Item with surface provided with a plurality micromechanical locking units and method of manufacturing of such item

Abstract

An item (1) and a method of manufacturing such item, the item comprising: a steel substrate (2) having a surface (3), the surface (3) being provided with a plurality of micromechanical locking units for creating a micromechanical lock with another object when the micromechanical locking units are pressed into a surface of another object, the micromechanical locking unit comprising: a dimple (6) surrounded by a ridge (7), wherein the angle of the surface of the dimple medially between the bottom of the dimple (6) and the top of the ridge (7) is between 30 and 75° relative to the surface (3), preferably between 45 and 70°.

Description

[0001] ITEM WITH SURFACE PROVIDED WITH A PLURALITY MICROMECHANICAL

[0002] LOCKING UNITS AND METHOD OF MANUFACTURING OF SUCH ITEM

[0003] TECHNICAL FIELD

[0004] The disclosure relates to items with a steel or coated steel surface that is provided with a plurality of micromechanical locking units and methods of manufacturing and using such items .

[0005] BACKGROUND

[0006] The coef ficient of static friction between clamped steel items with smooth surfaces is in the absence of lubrication ( clean and dry) between 0 , 12 and 0 , 25 .

[0007] 1 , Roymech . org)

[0008] When constructing with steel items that are clamped together, e . g . , by a bolt connection, the shear force , i . e . , the force in the direction along the contact surfaces is limited by the clamping force times the coef ficient of static friction minus a security margin . Since the coef ficient of static friction of steel on steel items varies in an unpredictable way, its lowest value has to be used minus the security margin, which means that engineers have to design with an ef fective coef ficient of static friction of 0 , 15 ( sometimes a more conservative value of 0 , 10 is used) . There are various ways known to increase steel-to-steel static friction, such as :

[0009] - roughening the surface as known from W02010118747 , which provides a steel or iron friction member with a predetermined exact thickness for creating high resistance to shear movement when the friction member is squeezed between two mating metallic surfaces of at least two machine parts by at least two clamping devices per friction element . For providing the squeeze force the friction member is provided with at least one friction face to mate with a mating face of one of the machine parts , and provides a method involving roughening the friction face followed by non-depositing surface hardening the roughened friction face . surface texturing as known from "A Novel Process for Manufacturing High-Friction Rings with a Closely Defined Coefficient of Static Friction (Relative Standard Deviation 3 , 5% ) for Application in Ship Engine Components" Materials 2022 , 15 , 448 , applying coatings , applying hard particles in the surface , applying a Tungsten Carbide coating as known from EP2773881B1 which discloses a method of making a brake disc comprising the following operating steps : a ) providing a disc brake , comprising a braking band 2 made of grey cast iron or steel and provided with two opposite braking surfaces 2a, 2b, each of which defines at least partially one of the two main sides of the disc ; b ) depositing a material in particle form on the disc using a HVOF (High Velocity Oxygen Fuel ) technique , or HVAF (High Velocity Air Fuel ) technique or KM technique (Kinetic Metalli zation) to form a protective coating 3 which covers at least one of the two braking surfaces of the braking band, The material in particle form- is composed of 70 to 95% in weight of tungsten carbide , 5% to 15% in weight of cobalt and 1 % . to 10% in weight of chromium, applying discs with hard particles between the mating surfaces of the items , as known from US 6347905B1 which discloses a connecting element for the friction- increasing connection of workpieces which are to be j oined, which is a thin resilient element that bears particles of a defined si ze at its surface, the particles being made from a material with a compressive and shear strength which exceeds that of the workpieces to be joined.

[0010] Materials 2022, 15, 448, A Novel Process for Manufacturing High-Friction Rings with a Closely Defined Coefficient of Static Friction (Relative Standard Deviation 3,5%) for Application in Ship Engine Components, Wojciech S. Gora, Jesper V. Carstensen, Krystian L. Wlodarczyk, Mads B. Laursen, Erica B. Hansen and Duncan P. Hand (Materials 2022, 15, 448. https: / / doi.org / 10.3390 / mal5020448) disclose a laser surfacetexturing technique to manufacture a surface with a tailored high static friction coefficient for application within driveshafts of large marine engines, the friction coefficient was kept within a narrow range. This was obtained by using nanosecond-pulsed fibre lasers to generate a hexagonal pattern of craters on the surface. To provide a suitable friction coefficient, after laser processing, the surface was hardened using a chromium-based hardening process so that the textured surface would embed into its counterpart when the normal force was applied in the engine application. However, the resulting friction rings can only be clamped once, and relatively rapidly lose their predetermined coefficient of friction when clamped multiple times.

