Method for separating layers from articles

Details Method for separating layers from articles Method for separating layers from articles

2000-04-24

2002-08-13

Gulakowski, Randy (Department: 1746)

Cleaning and liquid contact with solids

Processes

Metal base work, acid treating

C134S002000, C134S003000, C134S028000, C216S083000, C216S100000, C216S102000, C216S103000

Reexamination Certificate

active

06432219

ABSTRACT:

FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to a method for separating layers from articles provided with a hard material layer comprising a Ti compound, in an alkaline solution comprising
hydrogen peroxide
at least one base
at least one acid and/or a salt of an acid.
DD 228 977 describes a method for separating of TiN layers, in particular for separating TiN layers applied onto nickel substrates. The articles to be treated are therein placed into a hydrogen peroxide solution with a content of 35 Ma % peroxide for approximately 3 minutes at a temperature of approximately 70° C. to 80° C., subsequently rinsed in water, dried and then mull-wiped off. For the separating of TiAlN layers, this method is unsuitable, since TiAlN is poorly soluble in hydrogen peroxide solution.
According to GB 2 127 042 titanium nitride hard material layers on substrates of stainless steel are separated in aqueous nitric acid at temperatures above 70° C. The layer separation time for a 1 &mgr;m thick layer at 70° C. is approximately 50 hours. This extremely long layer separation time is of great disadvantage.
A method for the layer separation of hard material layers on different metal substrates is known from U.S. Pat. No. 4,746,369. The acidic layer separation bath is composed of hydrogen peroxide as oxidant and a phosphoric acid or nitric acid. Further, different surface-active materials are used. The very low pH value of the solution of less than 0.5 is of disadvantage for the application on high-speed steel-substrate-HSS (High Speed Steel).
DE 41 10 595 proposes to carry out hard material layer [separation] from tool surfaces in a hydrogen peroxide solution stabilized by complexing agents with potassium sodium tartrate ttrahydrate or sodium gluconate being used as the complexing agent. On the one hand, TiAlN layers are thereby not separated at a satisfactory rate and, on the other hand, the stabilizers used exhibit only a conditionally stabilizing effect.
From DE 41 01 843 a method is known for the layer separating of objects layered with hard material layers, wherein the objects are treated with a solution comprising tetrasodium diphosphate and hydrogen peroxide. Typical are hydrogen peroxide concentrations of 8 to 12%, the relatively high tetrasodium diphosphate concentration of 8 to 12%, high process temperature at boiling temperature, and high pH values of 8 to 12. If the solution is concentrated by evaporation—which occurs relatively rapidly at the high temperatures—phosphatization of the already delayered surface can occur. Titanium nitride and/or titanium nitride/carbide hard material layers are separated.
Lastly, from DE 43 39 502 methods are known which are specific to the layer material, for the layer separating of metal substrates, in particular also of hard metal substrates, which comprise hard material layers comprised of either TiN, TiCN or TiAlN or of layer systems comprising TiN/TiAlN.
Therein an alkaline solution with hydrogen peroxide, at least one base as well as at least one salt of mono- and dicarboxylic acids is used.
Depending on the layer to be separated, and while protecting the substrate, the solution bath is composed of a multiplicity of components, specific to the layer material.
SUMMARY OF THE INVENTION
Building on the last-cited method specific to the layer material, it is the task of the present invention to propose a method with which significantly simpler and more flexibly large-scale industrial high-speed steel substrates can be delayered, and specifically independently of whether or not they are layered with a TiN, a TiCN and/or a TiAlN hard material layer. In contrast to the above described method, according to the invention one and the same method becomes possible for the separation of all cited hard material layers from HSS substrates.
Definitions
1) High-Speed Steel
A high-speed steel is characterized by high carbon concentrations of up to 1.5%, and additions of strongly carbide-forming elements such as chromium, molybdenum, tungsten and vanadium. Up to 12% of cobalt is comprised in some of the more complex grades.
This steel is referred to as high-speed steel because it retains its high hardness at high-speed applications (see D. T. Llewellyn, Steel: Metallurgy and Application, Butterworth-Heihemann Ltd., Oxford 1992, p. 174).
2) Phosphate
As a phosphate is defined a salt of a phosphoric acid, diphosphoric acid, triphosphoric acid, etc. For example, the phosphate “calcium phosphate” is a salt of phosphoric acid, “disodium dihydrogen phosphate” is a salt of diphosphoric acid, further “pentasodium triphosphate” is a salt of triphosphoric acid.
3) Phosphonate
By a phosphonate is understood a salt of a phosphonic acid, in particular of an organic phosphonic acid, i.e. of a phosphonic acid with organic substituents.
The posed task is solved thereby that for the layer separation of HSS substrates with at least one layer comprising TiN, TiCN or TiAlN, at least one substance from the group of phophates, phosphonates and phosphonic acids is used.
Preferably the following specific method guidances are used alternatively or in combination:
the phosphate disodium dihydrogen pyrophosphate, Na
2
H
2
P
2
O
7
and/or pentasodium triphosphate (Na
5
P
3
O
10
) are preferably used;
as the phosphonic acid is preferably used aminotri(methylene phosphonic acid) and/or 1-hydroxyethane (1, 1-diphosphonic acid). These phosphonic acids are added to the solution as such. This applies generally to the use of phosphonates, phosphates and phosphonic acids.
It has been found, at least preliminarily, that the use of 1-hydroxy ethane(1, 1-diphosphonic acid) is especially suitable.
The process temperature of the solution bath is maintained at 20° C. to 80° C. (the range limits are included), if appropriate by heating and/or cooling;
The peroxide concentration is s elected between 5 and 50 wt. % (the range limits are included);
The concentration of phosphate and/or phosphonate and/or phosphonic acid is selected between 0.1 and 10 wt. % (the range limits are included);
Relatively large solution bath volumes, for example ≧50 l or even ≧100 1 can also be stably operated;
The solution comprises preferably distilled water, hydrogen peroxide, the cited base, for example NaOH, and the cited phosphates and/or phosphonates and/or phosphonic acids, at least by a far predominant fraction.
This permits circumventing a layer material-specific and complex solution composition and the feasibility is created of separating layers of each of the listed hard material layers from HSS substrates with the same solution. Furthermore, the extremely high apparatus expenditure is dispensed with, which must be expended if an alkaline hydrogen peroxide bath with a pH value of 8 to 12 is operated in the boiling temperature range. Due to the low process temperature at which the solution bath according to the invention can be operated, the danger of phosphatization is also absent, which exists at high process temperatures in the boiling temperature range due to rapid concentration through evaporation.
This offers the capability for economic and large-scale industrial layer separation to operate stably delayering baths with large volumes, for example of more than 50 l or even of more than 100 l . Therewith large quantities of hard-material layered HSS substrates, such as for example tools, can be delayered within a few hours.
In contrast to TiN and TiCN, TiAlN does not dissolve in hydrogen peroxide solutions even at increased temperatures. If the pH value of the hydrogen peroxide solution is raised by adding a base, such as NaOH, into the alkaline range with a pH≧7, in addition to the cited TiN and TiCN layers, TiAlN layers are also dissolved. It was found according to the invention that this is also the case at low process temperatures.
An advantage of the alkaline hydrogen peroxide is the high process certainty with respect to corrosion of HSS material. In an alkaline medium HSS is highly inert. Thus, no corrosion danger for the HSS substrate exists even if relatively long layer

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