WO2012168222A1

WO2012168222A1 - Test method for coatings

Info

Publication number: WO2012168222A1
Application number: PCT/EP2012/060573
Authority: WO
Inventors: Markus Hoidis
Original assignee: Abb Research Ltd
Priority date: 2011-06-09
Filing date: 2012-06-05
Publication date: 2012-12-13

Abstract

The invention relates to a test method for testing the adhesion of a metal coating (110) on an object (100), comprising the steps of shooting dry ice at the metal coating (110) of the object (100) and checking if the coating (110) was damaged by the shooting.

Description

Test method for coatings

Field of the invention

The invention relates to a method for testing the adhesion of a metallic coating according to claim 1 and the use of a dry ice blasting device for testing the adhesion of a metallic coating on an object according to the independent claim.

State of the art

In electrical engineering mainly electrochemically deposited layers, for example made of silver are used in the field of electrical contacts. As a result, an improvement in the contact properties is achieved or the heat transfer improved. Metallic objects are mainly made of aluminum, aluminum alloys, copper or copper alloys as well as of steel with electroplated silver coatings. Depending on the base material, the silver coating does not occur directly, but one or more intermediate layers are applied first. Such silver plating is widespread at all Types of contacts to improve contactability, that is to increase resistance to oxidation and corrosion, increase electrical conductivity and allow higher operating temperature limits.

For highly stressed layers such as those required for sliding contacts, the adhesion or adhesion of the silver incl. Interlayer on the object is a key property to ensure reliable operation. It must be ensured that the silver adheres sufficiently reliably to the silvered object. Insufficient adhesion of the silver can result in high follow-up costs, which can result from costly replacement of components during assembly or, worse, during operation. Even malfunctions occurring during operation may be associated with high financial losses. There is a lot of effort to ensure the quality of silver coatings. Various methods are known and described for testing the adhesion of coatings, for example ISO 2819: 1980 generally describes the methods suitable for assessing the adhesion of electroplated coatings, while ISO 4521: 2008 describes test methods for evaluating silver coatings , In addition to the destructive character of most of the described test methods, these are sometimes not applicable in practice on series parts. For example, ISO 2819 describes the testing of silver plating by means of shot peening. Steel balls (0.4mm) are used and the required test plate must be fixed in a holder. As usual with blasting processes, for safety and environmental reasons it is not possible to blast against the environment, so the test must be carried out in a closed test chamber. Since silver coatings are made partly on objects having an extension of, for example, more than one cubic meter, a large enclosed space is required for such a test, even if only a small area, local silver coating is to be tested. In US 20020166328 AI an abrasive blasting technique for the treatment of surfaces is described in which water ice particles are blown from an extruder plant by means of a high pressure gas jet against the surface. In this way, the irradiated surface of the paint or coating can be freed, decontaminated, smoothed or deburred.

Another possibility is to stick an adhesive tape on the coating and then withdraw the tape from the object again. In this way it is only checked whether the adhesion of the coating on the object is better or worse than the adhesion of the adhesive tape to the coating. Such a test may only be of limited significance.

Yet another way to test coatings is the so-called oven test. In this case, the coated object is heated, which in case of poor adhesion of the coating due to different thermal expansion coefficients of the material of the object on the one hand and the coating on the other hand comes to blistering, which is optically detectable. The problem may be that due to the metallurgy of the object usually only low test temperatures are possible without causing damage to the coated component. The small allowable temperature differences cause correspondingly small differences in the dimensions so that it hardly leads in practice to show liability errors. Heating to, for example, 700 ° C would have metallurgical consequences for the material of the coated object with commonly used material.

Disclosure of the invention

There is a need for an easy-to-use, non-destructive, testable or effective method on the series part to verify that the adhesion of a coating, particularly an electrogalvanic silver coating, is sufficient. In general, it is an object of the invention to specify methods or devices with which an improved checking of a coating is possible.

The object is achieved by a method according to claim 1. Another aspect is the use of a blasting device for dry ice blasting to check the adhesion of a coating.

In typical embodiments, the metallic coating of the object is bombarded with dry ice and then checked to see if the coating has been damaged by the dry ice bombardment. Preferably, upon at least partial removal of the metallic coating by the bombardment, a determination is made that the adhesion of the metallic coating is insufficient. In experiments, it was found that a metallic coating usually dissolves or adheres almost completely. Therefore, the method offers the advantage that it is easy to check whether the adhesion of the coating is sufficient.

