EP0438031B1 - Method for machining the surface of workpieces and workpiece manufactured with this method - Google Patents

Description

The present invention relates to a method for processing surfaces of structures such as sheets, plates and the like, in which the surface is prepared by grinding or brushing for subsequent coating, oxidation or gluing, and a structure produced therewith in accordance with the preambles of claims 12 and 13.

To protect against corrosion or only for coloring, surfaces are treated by applying a protective layer, for example in the form of lacquer as paint. There is also the possibility of artificially oxidizing the surface, which is very common, especially with aluminum sheets. Furthermore, the properties of surfaces can also be changed by applying a coating of a different metal, protected against corrosion.
In most cases, the surface is contaminated as a result of the inherent peculiarities of the production, for example in the case of metal sheets, with a fat-containing layer which was applied during the rolling process. This layer subsequently prevents perfect adhesion of paints as well as artificial oxidation, whether in the air or in a plunge pool with a reaction liquid.
Usually, these so-called rolling greases are removed by means of solvents in order to achieve better adhesion. The disposal of the volatile parts of the solvents on the one hand and the liquid waste of the solvents contaminated with the fatty substances on the other hand is becoming increasingly difficult and costly.
Another possibility for the formation of a good primer is roughening by blasting, for example with sand, broken glass or steel particles etc. In the case of thick sheets, the surface can be cleaned of grease on the one hand and processed with a corresponding roughness for the absorption of the paint on the other hand. In the case of metal sheets that are thinner than approx. 2 mm, the surface can probably be treated in the manner mentioned, but due to the necessarily intensive bombardment with blasting material, compaction of the material occurs, which leads to buckling of the metal sheet and to surface hardening. On the one hand, this is for aesthetic reasons undesirable and on the other hand, such densifications can lead to uncontrollable changes in the properties in the further processing of the sheet. Cracks or material breaks can occur, particularly in the case of sheets which are subjected to folding or folding operations after blasting.
It is also already known to roughen the surface of metal sheets by longitudinal grinding or by cross grinding or also by a brush operation and thus to remove fat particles at the same time. In this way, a surface quality can already be achieved which has a relatively good adhesion and, compared to smooth sheet metal, brings about an increase in surface area which enables material to be oxidized naturally or using an artificial process.

If thin sheet metal is subjected to one of the mechanical pretreatments mentioned without compressing its material on the surface in order to exclude tensions or buckling or warping, such a procedure with the subsequently applied lacquer or even oxidation layers, in particular in edging or Fold areas not to give sufficient liability.

From US-A-2 907 151 it is known to clean the surface of the material by means of rotating brushes, optionally with the addition (sprinkling) of abrasive bodies and a stretching of the material with wavy passage through successive pairs of rollers.
This way of working not only proves to be complex, but cannot be carried out in a number of application areas. In addition, a compression of the material surface by the pressure rollers exerting pressure cannot be avoided.

The same applies to the method according to US Pat. No. 3,082,517, in which the abrasive particles interspersed between two sheets are clamped in by means of rolling forces acting on the sheet metal surfaces.

A roughening of a surface has also already been proposed by the method according to GB-A-495 421. In order to create depressions in soft, smooth aluminum sheets, a harder fabric is pressed in and then removed again. This also inevitably creates harmful hardening of the surface.

The object of the invention is to provide a method for processing the surface of structures, such as solid plates and sheets and the like, by means of which the surface forms an excellent base for subsequent coating operations without notable hardening. Another task is to create a structure that meets these requirements.

According to the invention, this is achieved according to the features of claims 1, 12 and 13.

Figur 1

eine 200fach vergrösserte photographische Aufnahme einer kreuzgeschliffenen Oberfläche,

Figur 2

eine Photographie derselben Oberfläche mit eingebrachter Rändelung (ein Durchgang), wobei die Eindrücke zur besseren Erklärung zu tief in die Oberfläche eingelassen sind,

Figur 3

ein Rauhtiefendiagramm einer mit Kreuzschliff bearbeiteten Oberfläche, in Längsrichtung abgetastet (Tastlänge zur Tasttiefe verkürzt dargestellt),

Figur 4

ein Rauhtiefendiagramm einer zusätzlich mit einer Rändelung versehenen Oberfläche,

Figur 5

eine schematische Darstellung eines Rändelwerkzeuges und ein gerändeltes Gebilde und

Figur 6

eine schematische Darstellung eines Teil-Querschnittes durch die Rändelwalze und eine geschliffene Oberfläche, die mit einer Rändelspitze an einer Stelle bearbeitet ist.

