GB2024252A

GB2024252A - Brightening aluminium surfaces

Info

Publication number: GB2024252A
Application number: GB7903823A
Authority: GB
Original assignee: HUETOEGEPGYAR
Current assignee: HUETOEGEPGYAR
Priority date: 1978-06-26
Filing date: 1979-02-02
Publication date: 1980-01-09
Also published as: CS205142B2; ATA64679A; DD144175A5; AT360300B; HU177328B; DE2902162A1; DE2902162C2

Abstract

The invention relates to a process and an equipment for brightening the surfaces of hollow objects made of aluminium and/or aluminium alloy. According to the process a direct current of potential 15 to 18 V, preferably 15 V, and of heat load 1.5 to 2 A/dm<2>, preferably 2 A/dm<2> is passed through an electrolyte and the electrolyte is passed through the hollow object in turbulent flow for 15 to 20 minutes, preferably 20 minutes. A hollow body, 2, preferably a jar is dipped into the electrolyte (preferably sulphuric acid) in a vessel. An electrode 8 and a plastic tube 10 are attached to the hollow object and the said plastic tube is joined to a container 3, to which a further electrode 9 is attached. The end of the container opposite to the connection of the jar is joined to the vessel containing the electrolyte through tubing and preferably via a pump 13. <IMAGE>

Description

SPECIFICATION Process and apparatus for brightening the surfaces of hollow objects made of aluminium or an aluminium alloy The invention relates to a process and apparatus for brightening the surfaces of hollow objects made of aluminium or an aluminium alloy.

It is known that according to the current stand of technology the anodic oxidation of the internal surfaces of hollow objects made of aluminium requires the use of an auxiliary electrode reaching into the hollow. If the orifice of the hollow is small, this may cause a great deal of difficulties. The difficulties are mainly caused by the fact that in such cases the ideal anode:cathode ratio of 1:1 cannot even be approximated.

It is a fact that an anode having a small area can only produce a very thin layer even in the case of prolonged treatment.

The aim of the present invention is to devise a process and to design an equipment suitable for carrying out the process with which the abovementioned disadvantages may be eliminated.

The aim set forth above is realized by a process which may be characterized by the following. Direct current of potential of 15-18 V, preferably 15 V and of electric current density of 1.5-2 Aids2, preferably 2 A/dm2 is passed through the electrolyte and the electrolyte is passed through the hollow object for 15-20 minutes, preferably 20 minutes, in turbulent flow using a special apparatus positioned outside, preferably in a quantity of 2-4 I/dm2.min.

Apparatus suitable for carrying out the process may be characterized by the following. A hollow body, preferably a jar, is dipped into the electrolyte being in a vessel. An electrode and a plastics tube are attached to the jar and said plastics tube is joined to a container provided with a diaphragm. Afurther electrode is attached to the container and the end of the container opposite the connection to the jar is joined to the vessel containing the electrolyte through tubing and preferably via a pump. The internal surface of th is container, which is preferably ribbed, is the actual cathode, whereby the necessary, preferably 1:1, ratio of anode to cathode may be ensured.

In the process according to the invention a 15% aqueous solution of sulphuric acid is used as electrolyte and eloxing (anodising) liquid, wherein said solution also conducts eletricity.

The sulphuric acid is pumped through the tube into the inside of the hollow object - in the present case a siphon-container - and is circulated con tenuously.

The inlet tube is made of a plastics so as to prevent a short-circuit between the object to be treated being at a + potential and the apparatus being at a potential. The electrical connection between them should only be provided by the flowing electrolyte.

The electrode may be constructed without inlet tube through appropriate geometrical design if the shape is suitable. This electrode passes the electric current to the electrolyte, the continuous flow whereof ensures the conduction of the electric charge, the expulsion of the hydrogen formed and the supply of fresh acid necessary for the eloxation (anodisation). The other pole is the hollow body itself.