[0011] W02010118747A1 discloses a steel or iron friction member with an adapted thickness for creating high resistance to shear movement when the friction member is squeezed between two mating metallic surfaces of at least two machine parts by at least two clamping devices per friction element for providing the squeeze force the friction member is provided with at least one friction face to mate with a mating face of one of the machine parts . The friction face has been created by a roughening step followed by non-depositing surface hardening the roughened friction face . W02010118747A1 also discloses a method for providing a steel or iron friction member with a predetermined adapted thickness for creating high resistance to shear movement when the friction member is squeezed between two mating metallic surfaces of at least two machine parts by at least two clamping devices per friction element for providing the squeeze force , the friction member is provided with at least one friction face to mate with a mating face of one of the machine parts , comprising roughening the friction face followed by non-depositing surface hardening the roughened friction face . Thus , a rough and hard surface is provided, with proj ections of the rough surface being able to penetrate a mating surface for achieving mechanical lock .

[0012] EP3339658A1 discloses an item with a surface provided with a plurality of micromechanical locking units according to the preamble of claim 1 . In EP3339658A1 the micromechanical locking units are formed by hard particles that are fixed on a metal substrate by means of a metallic binding layer . However, none of the known measures provide an accurately controlled coef ficient of static friction independent of the presence of lubrication or dirt and that remains substantially constant after several times clamping the surfaces together .

[0013] SUMMARY

[0014] It is an obj ect to provide an item with a surface and a method for manufacturing such a surface that overcomes or at least alleviates the problems mentioned above . The foregoing and other objects are achieved by the features of the independent claims. Further implementation forms are apparent from the dependent claims, the description, and the figures .

[0015] According to a first aspect, there is provided an item comprising : a steel substrate having a surface, the surface being provided with a plurality of micromechanical locking units for creating a micromechanical lock with another object when the micromechanical locking units are pressed into a surface of another object, the micromechanical locking unit comprising: a dimple surrounded by a ridge, wherein the angle of the surface of the dimple medially between the bottom of the dimple and the top of the ridge is between 30 and 75° relative to the surface, preferably between 45 and 75°.

[0016] The resulting object has an accurately predictable coefficient of static friction against the surface of another object, for example, a steel object, regardless of the presence of lubrication and or dirt, and substantially maintains this coefficient of friction after multiple clamping / and unclamping events. Since the coefficient of static friction is substantially independent of the circumstances under which the surfaces are clamped and from the number of times that the surfaces have been clamped, engineers can use the reliable coefficient of static friction provided by this object. This has the significant advantage that engineers can use the much higher coefficient of static friction provided by the object as the basis for their calculations in constructions where services are e.g., clamped by bolts / screws and the resulting shear force that the construction can handle. The present item can provide a reliable coefficient of static friction between approximately 0,8 and 1,2, which, compared to the generally used reliable coefficient of static friction of untreated steel on steel of 0,15 is an increase of approximately a factor five to eight. Thus, the present object allows e.g., a bolted flange connection to resist approximately five times more shear load compared to a conventional steel and steel bolted flange connection, which is an enormous improvement that will allow engineers to construct significantly lighter and more compact constructions .

[0017] According to a possible implementation of the first aspect, the spacing between the centers of the dimples is between 60 and 200 pm .

[0018] According to a possible implementation of the first aspect, the depth d of a dimple measured from the bottom of a dimple to the top of the ridge is 15 to 100 pm, preferably 30 to 1000 pm.

[0019] According to a possible implementation of the first aspect, the steel has a tensile strength between 420 and 1630 N / mm2, preferably between 600 and 1200 N / mm2. According to a possible implementation of the first aspect , a hard layer or coating is provided on the surface , the hard layer preferably having a substantially uni form thickness . According to a possible implementation of the first aspect , the coating thickness is between 3 and 20 pm, preferably between 5 and 15 pm.

[0020] According to a possible implementation of the first aspect , the ridge extends substantially in the form of a circle .

[0021] According to a possible implementation of the first aspect , the ridge has a diameter of 60 to 200 pm . According to a possible implementation of the first aspect , the item is or comprises a sheet that has a thickness of 1 mm or less , preferably 0 , 5 mm or less , and / or wherein the item is a shim . According to a possible implementation of the first aspect , the surface of the item that is provided with the plurality of micromechanical locking units is configured to establish micromechanical lock between the surface of the item 1 and a mating surface of another item by the peaks and / or ridges being pressed into the mating surface , preferably with a surface pressure between 5 and 400 MPa .

[0022] According to a possible implementation of the first aspect , the micromechanical locking units are arranged on the surface in a pattern that results in a substantially higher coef ficient of static friction in a first direction compared to an orthogonal second direction .

[0023] According to a possible implementation of the first aspect , the pattern comprises a plurality of straight arrays of micromechanical locking units that are arranged substantially parallel with the second direction .

[0024] According to a possible implementation of the first aspect , the number of micromechanical locking units per unit of surface area is selected to obtain a speci fic magnitude for the coef ficient of static friction .

[0025] According to a possible implementation of the first aspect , the micromechanical locking unit is formed on a smooth surface of the steel substrate by applying a number of laser pulses .

[0026] According to a possible implementation of the first aspect , the hard layer or coating is deposited subsequently on the steel substrate , preferably by chromium carbide di f fusion coating .

