KR20020070975A - Engraved shaft and method for manufacturing thereof - Google Patents

Abstract

The present invention relates to a sculpted roll made entirely or mostly of aluminum alloy, with a screen surface consisting of a calculated volume of cell-recess formed on a cylindrical surface. On the screen surface, a plasma electrolytic oxidation process forms a ceramic oxide layer having a thickness of 15-50 mu m and a fine hardness of 700-1500 Hv, which suitably reforms the outer surface of the screen. Due to the high hardness and strength of the ceramic oxide layer, the screen cell can maintain the correct size and shape even if the rolls run for a long time.

Further penetration of metals or organic materials into the porous ceramic oxide layer further hardens the screen surface, increases corrosion resistance, and provides the necessary properties (lipophilic, hydrophilic, hydrophobic, etc.) for different systems for quantitative transport of liquids and suspensions. Grant.

Description

Engraved Shaft and Manufacturing Method thereof {ENGRAVED SHAFT AND METHOD FOR MANUFACTURING THEREOF}

During printing, an ink layer is applied to the screen surface of a roll consisting of recess-cells arranged regularly. Surplus is removed by the doctor. Thus, the cell will receive an appropriate amount of ink, which is then delivered to the surface of the printing foam or ink roller. To obtain high quality printing, high precision is required for placing the cell on the cylindrical surface of the screen and for the shape and depth of the cell itself. The depth of the cell is 10-50 μm. Continuous contact with the hard steel doctor results in wear of the screen surface. The progress of mechanical wear is enhanced by the corrosive action of the ink containing solutions such as salts, organic solvents, etc., which reduce the useful life of the sculpted rolls.

Indeed, the most widely used screen rolls are those made of structural steel. The cell is wound on a cylindrical surface by a knurling roller made of tool steel. The high cost of knurling rollers (which must be made with higher precision than screen roll cells) and low strength have to be used at low speeds and are undesirable in rolling systems, which lowers the productivity of the process.

To increase resistance to wear and corrosion, steel rolls are plated with chromium. Examples of such rolls are known from US Pat. No. 3,613,578. The thickness of the chromium plating should be less than a few microns (up to 15 μm) because the thickness of the plating changes the shape and volume of the cells on the screen surface. Strong adherence to the doctor during operation quickly wears out the thin chromium layer and severely shortens the roll's useful life.

A further improved method of imparting abrasion and corrosion resistance to the screen surface of steel rolls is the ion nitriding treatment described in US Pat. Nos. 5,514,064 and 5,662,573. By chemically changing the steel surface with iron nitride, a hard and well bonded protective layer (Hv 700-1000) is formed. However, there is a serious problem with this method. That is, since the nitriding treatment takes place at a high temperature, warping of the roll due to thermal deformation occurs, which means that the work of straightening the roll must be accompanied. In addition, the use of high chrome steel for this treatment makes the screen more difficult to knurled and shortens the life of the knurled tool.

Attempts to increase the wear resistance of the screen by applying a ceramic coating to the screen surface by the plasma spray process (US Pat. Nos. 4,009,658, 4,601,242, 4,912,824) have been found to be unsuccessful because the thin ceramic coating The rolls were not protected against this premature wear, and filling the screen roll with a significantly thicker coating significantly reduced the size of the cell.

The heavy weight of the steel rolls is a disadvantage in using these rolls. The 1 meter long roll weighs approximately 70 kg. This is not easy as it requires special skills and tools to fix and replace the rolls and is likely to damage the screen surface.

In addition, during use at relatively high speeds, even slight deviations in the balance of the steel rolls cause dynamic vibrations, causing "judder" on the rolls, which adversely affects the quality of printing.

The use of lightweight rolls made of rigid aluminum alloys, such as steel rolls, has significant advantages. Aluminum alloys are easy to machine with high precision at high cutting speeds. Aluminum alloys are lightweight and can be processed with high precision, resulting in low dynamic inertia and dynamic imbalances. This allows the roll to rotate more evenly during operation and reduces or eliminates vibration and "judders".