The method further offers the advantage that with a sufficient adhesion of the metallic coating no damage or change in the coating occurs, so that a non-destructive examination is possible. In addition, the blasting with dry ice is typically not abrasive so there is no reduction of the layer thickness by the test. Other benefits are that no Residues remain as dry ice is frozen carbon dioxide which evaporates after bombardment. Carbon dioxide is not toxic either.

In advantageous embodiments of the invention, therefore, the method is carried out in a so-called open test arrangement. In this case, "open test arrangement" means that the spray device for accelerating the dry ice and the object need not be housed in a confined space such as steel shot or sand blasting, if any, personal protective equipment is typically used be, additional individual protection plates can be used.

When using a dry ice blasting machine to test the adhesion of a metallic coating to an object, open arrangements are used in typical embodiments. This offers the advantage that even large objects, which only have locally a coating that has to be tested, can be checked by using a blasting device for dry ice.

Typically, in embodiments of the invention, it is checked whether the coating has been at least partially removed from the object by the bombardment. A check as to whether the coating has been removed is typically automated or semi-automated. For this purpose, optical sensors can be used, which check whether the coating has been at least partially removed by the bombardment. If it turns out that the coating has been at least partially removed, it is determined that the adhesion is insufficient. Optical sensors offer the advantage that verification can be automated.

In one aspect of the invention, the metallic coating is a coating which has been applied by electroplating. In embodiments, the test method is used for coatings which have been applied by the following galvanic methods. With galvanic coatings usually metallic layers of individual chemical elements are produced, examples are chromium, noble metal, nickel, and zinc layers. Furthermore, layer combinations, alloying, dispersion, conversion and anodizing layers as well as Galvano formation are galvanically possible. Embodiments of the invention are suitable for Galvanic coatings, as in the case of galvanic coatings in the case of insufficient adhesion, a partial flaking of the coating takes place.

Typically, the metallic coating has a thickness in the range of 0.1 to 300μιη, in particular 5-100μιη. An advantage of typical methods of embodiments is that review of coatings in a wide range of thicknesses is possible.

One aspect relates to checking the adhesion of coatings comprising silver. Typically, the coating comprises at least 90% silver. Other possible coating materials are silver alloys, copper or copper alloys, aluminum or aluminum alloys. In typical embodiments, the object is only partially coated with the coating. For such coated objects, the method offers particular advantages, since no completed device as in a steel shotgun is necessary. Furthermore, the entire component does not have to be tested as in an oven test, the test can be carried out locally. Methods of embodiments are faster to perform than oven tests with heating and cooling of a large component. Typically, less than 50%, in other embodiments, less than 30% of the object is coated with the metallic coating. Typically, metallic coatings are tested on objects which have a size of more than 0.2 μm more than 0.5 m, at least in an expansion direction.

The object typically consists at least substantially of metal or a metallic alloy. In the case of silver coatings on metallic objects, the method is suitable since the check as to whether the adhesion is sufficient can be made very simply by whether removal of the coating takes place by the bombardment or not. In typical embodiments, this comprises the material of which the object at least substantially consists, at least 90%> copper or at least 90%> aluminum. Typical embodiments are used to check coatings on objects consisting at least essentially of EN AC-Al Si 7 Mg 0.3 or EN AC-42100, EN AW-6060 or ALMgSiO, 5 or CW004A or Cu-ETP , In combination with a coating of silver can in this way objects in the form of high-performance Contacts or contact pieces are produced. With the method even large assemblies can be tested by only selectively bombarded the coated area. It is possible to selectively carry out random checks on selected areas or to adjust the test rate, ie the number or the size of the parts to be tested, as needed.

In typical embodiments, the object is part of a switching device for the high voltage range, in particular a generator switch or a gas-insulated switchgear. The object may in particular be an electrical contact piece for the high-voltage region, that is to say an electrical contact piece of a generator switch or a circuit breaker in a gas-insulated switchgear. The coating is then applied in particular or exclusively in a contact region of the object. This contact area must meet the highest electrical, thermal and mechanical loads. In particular, electrical contact pieces of a generator switch or contacts of a circuit breaker of a gas-insulated switchgear S ehalt act in the high voltage and high current areas strongest loads and must be safe in operation voltages of well over 70kV in a gas-insulated switchgear or currents of well over 250kA in a generator switch being able to lead. The term "high voltage range" is understood in particular to mean voltages which are above 1 kV, in particular above 15 kV or above 70 kV in the case of gas-insulated switchgear. For the high voltage and high current range embodiments offer special advantages, since only a reliable check of the coating ensures a faultless functioning of these electrically, thermally and mechanically highly stressed contacts and thus ensures reliable operation of a switching device in the high voltage and high current range.

