1、STD-AECMA PREN 2437-ENGL 1998 LOL232L 0034847 080 AECMA STANDARD NORME AECMA AECMA NORM prEN 2437 Edition 1 September 1998 PUBLISHED BY THE EUROPEAN ASSOCIATION OF AEROSPACE INDUSTRIES (AECMA) Gulledelle 94 - 8-1200 BRUXELLES - Tel. (+32) 2 775 81 10 - Fax. (+32) 2 775 81 11 ICs: Descriptors: ENGLIS
2、H VERSION Aerospace series Chromate conversion coatings (yellow) for aluminium and aluminium alloys Srie arospatiale Luft- und Raumfahrt Chromatation jaune Gelbchromatieren de laluminium et des alliages daluminium von Aluminium und Aluminiumlegierungen This “Aerospace series“ Standard has been drawn
3、 up under the responsibility of AECMA (The European Asso cia tion of Aerospace In dus tries). It is published on yellow paper in three equivalent versions (English, French, German). It will be submitted as a draft European Standard to CEN (European Committee for Standardization) for formal vote. Edi
4、tion approved for publication 1998-09-30 The equivalent versions in French and German languages can be supplied by B.N.A.E. - Technopolis 54 - 199, rue Jean-Jacques Rousseau 92138 ISSY - LES - MOULINEAUX CEDEX - FRANCE I I aecma 1998 COPYRIGHT Association Europeene Des Constructeurs de Materiel Aero
5、spaceLicensed by Information Handling ServicesSTDmAECMA PREN 2437-ENGL 1998 m 1012311 0014848 TL7 m Page 3 prEN 2437: 1998 I Scope This standard specifies yellow chromate conversion coating of aluminium and aluminium alloys. It shall be applicable wherever referenced. 2 Purpose of process To increas
6、e corrosion resistance and to improve the adhesion of paints and varnishes. Type B coatings are also suitable for the repair of mechanically damaged anodic coatings. 3 Normative references This European Standard incorporates by dated or undated reference provisions from other publications. These nor
7、mative references are cited at the appropriate places in the text and the publications are listed hereafter. For dated references, subsequent amendments to or revisions of any of these publications apply to this European Standard only when incorporated in it by amendment or revision. For undated ref
8、erences the latest edition of the publication referred to applies. IS0 8081 Aerospace process - Chemical conversion coating for aluminium alloys - General purpose IS0 9227 Corrosion tests in artificial atmospheres - Salt spray tests EN 2000 Aerospace series - Quality assurance - EN aerospace product
9、s - Approval of the quality system of manufacturers EN 2334 EN 3997 Aerospace series - Acid chromate pickling of aluminium and aluminium alloys 1) Aerospace series - Aluminium alloy AL-P2024- - T3 - Sheet and strip - 0,4 mm 5 a I 6 mm 2) 4 Definitions For the purposes of this standard, the following
10、 definition applies: batch parts treated at the same time in the same bath. 5 Classification 5.1 Thickness - Type A: Mass per unit area from 0,2 g/m2 to 0,42 g/m2 for slight corrosion protection, where low electrical resistance is required; - Type B: Mass per unit area from 0,42 g/mZ to 1,2 g/m2 for
11、 good corrosion protection, with or without painting. 1) Published as AECMA Standard at the date of publication of this standard 2) Published as AECMA Prestandard at the date of publication of this standard Previous page is blank COPYRIGHT Association Europeene Des Constructeurs de Materiel Aerospac
12、eLicensed by Information Handling Services5.2 Materials - Category 1: Aluminium alloy with an Si-content I 3,5 %; - Category 2: Aluminium alloy with an Si-content 3,5 %. 6 Information for the processor - Designation, see 16. - Areas not to be chromated. 7 Condition of parts prior to processing Solde
13、ring, welding, mechanical operations and heat treatments (except for cold storage) shall be completed. The parts to be chromate coated after assembly (e.g. by spot welding) shall be pickled prior to assembly. Areas not to be chromate coated shall be suitably masked. 8 Pre-treatment 8.1 Cleaning The
14、cleaning method shall be chosen according to the degree of contamination of the materials to be treated. In general, the most effective method is degreasing with solvents followed by cleaning in an alkaline solution (see annex A, A.2). 8.2 Rinsing The parts shall be rinsed thoroughly, e.g. by immers