In der Figur 1, welche eine durch Kreuzschliff mit einem flexiblen Schleifmittel, z.B. einem Schleifband, behandelte Oberfläche darstellt, sind in vertikaler Richtung verlaufende Riefen 1 des ersten Schleifdurchganges und horizontal verlaufende Riefen 3 des zweiten darüberliegenden Schleifdurchlaufes deutlich sichtbar. Die Riefen haben je nach gewählter Korngrösse auf dem Schleifmittel unterschiedliche Tiefen bis ca. 0,1 mm und Breiten bis ca. 0,2 mm, welche von der unterschiedlichen, sich durch Abnutzung stets verändernden Korngrösse des Schleifmittels herrühren. Die Riefen 1 und 3 können auch in einem spitzen Winkel verlaufend erzeugt werden.With the stated method it is surprisingly possible to optimally prepare the surface structure for the coating, oxidation or gluing with the knurling process following the brushing or grinding process, without the disadvantageous hardening of thin sheets by compression of the surface and the resulting denting of the sheets he follows.
The knurled tool compensates for the increases (mountains) between the grooves during grinding or brushing, so that even very thin coatings can be applied that cannot be broken through by grinding edges and can form the point of attack for corrosion. The material displaced by the tips of the knurling tool is not pressed into the base plate thanks to the presence of fine grooves, but instead causes the grooves to dodge to the side, so that the base material is not subjected to compression or hardening. The smoothed surface created during the grinding or brushing process due to the partial melting of the material on the surface of the grooves is broken up again by the pushing forces of the knurling tool tips, which run essentially parallel to the surface of the sheet metal, so that fine gaps and folds arise into which the coating material or the oxidation medium can penetrate and be anchored there.
If several knurling processes are carried out in succession, in which the tips of the knurling tool each act laterally and longitudinally in the material surface, part of the material displaced by the knurling tips is also displaced into the recesses produced by the preceding knurling tips, which increases the gap leads.
With small spacings of the impressions, the effect of the breaking open of the impression surfaces increases because the material displaced in a subsequent, closely adjacent impression further deforms the surfaces of the already existing impressions, so that the gaps enlarge.
The surface roughening that occurs during grinding or brushing is carried out by the Knurled tips are not smoothed, but remain in the knurled tip craters.
Another advantage of the knurling that follows the brushing or grinding process is that the surface, which is regularly roughened during brushing or grinding and provided with grooves, is given a visually regular pattern by the knurling tool, the tips of which are preferably pyramid-shaped and geometrically evenly distributed.
Another advantage of the invention is that no chemicals harmful to the environment have to be used for the surface preparation or that they can arise during the process.
The application of the shaving tips on a flat carrier material, for example a sheet metal, makes it possible to use a smooth cylinder as the knurling roller, to which the sheet metal covered with tips can be attached and replaced when worn.
The invention is explained in more detail with the aid of an illustrated embodiment. Show it:

Figure 1

a 200x enlarged photograph of a cross-ground surface,

Figure 2

a photograph of the same surface with knurling inserted (one pass), the impressions being embedded too deeply in the surface for a better explanation,

Figure 3

a surface roughness diagram of a surface machined with cross-section, scanned in the longitudinal direction (key length shown shortened to key depth),

Figure 4

a surface roughness diagram of a surface additionally provided with a knurling,

Figure 5

a schematic representation of a knurling tool and a knurled structure and

Figure 6

is a schematic representation of a partial cross section through the knurling roller and a ground surface, which is processed with a knurled tip at one point.

In FIG. 1, which shows a surface treated by cross-grinding with a flexible abrasive, for example an abrasive belt, grooves 1 of the first grinding pass running in the vertical direction and grooves 3 of the second grinding pass lying horizontally running are clearly visible. Depending on the selected grain size on the abrasive, the grooves have different depths of up to approx. 0.1 mm and widths of up to approx. 0.2 mm, which result from the different grain size of the abrasive, which always changes due to wear. Grooves 1 and 3 can also be created at an acute angle.

On the illustration visible in FIG. 2, the diamond-shaped (diamond = pointed rhombus) impressions 5 of a depth-adjustable knurling tool can be seen after a first pass. Almost all impressions 5 have approximately the same size and thus the same depth and they dominate the appearance of the surface and give it a more regular structure; in the case of thin sheets, they have a depth which is equal to or less than the average depth of the grooves 1 and 3. With thicker structures, the depth of penetration can exceed the average depth of the grooves. The grooves 1,3 run at an angle of 90 °; they can also be generated in an angular range of 90 ° ± 45 °. The impressions 5 shown in FIG. 2 have been applied deeper than necessary for better visibility.
In order to be able to obtain a fine grid of the impressions 5, a plurality of knurled rollers arranged in series with the same or different tip design and arrangement are used, thus achieving a surface-covering treatment of the surface. The knurled tips can also be conical instead of pyramid-shaped.

