DE3029166A1 - CLEANING METHOD FOR SOLDERED ALUMINUM COMPONENTS - Google Patents

Description

INTERATOM 24.515.5

Internationale Atomreaktorbau GmbH D-5O6O Bergisch Gladbach 1

Cleaning process for soldered aluminum components

The present invention relates to a cleaning method for soldered hollow aluminum components with a low ratio of internal volume to internal surface, especially those that are thin-walled. In addition, the present invention relates to a cleaning method for aluminum components like this, whose solder contains elemental silicon, and which later come into contact with gases, the uranium hexafluoride (UF,) included. For example in hot

Salt bath brazed aluminum plate heat exchangers are made from very thin sheet metal and contain numerous channels that have only a small clear cross-section. After soldering inevitably remain Soluble and insoluble as well as dust-like impurities, the malfunctions in the heat exchangers or in the associated system. In the presence of UF, the im

Elemental silicon occurring in solder leads to a further disruption through the formation of solid and gaseous reaction products .

Aluminum components are usually briefly used in a fast acting stain, e.g. B. dipped from nitric acid and hydrofluoric acid. This procedure is however for components that are thin-walled and have small interiors, therefore difficult to access for the stain are not suitable. When the pickle comes into contact with the metal, heat is generated, which increases the reactivity the stain used increases so the chemical

We / Wa 29.07.1980

24.515.5

Process accelerates and leads to an undesirably heavy removal of metal surfaces near the inlet leads, since the amount of liquid filling such an interior space is only small and heats up quickly; the heat generated can only be dissipated poorly due to the shape of the component. On the other hand, the The effectiveness of the stain is quickly reduced, so that the parts that come into contact with it later not cleaned sufficiently. The also desired selective removal of the elementary Silicon from the soldering zones was not possible with the previously known pickling agents.

The object of the present invention is a cleaning method for soldered aluminum components that Are thin-walled and have small cavities, especially for heat exchangers made of thin aluminum sheets. A special object of the present invention is a cleaning method for such components, whose solder contains elemental silicon and which later come into contact with gases containing UF

should.

In the first claim a method is proposed in which by circulating a pickle of intentionally Reduced initial reactivity ensures that the ramp of the reactivity changes due to the Exhaustion of the pickling liquid on the one hand and the temperature increase occurring during the pickling process on the other is flatter on the one hand. These opposing effects are essentially the same (i.e. with a deviation of not more than + 10%), so that all parts are pickled evenly and therefore neither Damage due to high reactivity or insufficient pickling due to insufficient reactivity can result. This process is necessarily applied in a cycle until the pickling process is finished, whereby

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the final reactivity of the stain should not fall below the level mentioned in the claim in order to counteract the anyway not to let the previously usual procedure increase the duration of the process too much.

The aluminum nitrate proposed as an inhibitor in the second claim is a substance that is used when pickling Aluminum with a stain of the type mentioned is formed anyway and the effectiveness of the stain gradually increases belittles. Its deliberate addition before the start of the pickling process effectively cuts off the first, highly reactive one Phase of the stain and immediately transforms it into a state that is otherwise only after a certain Exposure time is reached.

The embodiment of the method proposed in the third claim also serves to make things more uniform of the pickling process, the pickling liquid, for example, a plate heat exchanger flows through in an ascending manner in the vertical direction; the throughput speed can be improved check and limit the temperature increase. When filling from above, the pickling liquid would be Distribute unevenly and in individual strands, so that the exposure time and the staining result are different would be.

The additional alkaline pickling proposed in the fourth claim is used for selective purposes. distance of the elementary silicon from the surface of soldering zones. In the case of the particular one proposed in the fifth claim Design of the process causes the addition of sodium silicate as an inhibitor that the otherwise significant removal of the aluminum that takes place

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is reduced so far that the concentration and exposure time required to remove the silicon the stain becomes possible. The proportion of aluminate proposed in the sixth claim improves the surface quality of the treated component.

The following is a tried and tested method for cleaning and removing silicon from soldered aluminum plate heat exchangers which have approximately the following dimensions and arrangement geometries:

Ratio of internal volume to internal surface

2 2

0.3-3 l / m, preferably 1 l / m, construction height 1 - 6 m, preferably 2.50 m

2 2

Cross-section 0.04 - 4 m, preferably 1 m sheet thickness of the heat exchange fins 0.1 - 0.8 mm, preferably 0.2 mm

clear distance between the heat exchange fins 1-10 mm, preferably 2 mm.

