DE202014010831U1 - Holder for stripping ceramic hard coatings of steel and carbide substrates - Google Patents

Abstract

Holder for stripping ceramic hard material layers on workpieces (10) having uncoated surfaces on a plurality of subsections, in particular of milling cutters, having a bottom plate (75) in which an insulating receptacle protects the workpiece to be picked up from chemical attack, electrical contact (76) for power supply and as an anode, a conductive cylinder (72), which is provided as a cathode and which can be contacted via electrical contacts, preferably a busbar (56), and an insulating plug (60), which supports the workpiece (10). Protected elsewhere from chemical attack.

Description

Technical area

The invention relates to a method for stripping ceramic hard coatings of steel and hard metal substrates, namely of steel and hard metal substrates, which have a ceramic hard material layer on a part of their surface. Furthermore, the invention relates to the method suitable mounts.

State of the art

Carbide tools are used in the tool industry, among other things, and usually consist of tungsten carbide grains and cobalt as a matrix. In order to achieve an improvement in the surface properties, these tools, depending on the application with a hard material layer, such. As titanium nitride or chromium nitride, coated by vacuum coating method. Hard coatings, depending on the application of the tool, may exist as a single layer or as a multilayer, and include at least one of the chemical elements Al, Ti, Cr, Si, which may be oxides, nitrides, carbides or mixed compounds, e.g. Carbonitrides acts. These hard coatings are also called ceramic layers.

Decoating the hard material layer, namely a ceramic layer, becomes necessary if the tool is to be reused after use and regrinding, or if a defective coating has to be removed from the tool. The difficulty with the stripping consists on the one hand in the different applied materials which are used in a hard material layer or whether multilayers or single layers are present and on the other hand in the chemical instability of the cemented carbide per se. Tools made of high-speed steel are coated with the same hard-coat materials as carbide tools. However, they are cheaper to manufacture and, due to their chemical resistance, are easier to decoat than carbide tools.

The stripping processes are subdivided into groups of different layers of hard material, a first group comprising Ti and Al based on carbide tools and high speed steel tools, e.g. As TiN, TiCN, TiAlN, AlTiN, TiAlN / SiN, present as a monoblock layer, gradient layer or multilayer coating. A decoating method which is based on the wet-chemical removal of hard material layers using complexly composed hydrogen peroxide solutions is customary here, wherein typically the hard metal tool is protected by the application of a protective voltage. The decoating time is based on a 2 micron thick, monoblock hard material layer between 4-24 h and is thus very long. Similarly, the consumption of chemicals that need to be constantly renewed at these very long stripping times, very high. For complex layer systems, such as AlTiCrN, this method fails. A stripping is no longer possible.

For high speed steel tools, wet-chemical removal of hard coatings is also performed using complex-composed hydrogen peroxide solutions, but without application of protective stress on the tool, but at elevated temperature. The decoating time is based on a 2 μm thick monoblock hard material layer between 1-4 h.

A second group comprises Cr-based coatings on cemented carbide tools and high speed steel tools, e.g. B. CrN, AlCrN. A decoating method for both types of tools is customary here, which is based on the wet-chemical use of a mixture of permanganate solution and alkali. The consumption of chemicals here is low and the stripping times of a 2 micron thick layer of hard material, which is 1 hour, is relatively short.

A third group includes CrTi based coatings on cemented carbide tools and high speed steel tools, e.g. CrTiN, AlTiCrN. For these highly complex structured hard material layer systems, no chemical decoating possibilities on carbide tools are known. Such coated tools had to be stripped by mechanical methods and the effort is very high.

The stripping of high-speed steel tools is based on an electrochemical process, which as electrolytes has a complex composition of basic peroxide solution. The Chemicals are quickly consumed during stripping and thus the effort is very high. However, in some variants of the AlTiCrN hard-material layer, the method fails here.

Further decoating processes which are accessible on the market also work in the wet-chemical field and showed good results with regard to the vulnerability of the carbide tool in the hard material layer systems of groups 1 and 2. However, the stripping time was also unreasonably high. In the field of stripping the first and second group of high-speed steel tools, the known processes are partly similar to the above-mentioned method.

With the known stripping processes, in the case of the hard material layer systems of the third group, if they can be used at all, only very slow stripping times on carbide tools of considerably more than 24 h are to be accepted.

The table below lists the known hard coatings used in industry by group and adhesion-promoting layer. # layer type layer structure adhesive layer group 1 TiN TiN TiN 1 2 TiCN TiN + TiCN TiN 1 3 TiAlN TiAlN - 1 4 TiN + TiAlN TiN 1 5 AlTiN AlTiN - 1 6 TiN + AlTiN TiN 1 7 TiAlN / SiN TiN + TiAlN / SiN TiN 1 8th TiN + AlTiN / SiN TiN 1 9 TiN + AlTiN + TiAlN / SiN TiN 1 10 TiN + TiAlN / SiN + TiN / SiN TiN 1 11 TiAlN / SiN / Alcron TiN + TiAlN / SiN + AlCrON TiN ? 12 TiAlCrN / SiN TIN / CrN + TiAlN / SiN + AlTiCrN / SiN + TiN / SiN CrN o. TiN ? 13 TiN / CrN + TiAlCrN / SiN CrN o. TiN 3 14 TiN / CrN + AlTiCrN / SiN CrN o. TiN 3 15 CrN CrN CrN 2 16 AlCrNN AlCrNN - 2 17 CrN + AlCrN CrN 2 18 AlCrNN / TiAlN CrN + AlCrN + TiAlN CrN 2 19 AlCrNN / SiN CrN + AlCrN / SiN CrN 2 20 CrN + AlCrN + AlCrN / SiN CrN 2 21 CrTiN CrTiN CrN o. TiN 3 22 AlTiCrN AlTiCrN - 3 23 TiN / CrN + AlTiCrN CrN o. TiN 3 24 TiN / CrN + AlCrN + AlTiCrN CrN o. TiN 3 25 TiN / CrN + AlCrN + AlCrTiN CrN o.TiN 3