[0027] According to a possible implementation of the first aspect , the ridge is a sharp-crested ridge .

[0028] According to a possible implementation of the first aspect , the hard layer is a hard chromium carbide layer, preferably a hard chromium carbide layer formed by di f fusion coating on the steel substrate . According to a possible implementation of the first aspect , the item is a disc with a central hole and both sides of the disc are formed by the first contact surface .

[0029] According to a possible implementation of the first aspect , the item is a gripper comprising at least one gripping surface for engaging in obj ects to be gripped and wherein the gripping surface is formed by the first contact surface

[0030] According to a possible implementation of the first aspect , the item is or comprises a sheet that has a thickness of 1 mm or less , preferably 0 , 5 mm or less and / or wherein the item is a shim .

[0031] According to a second aspect , there is provided a method of manufacturing an obj ect having a steel substrate with a surface provided with a plurality of micromechanical locking units for creating a micromechanical lock with another obj ect when the micromechanical locking units are pressed into a surface of another obj ect , the method comprising : a) applying a laser pulse a number of times with a given intensity to the same position on the surface to create a dimple surrounded by a ridge , b) adj usting the number of times and / or the intensity of the laser pulse to obtain a dimple with an angle of the surface of the dimple medially between the bottom of the dimple and the top of the ridge being between 30 and 75 ° relative to the surface , preferably between 4555 and 75 ° , and c) repeating a ) and b ) at a plurality of other positions on the surface . According to a possible implementation of the second aspect , c) is performed at positions on the surface to obtain a spacing between the centers of the dimples between 60 and 200 pm .

[0032] According to a possible implementation of the second aspect , the number of times and / or the intensity of the laser pulse in b ) is adj usted to obtain a dimple with a depth d measured from the bottom of a dimple to the top of the ridge between 30 and 100 pm, preferably between 40 and 70 pm .

[0033] According to a possible implementation of the second aspect , the steel has a tensile strength between 420 and 1630 N / mm2 , preferably between 600 and 1200 N / mm2 .

[0034] According to a possible implementation of the second aspect , the method comprises applying a hard layer or coating to the surface after the dimples have been created, the hard layer preferably having a substantially uni form thickness .

[0035] According to a possible implementation of the second aspect , the thickness is between 3 and 20 pm, preferably between 5 and 15 pm .

[0036] According to a third aspect there is provided a method of providing controlled static friction between an item and another item that are in contact through a surface of the item and a surface of the other item, the method comprising : providing the surface of the item with a plurality of micromechanical locking units that each comprise : a peak comprising a core peak formed by a steel substrate of the item, the core peak being covered by the hard layer, and / or a ridge comprising a core ridge formed by the steel substrate of the item, the core ridge being covered by the hard layer, arranging the micromechanical locking units non-evenly distributed over the surface to obtain a directionally noneven coef ficient of static friction, and / or selecting the number of micromechanical locking units per unit of surface area to obtain a speci fic magnitude for the coef ficient of static friction, and / or arranging the micromechanical locking units in curved or straight arrays for obtaining a direction-speci fic largest coef ficient of static friction .

[0037] According to a possible implementation of the third aspect , the coef ficient of static friction is between 0 , 8 and 1 , 2 .

[0038] According to a possible implementation of the third aspect , the method comprises forming each micromechanical locking unit on a smooth surface of the steel substrate by applying a laser pulse , and preferably depositing the hard layer subsequently on the steel substrate , preferably by chromium carbide di f fusion coating .

[0039] According to a possible implementation of the third aspect , the method comprises establishing a micromechanical lock between the surface of the item and the surface of the other item by the peaks and / or ridges being pressed into the other surface .

[0040] According to a fourth aspect , there is provided a method of preventing displacement between a first steel item and a second steel item, the first item has a first contact surface and the second item has a second contact surface , the method comprising : providing the first contact surface with dimples with each dimple being surrounded by a ridge using a pulsed laser to form a micromechanical locking unit , with the dimples spaced from one another at a distance between 60 to 200 pm, the first contact surface being a hardened steel surface due to the first steel item being a hardened steel item or due to the first steel item being a non-hardened steel item and the method comprising hardening the first contact surface by applying a hard layer after providing the first contact surface against with dimples , pressing the first contact surface onto the second contact surface with or without a lubricant therebetween with a first force thereby preventing displacement between the first steel item and the second steel item when a second force urging displacement between the first steel item and the second steel item in a direction along the first contact surface until the second force exceeds at least 80% of the first force .

[0041] According to a possible implementation of the fourth aspect , the method comprises adj usting the power applied by the pulsed laser for each dimple to the first contact surface to obtain a dimple diameter between 35 and 65 pm.

[0042] According to a possible implementation of the fourth aspect , the method comprises adj usting the power applied by the pulsed laser for each dimple to the first contact surface to obtain a ridge height between 15 and 30 pm .

[0043] According to a possible implementation of the fourth aspect , the method comprises applying the dimples to the first contact service in a hexagonal pattern .