Processes for applying protective coatings to screen rolls of aluminum alloys are known from US Pat. Nos. 5,411,462 and 5,548,897, and the following working procedure is proposed.

Making a high precision roll from an aluminum alloy,

Applying a corrosion resistant and wear resistant ceramic layer to the cylindrical outer surface,

Polishing and finishing the cylindrical surface of the roll,

-Engraving the screen cell on the ceramic surface using a laser beam.

This proposal includes two types of protective coatings. The first type is a chromium oxide layer or aluminum oxide layer coated to a thickness of 200-250 μm by a plasma spray process. The second type is an aluminum oxide layer formed to a thickness of 25-50 μm on the cylindrical surface of the roll by anodizing in sulfuric acid electrolyte. In this case, the depth of the screen cell cut by the laser beam must not exceed the thickness of the oxide-oxide.

The main problem with the laser engraving (burn-out) process is the need to use very expensive equipment for automatic control of the laser. Also, the recess engraved by the laser beam is not always the correct shape. Differences in the roughness of the walls and bottoms of the cells are a factor in degrading the quality of printing in a given volume and any discharge containing ink.

However, despite these problems, there is an increasing use of "ceramic" rolls on steel and aluminum bodies because there is no alternative that can provide high wear resistance and durability in the work of the rolls. "Ceramic" rolls are 5-10 times more durable than chrome plated steel rolls but are 4-6 times more expensive.

The oxide film coating mainly consists of an amorphous state of aluminum oxide so that its strength and microhardness are not large. These coatings have a significant moisture content (water content exceeding 10%) and these compositions also contain 10-20% of electrolyte anions that form part of the coating composition. When the roll is heated during use, the electrolyte components and moisture are removed from the composition of the coating, resulting in the oxide layer splitting and decomposition and deteriorating its protective properties.

Processes for making aluminum screen rolls for lithographic printing are also known from US Pat. No. 4,862,799. The screen cell is precisely made on the cylindrical surface of the roll by first engraving (pricking) the diamond needle. This surface is coated to form a thin, relatively hard 1-3 μm thick layer, and finally a relatively soft 5-8 μm thick copper layer is formed on top of the coat layer. This gives the surface properties necessary for lithography in terms of lipophily and hydrophoby to the screen surface.

The problem with this process is that the copper oxide layer on the screen surface of the roll is thin. This layer does not withstand the mechanical and chemical stresses occurring in the corrosive medium when the screen is in frictional contact with the Steel Doctor. Increasing the thickness of the oxide layer to 15-20 microns makes it unacceptable to change in shape and size of the screen surface cells. This is because at least 50% of the thickness of the oxide layer in the film treatment becomes thick from the surface to be treated. Accepting the thickness of the copper layer applied on top of the anodized layer makes it impossible to obtain a substantially acceptable volume of screen cell. Serious problems with the oxide layer itself have already been described.

FIELD OF THE INVENTION The present invention relates to the manufacture of fabrics, the manufacture of wallpaper, and the manufacture of highly precise rolls with carved reliefs used in printing equipment for applying lacquers, adhesives or suspensions to sheet materials, fabrics and the like. More specifically, the present invention relates to flexographic printing and offset lithographic printing screens (Anilox) rolls having finely carved relief surfaces.

1 shows a small carved roll up to 500 mm in length, rolled entirely of a single body 1 of an aluminum alloy rod.

FIG. 2 is a cross sectional view of a medium sized sculpted roll with an opening 3 in the end face having a journal (shank) 2 pressed in up to 1000 mm in length; FIG.

3 is a cross-sectional view of a large carved roll of 1000 mm or more in length in which a thick walled aluminum bush 5 is pressed onto a roll (core) 4 of hardened steel.

4 is a cross-sectional view of the surface screen surface of an aluminum roll 1 having a standard cell 6 engraved in a predetermined shape and volume.

