violent and almost explosive generation of steam to ta;e pl~ce at the interEace between the roll and the moist s~eb. The steam thus formed tends to pass straight throush the -~eb, carrying with it any free water remaining in the ca~iLies between the fibers of the web.
Thus, the heat 'rans^~r between the steam and remaining fibers and water in 'he ~eb is very effective and cools the s'eam so effec.iv21~ that practically all of its heat _~ energy is transferred to the web and the water remaining therein.
While the roll surface can be heated in many different ways, this can most readily be done in an exist-ing p per machine by direct heating of the roll surface with liquid, pulverized, or gaseous fuel, preferably gas or oil. Direct firing with gas enables very great power densities to be achieved simply and inexpensively. Simple burners can be used to attain powers of up to 1 ~lW/m2, i.e.
twen,y to thirty times higher than power densities achiev-able with a modern Yan~ee dryer. It is not possible, however, to achieve a lOO~ transfer of the heat in the gases of combustion, even with the use of special blowingdevices and burbulence-generating elements near the roll sur-face.
Nearly lOO~ utilization of the heat supplied iseffecLed, according to the invention, by conveying the web, adhered to a felt or wire or a combination thereof, to a suction roll ~;hich constitutes the porous roll in the press nip. A hood is disposed around the co.~bustion chamber such _~_ ~2~0 23836 i that all of the ho_ cas ge~erated, eYcept for a minimum air surplus or de'ici., is dra~n through the fibrous web into the suction roll. In this fashion, practically the entire quantity of heat re~aining in the combustion gases S is utilized for heat-ng and, to some extent, for drying the paper web. Accordingly, almost the entire heat quan-tity supplied is utilized in the consolidation process without losses.
Descri~tion o~ RePresentative Embodiments For a better understanding of the invention, reference is made .o .he following detailed description taken in conjunction ~ith the accompanying drawings, in which:
-Figure 1 is a schematic showing of apparatus constructed according to the invention for consolidating a porous, moist ~7eb or fibrous material;
-Figure 2 sho-~s schematically a modification of the apparatus sno-~m in Figure 1 in which the web runs downwardly out of the press nip;
-20 -Figure 3 illustrates schematically another embodiment in which the roll is heated by a liquid medium;
and -Figure 4 is a schematic showing of another embodiment in ~hich the heated roll is perforated.
In Figure 1, a heated roll 1 and a suction roll
2 having a suction zone 3 connected to a vacuum source are disposed to form a press nip. The two rolls rotate ~ ZO~O
in the directiona ir.~ica.ed by t~e arrows and conventional means (not sho.~n) are provided for pressing the rolls together under z his-. linear load (typically, 5-250 kN/m), so that a hiah ?resslre in the range 0.1 - 5 MN/m is pro-duced in the press ni?. A wire or felt 4 carrying a web 5 runs over the suc~ion roll 2, formin~ a permeable surface thereon, and then p~sses throush the press nip.
The sur~a_e Or ,he roll 1, which can be smooth or patterned, is ad~pt-d .o be heated by means of gas burners 6 supplied with saseouâ ,uel through a pipe 7. The gas bur-ners 6 are dis?osed .,ithin a co~bustion chamber 8 which encloses a sector of t`he roll 1 in front of the press nip and also the majo~ part of the vacu~m zone 3. Doctor blades 9 and 10 engage the side of the roll 1 opposite the suction roll 2 and are dis?oaed between a broke chute 12 for receiv-_J ing m~terial doc~ored o r the roll 1 and a hood 11 which encloses the majo- p rt of the side of the roll facing away from the com~us,ion chamber 8.
~ .
In operation, the web 5 deposited on the felt or wire 4 by direct for-.ins, suction pickup, pressing, etc., is conveyed into t~e press nip between the rolls 1 and 2~
As it passes over the vacuum zone 3 of the suction roll 2, it is sub~ected to ho. gases drawn from the combustion chamber 8 into the vacu~m zone. Adequate sealing of the combustion c.~mber 8 -rom the atmosphere is provided by an inlet plate 12a.
The web ~ t:~us pre-dried is then conveyed into the press nip betwee~ the suction roll 2 and the heated ~ L2~
roll 1, ~ith the linear load between the rolls set to the desired high ~alue. The roll 1 is made of a material of relatively hish tnermal conductivity and it is so heated that in combination with the loading of the press nip, the web 5 is firmly ~~essed against the surface of the roll 1.
Depending on operating conditions, a-large or small amount of steam may be senerated in the press nip between the rolls 1 and 2, and a small or large, respectively, amount of steam may be generated over the peripheral segment of the roll 1 enclosed by the hood 11.
Depending on the operating conditions selected, the web 5 is either completely or incompletely dried before it reaches the first doctor blade 9; which doctors it off the web while giving it a creped appearance. The second doctor blade lO (and any other doctors that may be provided) acts as a cleaning or polishing doctor, as known in the art.
