Home>ASTM Standards>ASTM B319-91(R2020) pdf free download

ASTM B319-91(R2020) pdf free download

ASTM B319-91(R2020) pdf free download.Standard Guide for Preparation of Lead and Lead Alloys for Electroplating
1. Scope
1.1 This guide provides methods for preparing lead or lead alloy products for the application of electroplated or autocata- lytic coatings. 1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appro- priate safety, health, and environmental practices and deter- mine the applicability ofregulatory limitations prior to use. 1.3 This international standard was developed in accor- dance with internationally recognized principles on standard- ization established in the Decision on Principles for the Development of International Standards, Guides and Recom- mendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
4. Nature of Lead
4.1 The tensile strength of lead and lead alloys ranges from 15 to 35 MPa (2000 to 5000 psi), therefore, the measured adhesion of electroplated coatings cannot be greater than these values. 4.2 Difficulties in applying high-quality electroplated coat- ings to lead are due to the following properties of lead: 4.2.1 The very active chemical nature oflead, leading to the formation of oxide films in air, 4.2.2 The fact that the lead surface will form films of insoluble lead salts with most acids used in pickling, 4.2.3 The ease with which lead diffuses in contact with nonferrous metals, and 4.2.4 The poor resistance to plastic deformation during polishing.
5. Process Precautions
5.1 The following process precautions should be observed: 5.1.1 Precleaning of raw castings is sometimes necessary to remove mold parting compounds, surface oxides, and residues from recessed areas which are never reached by polishing- wheel or scratch-brush operations (Section 6). 5.1.2 In high-speed type cyanide electroplating solutions, the initial current density must be controlled and kept low enough so that no gassing occurs to cause poor adhesion. This is revealed as groups of blisters in the high-current-density areas of the electroplate. 5.1.3 If a strike electroplate is used, it should be thick enough to prevent the next electroplating solution from attack- ing the basis lead. Acopper or nickel strike 2.5 µm thick should be used, but because there are so many variables involved, no specific recommendations can be made. 5.1.4 Preplates should be of such thickness that complete alloying with the lead does not take place, an occurrence that causes poor adhesion of subsequent deposits. This defect is indicated by blistering after prolonged storage or after an accelerated aging test. 5.1.5 The lead compounds formed by the action ofacids and alkalies most often used in electroplating are not water soluble. Caution must be taken to remove or prevent the formation of these to eliminate subsequent adhesion failure. Acids that cannot be used are sulfuric, hydrochloric, and hydrofluoric. (Acids that can be used are sulfamic and fluoboric.) Alkalies should not be high in caustic content. Mild or buffered cleaners are preferred in order to minimize attack on the basis lead surface. 5.1.6 Engraving of electroplated finishes on lead cannot be performed on deposits over 5 µm thick as the deposit will tear away from the lead at cross cuts. Engine turning by burnishing can be done on any thickness of deposits. 5.1.7 Polishing and coloring of the deposit must be per- formed at slow speeds, and with loose or cooled buffs to eliminate overheating and flowing of basis metal.
6. Precleaning
6.1 Remove fins and parting lines by use oftrimming dies or by scraping, filing, or grinding. Some machining may be done at this point, such as drilling holes, or milling or cutting slots, groove, flats, or squared surfaces. 6.2 Clean in alkaline, emulsion type, or other standard cleaning material to remove surface materials (5.1.5). 6.3 After rinsing, transfer the parts into one ofthe following pickling solutions, the function of which is to remove surface oxides, without significant attack on the lead surface. 6.3.1 An aqueous solution containing 250 mL of48 mass %, fluoboric acid with or without 45 mL of 30 mass % hydrogen peroxide diluted to 1 L. The addition ofhydrogen peroxide will increase the aggressiveness of the pickling solution. 6.3.2 An aqueous solution containing 80 mL of glacial acetic acid and 45 mL of30 mass % hydrogen peroxide diluted to 1 L. 6.3.3 An aqueous solution containing 100 g ofsulfamic acid diluted to 1 L. N OTE 1—These pickling solutions should be held in tanks having suitable nonmetallic linings. 6.4 After rinsing, an immersion in a water-displacing, film- forming material is advantageous. Sometimes a neutral soap, oil, or synthetic emulsion film may be used according to the type of polishing compound to be used. These materials are removed in subsequent operations.

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