FI93183C - A method and apparatus for applying fluoroplastic to the surface of a paper machine roll - Google Patents

Description

93183

Method and apparatus for applying fluoroplastic to the surface of a paper machine roll Förfarande och anordning för utbredning av Fluorplast över ytan av en Vals i en pappersmaskin 5

The invention relates to a method for applying fluoroplastic to the surface of a roll, in particular a roll of a paper machine.

The invention also relates to devices for carrying out the method according to the invention.

There are various needs in a paper machine to improve surface release properties; paper guide rolls and drying cylinders are often coated with fluoroplastics to reduce adhesion, and on the other hand, the suitability of new granite replacement materials has been impaired by their web release properties (usually too high adhesion). In addition, the center roll has had the problem of changing the release properties over time over the surface.

20

Fluoroplastics are the most preferred materials for surface release properties because their surface energy is about half that (15-18 m N / m vs. the other 30-50 m N / m) than metals, other polymers, or ceramics, including granite.

25

There are various options for applying fluoroplastics such as Teflon (Teflon - Du Pont trademark - poly-tetrafluoroethylene - PTFE) to the surface, such as crimping the plastic socks around the roll or spraying the polymer and solvent to the surface and subsequent drying heating and polymerization. This is usually done on an electrolytically coated chromium or thermally sprayed carbide coating.

In addition, smaller pieces can be coated by other methods, such as e.g. leijutusmenetelrnällä.

An example of an electrolytic coating is the applicant's FI publication 74 308, in which a desired coating is obtained by a coating method by adjusting the running parameters of the coating and by impregnating the polymer into this coating.

The following disadvantages have been observed in the methods currently used: high polymerization temperature (up to 360 ° C) has caused hydrogenation in the rolls, hydrogen trapped in the pores of the roll body during chromium plating has bubbled during Tefloning, 10 - Teflon socks have been damaged during transport and installation, Tefloning ), the reduction in adhesion caused by Tefloning is so strong that after Tefloning of the center roll the web travels with the felts, i.e. the adhesion cannot be controlled, 15 - Fluoroplastics are soft materials and wear quickly, injectable Teflon solvents are in some cases toxic and thinner.

The invention relates to a method and a device for applying fluoroplastic to the surface of a roll 20 which do not suffer from the disadvantages described above and with which the release properties of the roll can be adjusted.

In accordance with the above objects, the method according to the invention is mainly characterized in that the application of the fluoroplastic takes place by pressure polishing by pressing a fluoroplastic plate or rod on the surface of a rotating roll.

A first embodiment of the device according to the invention applying the above method is mainly characterized in that a piece of fluoroplastic is attached to the movable beam 30, which is pressed against a rotating roll.

Another embodiment of the device according to the invention applying the above method is mainly characterized in that a piece of fluoroplastic is attached to the scraper 35 of a paper machine, which is pressed against the surface of the moving roll, in the manner of a conventional scraper blade, • tl 93183 3

Preferred embodiments of the invention have the features of the subclaims.

The need to improve the release properties of some rolls 5 already in use can be met, in part by avoiding the above drawbacks, by the method according to this notice, in which a fluoroplastic sheet or rod is pressed against the surface of a rotating roll in a machine.

One spring for this invention has arisen from experience in which the roller 10 was driven with a steel scraper. As a result of the molding, the surface of the roll was roughened to Ra to 5-6 micrometers. The roll was then scraped with a glass fiber-reinforced epoxy scraper, whereupon the surface of the roll began to be smoothed, as the epoxy scraper pressure polished the surface of the roll and the Ra value dropped to about one-tenth.

15

A closer examination of the surface showed that the pores and pits on the surface had been filled with epoxy. However, epoxy does not have a release-improving effect.

20 Pressure polishing as described above has also been used with Yankee cylinders, the surfaces of which have been pressure polished after coating with bronze scrapers. In addition, on-site ground cylinders have been pressure-polished with a bronze scraper before commissioning, eg in connection with creep. In this case, the purpose of the pressure polishing is to fill the 25 grooves on the surface.

The method resembles scraping, in which case a normal scraper holder is suitable for doing so. The application of the method is particularly good in areas with a double scraper, in which case the rearmost formula-30 can be used for applying fluoroplastic, for example, while driving.

Another possibility to apply the method is to use a separate movable polishing beam, which can be taken to the factory and placed next to the roll temporarily or permanently. The construction of the beam then resembles the construction of a scraper beam, although it is lighter in construction 4 93183 and looser in manufacturing tolerances. However, in order to obtain a uniform result, it should preferably be oscillated.

The length of the required treatment is adjusted by adjusting the length and pressure of the pressure polish 5. During driving, it is possible to observe the correct result by means of the release angle and the traction difference, which are known per se. When correcting local detachment problems, a fluoroplastic scraper or bar can only be used in problem areas where detachment or soiling problems are greatest.

10

Suitable fluoroplastics for the process are, for example: polytetrafluoroethylene PTFE

copolymer of tetrafluoroethylene and hexafluoropropylene, FEP 15 - polychlorotrifluoroethylene, PCTFE

polyvinylidene fluoride, PVDF perfluoroalkoxy, PFA

The invention has clear advantages over previously known methods. Not only are the above objectives achieved, it has the advantage that the process can be performed "on site" and that the temperature in the process is not high.

