Device and method for testing the adhesion of a coating in a cylinder bore

Abstract

Method for testing the adhesion of a coating (11) to an inner surface of a cylindrical bore (12) located in a substrate (10), comprising the steps - a test ring (1) is attached coaxially to the coating (11) in the cylinder bore (12), wherein the outer diameter of the test ring (1) corresponds to the diameter of the coated cylinder bore (12), - Applying a test force (F) to the test ring (1) Prüf ) in a direction axial to the longitudinal axis (A) of the cylinder bore (12), - Increasing the test force (F Prüf ), until the test ring (1) shears off from the substrate (10) to which the test ring is attached, with at least the section of the coating (11) being applied, and measuring the test force (F Prüf) comprehensive the step - Creating at least one annular cutout (6,6') in the coating (11) at least on the force-away side of the test ring (1) and optionally also on the force-facing side of the test ring (1).

Description

[0001] The invention relates to a method for testing the adhesion of a coating to an inner surface of a cylindrical bore located in a substrate and to a corresponding device for carrying out the method.

[0002] The adhesion of a coating applied to a substrate, for example a coating on a cylinder bore that has been roughened to improve adhesion (e.g., by high-pressure water jet or mechanical means), is a fundamental functional characteristic of the corresponding component. This adhesion should be appropriately verified both during process development and in series production testing.

[0003] Several methods already exist for testing the tensile strength of coatings. In the so-called "tubular coating tensile test," the tensile strength is tested within the coating plane, i.e., perpendicular to the surface normal. Two cylindrical test specimens are positioned so that their respective bases are in contact. The specimens are fixed in this position and coated, at least in the area of ​​contact, on their outer surface. The fixation is then released, so that the specimens are held together solely by the coating, and a tensile force is applied along the axis of rotational symmetry of the cylindrical specimens. The tensile force is increased until the coating fails in the contact area. This provides a measure of the tensile strength of the coating itself, which is not influenced by the properties of the substrate.

[0004] A test method for testing an internal coating with a concave curvature, as used in automotive engineering, particularly in cylinder liners of internal combustion engines, is known from DE 10 2009 032 817 A1. In this method, two hollow cylindrical test specimens are arranged with their corresponding base surfaces abutting each other and fixed by means of a holding element. The inner surface of the test specimens is coated in the area of ​​contact, after which the holding element is released. The tensile strength of the coating is tested by applying a tensile force in the direction of the axis of symmetry of the test specimens until the coating fails.

[0005] DE 10 2012 012 764 A1 discloses a method for testing the adhesion of a component coating, particularly for coated cylinder liners. According to the invention, for a coating adhesion test, a test specimen of a test tool with a surface provided with a scribable grain is placed flat onto the component coating in a test process and pressed down and moved with a predetermined test force exceeding an operational load, so that the coating is subjected to defined frictional and / or shear forces. During the test process, force monitoring is performed to detect a drop in the applied test force as a reaction to and for the detection of a drop / failure of the coating adhesion, and / or a fine inspection is carried out after the test process.

[0006] In the so-called adhesion pull-off test, a test specimen is bonded to the coating of a component under test, and then a tensile force is applied in the direction of a surface normal of the coated area until the bond between the coating and the substrate breaks down. DE 10 2011 120 559 A1 describes a device for carrying out such a procedure on a coated cylinder running surface. However, in this case, the coating is subjected to tensile stress. This stress does not correspond to the loads that actually occur in operation, where the coating is subjected to shear stress.

[0007] Based on this state of the art, the object of the present invention is to provide a function-oriented testing method with which extended statements can be made about the adhesion of the coating under the loads actually occurring in operation, going beyond tensile stress.

[0008] This problem is solved by a method having the features of claim 1 and the corresponding testing device having the features of claim 3.

[0009] Further developments of the items are described in the respective subclaims.

[0010] A method according to the invention for testing the adhesion of a coating applied to the inner surface of a cylindrical bore in a substrate comprises coaxially attaching a test ring to the coating in the cylindrical bore, wherein the outer diameter of the test ring corresponds to the diameter of the coated cylindrical bore. The test ring is subjected to a test force in a direction axial to the longitudinal axis of the cylindrical bore. The test force is increased until the test ring shears away from the substrate with the coating, i.e., with at least the portion of the coating to which the test ring is attached. The test force is then measured. In this way, the adhesion test is functionally oriented and uses a shear load similar to that encountered in actual operation.

[0011] To achieve the defined shearing of the test ring, along with the coating to which the test ring is attached, from the cylinder bore, an annular relief or indentation can be created in the coating on the side of the test ring opposite the force, either after or preferably before its attachment. The depth of the relief essentially corresponds to the thickness of the coating, but may optionally exceed it. Alternatively, an annular relief or indentation can also be provided on the side of the test ring opposite the force and created accordingly before or after the test ring is attached to the cylinder bore.

[0012] To achieve good adhesion of the test ring to the coating, the test ring can be attached to the coating by gluing or soldering.

[0013] Furthermore, the force application device is designed in such a way that a force is applied to the test ring without transverse forces.