A method for stripping carbide tools is from WO 99/54528 A1 known, which allows the breaking off of a hard material layer of the hard metal tool. In this case, a tungsten oxide layer is electrolytically formed on the hard metal tool, which then has to be removed in a mechanical aftertreatment. This procedure is very fast, as it has the first stripping times and second group under 30 min. The disadvantage here is the need for a mechanical aftertreatment of the tungsten oxide layer formed.

From the WO 2003/085174 A2 For example, a method is known which removes surface areas by means of pulsed current from components. As a component, a turbine blade is specified by way of example, which consists of a nickel-cobalt superalloy. The layer to be removed is metallic, in particular of the composition MCrAlY, where M stands for an element from the group consisting of iron, cobalt or nickel. For a stripping of ceramic layers of workpieces, namely of steel and hard metal substrates, which have a ceramic hard material layer on a part of their surface, that is from the WO 2003/085174 A2 known methods in the form disclosed therein are not suitable.

Presentation of the invention

The object of the present invention is to propose a process for stripping which removes hard material layers of the first group more quickly and easily from cemented carbide tools but nonetheless removes layers of hard material of the second group of cemented carbide and high speed steel tools, and third group stratum materials, which can not yet be removed chemically, or only partially, can decoat quickly and easily on carbide and high-speed steel tools.

The object of the invention is achieved by a method according to claim 1. The measures of the invention initially have the consequence that for ceramic-coated hard metal workpieces and for workpieces with a ceramic hard material layer, a method is provided which removes the ceramic layer up to an adhesive layer or up to the hard metal layer. As a result, the workpiece, in particular in the area in which there is no ceramic layer, is spared from chemical attack. According to the present invention, at most only in a second step, this very thin primer layer is removed, namely - as is well known and customary - with peroxide solutions under protective stress on the tool.

Since the decoating time in the method step according to the present invention in the minute range and in the second, conventional step due to the very thin adhesive layer also in the minute range, no attack takes place on the hard metal. Thus, the disadvantage of the method from the WO 2003/085174 A2 resolved that the workpiece would be attacked in the area in which there is no surface layer to be decoated.

In the case of hard material layer systems of the first and third group without a TiN adhesion-promoting layer, the process according to the present invention will lead to rapid stripping times, but the hard metal will be attacked here and has to be aftertreated by mechanical methods, such as regrinding, polishing or microblasting. For high speed steel tools, the method according to the present invention is intended for ceramic hard coatings of the second and third groups. If an adhesion-promoting layer of TiN is present, it is stripped to this with the new process and removed in a second step with conventional methods, this very thin primer layer. This is done with peroxide solutions at elevated temperature. If there is no bonding layer of TiN, the process is completely stripped. However, in a further step, it is advisable to use a peroxidic stripping bath customary in the prior art under elevated temperature in order to remove discolorations which may arise during use of the novel process.

It is advantageous if the end point detection is carried out by measuring or determining the voltage required to reach a certain current, after observing a drop in the voltage, the voltage returns to its original value.

It is particularly advantageous if the workpieces are placed in a holder which is designed to accommodate workpieces of different diameters, to contact them and at the same time to protect the uncoated material surfaces against attack, in order to then dispose them in a pulsed process ,

Suitable and advantageous electrolytes are 2 to 50% mineral acids having a pH of 0.5 to -1.1, preferably 5 to 25% nitric acid having a pH of 0.09 to -0.7 and a molar concentration c = 0.81 mol / dm ^3rd to 4.54 and most preferably 8 to 15% nitric acid with a pH of -0.12 to -0.41 and a molar concentration c = 1.32 mol / dm ³ to 2.58 as acidic Electrolyte and a solution of 1 L of water, 10 ml to 500 ml of a 50% lye with a pH of 13.1 to 14.8 and a molar concentration c = 0.14 mol / dm ³ to 6.9, preferably 20 ml to 100 ml of a 50% Lye with a pH of 13.4 to 14.1 and a molar concentration c = 0.27 mol / dm ³ to 1.36 and most preferably 30 ml to 80 ml of a 50% KOH with a pH of 13.6 to 14.0 and a molar concentration c = 0.405 mol / dm ³ to 1.0 and 4 g to 55 g of an oxidizing agent, preferably 10 g to 35 g of a permanganate with a molar concentration c = 0.06 mol / dm ³ to 0.23 and most preferably 15 g to 25 g of potassium permanganate with a molar concentration c = 0.095 mol / dm ³ to 0.158 exposed as basic electrolyte.