The web doctored oSf the roll 1, as well as the web during starting and tem~orary shutdown, is collected in the broke chute 12.
While the hood 11 is shown as a 5imple ventilation hood for the extraction of steam, it can be provided with heat generating means in the form of burners or the like for heating the gaseous medium in the hood and, directly or indirectly, also the web 5. The hood 11 can also form a seal with the heat~d roll 1 so that steam can be collected without appreciable entry of air for subsequent economical r:ecovery of the heat of evaporation in suitable apparatus.
20~
In such case, suction slots may be formed in the inlet and outlet ends of t:ne ~ood 11 to acco~modate a small quantity of surplu, steam lea~age from the hood to insure that an absolute ~inim~ amount of air is intermixed with the stea.~ that is to be treated subsequently.
The hoo~ 11 may also be provided with seals against the heate~ roll at its inlet and outlet ends, preferably in the fo~ o' roll seals or doctor seals, so as to en2ble .~e p~essure in the hood to be reduced consider~ly belo~. a.~os~eric pressure by extraction of the steam. Lo~ering the steam pressure in the hood 11 appreciably increases the rate OL steam removal from the web and also reduces the amount of heat energy required for drying. This resul.s in a further advantage for `
certain types OL- SOf . cre?ed products, namely, an increase in bul~ resultin fro~ a reduction in the internal bonding condition in the paper web 5.
While t:~e bur~ers 6 in Figure 1 are shown sche-matically as simple gas burners fed from a common gas supply 7 enclosed by a hood 8, burners for the combustion of fuels other than sas, such as oil or other liquid fuel, two-phase fuel, or pulverize2 fuel, may be employed. Also, the burners may be made in sections in the machine direction and cross-machine direc~ion in order to provide optimum control of the heat supply and thereby the degree of dry-ing of the web on an average and in cross-machine profile.
In tne embodi~ent shown in Fi~ure 2, the web leaves the neate2 roll .~it;~out its structure being changed Z~
by creping and, afier the press section,is conveyed to means for adjusting its dryness profile to the required uniformity. It di~~fers from the apparatus of Figure 1 in that the web 5 ad:~ered to the top of the permeable surface (the wire or felt) 4 runs into the press nip between the rolls 1 and 2, which it leaves with a down-ward motion, as shown in Figure 2. Accordingly, the combustion cha~ber 8 ~ith the burner 6 is positioned above the rolls 1, 2. To the extent that the web tends to follow the heated roll 1 to the doctor blades 9, lO, the broke produced ,h.ereat will be above the desired web run and must, therefore, be collected on a platform which is usually made in the form of a walkway 16, possibly provided with a conveyor belt 17 for broke removal in the well-known manner.
In operation of the embodiment shown in Figure 2, the surface of the roll 1 is heated to a high tempera-ture and/or treated with a suitable releasing agent, so that the web tends to come away from the roll at the exit from the press nip between the rolls 1 and 2, or a short distance thereafter, as illustrated by the dashed line 5' in Figure 2. Aside from this difference, operation is essentially in the same manner as described above in con-nection with Figure 1.
By virtue of the fact that the roll 1 is made of material having good releasing properties and adapted to produce a high temperature in its surface layer, because of its low thermal conductivity, for example, a very high _g_ _~___ 23~36 tem?erature is o~tai~e~ at the roll surface, which can result in a very ra~id, violent, almost explosive genera-tion of steam in the ?ress ni? between the rolls. This results in i~roved cr~ins of the web and improved sepa-ration of the web ~r_m .he heated roll 1.
In the e~bociment shown in Figure 3, a hot liquid medium is used for heating the roll 1. To this end, hot J liquid is supplied to a duct 21 having an opening at its upper end conrormable to the contour of a segment of the roll 1. A modera.ely tight seal 2 provides sufficient upstream clearance relative to the direction of rotation of the roll *o allow the ho. liguid to flow over the sur-face to be heated in the direction opposite its motion.
Turbulence genera.ors or other suitable agitating devices 24 are disposed so as to i~prove the heat transfer from the heating liquid to tne roll surface, and one or more doctor blades 25 are ?ositioned to remove heating medium adhering to tne roll surface. Excess liquid is collected in a ventilating hood 26 and directea to an outlet 23 for recovery and recircula.ion. The hood 26 also collects any air and vapors emitted by the heating liquid for cleaning and recovery of heating medium therefrom.
The heatins medium may be any liquid that can be brought to the correct tem?erature without needing to be Xep-t under pressure and without emitting noxious vapors, although some small amount of such vapor can be tolerated if the hood 26 is suitably ventilated. Suitable liquid 23~36 ~L'~Z~
media may include a heat resistant oil, a liquid metal such as sodium or ~ood's metal, or a molten salt.
