GB2248070A

GB2248070A - An apparatus for removing impurities contained in chrome plating bath

Info

Publication number: GB2248070A
Application number: GB9020548A
Authority: GB
Inventors: Yun-Fu Huang
Original assignee: Individual
Current assignee: Individual
Priority date: 1990-09-20
Filing date: 1990-09-20
Publication date: 1992-03-25
Also published as: GB9020548D0

Abstract

Apparatus for removing impurities contained in a chrome plating bath, comprises a membrane tank 1, a precipitating tank 2 and a plating tank 3, at least one membrane cylinder 11 being disposed within the membrane tank for receiving cathode electrolytic solution, the membrane tank communicating with the plating tank 3 for circulation of anode electrolytic solution, and the membrane cylinder being connected with the precipitating tank by pumping means 15 for drawing cathode electrolytic solution to the precipitating tank. The metallic impurities contained in the cathode electrolytic solution can be separated and the regenerated cathode electrolytic solution can be reused for the chrome plating bath. <IMAGE>

Description

TITLE: AN APPARATUS FOR REMOVING IMPURITIES CONTAINED IN THE CHROME PLATING BATH IN THE CHROME PLATING BATH This invention relates to an apparatus for removing impurities contained in the chrome plating bath.

BACKGROUND OF THE INVENTION In plating industry, current efficiency used in chrome plating is lower than that of the other metal plating process. The only way to ipprove the quality of chrome plating is to use a clean electrolyte. However, the cupper plating step and the nickel plating step are the necessary steps in the decorative chrome plating.

It will cause impurities generated in the plating tank.

Furthermore, in the hard chrome plating, the substrate to be plated is subject to the etching process and therefore, causes a large amount iron to contaminate the plating bath.

The main disadvantage of chrome plating is electrolYte Poison. The cost for recovering the wastewater including concentrated chromic acid is high and the treatment thereof generates the secondary pollution.

The conventional apparatus for removing metallic impurities contained in the plating bath is unglazed pottery cylinder However the typical unglazed pottery cylinder includes the disadvantages, such as large thickness (10 to 15 mm), low porosity and low permeability (0.0016 ml/cm > ' /hr). Furthermore, the sintering temperature for the preparation of the unglazed pottery cylinder cannot be actually control.

It will cause the membrane to be clogged or be corroded by chromic acid. The other technology for removing metallic impurities contained in the plating bath is ion exchange membrane or fluorinated membrane.

With the use of the afore-mentioned organic films, the temperature and the concentration of chromic acid should be carefully control to prevent the functional groups of the organic films from decomposition. The permeability (6 ml/cm7/hr) of the fluorinated membrane is higher than that of ion exchange membrane. The difference of the liquid level between the inside and ouside of the fluorinated membrane cannot be too large.

The liquid cannot be stirred to prevent liquid from permeating the membrane. The effect of this membrane is reduced due to the above-mentioned Phenomena.

Furthermore, with the use of the membrane, the temperature of the plating bath will raise due to the increase of the electric voltage and hence generate the gas vigorously. The difference of the level inside and outside will greatly increase. Voter should be added to replenish the electrolyte evaporated, therefore, the operation condition of the ion exchange membrane and the fluorinate membrane is limited. The other disadvantage of the membrane is the blocking Problem If the membrane tank is small, the blocked membrane could be washed with HCI and water. If a larger membrane is used, to clean the membrane or change the electrolyte used will be more inconvenient.

SUMMARY OF THE INVENTION Therefore. the prirary object of this invention is to provide an apparatus for removing impurities contained in the chrome plating bath.

The present apparatus for removing impurities contained in the chrome plating bath comprises a plating tank; a membrane tank; a membrane cylinder disposed within the membrane tank for receiving cathode electrolytic solution; a precipitating tank for receiving cathode electrolytic solution to be precititated; a circulating means communicated with the plating tank and the membrane cylinder for circulating anode electrolytic solution; a pumping means connected with the membrane cylinder and the precipitating tank for pumping cathode electrolytic solution with impurities from the membrane cYlinder to the precipitating tank; and means for returning the regenerated cathode electrolytic solution from the precipitating trank to the membrane cylinder.

