DE2124935A1 - Electrolyte for electro-chemical metal working - partic of titanium (alloy) - Google Patents

Abstract

An electrolyte contg. a mixture of sodium chloride and nitrate can be used for electrochemical working of alloys in partic. Ti alloys and pure Ti. For pure Ti workpieces the electrolyte contains 80-120 g NaCl and 80-110 gm NaNO3 per litre. For Ti alloys these quantities become 90-120 g/l and 160-230 g/l respectively.

Description

Electrolyte for electrochemical metalworking The invention relates to an aqueous electrolyte containing sodium chloride and sodium nitrate for electrochemical metalworking.

It is known that metal is removed during electrochemical machining of a workpiece in that between this and a correspondingly profiled Working electrode a high strength electrical current flow is established while in the space between the workpiece and the working electrode - called the working gap - there is an electrolyte which is generally kept in circulation by pressure is.

The workpiece is attached to the positive terminal (amide) and the working electrode connected to the negative terminal (cathode) of an electrical DC voltage source.

Basically, all metallic materials can be electrochemically edit, whereby the machinability depends on the electrochemical resp. the various chemical-physical properties of the materials. An important The characteristic value for the machinability of a material is known to be the rate of removal; it is a function of the specific removal, the current density and the current yield.

The optimally achievable removal rate is in addition to the chemical The composition of the material to be processed depends on the material used. Electrolyte solution and the other processing conditions, such as the electrolyte conc entrat ion the electrolyte temperature and the flow conditions for the electrolyte within the working gap.

Choosing a suitable electrolyte for electrochemical Machining a workpiece is therefore primarily based on the one to be machined Material and the requirements on the surface quality, the removal rate and the machining accuracy.

The electrolytes currently used are predominantly containing sodium salts aqueous solutions with different concentrations and in different Temperature ranges used. As salts come, for example, depending on the intended use, Sodium chloride, sodium nitrate or sodium chlorate for use. Beyond that mixtures of the electrolytes mentioned are also used. The use of such Electrolytes for the electrochemical processing of metals, in particular of However, titanium and titanium alloys have not yet led to fully satisfactory results In the case of such electrolytes, either the surface of the workpiece is passivated so strong that almost no erosion takes place, or there are easily pits-like races Signs of corrosion.

There were also electrolytes for machining titanium and titanium alloys suggested that from a solution with a high concentration of mineral acids exist. However, these electrolytes are dangerous to handle and their composition changes during processing. In addition, when using these electrolytes There are very high structural demands on the processing system. aside from that the workpieces must be completely neutralized after machining, what makes complex post-treatment necessary.

Electrolytes are also sodium chloride solutions with additives of alkali fluorides operating at high temperatures. However, these electrolytes have a strong scattering effect, which leads to corrosion at the machined areas of the workpiece and thus to a rough surface to lead. Furthermore, these electrolytes are physiological due to the addition of fluoride ions dubious.

Furthermore, electrolytes are made from a sodium chloride solution with complexing agents Additives such as alkali salts of tartaric acid or alkali salts of citric acid are known. When using these electrolytes for machining titanium and titanium alloys there are similar phenomena as in the above-mentioned electrolyte. In addition there is the strong tendency of this electrolyte to passivate the workpiece surface, whereby there is a risk that the tool electrode touches the workpiece and is destroyed by a short circuit.

The invention has for its object to provide an electrolyte for e electrochemical machining of metals, especially titanium and titanium alloys to create, with which one single-walled at a high removal rate Machining surface receives and which has a good service life, with the electrolyte must be safe for the operating personnel and this must be the metallic facilities the processing machines should not attack.

It has now been made from a wide variety of examined electrolytes found the electrolyte according to the invention, which essentially consists of an aqueous Solution with a content of 80 to 120 g sodium chloride and 80 to 230 g sodium nitrate per liter of water.

In the most effective and preferred embodiment of the invention For the processing of pure titanium, the electrolyte has a content of 80 to 120 g sodium chloride and 80 to 110 g sodium nitrate per liter of water and for processing titanium alloys have a content of 90 to 120 g sodium chloride and 160 to 230 g g sodium nitrate per liter of water.

The following tables 1 and 2 make a selection from a large Wide variety of investigate solutions listed.