Since no hot gases are generated in heating the roll 1, a suction roll is not required for pressing the web against the heating ro]Ll. However, the web must be conveyed to the press nip on a surface which is suffi-ciently permeable to allow steam to leave the web without developing high pressure in the sheet which could damage it and impair drying of the web. Accordingly, in Figure
in the directiona ir.~ica.ed by t~e arrows and conventional means (not sho.~n) are provided for pressing the rolls together under z his-. linear load (typically, 5-250 kN/m), so that a hiah ?resslre in the range 0.1 - 5 MN/m is pro-duced in the press ni?. A wire or felt 4 carrying a web 5 runs over the suc~ion roll 2, formin~ a permeable surface thereon, and then p~sses throush the press nip.
The sur~a_e Or ,he roll 1, which can be smooth or patterned, is ad~pt-d .o be heated by means of gas burners 6 supplied with saseouâ ,uel through a pipe 7. The gas bur-ners 6 are dis?osed .,ithin a co~bustion chamber 8 which encloses a sector of t`he roll 1 in front of the press nip and also the majo~ part of the vacu~m zone 3. Doctor blades 9 and 10 engage the side of the roll 1 opposite the suction roll 2 and are dis?oaed between a broke chute 12 for receiv-_J ing m~terial doc~ored o r the roll 1 and a hood 11 which encloses the majo- p rt of the side of the roll facing away from the com~us,ion chamber 8.
~ .
In operation, the web 5 deposited on the felt or wire 4 by direct for-.ins, suction pickup, pressing, etc., is conveyed into t~e press nip between the rolls 1 and 2~
As it passes over the vacuum zone 3 of the suction roll 2, it is sub~ected to ho. gases drawn from the combustion chamber 8 into the vacu~m zone. Adequate sealing of the combustion c.~mber 8 -rom the atmosphere is provided by an inlet plate 12a.
The web ~ t:~us pre-dried is then conveyed into the press nip betwee~ the suction roll 2 and the heated ~ L2~
roll 1, ~ith the linear load between the rolls set to the desired high ~alue. The roll 1 is made of a material of relatively hish tnermal conductivity and it is so heated that in combination with the loading of the press nip, the web 5 is firmly ~~essed against the surface of the roll 1.
Depending on operating conditions, a-large or small amount of steam may be senerated in the press nip between the rolls 1 and 2, and a small or large, respectively, amount of steam may be generated over the peripheral segment of the roll 1 enclosed by the hood 11.
Depending on the operating conditions selected, the web 5 is either completely or incompletely dried before it reaches the first doctor blade 9; which doctors it off the web while giving it a creped appearance. The second doctor blade lO (and any other doctors that may be provided) acts as a cleaning or polishing doctor, as known in the art.
The web doctored oSf the roll 1, as well as the web during starting and tem~orary shutdown, is collected in the broke chute 12.
While the hood 11 is shown as a 5imple ventilation hood for the extraction of steam, it can be provided with heat generating means in the form of burners or the like for heating the gaseous medium in the hood and, directly or indirectly, also the web 5. The hood 11 can also form a seal with the heat~d roll 1 so that steam can be collected without appreciable entry of air for subsequent economical r:ecovery of the heat of evaporation in suitable apparatus.
20~
In such case, suction slots may be formed in the inlet and outlet ends of t:ne ~ood 11 to acco~modate a small quantity of surplu, steam lea~age from the hood to insure that an absolute ~inim~ amount of air is intermixed with the stea.~ that is to be treated subsequently.
The hoo~ 11 may also be provided with seals against the heate~ roll at its inlet and outlet ends, preferably in the fo~ o' roll seals or doctor seals, so as to en2ble .~e p~essure in the hood to be reduced consider~ly belo~. a.~os~eric pressure by extraction of the steam. Lo~ering the steam pressure in the hood 11 appreciably increases the rate OL steam removal from the web and also reduces the amount of heat energy required for drying. This resul.s in a further advantage for `
certain types OL- SOf . cre?ed products, namely, an increase in bul~ resultin fro~ a reduction in the internal bonding condition in the paper web 5.
While t:~e bur~ers 6 in Figure 1 are shown sche-matically as simple gas burners fed from a common gas supply 7 enclosed by a hood 8, burners for the combustion of fuels other than sas, such as oil or other liquid fuel, two-phase fuel, or pulverize2 fuel, may be employed. Also, the burners may be made in sections in the machine direction and cross-machine direc~ion in order to provide optimum control of the heat supply and thereby the degree of dry-ing of the web on an average and in cross-machine profile.
In tne embodi~ent shown in Fi~ure 2, the web leaves the neate2 roll .~it;~out its structure being changed Z~
by creping and, afier the press section,is conveyed to means for adjusting its dryness profile to the required uniformity. It di~~fers from the apparatus of Figure 1 in that the web 5 ad:~ered to the top of the permeable surface (the wire or felt) 4 runs into the press nip between the rolls 1 and 2, which it leaves with a down-ward motion, as shown in Figure 2. Accordingly, the combustion cha~ber 8 ~ith the burner 6 is positioned above the rolls 1, 2. To the extent that the web tends to follow the heated roll 1 to the doctor blades 9, lO, the broke produced ,h.ereat will be above the desired web run and must, therefore, be collected on a platform which is usually made in the form of a walkway 16, possibly provided with a conveyor belt 17 for broke removal in the well-known manner.