15、ion followed by spray washing. It is recommended that a further rinsing be carried out in deionised water with a maximum specific conductivity of 100 pS e cm-. 8.3 Pickling It shall not cause pitting or any alterations to the metallurgical characteristics or mechanical strength of the material. The
16、dimensions and the surfaces roughness value indicated on the drawings shall be observed. Pickling is normally carried out in a solution containing chromate. Other methods may be used (see annex A, A.4). 8.4 Rinsing See 8.2. COPYRIGHT Association Europeene Des Constructeurs de Materiel AerospaceLicen
17、sed by Information Handling ServicesSTD-AECMA PREN 2437-ENGL L998 10123lL 0034850 b75 W Page 5 prEN 2437: 1998 9 Treatment The parts are submerged in a still or agitated bath or treated by spraying or by brushpainting An exemple of the possible composition of the chromate solution is given in annex
18、A, A.5. However, a commercial product is generally used according to the manufacturers instructions. 10 Post-treatment 10.1 Rinsing See 8.2. The quality of the water shall not adversely affect the adhesion of paints or varnishes. Rinsing in hot water at 50 “C to 60 “C helps the drying process though
19、 the parts shall not be submerged for longer than 1 min. 10.2 Drying Drying may be carried out at ambient temperature using dry, oil-free compressed air or hot air, at max. 60 “C. Alternative drying processes are permissible, provided that they do not have an adverse effect on the quality of the chr
20、omate coating and subsequent treatments. 10.3 Paints or varnishes The primer or the varnish coat shall be applied as soon as possible (max. 48 h after chromate coating). 11 Removal of the chromate coating Either by using a nitric acid solution (e.g. d = 1,4) at ambient temperature or a chromic acid
21、solution (e.g. 40 g/l to 60 g/I) at 40 “C or mechanically by light abrasion. Strong alkaline pickling shall be avoided. i2 Requirements 12.1 Appearance The chromate coating shall be iridescent and range in colour from light yellow to dark yellow depending on the type of alloy. It shall be uniform an
22、d free from defects. Powdey coatings are not acceptable. Differences in colour due to different surface textures are permissible. 12.2 Mass of coating See 5. COPYRIGHT Association Europeene Des Constructeurs de Materiel AerospaceLicensed by Information Handling ServicesSTD-AECMA PREN 2q37-ENGL 1998
23、m LOL2311 001485L 501 m Page 6 prEN 2437: 1998 12.3 Corrosion resistance After testing, a maximum of five corroding points is permissible per test piece and the diameter of each point shall not exceed 0,8 mm. The inspection shall not be carried out at less than 6 mm from: - the test piece edges; - t
24、he marking; - the mounting points. 13 Inspection and test methods 13.1 Parts Each batch shall be subjected to a visual inspection with the naked eye. The number of parts to be tested per batch shall be agreed between the purchaser and processor. For pipes, the inspection shall be carried out using e
25、ither an endoscope, or a cross section at a position where the geometry is the least favorable. 13.2 Test pieces The quality of the chromate coating shall be checked regularly and at least once every three months on at least three test pieces: - in aluminium alloy EN 3997 unplated; - dimensions: 75
26、mm x 250 mm x 0,8 mm to 1 mm. 13.2.1 Mass per unit area See IS0 8081. 13.2.2 Corrosion resistance Chromate coated test pieces shall be: - aged for at least 24 h at ambient temperature; - exposed to a continuous salt spray test according to IS0 9227 at an angle of inclination of 6“ to the perpendicul
27、ar line: - thickness type A: 72 h; - thickness type B: 168 h; - rinsed in cold, running water, to remove sodium chloride residues; - air dried. Inspection shall be made visually. 13.3 Baths The solution shall be checked daily, prior to use, for liquid level, cleanness and temperature. Chemical analy
28、ses shall be carried out on the constitution of the bath and at regular intervals during operation. A fresh preparation is required if corrections remain ineffective. COPYRIGHT Association Europeene Des Constructeurs de Materiel AerospaceLicensed by Information Handling ServicesSTD.AECMA PREN 2437-E
