Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F7/00—Other details of machines for making continuous webs of paper
  • D21F7/04—Paper-break control devices

Definitions

• PATENT APPLICATION TITLE A SHEET BREAK DETECTOR APPARATUS
• the present invention relates to a sheet break detector apparatus for detecting a sheet break in a dryer section of a paper machine. More particularly, the present invention relates to a sheet break detector for particular application to a dryer section having no open draws therein.
• Bel-Champ is a common law trademark of Beloit Corporation.
• the Bel-ChampTM single tier drying section has provided a means for drying alternate sides of a web of paper without subjecting the paper to the long open draws typically incorporated into a conventional two-tier, double felted dryer section.
• the excellent runnabiiity of the Bel-ChampTM also contributes to the increased likelihood that the web will wrap one of the dryers.
• the geometry of the Bel-ChampTM dryer section makes it difficult to remove the wrapped paper from the dryer if the wound layers around the drying cylinder become excessively thick.
• a reliable sheet break detector would sense the absence of a web and would initiate a dropping of the sheet upstream relative to the dryer section, thereby preventing excessive wrapping of a dryer cylinder.
• the Bel-ChampTM concept does not include any open draws. Therefore, the employment of a conventional sheet break detector is not possible.
• a prior art break detection method includes an optical sensor to determine if a web is present.
• a light emitter is located on one side of the web and a receiver on the other. When a web is running between the emitter and receiver, the passage of light is obstructed, indicating the presence of the web.
• an optical sensor includes an emitter and a receiver.
• the emitter and receiver are located on the same side of the web.
• Such configuration utilizes reflected light rather than transmitted light in order to detect the presence of a web.
• the sensor is of a type that can detect a color difference. Therefore, in order for the aforementioned method to be effective, a colored felt must be used. The sensor senses the color difference between a felt and a sheet of paper so that in the event of a sheet break, such color difference is sensed by the sensor.
• optical sensors are sensitive to dust and the build-up of dirt on the light sensitive lenses thereof. Such build-up of dust and dirt restricts the passage of light, thus indicating the presence of a web even when the web is absent due to a web breakage. When such a false indication occurs, there can be a significant amount of paper wrapped up on a dryer before a sheet break is discovered. Cleaning the wrapped paper from the dryer cylinder leads to excessive downtime of the dryer section.
• Vacuum sensors are not as sensitive to dust and dirt as optical transducer type counterparts.
• the present invention provides a vacuum transducer for detecting a sheet break which is insensitive to operational changes in the normal adjustments in vacuum levels of the vacuum rolls, while reliably detecting a sheet break.
• Another object of the present invention is the provision of a vacuum sheet break detecting apparatus which overcomes the aforementioned problems of the prior art arrangements and which makes a considerable contribution to the art of detecting a sheet break in a dryer section.
• the present invention relates to a sheet break detector apparatus and method for detecting a sheet break in a dryer section of a paper machine.
• the apparatus includes a vacuum transducer which is sensitive to the vacuum level within a vacuum roll of the dryer section.
• the transducer detects only a sudden change in the vacuum level within the vacuum roll resulting from a sheet break, rather than a relatively gradual change in the vacuum level resulting from an operator augmented vacuum level change.
• the apparatus also includes means connected to the transducer and responsive to the transducer for redirecting the sheet to a broke chute or pit upstream relative to the transducer when the transducer detects the sudden change in vacuum level.
• the arrangement is such that excessive wind-up of the broken sheet around a dryer of the dryer section is inhibited.
• the transducer is a piezoelectric pressure transducer which senses the vacuum level within a center shaft of the vacuum roll.
• the transducer senses the vacuum level within a duct which connects the vacuum roll to a source of partial vacuum.
• the transducer is such that during normal operation of the dryer section, when the unbroken sheet extends through the dryer section, a first output from the transducer is zero, and when a sheet break occurs, an output signal is generated which is proportional to the change in vacuum level within the vacuum roll as a result of the sheet break.
• Figure 1 is a side-elevational view of a portion of a Bel-ChampTM type dryer section showing the location of the transducer;
• Figure 2 is a similar view to that shown in Figure 1 , but shows how the web is directed to a broke chute or pit in the event of a downstream web breakage;
• FIG. 3 is a schematic representation of a sheet break detector apparatus including a vacuum transducer according to the present invention
• Figure 4 is a schematic representation of the sheet detector apparatus according to a further embodiment of the present invention in which the transducer detects the vacuum level within a duct;
• Figure 5 is a graph showing the transducer response to a steady state condition
• Figure 6 is a graph showing the transducer response to a sheet break.
• Figure 7 is a graph showing the transducer response to an operator augmented damper adjustment.
• FIG. 1 is a side-elevational view of a portion of a Bel-ChampTM type dryer section including a sheet break detector apparatus, generally designated 10 according to the present invention, for detecting a sheet break in the dryer section, generally designated 12.
• the apparatus 10 includes a vacuum transducer 14 which is sensitive to the vacuum level within a vacuum roll 16 of the dryer section 12.
• the transducer 14 detects only a sudden change in the vacuum within the vacuum roll 16 resulting from a sheet break rather than a relatively gradual change in vacuum resulting from an operator augmented vacuum level change.
• Figure 2 is a view similar to that shown in Figure 1 , but showing the operation of the apparatus 10 in the event of a web breakage. More particularly, means 18 are connected to the transducer 14 and responsive to the transducer 14 for redirecting the sheet W to a broke pit 22 disposed upstream relative to the transducer 14 when the transducer 14 detects a sudden change in vacuum level. The' arrangement is such that excessive wind-up of the broken web W around a dryer 24 of the dryer section 12 is inhibited.
• the broken web W is shown as wrapping around dryer cylinder 24 and the trailing end of the downstream broken web passing the vacuum roll 16 in order to extend around drying cylinder 26.
• the means 18 may include a transverse web cutting device for cutting the web as it extends around a vacuum transfer roll 28. Additionally, the means 18 may include an arrangement for cutting off the vacuum to the vacuum roll 28 such that the moving web will fall to the broke pit 22 rather than extending around the vacuum roll 28 for transfer into the downstream dryer group, which includes drying cylinders 24 and 26 and vacuum roll 16.
• the present invention is directed particularly to the transducer 14, which senses the sudden change in vacuum level, and it will be understood by those skilled in the art that such transducer may be used for triggering a visual or audible alarm so that an operator may manually direct the web to the broke pit.
• the aforementioned transducer 14 may generate a signal for cutting the web upstream of the entire dryer group or, for in any other manner, interrupting the movement of the web along the dryer section.
• the transducer 14 is a piezoelectric pressure transducer.
• Figure 3 is a schematic representation showing the transducer 14 for sensing the vacuum level existing within a center shaft 30 of the vacuum roll 16.
• FIG 4 is a similar view to that shown in Figure 3, but shows an alternative embodiment of the present invention in which a transducer 14A senses the vacuum level within a duct 32 which connects the vacuum roll 16A to a source of partial vacuum 34.
• the transducer 14 is arranged in such a manner that during normal operation of the dryer section 12, when the unbroken web W extends through the dryer section 12, the output from the transducer is zero.
• the change in vacuum is sensed by the transducer and an output signal is generated which is proportional to the change in vacuum level within the vacuum roll 16 as a result of the sheet break.
• Figure 5 is a graph 36 showing the response of the piezoelectric transducer 14 to a steady state condition with the graph 36 representing the pressure against a number of time constants.
• Figure 6 shows four graphs 38,40,42 and 44 indicating the transducer output for various time constants in response to a sheet break.
• Figure 7 shows graphs 46,48 and 50 indicating the response of the transducer 14 to routine damper adjustments of the vacuum roll for various time constants.
• Figure 7 shows the graphs for the pressure relative to the time of adjustment.
• the output from the transducer 14 decays to zero when a new steady state condition exists, as shown particularly in the graph 44 shown in Figure 6, following the sheet break.
• the difference in the output signal between a fast and a relatively slow change makes it possible to detect the difference between a sheet break and damper movement.
• the time constant is within the range 1 millisecond to 3 seconds.
• the time constant is defined as the period required for the output to reach e ' ⁇ or .368, of its original value.
• Figure 5 shows the graph 36 of this curve.
• the objective is to configure the transducer system such that it has a time constant on the order of milliseconds.
• the vacuum change occurring during a sheet break happens fast enough to be fully sensed by the transducer, as shown in the graph depicted in Figure 6.
• the much slower change in vacuum that occurs when an operator adjusts a vacuum damper is competing with the constantly decaying output of the transducer. Given a sufficiently short time constant, the sensor will exhibit only a slight ripple in its output, as shown in Figure 7.
• the means may include a cross-machine web cutter such that the web is directed to the broke chute 22.
• the means may include an audible or visible alarm for directing an operator to the presence of a sheet break.
• the present invention provides a reliable means for detecting a sheet break that is particularly advantageous for detecting a sheet break within a dryer section having no open draws.