[0044] According to a f ifth aspect , there is provided an item comprising an outer surface , the outer surface having at least a first contact surface formed by a steel substrate , the first contact surface having dimples with each dimple being surrounded by a ridge to form a micromechanical locking unit for providing the first contact surface with a coef ficient of static friction of the contact surface of at least 0 , 78 regardless of the presence of lubricant on the first surface , the steel substrate being a hardened steel substrate or a non-hardened steel substrate with a hard layer thereon, the dimples being spaced from one another at a distance between 60 to 200 pm and a dimple diameter between 35 and 65 pm .

[0045] According to a possible implementation of the fifth aspect , the ridge height is between 15 and 30pm .

[0046] According to a possible implementation of the fifth aspect , the number of micromechanical locking units per unit of surface area is selected to obtain a speci fic magnitude for the coef ficient of static friction .

[0047] These and other aspects will be apparent from the examples and embodiments described below .

[0048] BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In the following detailed portion of the present disclosure , the aspects , embodiments , and implementations will be explained in more detail with reference to the example embodiments shown in the drawings , in which :

[0050] Fig . 1 is a metallographic cross-sectional image of an item according to an embodiment with epoxy embedding on both sides for visuali zation,

[0051] Fig . 2 is a detailed cross-sectional image of an item according to the amendment with epoxy embedding for visuali zation,

[0052] Fig . 3 is a top view of a surface of an item according to an embodiment ,

[0053] Fig . 4 is a cross- sectional view of an embodiment of the item in the form of a thin friction disk clamped in a bolted connection between two plate-like items ,

[0054] Figs . 5 and 6 are top and elevated views , respectively of the thin friction disk of the embodiment of Fig . 5 , and

[0055] Figs . 7 to 9 are diagrams showing test results of examples .

[0056] DETAILED DESCRIPTION

[0057] With reference to Figs . 1 to 3 an item 1 with steel substrate 2 having a surface 3 that is provided with a plurality of micromechanical locking units for creating a micromechanical lock with another obj ect when the micromechanical locking units are pressed into a surface of another obj ect , preferably to thereby obtain a high coef ficient of static friction, preferably a precisely determined high coef ficient o f friction that is largely af fected by the presence of dirt or lubricant . Each micromechanical locking unit comprises a dimple ( 6 ) surrounded by a ridge ( 7 ) . The micromechanical locking units are created by a laser texturing method that is described in greater detail below .

[0058] The dimples 6 are essentially rotation symmetric relative to a normal to the surface . From a lowest point in the dimple 6 , the surface of the dimple 7 extends to the crest or ridge 7 of the dimple 6 . The angle of the surface of the dimple medially between the bottom of the dimple 6 and the top of the ridge 7 is between 30 and 75 ° relative to the surface 3 , preferably between 45 and 70 ° to obtain the desired properties surface 3 provided with the micromechanical locking units as described below . The spacing between the centers ( deepest point ) of the dimples 6 is between 60 and 200 pm . The depth d of a dimple 6 measured from the bottom of a dimple 6 to the top of the ridge / crest 7 is 15 to 100 pm, preferably 30 to 70 pm . 16 . The ridge 7 is preferably a sharp-crested ridge .

[0059] The steel substrate 2 preferably has a tensile strength between 420 and 1630 N / mm2 , preferably between 600 and 1200 N / mm2 .

[0060] Optionally, a hard layer or coating 9 is provided on the surface 3 , the hard layer preferably has a substantially uniform thickness tl . The thickness tl is preferably between

[0061] 3 and 20 pm, more preferably between 5 and 10 pm.

[0062] The ridge or crest 7 may extend substantially in the form of a circle and have a diameter of 60 to 200 pm.

[0063] In an embodiment, the item 1 is or comprises a sheet that has a thickness t2 of 1 mm or less, preferably 0,5 mm or less and / or wherein the item 1 is a shim. Figs. 5 and 6 show an embodiment in which the item 1 is a friction disk. Fig. 4 shows such the item 1 / friction disk in a bolted connection between two plate-like objects 10, which could, for example, be flanges in a bolted flange connection. The bolt 12 (with the nut 14) applies a force in the normal direction to the surface of the plates 10 and the friction disk 1 as shown by the vertical arrows. A shear force, as shown by the horizontal arrows, is applied to the 2 plate-like objects 10. The high coefficient of static friction provided by the friction disk allows for the bolted connection to withstand a relatively high shear force, as explained below in the examples.

[0064] During use of the item 1 the ridges 7 are pressed into the mating surface, preferably with a surface pressure between 5 and 450 MPa.

[0065] In an embodiment (not shown) the micromechanical locking units are arranged on the surface in a pattern that results in a substantially higher coefficient of static friction in a first direction compared to an orthogonal second direction. This pattern may comprise a plurality of straight arrays of micromechanical locking units that are arranged substantially parallel with the second direction .