In operation of the embodiment shown in Figure 2, the surface of the roll 1 is heated to a high tempera-ture and/or treated with a suitable releasing agent, so that the web tends to come away from the roll at the exit from the press nip between the rolls 1 and 2, or a short distance thereafter, as illustrated by the dashed line 5' in Figure 2. Aside from this difference, operation is essentially in the same manner as described above in con-nection with Figure 1.
By virtue of the fact that the roll 1 is made of material having good releasing properties and adapted to produce a high temperature in its surface layer, because of its low thermal conductivity, for example, a very high _g_ _~___ 23~36 tem?erature is o~tai~e~ at the roll surface, which can result in a very ra~id, violent, almost explosive genera-tion of steam in the ?ress ni? between the rolls. This results in i~roved cr~ins of the web and improved sepa-ration of the web ~r_m .he heated roll 1.
In the e~bociment shown in Figure 3, a hot liquid medium is used for heating the roll 1. To this end, hot J liquid is supplied to a duct 21 having an opening at its upper end conrormable to the contour of a segment of the roll 1. A modera.ely tight seal 2 provides sufficient upstream clearance relative to the direction of rotation of the roll *o allow the ho. liguid to flow over the sur-face to be heated in the direction opposite its motion.
Turbulence genera.ors or other suitable agitating devices 24 are disposed so as to i~prove the heat transfer from the heating liquid to tne roll surface, and one or more doctor blades 25 are ?ositioned to remove heating medium adhering to tne roll surface. Excess liquid is collected in a ventilating hood 26 and directea to an outlet 23 for recovery and recircula.ion. The hood 26 also collects any air and vapors emitted by the heating liquid for cleaning and recovery of heating medium therefrom.
The heatins medium may be any liquid that can be brought to the correct tem?erature without needing to be Xep-t under pressure and without emitting noxious vapors, although some small amount of such vapor can be tolerated if the hood 26 is suitably ventilated. Suitable liquid 23~36 ~L'~Z~
media may include a heat resistant oil, a liquid metal such as sodium or ~ood's metal, or a molten salt.
Since no hot gases are generated in heating the roll 1, a suction roll is not required for pressing the web against the heating ro]Ll. However, the web must be conveyed to the press nip on a surface which is suffi-ciently permeable to allow steam to leave the web without developing high pressure in the sheet which could damage it and impair drying of the web. Accordingly, in Figure
3 the web is conveyed to the press nip by a felt 4 running over a conventional grooved roll 20 having grooves communi-cating with the ambient atmosphere.
A wire 27 can also be used instead of or with the grooved roll to ventilate the side of the felt facing away from the sheet. Alternatively, the wire can be part of the permeable surface on which the web runs. It is -_~
also possible to use a second wire 28 to convey the web 5a to the press nip and to press it onto the heated roll in a so-called knuckle pattern. In this way, the bulk of 2~ areas of the web between the knuckles of the wire 28 will be preserved so that the web, after having been doctored off the roll and possibly after being dried and calendered, will become softer and more absorbent than it othen~ise would be.
An alternative way of reducing the steam pressure in the felt, thereby facilitating rapid dr~ing of the web (5 or 5'), is to use a smooth surfaced roll and to cool it so that steam passing through the felt condenses on the roll surface an- can bQ re~oved by doctoring. Such effective cooli.c ^a-. be difficult to attain in a ~ay that is economic2l1~ ju,tifiable. Therefore, the sur-face of the roll 20 can be replaced by a belt or wire with substantiall; the sar.~e run as the wire 27 in Figure 3, which can be coolec. eCfectively in its run in a sir~lple way.
The emb~di..en~ shown in Figure 4 is similar to that illustrated in ~igure 1 except that a heated roll 41 is used ~lhich .h2s a perforated surface. The roll sur-face may be drill_c, possibly provided with an overlying, fine mesh, metal sleeve or the like, or made of sintered material. Inside the roll 41 is disposed a stationary stea~ receiver 4~ which is adapted to collect steam pressed out of the sheet. The collected steam can be.
extracted, possib'y at considerable pressure, and con-veyed elsewhere fo_ reuse, thus effecting an energy saving.
By ~ovi?~ the steam receiver 42 to a downstream location 42', the steæm ?ressure can be utilized to blow the web loose. Also, the sheet can-be loosened at another location on the peri~h2.y of the roll 41 by connecting the ste~m receiver 4~ to a blow box 43 located at an arbitrary position.
