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   As for the chemical handing pump, its material is very important. Because it should have a chemical resistance against the liquid, which is handled with. Basically, we should select a suitable chemcial material according to the chemcial liquid type and its working condition, such as temperature, viscosity, S.G. and so on.

   In SIKO pump range, we widely use three types of material, they are Stainless steel, PP, and PTFE. They are also very widely used in most chemical industry area. Here we have a biref introduction about them.  Go to our download center, to download a much complete Chemcial Resistance Sheet(click here).


  

   Stainless steel

   High oxidation-resistance in air at ambient temperature is normally achieved with additions of a minimum of 13% (by weight) chromium, and up to 26% is used for harsh environments. The chromium forms a passivation layer of chromium oxide (Cr2O3) when exposed to oxygen. The layer is too thin to be visible, and the metal remains lustrous. The layer is impervious to water and air, protecting the metal beneath. Also, this layer quickly reforms when the surface is scratched. This phenomenon is called passivation and is seen in other metals, such as aluminium and titanium. Corrosion-resistance can be adversely affected if the component is used in a non-oxygenated environment, a typical example being underwater keel bolts buried in timber.

   Two corrosion-resistant stainless steel alloys, Type 304 and Type 316, are ideally suited for a variety of applications.  

   Type 304 is commonly used for chemical processing equipment, for food, dairy, and beverage industries, for heat exchangers, and for the milder chemicals.

   Type 316 contains molybdenum to control pit type attack so it is slightly more corrosion-resistant than Type 304 stainless steel. Type 316 is ideal for chemical and pulp handling equipment, for photographic equipment, food and beverage processing and for dispensing equipment and equipment that will be exposed to salt water.
Type 316L is an extra-low carbon modification of Type 316 stainless steel used when applications are welded.  


    PP(polypropylene)

   Most commercial polypropylene is isotactic and has an intermediate level of crystallinity between that of low-density polyethylene (LDPE) and high-density polyethylene (HDPE). Polypropylene is normally tough and flexible, especially when copolymerized with ethylene. This allows polypropylene to be used as an engineering plastic, competing with materials such as ABS. Polypropylene is reasonably economical, and can be made translucent when uncolored but is not as readily made transparent as polystyrene, acrylic, or certain other plastics. It is often opaque or colored using pigments. Polypropylene has good resistance to fatigue.

   The melting of polypropylene occurs as a range, so a melting point is determined by finding the highest temperature of a differential scanning calorimetry chart. Perfectly isotactic PP has a melting point of 171 degree. Commercial isotactic PP has a melting point that ranges from 160 to 166 degree.

   The melt flow rate (MFR) or melt flow index (MFI) is a measure of molecular weight of polypropylene. The measure helps to determine how easily the molten raw material will flow during processing. Polypropylene with higher MFR will fill the plastic mold more easily during the injection or blow-molding production process. As the melt flow increases, however, some physical properties, like impact strength, will decrease. 


   PTFE(Teflon)

   PTFE is a thermoplastic polymer, which is a white solid at room temperature, with a density of about 2.2 g/cm3. According to DuPont, its melting point is 327 degree, but its properties degrade above 260 degree. PTFE gains its properties from the aggregate effect of carbon-fluorine bonds, as do all fluorocarbons.

   Because of its chemical inertness, PTFE cannot be cross-linked like an elastomer. Therefore, it has no "memory" and is subject to creep. This is advantageous when used as a seal, because the material creeps a small amount to conform to the mating surface. However, to keep the seal from creeping too much, fillers are used, which can also improve wear resistance and reduce friction. Sometimes, metal springs apply continuous force to PTFE seals to give good contact, while permitting a beneficially low percentage of creep.

   PTFE's high corrosion resistance makes it ideal for laboratory environments as containers, as magnetic stirrer coatings, and as tubing for highly corrosive chemicals such as hydrofluoric acid, which will dissolve glass containers.

   PTFE is also widely used as a thread seal tape in plumbing applications, largely replacing paste thread dope.


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