In an acidic electrolyte, it is advantageous if the voltage source is a current of 10 A to 50 A, preferably 20 A to 40 A and most preferably 26 A to 35 A, current-controlled pulsed, preferably unipolar and most preferably unipolar with a rectangular pulse shape with a Frequency of 1 Hz to 40 Hz, preferably 2 Hz to 20 Hz and most preferably 3 Hz to 8 Hz and a duty cycle (duty cycle) of greater than 25%, preferably greater than 50% and most preferably greater than 75%.

In contrast, it is advantageous for a basic electrolyte, when the voltage source is a current of 50 A to 200 A, preferably 80 A to 150 A and most preferably 90 A to 115 A, current-controlled pulsed, preferably unipolar and most preferably unipolar with a rectangular pulse shape with a frequency of 5 Hz to 40 Hz, preferably 10 Hz to 35 Hz and most preferably 20 Hz to 30 Hz and a duty cycle (duty cycle) of less than 50%, preferably less than 35% and most preferably less than 25%.

An advantageous holder for carrying out the method for a plurality of workpieces has a conductive base housing with electrical contact and at least one power supply, a lid with bore openings and seals for different plugs, which are preferably in turn provided with holes of different diameters.

It is advantageous if the holder, the base housing and the cover and the power supply rails are coated with an electrically insulating layer, the insulator material is resistant to chemicals and not applied to the contact surfaces, the plug, which are provided with holes of different diameters to different To be able to accommodate diameters of workpieces, made of electrically non-conductive materials that are resistant to chemicals, preferably made of polyoxymethylene. The plugs may be equipped with O-rings to prevent the ingress of chemicals between the workpiece and the plug.

An advantageous holder for carrying out the method for workpieces which have uncoated surfaces on several subregions, in particular hobs, comprises an insulating base plate into which a steel receptacle with electrical contacts and power supply is inserted and serves as an anode and at the same time protects the male workpiece against chemical attack and preferably the workpiece holds upright. A conductive cylinder, which is provided as a cathode and which can be contacted via electrical contacts, a plastic plug 60 which protects the workpiece from chemical attack elsewhere. In this case, the cylinder, the plastic receptacle and the steel receptacle can be exchangeable designed to cover the different sizes and shapes of workpieces and can contact.

The above-mentioned as well as the claimed and described in the following embodiments, according to the invention to be used elements are subject to their size, shape design, material usage and their technical conception no special conditions of exception, so that the well-known in the respective field of application selection criteria can apply without restriction.

Brief description of the drawings

Further details, advantages and features of the subject matter of the present invention will become apparent from the following description of the accompanying drawings, in which - exemplary - inventive screens are explained. In the drawings shows:

1 a schematic representation of the arrangement for carrying out the method according to a first embodiment of the invention with a holder for a plurality of workpieces;

2 a perspective view of a holder for receiving a plurality of workpieces, in this case of shaft tool, for positioning in the electrolyte;

3 a detailed representation of the functional elements according to 2 ;

4 a view from the side of the bracket according 2 and 3 ;

5 a schematic representation of the arrangement for carrying out the method according to a second embodiment of the invention;

6 a perspective view of an alternative holder for receiving a workpiece, here a mill in which the surfaces to be stripped between two uncoated portions is, according to the arrangement 5 ;

7 a detailed representation of the functional elements according to 6 ;

8th a perspective view, namely a photograph of the holder according to 2 to 4 in which shank tools are used;

9 a representation, namely a photograph of the holder according to 2 to 4 in which shank tools are used;

10 a representation, namely a photograph of the shank tools according 8th and 9 , after the stripping;

11 a perspective view, namely a photograph of a workpiece for use in the holder according to 5 to 7 ; and

12 a representation of the voltage curve, which is used for the end point detection.

Ways to carry out the invention

Hard material layers of the first group and of the third group may have a TiN adhesion-promoting layer with a layer thickness of <0.5 μm between the tool and the actual hard material layer as a result of the layer structure. It forms a transition phase to the actual functional hard material layer.

It has been found that these hard material layers of the first and third groups in a suitable wet chemical approach with the help of electrical pulses targeted from the surface to the adhesive layer of TiN can be stripped in no time.

It has also been found from the experiments that if hard material layers do not have a TiN adhesion layer between carbide tool and hard material layer, the same wet-chemical approach and with the aid of electrical pulses can also be used to decoat just as quickly. This is especially true for the hard material layers of the second group. However, here the hard metal tool is attacked on the surface and must be post-treated.

Furthermore, it was found by experiments that hard coatings of the second and third group in a suitable wet chemical approach by means of electrical pulses targeted to either the TiN-adhesive layer or in the absence of such to the surface of the high-speed steel tool within a short time can be stripped.

Hard material layers of the first group can not be stripped by this method on high speed steel tools because the wet chemical approach used here destroys the high speed steel substrate.

In pulsed stripping, the coated tool serves as a positive pole (electrical anode), steel sheets or steel rings or other metallic objects as a negative pole (electric cathode). The electrolyte used depends on the ceramic constituents in the hard material layer.

