Copper and Copper Alloy Products
These include sheet, strip, tube, wire, other wrought shapes and castings. When thin and of a high surface, scratches, gougings, tears, etc., may ruin de product to the extent of the damaged area. Sea-water and fresh water produce stains, and sea water may give rise to some corrosion. If stains are superficial, the product can be used, but if rough and pitted, the material may be rejected.
Slight corrosion by general atmospheric conditions may also occur. Manufacturing defects in castings, such as scabbiness, roughness or folds (‘pinches’), can be readily identified, as these cannot be produced by rough handling or by corrosion in transit.
Surface defects to cast or wrought products, apart from corrosion pits, scratches and dents, can usually be attributed to faulty manufacture. Scabbiness is caused by the metal splashing when it is poured into the mould and cooling in droplets on the side. An oxide film is formed around these droplets which prevents them uniting with the rest of the metal in the ingot.
Roughness is caused by the ingot sticking to the mould, causing a tearing of the surface on removal. Folds (‘pinches’) are caused in casting with too low a pouring rate, allowing a series of oxide films to be formed. All three defects originate in a faulty ingot and the faults remain because of the inability of oxidized surfaces to weld together.
Superficial staining or light corrosion to wrought products may be removed by the use of mild abrasives, and provided the product is not made to accurate dimensions, scratches, etc., may also be polished out with an abrasive. Solutions containing ammonia should not be used for cleaning.