29、NGL 1998 1012311 0014852 448 H Description block CHROMATATE COATING Page 7 prEN 2437: 1998 Identity block EN2437-2A 14 Quality assurance 14.1 Approval of the processor See EN 2000. 14.2 Process approval The processor shall carry out: - chromate coating on a series of pre-production parts made up of
30、the first batch of the parts; - tests specified in this standard, unless otherwise agreed between the purchaser and processor. When the test results have been accepted as satisfactory by the purchaser, he shall give his written approval to start production. The procedure shall not be changed without
31、 previous agreement from the purchaser. 14.3 Acceptance The frequency and nature of the inspection of parts and test pieces shall be defined in the definition documents or determined by agreement between the purchaser and processor. The parts showing defects on visual inspection shall be removed. Fa
32、ulty areas can only be touched up with the purchasers agreement. 15 Locally applicable regulations and laws shall be observed. Health, safety and environmental aspects 16 Designation EXAMPLE: Type (see 5.1) Category (voir 5.2) COPYRIGHT Association Europeene Des Constructeurs de Materiel AerospaceLi
33、censed by Information Handling ServicesPage 8 prEN 2437: 1998 Annex A (normative) Recommendations for surface preparation A.1 Scope This annex describes solvents and bath preparation as well as processes for cleaning, pickling and yellow chromate conversion coating of aluminium and aluminium alloys.
34、 All processes providing results which are at least equivalent to the one described may also be applied. A.2 Degreasing A.2.1 In organic solvents This process comprises hot or cold degreasing at liquid or vapour state with authorized products. A22 Alkaline cleaning This process may be used either al
35、one or in addition to degreasing with solvents. Inhibitors shall be added to the degreasing baths in order to prevent the metal surfaces from being attacked. They can be used in a hot or cold state and with or without electric current. , I A.3 Cleaning by abrasive blasting A.3.1 Coarse cleaning This
36、 type of cleaning is achieved by means of blasting with a grain size 1 O0 pm, with or without water. This process is not applicable to thin parts or parts with low surface roughness. A.3.2 Fine cleaning This type of cleaning is achieved by blasting with a grain size e 100 pm, with or without water.
37、After cleaning remove any blasting medium still adhering to the parts and decontaminate the parts by suitable pickling. COPYRIGHT Association Europeene Des Constructeurs de Materiel AerospaceLicensed by Information Handling ServicesSTD-AECMA PREN 2437-ENGL 1998 W 1012311 0014854 210 Page 9 prEN 2437
38、: 1998 A.4 Pickling A.4.1 Acid pickling A.4.1.1 Acid chromate pickling for class 1 materials See EN 2334 A.4.1.2 Other acid pickling media for materials of classes 1 and 2 Commercial or other products, e.g. those containing fluorides, may be used. A.4.2 This process, based on sodium hydroxide shall
39、not be used for parts with close tolerances or for parts fastened by rivets or spot welding. Moreover, it increases surface roughness. The degreased metal is immersed in the following solution: Alkaline pickling for class 1 materials - Sodium hydroxide : 26gto50g; - Sodium heptonate or gluconate : 0
40、,75 g to I ,O g; - Temperature : 40 “C to 65 OC. The reaction is very strong and normally an immersion time of 15 s to 1 min is sufficient. The rate of removal by the alkaline bath is 0,6 pmlmin to I ,5 pmlmin. A.4.3 De-smutting The film remaining after akaline pickling and some acid-pickling proces
41、ses shall be rem a solution of 30 % to 50 % by volume of nitric acid (d = I ,4) at ambient temprature. ved by immersion i AS Chromate coating The following preparation may be used as the bath solution: - Na,Cr,O, .2H,O : 73 gil; - NaF : 1 g/l; - K3 Fe (CN),I : 5 gll; - “03 : 1,15gll; - Water - Solution temperature - Treatment time - PH : : 1,2 to 2,2; maximum specific conductivity 1 O0 pS . cm-; 15 “C to 55 “C; 5 s to 8 min. : : COPYRIGHT Association Europeene Des Constructeurs de Materiel AerospaceLicensed by Information Handling Services
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