[0014] For this purpose, the force application device in the test arrangement can have a centrally arranged ball or spherical element on the side of the punch facing away from the test ring.

[0015] These and other advantages are explained in the following description with reference to the accompanying figure. The reference to the figure in the description serves to facilitate understanding of the subject matter. The figure is merely a schematic representation of an embodiment of the invention and shows a side section view through a coated cylindrical bore with a test device according to the invention.

[0016] The device according to the invention relates to a method and a device for the function-oriented testing of the adhesion of a coating to a cylinder bore activated by high-pressure water jets, mechanical roughening, or similar processes. Coating adhesion is a fundamental functional characteristic and must be tested during process development and series production testing.

[0017] In the adhesion tests used so far, where a test stamp is glued to the coated surface and then pulled off while the pull-off force is measured, the coating is subjected to tensile stress. However, this stress does not correspond to the actual loads experienced during operation. In an engine, the coating is subjected to shear stress by the axial movement of the piston ring and by the rotation of the piston ring within the piston. Furthermore, the measurement results vary considerably due to the spot-based nature of the adhesion tests.

[0018] According to the invention, as in Fig. As outlined in Figure 1, a test ring 1 is applied to the coated substrate surface 10 in the cylinder bore 12 for functional testing of the coating 11. The test ring 1 has an outer diameter that corresponds to the diameter of the cylinder bore 12 with the coating 11, so that the test ring 1 can be mounted coaxially in the cylinder bore 12 against the coating 11. The test ring 1 can be attached to the coating 11 by means of an adhesive or soldered connection 5 or similar.

[0019] The test ring is then subjected to a test force F by a force application device. Prüf The test force F is applied in a direction axial to the longitudinal axis A of the cylinder bore 12, so that the coating 11 is subjected to shear stress at the point where the test ring 1 is attached. Prüf The force is increased until the test ring 1, together with the coating 11, shears off the substrate 10, whereby the test force F PrüfThe force is measured by the force application device, so that the force at which the test ring with coating is sheared off provides a function-oriented statement about the adhesive force of the coating on the cylinder wall, corresponding to the actual load in operation.

[0020] To determine the test force F Prüf To ensure that the force is transmitted evenly to the test ring 1, the force application device has a cylindrical plunger 2 with a diameter that approximately corresponds to the outer diameter of the test ring 1, so that the plunger 2 makes contact with the test ring 1 over its entire surface. As shown in Fig. As indicated in Figure 1, the diameter of the punch 2 can be slightly smaller than the outer diameter of the test ring 1 to allow the punch 2 to penetrate the cylinder bore 12 without friction.

[0021] The test force F PrüfThe force is applied without shear force, in this example by means of a centrally arranged spherical element 3 using a punch 2 on the test ring 1. In general, however, other elements for shear-force-free force application are also conceivable.

[0022] Applying the test force F Prüf as well as measuring the test force F Prüf This can be achieved, for example, with a press.

[0023] To prevent the coating 11 from shearing off with the test ring 1 when the corresponding test force F is reached. PrüfTo enable defined shearing, the coating 11 below the test ring 1, i.e., on the side opposite the force, is cut free, meaning an annular indentation 6 is created into which the section of the coating 11 connected to the test ring 1 can shear off. For further improvement, the coating can also be cut free above the test ring 1, i.e., on the side opposite the force; this indentation 6' also limits the shearing section of the coating 11 from above and thus precisely defines its area.

[0024] In the present example, the substrate 10 is a crankcase and the coating 11 is a thermal spray coating with which the cylinder bore 12 is lined. Known thermal spraying processes for producing a coating in a cylinder bore include, for example, LDS (arc wire spraying) or PTWA (plasma transferred wire arc).

[0025] With the device or method according to the invention, the adhesion of the coating can be carried out in an unprocessed state of the sprayed layer ("as sprayed"), but also in a rough-honed or rough-turned state or in the finished state of the coating, which advantageously provides a testing possibility of the actual functional layer as it will later be present in operation.

Claims

[1] Method for testing the adhesion of a coating (11) to an inner surface of a cylindrical bore (12) located in a substrate (10), comprising the steps - a test ring (1) is attached coaxially to the coating (11) in the cylinder bore (12), wherein the outer diameter of the test ring (1) corresponds to the diameter of the coated cylinder bore (12), - Applying a test force (F) to the test ring (1) Prüf ) in a direction axial to the longitudinal axis (A) of the cylinder bore (12), - Increasing the test force (F Prüf ), until the test ring (1) shears off from the substrate (10) to which the test ring is attached, with at least the section of the coating (11) being applied, and measuring the test force (F Prüf) comprehensive the step - Creating at least one annular cutout (6,6') in the coating (11) at least on the force-away side of the test ring (1) and optionally also on the force-facing side of the test ring (1). [2] Method according to claim 1, characterized by , that the attachment of the test ring (1) to the coating (11) in the cylinder bore (12) is carried out by means of gluing or soldering. [3] Device for carrying out the test method according to claim 1, characterized by , that the force application device has a centrally arranged spherical or cap element (3) on a side of a punch (2) facing away from a test ring (1), which provides the transverse force-free force application.

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