Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F1/00—Wet end of machines for making continuous webs of paper
  • D21F1/48—Suction apparatus
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F1/00—Wet end of machines for making continuous webs of paper
  • D21F1/48—Suction apparatus
  • D21F1/483—Drainage foils and bars

Definitions

• the invention relates to a fixed water removal element according to the preamble of claim 1 in a paper or board machine, said element being adapted to squeegee the wire or press felt of the machine from the side opposite to the sheet side of the wire/felt.
• the invention also concerns a method of manufacturing such a water removal element.
• Water removal elements are subjected to high wearing stresses. As web speeds in modern paper machines are today in the range 1000 - 1500 m/min, a wire or felt travelling over the surface of the water removal element hurls past the element at a substantial velocity. The wear is increased by the fillers used in papermaking such as clay, talc and chalk, and by unwanted impurities of the papermaking process.
• Fixed water removal elements are located at the wet end of the paper machine along its wire section and press section. Passing over the water removal element in the wire section is a wire woven from polymer monofilament, whereby the wire permits drainage of water from the paper sheet of high moisture content at this stage.
• the water removal elements squeegee water off the wire or impose a vacuum or pressure shocks on the wire. In the press section water is removed from the felt by suction.
• ceramic water removal elements are fabri- cated by assembling a long slice comprising adjoining ceramic pieces.
• the length of the slice is determined by the web width of the machine.
• the slice may be prepared from pieces machined to exact dimension that are mounted onto a precision pedestal, whereby a relatively smooth surface of the slice results.
• a better end result is achieved by means of a structure in which the ceramic pieces are adjacently glued to each other and the ready-assembled slice is ground to correct shape, whereby no height differences remain between the pieces.
• the most common materials for the pieces are aluminium oxide, silicon carbides and zirconium oxide.
• a slice structure assembled from ceramic pieces has several shortcomings. Even if the water removal ele- ment is assembled from pieces, the pieces become rela ⁇ tively massive and thus rather vulnerable to thermal shocks. Temperature variations in a piece pressed against a web moving at a high speed may be substantially rapid at, e.g., loss of water film lubrication between the piece and the web. Such thermal shocks cause local fractures of the pieces and erosion of the piece surfaces which increases the wear rate of the wire massively. A slice assembled from pieces may become deformed due to wear or displacement of the pieces. Shape defects of the slices cause disturbances in water removal and can ruin the sheet being manufactured.
• the greatest problems plaguing water removal ele ⁇ ments made from ceramic pieces are associated with the inferior chemical and thermal resistance of adhesives used for joining the pieces.
• the adhesive applied to the joint has insufficient resistance to the wide temperature variations and strong chemicals occurring in a paper machine.
• the heaviest thermal loads occur when the wire travels without lubrication, that is, the machine is running dry. In this case the heat of friction can elevate the surface temperature of the ceramic piece in a few minutes by 120 - 200 C C. Since the thermal expansion coefficients of the ceramic material, the adhesive and the glass-fiber reinforced plastic body are different and the temperature profile of the slice is not homogeneous, substantial thermal stresses will develop in the slice that may detach the ceramic pieces from each other or totally separate them from the slice body.
• Adhesives employed for bonding the ceramic pieces are not sufficiently resistant to the warm waters of the paper machine which are chiefly detached from the web being dried.
• the degrading effect of the waters is amplified by the residual chemicals of the papermaking process contained in the waters.
• Experimental tests on the strength of an adhesive-bonded joint indicated that already after 200 hours of aging the bond strength of almost all adhesives was lowered by tens of percent and in some adhesive grades even below half of their initial strength during this aging period. Because the strength impairment of the adhesive bond may result in the detachment of the ceramic pieces, such a drastic loss of bond strength is not acceptable.
• the ceramic pieces may also rise above the slice surface which results in a so- called keyboard effect. Then, the elevated pieces mark the web with detrimental streaks. Hence, a water removal element requiring no adhesive bonds in its manufacture would be desirable.
• the goal of the invention is accomplished by manufactur ⁇ ing the water removal element from a continuous section of metal having its one side covered with a ceramic coat applied by thermal spray-coating and its interior filled with a cast thermoset plastic compound.
• the water removal element according to the invention is characterized by what is stated in the characterizing part of claim 1.
• the invention offers significant benefits.
• the invention is capable of entirely avoiding the use of an adhesive in the manufacture of a water removal element with a ceramic surface.
• the vulnerability of the element to damage is reduced as no piece can become detached therefrom under use.
• the thin, ceramic surface of the water removal element is most resistant to thermal shocks, this making it less sensitive to damage under rapid variations of the element temperature as compared with conventional ceramic elements.
• spray- coating a continuous surface is obtained, whereby the keyboard effect is avoided which plagues water removal elements assembled from ceramic pieces.
• the element has a relatively good inherent stiffness, because the metallic continuous section forms a shell structure with good resistance to stresses about the thermoset plastic compound core.
• the bodies of the water removal elements can have a relatively lightweight construction and dispose of the need for a separate plastic body for ceramic pieces.
• the element structure according to the invention is capable of minimizing the use of required expensive, stainless material to a very small amount, whereby a cost-efficient construction results.
• the present type of water removal element may be used in applications where conventional embodi ⁇ ments made from ceramic pieces have been too costly.
• the porous coat made by thermal coating is sealed, whereby good wear resistance and advantageous friction properties are obtained.
• Figure 1 is the cross section of a water removal element according to the invention after its first manufacturing step
• Figure 2 is the cross section of the element illustrated in Fig. 1 after its second manufacturing step
• Figure 3 is the cross section of the element illustrated in Figs. 1 and 2 after its third manufacturing step
• a complete water removal element comprises a U-shaped continuous section 1 having, e.g., a ceramic coat 5 applied onto the base part 3 of the U-shaped continuous section so as to form a wear- resistant surface, and a thermoset plastic compound core 6 cast into the continuous section 1.
• a T-slot is machined into the thermoset plastic compound core 6, in the area between the legs of the U-shape, for mounting the water removal element.
• the continuous section of the water removal element body is made from stainless steel having its cross section comprising a base part 3 of the U-shaped continuous section forming a plane to which the legs 2 of the continuous section are joined extending orthogonally upward from the base part 3.
• the joining edge between the base part 3 and the legs 2 is provided with a chamfer 8, and the legs 2 end at inward bent flanges 4.
• the entire interior of the conti ⁇ nuous section is filled by a thermoset plastic compound core 6.
• a water removal element with the above-described struc ⁇ ture is manufactured in the following manner.
• a ceramic coat 5 is applied onto the base part 3 of the continuous section 1 cut to a suitable length by means of thermal spray-coating.
• the coat is sealed by impregnating the coat with a low-viscosity material having a high penetration capability into the coat.
• the interior of the continuous section is filled by casting it full of a thermoset plastic compound which is cured, whereby it adheres to the interior walls of the continuous section 1 thus stiffening the conti ⁇ nuous section 1.
• the interior walls of the continuous section 1 may be sand-blasted or cleaned by any other suitable method.
• a mounting slot 7 is machined into the cast compound for mounting the water removal element at the desired place in the paper machine by means of a support frame.
• the outer surface of the coat is precision ground to correct shape.
• the water removal element according to the invention may be made from a variety of different materials. While the optimal material for the base part continuous section 1 is stainless steel, also aluminium, brass, duplex steel and other corrosion-resistant materials may be employed.
• the ceramic coat can be made from the following materials or mixtures thereof: Al,0 3 , Cr,0 3 , ZrO,, TiB 2 , SiO,, TiO,, WC and Cr 2 C 3 . However, when applied by thermal spray- coating, these materials remain more porous and softer than ceramic pieces made by sintering. Such a porous coat may wear down paper machine wires by the cutting action of the edges of the pores and the abrading action imposed on the wire by the filler particles and impurities lodg ⁇ ing in the pores.
• Suitable mate ⁇ rials are, e.g., organic resins and inorganic compounds. Of organic materials, the most suitable are low-viscosity epoxy resins which can be made to impregnate almost the entire porous volume of the coat. Moreover, such a seal- ing treatment improves the durability of the coat. Of inorganic materials can be used, e.g., phosphate com ⁇ pounds which are impregnated into the coat from aluminium hydroxide and phosphoric acid solutions. These compounds are then converted into crystalline form by a heat treat- ment.
• these compounds are capable of improving the wear resistance of the coat and their friction properties may further be enhanced by complementing the sealing treatment by auxiliary compounds with fluorinated resins.
• auxiliary compounds with fluorinated resins are well suited for use as sealing compounds.
• Thermal spray-coating can be used for applying coats on metallic surfaces only. Since the body of a water removal element must be of a non-rusting material, it would become excessively expensive with respect to competing solutions when made on, e.g. a solid stainless steel beam. According to the invention, this problem is overcome by manufacturing the body from a thin-walled continuous section which is stiffened by filling it with a thermoset plastic compound.
• thermoset plastics are suit ⁇ able for use as the fill material of the continuous section including epoxy resins, methacrylate resins, polyester resins, vinyl ester resins, phenolic resins and mixtures thereof.
• the resin may be reinforced with, e.g., chopped glass fiber or ceramic particles.
• the above-described type of water removal element is suited for use as a water removal element squeegeeing a wire or felt.
• the invention may also be applied to other water removal elements of a paper machine that are in contact with a moving wire or felt.
• the shape of the element must be modified to suit the application.
• the shape of the continuous section can be widely varied and, for instance, the use of a continuous section with a closed perimeter is possible. Then, the outer surface of the section may be contoured so as to provide the mounting facility of the water removal element.

