DEVICE FOR REPRODUCTIVE USE OF TEST STANDS

Description

[0001] The present invention relates to subjecting test specimens to a defined stress with the aim of being able to draw conclusions about the quality of a coating of the test specimen from the reaction of the test specimen to this stress. State of the art

[0002] Many components consist of a relatively inexpensive base material whose surface is coated with a hard coating or other functional layer. The proper functioning of the component may then depend on the functional layer remaining intact. If the base material is coated with an adhesion promoter layer and the functional layer is applied to this adhesion promoter layer, failure of the adhesion promoter layer can also lead to the functional layer detaching.

[0003] During operation of the component, the aforementioned layers can be locally overloaded. It is an important quality characteristic for the layers whether such damage remains locally confined or whether it propagates further, for example through stress corrosion cracking, even after the overload has ended, and in extreme cases, even a brief local overload can ultimately lead to the layer's failure.

[0004] Therefore, DE 10 2017 220 946 A1 proposes a method by which a coating on a test specimen can be locally stressed in a defined and reproducible manner and the resulting damage to the coating can be evaluated.

[0005] KR 101 484 440 B1 concerns the application of a clearly recognizable and exact marking to a pipe for further processing.

[0006] JP H02 243204 A deals with planing the surface of a plastic pipe. Disclosure of the invention

[0007] Within the scope of the invention, a device for subjecting test specimens to a defined stress was developed. This device is specifically designed to subject a large number of nominally identical test specimens, generated during quality control in series production, to precisely identical stresses. If the resulting damage to the coatings of the components differs, it can be concluded, for example, that there are variations in the quality of the coatings.

[0008] The device is defined in independent claim 1.

[0009] The device comprises a guide with which the test specimens can be guided to a machining position in a defined and reproducible manner. For this purpose, the guide has an inner circumference whose shape corresponds to the shape of an outer circumference of the test specimens and whose size allows translational movement of the test specimens through the guide with only one degree of freedom to the machining position. The guide can, in particular, lead the specimens to the machining position in a straight line.

[0010] Any suitable mechanism can be used to propel the test specimens to the processing position. A particularly advantageous solution is to design the guide as a drop tube into which the test specimens can be thrown, accelerating them by gravity to a defined speed until they reach the processing position. This is especially cost-effective and reliable.

[0011] The device further includes engraving means. These engraving means are designed to exert a predetermined cutting force on the surface of a test specimen when it reaches the processing position. If this force is identical for all test specimens processed in a series of tests, the resulting damage to surface coatings is objectively comparable.

[0012] The engraving device comprises at least one engraving element and at least one spring element. The spring element drives the engraving element towards a rest position. A test specimen reaching the machining position deflects the engraving element from this rest position. In this state, the spring element presses the engraving element against the surface of the test specimen with a restoring force. Provided that the spring element operates in its elastic state, this restoring force is the same for all nominally identical test specimens. Thus, all test specimens are subjected to the same qualitative and quantitative stress.

[0013] The engraving element can, for example, be located within the cross-section of the guide in its rest position or at least project into this cross-section. For this purpose, the guide can, for example, have one or more recesses. The machining position is then the point where the test specimen comes into contact with the engraving medium. The stress applied to the test specimen can, in particular, be a scribing stress.

[0014] In a particularly advantageous embodiment, a region of the spring element designed to exert a cutting force functions as an engraving element. For example, one or more points can be applied to the spring element in this region. The spring element can also be coated, for example, with diamond paste or another substance containing solid abrasive particles.

[0015] The engraving element, which exerts a cutting force on the surface of the test specimen, is itself a wear part and must be replaced at regular intervals. To ensure that the stresses applied to the test specimens before and after replacement are identical, it is advantageous if engraving elements can be manufactured in a precisely reproducible manner. Spring elements, like diamond paste or points, are available as standardized products with consistently uniform properties, so that a replacement does not change the stress applied to the test specimens.

[0016] In a further particularly advantageous embodiment, the engraving means comprise at least one drive source that sets at least one engraving element into periodic motion. This periodic motion can, in particular, be, for example, a vibration or rotation. The periodic motion causes the engraving means to rub against the surface of a test specimen when the engraving element is in contact with the surface. By additionally utilizing the drive source, the engraving element can, in particular, be moved against the surface at a higher relative speed than the speed at which the test specimen moves along the guide. In this way, the stress on the surface can be intensified. This can be advantageous, for example, if a particularly resistant hard coating is applied to the surface.

[0017] In particular, at least one engraving element can be designed as a saw blade. Saw blades are available as standardized products, thus ensuring a continuous supply of engraving elements with consistent properties.