The apparatus suitable for carrying out the pro cuss forms or contains in essence an electrode which charges the electrolyte passing over or through themselves electrically. The electrode is connected to the negative pole. In the case of oxidation with sulphuric acid the cathodic process may be illustrated by the following equation: 2e + 2H+ + S04 H2+SO4 The hydrogen ions take up negative charge from the cathode. The acidic residue left in the electrolyte remains reactive so far as its oxidizing ability is concerned. If we consider this system as static oxidation will start also without circulating the electrolyte, although only very slowly, because the conductivity of the electrolyte and the crosssectional area of the liquid column are relatively small and the distance between the poles relatively large.

In order to eliminate this phenomenon the electrolyte is continuously circulated. The current may be increased with increasing the flow rate of the electrolyte. This is proved by the practice. The greater is thus the rate of flow of the active S04 ions into the hollow, the faster is the rate of the oxidation process.

It follows from the above that the design of the apparatus and the connection of the individual elements of it to each other is of great importance.

Laminarflow may be eliminated by using ribbing or some other structural element e.g. diaphragm in order to ensure that the degree of efficiency of the charging of the electrolyte is as high as possible.

Using the abovementioned structural elements the laminar flow is changed into turbulent flow. In this case it is essential that the electrolyte should be able to be charged within the apparatus itself, because if, for instance, the electrolyte is passed through a body of larger volume in a narrow stream in laminar flow, it cannot be charged and the process will not start up.

The essence of the invention is illustrated by the attached drawing of the apparatus suitable for carrying out the process, where Figure 1 shows a perspective view of the apparatus and Figure 2 shows the A - A cross-section of the apparatus illustrating the shape of the insert of diaphragm.

As can be seen in Figure 1 and Figure 2, the jar 2, whose surface is to be treated, is inside the vessel 11 containing the electrolyte 1. Said jar is joined through plastics tube 10 to container 3, which has according to the example a quadrangular crosssection and there are 4 diaphragms 4 in it. Container 3 is supplied with seal 6 held between clamps 5 and 7, one of which (5) is joined to a tapered section of container 3. A pipe 12 connects jar 2 to container 3 via pump 13.

Electrode 8 is attached to jar 2, while electrode 9 is attached to container 3. The preferred parameters of the process which may be carried out using the apparatus are as follows: Direct current of potential of 15-18 V, preferably of 15 V, and of current density 1.5 to 2 A/dm2, preferably 2 A/dm2, is passed through the electrolyte, which is at 25"C flowing in turbulent flow. This electrolyte is passed through the hollow object to be treated for 15 to 20 minutes, preferably 20 minutes.

The thickness of the plating so obtained is approximately 10 to 12 u

Claims

1. A process for brightening the surfaces of hollowobjects made of aluminium or an aluminium alloy with the characteristics, that the flowing electrolyte as charge carrier conducts direct current of potential 15 to 18 V, preferably 15 V, and of heat load (current density) 1.5 to 2 A/dm2, preferably 2 Aim2, and that the electrolyte is passed through the hollow object in turbulent flow for 15 to 20 minutes, preferably 20 minutes.

2. Apparatus for carrying out the process according to claim 1, with the characteristics that the hollow body, preferably a jar is dipped into the electrolyte in a vessel and that an electrode and a plastics tube are attached to the hollow object and the said plastics tube is joined to a container with diaphragm to which a further electrode is attached, and that the end of the container opposite the connection of the jar is joined to the vessel containing the electrolyte through tubing and preferably via a pump.

3. A process according to claim 1 wherein the flow rate of electrolyte is 2-4 11dim2 min.

4. A process according to claim 1 or claim 3 wherein the electrolyte is suphuric acid at 25"C.

5. A process according to claim 1 substantially as herein described with reference to and as shown in the accompanying drawing.

6. Apparatus according to claim 2 substantially as herein described with reference to and as shown in the accompanying drawing.