Thus, two different electrolyte media are used for the classified hard material layers, namely for hard material layers of the first group, ie Ti, Al-based layers an acidic electrolyte, in the embodiment described here consisting of 10-15% nitric acid (c = 1.67-2.58 mol / l) and a pH of -0.23 pH to -0.41 pH and for hard material layers of the second and third group, so Cr and CrTi based layers a basic electrolyte, in the embodiment described here consisting of 1 L of water with 50 mL KOH 50th % (c = 0.67 mol / l) and 20.6 g of potassium permanganate (c = 0.13 mol / l) and a pH of the solution: from 13.5. In the embodiment described here, both electrolytes are operated at room temperature. By means of a pulse generator, a uniformly positive current-pulsed signal is now induced until the descaling has occurred. The decoating time is 2 microns thick hard material layer between 10 sec and 5 min., Depending on the hard material layer, electrolyte used and tool material used.

The applied current per tool is dependent on the coated surface, thus also on the diameter and geometry of the tool, on the type of ceramic coating and thus also on the electrolyte and can be determined specifically by means of experiments. The applied current for a carbide end mill (Ø = 8mm, coated length 40mm) with coating of the layer type of the second group with a layer thickness of 3 μm, which is stripped in the basic electrolyte is 10-11 A. The applied current at the same Carbide shank tool as described above, but coated with a layer type of the first G group, but which is stripped with the acidic electrolyte is 3 A. If several tools clamped in the holder, the tools behave like resistors in a parallel circuit.

For high speed steel tools, the same dependencies were found as for carbide tools. The applied current per high-speed steel tool with a diameter between 6 mm to 12 mm, which is stripped in the basic electrolyte, is 10-11 A. In the acidic electrolyte, a corresponding stripping is not possible because the tool would be destroyed.

The frequency of the pulse and its functional form are also critical parameters in this type of stripping. It is pulsed current controlled, preferably with a uniform geometry and most preferably with a rectangular bipolar pulse shape. The frequency of the pulse is in the basic electrolyte at 5 Hz to 40 Hz, preferably 10 Hz to 35 Hz and most preferably 20 Hz to 30 Hz and a duty cycle (duty cycle) of less than 50%, preferably less than 35% and most preferably less than 25 %. In the acidic electrolyte, the frequency is 1 Hz to 40 Hz, preferably 2 Hz to 20 Hz and most preferably 3 Hz to 8 Hz and a duty cycle (duty cycle) of greater than 50%, preferably greater than 70% and most preferably greater than 85%.

The remaining on the tools TiN adhesive layer is then stripped using a suitable for the base material, so high-speed steel or carbide, wet-chemical process. When using e.g. Hydrogen peroxide solutions, where the cemented carbide tool is protected by the application of a protective voltage, can remove the TiN adhesion layer within 5-10 minutes. An attack of the carbide does not take place in this short time.

If hard coating systems are stripped with the pulsed process, which do not have TiN adhesion layers, then the hard metal is attacked in the acidic as well as in the basic electrolyte. A subsequent treatment by regrinding or micro-blasting or polishing is then necessary. Also, a slight attack on high speed steel tools using the basic electrolyte may occur. However, this attack is minimal and causes a slight optical matting of the surface.

Uncoated surfaces, such as shafts of shank tools, are attacked by the pulsed process in the acidic and basic electrolytes and must therefore be covered by a suitable holder with protective plugs. For shank tools, a holder with protective plug for the pulsed decoating method was specially developed. However, the holder can also be used for z. For example, other chemical stripping methods where attacks on the cemented carbide can take place can be used. The fixture has the function of receiving shank tools of different diameters, contacting them while protecting the uncoated shank surfaces from attack, and then stripping them in a pulsed process.

The holder 50 for shank tools consists of a conductive base housing 52 with electrical contact and at least one power supply element, in the present embodiment, a power supply rail 56 , a lid 55 with bore holes and seals for different plugs 54 , which are preferably in turn provided with holes of different diameters. Headers 52 and lid 55 and power supply rails 56 be coated with an insulator, the insulator material must be resistant to chemicals and must not be applied to the contact surfaces. The plugs 54 , which are provided with holes of different diameters to accommodate different diameters of shank tools, are made of non-conductive materials that are resistant to chemicals. The plug height varies to cover different high uncoated shaft lengths. The plugs 54 are equipped with O-rings to prevent chemicals from entering the shaft and plug 54 to prevent. In 3 is also a contact rail 57 shown on the tool 10 stands, and a two-sided contact spring 58 , where the contact rail 57 serves as a clamping device for the contact spring.

A characteristic feature of using the holder in combination with the guide plugs is that after the pulsed stripping and subsequent removal of the TiN adhesion layer, a small ring of undeclared or slightly attacked surface remains on the shaft tool, as there is little overlap between plug and coated skirt surface and / or there is a slight overlap between free shaft surface and electrolyte.

A special embodiment of a holder has the function, e.g. To take hobs of different diameters, thereby contacting them while protecting the uncoated surfaces from attack, and then to disband them in a pulsed process.