In embodiments, only a portion of the object or a portion of the coating is bombarded with dry ice. Typically, unless the entire object is bombarded, however, the coated area is at least completely bombarded. In this way, it is possible with the least possible effort to check the coating. Typically, the dry ice is accelerated for the bombardment with compressed air. An acceleration of the dry ice with compressed air, in combination with the fact that dry ice consists only of carbon dioxide, means that no residues or toxic substances are introduced into the environment through the process. For the bombardment, the parameters are selected such that the dry ice strikes the coating with an energy below a certain energy threshold value, at which point the energy threshold value destroys the adhesion of the metallic coating. As a parameter, for example, the speed for the accelerated dry ice or the pressure of the air for accelerating the dry ice is set. Typical speeds for accelerated dry ice are between 50% and 100% of the speed of sound at 20 ° C and normal pressure. The air for accelerating is typically compressed to at least 2 bar and at most 10 bar before it is used to accelerate the dry ice. The bombardment is typically carried out with at least 5 cm or at least 10 cm distance or at most 50 cm or at most 20 cm distance. The volume flow is typically 10-100 kg / h of dry ice or 30-50 kg / h.

The dry ice consists at least substantially of carbon dioxide in typical embodiments. In this context, "essentially" means that the dry ice is pure or at least 99% or 99.95% carbon dioxide, so that there are no toxins.The dry ice typically has a temperature of less than -70 ° C or of less than -75 ° C. In embodiments, the dry ice has a temperature of more than -100 ° C., typically a temperature of more than -85 ° C. Some embodiments use dry ice in the temperature range between -78 ° C. and -79 ° C, so that dry ice can be used as a blasting medium in ambient conditions, thus enabling the use of dry ice with minimum energy input.

Typically, the dry ice for irradiation consists of at least 80% or at least 95% of particles or pellets having a maximum extension of at least 1 mm, more preferably at least 2 mm. In embodiments, the dry ice for irradiation consists of at least 80% or at least 95% of particles or pellets having a maximum expansion of not more than 20 mm, not more than 10 mm or not more than 5 mm. In typical embodiments, the dry ice for bombardment consists of at least 80%, or at least 95% of particles having a size of 2 to 4 mm. The particles or pellets are typically compressed mass which is molded under pressure or forced through an extruder plate.

Advantages of methods and uses of the invention are further that a quick review and effective review is possible. A selective review of specific areas, a random review of just a few areas, or a one-hundred-percent review will each provide benefits. The costs for carrying out typical processes are low; in particular, only dry ice is needed as consumable material. Furthermore, it is easy to adapt the blasting device to different coating situations, for example by varying the speed of movement of the nozzle through which the dry ice exits, the distance of the nozzle to the object and the mass flow of the dry ice. A non-destructive test is achieved, at least in cases where the adhesion is sufficient. Furthermore, checks can be carried out independently of the geometry of the object, whereby automation is also possible. Typically, the process is carried out at temperatures between 10 ° C and 30 ° C, preferably room temperature, that is between 16 ° C and 24 ° C. Dry ice has the advantage that it evaporates without residue at room temperature.

Another aspect relates to the use of a jet device, which is suitable for carrying out the above-mentioned method for checking the adhesion of a coating, in particular a galvanically applied metallic coating, in particular silver.

Brief description of the drawings

In the drawings, typical embodiments of the invention are shown and will be described in more detail in the following description. The drawings show: Fig. 1 shows schematically an arrangement for carrying out a method according to the invention; and

Fig. 2 shows in a schematic flow diagram the sequence of a typical embodiment of the invention.

Description of preferred embodiments

In Fig. 1 a preferred arrangement for carrying out typical methods of the invention is shown. An object 100 has a nose-shaped formation, which is partially provided with a coating 110 of silver. The method is to check the adhesion of the coating 110 of silver on the object 100, which consists of a metal alloy.

The coating 110 was applied galvanically. The object 100 essentially comprises aluminum, wherein the silver coating 110 is intended to ensure improved contact in the area of the nose-shaped formation of the object 100. The dimensions of the object 100 are about 1 m along the edge lengths.

To carry out the method, a blasting device 120 is provided for dry ice, which is adapted to apply in the direction of an arrow 130, which indicates the beam direction, accelerated by compressed air dry ice on the silver coating 110. The dry ice consists at least almost completely of carbon dioxide. In this case, "at least almost completely" means that only minor impurities can be contained.The dry ice pellets or pellets are accelerated by means of compressed air and thus poured onto the coating 110.