In the diagram in FIG. 3, which has been recorded in abbreviated form with a "Perthometer" roughness measuring device from Feinprüf GmbH, D-3400 Göttingen, and represents a tactile section of the surface in which the roughness depths due to the crosswise grinding process can be seen, the structure of the Surface can be read out. The surface of the sheet is divided into a multiplicity of intersecting mountains 2 and valleys 4 by the cross grinding.

In FIG. 4, the surface provided with a cross-cut was subsequently machined with a knurling tool of the type mentioned above. This machining process allows the tips to have a precisely adjustable roughness depth d without the base material being significantly hardened by the impressions of the tips of the knurling tool. The finest marks and elevations, which do not form an optimal base for the aftertreatment, because the particles of the applied coating material are unable to wet them, have disappeared. The larger differences between the mountains 2 and valleys 4 result in a large surface on the flanks, which thereby enables excellent adhesion of paints or oxidation. This is particularly so because the minimum width of the valleys 4 in the resulting gaps is large enough for the coating material or oxidizing agent to enter safely to guarantee. The formation of undesired caverns is excluded. The impressions 5 shown in FIG. 4 were generated by a knurling tool with a mutual spacing (a = tangential division, t = axial division) of the tips of approximately 0.3 mm. The pitch can be chosen between 0.2 and 04 mm. Instead of one pass, several knurled passes can of course also be carried out or several knurled rollers with identical or different tips and penetration depths can be guided in a row. This enables an optimized structure of surface enlargement. In the case of subsequent knurling, the tips are preferably displaced both transversely and lengthwise, so that a regular image is again formed. In the case of several passes, the impressions mutually influence one another and the displaced material can also escape into the impressions previously generated.
The depth of penetration of the knurled tips into the material surface corresponds to the mean depth of the grooves 1.3; it can also be somewhat smaller or larger and depends on the material, its thickness and the surface and the type of coating. The flat area at the bottom of the impressions 5 results from the slight flattening of the knurled tips in order to minimize their wear. The flat areas are only visible because of the 100x magnification.

• LT = Taststrecke des Rauhigkeitsmessgerätes
• RA = errechnete mittlere Rauhtiefe
• RZ = errechnete untere mittlere Rauhtiefe
• RMAX = obere mittlere Rauhtiefe

In Figures 3 and 4 it means:

• LT = sensing distance of the roughness measuring device
• RA = calculated average roughness
• RZ = calculated lower average roughness
• RMAX = upper average roughness

Not only can metal surfaces be prepared for coating in this way. but also plastic plates or plastic surfaces of plates to which, for example, a metal layer or a metal coating is to be applied with good adhesion. In certain cases, heating the surface to be machined and / or the knurled rollers can be advantageous.
If the requirements for the liability of the coating are less stringent, grinding can also be replaced by a brushing process.

The following example serves to explain the invention further.

Example: (Fig. 5,6)

A 0.7 mm thin, smooth sheet 9 made of oxygen-free roofing copper is longitudinally sanded in two passes with a sanding belt from SIA AG, 8500 Frauenfeld, Switzerland, type 1920, SIARAL F, corundum paper on linen, grain size 80. The speed of the sanding belt compared to the copper sheet at a surface pressure of approx. 0.7 bar is 30 m / s. The maximum depth of the grooves is 0.3 mm. After these two longitudinal cuts, there are no longer any scratch-free spots on the surface. Now a plurality of impressions 5 are introduced into the sheet 9 by means of a free-running knurling roller 7. The knurling roller 7 used for this purpose consists of a circular cylinder Z, the diameter of which is D = 42 mm and which is fitted with a set of pyramidal, radially protruding tips 11. These tips 11 lie in rows, with a division t = 0.3 mm, on a line A running parallel to the longitudinal axis of the roll, the mutual tangential distance of which is a = 0.3 mm. The intersection lines L of the tip surfaces with the cylinder Z have approximately the shape of a rhombus Rb which is pointed in the circumferential direction and in which two sides which abut one another form an angle of beta = 60 °. The height of the tips relative to the cylinder Z is h = 0.3 mm and the tip angle alpha = 90 ° (cf. FIG. 6). The ends of the tips 11 can be flattened (cf. impressions in FIG. 4).
By turning this knurling roller 7 and / or its cylinder Z parallel along the surface at a distance of f = 0.1 mm, the tips 11 into the surface of the sheet metal at a feed rate of 10 m / min with a bearing load P = 135 N / mm 9 depressed. Complementary 0.2 mm deep impressions 5 with rhombuses Rb (contour of the impression 5) are formed on the surface, the length of which is 1 = 0.3 mm and the width q = 0.2 mm. The tips 11 therefore penetrate mainly into the groove flanks and not into the lower-lying sheet metal area, which has been left untouched by the grinding process, and break up the flanks of the mountains 2 that were previously smoothed by partial melting due to the resulting pushing forces, so that microscopic gaps at the impressions arise, the width of which is of the order of a few hundredths of a millimeter.