The holder consists of a base plate 75 into which an insulating receptacle 74 is introduced and the male workpiece 10 protects against chemical attack and preferably the workpiece 10 standing firm. An electrical contact 76 for the workpiece serves as an anode, a conductive cylinder 72 which is provided as a cathode and which can be contacted via electrical contacts, and an insulating plug 60 which the workpiece 10 elsewhere protects against chemical attack. The cylinder 72 , the insulating picture 74 and the insulating plug 60 can be exchanged for the different sizes and shapes of the workpieces 10 cover and contact.

• 1. Die zu entschichtenden Schaftwerkzeuge 10 werden in die von Durchmesser und Höhe passenden Schutzstopfen gesteckt und in die Halterung 50 eingedrückt.
• 2. Die Halterung mit den zu entschichtenden Schaftwerkzeugen 10 wird mit dem Pluspol eines Strompulsgebers 40 kontaktiert.
• 3. Es muss entschieden werden, welches elektrolytische Bad 30 verwendet werden soll, nämlich ein saurer Elektrolyt für Schichten der ersten Gruppe und ein basischer Elektrolyt für Schichten der zweiten und dritten Gruppe.
• 4. Die kontaktierte Halterung 50 wird in das ausgewählte Elektrolytbad 30 gestellt.
• 5. Zwei Elektroden 20 aus Stahl werden beidseitig der Halterung platziert und diese mit dem negativen Pol des Strompulsgebers kontaktiert. Der Abstand der Stahlelektroden zum Schaftwerkzeug liegt bei 0.5 cm bis max. 2.5 cm.
• 6. Am Pulsgenerator 40 werden für Schaftwerkzeuge (mit Durchmesser 6 mm bis 12 mm) die Bedingungen eingestellt. Es wird dabei von 9 Schaftwerkzeugen pro Entschichtung ausgegangen. Die Halter im hier beschriebenen Ausführungsbeispiel sind für 9 Werkzeuge konzipiert.)

Schichten der 1. Gruppe: Schichten der 2. und 3. Gruppe: 1. Beispiel: Anzahl Schaftwerkzeuge 9 mit Durchmesser 12 mm Strom: 15 A Spannung (U_0Max): 40 V Stromgesteuert, Pulsform rechteckig Frequenz 5 Hz Symmetrie/Tastverhältnis: 98% 1. Beispiel: Anzahl Schaftwerkzeuge 9 mit Durchmesser 12 mm Strom: 100 A Spannung (U_0Max): 50 V Stromgesteuert, Pulsform rechteckig Frequenz 25 Hz Symmetrie/Tastverhältnis: 20% 2. Beispiel: Anzahl Schaftwerkzeuge 9 mit Durchmesser 6 mm Strom: 15 A Spannung (U_0Max): 40 V Stromgesteuert, Pulsform rechteckig Frequenz 5 Hz Symmetrie/Tastverhältnis: 98% 2. Beispiel: Anzahl Schaftwerkzeuge 9 mit Durchmesser 6 mm Strom: 100 A Spannung (U_0Max): 50 V Stromgesteuert, Pulsform rechteckig Frequenz 25 Hz Symmetrie/Tastverhältnis: 20%

• 7. Einschalten des Pulsgenerators 40. Die Entschichtung beginnt augenblicklich.
• 8. Bei Schaftwerkzeugen 10 der ersten Gruppe wird eine Endpunkterkennung verwendet. Bei Werkzeugen der ersten Gruppen wurde überraschenderweise ein Effekt erkannt, der als Endpunkterkennung dienen kann. Die elektrische Spannungsquelle generiert eine Funktion des Stroms über die Entschichtungszeit, dadurch wird ein ständig exakter stabiler Strom generiert. Da sich die Oberfläche der Werkzeuge im Entschichtungsprozess und somit auch der Widerstand verändert ist ein Absinken der Spannung festzustellen. Wenn die Titannitridschicht erreicht ist steigt der Widerstand so stark an bis die Spannung ihren Ursprünglichen Wert erreicht hat. Die Spannungskurve liegt hierbei im Bereich von ca. 2–10 V und es ist eine Spannungsdifferenz von ca. 2–4 V zu erwarten. Bei Werkzeugen der zweiten und dritten Gruppe wird alle 20 bis 30 sec. die Stromzufuhr gestoppt und die Halterung mit den Schaftwerkzeugen auf Entschichtung kontrolliert.
• 9. Die Entschichtung ist je nach Zusammensetzung der Hartstoffschicht bei 2 µm Schichtdicke innerhalb 10 sec bis 30 min bis auf das Werkzeug oder den TiN-Haftlayer beendet.

The method for stripping shank tools is described in the exemplary embodiment described here 1 - made as follows:

• 1. The shank tools to be stripped 10 are plugged into the matching diameter and height protective plugs and into the holder 50 pressed.
• 2. The holder with the shank tools to be stripped 10 is connected to the positive pole of a current pulser 40 contacted.
• 3. It must be decided which electrolytic bath 30 is to be used, namely an acidic electrolyte for layers of the first group and a basic electrolyte for layers of the second and third group.
• 4. The contacted holder 50 gets into the selected electrolyte bath 30 posed.
• 5. Two electrodes 20 Steel is placed on both sides of the bracket and contacted with the negative pole of the current pulser. The distance between the steel electrodes and the shaft tool is 0.5 cm to max. 2.5 cm.
• 6. At the pulse generator 40 For shank tools (diameter 6 mm to 12 mm), the conditions are set. It is assumed that 9 shank tools per stripping. The holders in the embodiment described here are designed for 9 tools.)

