Download DZR Brass Certificate - Cobra
Download DZR Brass Certificate - Cobra
Download DZR Brass Certificate - Cobra
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RecognitionDezincification may show itself as dull red spots developing on the surface of brass after periods ofexposure to urban or industrial atmospheres. These do not usually represent any significant loss ofstrength in the component concerned but since they are more than simply superficial they cannot beremoved by the cleaning and polishing procedures that would normally the brass to its originalappearance.Dezincification in water fittings, taps and valves etc. can show itself in a variety of ways depending onthe water composition and service conditions. Water may be seen seeping through the walls of fittingswith an accompanying whitish deposit of zinc and lime scale on and around the leak site. In exposedfittings this would probably be the time when the corrosion and resultant water leak is noticed andattended to. On under wall or underground fittings dezincification takes on worse proportions as thedezincification could be occurring from both inside and outside of the fitting. The first small loss ofwater will probably be noticed until the time that flooding occurs due to gross breakage.Conditions for dezincificationThere are a number of factors that will predispose brass to dezincify.• Water hardness and the acidity or alkalinity of water away from a PH of 7.• Temperature. The higher the temperature the greater the risk• Water flow. Less flow equals greater risk• Polluted atmosphere• Large brass grain size• Sea or brackish water• Corrosive soils such as acid peat, salt marsh, waterlogged clay, or ‘made up’ groundcontaining cindersWhat is <strong>Cobra</strong> Dezincification resistant brass?<strong>Cobra</strong> <strong>DZR</strong> brass for casting ingot follows the specification of SA alloy code 9A which is a derivativeof British Standard <strong>DZR</strong> brass composition CZ132. In addition to this extra grain refining processesare exerted on the material in the foundry. There is a definite link between grain size anddezincification resistance that is both documented within the industry and has been the subject ofextensive study in our two <strong>Cobra</strong> foundry laboratories. The smaller the grain size the greater theresistance to corrosion. <strong>Cobra</strong> brass is refined to the point that individual grains no longer exist andour brass is one homogenous mass. These refining processes are in addition to the compositionrequirements. <strong>Cobra</strong> brass for pressing and turning follows the same specification as the castingmaterial but with slight modifications to suit the machining processes to which it will be exerted.In order to maintain impurity levels lower than can be expected from raw material brass suppliers<strong>Cobra</strong> has built a smelting plant and we produce our own raw material brass ingot.Each of our two brass foundries is has its own on-site laboratory equipped with Fisons 3460 sparkemission spectrometers. The chemical composition of each production furnace is constantlymonitored and kept within the written specification for 14 separate elements. Each <strong>Cobra</strong> componenthas a sub chemical composition specification, which allows for the best composition for a givencomponent within the broader <strong>DZR</strong> specification. For example, one head part cover casts best at0.25% aluminum and another similar item is best at 0.18%. Composition control is maintained inmass production right down to these miniscule amounts.3