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Method for the Wet Chemical Polishing of Molded Zinc Parts

20170314140 · 2017-11-02

    Inventors

    Cpc classification

    International classification

    Abstract

    A method for the wet-chemical polishing of molded zinc parts, the molded parts being brought in contact with an acid solution and said acid solution containing only sulfuric acid and phosphoric acid as the strong acids.

    Claims

    1. A method for the wet chemical polishing of a molded part made of zinc, comprising: bringing the molded part into contact with an acid solution, wherein the acid solution contains only sulfuric acid and phosphoric acid as the strong acids, and the total acid concentration of the strong acids is in a range of 40 to 90% by weight, wherein the acid solution contains no chromic acid/chromates, no nitric acid/nitrates, no hydrofluoric acid/fluorides, and no hydrochloric acid/chlorides, and wherein the acid solution additionally contains an oxidizing agent.

    2. The method according to claim 1, wherein the molded part is treated with the acid solution until the average roughness value R.sub.a has been reduced at least by 30%, based on the original R.sub.a value.

    3. The method according to claim 1, wherein the ratio (% by weight) of phosphoric acid to sulfuric acid in the acid solution is in a range of 30%:70% to 70%:30%.

    4. The method according to claim 1, wherein the oxidizing agent is selected from the group consisting of persulfates, perchlorates, and peroxides.

    5. The method according to claim 1, wherein the oxidizing agent is present in a concentration of 1% to 20% by weight.

    6. The method according to claim 1, wherein the solution additionally contains surface-active substances.

    7. The method according to claim 1, wherein the contact time between the acid solution and the molded part is up to 20 minutes.

    8. The method according to claim 1, wherein the method is carried out at a temperature in a range of 15° C. to 60° C.

    9. The method according to claim 8, wherein the temperature is in a range of 30° C. to 40° C.

    10. The method according to claim 2, wherein the ratio (% by weight) of phosphoric acid to sulfuric acid in the acid solution is in a range of 30%:70% to 70%:30%.

    11. The method according to claim 10, wherein the oxidizing agent is selected from the group consisting of persulfates, perchlorates, and peroxides.

    12. The method according to claim 2, wherein the oxidizing agent is present in a concentration of 1% to 20% by weight.

    13. The method according to claim 3, wherein the oxidizing agent is present in a concentration of 1% to 20% by weight.

    14. The method according to claim 4, wherein the oxidizing agent is present in a concentration of 1% to 20% by weight.

    15. The method according to claim 2, wherein the solution additionally contains surface-active substances.

    16. The method according to claim 3, wherein the solution additionally contains surface-active substances.

    17. The method according to claim 4, wherein the solution additionally contains surface-active substances.

    18. The method according to claim 5, wherein the solution additionally contains surface-active substances.

    19. The method according to claim 2, wherein the contact time between the acid solution and the molded part is up to 20 minutes.

    20. The method according to claim 3, wherein the contact time between the acid solution and the molded part is up to 20 minutes.

    Description

    EXAMPLE 1

    [0027] Hinge part made of diecast zinc with a milled groove and a cross hole, part size approximately 30×20×8 mm

    [0028] Task: to remove burrs at the cross hole in the groove and smooth the surface for subsequent electroplating.

    [0029] Bath: 25% sulfuric acid [0030] 25% phosphoric acid [0031] 5% potassium persulfate [0032] 0.6% Lutensol FA 12 [0033] Remainder: water

    [0034] The parts were degreased for 10 minutes in an alkaline hot degreasing process as pretreatment, then rinsed with water, treated for 10 minutes in the solution according to the invention at 35° C., then rinsed with water and dried. The parts treated in this way were burr-free, and had a smooth, lustrous light-gray surface that was suitable for electroplating.

    EXAMPLE 2

    [0035] Actuation buttons made of diecast zinc for fittings having boreholes and milled edges were to be deburred and their surfaces smoothed for subsequent chrome plating.

    [0036] Bath: 20% sulfuric acid [0037] 30% phosphoric acid [0038] 10% hydrogen peroxide [0039] 0.8% Lutensol FA 12 [0040] Remainder: water

    [0041] The parts were pretreated according to Example 1, then treated for 15 minutes in the bath at 30° C., rinsed with water, and dried.

    [0042] The parts treated in this way were burr- and pore-free, and had a smooth, lustrous light-gray surface with smooth, slightly rounded edges. The parts showed perfect surface quality after the chrome plating.