The invontion is, of course, not limited to apparatus in which the web runs substantially horizontally as in Figures 1 tnrough 4, but is equally applicable to apparatus in wnich the web runs substantially vertically ~_ ___ Z(~
upwards or do~;n:.ards. Further, two or more devices according to the in~ention can be combined or operated in series. It is also within the scope of the invention to consolidate and/~r dry webs of other materials than those usually incluced in paper and similar products, and even to dry pulverized or finely-granulated materials, which can be conveyed to a press nip on a permeable sur-face according to ~e invention.
In nor~.al cases, a major part of the drying must take place in the press nip, but the sheet must stick to - the roll and the final drying takes place after the nip.
Accordingly, the conductivity of the material of which the heating roll is made must be high so as not to dry at temperatures hisner than necessary. A high conductivity means that the heat can be conducted to a greater depth in the roll and even extracted from a greater depth, which in itself means that a lower temperature can be used.
On the other hand, if intense drying is required in the press nip, a high temperature is needed at the roll ~0 surface. This can be attained either by heating a roll made of high conductivity material to a high temperature, which will involve rather large heat losses through the roll material and the roll ends to the air and the journals, etc., or by using a surface material of low conductivity.
The latter should involve lower heat losses and is easier to heat to a high temperature.
However, the choice of material is limited by the risk of ther~.al fatigue and, in this respect, at least 23n36 0~
the su-face ].a,-e- o~ the roll should be made of a material for ~hich the ~U2r-`ti~
,~. (l~v) ~'P c ~
C
has a hi5h value, cesir2~l~ at least 0.6 x 106, where a~
is the fa~igue stre..c~h, ~, is Poisson's ratio, P is the density, c is the specific thermal capacity, ~ is the thermal conducti~ity, E is the modulus of elasticity, and ~c is the ccefficien~ of thermal expansion .or tho material. Copper 21l oys have the highest values, approxi-mately 1.3 ~ 106. Y,o.;ever, they have rather poor resistance to wear and are no_ sui~2Dle for doctoring. Other suit-able materials are du-al~in (0.7 x 106), cast iron (0.67 x 106 - 0.85 x 106), steel ~0.8 x 106), and nickel tapproximately 0.8 x 1~6 - 0.9 x 106).
If heat is supplied to the heated roll by gas _J burners, a major ?-rt of the heat energy wlll be emitted in the form OI in~rared radiation ~s o~posed to ~onve~t.ion).
The ~laterial of the roll should then have a high absorption coefficient for in~rared radiation if all of the heat is to be utilized e~fectively. A sui,able material in this respect is alu~inum. The absorption coefficient ~or infra-red radiation should desirably be higher in the temperature range applicable to gas burners (500 - 2500C) than in the temperature range ,o be imparted to the paper web (50 -150C) In this ~ay, the incoming radiation is utilizedeffectively ar.d is con~erted into.heat in the roll material, while losses due to radiation to the surroundings are mini-mized.
_.
ZC~)0 Heatin~ of the heated roll has been ~xcmplified above by direct combustion of fuel or by means of a liquid heat carrier brought into contact with the roll. Other methods are also possible. Thus t hot gases for heating the roll can be senerated in a separate combustion space by burning a gaseous, liquid or pulverized fuel and then brought against the roll surface. Another possibility is the use of electrical discharges and/or electric resistance losses in wiring against, connected to, or in the surface of the heated roll.
As suggested above in connection with Figure 2, in certain cases the xoll may be heated to a high tempera-ture and~or heat energy may be supplied to the press nip at a high temperature, such that the surface of the web facing the heated roll dries up completely or partially and, therefore, due to the lack of adhesion and/or steam pres-sure remaining between the web and the roll, releases its hold on the roll directly or shortly after its passage j through the press nip. In these cases, release o~ the web can be facilitated by providing a suitable releasing or lubricating agent. This can be or be included in the medium used to heat the heated roll. For example, a heat resistant oil with suitable releasing and lubricating properties could be used.
The method can be carried out, however, so that the web while still adherent to the heated roll continues to dry but, due to drying stresses present in the web, successively shrinks away from the roll (with or without the aid of a releasi~s or lubricating agent), whereby the process is ter~i~ateG before the web is doctored from the surrace of the heated roll.
In embodi."ents like that illustrated in Figure 1, for handlinq sof~-?a?er srades, it is desired that the web in the press nip be pressed so hard against the heated roll that it cannot be induced to shrink away therefrom but remains in place until doctored of by a I creping doctor. In such cases, the adhesion of the web ¦ 10 to the heated roll can suitably be reinforced by means of an additive, ~hich acts as an adhesive, at least at the temperature in the press nip and immediately there-after. Such additives can be supplied to the surface of the s~eb facing the heated roll or to the surface of the heated roll before it arrives at the press nip, or can be added to the furnish fro~ ~hich the paper is being pro-~J .
duced.
The several embodiments described herein are ~ only illustrative a~d are susceptible of modification in ¦ 20 form and detail within the cope of the following claims.
