Cartridges & Mechanical Seals

79 • Code U: Inserted / welded tugsten carbide. An extremely hard and tenacious material. It is appropriate for applica- tions with a pH of more than 6 (in the case of welded parts). Good behaviour with respect to wear under severe conditions. Good thermal conductivity. High elastic modulus, meaning it is not likely to become deformed, especially in high pressure applications. Limited chemical resistance, especially to acid products. A very high density material, which can be critical in high speed rotating operations. Limited capacity to withstand dry operation conditions or extremely li- mited lubrication conditions, especially when working with the same material . • Code U 1 : Solid tungsten carbide with nickel. An extremely hard and tenacious material. Limited chemical re- sistance, especially to acid products. Suitable for applications with pH values above 2. Good behaviour with respect to wear under severe conditions. Good thermal conductivity. High elastic modulus, meaning it is not likely to become deformed in compari- son with metal materials. A very high density material, which can be critical in high speed rotating operations. Limited capacity to withstand dry operation conditions or extre- mely limited lubrication conditions, especially when working with the same material. M etal carbides Metal carbides are extremely hard materials manufactured by sintering. They have high chemical and wear resistance and are used in environ- ments with solids or particles which can attack soft materials such as carbon. • Code Q: Silicon carbide. Good resistance to wear and to friction in heavy duty work. It is the per- fect material for working in contact with abrasive and corrosive fluids, and at high pressures. Its main characteristics are as follows: -High thermal conductivity, comparable to tungsten carbide. -Low resistance to thermal shock. -High elasticity modulus. -Good chemical resistance. -Lower density than tungsten carbide. May be subject to chemical attack by certain strong alkaline products. For that reason it is important to choose the most appropriate silicon carbide grade: Q 1 : Contains no free silicon. It has the best chemical resistance of all carbides, but low tenacity. Its friction characteristics are poorer than grade Q2, but higher than those of tungsten carbide. Q 2 : Contains free silicon. It has the best friction characteristics of all silicon carbides. Some acid or alkaline substances may cause lixiviation in free silicon but in general, it is more inert than tungsten carbide. Q 6 : Has a silicon and graphite carbide base. This mixture combines the high resistance to wear of silicon carbide and the lubricant properties of graphite. Silicon carbide normally runs against resin-impregnated graphite (B), but metal carbons may also be used for high performance (hot water applications). The silicon carbide and carbon combination is frequently used, providing long life in a wide range of conditions due to its excellent resistance to thermal shock. In applications with abrasives, it is advisable to use silicon carbide against tungsten carbide, which is the most effective combination due to its resistance to wear and friction. Silicon carbide may work against itself in very abrasive conditions but the friction characteristics are not as good as silicon carbide against tungsten carbide. When silicon carbide is used against itself, the best results are obtained using different types, for instance Q 1 against Q 2 or Q 2 against Q 6 . When hard material is worked against hard, the limited conditions of the application may give rise to sudden changes in surface tem- perature and dry operation. Although this occurs with a short space of time, it is best to use silicon carbide with graphite-impregnated silicon carbide (Q 6 ). Due to its graphite content, this combination is resistant to the absence of lubrication for a limited time. Metals • Code E: AISI 420 chromium steel. This is tempered stainless steel with a surface hardness of less than 50 HRc. It is used with fluids such as water or oils. • Code F: Nickel-chromium steel AISI 304. Stainless steel used to manufacture springs and auxiliary parts. • Code F 1 : Nickel-chromium steel. Stainless steel with good chemical resistance, used for fluids such as water, oils, chemicals, etc. • Code G: AISI 316 nickel-chromium-molybdenum steel. Stainless steel with very good chemical resistance used with water, oils, hydrocarbons and chemicals. • Code G 2 : AM350 nickel-chromium-molybdenum steel. Specifically for metal bellows that must work at high temperatures up to +300ºC. • Code L: Nickel-chromium-molybdenum steel; AISI 316L. Stainless steel with excellent chemical resistance. It provides a homogeneous surface with no pores and is recommended for hygienic applications. • Code Z: Nickel-chromium-molybdenum steel with chrome oxide. It is a coating of Chromium Oxide deposited on the steel by means of plasma. The hardness is superior to that of stellite steel. • Code Z 2 : Nickel-chromium-molybdenum stellite steel. To obtain it, the steel surface is treated with plasma, leaving a thickness of 0.2 to 0.3 mm. with considerable surface hardness and increased resistance to wear.