7/23/2023 0 Comments Pumping high viscosity liquids![]() ![]() Typically, urethane rubbers are considerably higher in price than natural rubber, however, this is compensated for with a simpler manufacturing process by forming in open moulds.įigure 4.4a Pump impeller made of urethane coated steel and pump casing of solid urethane rubber.A strong, vibrant research and development group is the lifeblood of all industries. In this respect, polyester based urethane rubber (Adiprene) is better. Urethane rubber has excellent wear properties and good resistance to oils, but polyester-based qualities are sensitive to hydrolysis. Urethane rubber has become popular for parts of pumps used for abrasive pumping for temperatures up to about 50☌, see figure 4.4a. ![]() Natural rubber is suitable for temperatures up to +70☌, whilst nitrile rubber can be more suitable when mineral oil contaminants are present although it is not so wear-resistant.Sharp particles can cut the surface of the rubber to pieces.The thickness of rubber should be 2 or 3 times the size of the particle in order to exploit the bouncing effect.If the angle of incidence lies between 5° and 30° the results will be Rubber gives favorable results if the particles strike the surface at right-angles, angle of incidence 90°, or if they move along the surface of the rubber.Soft rubber is better than hard rubber.The following applies to rubber claddings: The wear-resistance of rubber cladding is due to the fact that solid particles more or less bounce on the rubber surface without actually damaging it. Examples of this are Ni-Hard, a martensitic chromium steel, wherein the wear-resistance is obtained from chromium carbide granules embedded in a hard matrix. Combination of general hardness in the pump material with wear-resistance in individual elements in the pump material is a good thing.Wear-resistance is improved by increasing the hardness of the pump material, but this effect can only be significant if the pump material hardness figure exceeds about 300 Brinell.Material losses increase with the size and shape (sharp edged etc.) of the grain and in relation to the particle content.Material losses increase greatly when the hardness of the particles is greater than the material in the pump or liner.The following applies to hard materials, mainly steel with a high content of carbon and chromium: Hard metallic pump materials for abrasive liquids Delivery head per pump stage is limited therefore and is a maximum of about 50 m for rubber-clad pumps and about 100 m for pumps made of wear-resistant metals. This relationship infers that wear for a centrifugal pump with delivery head H increases in the proportion H 3/2 to H 7/2. It increases at least to the power of 3 with velocity, and cases are recorded of increases to the power of 7. Wear increases greatly with flow velocity for all qualities of material. Ceramics are also very good but, so far, plastics have not given very good results as pump materials for abrasive liquids. Wherever rubber cladding can be used, with regard to particle size and liquid temperature, it is superior to the hard metal materials. Two main groups of material are used for abrasive liquids, hard metals and various types of rubber cladding. In these pumps, not only are the wear margins large but even the pump shaft systems are designed to cope with the imbalance resulting from such wear. Examples of this are those pumps which are used for transporting abrasive solid materials such as ash, sand, macadam, etc. Surfaces subject to wear can also be fitted with replaceable liners or designed with a good margin for wear. To some extent the problems can be eased by choosing a pump design suitable for abrasive liquids. Liquids containing solid particles usually present considerable problems and demand pump materials for abrasive liquids.
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