AASHTO M298-10 pdf free download
AASHTO M298-10 pdf free download.Coatings of Zinc Mechanically Deposited on lron and Steel.
5. Workmanship
5.1 The coating shall be uniform in appearance and free of blisters, pits, nodules, flaking, and other defects that are capable of adversely affecting the function of the coating. The coating shall cover all surfaces as stated in 6.3 including roots of threads, thread peaks, corners, recesses, and edges. The coating shall not be stained or discolored throughout to an extent capable of adversely affecting appearance as a functional requirement. However, superficial staining, that results from rinsing or drying, and variations in color or luster shall not be cause for rejection.
NOTE 2—The nature of the mechanical plating process is such that coatings characteristically will not be as smooth or as bright as some electroplated coatings.
6. Requirements
6. 1 Appearance—The coating as deposited shall have a uniform silvery appearance, and a matte to medium-bright luster.
6.2 Process:
6.2.1 Stress-Relief Treatment—All steel parts that have an ultimate tensile strength of 1000 MPa and above and that contain tensile stresses caused by machining, grinding, straightening, or cold-forming operation shall be given a stress-relief heat treatment prior to cleaning and metal deposition. The temperature and time at temperature shall be 190 ± 1 5°C for a minimum of 3 h SO that maximum stress relief is obtained without reducing the hardness below the specified minimum.
6.2.2 High-strength steels (which become embrittled when charged with hydrogen) and that have heavy oxide or scale shall be cleaned before application of the coating in accordance with Practice . In general, nonelectrolytic alkaline, anodicalkaline, and some inhibited acid cleaners are preferred to avoid the risk of producing hydrogen embrittlement from the cleaning procedure.
6.2.3 For low-carbon steels, see Practice. Useful guidelines are also given in Guide
6.2.4 Mechanical deposition of zinc coatings shall consist, in general, of all of the steps listed below, and in the sequence as shown:
6.2.4.1 Preparation of the surface of the parts to be coated, by chemical (generally acidic) procedure to an extent that permits uniformly satisfactory results from subsequent steps.
6.2.4.2 Deposition of a thin metal coating, generally of copper, by immersion in appropriate chemical solutions, without the use of electric current. There are no thickness requirements for this coating.
6.3.1 The thickness of the coating everywhere on the significant surfaces shall be at least that of the specified class as defined in 3.1.
6.3.2 Significant surfaces are defined as those normally visible (directly or by reflection) that are essential to the appearance or serviceability of the article when assembled in normal position; or that are capable of providing the source of corrosion products that deface visible surfaces on the assembled article. When necessary, the significant surfaces shall be indicated on the drawing for the article, or by the provision of suitably marked samples.
NOTE 6—The thickness of mechanically-deposited coatings varies from point-to-point on the surface of a product. characteristically tending to be thicker on flat surfaces and thinner at exposed edges. sharp projections. shielded or recessed areas, interior corners and holes, with such thinner areas often being exempted from thickness requirements.
6.3.3 When significant surfaces are involved on which the specified thickness of deposit cannot readily be controlled, it is incumbent upon the purchaser and manufacturer to recognize the necessity for either thicker or thinner deposits. For cxample, to reduce buildup in thread roots, holes, deep recesses, bases of angles, and similar areas, the deposit thickness Ofl the more accessible surfaces will have to be reduced proportionately.AASHTO M298-10 pdf download.