.`
A wire 27 can also be used instead of or with the grooved roll to ventilate the side of the felt facing away from the sheet. Alternatively, the wire can be part of the permeable surface on which the web runs. It is -_~
also possible to use a second wire 28 to convey the web 5a to the press nip and to press it onto the heated roll in a so-called knuckle pattern. In this way, the bulk of 2~ areas of the web between the knuckles of the wire 28 will be preserved so that the web, after having been doctored off the roll and possibly after being dried and calendered, will become softer and more absorbent than it othen~ise would be.
An alternative way of reducing the steam pressure in the felt, thereby facilitating rapid dr~ing of the web (5 or 5'), is to use a smooth surfaced roll and to cool it so that steam passing through the felt condenses on the roll surface an- can bQ re~oved by doctoring. Such effective cooli.c ^a-. be difficult to attain in a ~ay that is economic2l1~ ju,tifiable. Therefore, the sur-face of the roll 20 can be replaced by a belt or wire with substantiall; the sar.~e run as the wire 27 in Figure 3, which can be coolec. eCfectively in its run in a sir~lple way.
The emb~di..en~ shown in Figure 4 is similar to that illustrated in ~igure 1 except that a heated roll 41 is used ~lhich .h2s a perforated surface. The roll sur-face may be drill_c, possibly provided with an overlying, fine mesh, metal sleeve or the like, or made of sintered material. Inside the roll 41 is disposed a stationary stea~ receiver 4~ which is adapted to collect steam pressed out of the sheet. The collected steam can be.
extracted, possib'y at considerable pressure, and con-veyed elsewhere fo_ reuse, thus effecting an energy saving.
By ~ovi?~ the steam receiver 42 to a downstream location 42', the steæm ?ressure can be utilized to blow the web loose. Also, the sheet can-be loosened at another location on the peri~h2.y of the roll 41 by connecting the ste~m receiver 4~ to a blow box 43 located at an arbitrary position.
The invontion is, of course, not limited to apparatus in which the web runs substantially horizontally as in Figures 1 tnrough 4, but is equally applicable to apparatus in wnich the web runs substantially vertically ~_ ___ Z(~
upwards or do~;n:.ards. Further, two or more devices according to the in~ention can be combined or operated in series. It is also within the scope of the invention to consolidate and/~r dry webs of other materials than those usually incluced in paper and similar products, and even to dry pulverized or finely-granulated materials, which can be conveyed to a press nip on a permeable sur-face according to ~e invention.
In nor~.al cases, a major part of the drying must take place in the press nip, but the sheet must stick to - the roll and the final drying takes place after the nip.
Accordingly, the conductivity of the material of which the heating roll is made must be high so as not to dry at temperatures hisner than necessary. A high conductivity means that the heat can be conducted to a greater depth in the roll and even extracted from a greater depth, which in itself means that a lower temperature can be used.
On the other hand, if intense drying is required in the press nip, a high temperature is needed at the roll ~0 surface. This can be attained either by heating a roll made of high conductivity material to a high temperature, which will involve rather large heat losses through the roll material and the roll ends to the air and the journals, etc., or by using a surface material of low conductivity.
The latter should involve lower heat losses and is easier to heat to a high temperature.
However, the choice of material is limited by the risk of ther~.al fatigue and, in this respect, at least 23n36 0~
the su-face ].a,-e- o~ the roll should be made of a material for ~hich the ~U2r-`ti~
,~. (l~v) ~'P c ~
C
has a hi5h value, cesir2~l~ at least 0.6 x 106, where a~
is the fa~igue stre..c~h, ~, is Poisson's ratio, P is the density, c is the specific thermal capacity, ~ is the thermal conducti~ity, E is the modulus of elasticity, and ~c is the ccefficien~ of thermal expansion .or tho material. Copper 21l oys have the highest values, approxi-mately 1.3 ~ 106. Y,o.;ever, they have rather poor resistance to wear and are no_ sui~2Dle for doctoring. Other suit-able materials are du-al~in (0.7 x 106), cast iron (0.67 x 106 - 0.85 x 106), steel ~0.8 x 106), and nickel tapproximately 0.8 x 1~6 - 0.9 x 106).
If heat is supplied to the heated roll by gas _J burners, a major ?-rt of the heat energy wlll be emitted in the form OI in~rared radiation ~s o~posed to ~onve~t.ion).
The ~laterial of the roll should then have a high absorption coefficient for in~rared radiation if all of the heat is to be utilized e~fectively. A sui,able material in this respect is alu~inum. The absorption coefficient ~or infra-red radiation should desirably be higher in the temperature range applicable to gas burners (500 - 2500C) than in the temperature range ,o be imparted to the paper web (50 -150C) In this ~ay, the incoming radiation is utilizedeffectively ar.d is con~erted into.heat in the roll material, while losses due to radiation to the surroundings are mini-mized.
_.
