FI120514B - Suction roll gasket and method of manufacture - Google Patents

Description

Suction roll gasket and method of manufacture

BACKGROUND OF THE INVENTION The invention relates to an improved suction roll sealing strip made by curing an extruded pulp, the bulk of which consists of polymer and graphite. The invention also relates to a method of making a sealing strip.

Suction rollers are particularly used in paper machines to remove water from the paper web. The suction roll has a perforated jacket and an internal vacuum box 10, whereby the portion of the jacket at which it is exposed is exposed to suction. The seal, or sealing strip, is fitted from its holder to the suction box structures, generally a U-shaped holder, with loading hoses at the bottom and possibly at the sides to initially press the seal against the diaper. Subsequently, the vacuum 15 holds the seal against the jacket.

In the longitudinal direction of the roll, the elongated suction box is limited by the long side seals, the first one, i.e. the wet side sealing strip, is narrower compared to the second, the dry-side 20a sealing strip. In addition, the ends of the suction box have end seals positioned with a slight clearance to the sheath. One such suction roll gasket structure is disclosed in U.S. Patent No. 5,746,891.

25 The wear of seals has posed a rather significant problem. In addition, the noise caused by seals and the power consumption they produce are important factors. Thus, gaskets are primarily required for wear resistance, but low noise and power requirements would also be desirable characteristics.

Sealing strips, in short, are a vulcanized graphite-rubber compound. A typical form of sealing strip is a continuous piece of the same length as the suction box (3 - 12 m). 35 Multi-component sealing strips exist, but require special machining and installation. The material wears out during use and has to be replaced quite often. The material has a rigid and 2 brittle structure. The seals are shipped to the factory in rigid boxes with space for the entire length of the mold. The length and stiffness of the packaging cause considerable transport and storage costs. Fragmentation of the sealing material causes deterioration in the manufacturing process and fractures during transport and installation.

During operation, the sealing strips are loaded against the inner sheath by said loading hoses. The elasticity of the loading means 10 allows for a slight end-to-end alignment of the sealing strip, but the rigidity of the sealing strip prevents local deformation against the roll casing. Thus, any irregularities or deflections due to the manufacture of the sheath can only be compensated by the wear of the sealing strip. When the seal is intended to be a critical element, its useful life is shortened.

The most common construction material for a sealing strip is a vulcanized graphite rubber compound. It is in use on most rolls these 20 days.

US 5649719 (Beloit) discloses the preparation of a resin impregnated graphite for a suction roll sealing strip. US 4,714,523; Sawyer, proposes a sealing strip structure with a PTFE strip installed from his graphite-25 account to improve the sliding properties. US 4915787 (Cline Comapany) discloses a sealing strip construction in which a long sealing strip is formed of pieces whose ends are specifically shaped to form tight limiting joints. US 5876566 (Appleton) discloses a sealing strip consisting of nitrile rubber, graphite, carbon black, PTFE and optionally a phenolic shoulder. U.S. Patent No. 2,893,487 (Beloit) discloses a suction box arrangement in which the latter sealing strip has a groove formed against the diaper on the back of the mold. This reduces the risk of rapid pressure-35 change, especially noise.

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The combination of graphite and rubber is desirable because it provides good lubricating properties, does not wear unduly in normal use and is easy to manufacture. It can be manufactured in any length required by papermaking equipment.

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All graphite rubber sealing strips are manufactured as follows:

The graphite rubber mixture is ground to an acceptable consistency for extrusion 10 - The compound is extruded into approximately the final or intermediate product form

The blanks are vulcanized to a final rigid space.

Rigid billets are machined to their final shape.

15 Traditionally, all graphite rubber sealing strips have the same physical properties, are manufactured in the same way and function in the same way. They are all limited by transportation and handling restrictions due to their rigid and brittle nature.

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The usual vulcanization temperature is about 150 ° C and the treatment time is 3 hours. Additives are used for example. to guide the chemical structure of the final product. Some additives, for example sulfur, affect the amount of carbon bonds. Some additives act as accelerators

Other materials have been tried as a seal, but nothing has been as successful as graphite rubber.