FIG. 5 is a cross-sectional view illustrating the formation of a ceramic oxide coating 7 on the screen surface in the roll of FIG. 4.

FIG. 6 is a cross-sectional view showing the coating of the metal or organic compound layer 8 on top of the ceramic oxide layer 7 in the roll of FIG. 5.

FIG. 7 is a cross-sectional view illustrating a form after circular polishing processing in the roll of FIG. 6. FIG.

The photograph which enlarged the screen surface of the flexographic graph roll after plasma electrolytic oxidation process 1000 times.

It is a primary object of the present invention to produce lightweight, relatively inexpensive engraving rolls that are substantially inertial and have a long useful life for use in various systems for delivering liquids and suspensions in suitable quantities.

Another object of the present invention is to develop an effective process for producing sculpted rolls. This process includes state-of-the-art techniques for treating screen cells with high precision and high productivity, and for hardening the screen surface by forming wear and corrosion resistant coatings without significantly changing the set volume and shape of the screen cells.

The object of the present invention will be described in detail.

The engraved rolls presented in the present invention are made in high precision form in a deformable aluminum alloy cylinder. The screen surface, given the location, shape, and volume of the recess-cell, is carved by machining the (outer) cylindrical surface. The plasma electrolytic oxidation method forms a 15-50 μm thick rigid wear resistant ceramic oxide coating with a fine hardness of 700-1500 Hv on the screen surface of the roll. This oxide layer is firmly bonded to the aluminum substrate and has a uniform thickness to properly repeat the construction of the screen. In order to impart various functional characteristics to the screen surface, and also to give the coating strength and corrosion resistance, and to have a smooth surface for easy cleaning of the ink, a thin layer of metallic or organic material on the porous ceramic oxide surface (1-5) Μm) layer is applied. And finally, to smooth the outside of the screen surface, which consists of boundary ribs between the cells and is as symmetrical as possible with respect to the center axis of the roll, the surface has a thin circular polishing with a tolerance of 2-10 μm on each side. It is preferable to finish the form.

Plasma Electrolytic Oxidation (PEO) processes are known, but have not been used at all for the production of sculpted rolls. Unlike anodizing, the PEO process allows for the formation of coatings of uniform thickness on complex shaped surfaces because more portions (80-90%) are coated as the PEO proceeds inward from the surface.

Choosing an optimal oxidation method for the screen surface of the roll ensures the formation of a hard, relatively thin coating that is sufficient for long operation.

Oxidation is carried out at an ecologically safe and weakly alkaline aqueous electrolyte at a temperature of 15-55 ° C., and an impulse voltage of 50-1000 V is supplied. The frequency is 50-3000Hz and the current density is 2-100A / dm ² .

The effect of the plasma-chemical reaction forms a 15-50 μm thick intercrystalline oxide layer with a fine hardness of 700-1500 Hv on the screen surface of the aluminum alloy roll.

The ceramic oxide coating formed on the surface of the aluminum member mainly consists of the composition of different crystal states (alpha, beta, gamma, etc.) of aluminum oxide. Therefore, although the hardness is very high, it has a certain plasticity and less falling off or peeling of unavoidable fine pieces occurring on the surface as compared with the ceramic coating formed by the plasma spray process.

The porous structure of the oxide coating allows the formation of an ideal matrix filled with compounds with specific functional characteristics to form a synthetic coating.

To this end, the present invention uses a variety of metals and organic compounds (depending on the required functional features).

These materials, which permeate inside the pores and capillary and form a 1-5 μm thick film on top, protect the oxide coating with little change in the volume of the screen cell or little smoothing of the rough surface. Ceramic oxides that do not penetrate strongly absorb the ink and cause difficulties when cleaning the rolls to replace the ink in the system.

The strongly treated surface of the porous structure of the oxide layer gives an excellent bond between itself and the absorbent compound, which in turn gives an excellent bond strength to the entire compound.

