Presses – Methods – Forcing through constricted passage
Reexamination Certificate
2000-05-17
2003-09-09
Ostrager, Allen (Department: 3725)
Presses
Methods
Forcing through constricted passage
C100S099000, C100S161000, C100S176000
Reexamination Certificate
active
06615709
ABSTRACT:
FIELD OF THE INVENTION
The invention concerns a method for detecting contamination and/or damaging of a face that runs through a nip or nips in a calender for paper, in which method vibrations occurring in connection with the constructions of a calender are detected and processed.
The present invention is related to calenders for paper, in particular so-called soft calenders and supercalenders, in which soft-coated rolls are used, which are particularly susceptible of damage.
A particularly advantageous embodiment of the present invention is related to monitoring of the condition of soft-coated calender rolls in view of detecting their surface damage at a sufficiently early stage and, thus, in view of permitting prevention of damage in advance.
BACKGROUND
As is known from the prior art, calenders comprise two or more hard-faced and/or soft-faced calender rolls, which form a calendering nip or nips with each other, through which nip
ips the paper web to be treated is passed. In particular, rolls with soft faces, such as paper rolls or equivalent in supercalenders and rolls provided with soft coatings, in particular polymer coatings, in what is called soft calenders, are susceptible of damage. The reason for the damage is frequently contaminations, such as local fibre strings, which cause a pressure impact when they pass through the nip, which impact loads the soft coating on the calender roll and first causes its heating and, in the long run, a permanent deformation in the coating and damage. Similar deformations and, damage may also occur in metallic faces of calender rolls and in the faces of bands running through calendering nips.
In respect of the particular problems that constitute the starting point of the present invention, the following is stated. The polymer-coated rolls in prior-art calenders endure uniform loading and wear well, but they are damaged very easily is some limited, even small area is heated even to a relatively little extent, for example, to a temperature higher than its environment. Owing to the high thermal expansion coefficient and to the very poor thermal conductivity of polymers, such an even little area expands rapidly and is heated further to such high temperatures that it can be deformed. If the coating on the roll has been made of so-called thermosetting resins, on re-melting it, at the same time, loses its original properties. A heating reaction of the sort described above can be caused, for example, by a little piece of paper, fibre string or “clod”, or a stain separated from the coating on the paper, which adheres to the roll face and which, when entering into a calendering nip, causes a local yielding of the coating more intensive than in the environment, which heats the roll coating unevenly.
Prevention of local contamination, for example, by means of constant doctoring is, as a rule, not reasonable, neither economically nor in view of optimal quality of paper, for most of the polymer coatings that are.in use do not tolerate rubbing very well, in which case the preventive cleaning itself might wear the coating to a greater extent than the calendering proper does.
However, if contaminations could be detected early enough, for example, a cleaning doctor or some other device that cleans the roll face could be operated during short periods of time without damaging the roll coating as a result of constant or frequently repeated doctoring. In such a case, the service lives of soft-faced calender rolls could be extended to a considerable extent.
As is known from the prior art, for monitoring the condition of calender rolls, in particular of soft-faced rolls, thermometers traversing in the cross direction of the machine have been used, by whose means the temperature of the coating is monitored. In said temperature monitoring application and in corresponding other prior-art systems, problems arise from the fact that the resilient roll coating, whose temperature is monitored, is, as a rule, at least to some extent electrically insulating. Thus, in the partly rubbing contact between the web and the coating, quite high charges of static electricity arise in the faces of the roll coating and of the relatively dry paper web. These charges tend to be discharged along the available routes with the lowest resistance. A thermographic camera must often be installed so that it projects from its support construction, in which case said static electric charges find exactly the thermographic camera as the easiest route of discharge, in which connection the sensitive electronic system of the thermographic camera is subjected to quite high voltages, and it must be protected specifically against such voltages.
Even if monitoring of the temperature of the face of a calender roll usually permits detecting of a local raised temperature resulting from an excessive load applied to the coating or from a local inner non-homogeneity at a sufficiently early stage, this requires installation of quite heavy, expensive and spacious equipment in the vicinity of the roll to be monitored. In particular, congestion of space causes great difficulties in connection with multi-roll treatment devices, at which every device that is not included in the web treatment process proper makes the maintenance and servicing of the device more difficult.
As is also known from the prior art, DE 43 40 700 discloses a method for detecting contamination or damages in a calender roll by detection of vibrations with vibration sensors. Damaged rolls are replaced in accordance with detected information to stop further damage in a papermaking process.
OBJECTS AND SUMMARY OF THE INVENTION
The object of the present invention is to provide a method by whose means contamination and/or damage in faces of rolls that form a calendering nip or nips and/or in faces of bands that run through nips can be monitored efficiently and by means of relatively simple devices that require little space.
It is a further object of the invention to provide a method in which the operations to be controlled based on the monitoring of the face running through the nip can be arranged to be so quick that, as a rule, permanent substantial damage does not have time to be produced in the face concerned before cleaning operations or equivalent have been started.
It is a further object of the invention to provide a method by means, of whose application, when necessary, the cleaning of the face running through the nip can be applied sufficiently precisely expressly to the area that has been noticed to be contaminated, whereby economies can be obtained in respect of the medium and the energy used for the cleaning. In some cases, owing to the invention, the cleaning equipment can be dimensioned so that its capacity is lower than in the prior art.
In view of achieving the, objectives stated above and those that will come out later, the method in accordance with the invention is mainly characterized in that said vibrations are detected by means of at least one vibration detector fitted in connection with the bearing supports of calender rolls or in connection with constructions related to said bearing supports, by means of which vibration detector(s) the calender roll(s) is/are identified from which the vibration derives.
In a preferred embodiment of the invention, on the bearing housings of the calender rolls or at least on a part of said bearing housings and/or on the roll frames, at least one acceleration detector which measures vibration of the calender roll or a strain gauge detector which measures deformations arising from vibration or other, equivalent detectors is/are fitted. The measurement signals from these detectors.are monitored and analyzed so that the portion of the measurement signal that arises from rotation and unbalance of the rolls is “filtered” off, and the development of the portion that arises from the geometry of the roll face is monitored. When the signal to be monitored reaches a predetermined level or when its spectrum is placed within the measurement window, the control system reports this further, and action can
Karjalainen Arto
Mäenpää Tapio
Suomi Eero
Metso Paper Inc.
Steinberg & Raskin, P.C.
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