[0018] Alternatively, or in combination, at least one engraving element can comprise a metallic base body coated with particles harder than the base body material. For example, an engraving head can be used that is designed as a steel ball coated with diamond particles. Such engraving heads are also available as standardized accessories for engraving machines. The engraving head does not necessarily have to be rotated to exert a cutting force on the test specimen; such a force is also exerted when the test specimen merely passes by the engraving head. However, the force is more intense when the engraving head rotates axially.

[0019] As previously explained, the passage of a test specimen, particularly one falling through the guide, past one or more engraving elements can, by purely mechanical means, cause the engraving element to come into contact with the surface of the test specimen. However, this is not mandatory. In a further advantageous embodiment, the device comprises at least one sensor that emits a signal in response to a test specimen reaching the processing position. Furthermore, at least one drive is provided, which is configured to bring at least one engraving element into contact with the surface of this test specimen in response to this signal. In this way, the application of the cutting force can be decoupled from the transport of the test specimen to the processing position. The test specimen can therefore, for example, be stopped in the processing position and processed with the engraving element while stationary.

[0020] In a further particularly advantageous embodiment, at least one outlet for a gas is provided on the inner circumference of the guide, which pushes a test specimen through the guide as it moves towards the processing position. For example, a test specimen falling through a drop tube can push a column of air ahead of it, which can slow its movement. However, if, for example, the air can escape laterally from the drop tube, this braking effect is greatly reduced. In this way, the speed reached at the processing position during the fall becomes less dependent on the geometric shape of the test specimen. It is then easier to use one and the same device for several different types of test specimens.

[0021] In a further particularly advantageous embodiment, the guide extends beyond the machining position to an outlet opening. Additionally, at least one container is provided that can hold both a liquid corrosion medium and at least one test specimen exiting the outlet opening. The device is then particularly well suited for testing whether a coating on the test specimen is susceptible to stress corrosion cracking.

[0022] In stress corrosion cracking, the coating is attacked and further damaged by a corrosive medium, such as atmospheric humidity, starting from the point of the initial local overload. By immersing the test specimens in such a corrosive medium, the device can be used to test whether an initial local overload remains localized or leads to further damage through corrosion. It is advantageous that the test specimens are placed in the corrosive medium immediately after the application of the stress force, without any unnecessary delay. This prevents any potential local overload from becoming passivated against the attack of the corrosive medium in dry air.

[0023] The container can be designed to hold one or more test specimens. For comparability and reproducibility, it is not essential that all test specimens being compared are exposed to the corrosive medium for precisely the same duration. Rather, it is possible, for example, to collect test specimens in the container for 5 minutes and then allow the corrosive medium to act for a further 30 minutes. The main reason for this is that the eventual destruction of a coating, particularly in applications where a pressure-stressed functional layer is bonded to the base material via an adhesion promoter layer, is a three-stage process.

[0024] Starting with a local overload, the adhesion promoter layer is initially damaged by stress corrosion cracking. This process eventually comes to a halt because the damaged areas become impermeable to the corrosive medium. Thus, the corrosive medium eventually no longer has the opportunity to reach further, as yet undamaged, areas of the layer.

[0025] Stress corrosion cracking, however, leads to an increase in the stress difference between the functional layer and the adhesion promoter layer. This results in blistering, also known as "buckling." Pieces of the layer can break off, and / or the buckling can stabilize into sinusoidal or linear blisters resembling wormholes. Both of these processes, in turn, allow the corrosive medium to reach areas of the adhesion promoter layer that are not yet damaged. Thus, the cycle begins anew.

[0026] Therefore, if stress corrosion cracking has ceased because no previously undamaged areas can be reached, it makes no significant difference how long the test specimen remains exposed to the corrosion medium until further previously undamaged areas become accessible through buckling or breakout.

[0027] After exposure to the corrosive medium for a defined period, the total damage to the coating of the test specimen can be assessed using various methods, such as microscopy. For example, images from a microscope camera can be analyzed for damage by an employee or through digital image recognition. The images can then be fed to a trained classifier based on an artificial neural network. This classifier can be trained, for instance, to categorize the images into graded damage classes ranging from 1 (no to very minor damage) to 5 (complete destruction of the coating).

[0028] To further suppress the tendency towards passivation in dry air, a particularly advantageous embodiment provides a supply for an inert gas at least in the area of ​​the guide between the processing position and the outlet opening. This prevents passivation from skewing the final test result towards a lower overall coating damage and thus a better than appropriate rating.

[0029] In a further particularly advantageous embodiment, the engraving means are arranged in a chamber that surrounds an outer circumference of the guide. This chamber is divided into several segments that can be separated from one another by moving segments perpendicular to the axis of the guide.