Oxide treatment rolls impregnated with Ni, Cr, Mo-based metals or one compound having oxides and carbides of these metals are supplied by letter book printing, gravure printing and flexographic printing, i.e. aqueous, oily or synthetic liquids. If so, it can be used successfully in the system.

In offset lithograph printing where oily ink is used where water is present, the surface of the sculpted rolls requires lipophilic and hydrophobicity. Copper is known as a material of this characteristic. Therefore, in lithographic printing, it is effective to use engraved rolls coated with ceramic oxide impregnated with copper.

The thin protective layer of the metal compound is coated by chemical or electrochemical deposition from an aqueous or organic solution, by chemical deposition from a gaseous state, or by a physical deposition method.

The organic material for the penetration of the microporous structure of the ceramic oxide coating should have a good binding force to the ceramic surface or at least be bound by the cavity of the ceramic coating. These organic materials form a hard and smooth corrosion resistant layer during the reaction process (heating, ultraviolet radiation, etc.).

Since organic materials must penetrate as deeply as possible into the porous structure of the ceramic coating, it is preferable to use a low viscosity diluted solution or super dispersible suspension.

To coat the organic material, simple techniques of immersion of rotating rolls in the liquid, spraying onto the solution with the nebulizer, and deposition from the gaseous state can be used.

The organic layer can have certain properties (lipophilic, hydrophilic or hydrophobic) in addition to corrosion resistance and thus can be used in different printing systems.

The most suitable composition for penetration is the well-known self-vulcanising elastomers, including butadiene-styrene, butadiene-nitrile, acryl-nitrile, and paired controlled epoxy and formaldehyde resins and modified elastomers. . In addition, polymethyl methacrylate, chlorosulfonated polyethylene, ethylene-propylene elastomer, and the like may also be used.

The outer surface of the screen, which consists of gaps (ribs) protruding between the cells, is preferably finely circular polished in a precise circular polishing apparatus. Polishing depth is 2-10 μm. The purpose of this operation is to ensure that the outer surface is as symmetrical as possible with respect to the central axis of the roll and that the printing system runs smoothly. In addition, the sophisticated polishing can eliminate the risk of contacting the steel doctor on the ceramic oxide outer surface of the roll and causing severe vibration and wear of the doctor.

It is easy to find that the ceramic oxide layer is rough at the cell boundary (rib).

Rolls of aluminum alloy are easy to machine. Therefore, the use of high precision metal cutting equipment makes it possible to produce high precision rolls whose outer surface is cylindrical and coaxial with the central axis of the roll. This lightweight, small inertia, and dynamically balanced roll does not require additional balancing after manufacture.

However, the roll must be strong and rigid enough to prevent deformation due to forces generated by the hydrodynamic pressure of the ink wedge between the roll and the substrate during operation.

The rolls produced are selected according to the size (diameter and length) of the rolls required and the pre-calculated strength, depending on the appropriate design of the rolls and the grade of the aluminum alloy.

Small rolls up to 500 mm in length (FIG. 1) include SAE 5000 series (5082, 5086, 5056, 5356), 6000 series (6061, 6063, 6067, 6082), 2000 series (2021, 2024, 2018, 2618) and 7000 series (7075, 7175, 7475) grades of deformable aluminum alloy rods are manufactured by fully (in one piece) rolling. Medium-sized rolls of up to 1000 mm in length (Fig. 2) are manufactured partially by pressing the journal (shank) 2 of steel or aluminum alloy into an aluminum cylinder with a deep opening 3 by coaxially processing the end face. do. Large rolls of greater than 1000 mm in length (FIG. 3) are also partially manufactured and pressed with a high precision thick walled aluminum alloy bush 5 onto a high precision roll (core) 4 of hardened steel.

Only 2000 or 7000 series high strength heat-treated aluminum alloys are used to make medium and large rolls.

A distinct advantage of the present invention is that the cells on the screen surface can be easily knurled at low pressure and the productivity is also high and precise. This ensures a long life of the knurled rollers. However, the most advantageous result of the screen's precision and the good productivity of the process is that it can produce electronically controlled high speed engraving (approximately 3000 cells per minute) using diamond needles.

