Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23H—WORKING OF METAL BY THE ACTION OF A HIGH CONCENTRATION OF ELECTRIC CURRENT ON A WORKPIECE USING AN ELECTRODE WHICH TAKES THE PLACE OF A TOOL; SUCH WORKING COMBINED WITH OTHER FORMS OF WORKING OF METAL
  • B23H3/00—Electrochemical machining, i.e. removing metal by passing current between an electrode and a workpiece in the presence of an electrolyte
  • B23H3/08—Working media
• • 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

Definitions

• electrolyte which conducts current between the two electrodes allowing material to be eroded electrochemically from the workpiece.
• electrolytes In order to provide adequate conductivity in electrolytes, thus to lower the resistance to flow of current between the electrodes, a variety of salts, acids and the like are used.
• electrolytes are highly corrosive to equipment, or produce intergranular attack on material of the workpiece. This is particularly true when the electrolyte conductivity is adjusted to provide optimum feed rates for the tool and workpiece one toward the other in order to achieve maximum material removal rates.
• Another object is to provide an electrolyte which can be inexpensively and easily prepared, which does not become rancid and which is safe with regard to the health of workmen.
• the electrolyte of the present invention consists essentially of an aqueous solution of 90240 grams of sodium formate and about 20-80 grams of sodium nitrite per liter of water.
• the most effective and preferred form of the invention consists essentially of about 120 grams of sodium formate and about 26 grams of sodium nitrite per liter of water.
• the sodium formate provides the principal amount of electrical conductivity while the sodium nitrite provides principally corrosion resistance.
• both are salts which will ionize in water so that both will contribute some conductivity to the electrolyte.
• the solutions resistivity decreases from about 20 ohms at about Patented Jan. 18, 1966 50 grams per liter to about 9 ohms at 400 grams per liter.
• the resistivity further decreases so that at 50 grams per liter of sodium formate and about 175 grams per liter of sodium nitrite, the specific resistivity of an aqueous solution is between 7 and 7.5 ohms. This same condition exists up to a concentration of about 300 grams per liter of sodium formate with the same amount of sodium nitrite.
• the specific resistivity of the solution progressively decreases until at about 400 grams per liter of sodium nitrite the specific resistivity is between 5 and 5.5.
• a chart of aqueous solutions of the two salts sodium formate and sodium nitrite show specific resistivity areas which might appear more favorable than that of the present invention.
• the particular composition of 120-240 grams of sodium formate and 2570 grams of sodium nitrite per liter of water unexpectedly provides an electrolyte having an overall balance of (1) relatively low specific resistivity, (2) resistance to corrosion of equipment and (3) resistance to intergranular attack on workpiece material.
• the conductivity of aqueous electrolyte solutions including less than about grams of sodium formate and sodium nitrite up to about 80 grams per liter of water have excessively high specific resistivity. Therefore it is less desirable and less practical an electrolyte.
• Example 1 The data of the following Table I is typical of a wide variety of solutions studied in connection with the present invention. As shown :by Examples 1, 2 and 3, the range of 2570 grams of sodium nitrite and -240 grams of sodium formate per liter of water is specifically preferred with regard to pitting of the specimen. Examples 4 and 5 show that sodium nitrite alone or in the presence of too much sodium formate will not prevent pitting of the specimen. In addition, Example 6 shows that a large amount of sodium nitrite can do more harm from a pitting corrosion point of view than can the relatively large amount of sodium formate in Example 5.
• Example NaNOz (5/ HCOONa Specimen (al Condition) The most desirable amount of sodium formate in the electrolyte of the present invention is at about 1 pound per gallon of water (about 120 grams per liter of Water) in the presence of a particular amount of sodium nitrite.
• the data of Table II shows that with such an amount of sodium formate, less than about 20 grams per liter of sodium nitrite will result in a large amount of corrosion, with about 20 grams per liter representing a point at which only slight corrosion of the specimen takes place. It was found that between about 25 and 80 grams of sodium nitrite per liter of Water in such a solution did not corrode the specimen Whereas about 80 grams per liter resulted in the specimens surface being pitted.
• an unusual combination of resistance to surface corrosion and resistance to intergranular attack, along with proper conductivity, can be achieved in an electrolyte within the range of the present invention.
• an electrolyte consisting essentially of, 25-70 grams of sodium nitrite and 120-240 grams of sodium formate per liter of water. From an economical and health point of view along with optimum material removal rates, it has been found that an electrolyte including about 25 grams of sodium nitrite and about 120 grams of sodium formate for each liter of water is particularly desirable.
• An aqueous solution suitable for use as an electrolyte in electrochemical material removal, consisting of sodium formate, sodium nitrite and water, the sodium formate content being -240 grams per liter of water and the sodium nitrite content being 20-80 grams per liter of water.
• An aqueous solution suitable for use as an electrolyte in electrochemical material removal, consisting of sodium formate, sodium nitrite and water, the sodium formate content being -240 grams per liter of water and the sodium nitrite content being 25-70 grams per liter of water.
• An aqueous solution suitable for use as an electrolyte in electrochemical material removal, consisting of sodium formate, sodium nitrite and water, the sodium formate content being about 120 grams per liter of water and the sodium nitrite content being about 25 grams per liter of water.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Internal Circuitry In Semiconductor Integrated Circuit Devices (AREA)
• Electrical Discharge Machining, Electrochemical Machining, And Combined Machining (AREA)
• Preventing Corrosion Or Incrustation Of Metals (AREA)

Priority Applications (5)

Applications Claiming Priority (1)

Publications (1)

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Cited By (3)

Citations (3)

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• 1962
  • 1962-09-19 US US224834A patent/US3230160A/en not_active Expired - Lifetime
• 1963
  • 1963-07-10 CH CH862663A patent/CH428369A/de unknown
  • 1963-09-05 DE DEG38611A patent/DE1258232B/de active Pending
  • 1963-09-17 GB GB36531/63A patent/GB985158A/en not_active Expired

Patent Citations (3)

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