[0030] The chamber protects, for example, the engraving materials from contaminants that could distort the impact force on the surface.

[0031] By providing sufficient wall thickness or material stiffness, it can also protect the mechanical structure of the engraving device from external forces, thus preventing, for example, the distortion of contact forces between an engraving element and the surface of the test specimen.

[0032] As explained previously, the engraving elements in particular are wear parts that need to be replaced regularly. Making the segments separable facilitates access to the engraving elements and thus also their replacement.

[0033] Further measures improving the invention are described in more detail below, together with a description of preferred embodiments of the invention, with reference to figures. Examples of implementation

[0034] It shows: Figure 1First embodiment of the device 1, designed for treating test specimens 2 during their fall through the guide 3; Figure 2 Second embodiment of the device 1, designed for treating test specimens 2 at rest at the processing position 4; Figure 3 Saw blades 51a ( Figure 3a ) and metallic substrates functionalized with particles 51c 51b ( Figure 3b ) as engraving elements 51; Figure 4 Chamber 12 around guide 3, subdivided into four segments 12a-12d.

[0035] Figure 1Figure 1 shows a first embodiment of the device 1 in a sectional drawing. A guide 3 for test specimens 2 has an outer circumference 3a, an inner circumference 3b, and a cross-section 3c. The shape of the inner circumference 3b of the guide 3 corresponds to the shape of the outer circumference 2a of the test specimens 2. The test specimens 2 can move through the guide 3 with only one degree of freedom along the top-to-bottom axis 3f of the guide 3 to the processing position 4 and further to the exit opening 3e from the guide 3. To prevent this movement of the test specimens 2 from being hindered by an air blockage, the guide 3 has outlets 3d for the air that each test specimen 2 pushes ahead of it in the guide 3.

[0036] At processing position 4, a predetermined cutting force is exerted on the surface of the test specimen 2 using engraving means 5. In the Figure 1In the illustrated example, the test specimen 2 is machined along its entire height. Two possible embodiments of engraving devices 5 are shown as examples.

[0037] To the left of guide 3, engraving devices 5 are shown as examples, which operate with auxiliary energy. An engraving element 51, designed here as an engraving head, is set in rotation by a drive source 53 using auxiliary energy, for example, electrical energy, and is moved into the in by means of a spring element 52. Figure 1 The engraving element 51 is pressed into the rest position shown, in which it projects into the cross-section 3c of the guide 3. When the test specimen 2 completely fills the cross-section 3c of the guide 3 at the processing position 4, the engraving element 51 is deflected from its rest position. The spring element 52 exerts a restoring force in the direction of the rest position. This restoring force presses the engraving element 51 against the surface of the test specimen 2.

[0038] To the right of the guide 3, engraving elements 5 are shown as examples, which operate without auxiliary energy. A spring element 52 is mounted with one end on the outside of the guide 3 and has a region at its free end which, by coating it with diamond paste 51d, has been functionalized for exerting a cutting force and can thus serve as an engraving element 51. This engraving element 51 also protrudes in its Figure 1 The engraving element 51 moves into the cross-section 3c of the guide 3 in the rest position shown and is deflected from the rest position when the test specimen 2 completely fills the cross-section 3c of the guide 3 at the processing position 4. The spring element 52 in turn exerts a restoring force in the direction of the rest position, and with this restoring force the engraving element 51 is pressed against the surface of the test specimen 2.

[0039] All engraving elements 5 are arranged in a chamber 12 surrounding the guide 3 to protect them from damage, contamination, and external forces. This chamber 12 has a feed 11 through which an inert gas can be introduced and displace the ambient air, at least at the processing position 4.

[0040] The guide 3 has an outlet opening 3e at its lower end, through which the test specimen 2 can be transferred into a container 9 containing a corrosion medium 10 after machining. In this way, a defined stress corrosion cracking process can be initiated starting from the damage introduced into the surface of the test specimen 2 by the engraving means 5. In this example, the container 9 is intended to hold only one test specimen 2. It is therefore located on a conveyor belt 9a, which can move another container 9 for the next test specimen 2 below the outlet opening 3e of the guide 3.

[0041] Figure 2 Figure 1 shows a second embodiment of device 1 in a sectional drawing. As in Figure 1 The axis 3f of guide 3 runs from top to bottom. In contrast to Figure 1Here, the test specimen is held at processing position 4 by gate 8. The engraving means 5, in this example, comprise an engraving element 51 designed as a saw blade 51a and a drive 7 with which this saw blade 51a can be brought into contact with the surface of the test specimen 2. This occurs when light 6b, which is emitted by the sensor 6 towards the mirror 6c and should actually be reflected back to the sensor 6 by this mirror 6c, is blocked by the test specimen 2. In this case, the sensor 6 sends a corresponding signal 6a to the drive 7. When the processing of the test specimen 2 is complete, gate 8 opens, and the test specimen 2 falls downwards out of the exit opening 3e of the guide 3.