[0066] The number of micromechanical locking units per unit of surface area is in an embodiment selected to obtain a speci fic magnitude for the coef ficient of static friction .

[0067] The micromechanical locking units are formed in a smooth surface of the steel substrate 2 by applying a number of laser pulses .

[0068] In an embodiment , a hard layer or coating 9 is deposited subsequently on the steel substrate , preferably by chromium carbide di f fusion coating . The hard layer 9 can be a hard chromium carbide layer, preferably a hard chromium carbide layer formed by di ffusion coating on the steel substrate 2 .

[0069] The plurality of micromechanical locking units are provided on the surface 3 of the item 1 by a applying a laser pulse a number of times with a given intensity to the same position on the surface 3 to create a dimple 6 surrounded by a ridge 7 . The power of each pulse may di f fer from pulse to pulse , it may be adj usted properties of the steel in order to obtain the desired shape and si ze of the dimples 6 and their ridge 7 . The number of pulses and / or the intensity of the laser pulse is adj usted to obtain a dimple 6 with an angle of the surface of the dimple 6 medially between the bottom of the dimple 6 and the top of the ridge 7 being between 30 and 75 ° relative to the surface 3 , preferably between 40 and 70 ° , and The process is repeated a plurality of other positions on the surface 3 to obtain a complete pattern of micro locking units on the surface 3, preferably, with a spacing between the centers of the dimples 6 between 60 and 200 pm.

[0070] The number of times and / or the intensity of the laser pulse is adjusted to obtain a dimple 6 with a depth d measured from the bottom of a dimple 6 to the top of the ridge 7 between 15 and 100 pm, preferably between 30 and 70 pm.

[0071] Optionally, after the laser treatment where dimples 6 are created, a hard layer or coating 9 is applied to the surface 3, the hard layer 9 preferably having a substantially uniform thickness tl. Preferably the thickness tl is between 3 and 20 pm, preferably between 5 and 10 pm.

[0072] EXAMPLES :

[0073] Example 1: Two-sided thin, coated disc for increasing static friction of a bolted connection, cross-sectional view shown in Fig. 1 and top view of the surface shown in Fig. 3

[0074] • Discs made of annealed carbon steel 1,1248 is laser cut to a size of 034x019x0, 5mm, i.e. the disc has a central opening for allowing a bolt shaft to pass therethrough,

[0075] • Each side of the disc is laser textured with a pulsed fiber laser to create a hexagonal pattern of dimples. The spacing between the dimples is 85 + / - 1 pm and with a dimple depth of 45 + / - 3 pm, Fig. 2.

[0076] • The discs are subsequently subjected to a thermo- reactive diffusion treatment to produce a chromium carbide coating with a coating thickness of 5 + / - 0,8 pm covering both sides of the disc, Fig. 1. • To evaluate the micromechanical interlocking effect, the discs are placed between two flanges of QT steel 1,2311 with a tensile strength of 1100 N / mm2, which is pre-loaded to a clamping pressure on the discs of 220 MPa with a grade 10,8 M18 bolt. One flange is fixed while the other is increasingly subjected to a rotational force. As the rotational force exceeds the frictional forces between the disc and the flanges, one flange will rotate.

[0077] • Five discs are tested, resulting in an average coefficient of static friction of 1,18 + / - 0,03, Diagram in Fig. 7. A set of non-treated discs are also evaluated and tested to a coefficient of static friction of 0,23 + / - 0,06.

[0078] Example 2: Re-use of non-slipped, two-sided, thin, coated discs in bolting applications.

[0079] • Fifteen discs are prepared in the same manner as in Example 1.

[0080] • The coefficient of static friction is evaluated as in Example 1, now preloaded to a clamping pressure of 100 MPa acting on the discs. Five discs are tested as prepared (a) , and in order to simulate re-use of the discs, two sets of five other discs are clamped and released five (b) and twenty (c) times, respectively, prior to slip-testing . The discs are slip-tested, and the three sets of five discs (a) , (b) , and (c) shows a coefficient of static friction of 0, 86+ / -0,04, 0,84+ / -0,04, and 0,85+ / -0,03 respectively, Diagram in Fig. 8, showing that re-tightening does not deteriorate the performance of the discs.

[0081] Example 3: Re-use of tested and slipped discs • Five discs made of annealed steel 1,1248 are laser cut to a size of 034x019x0, 5mm.

[0082] • Each side is laser textured with a pulsed fiber laser to create a hexagonal pattern of dimples. The spacing between the dimples is 85 + / - 1 pm and with a depth of the dimples of 55 + / - 3 pm.

[0083] • The discs are then subjected to a thermo-reactive diffusion treatment to produce a chromium carbide diffusion coating with a coating thickness of 10 + / - 1,4 pm covering every surface of the discs.

[0084] • The coefficient of static friction is evaluated as in Example 1, now with a clamping pressure of 70 MPa. The coefficient of static friction is measured to 0,82 + / - 0,04. The same five discs are then slip-tested once again with the exact same parameters, and the test shows no decrease in the coefficient of static friction as the average value is evaluated to 0,84 + / - 0,03, (Diagram in Fig. 9) .