An object of the present invention is to provide an improvement over known seals. Characteristic features of the invention are set forth in the appended claims. The sealing strip according to the invention is so flexible that it can be wound on a roll. In addition to flexibility, the invention gives the seal a smoother run and the power requirement it requires is reduced. Transport and handling damage is reduced when the material is less brittle than before.

The invention will now be described with reference to the accompanying drawings and the preambles. In the drawings, Fig. 1 shows a schematic structure of a suction roll, Fig. 2 shows a comparison of wear in a standard and inventive (FlexSeal) sealing strip, Fig. 3a shows a comparison of required power in a conventional and FlexSeal sealing strip, Fig. 3b shows a noise level comparison ) sealing strip.

Referring to Figure 1, reference numeral 10 generally describes a suction box arrangement for a pape-15 crusher. This includes a stationarily supported suction box 12 disposed inside a perforated cylindrical roll 14 which rotates about the suction box 12. The cylindrical roll 14 has an inner surface 16 and an outer surface 17 and is made of bronze, stainless steel or the like. The suction box 12 has a slot aperture 18 and a U-shaped slot 21 and 23 on both sides of the drum roll 14, in particular holders, in which sealing strips 20 and 22 are mounted. The latter is generally wider. The sealing strips 20, 22 are loaded from below by the loading lines 24 and 25 respectively. The sealing strips 20 and 22 wipe the inside surface of the cylindrical roller 14 as it rotates.

The inner part of the suction box 12 is connected to a vacuum source (not shown), whereby the inner surface 16 30 of the cylindrical roll 14 is subjected to suction in the area of the slot 18. The sealing strips 20 and 22 are the length of the suction box 12 (covering the width of the web to be dried) and the ends of the suction box 12 have special end seals (not shown).

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Previously, for example, the following recipe was used to make a pulp: EXAMPLE 1% by weight 5 Polymer Nipol N612B 20 -i

Nipol 1312 Liquid Rubber 10 J Total. 30% acrylonitrile rubber stearic acid 0.6 magnesium oxide 1.5 graphite 56 ίο accelerator MBTS 0.4 sulfur 12

The pulp was mixed, carefully ground, and extruded through a mold to form a blank. The billet was transferred to an oven where treatment took place for 3 hours at 150 ° C. During the treatment, the chemical reactions are completed. As a result, the mold produced a somewhat flexible solid body (density 1.63 g / cm 3) which had to be transported in full length, since the strip of about 1.9 cm x 4.8 cm could not be bent into a practical radius of curvature.

In particular, the invention seeks to find a solution to the problems of transporting and storing sealing strips, mainly due to the rigidity of known strips. These problems have been solved by a new sealing material, which mainly uses the following substances (% by volume): rel. omine color.

NBR rubber is 30-60%, most preferably 40-50% 0.98

Graphite 30-60%, most preferably 40-50% 2.25 30 Wax 1-20%, most preferably 2-6% 0.97

Preferably, small amounts of known auxiliaries and additives are used. These include e.g. vulcanizing agents such as sulfur; accelerators such as peroxides; stabilizers such as stearic acid; machining agents such as MgO and ZnO.

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In one preparation according to the invention the following recipe was used: EXAMPLE 2% by weight PHR% by volume 5 NBR rubber 28 100 45 graphite 66 235 46 waxes 3 10.5 4.5

Vulcanizing agent 3 10 4.5 PHR = parts per hundred parts of rubber ίο (parts per hundred parts rubber)

The extrusion, vulcanization and machining of the product were performed in a known manner. The vulcanization temperature was 150 ° C and the treatment time was 3 hours. At lower temperatures, reactions occur slower and at higher speeds, thus affecting processing time.

The base material is composed of NBR rubber (acrylo Nitrile rubber), a copolymer of butadiene and acrylonitrile. The NBR rubber used in the example was Nipol N612B, Zeon Chemicals. The graphite used in the example was synthetic, but it could also be natural graphite.