Another advantage of the present invention is that the volume of the cell can be increased and is sculpted 10-25% larger than the required final volume of the cell of the finished cylinder. This is necessary to correct for a certain amount of reduction in the volume of the cell during oxidation, penetration and finishing of the screen surface.

PEO-oxidized specimens of aluminum alloys were subjected to corrosion testing in a hydrochloric acid spray chamber. It was confirmed that a sculpted roll can be made without any signs of corrosion.

The examples described below illustrate the practical implementation of the invention. High precision rolls of length 165 mm and diameter 38.6 mm were made from the heat treated SAE 6083 alloy. The diamond engraving method produced a screen surface having a cell volume of more than 20% of the volume required for the cylindrical machining surface. The density of the screen was 100 lines per centimeter. The rolls were subjected to plasma electrolytic oxidation. The roll was immersed in an aqueous solution bath of alkaline electrolyte (pH 11.5) at a temperature of 30 ° C. The electrolytic environment was set at a frequency of 1000 Hz, a current density of 40 A / dm ² , and a process termination voltage of 900 V of anode and 250 V of cathode. The oxidation treatment time was 15 minutes. The thickness of the ceramic oxide coating on the screen and shank was 25 ± 2 μm. A portion of the enlarged picture of the oxidized screen is shown in FIG. 8. The rolls were subsequently subjected to chemical nickel plating to form a uniform nickel layer of 2-3 mu m thickness on the oxidized surface. The shaft was then polished in a circular polishing apparatus such that each side had a tolerance of 2 μm.

The rolls were installed on flexographic presses to print the packaging. The roll showed excellent print quality. After 3,000,000 and 6,000,000 prints, the prints were actually the same.

See above

Claims (10)

A cylinder substrate made of an aluminum alloy completely or mostly deformable, having a plurality of cell-recesses formed on the outer cylindrical surface to form a screen surface, A hard wear resistant ceramic oxide coating formed on the screen surface with a uniform thickness, Outer layer of metal compound or organic material applied directly on the ceramic oxide coating Carved roll containing. The method of claim 1, The ceramic oxide coating has a thickness of 15-50 μm and a fine hardness of 700-1500 Hv. The method of claim 1, The outer layer has a thickness of 1-5 μm. The method of claim 1, Wherein the outer layer applied to the ceramic oxide layer is hydrophilic and lipophilic and is made of at least one metal compound selected from carbides or oxides of Ni, Cr, Mo or one of these metals. The method of claim 1, Wherein the outer layer applied to the ceramic oxide coating is hydrophobic and lipophilic and is made of copper. The method of claim 3, The outer layer applied to the porous ceramic oxide coating includes butadiene-styrene, butadiene-nitrile, acryl-nitrile, epoxy and phenolformaldehyde elastomers, polymethyl methacrylate, chlorosulfonated polyethylene, and ethyl propylene elastomer. Roll consisting of at least one organic compound selected from the group of compounds comprising a. In the method for producing a carved roll, Manufacturing a cylinder substrate made entirely or mostly of deformable aluminum alloy, Engraving a cell-recess on the outer surface of the cylinder, Forming a ceramic oxide coating on the engraved surface of the cylinder by a plasma electrolytic oxidation method, Coating an outer layer of a metal compound or an organic material on the ceramic oxide coating, and Mechanically finishing the outer surface of the cylinder How to include. The method of claim 7, wherein When engraving on the surface of the cylinder, the cell is formed with a volume exceeding 10-25% of the required final volume. The method of claim 7, wherein The plasma electrolytic oxidation is carried out in a weakly alkaline electrolyte at a temperature of 15-55 ° C., a current density of 2-100 A / dm ² , a frequency of 50-3000 Hz, and an impulse voltage of 50-1000 V. The method of claim 7, wherein The finish of the cylinder surface is circular polishing, with a polishing depth of 2-10 μm on each side.