Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25F—PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
  • C25F5/00—Electrolytic stripping of metallic layers or coatings
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25F—PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
  • C25F3/00—Electrolytic etching or polishing
  • C25F3/02—Etching
  • C25F3/06—Etching of iron or steel
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25F—PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
  • C25F7/00—Constructional parts, or assemblies thereof, of cells for electrolytic removal of material from objects; Servicing or operating

Definitions

• 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.
• 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 may be present as a single layer or as a multilayer, depending on the application of the tool, 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 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 in the production Because of their chemical resistance, they are easier to decoat than tungsten carbide tools.
• the stripping processes are subdivided into groups of different hard material layers, a first group comprising Ti and Al based layers on carbide tools and high speed steel tools, e.g. As TiN, TiCN, TiAIN, ⁇ , TiAIN / 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 ⁇ thick, monoblock hard material layer between 4 - 24 h and is thus very long.
• the consumption of chemicals which must be constantly renewed during these very long stripping times, is very high.
• complex layer systems such as AITiCrN this method fails. A stripping is no longer possible.
• a wet-chemical removal of hard coatings is also carried out using complex-composed hydrogen peroxide solutions, but without application of protective stress on the tool, but at elevated temperature.
• the stripping time is based on a 2 ⁇ 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, AICrN.
• 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 is low here and the stripping times of a 2 ⁇ m thick hard material layer, 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, AITiCrN. For these highly complex hard coating systems, no chemical removal options 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 an electrolyte, has a complex basic peroxide solution.
• the chemicals are quickly consumed during stripping and thus the effort is very high.
• the process fails here.
• Further decoating processes which are accessible on the market also work in the wet-chemical field and showed good results with respect to the attackability of the carbide tool in the hard-material layer systems of FIG. 1. and 2nd group.
• the stripping time was also unreasonably high.
• a method for stripping hard metal tools is known from WO 99/54528 A1, which enables the blasting off of a hard material layer from the hard metal tool.
• 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 allows the first and second groups to disperse in less than 30 minutes. speaks.
• the disadvantage here is the need for a mechanical aftertreatment of the tungsten oxide layer formed.
• a method which removes surface areas by means of pulsed current from components.
• 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 MCrAIY, where M stands for an element from the group consisting of iron, cobalt or nickel.
• M stands for an element from the group consisting of iron, cobalt or nickel.
• 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 nevertheless can dispose of hard material layers of the second group of cemented carbide and high speed steel tools, and hard material layers of the third Group that can not be removed chemically, or only partially removed, can quickly and easily decoat 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.
• the workpiece in particular in the area in which there is no ceramic layer, is spared from chemical attack.
• this becomes very thin adhesion-promoting layer removed, namely - as is well known and customary - with peroxide solutions under protective voltage on the tool.
• the process according to the present invention will lead to rapid stripping times, but the hard metal is attacked here and must be aftertreated by mechanical methods, such as regrinding, polishing or microblasting.
• 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 art at elevated temperature in order to remove discolorations which may occur during use of the novel process.
• the end point detection is carried out by measuring or determining the voltage required to reach a certain current, after observing a decrease 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 ,
• 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%.
• 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%.
• the voltage source in the case of a basic electrolyte, it is advantageous for the voltage source to have a current of 50 A to 200 A, preferably 80 A to 150 A and most preferably 90 A to 15 A, current-controlled pulsed, preferably unipolar and most preferably unipolar with a rectangular pulse shape at 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%.
• a current of 50 A to 200 A preferably 80 A to 150 A and most preferably 90 A to 15 A
• current-controlled pulsed preferably unipolar and most preferably unipolar with a rectangular pulse shape at 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 contacting 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 is connected via electrical con can be contacted, a plastic plug 60 which protects the workpiece elsewhere from chemical attack.
• 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.
• FIG. 1 shows a schematic representation of the arrangement for carrying out the method according to a first exemplary embodiment of the invention with a holder for a multiplicity of workpieces;
• Figure 2 is a perspective view of a holder for receiving a plurality of workpieces, in this case from Schaftttechnikmaschinees, for positioning in the electrolyte.
• FIG. 3 is a detailed representation of the functional elements of FIG.
• Figure 4 is a view from the side of the holder according to Figures 2 and 3; a schematic representation of the arrangement for carrying out the method according to a second embodiment of the invention;
• FIG. 5 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 of Figure 5; a detailed representation of the functional elements of Figure 6;
• a perspective view, namely a photograph of the holder according to Figure 2 to 4, are used in the shaft tools;
• a representation, namely a photograph of the holder according to Figure 2 to 4 are used in the shaft tools;
• Hard material layers of the first group and the third group can have a TiN adhesion-promoting layer with a layer thickness of less than 0.5 ⁇ between the tool and the actual hard material layer from the layer structure. It forms a transition phase to the actual functional hard material layer.
• 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 was also apparent from the experiments that if hard material layers do not have a TiN adhesion layer between carbide tool and hard material layer, they can be stripped off just as quickly by the same wet-chemical approach and with the aid of electrical pulses. 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.