In the following, the invention will be described by presenting two embodiments of the invention with reference to the accompanying Figures 1-2, to which the invention is in no way intended to be limited.

Figure 1 shows a first alternative of a device applying the method according to the invention.

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Figure 2 shows another alternative of a device applying the method according to the invention.

A double scraper of the type of Figure 1 is also disclosed in the applicant's FI patent-35 application 890733, from which further details will become apparent.

5 93183

Figure 1 shows an end view of a paper machine double scraper 10 according to the invention. The paper machine double scraper body according to the invention comprises a first scraper bar 11 and a first scraper 12 and a second scraper bar 13 and a second scraper 14. The frame structure 5 comprises end plates 15 by means of scraper bars 11 and 13 to each other.

Scrapers 12 and 14 can be adjusted with their own adjustment devices.

The double scraper structure used in the invention thus consists of two separate scraper bars, which are connected into a single scraper structure at their ends by using rigid end plates. Each scraper bar is individually adjustable with respect to the end plates.

The scrapers 12,14 are arranged in their own scraper bars, whereby the scrapers connected to the scraper bars are adjusted by turning the scraper bar with respect to the end plates associated with the scraper bars by means of a control device.

Scrapers 12,14 can be further fine-tuned. For example, a piece of fluoroplastic connected to the scraper 12,14 20 can be turned by a control device so that the body of the scraper pivots on a joint.

In Fig. 1, the entire scraper structure 10 is turned by a cylinder device 29 to the roll T, and the fine adjustment of the scrapers 12 and 14 is performed by turning the scraper bars 11 and 13 associated with the scrapers with respect to the end plates 15. According to the invention, a piece of fluoroplastic 16 is attached to the holder 14 of the scraper blade instead of the scraper blade, which is pressed on the surface 1 of the rotating roll T at a certain pressure. The line pressure in the application is in the range 30-200 N / m. When using the invention in a double cabinet, such as Figure 1, the purpose of the first scraper is to clean the surface of the roll of contaminants and to prevent the water of the washing jets from passing along the surface of the roll onto the paper web.

35 Thus, the roll is coated with fluoroplastic, because the scraper 14 pressure polishes the surface Tx of the roll T and Ra falls to a value Ra <1.0 / zm, (preferably the initial roughness is 2-3.5 μπι). A scraper with only one scraper blade can equally well be used in the invention, which is then replaced by a piece of fluoroplastic. But when using a double scraper, a piece of fluoroplastic is attached to the rear holder during papermaking. In this case, the front holder usually has a normal (fiberglass-reinforced epoxy, stainless steel or carbon steel) scraper. When paper is not made, a piece of fluoroplastic is attached to either holder or even both.

Figure 2 shows a movable polishing beam 10 'for use in the invention, which is preferably operated by a pneumatic hydraulic cylinder 29'. Similar to the double scraper, the beam 10 'has a holder 12' for a piece of fluoroplastic 16 'which is pressed against a rotating roll at a pressure of 30-200 N / m.

The following are claims which, within the scope of the inventive idea defined by it, may vary in the details of the invention.

K

Claims (10)

A method for spreading fluorine plastic over the surface of a roll, especially a roll in a paper machine, characterized in that the spreading of the fluorine plastic takes place by pressure smoothing by pressing a sheet or closure (16,16 ') of fluorine plastic against the surface. (Τχ) of a rotating roller (T). 2. A method according to claim 1, characterized in that a scourer, especially a double scraper, is used for spreading the fluorine plastic. 3. A method according to claim 1, characterized in that an oscillating smoothing beam is advantageously used for spreading the fluorine plastic, preferably an oscillating smoothing beam. 4. A method according to claims 1-3, characterized in that the result of the treatment, ie the release properties, is controlled by controlling the length and pressure of the pressure relief. 20 Process according to any of claims 1-4, characterized in that the line pressure at the propagation is 30-200 N / m. 6. A process according to any one of claims 1-5, characterized in that the fluorine resin (16,16 ') used consists of polytetrafluoroethylene (PTFE), a mixed polymer (FEP) of tetrafluoroethylene and hexafluoropropylene, polychlorotrifluoroethylene ( PCTFE), polyvinylidene fluoride (PVDF) or perfluoroalkoxy (PFA). Apparatus for carrying out the method according to any of claims 3-6, which comprises a slidable beam (10, 10 ') which is attached to a functional device, e.g. a cylinder (29,29 '), characterized in that a piece of fluorine plastic (16,16') has been attached to the beam pressed against the rotating roller (T). 35 93183 Device according to claim 7, characterized in that the slidable beam (10 ') is oscillating. Device intended to carry out the method according to claims 25 or 4-5, which comprises a first scraper beam (11) and a first scraper (12) therein, a second scraper beam (13) and a second scraper (14) therein, and end plates (15), by means of which the scraper beams (11 and 13) are joined to each other at the ends, characterized in that a piece of fluorine plastic (16) is pressed onto the surface (Τ ') of the paper machine's scraper (14). of the movable roller (T) in the same way as a conventional blade. II