Method for chroming by using trivalent chromium

Abstract

The invention discloses a method for chroming by using trivalent chromium. A plating liquid is prepared from the following raw materials: 125-120 g / L of chromic chloride, 110-130 g / L of urea, 25-30 g / L of ammonium chloride, 9-10 g / L of boric acid, 8.5-9.5 g / L of methanoic acid, 200ml / L of carbinol, 25-35 g / L of sodium chloride and 0.05-0.2 g / L of thioformamide. The method comprises the steps of: during electroplating, electrolyzing for 24 hours by adopting the plating liquid, regulating the pH value to be 1.65-1.75, cleaning a part to be electroplated, then feeding into a plating groove in the electrifying state at the temperature of 20-40 DEG C, keeping constant potential of -3.5V to ensure that a cladding material reaches a specified thickness, fishing out, and drying by hot air. The invention has the advantages that complex ions formed by trivalent chromium and a ligand are completely depolymerized by using the thioformamide, the plating liquid is stable, the deposition speed is high, the generation of hydroxyl polymers can be inhibited when the pH value raises, and an electroplated chrome coating is in a stainless steel ground color and has better corrosion resistance and abrasive resistance.

Description

technical field [0001] The invention relates to a chromium plating process, in particular to a chromium plating method using trivalent chromium. Background technique [0002] Chrome plating has good hardness, wear resistance, corrosion resistance and decorative appearance. It is widely used in the outer layer and functional coating of the protective-decorative coating system. It has always occupied an important position in the electroplating industry. At present, chrome plating has become a One of the most widely used plating types in the industry. For a long time, hexavalent chromium has been used in chrome plating. Due to its high toxicity and carcinogenicity, hexavalent chromium has attracted widespread attention. Governments of various countries have also strengthened legislation management, such as the United States changed the emission standard of hexavalent chromium from 0. 05 mg / L to 0. 01 mg / L, and began to implement it in 1997; the European Union passed ROHS (EU R...

AI Technical Summary

Problems solved by technology

Trivalent chromium electroplating, as the most important and most direct and effective substitute for hexavalent chromium electroplating, has incomparable advantages over hexavalent chromium electroplating in terms of process performance and environmental protection. The complex ions formed by trivalent chromium and ligands in the solution are relatively stable and difficult to precipitate on the cathode, resulting in the precipitation of a large amount of hydrogen gas on the surface of the cathode, causing the pH near the surface of the cathode to rise rapidly, even exceeding 8

Under these conditions, the Cr on the surface of the cathode 3+ New polycomplexes or colloidal substances will be formed, resulting in trivalent chromium plating. The coating crystallization is not dense, loose or even falls off and cannot be thickened.