Landscapes

• Paper (AREA)
• Controlling Rewinding, Feeding, Winding, Or Abnormalities Of Webs (AREA)
• Controlling Sheets Or Webs (AREA)

Applications Claiming Priority (3)

Publications (2)

Family

ID=25528481

Family Applications (1)

Country Status (13)

Cited By (1)

Families Citing this family (9)

Family Cites Families (3)

• 1993
  • 1993-10-19 KR KR1019950702070A patent/KR950704569A/ko active IP Right Grant
  • 1993-10-19 JP JP6513120A patent/JP2562799B2/ja not_active Expired - Lifetime
  • 1993-10-19 CA CA002150021A patent/CA2150021C/en not_active Expired - Fee Related
  • 1993-10-19 DE DE69304545T patent/DE69304545T2/de not_active Expired - Fee Related
  • 1993-10-19 BR BR9307486A patent/BR9307486A/pt not_active Application Discontinuation
  • 1993-10-19 DE DE0660898T patent/DE660898T1/de active Pending
  • 1993-10-19 PL PL93308218A patent/PL172455B1/pl not_active IP Right Cessation
  • 1993-10-19 WO PCT/US1993/009974 patent/WO1994012724A1/en active IP Right Grant
  • 1993-10-19 EP EP93924356A patent/EP0660898B1/de not_active Expired - Lifetime
  • 1993-11-16 CN CN93114519A patent/CN1035076C/zh not_active Expired - Fee Related
  • 1993-11-18 MY MYPI93002420A patent/MY110025A/en unknown
  • 1993-11-23 TW TW082109841A patent/TW229270B/zh active
  • 1993-11-24 MX MX9307387A patent/MX9307387A/es not_active IP Right Cessation
• 1995
  • 1995-05-24 FI FI952548A patent/FI952548A0/fi not_active Application Discontinuation

Non-Patent Citations (1)

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