ZC~)0 Heatin~ of the heated roll has been ~xcmplified above by direct combustion of fuel or by means of a liquid heat carrier brought into contact with the roll. Other methods are also possible. Thus t hot gases for heating the roll can be senerated in a separate combustion space by burning a gaseous, liquid or pulverized fuel and then brought against the roll surface. Another possibility is the use of electrical discharges and/or electric resistance losses in wiring against, connected to, or in the surface of the heated roll.
As suggested above in connection with Figure 2, in certain cases the xoll may be heated to a high tempera-ture and~or heat energy may be supplied to the press nip at a high temperature, such that the surface of the web facing the heated roll dries up completely or partially and, therefore, due to the lack of adhesion and/or steam pres-sure remaining between the web and the roll, releases its hold on the roll directly or shortly after its passage j through the press nip. In these cases, release o~ the web can be facilitated by providing a suitable releasing or lubricating agent. This can be or be included in the medium used to heat the heated roll. For example, a heat resistant oil with suitable releasing and lubricating properties could be used.
The method can be carried out, however, so that the web while still adherent to the heated roll continues to dry but, due to drying stresses present in the web, successively shrinks away from the roll (with or without the aid of a releasi~s or lubricating agent), whereby the process is ter~i~ateG before the web is doctored from the surrace of the heated roll.
In embodi."ents like that illustrated in Figure 1, for handlinq sof~-?a?er srades, it is desired that the web in the press nip be pressed so hard against the heated roll that it cannot be induced to shrink away therefrom but remains in place until doctored of by a I creping doctor. In such cases, the adhesion of the web ¦ 10 to the heated roll can suitably be reinforced by means of an additive, ~hich acts as an adhesive, at least at the temperature in the press nip and immediately there-after. Such additives can be supplied to the surface of the s~eb facing the heated roll or to the surface of the heated roll before it arrives at the press nip, or can be added to the furnish fro~ ~hich the paper is being pro-~J .
duced.
The several embodiments described herein are ~ only illustrative a~d are susceptible of modification in ¦ 20 form and detail within the cope of the following claims.
.`
Claims (27)
1. In a method for consolidating and drying a moist, porous web or the like, the steps of running the web through the nip between a pair of rotatable rolls with one side in contact with one roll and its other side facing a permeable surface, heating the surface of said one roll as it approaches said nip, and pressing the rolls together to develop a high pressure, linear load in the press nip sufficient to produce good thermal contact be-tween said one roll and the web at least in areas subjected to said high pressure, linear load and to overcome any steam pressure developed between the web and said one roll.
2. A method as defined in claim 1 in which the web is run through the nip between a rotatable roll having a permeable surface and a second roll, the surface of which is heated as it approaches said nip.
3. A method as defined in claim 1 in which the web is run through the nip between said rolls on a permeable belt with one side of the web in contact with said heated roll.
4. A method as defined in claim 2 in which the web is run through the nip between a roll having a grooved surface and a second roll, the surface of which is heated as it approaches said nip.
5. A method as defined in one of claims 2 and 3 in which the web is run through the nip between a pair of rotatable rolls, one of which is a suction roll, with one side facing said suction roll and its other side in contact with the surface of the other roll.
6. A method as defined in claim 1 in which the web is consolidated and dried on the heated roll and is then removed therefrom by doctoring.
7. A method as defined in claim 1 in which said one roll is heated by combustion of a fuel in close proximity to the surface thereof.
8. A method as defined in claim 7 in which hot gases produced by combustion of said fuel are flowed against the surface of said heated roll as it approaches said nip.
9. A method as defined in claim 8 in which part of the hot gases produced by combustion of said fuel are flowed through the web, thereby supplying heat to the latter.
10. A method as defined in claim 1 in which said one roll is heated by exposing part of the surface thereof to a liquid heating medium.
11. A method as defined in claim 10 in which the liquid medium is a heat resistant oil.
12. A method as defined in claim 10 in which the liquid medium is a molten metal.
13. A method as defined in claim 10 in which the liquid medium is a molten salt.
14. A method as defined in claim 10 in which the liquid medium is flowed against the surface of the heated roll.
15. A method as defined in claim 14 in which the principal direction of flow of the liquid is opposite the direction of travel of the roll surface.
16. A method as defined in claim 1 in which the pressure in the press nip lies in the range of 0.1 - 5MN/m2.
17. In apparatus for consolidating and drying a moist, porous web or the like, the combination of a pair of rotatable rolls defining a nip, means for running a web through said nip with one side in contact with the surface of one of said rolls and with the other side facing a permeable surface, means disposed externally of said one roll for heating a portion of the outer surface thereof as it approaches said nip, and means for pressing said rolls together under a load sufficient to produce good thermal contact between the web and said one roll in said nip, at least in areas subjected to high pressure in said nip, and to overcome any steam pressure developed between the web and said one roll.
18. Apparatus as defined in claim 17 in which said web running means comprises a permeable belt having a run around the other of said rolls and comprising said permeable surface.