[0085] Example 4 : High friction grippers for tubes

[0086] • Mechanical grippers made of steel 1,2363 with dimensions 40x32x24 are used for clamping onto a stainless steel tube during CNC machining of internal threads. The four gripper working areas measuring 20x12mm are subjected to laser texturing with a pulsed fiber laser to create a hexagonal pattern of dimples equivalent to those in example 1. The work area has a curved surface corresponding to that of the stainless steel tubes, 0120.

[0087] • The grippers are then subjected to a thermo-reactive diffusion treatment to produce a chromium carbide diffusion coating with a coating thickness of 10 + / - 1,1 pm covering every surface of the grippers.

[0088] • As a result of the micromechanical interlocking surface, the holding power of the grippers has increased 4,2X compared to a regular machined gripper surface when exerting a clamping force of 40 tons.

[0089] Example 5: Directional static friction

[0090] • Five plates made of annealed steel 1,1248 is laser cut to a size of 40x20x2mm.

[0091] • Each side is laser textured with a pulsed fiber laser to create a linear pattern of stadiums with a width of 75 + / - 1 pm, a height of 30 + / - 5 pm and a length of 200 + / - 1 pm. The stadiums are parallel to the longest side of the plates.

[0092] • The plates are then subjected to a thermo-reactive diffusion treatment to produce a chromium carbide coating with a coating thickness of 10 + / - 1,4 pm covering every surface of the plates.

[0093] • The coefficient of static friction is evaluated by clamping the plates on both sides in two areas of 15x15mm with a clamping pressure of 70 MPa. By pulling the plate to a slip either in parallel or perpendicular direction to the stadiums, a directional coefficient of static friction can be measured. In parallel direction to the stadiums, the coefficient of friction is measured to 0,48 + / - 0,07, and in perpendicular direction, the value is measured to be 0,78 + / - 0, 06.

[0094] Example 6:

[0095] High pressure bolting application with shallower dimples • Five discs are prepared in the same material and dimensions as in Example 1 .

[0096] • Each side of the disc is laser textured with a pulsed fiber laser to create a hexagonal pattern of dimples . The spacing between the dimples is 80 + / - 1 pm, with a dimple depth of 24 + / - 2 pm .

[0097] • The discs are subsequently subj ected to a thermoreactive di f fusion treatment to produce a chromium carbide coating with a coating thickness of 6 + / - 0 , 7 pm covering both sides of the disc .

[0098] • The coef ficient of static friction is evaluated against structural steel S235 with testing procedure as in Example 1 , now preloaded to a clamping pressure of 300 MPa acting on the discs . The discs are slip-tested and show a coefficient of static friction of 1 , 06 + / - 0 . 06 .

[0099] In another embodiment , a method is provided for providing controlled static friction between an item and another item that are in contact through a surface of the item and a surface of the other item . The method comprises : providing the surface of the item with a plurality of micromechanical locking units that each comprise : a peak comprising a core peak formed by a steel substrate of the item, the core peak being covered by the hard layer, and / or a ridge comprising a core ridge formed by the steel substrate of the item, the core ridge being covered by the hard layer, arranging the micromechanical locking units non-evenly distributed over the surface to obtain a directionally noneven coef ficient of static friction, and / or selecting the number of micromechanical locking units per unit of surface area to obtain a speci fic magnitude for the coef ficient of static friction, and / or arranging the micromechanical locking units in curved or straight arrays for obtaining a direction-speci fic largest coef ficient of static friction . Preferably, the coef ficient of static friction is between 0 , 8 and 1 , 2 .

[0100] The method may further comprise forming each micromechanical locking unit on a smooth surface of the steel substrate by applying a laser pulse and preferably depositing the hard layer subsequently on the steel substrate , preferably by chromium carbide dif fusion coating .

[0101] The method may also comprise comprises establishing a micromechanical lock between the surface of the item and the surface of the other item by the peaks and / or ridges being pressed into the other surface .

[0102] According to another embodiment , there is provided a method of preventing displacement between a first steel item and a second steel item, the first item has a first contact surface and the second item has a second contact surface . The method comprises : providing the first contact surface with dimples with each dimple being surrounded by a ridge using a pulsed laser to form a micromechanical locking unit , with the dimples spaced from one another at a distance between 60 to 200 pm, the first contact surface being a hardened steel surface due to the first steel item being a hardened steel item or due to the first steel item being a non-hardened steel item and the method comprising hardening the first contact surface by applying a hard layer after providing the first contact surface against with dimples , pressing the first contact surface onto the second contact surface with or without a lubricant therebetween with a first force thereby preventing displacement between the first steel item and the second steel item when a second force urging displacement between the first steel item and the second steel item in a direction along the first contact surface until the second force exceeds at least 80% of the f irst force . Preferably, the method comprises , adj usting the power applied by the pulsed laser for each dimple to the f irst contact surface to obtain a dimple diameter between 35 and 65 pm.

