BS 4641-103:2010 pdf download – Method for specifying Electroplated coatings of chromium for engineering purposes
3.2 Information to be supplied to the purchaser by the electroplater Before processing, the electroplater shall inform the purchaser of visible surface defects such as porosity, cracks or undesirable coatings that are revealed by preliminary visual inspection and will prevent the production of a satisfactory electroplated finish. NOTE Guidance is given in A.3.
4 Sampling If specified by the purchaser [see 3.1.2 f)], samples for test purposes shall be selected in accordance with the procedures given in BS 6001. NOTE The choice of a suitable sampling plan should be agreed between the purchaser and the supplier.
5 Treatment of basis metals before electroplating
5.1 Stress relief If the purchaser specifies that stress relief treatment is required [see 3.1.1 d)], the necessary heat treatment shall be carried out in accordance with Appendix B.
5.2 Shot peening
5.2.1 If the purchaser specifies that shot peening treatment is required before electroplating [see 3.1.1 e)], the peening intensity, measured in accordance with Appendix C, shall be in accordance with Table 2 unless more specific requirements are stated on the drawing or in the peening schedule.
5.2.2 Freshly treated surfaces present conditions particularly favourable to corrosion. The first stage of electroplating shall therefore commence within 2 h of peening or, if this is not possible, a temporary protective coating shall be applied.
6.1 Properties of regular chromium
6.1.1 Appearance. Inspection of the coating [see 3.1.1 j)] shall be by normal or corrected vision to evaluate the significant surface for freedom from defects such as pits, cracks, blisters, exfoliation and nodular growths, except as are tolerated by the purchaser [see 3.1.2 b)].
6.1.2 Surface roughness. If a final surface roughness is specified by the purchaser [see 3.1.2 c)], the method of measurement shall be in accordance with BS 1134-1. NOTE 1 As a guide, for ground finishes, 0.4 4m R a may be regarded as a “commercial finish” and 0.2 4m R a as a “good commercial finish”. NOTE 2 Chromium, being brittle, has to be ground carefully with care being taken not to generate local hot spots or to induce cracking. NOTE 3 Chromium can be readily polished or lapped to improve surface finish. Super finishing can produce reflective surfaces of 0.05 4m R a .
6.1.3 Thickness. The minimum local thickness, as defined in BS 5411-1, of the chromium coating on the significant surface, when specified by the purchaser [see 3.1.1 i)], and of any undercoats, if required [see 3.1.1 h)], shall be determined in accordance with one of the methods listed in Appendix D, as agreed between the purchaser and the electroplater [see 3.1.2 g)]. The method selected shall be capable of giving an accuracy better than 10 % of the value measured. In the case of dispute, the microscopical method referred to in Appendix D shall be used. If the thickness of any undercoat is required, it shall be determined using the microscopical method referred to in Appendix D.
6.1.4 Final dimensions of the finished article. The final dimensions of the finished article, when specified by the purchaser [see 3.1.1 i)], shall be determined by the means of direct measurement agreed between the purchaser and the electroplater [see 3.1.2 h)].
6.1.5 Hardness. The hardness of the coating, if specified by the purchaser [see 3.1.2 d)], shall be measured using the Vickers method given in BS 5411-6.
6.1.6 Adhesion. If an adhesion test is specified by the purchaser [see 3.1.2 i)] the method shall be selected by the purchaser from those given in BS 5411-10.
6.1.7 Porosity. If a limit is specified by the purchaser in respect of cracks or porosity [see 3.1.2 e)], electroplated ferrous articles shall be subjected to the test given in Appendix E. The results of the test shall be evaluated in accordance with BS 3745. The rating shall be not less than that specified by the purchaser. NOTE For coatings of thickness greater than 30 4m, the rating should normally be at least 8.
6.2 Properties of other types of chromium
6.2.1 General. With these coatings the appearance, and also other properties such as hardness, may vary considerably from the requirements of regular chromium coatings. Inspection of the coating shall be by normal or corrected vision to evaluate the significant surface for smoothness, uniformity and freedom from electroplating defects which may affect their proper functioning or protective value. If appropriate, the requirements of 6.1 shall apply to these other types of chromium. NOTE See the guidance notes given in A.2.2.
6.2.2 Number and size of cracks. If the purchaser specifies that a micro-cracked chromium coating is required [see 3.1.1 j)], the number of cracks shall be measured in accordance with Appendix F.