19. Apparatus as defined in claim 17 in which the other of said rolls has a permeable surface.
20. Apparatus as defined in claim 19 in which the surface of said other roll is grooved.
21. Apparatus as defined in any one of claims 18 or 19 in which said other roll comprises a suction roll.
22. Apparatus as defined in claim 17 together with doctor means for removing the web from said one roll after its passage through said nip.
23. Apparatus as defined in claim 17 together with fuel combustion burner means disposed to direct hot combustion gases to the surface of said one roll to heat the same.
24. Apparatus as defined in claim 23 together with means defining a combustion chamber enclosing said burner means and an area of the heated roll upstream of the press nip.
25. Apparatus as defined in claim 24 in which said combustion chamber also communicates with part of the surface of the other of said rolls providing access for said hot combustion gases thereto for passage through the web.
26. Apparatus as defined in claim 17 together said heating means comprises conduit means having outlet means generally conforming to the shape of part of said one roll in closely adjacent relation to the surface thereof and disposed upstream of said nip, and means for supplying a liquid heating medium to said conduit means.
27. Apparatus as defined in claim 26 together with means providing clearance between said outlet means and the adjacent surface of said one roll on the upstream side of said outlet means for flowing liquid therethrough in a direction opposite the direction of motion of said one roll.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| SE7803672-0 | 1978-03-31 | ||
| SE7803672A SE423118B (en) | 1978-03-31 | 1978-03-31 | PROCEDURE AND DEVICE FOR CONSOLIDATION AND DRYING OF A MOISTURIZED POROS COAT |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1122000A true CA1122000A (en) | 1982-04-20 |
Family
ID=20334463
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000324280A Expired CA1122000A (en) | 1978-03-31 | 1979-03-27 | Methods and apparatus for the rapid consolidation of moist porous webs |
Country Status (3)
| Country | Link |
|---|---|
| US (1) | US4324613A (en) |
| CA (1) | CA1122000A (en) |
| SE (1) | SE423118B (en) |
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| DE102005000782A1 (en) * | 2005-01-05 | 2006-07-20 | Voith Paper Patent Gmbh | Drying cylinder for use in the production or finishing of fibrous webs, e.g. paper, comprises heating fluid channels between a supporting structure and a thin outer casing |
| DE102005000795A1 (en) * | 2005-01-05 | 2006-07-13 | Voith Paper Patent Gmbh | Apparatus and method for producing and / or refining a fibrous web |
| DE102006015796A1 (en) * | 2005-05-13 | 2006-11-16 | Voith Patent Gmbh | drying cylinders |
| US7767060B2 (en) * | 2006-03-22 | 2010-08-03 | E. I. Du Pont De Nemours And Company | Creping machine |
| US7614161B2 (en) * | 2006-04-21 | 2009-11-10 | Osvaldo Ricardo Haurie | Cylindrical dryer having conduits for heating medium |
| US8127462B2 (en) | 2006-04-21 | 2012-03-06 | Osvaldo Ricardo Haurie | Cylindrical dryer having conduits provided within a plurality of holding plates |
| DE102006062235A1 (en) | 2006-12-22 | 2008-06-26 | Voith Patent Gmbh | Method and device for drying a fibrous web |
| US7803248B2 (en) * | 2007-05-23 | 2010-09-28 | Johns Manville | Method of drying mat products |
| US9670617B2 (en) | 2011-02-15 | 2017-06-06 | Georgia-Pacific Consumer Products Lp | System and methods involving fabricating sheet products |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3073038A (en) * | 1959-11-05 | 1963-01-15 | Woodrow C Lodding | Drying drum |
| GB922296A (en) * | 1961-02-16 | 1963-03-27 | Strattwell Developments Ltd | Improvements in apparatus for drying continuous webs of textile and other materials |
| US3206869A (en) * | 1961-12-01 | 1965-09-21 | Beloit Iron Works | Apparatus for applying a gloss to paper in drying thereof |
| US3303576A (en) * | 1965-05-28 | 1967-02-14 | Procter & Gamble | Apparatus for drying porous paper |
| US3560333A (en) * | 1967-08-15 | 1971-02-02 | Scott Paper Co | Method and apparatus for drying paper on a yankee dryer |
| US4146361A (en) * | 1972-09-07 | 1979-03-27 | Cirrito Anthony J | Apparatus for hot gas heat transfer particularly for paper drying |
| US3903961A (en) * | 1973-11-08 | 1975-09-09 | Morrison Machine Co | Hot oil drum |
-
1978
- 1978-03-31 SE SE7803672A patent/SE423118B/en not_active IP Right Cessation
-
1979
- 1979-03-27 CA CA000324280A patent/CA1122000A/en not_active Expired
-
1980
- 1980-06-10 US US06/158,080 patent/US4324613A/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| SE7803672L (en) | 1979-10-01 |
| US4324613A (en) | 1982-04-13 |
| SE423118B (en) | 1982-04-13 |
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