[0103] Preferably, the method comprises applying the dimples to the first contact service in a hexagonal pattern .

[0104] According to a further embodiment , there is provided an item 1 comprising an outer surface 3 , the outer surface 4 having at least a first contact surface formed by a steel substrate 2 , the first contact surface 3 having dimples 6 with each dimple 6 being surrounded by a ridge 7 to form a micromechanical locking unit for providing the first contact surface with a coef ficient of static friction of the contact surface of at least 0 , 78 regardless of the presence of lubricant on the first surface 3 , the steel substrate 2 being a hardened steel substrate or a non-hardened steel substrate with a hard layer thereon, the dimples 6 being spaced from one another at a distance between 60 to 200 pm and a dimple diameter between 35 and 65 pm. Preferably, the surface area is selected to obtain a specific magnitude for the coefficient of static friction.

[0105] The various aspects and implementations have been described in conjunction with various embodiments herein. However, other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed sub ect-matter, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality.

[0106] The reference signs used in the claims shall not be construed as limiting the scope. Unless otherwise indicated, the drawings are intended to be read (e.g., cross-hatching, arrangement of parts, proportion, degree, etc.) together with the specification, and are to be considered a portion of the entire written description of this disclosure. As used in the description, the terms "horizontal", "vertical", "left", "right", "up" and "down", as well as adjectival and adverbial derivatives thereof (e.g., "horizontally", "rightwardly", "upwardly", etc.) , simply refer to the orientation of the illustrated structure as the particular drawing figure faces the reader. Similarly, the terms "inwardly" and "outwardly" generally refer to the orientation of a surface relative to its axis of elongation, or axis of rotation, as appropriate.

Claims

CLAIMS :

1. An item (1) comprising: a steel substrate (2) having a surface (3) , the surface (3) being provided with a plurality of micromechanical locking units for creating a micromechanical lock with another object when the micromechanical locking units are pressed into a surface of another object, characterized by the micromechanical locking units comprising : a dimple (6) surrounded by a ridge (7) , wherein the angle of the surface of the dimple medially between the bottom of the dimple (6) and the top of the ridge (7) is between 350 and 75° relative to the surface (3) , preferably between 4555 and 75° .

2. The item (1) of claim 1, wherein spacing between the centers of the dimples (6) is between 60 and 200 pm.

3. The item (1) of claim 1 or 2, wherein the depth (d) of a dimple (6) measured from the bottom of a dimple (6) to the top of the ridge (7) is 15 to 100 pm, preferably 30 to 100 pm.

4. The item (1) of any one of claims 1 to 3, wherein the steel of said substrate has a tensile strength between 420 and 1630 N / mm2, preferably between 600 and 1200 N / mm2.

5. The item (1) of any one of claims 1 to 4, wherein a hard layer or coating (9) is provided on the surface (3) , the hardlayer preferably having a substantially uniform thickness6. The item (1) of claim 5, wherein the thickness (tl) is between 3 and 20 pm, preferably between 5 and 10 pm.

7. The item (1) of any one of the preceding claims, wherein the ridge (7) extends substantially in the form of a circle.

8. The item (1) of claim 7, wherein the ridge (7) has a diameter of 60 to 200 pm.

9. The item (1) of any one of the preceding claims, wherein the item (1) is or comprises a sheet that has a thickness (t2) of 1 mm or less, preferably 0,5 mm or less and / or wherein the item (1) is a shim.

10. The item (1) of any one of the preceding claims, wherein the surface of the item (1) that is provided with the plurality of micromechanical locking units is configured to establish micromechanical lock between the surface of the item (1) and a mating surface of another item (10) by the ridges (7) being pressed into the mating surface, preferably with a surface pressure between 5 and 450 MPa.

11. The item (1) of any one of the preceding claims, wherein the micromechanical locking units are arranged on the surface in a pattern that results in a substantially higher coefficient of static friction in a first direction (dl) compared to an orthogonal second direction (d2) .

12. The item (1) of claim 11, wherein the pattern comprises a plurality of straight arrays (9) of micromechanical locking units (40) that are arranged substantially parallel with the second direction (d2) .

13. The item (1) of any one of claims 1 to 12, wherein the number of micromechanical locking units per unit of surface area is selected to obtain a specific magnitude for the coefficient of static friction.

14. The item (1) of any one of claims 1 to 21, wherein the micromechanical locking unit is formed in a smooth surface of the steel substrate (2) by applying a number of laser pulses.

15. The item (1) claims 14 when dependent from claim 5, wherein the hard layer or coating (9) is deposited subsequently on the steel substrate, preferably by chromium carbide diffusion coating.

16. The item (1) of any one of claims 1 to 15, wherein the ridge (7) is a sharp-crested ridge.

17. The item (1) of any one of claims 5 to 16, wherein the hard layer (9) is a hard chromium carbide layer, preferably a hard chromium carbide layer formed by diffusion coating on the steel substrate (2) .