The following table shows the most common sizes of bending strips and their minimum bending radii

Example 1 size [cm] bending radius [cm] (prior art) 1.9x4.76 infinity 7x4.76 infinity

Example 2 1,9x4,76 30-100 (invention) 2x4,1 30-100 7x4,76 <130 7x4,4 <130 35 7

An essential new component is a wax which is preferably N, N'-ethylene bis-stearamide wax, e.g. hydroxy-bis-amide waxes. Other synthetic or natural waxes, such as carnauba waxes, esparto waxes and the like, are also contemplated. Examples of synthetic waxes include polyolefin waxes and other amide waxes. A suitable wax may have a high melting point above 100 ° C, most preferably in the range of 110 ° C to 150 ° C.

Wax provides a significant addition to the flexibility of the product. A seal of the same size (1.9 x 4.8, density 1.59) as above can be bent to a relatively small radius of curvature (R = 30 15 cm) and form a product, for example, a reel for transport. As a general rule, wax is used to such an extent that the sealing elasticity is sufficient for transportation (bendable to a coil with a radius R <1.5 m). Even larger sealing strips prepared by the recipe of the invention meet this criterion.

Synthetic graphite provides anisotropic sealant. Graphite is most preferably used in the form of flakes or crystalline.

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The vulcanizing agent used in the example was Vulcup 40KE, Hercules, T-butyl peroxide diisopropylbenzene, but also other vulcanization peroxides as well as sulfur, reaction accelerators, e.g. -hexylbenzothiazylsulfamide (Santocure MOR, Monsato) may be used.

The sealing strip 35 (FlexSeal) produced by the method of the invention was compared with commercially available sealing strips known in several experiments.

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As shown in Figure 2, the seal according to the invention will wear relatively less compared to a conventional sealing strip. The sealing strip according to the invention behaves moderately as the load increases, compared to the conventional sealing strip, which, at a given load, exhibits a sharp change in wear as the load continues to increase. The seal according to the invention has low wear in both humid and dry conditions.

As shown in Figure 3a, the sealing strip according to the invention requires less operating power than a conventional sealing strip. Similarly, the noise production value was significantly lower with the sealing strip according to the invention compared with the conventional sealing strip, Figure 3b.

It will be appreciated that a person skilled in the art can vary the recipe of the invention within a wide range, while remaining within the scope of the claims.

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Claims (11)

1. A sealing strip for a suction roll, which is made of a mixture, the main part being nitrile rubber and graphite, characterized in that the mixture comprises wax. 2. A sealing strip according to claim 1, characterized in that the amount of wax in the mixture is determined such that the flexibility of the sealing strip allows it to bend into a roll whose radius is less than 130 cm. A process for preparing a sealing strip for a suction roll of a mixture, the main part of which is nitrile rubber and graphite and of which a substance is formed into a sealing strip which is cured at the selected temperature, characterized in that the mixture which is cured includes wax. A method according to claim 3, characterized in that the amount of wax is 1 - 15% most preferably 2 - 4%. 20 A process according to claim 3 or 4, characterized in that the amounts of nitrile rubber and graphite are within the range: nitrile rubber 30 - 60% by volume, and graphite 30 - 60% by volume. A process according to any of claims 3-5, characterized in that the curing temperature is in the range 140-160 ° C, preferably 145-115 ° C and the curing time in the interval 3-5 hours. A process according to any of claims 3-6, characterized in that the pulp contains 1 to 15% sulfur or peroxide. 8. A process according to any of claims 3-7, characterized in that the graphite used is natural graphite. 9. A process according to any of claims 3-7, characterized in that the graphite used is synthetic graphite. 10. A method according to any of claims 3-9, characterized in that the melting point of the wax used is above 100 ° C, most preferably in the range 110 ° C - 150 ° C. 11. A method according to any of claims 3-10, characterized in that the amount of wax is arranged to ensure that the flexibility of the sealing strip allows it to be rolled on a roll whose radius is less than 1.5 m.