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Salt spray test – Portable Ebook Reader Manufacturer – Touch Screen Tablet Notebook

Article by hi joiney

Testing equipment a salt spray cabinet The apparatus for testing consists of a closed testing chamber, where a salted solution (mainly, a solution of sodium chloride) is atomized by means of a nozzle. This produces a corrosive environment of dense saline fog in the chamber so that parts exposed in it are attacked under this severe corroding atmosphere. Typical volumes of these chambers are of 15 cubic feet (420 L) because the smallest volume accepted by ASTM-B-117, ISO 9927 (400 litres) and now discontinued DIN 50021 (400 litres). It has been found very difficult to attain constancy of corrosivity in exposure regions within the test chambers below 400 litres. Chambers are available from sizes as small as 9.3 cu ft (260 L) up to 2,058 cubic feet (58,300 L), most common machines range from 15 to 160 cubic feet (4204,500 L). Tests performed with a standardized 5% solution of NaCl are known as NSS (neutral salt spray). Results are represented generally as testing hours in NSS without appearance of corrosion products (e.g. 720 h in NSS acc. to ISO 9227). Other solutions are acetic acid (ASS test) and acetic acid with copper chloride (CASS test), each one chosen for the evaluation of decorative coatings, such as electroplated copper-nickel-chromium, electroplated copper-nickel or anodized aluminium. Some sources do not recommended to use ASS or CASS test cabinets interchangeably for NSS tests, as it is claimed that a thorough cleaning of the cabinet after ASS or CASS test is very difficult. ASTM does not address this issue, but ISO 9227 does not recommend it and if it is to be done, advocates a thorough cleaning. Standardization Electroplated and yellow chromated bolt with white corrosion Zinc flake coated bolt with red rust after testing Chamber construction, testing procedure and testing parameters are standardized under national and international standards, such as ASTM B 117 and ISO 9227. These standards describe the necessary information to carry out this test; testing parameters such as temperature, air pressure of the sprayed solution, preparation of the spraying solution, concentration, pH, etc. Daily checking of testing parameters is necessary to show compliance with the standards, so records shall be maintained accordingly. ASTM B 117 and ISO 9227 are widely used as reference standards. Testing cabinets are manufactured according to the specified requirements here. However, these testing standards neither provide information of testing periods for the coatings to be evaluated, nor the appearance of corrosion products in form of salts. Requirements shall be agreed between customer and manufacturer. In the automotive industry requirements are specified under material specifications. Different coatings have different behaviour in salt spray test and consequently, test duration will differ from one type of coating to another. For example, a typical electroplated zinc and yellow passivated steel part lasts 96 hours in salt spray test without white rust. Electroplated zinc-nickel steel parts can last more than 720 hours in NSS test without red rust (or 48 hours in CASS test without red rust) Requirements are established in test duration (hours) and coatings shall comply with minimum testing periods. Uses Typical coatings that can be evaluated with this method are: Phosphated surfaces (with subsequent paint/primer/lacquer/rust preventive) Zinc and zinc-alloy plating (see also electroplating). See ISO 4042 for guidance Electroplated chromium, nickel, copper, tin Coatings not applied electrolytically, such as zinc flake coatings acc. to ISO 10683 Organic coatings Hot-dip galvanized surfaces are not generally tested in salt spray test (see ISO 1461 or ISO 10684). Hot-dip galvanizing produces zinc carbonates when exposed to the environment, thus protecting the coating metal and reducing the corrosion rate. These by-products are not produced when a hot-dip galvanized specimen is exposed to a salt spray fog. Hence, hot-dip galvanized steel is not normally tested according to this test method and corrosion resistance is expressed as years of corrosion protection in different environments. See ISO 9223 for guidance. Painted surfaces with an underlying hot-dip galvanized coating can be tested according to this method. See ISO 12944-6. Testing periods range from a few hours (e.g. 8 or 24 hours of phosphated steel) to more than a month (e.g. 720 hours of zinc-nickel coatings, 1000 hours of certain zinc flake coatings). Examples of application of this test as an acceptance method for coated surfaces are the automotive, construction and aerospace industries. References Notes ^ http://www.singletoncorp.com/scch.html ^ http://www.autotechnology.net/Standard_Physical.asp ^ http://www.mahipindustries.com/files/Why_Mahip_Salt_Spray_Chambers.pdf Bibliography Metal Finishing. Guidebook and directory issue. Published by Metal Finishing Magazine, 1996 Further reading ASTM American Society for Testing of Materials. ASTM B 117-07a Standard Practice for Operating Salt Spray (Fog) Apparatus, 2007 Deutsches Institut fr Normung e.V. DIN 50021 Sprhnebelprfungen mit verschiedenen Natriumchloridlsungen. Beuth Verlag GmbH, 1988. This standard has been superseded by ISO 9227 and it is only mentioned for bibliographic purposes ISO International Organization for Standardization. ISO 9227 Corrosion tests in artificial atmospheres -- Salt spray tests, 2006 ISO International Organization for Standardization. ISO 4628-3 Paints and varnishes. Evaluation of degradation of coatings. Designation of quantity and size of defects, and of intensity of uniform changes in appearance. Part 3 Assessment of degree of rusting Categories: Metallurgical processes | Measuring instruments | Corrosion | Coatings