The membrane usage in this invention is prepared by a specific ceramic which was sintered at 1100 to 1150 "J to form a product with 2 to 3 mm thickness and 0.1 to 0.2 ml/cm > /hr permeability. The permeability of this invention is 62 to 124 times of that of the conventional art. During the electroplating process, CrW flows from cathode to anode. While the metallic impurities contained in the anode electrolytic solution entered to cathode. Trivalent chromium at anode is electrooxidized to hexavalent chromium at the same time. Therefore, it is a reaction of double sides.

Conventional unglazed pottery cylinder is formed of high density and low porositY structure, so that CrOa flows to anode and metallic impurity flows to cathode slowly. This is the most difference between prior art and the present invention. In this invention, the slurry formed at the membrane cylinder can be drawn to the precipitating tank by a pump to prevent the membrane from blocking and washing.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a brief drawing showing a preferred embodiment of the present apparatus.

DESCR JPTION OF TIlE PREFERRED E!.!BOD IMENT Referring to Fig. 1. the apparatus of this invention comprises a membrane tank 1, a precipitating tank 2 and an electroplating tank 3. Three membrane cylinder 11 respectively disposed within the membrane tank as cathode. The configuration of the membrane cylinder 11 provide an uniform circuit distribution and the operated circuit thereof is 50 to 60 A which is much higher than that of conventional cylinder.

As CrO4 flows from cathode to anode and the metallic impurities enter to cathode. slurry generat.

The cathode electrolytic solution was contained within the membrane cylinder 11 and the anode electrolytic solution was kept ouside of the membrane cylinder 11.

The slurry produced during the electroplating process was held within the membrane cylinder 11. The anode electrolytic solution was clean and was circulated from the membrane tank 1 to the plating tank 3 through tube 12 and returned to the membrane tank 11 through tube 13. The membrane cylinder 11 was connected with the precipitating tank 2 by a tube 14 and a diverter valve 15. Therefore, slurru formed during the plating process was dragout from the bottom portion of the membrane tank 11 to the upper portion of the precipitating tank 2. After precipitating, the precipitate maintained within the bottom of the precipitating tank 2 and the clean cathode electrolytic solution was returned to the membrane cylinder 11 by a tube means 16 and a return pump 17. The membrane cylinder 11 used in this invention will not be blocked by slurry or metallic impurities.

Example 1 The metallic content of the electrolytic solution to be treated comprises 11073 mg/l iron, 650 mg/l copper and 272 mg/l zinc. After 192 hours circulation with the present apparatus having two membrane cylinders 11, the metallic content was 4490 mg/l iron, 172 rg/l copper and 57.3 mg/l zinc. The concentration of trivalent chromium was varied from 15 g/l to 2 g/l.

Example 2 This example utilized a prior apparatus. After 21 hours. 9Y. 40A and 30"J operation. the specific gravity of the electrolyte was charged from 1.22 to 1.18. After 43 hours, the specific gravity is 1.15 and after 137 hours, the specific gravity is 1.07. The average temperature was 60"J. The weight of cathode was increased 2.3 kg and the weight of slurry contained in the cathode was 3.1 kg.

The membrane cylinders 11 each comprise a tube and a wire material encapsulated in said tube.

Claims

1. Apparatus for removing impurities contained in a chrome plating bath, comprising a plating tank; a membrane tank; a membrane cylinder disposed within said membrane tank for receiving cathode electrolytic solution; a precipitating tank for receiving cathode electrolytic solution to be precipitated; a circulating means communicated with said plating tank and said membrane tank for circulating anode electrolytic solution; a pumping means connected with said membrane cylinder and said precipitating tank for pumping cathode electrolytic solution with impurities from said membrane cylinder to said precipitating tank; and means for returning the regenerated cathode electrolytic solution from said precipitating tank to said membrane cylinder.

2. Apparatus as claimed in Claim 1, wherein said membrane cylinder comprises a tube and a wire material encapsulated in said tube.

3. Apparatus for removing impurities contained in a chrome plating bath, substantially as hereinbefore described with reference to the accompanying drawings.