18. A method of manufacturing an object having a steel substrate (2) with a surface (3) provided with a plurality of micromechanical locking units for creating a micromechanical lock with another object when the micromechanical lockingunits are pressed into a surface of another object, the method comprising : a) applying a laser pulse a number of times with a given intensity to the same position on the surface (3) to create a dimple (6) surrounded by a ridge (7) , b) adjusting the number of times and / or the intensity of the laser pulse to obtain a dimple (6) with an angle of the surface of the dimple (6) medially between the bottom of the dimple (6) and the top of the ridge (7) being between 30 and 75° relative to the surface (3) , preferably between 45 and 75°, and c) repeating a) and b) at a plurality of other positions on the surface (3) .

19. The method of claim 18, wherein c) is performed at positions on the surface (3) to obtain a spacing between the centers of the dimples (6) between 60 and 200 pm.

20. The method of claim 18 or 19, wherein the number of times and / or the intensity of the laser pulse in b) is adjusted to obtain a dimple (6) with a depth d) measured from the bottom of a dimple (6) to the top of the ridge (7) between 15 and 100 pm, preferably between 3040 and 100 pm.

21. The method of any one of claims 18 to 20, wherein said steel has a tensile strength between 420 and 1630 N / mm2, preferably between 600 and 1200 N / mm2.

22. The method of any one of claims 18 to 21, comprising applying a hard layer or coating (9) to the surface (3) after the dimples (6) have been created, the hard layer (9) preferably having a substantially uniform thickness (tl) .23 . The method of claim 22 , wherein the thicknes s ( tl ) is between 3 and 20 pm, preferably between 5 and 10 pm .24 . A method of providing controlled static friction between an item and another item that are in contact through a surface of the item and a surface of the other item, the method comprising : providing the surface of the item with a plurality of micromechanical locking units that each comprise : a peak comprising a core peak formed by a steel substrate of the item, the core peak being covered by the hard layer, and / or a ridge comprising a core ridge formed by the steel substrate of the item, the core ridge being covered by the hard layer, arranging the micromechanical locking units non-evenly distributed over the surface to obtain a directionally noneven coef ficient of static friction, and / or selecting the number of micromechanical locking units per unit of surface area to obtain a speci fic magnitude for the coef ficient of static friction, and / or arranging the micromechanical locking units in curved or straight arrays for obtaining a direction-speci fic largest coef ficient of static friction .25 . The method of claim 24 , wherein the coef ficient of static friction is between 0 , 8 and 1 , 2 .26 . The method of claims 24 or 26 , comprising forming each micromechanical locking unit on a smooth surface of the steel substrate by applying a laser pulse , and preferably depositing the hard layer subsequently on the steel substrate , preferably by chromium carbide di f fusion coating .26 . The method of any one of claims 24 to 27 , comprising establishing a micromechanical lock between the surface of the item and the surface of the other item by the peaks and / or ridges being pressed into the other surface .27 . A method of preventing displacement between a first steel item and a second steel item, the first item has a first contact surface and the second item has a second contact surface , the method comprising : providing the first contact surface with dimples with each dimple being surrounded by a ridge using a pulsed laser to form a micromechanical locking unit , with the dimples spaced from one another at a distance between 60 to 200 pm, the first contact surface being a hardened steel surface due to the first steel item being a hardened steel item or due to the first steel item being a non-hardened steel item and the method comprising hardening the first contact surface by applying a hard layer after providing the first contact surface against with dimples , pressing the first contact surface onto the second contact surface with or without a lubricant therebetween with a first force thereby preventing displacement between the first steel item and the second steel item when a second force urging displacement between the first steel item and the second steelitem in a direction along the first contact surface until the second force exceeds at least 80% of the first force .28 . The method of claim 27 , comprising adj usting the power applied by the pulsed laser for each dimple to the first contact surface to obtain a dimple diameter between 35 and 65 pm .29 . The method of claims 27 or 28 , comprising adj usting the power applied by the pulsed laser for each dimple to the first contact surface to obtain a ridge height between 15 and 30 pm .30 . The method of any one of claims 27 to 29 , comprising applying the dimples to the first contact service in a hexagonal pattern .31 . An item comprising an outer surface , the outer surface having at least a first contact surface formed by a steel substrate , the first contact surface having dimples with each dimple being surrounded by a ridge to form a micromechanical locking unit for providing the first contact surface with a coef ficient of static friction of the contact surface of atleast 0,78 regardless of the presence of lubricant on the first surface, the steel substrate being a hardened steel substrate or a non-hardened steel substrate with a hard layer thereon, the dimples being spaced from one another at a distance between 60 to 200 pm and a dimple diameter between 35 and 65 pm.

32. The item of claim 31, wherein the ridge height is between 15 and 30pm.

33. The item of claim 32 or 33, wherein the number of micromechanical locking units per unit of surface area is selected to obtain a specific magnitude for the coefficient of static friction.

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