Method and cleaning system for cleaning the process gas in soldering installations

Abstract

The invention relates to a method for cleaning the process gas in soldering installations and solder suction systems, in particular for reducing the abietic acid in the process gas, wherein the process gas to be cleaned is conducted through a cleaning system which contains one or more of the following compounds (cleaning compounds): a) carboxylic acids with reducing properties, namely oxalic acid, formic acid, citric acid and/or ascorbic acid: b) metal compounds of higher oxidation states, namely manganates, permanganates, chromates and/or dichromates; c) alcohols which can be convened into the carboxylic acids mentioned in a) by means of oxidation; d) basic lime compounds.

Claims

1. A method for cleaning the process gas in soldering installations or solder suction systems by reducing abietic acid in the process gas comprising: conducting the process gas to be cleaned through a cleaning system comprising a cleaning chamber which contains one or more cleaning compounds selected from the group consisting of: a) carboxylic acids selected from oxalic acid, formic acid, citric acid, ascorbic acid, or combinations thereof; b) metal compounds of higher oxidation states selected from manganates, permanganates, chromates, dichromates, or combinations thereof; c) alcohols which can be converted into oxalic acid, formic acid, citric acid, and/or ascorbic acid by means of oxidation; d) basic lime compounds; and e) combinations thereof, wherein said abietic acid chemically reacts with said one or more cleaning compounds thereby reducing the abietic acid in said process gas.

2. The method according to claim 1, wherein the cleaning system comprises oxalic acid and a permanganate, calcium hydroxide, or combinations thereof.

3. The method according to claim 2, wherein the cleaning system comprises potassium permanganate.

4. The method according to claim 1, wherein the cleaning system comprises a filter material mixed with the one or more cleaning compounds.

5. The method according to claim 4, wherein the one or more cleaning compounds are mixed with the filter material by coating, impregnation, or combinations thereof whereby the filter material increases the reaction surface of the cleaning chamber compared to a cleaning system without the filter material.

6. The method according to claim 5, wherein the filter material is selected from the group consisting of aluminum oxide, silica gel, diatomaceous earth, zeolites, cellulose, glass wool, metal braiding, and combinations thereof.

7. The method according to claim 6, wherein the cleaning system further comprises potassium permanganate, calcium hydroxide, or combinations thereof.

8. The method according to claim 1, wherein cleaning of the process gas takes place inside or outside of a process zone at a temperature below 500° C.

9. The method according to claim 8, wherein the cleaning of the process gas is carried out at a temperature of 350° C.

10. A method of reducing condensed depositions of volatile flux elements on soldering installation or solder suction system surfaces by reducing abietic acid in the process gas comprising: introducing a process gas from the soldering installation or solder suction system comprising the volatile flux elements into a conductor, wherein the process gas comprises the volatile flux elements; conducting the gas from the conductor into a cleaning chamber; optionally conducting the gas from the cleaning chamber into a heat exchanger via a discharge; and optionally feeding the cleaned process gas from the heat exchanger back to the soldering installation or solder suction system, wherein the cleaning chamber comprises at least one cleaning compound selected from the group consisting of: a) carboxylic acids selected from oxalic acid, formic acid, citric acid, ascorbic acid, or b) combinations thereof; c) metal compounds of higher oxidation states selected from manganates, permanganates, chromates, dichromates, or combinations thereof; d) alcohols which can be converted into oxalic acid, formic acid, citric acid, and/or ascorbic acid by means of oxidation; e) basic lime compounds, and f) combinations thereof, wherein said abietic acid chemically reacts with said at least one cleaning compound thereby reducing the abietic acid in said process gas.

11. The method according to claim 10, wherein the volatile flux elements are generated from flux comprising colophony.

12. The method according to claim 10, wherein the at least one cleaning compound is selected from oxalic acid, potassium permanganate, calcium hydroxide, or combinations thereof.

13. The method according to claim 10, wherein the cleaning system comprises filter material mixed with the at least one cleaning compound.

14. The method according to claim 13, wherein the filter material is selected from the group consisting of aluminum oxide, silica gel, diatomaceous earth, zeolites, cellulose, glass wool, metal braiding, and combinations thereof.

15. The method according to claim 14, wherein the at least one cleaning compound is mixed with the filter material by coating, impregnation, or a combination thereof, whereby the filter material increases the reaction surface of the cleaning chamber compared to a cleaning system without the filter material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the drawing:

(2) FIG. 1 shows a schematic representation of a portion of a soldering installation (willow soldering installation) baying a cleaning system according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

(3) FIG. 1 shows a detail of a soldering installation 1 having a cleaning system according to the invention, comprising a cleaning chamber 4. The cleaning chamber 4 contains filter material in the form of Al.sub.2O.sub.3 granulate 3, which is mixed with oxalic acid 3a.

(4) For cleaning the process gas, the same is initially introduced into a conductor 2, from where the process gas to be cleaned (see arrow) is conducted into the cleaning chamber 4. After leaving the cleaning chamber 4, the process gas is fed to a heat exchanger 6 via a discharge 5.

(5) From the heat exchanger 6, the cleaned process gas is fed back to the soldering installation. In the present example, the process gas increasingly includes abietic acid from the colophony, i.e. the flux. After leaving the cleaning chamber, the process gas is almost free of abietic acid. Above all, this has to be attributed to the fact that the oxalic acid has split the abietic acid, (in particular, the methyl groups from the abietic acid have been split off.) The resulting products with lower molecular weights do not condense at the inner walls etc. of the soldering installation, but rather remain in the process gas and can be extracted from the same at some other point (e.g. by means of special filters).

(6) Table shows the compositions of different fluxes winch can occur in the process gas. With each of the fluxes mentioned, optimal cleaning of the process gas was possible, such that hardly any precipitations could be identified at the inner walls of the soldering installations.

(7) TABLE-US-00001 TABLE 1 Flux: Example 1 Composition: Resin 45-55% Activators  8-15% Solvents 30-40% Rest  2-10% CAS EC Ingredients No No Weight % alpha-terpineol 98- 202- 15 to 20 55-5 680-6 Dicarboxylic acid 124- 204-  5 to 10 04-9 673-3 Thermoplastic resins 8050- 232- 15 to 20 09-7 475-7 Example 2 Flux: CAS Ingredients No % Castor oil 8001- n/s 79-4 Colophony 8050- 40 to 70 09-7 Malonic acid 141- 3 to 7 82-2 2-ethylhexane-1,3-diol 94-96-2 15 to 40 Polyoxyethylene(15)docosyne 61791-  5 to 10 14-8 Polyethylene glycol 9004- n/s monobutyl ether 77-8 Example 3 Flux: CAS Ingredients No % Carboxylic acids 68603-  5 to 10 87-2 2-ethylimidazole 1072-  5 to 10 62-4 Succinic acid 110- 1 to 5 15-6 Solvents: the solvents used are, on the one hand, multi-branched glycol ethers having high boiling points (>260). On the other hand, alcohols having multiple hydroxy groups are used.(these solvents burn without residues and in a colorless manner) Resins: modified, color-stable natural resins are used. Partly hydrogenated, partly chemically modified in some other way.(as with all resins, after having been burnt, residues remain) Additives: micronized waxes, organic natural oil derivatives, multi-branched organic acids