• hard material layers of the second and third group can be stripped in a suitable wet chemical approach with the help of electrical pulses targeted to either the TiN adhesion layer or in the absence of such to the surface of Schnellarbeitsstahl- tool within a short time.
• 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.
• 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.
• both electrolytes are operated at room temperature.
• a uniformly positive current-pulsed signal is now induced until the EntSchichtung occurred.
• the decoating time is 2 ⁇ 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 (0 8 mm, coated length 40 mm) with coating of the layer type of the second group with a layer thickness of 3 ⁇ m, which is stripped in the basic electrolyte, is 10-1 1 A.
• the applied current in 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.
• 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 see electrolytes 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%.
• 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 TiN adhesive layer remaining on the tools is then stripped of a suitable wet-chemical process for the base material, ie high-speed steel or hard metal.
• a suitable wet-chemical process for the base material ie high-speed steel or hard metal.
• the TiN adhesion layer can be removed within 5 - 10 min. An attack of the carbide does not take place in this short time.
• the holder has the function of receiving shank tools of different diameters, contacting them while protecting the uncoated shaft surfaces from attack, and then decelerating 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 cover 55 with bore openings and seals for different plugs 54, which are preferably in turn provided with holes of different diameters.
• Base housing 52 and cover 55 and power supply rails 56 are coated with an insulator, which insulator material must be resistant to chemicals and must not be applied to the contact surfaces.
• the plugs 54 which are provided with bores of various diameters in order to accommodate different diameters of shank tools, are made of non-conductive materials which 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 ingress of chemicals between the stem and plug 54.
• a contact rail 57 is also shown, on which the tool 10 is, and a two-sided contact spring 58, wherein 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 shaft surface and / or a slight overlap between free shaft surface and electrolyte is present.
• a special design of a holder has the function, for example, to take hobs of different diameters, thereby contacting them and at the same time to protect the uncoated surfaces from attack, in order to then disassemble them in a pulsed process.
• the holder consists of a bottom plate 75, in which an insulating receptacle 74 is introduced and the male workpiece 10 protects against chemical attack and preferably the workpiece 10 holds upright.
• An electrical contact 76 for the workpiece serves as the 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 protects the workpiece 10 from chemical attack elsewhere.
• the cylinder 72, the insulating receptacle 74 and the insulating plug 60 can be exchanged to cover and contact the various sizes and shapes of the workpieces 10.
• the method for stripping shank tools is carried out in the exemplary embodiment described here-illustrated in FIG. 1-as follows: 1.
• the shank tools 10 to be stripped are inserted into the protective plugs matching the diameter and height and pressed into the holder 50.
• the holder with the shank tools 10 to be stripped is contacted with the positive pole of a current pulse generator 40.
• electrolytic bath 30 it has to be decided which electrolytic bath 30 to use, namely an acidic electrolyte for layers of the first group and a basic electrolyte for layers of the second and third group.
• the contacted holder 50 is placed in the selected electrolyte bath 30.
• Two steel electrodes 20 are 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.
• 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.
• the power supply is stopped every 20 to 30 seconds and the holder is checked for stripping with the shank tools.
• the EntSchichtung is finished depending on the composition of the hard material layer at 2 ⁇ layer thickness within 10 seconds to 30 minutes to the tool or the TiN adhesion layer.
• the TiN adhesive layer is then completely stripped off with a conventional wet-chemical approach.
• the stripping without TiN adhesion layer requires the same pulsed stripping time.
• a further chemical stripping is not necessary, but a mechanical aftertreatment takes place because of the attack of the substrate.
• the other hobbing process is provided in one exemplary embodiment for stripper milling, shown in FIG. 5:
• the hob 10 to be stripped is contacted with the positive pole of a current pulse generator 30 and placed in the holder according to FIGS. 6 and 7 and provided with a protective plug 60. 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.
• the contacted hob 10 is placed in the selected electrolyte bath 30. 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.
• Example 1 Example:
• the EntSchichtung is finished depending on the composition of the hard material layer at 2 ⁇ layer thickness within 1 to 10 minutes to the TiN adhesion layer.
• TiN adhesive layer is then completely stripped off with a conventional wet chemical approach.
• the stripping without TiN adhesion layer requires the same pulsed stripping time.
• a further chemical stripping is not necessary, but a mechanical aftertreatment due to the attack of the substrate.
• a carbide hob (d 470 mm) with a 7.2 ⁇ thick AITiN layer (layer type table: layer # 6), a Hurrbedeck harsh consisting of Al, Ti, N and existing TiN adhesion promoting layer was in a 12% nitric acid solution as Electrolyte immersed, with a pulsed current iconce Of 30 A with a frequency of 5Hz, a duty cycle of 98% stripped to the adhesive layer layer TiN.
• the ring-steel electrode had a distance to the HM tool of 1 .5 cm. The stripping time was 3 min.
• 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 the EntSchichtung were found.
• the ring-steel electrode had a distance to the HM tool of 1 .5 cm. The stripping time was 2 min.
• Example 6 Example 6:
• the TiN adhesion layer is dissolved in a peroxidic removal Under the influence of protective voltage on the shank tools, the bath is completely stripped.
• the stripping time here is about 10 to 15 minutes.
• the ring steel electrode was spaced from the high speed steel hob of 1 .0 cm.
• the stripping time was 1 1 min.
• the brownish discoloration which resulted from the pulsed stripping is removed in a peroxidic stripping bath at elevated temperature. The stay in the bath is about 5 minutes.

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• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Electrical Discharge Machining, Electrochemical Machining, And Combined Machining (AREA)
• Other Surface Treatments For Metallic Materials (AREA)

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• 2014
  • 2014-03-18 WO PCT/EP2014/055376 patent/WO2015139731A1/de not_active Ceased
  • 2014-03-18 EP EP14711234.6A patent/EP3119928B1/de active Active
  • 2014-03-18 KR KR1020167028952A patent/KR20170004970A/ko not_active Ceased
  • 2014-03-18 JP JP2017500129A patent/JP6440814B2/ja active Active
  • 2014-03-18 US US15/126,664 patent/US9879356B2/en active Active

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