Layers of the 1st group: Layers of the 2nd and 3rd group: 1st example: Number of shank tools 9 with diameter 12 mm Current: 15 A Voltage (U _0max ): 40 V _{Current-controlled} , pulse shape rectangular Frequency 5 Hz Symmetry / duty cycle: 98% Example 1: Number shank tools 9 with a diameter of 12 mm Current: 100 A Voltage (U _{0 max):} 50 V current-controlled, pulse shape rectangular frequency 25 Hz symmetry / duty cycle: 20% Example 2: Number of shank tools 9 with diameter 6 mm Current: 15 A Voltage (U _0max ): 40 V _{Current-controlled} , pulse shape rectangular Frequency 5 Hz Symmetry / duty cycle: 98% Example 2: Number of shank tools 9 with diameter 6 mm Current: 100 A Voltage (U _0max ): 50 V _{Current-controlled} , pulse shape rectangular Frequency 25 Hz Symmetry / duty cycle: 20%

• 7. Switch on the pulse generator 40 , The stripping begins instantly.
• 8. For shank tools 10 the first group uses endpoint detection. In tools of the first groups, an effect was surprisingly detected that can serve as an end point detection. The electrical voltage source generates a function of the current over the stripping time, thereby generating a constantly accurate stable current. Since the surface of the tools in the decoating process and thus also the resistance is changed, a decrease in the voltage is observed. When the titanium nitride layer is reached, the resistance increases so much until the voltage has reached its original value. The voltage curve lies in the range of approx. 2-10 V and a voltage difference of approx. 2-4 V is to be expected. For tools of the second and third group, the power supply is stopped every 20 to 30 seconds and the holder is checked for stripping with the shank tools.
• 9. The stripping is finished depending on the composition of the hard material layer at 2 micron layer thickness within 10 sec to 30 min down to the tool or the TiN adhesion layer.

The TiN adhesive layer is then completely stripped off with a conventional wet chemical approach. Decoating without TiN adhesion layer requires the same pulsed decoating time. A further chemical stripping is not necessary, but there is a mechanical aftertreatment because of the attack of the substrate.

• 1. Der zu entschichtende Wälzfräser 10 wird mit dem Pluspol eines Strompulsgebers 30 kontaktiert und in die Halterung gemäss 6 und 7 gestellt und mit einem Schutzstopfen 60 versehen..
• 2. Es muss entschieden werden, welches elektrolytische Bad 30 verwendet werden soll, nämlich ein saurer Elektrolyt für Schichten der ersten Gruppe und ein basischer Elektrolyt für Schichten der zweiten und dritten Gruppe.
• 3. Der kontaktierte Wälzfräser 10 wird in das ausgewählte Elektrolytbad 30 gestellt. Mit Abstand von 0.5 cm bis max. 2,5 cm wird eine Ring-Stahl-Elektrode aus rostfreiem Stahl, welche vergoldet wurde, um den Wälzfräser mittig platziert. Diese Stahlelektrode wird mit dem negativen Pol des Pulsgenerators 30 verbunden.
• 4. Am Pulsgenerator 30 werden die Bedingungen für den Wälzfräser 10 eingestellt.

Schichten der 1. Gruppe: Schichten der 2. und 3. Gruppe: 1. Beispiel: Wälzfräser mit Durchmesser 47 mm; Höhe 1510 mm Strom: 30 A Spannung (U_0Max): 40 V Stromgesteuert, Pulsform rechteckig Frequenz 5 Hz Symmetrie/Tastverhältnis: 98% 1. Beispiel: Wälzfräser mit Durchmesser 47 mm; Höhe 1510 mm Strom: 30 A Spannung (U_0Max): 50 V Stromgesteuert, Pulsform rechteckig Frequenz 25 Hz Symmetrie/Tastverhältnis: 20% 2. Beispiel: Wälzfräser mit Durchmesser 33 mm; Höhe 110 mm Strom: 30 A Spannung (U_0Max): 40 V Stromgesteuert, Pulsform rechteckig Frequenz 5 Hz Symmetrie/Tastverhältnis: 98% 2. Beispiel: Wälzfräser mit Durchmesser 33 mm; Höhe 110 mm Strom: 30 A Spannung (U_0Max): 50 V Stromgesteuert, Pulsform rechteckig Frequenz 25 Hz Symmetrie/Tastverhältnis: 20%

• 5. Einschalten des Pulsgenerators 30. Die Entschichtung beginnt augenblicklich.
• 6. Alle 20 bis 30 sec. wird die Stromzufuhr gestoppt und die Halterung 50 mit dem Walzfräser 10 auf Entschichtung kontrolliert.
• 7. Die Entschichtung ist je nach Zusammensetzung der Hartstoffschicht bei 2 µm Schichtdicke innerhalb 1 min bis 10 min bis auf den TiN-Haftlayer beendet.