The jet device 120 is movable, typically at, along arrows 140 which indicate the direction of movement of the jet device 120 a robotic arm with at least six degrees of freedom. In this way it is possible to bombard even complex geometries. Since the coating 110 of electroplated silver runs around the corner on the object 100, a complete testing of the coating 110 requires movement and rotation of the blasting device 120. This is possible with a robot with six degrees of freedom. Other options are gantry robots or fixed directions of movement, for example using rails with routine checking of recurring object geometries.

The control of the jet device 120 is performed by a control unit 150, which is connected to the jet device 120. The control unit 150 controls the movements of the jet device 120 along the arrows 140 as well as the bombardment with the dry ice beads themselves. Via the control device 150, pressure, distance, volume and mass flow of the dry ice can be determined.

2, a typical method of the invention is illustrated by way of example with reference to a schematic flow diagram. The method of FIG. 2 may typically be performed with a dry ice blasting apparatus as discussed in connection with FIG.

The method starts in a step 200. In step 210, the object is positioned. Further, the blasting apparatus (reference numeral 120 of Fig. 1) becomes a start position. Furthermore, the control unit 150 is initialized, that is programmed with the parameters for the bombardment. For example, a parameter may relate to pressure, distance, volume, or mass flow.

In step 220, the bombardment of the object 100 with dry ice takes place. Subsequently, it is checked in step 230 with an optical test whether the coating has been at least partially removed by the bombardment. The optical test is preferably carried out automatically with an optoelectronic sensor. In this way, the process can be automated.

Depending on what the optical test has revealed in step 230, the method branches to either step 250 or step 260. If it is determined in step 240 that at least a portion of the coating is affected by the bombardment has been solved, it is determined in step 250 that the adhesion of the coating was qualitatively insufficient. If, on the other hand, it is determined in step 240 that the coating still completely adheres to the object 100, it is determined in step 260 that the adhesion of the coating is sufficient. The object 100 is then released for further processing or use. The method ends in a step 270.

The scope of the invention is not limited to the embodiments described above, but rather is determined by the scope of the claims. The embodiments are not limiting to the scope of the invention, but are merely for the description of advantageous embodiments, in addition to the described embodiments, other embodiments may be useful and advantageous.

LIST OF REFERENCE NUMBERS

100 object

110 coating

120 blasting device

130 firing direction

140 direction of movement

150 control unit

200 to 270 process steps

Claims

claims

A test method for verifying the adhesion of a metallic coating (110) to an object (100), comprising the steps of:

- Shooting the metallic coating (110) of the object (100) with

dry ice; and

- Check if the coating (110) has been damaged by the bombardment.

2. Testveifiihren according to claim 1, characterized in that it is tested in the review, whether the coating (110) has been at least partially removed from the object (100) by the bombardment.

3. Test method according to claim 2, characterized in that an optical sensor is used for checking,

4. Test method according to claim 1 or 2, characterized in that the

Coating (110) is applied galvanically.

5. Test method according to one of the preceding claims, characterized in that the coating (110) comprises silver or at least substantially consists of silver.

6. Test method according to one of the preceding claims, characterized in that the object (100) is only partially coated with the coating (110).

7. Test method according to one of the preceding claims, characterized in that the object (100) has at least 90% copper or at least 90% aluminum.

8. Testverfahien according to any one of the preceding claims, characterized in that the object (100) is an electrical contact piece of a switching device for the

High voltage range, in particular a generator switch or a gas-insulated switchgear is.

9. Test method according to claim 8, characterized in that the coating is applied in a contact region of the object (100).

10. Test method according to one of the preceding claims, characterized in that the dry ice is accelerated for the bombardment with compressed air.

11. Test method according to one of the preceding claims, characterized in that the dry ice consists at least substantially of carbon dioxide.

12. Test method according to one of the preceding claims, characterized in that the dry ice has a temperature of less than -77 ° C and / or a temperature of more than -79 ° C.

13. Test method according to one of the preceding claims, characterized in that the dry ice used for the bombardment consists of at least 80% pellets having a maximum extension of at least 1 mm and / or having a maximum extension of at most 10 mm.

14. Test method according to one of the preceding claims, characterized in that for firing parameters are selected such that the dry ice strikes with an energy below an energy threshold, from which the adhesion of the metallic coating (110) is destroyed,

A test method according to claim 14, characterized in that as a parameter the accelerated dry ice speeds are between 50% and 100% of the

Sound velocity at 20 ° C and normal pressure are selected,

Use of a dry ice blasting apparatus (120) for testing the adhesion of a metallic coating (110) to an object (100).

17. Use according to claim 16, characterized in that the blasting device (120) is suitable for a test method according to one of claims 1 to 10.