Table 1 Aqueous electrolyte solutions Serial NaCl NaNO3 Condition of the sample (pure titanium) Assessment No. (g / l) (g / l) 1 100 0 very rough surface, strong, uneven Pitting corrosion is suitable 2 0 100 passivation of the surface, not low material removal is suitable 3 | 80 70 rough surface, partly pitting - not Corrosion is suitable 4 | 80 80 almost smooth surface, minor conditional Pitting corrosion | suitable 5 100 90 | smooth surface suitable 6 110 100 very smooth surface, very very good good material removal, none suitable Pitting corrosion 7 120 110 smooth surface, moderate conditionally Material removal is suitable Table 2 Aqueous electrolyte solutions Serial NaCl NaNO3 Condition of the sample Assessment No. (g / l) (g / l) (titanium alloy, Ti6Al4V) 8 80 150 very calm surface, strong unsuitable Pitting corrosion 9 90 160 rough surface, partly due to the hole eating corrosion 10 100 170 almost smooth surface, suitable rings pitting corrosion 11 100 180 smooth surface suitable 12 110 190 very smooth surface, very very good good material removal, none suitable Pitting corrosion 13 110 | 200- smooth surface, good well suited 220 Material removal, none Pitting corrosion 14 120 230 smooth surface, to a moderate extent Material removal | suitable Of the two salts contained in the electrolyte according to the invention, the sodium chloride makes the main contribution to a favorable material removal, while the sodium nitrate primarily causes the uniform removal without pitting corrosion.

The use of sodium chloride alone in an aqueous electrolyte is not suitable for machining titanium and titanium alloys (Table 1, No. 1) suitable, because a very rough workpiece surface is created here due to strong pitting corrosion receives. In many experiments with different solution concentrations one came always to the same negative results.

The use of sodium nitrate alone in an aqueous electrolyte It is also not suitable for machining titanium and titanium alloys. The material removal is too low due to the passivation of the workpiece surface (Table 1 serial number 2).

It has now been used surprisingly in a large number of attempts found that it is preferable to use a combination of about 110 g of sodium chloride and 100 g of sodium nitrate per liter of water contains an electrolyte (Table 1, serial no.

No. 6), which is excellent for electrochemical machining of pure titanium is suitable. With very good material removal, a very smooth one is obtained machined workpiece surface. There is no pitting corrosion.

As the experiments No. 4 to 7 in Table 1 show is the content from 80 to 120 g of sodium chloride and the content of 80 to 110 g of sodium nitrate each Liters of water, depending on the required quality of the to be processed Surface suitable for electrochemical machining of pure titanium. Under and Above these levels, no satisfactory results are achieved.

During the electrochemical machining of titanium alloys (as a sample If a sheet of Di6Al4V was used) it was found that the sodium nitrate content higher than that of pure titanium. The cheapest amount of sodium nitrate in the one according to the invention Electrolyte is about 190 g per liter of water in the presence of the same amount Sodium chloride as for pure titanium (Table 1, No. 6 and Table 2, No. 12). From consideration of Table 2, it can be seen that an electrolyte with a content from 90 to 120 g of sodium chloride and a content of 160 to 230 g of sodium nitrate per liter of water suitable for the electrochemical processing of titanium alloys is.

A voltage of 30 volts was used in the tests. The temperatures of the electrolytes were at room temperature.

The advantages achieved with the invention are in particular: that it has been possible to produce titanium and titanium alloys with a mixed electrolyte that neutral, cheap and physiologically harmless, perfectly electrochemically to edit.

The surface quality of the machined surfaces achieved is see well. In addition, the electrolyte can be operated at room temperature and therefore no special heating is required. Furthermore, the Electrolyte not only has a long service life but also has a low scattering effect. Finally, there is good imaging accuracy, especially with the electrochemical Lower, achieved.

Claims (3)

Expectations 1. Aqueous electrolyte containing sodium chloride and sodium nitrate for electrochemical metalworking, characterized by a content of 80 to 120 g of sodium chloride and 80 to 230 g of sodium nitrate per liter of water. 2. Electrolyte according to claim 1, in particular for the electrochemical Machining of pure titanium, marked; by a content of 80 to 120 g sodium chloride and 80 to 110 grams of sodium nitrate per liter of water. 3. Electrolyte according to claim 1, in particular for the electrochemical Machining of titanium alloys, characterized by a content of 90 to 120 g sodium chloride and 160 to 230 g sodium nitrate per liter of water.