[0042] A drive source 53 for rotation of the saw blade 51a is in Figure 2 Not shown for the sake of clarity.

[0043] Figure 3Figure 1 shows two examples of engraving elements 51 arranged symmetrically around a test specimen 2. The perspective here is a top view from the direction from which the test specimen 2 approached the processing position 4. The axis 3f of the Figure 3 The undrawn guide 3 is therefore perpendicular to the drawing plane.

[0044] Figure 3a Figure 51 shows four saw blades 51a as engraving elements 51. The saw blades 51a are circular and each rotates around an axis that is perpendicular to the respective saw blade 51a and parallel to the drawing plane.

[0045] Figure 3b Figure 1 shows four engraving elements 51, each comprising a metallic base body 51b and hard particles 51c arranged on it. These engraving elements 51 each rotate about an axis pointing away from the test specimen 2.

[0046] Figure 4Figure 1 shows a top view of chamber 12 composed of four segments 12a-12d. An opening in the guide 3 is left open so that test specimens 2 can be inserted into the guide 3. Engraving elements 51 are visible inside the chamber, each projecting into the cross-section 3c of the guide 3. As also in Figure 3 The axis 3f of guide 3 is perpendicular to the drawing plane.

Claims

1. Device (1) for applying a defined stress to test specimens (2), comprising • a guide (3) having an inner circumference (3b), the shape of which corresponds to the shape of an outer circumference (2a) of the test specimen (2) and the size of which permits a translational movement of the test specimen (2) to a machining position (4) through the guide (3) with only one degree of freedom, and ∘ engraving means (5) which are designed to exert a specified cutting action of force on the surface of this test specimen (2) in response to a test specimen (2) reaching the machining position (4), wherein the engraving means (5) comprise at least one engraving element (51) and at least one spring element (52), wherein the spring element (52) drives the engraving element (51) in the direction of an inoperative position and wherein a test specimen (2), which reaches the machining position (4), deflects the engraving element (51) out of this inoperative position.

2. Device (1) according to Claim 1, wherein the engraving element (51) is located within the cross section (3c) of the guide (3) or at least protrudes into this cross section (3c) in its inoperative position.

3. Device (1) according to either of Claims 1 and 2, wherein a region of the spring element (52) functionalized for exerting a cutting action of force acts as an engraving element (51).

4. Device (1) according to any of Claims 1 to 3, wherein the engraving means (5) comprise at least one drive source (53), which sets at least one engraving element (51) in periodic motion, wherein the periodic motion leads to the engraving element (51) rubbing against the surface of a test specimen (2) when the engraving element (51) is in contact with the surface.

5. Device (1) according to Claim 4, wherein at least one engraving element (51) is designed as a saw blade (51a).

6. Device (1) according to any of Claims 1 to 5, wherein at least one engraving element (51) comprises a metal main body (51b) which is studded with particles (51c) which are harder than the material of the main body (51b).

7. Device (1) according to any of Claims 1 to 6, further comprising at least one sensor (6), which emits a signal (6a) in response to a test specimen (2) reaching the machining position (4), and at least one drive (7), which is designed to bring at least one engraving element (51) into contact with the surface of this test specimen (2) in response to this signal (6a).

8. Device (1) according to any of Claims 1 to 7, wherein at least one outlet (3d) for a gas is provided on the inner circumference (3b) of the guide (3), the gas pushing a test specimen (2) through the guide (3) during the movement in the direction of the machining position (4).

9. Device (1) according to any of Claims 1 to 8, wherein the guide (3) continues up to an outlet opening (3e) on the other side of the machining position (4), and wherein at least one container (9) is additionally provided, which is capable of receiving both a liquid corrosion medium (10) and at least one test specimen (2) exiting from the outlet opening (3e).

10. Device (1) according to Claim 9, further comprising a feed (11) for an inert gas at least into the region of the guide (3) between the machining position (4) and the outlet opening (3e).

11. Device (1) according to any of Claims 1 to 10, wherein the engraving means (5) are arranged in a chamber (12) which surrounds an outer circumference (3a) of the guide (3), wherein this chamber (12) is divided into several segments (12a-12d), which can be separated from each other by a movement of segments (12a-12d) perpendicular to an axis (3f) of the guide (3).