A somewhat different sequence is provided in one embodiment for stripping of hobs, shown in FIG 5 :

• 1. The hob to be stripped 10 is connected to the positive pole of a current pulser 30 contacted and in the holder according to 6 and 7 put and with a protective plug 60 Mistake..
• 2. It must be decided which electrolytic bath 30 is to be used, namely an acidic electrolyte for layers of the first group and a basic electrolyte for layers of the second and third group.
• 3. The contacted hob 10 gets into the selected electrolyte bath 30 posed. At a distance of 0.5 cm to max. 2.5 cm, a stainless steel ring-steel electrode, which has been gilded, is placed centered around the hob. This steel electrode is connected to the negative pole of the pulse generator 30 connected.
• 4. At the pulse generator 30 become the conditions for the hob 10 set.

Layers of the 1st group: Layers of the 2nd and 3rd group: 1st example: hob with a diameter of 47 mm; Height 1510 mm Current: 30 A Voltage (U _0max ): 40 V _{Current-controlled} , pulse shape rectangular Frequency 5 Hz Symmetry / duty cycle: 98% 1st example: hob with a diameter of 47 mm; Height 1510 mm Current: 30 A Voltage (U _0max ): 50 V _{Current-controlled} , pulse shape rectangular Frequency 25 Hz Symmetry / _{Duty Cycle} : 20% 2nd example: hob with a diameter of 33 mm; Height 110 mm Current: 30 A Voltage (U _0max ): 40 V _{Current-controlled} , pulse shape rectangular Frequency 5 Hz Symmetry / duty cycle: 98% 2nd example: hob with a diameter of 33 mm; Height 110 mm power: 30 A voltage (U _{0 max):} 50 V current-controlled, pulse shape rectangular frequency 25 Hz symmetry / duty cycle: 20%

• 5. Switch on the pulse generator 30 , The stripping begins instantly.
• 6. Every 20 to 30 sec., The power supply is stopped and the holder 50 with the milling cutter 10 checked for deletion.
• 7. The stripping is finished depending on the composition of the hard material layer at 2 micron layer thickness within 1 min to 10 min to the TiN adhesion layer.

The TiN adhesive layer is then completely stripped off with a conventional wet chemical approach. Decoating without TiN adhesion layer requires the same pulsed decoating time. Another chemical stripping is not necessary, but a mechanical aftertreatment because of the attack of the substrate.

Entschichtungsbeispiele:

Example 1:

9 tungsten carbide shank tools (twist drill d = 12 mm, K grade) with a 3.4 μm thick AlTiN layer (layer-type table: layer # 6) and existing TiN adhesion-promoting layer were incorporated in the specially developed holder with protective stopper and in a 10% Nitric acid solution immersed as an electrolyte, stripped in a pulsed current IFunktion of 15 A with a frequency of 5Hz, a duty cycle of 98% to the adhesive layer layer TiN. The steel electrodes had a distance of 1-2 cm from the carbide tool. The stripping period was 2 minutes and was completed with the endpoint detection. In a further process step, which corresponds to the prior art, the TiN adhesion layer is completely stripped off in a peroxidic de-coating bath under the action of protective voltage on the shank tools. The stripping time here is about 5 to 10 minutes. In the scanning electron microscope, no attacks on the tools after decoating were found.

Example 2:

A carbide hob (d = 470 mm) with a 7.2 μm AlTiN layer (layer type table: layer # 6), a coloring cover layer consisting of Al, Ti, N and TiN bonding layer present in a 12% nitric acid solution Electrolyte immersed, stripped in a pulsed current IFunktion of 30 A with a frequency of 5Hz, a duty cycle of 98% to the adhesive layer layer TiN. The ring-steel electrode had a distance of 1.5 cm from the carbide tool. The stripping time was 3 min.

Example 3:

9 carbide rods (d = 6 mm, K grade), each with a 3.7 μm thick TiAlN / SiN layer (layer-type table: layer # 7) and existing TiN adhesion-promoting layer were introduced in a specially developed holder with protective stopper and in a 12 Dipped% of nitric acid solution as an electrolyte, stripped in a pulsed current IFunktion of 15 A with a frequency of 5Hz, a duty cycle of 98% to the adhesive layer layer TiN. The steel electrodes had a distance of 1-2 cm from the carbide tool. The stripping period was 2 minutes and was completed with the endpoint detection.

Example 4:

9 tungsten carbide shank tools (d = 12 mm, K grade) with a 3.1 μm thick AlTiCrN layer (layer type table: layer # 23) and existing TiN adhesion-promoting layer were introduced in a specially developed holder with protective plugs and in a basic potassium permanganate solution with the following Composition 1L H ₂ O; 50 ml KOH (50%); 20.6 g of KMnO ₄ dipped, with a pulsed current IFunktion of 100 A with a frequency of 25Hz, a duty cycle of 20% stripped to the adhesive layer layer TiN. The steel electrodes had a distance of 1-2 cm from the carbide tool. The stripping time was 2 min. In a further process step, which corresponds to the prior art, the TiN adhesion layer is completely stripped off in a peroxidic de-coating bath under the action of protective voltage on the shank tools. The stripping time here is about 5 to 10 minutes. In the scanning electron microscope, no attacks on the tools after decoating were found.

