Scale removal mechanical method

Unfortunately, not all scales are removable by chemical methods. For example, only calcium carbonate scale is readily removed by acid. Others, such as calcium sulfate, can be removed chemically, but inefficiently or only partially. Most scales require mechanical methods, such as milling, for complete removal. See chapter 14 for further discussion of scale removal. 

Deposits of all these types of scales can be removed using chemical cleaning additives. This method of removal is greatly superior to the alternative mechanical method of removal, such as sand blasting. Calcium carbonate and aluminium hydroxide scales are easily removed with acids while calcium oxalate scale and Barium sulphate scale are more difficult requiring specialised cleaning compositions. 

All oil, grease and other soluble contamination should be removed by solvent degreasing or alkaline cleaning. Rust, scale and other non-soluble contaminants should be removed by mechanical or chemical methods. Grit blasting is the most commonly used mechanical method, but wheel abrasion, grinding, wire brushing, emery cloth or steel wool can be used. Chemosil 211 primer should be applied as soon as possible after the surface preparation to reduce the risk of contamination or oxidation of the substrate. 

Abrasive cleaning. Mechanical methods for surface preparation include sandblasting, wire brushing, and abrasion with sandpaper, emery cloth, or metal wool. These methods are most effective for removing heavy, loose particles such as dirt, scale, tarnish, and oxide layers. 

Before steel strip or rod can be cold rolled, tinned, galvanised, or enamelled, etc. any scale formed on it by previous heat treatment must be removed. This can be done by mechanical and other special methods, but if a perfectly clean surface is to be produced, acid pickling is preferred, either alone or in conjunction with other pretreatment processes. 

Mechanical and biological methods are very effective on a large scale, and physical and chemical methods are used to overcome particular difficulties such as final sterilization, odor removal, removal of inorganic and organic chemicals and breaking oil or fat emulsions. Normally, no electrochemical processes are used [10]. On the other hand, there are particular water and effluent treatment problems where electrochemical solutions are advantageous. Indeed, electrochemistry can be a very attractive idea. It is uniquely clean because (1) electrolysis (reduction/oxidation) takes place via an inert electrode and (2) it uses a mass-free reagent so no additional chemicals are added, which would create secondary streams, which would as it is often the case with conventional procedures, need further treatment, cf. Scheme 10. 

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