The rinsing in the circuit with the liquids listed below is carried out in ascending order for the specified ones Temperatures and parameters.

The amount of pickling liquid, its concentration, the volume throughput and the pickling time are coordinated with one another and with the geometric parameters such as total surface, internal volume and overall height of the heat exchanger.
(Percentages are always given in percentages by mass).

The individual process steps are:

a) Rinsing with tap water at room temperature and a chloride content below 10 ppm or with deionized water

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b) pre-cleaning with an aqueous surfactant solution at 50-8O ⁰ C with a pH value of preferably 1, 5

c) rinsing as a)

d) Acid pickling at 70 - 95 ° C flow temperature with a solution of the following composition:

Nitric acid 2 - 10%, preferably 5% hydrofluoric acid 0.05 - 0.5%, preferably 0.2% Aluminum nitrate 0.5 - 5%, preferably 2.1%

where preferably the ratio of the liquid

volume to the inner surface 5 l / m, the dwell time 1.5 min, the total exposure time is 30 min.

e) Rinsing with fully demineralized water, conductivity below 1 / λ, S

f) Alkaline pickling for silicon removal at 70 - 95 ° C and the following composition:

Sodium hydroxide 0.3 sodium aluminate 1

Sodium silicate 0.5

- 2%, preferably 0.4% -0.5%, preferably 0.002% (as aluminum powder)

- 5%, preferably 2.5%

the ratio of the volume of liquid to the inner surface is preferably 3 1 / m ^ _{un (} j ^ ie total contact time 120 min. Alkalis with other suitable counterions can also be used.

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g) rinsing as e)

h) Acid pickling at 70 - 95 C flow temperature with a solution of the following composition:

Nitric acid 2 - 10%, preferably 3% Hydrofluoric acid 0.05 - 0.5%, preferably 0.1% aluminum nitrate 0.5 - 5%, preferably 1%

where the ratio of liquid volume to inner surface area is preferably 5 l / m, the dwell time 1.5 min and the total exposure time 5 min. /

i) rinsing as e)

j) Rinsing with technically pure, residue-free methanol or ethanol of at least 99% Room temperature. (This alcohol should not contain any dissolved organic substances, e.g. traces of paint Transport barrels included)

k) Evacuation to 10 ~ mbar under an oil-free vacuum at room temperature

1) Flooding with dry inert gas (nitrogen or argon) and airtight sealing.

A particulate filter should be provided in the inlet to the part to be pickled to prevent renewed contamination to prevent impurities already removed in previous runs.

ORIGINAL INSPECTED

Claims (6)

INTERATOM 24.515.5 Internationale Atomreaktorbau GmbH D-5O6O Bergisch Gladbach 1 Cleaning method for soldered aluminum components Patent claims / Cleaning process for soldered hollow aluminum components with a low ratio of internal volume to internal surface using a stain Nitric acid and hydrofluoric acid with the following characteristics: a) The stain is forced to circulate through the component. b) The reactivity of the stain is reduced by adding an inhibiting substance. c) The initial reactivity of the stain and its residence time in the component are mutually exclusive coordinated that the reactivity decrease due to exhaustion and during a run the increase in reactivity as a result of the Substantially compensate for the temperature increase caused by the exothermic pickling reaction. d) The pickling process is continued as long as the final reactivity of the pickle is at least one tenth the initial reactivity is. 2. The method according to claim 1 with the following feature: We / Wa 29.07.1980 - 2 - 24.515.5 a) Aluminum nitrate is added to the stain. 3. The method according to claim 1 or 2 with the following feature: a) The component is flooded starting with the pickling at its lowest point. 4. The method according to claim 1 for components whose solder contains elemental silicon with the following Characteristic : a) The component is additionally pickled with an alkaline agent with the addition of an inhibitor. 5. The method according to claim 4 with the following mark times: a) A stain made from sodium hydroxide and sodium silicate is used. 6. The method according to claim 5 with the following mark times: a) Sodium aluminate is added to the pickle.