Example 5:

A carbide hob (d = 470 mm) with a 5.7 μm thick AlTiCrN layer (layer type table: layer # 23) and existing TiN adhesion-promoting layer was dissolved in a basic potassium permanganate solution having the following composition: 1L H ₂ O; 50 ml KOH (50%); 20.6 g of KMnO ₄ immersed as an electrolyte, with a pulsed current IFunktion of 30 A with a frequency of 25Hz, a duty cycle of 20% stripped to the adhesive layer layer TiN. The ring-steel electrode had a distance of 1.5 cm from the carbide tool. The stripping time was 2 min.

Example 6:

9 carbide rods (d = 10 mm, K grade) each with a 3.4 micron thick AlTiCrN layer (layer type table: layer # 22) without TiN-adhesion promoting layer were introduced in a specially designed holder with protective stopper and in a basic potassium permanganate solution with the following Composition 1L H ₂ O; 50 ml KOH (50%); 20.6 g of KMnO ₄ immersed as an electrolyte, with a pulsed current IFunktion of 100 A with a frequency of 25Hz, a duty cycle of 20% completely stripped. The steel electrodes had a distance of 1-2 cm from the carbide tool. The stripping time was 2 min. The substrate was attacked. Subsequently, the attacked surface was wet-blasted at 1.5 bar. The surface was examined by SEM. You can see a roughening of the surface.

• • Beschichten mit AlTiCrN ohne TiN-Haftschicht
• • Entschichten mit gepulstem Verfahren / KMnO₄ basisch
• • Nassstrahlen mit F400A bei 1.2bar
• • Nachschärfen der Stirn (entschichtete Werkzeuge und ein Neuwerkzeug)
• • Kantenbehandlung in der Otec (KV1:2 / 25rpm / 5min)
• • Beschichten mit AlCrN
• • Otec: Polish walnut (Toppen)
• • Qualitätskontrolle: Alicona, SEM
• • Fehlmann: Frästest!

folgendes Resultat: Nach einmaligem Wiederaufbereiten von HM-Schaftfräsern ist eine sehr beachtliche Standmenge von rund 80% gegenüber dem Neuwerkzeug möglich. In a comparative milling test on the one hand with a carbide tool, which was stripped without TiN adhesive layer and then recoated and on the other hand, a new tool, which was only coated, showed the following workflow

• • Coating with AlTiCrN without TiN adhesive layer
• • Stripping with pulsed method / KMnO ₄ basic
• • Wet blasting with F400A at 1.2bar
• • sharpening the forehead (disassembled tools and a new tool)
• • Edge treatment in the Otec (KV1: 2 / 25rpm / 5min)
• • Coating with AlCrN
• • Otec: Polish walnut (Toppen)
• • Quality control: Alicona, SEM
• • Fehlmann: milling test!

the following result: After a single reprocessing of carbide end mills, a very considerable tool life of around 80% compared to the new tool is possible.

Example 7:

8 high-speed steel tools (d = 6 mm, standard) each with a 2.8 μm thick AlCrTiN layer (layer type table: layer # 25) with TiN adhesion-promoting layer were introduced in a specially developed holder with protective stopper and in a basic potassium permanganate solution having the following composition 1L H ₂ O; 50 ml KOH (50%); 20.6 g of KMnO ₄ is immersed as an electrolyte, stripped at a pulsed current IFunktion of 100 A with a frequency of 25 Hz, a duty cycle of 20%. The steel electrodes were spaced from the high speed steel tool by 1-2 cm. The stripping time was 1 min. In a further process step, which corresponds to the prior art, the TiN adhesion layer is completely stripped off in a peroxidic de-coating bath under the action of protective voltage on the shank tools. The stripping time here is about 10 to 15 minutes.

Example 8:

A high speed steel hob (d = 700 mm) with a 2.6 μm thick AlTiCrN layer without TiN coupling layer (layer type table: layer # 22) was dissolved in a basic potassium permanganate solution having the following composition: 1L H ₂ O; 50 ml KOH (50%); 20.6 g of KMnO ₄ immersed as an electrolyte, with a pulsed current IFunktion of 30 A with a frequency of 25Hz, a duty cycle of 20% stripped to the adhesive layer layer TiN. The ring steel electrode had a clearance of 1.0 cm from the high speed steel hob. The stripping time was 11 min. In a further process step, which corresponds to the prior art, the brownish discoloration that resulted from the pulsed stripping is removed in a peroxidic stripping bath at elevated temperature. The stay in the bath is about 5 minutes.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 99/54528 A1 [0012]
• WO 2003/085174 A2 [0013, 0013, 0016]

Claims (3)

Holder for stripping ceramic hard coatings on workpieces ( 10 ), which have uncoated surfaces on several subareas, in particular in the case of milling cutters, with a base plate ( 75 ), in which an insulating receptacle protects the workpiece to be picked up from chemical attack, an electrical contacting ( 76 ) for the power supply and as an anode, a conductive cylinder ( 72 ), which is provided as a cathode and which via electrical contacts, preferably a busbar ( 56 ), and an insulating plug ( 60 ), which the workpiece ( 10 ) elsewhere protects against chemical attack. Holder according to claim 1, characterized in that the cylinder ( 72 ), the insulating receptacle and the insulating plug ( 60 ) are designed to be interchangeable to accommodate different sizes and shapes of workpieces ( 10 ) and contact you. Holder according to claim 1 or 2, which is designed such that the workpiece to be stripped ( 10 ) is held upright by means of the insulating receptacle.

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