In a second pass, the knurled roller 7 is displaced such that the tips 11 are placed and pressed in between the already existing impressions 5 in both the transverse and longitudinal directions. By pressing in a part of the material is pushed laterally against the already existing, closely adjacent impressions 5, which leads to a deformation of the surfaces of the impressions. The result is an enlargement of the existing columns.

The arrangement of the tips 11 on the surface of the roller 7 can be selected such that the center thereof approximately with the intersection in a first group A1, A2, A3 of equidistant parallel lines with the same or different equidistant distances at an angle delta of 90 ° ± 45 ° parallel straight lines of a second group B1, B2, B3, .. coincide and the equidistances of this straight line correspond to approximately one to five times the dimension of the impressions 5 taken in the longitudinal direction.
A sheet 9 prepared in this way, which is coated with a protective lacquer, ensures a surprisingly better adhesion of the layer compared to conventional surface processing, which withstands high mechanical stresses and weather influences.

Instead of a knurled roller surface provided with tips, a roller with a smooth jacket can also be used. For this purpose, a sheet metal or the like covered with points is placed around the jacket of the roller and connected to it. The connection can be made in such a way that a new sheet is drawn on when the knurled tips wear out.

Claims (14)

1. Method of machining surfaces of sheets and plates, wherein the surface is prepared by grinding or brushing for a subsequent coating, oxidation or adhesion, characterised in that, after the plurality of grooves (1, 3) have been applied by grinding or brushing, knurling in the form of a plurality of indentations (5) is stamped subsequently and additionally into the surface which has thus been roughened.
2. Method according to claim 1, characterised in that the grooves (1, 3) are produced by crosswise grinding so as to extend in different directions.
3. Method according to claim 1 or 2, characterised in that the conical or pyramidal indentations (5) are produced in the sheet surface by means of knurling using a knurling tool (7).
4. Method according to claim 4, characterised in that knurling points (11) with spacings (a, t) of 0.2 to 0.3 mm are used on the casing of the knurling tool (7) or on a carrier material drawn over the casing.
5. Method according to one of claims 1 to 4, characterised in that the indentations (5) have a depth which is identical to or greater than the mean depth of the grooves (1, 3).
6. Method according to one of claims 1 to 4, characterised in that the indentations (5) are provided in successive rows, and an additional provision thereof in rows is subsequently effected in a centrally offset manner both in the longitudinal direction and in the transverse direction.
7. Method according to one of claims 1 to 6, characterised in that the knurling is produced by one or a plurality of knurling rollers (7), which are connected behind one another and have knurling points (11) offset relative to one another.
8. Method according to claim 1, characterised in that the depth to which the knurling points (11) penetrate the surface of the material is selectable during the knurling process.
9. Method according to claim 1, characterised in that the knurling is effected so as to cover the entire surface.
10. Method according to claims 1 and 9, characterised in that the prepared surface and/or the knurling tool are/is heated prior to the knurling process.
11. Method according to claims 1 to 10, characterised in that appropriate structural images (patterns) are produced by a special disposition of the knurling points.
12. Laminar structure formed from metal or plastics material and having a surface which has been roughened by a plurality of grooves (1, 3), which extend substantially parallel to one another and are produced by grinding or brushing, characterised in that a plurality of indentations (5) are stamped into the roughened surface, the depth of said indentations corresponding or approximately corresponding to the mean depth of the grooves (1, 3), and the centres of said indentations coinciding approximately with the intersections between a first group (A1, A2, A3) of equidistant straight parallel lines and the straight parallel lines of a second group (B1, B2, B3), which are equidistant from one another in an identical or different manner and extend at an angle (delta), and the equidistances between these straight lines correspond to about one- to five-times the dimension of the indentations (5) viewed with respect to the longitudinal direction.
13. Laminar structure formed from metal or plastics material and having a network which is formed from a plurality of grooves (1), which extend substantially parallel to one another and are produced by brushing or grinding, as well as from a plurality of grooves (3), which extend at an angle in the range of 90°±45°, characterised in that a plurality of indentations (5) are stamped into the network of grooves (1), the depth of said indentations corresponding or approximately corresponding to the mean depth of the grooves (1, 3), and the centres of said indentations coinciding approximately with the intersections between a first group (A1, A2, A3) of equidistant straight parallel lines and the straight parallel lines of a second group (B1, B2, B3), which are equidistant from one another in an identical or different manner and extend at an angle, and the equidistances between these straight lines correspond to about one- to five-times the dimension of the indentations (5) viewed with respect to the longitudinal direction.
14. Use of the structure according to one of claims 12 and 13 in order to produce a protective layer on sheets or plates (9) formed from metal or plastics material, such layer to be applied to said structure or produced by chemical treatment.

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