Landscapes

• Paper (AREA)
• Electrical Discharge Machining, Electrochemical Machining, And Combined Machining (AREA)
• Apparatuses And Processes For Manufacturing Resistors (AREA)
• Laminated Bodies (AREA)

Priority Applications (8)

Applications Claiming Priority (2)

Publications (1)

Family

ID=8541206

Family Applications (1)

Country Status (10)

Cited By (9)

Families Citing this family (2)

Citations (1)

• 1994
  • 1994-08-17 FI FI943777A patent/FI943777A/fi unknown
• 1995
  • 1995-08-03 DE DE69514925T patent/DE69514925T2/de not_active Expired - Fee Related
  • 1995-08-03 JP JP8507041A patent/JPH10504357A/ja active Pending
  • 1995-08-03 KR KR1019970700967A patent/KR100253986B1/ko not_active IP Right Cessation
  • 1995-08-03 EP EP95943511A patent/EP0776395B1/en not_active Expired - Lifetime
  • 1995-08-03 WO PCT/FI1995/000413 patent/WO1996005370A1/en active IP Right Grant
  • 1995-08-03 CA CA002196093A patent/CA2196093C/en not_active Expired - Fee Related
  • 1995-08-03 AU AU30796/95A patent/AU3079695A/en not_active Abandoned
  • 1995-08-03 AT AT95943511T patent/ATE189494T1/de not_active IP Right Cessation
• 1997
  • 1997-02-14 NO NO970679A patent/NO309685B1/no unknown

Patent Citations (1)

Non-Patent Citations (1)

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