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ISO 21940-31:2013 pdf free

ISO 21940-31:2013 pdf free.Mechanical vibration – Rotor balancing
This part of ISO 21940 specifies methods for determining machine vibration sensitivity to unbalance and provides evaluation guidelines as a function of the proximity of relevant resonance rotational speeds to the operating speed. This part of ISO 21940 is only concerned with once-per-revolution vibration caused by unbalance. It also makes recommendations on how to apply the numerical sensitivity values in some particular cases.
It includes a classification system that can be applied to machines which is related to their susceptibility to a change in unbalance. Machines are classified into three types of susceptibility and five ranges of sensitivity. The sensitivity values are intended for use on simple machine systems, preferably with rotors having only one resonance speed over their entire operating speed range. The sensitivity values can also be used for machines that have more resonance speeds in their operating speed range if the resonance speeds are widely separated (e.g. by more than 20 %).
The sensitivity values given are not intended to serve as acceptance specifications for any machine group, but rather to give indications regarding how to avoid gross deficiencies as well as specifying exaggerated or unattainable requirements. They can also serve as a basis for more involved investigations (e.g. when in special cases a more exact determination of the required sensitivity is necessary). If due regard is paid to the values given, satisfactory running conditions can be expected in most cases.
The consideration of the sensitivity values alone does not guarantee that a given magnitude of vibration in operating is not exceeded. Many other sources of vibration can occur which lie outside the scope of this part of ISO 21940.
Machines of this type have a high likelihood of experiencing significant unbalance changes during operation. Typically they are machines which run in deposit producing e.g. pumps operating in sludge) or corrosive environments.
EXAMPLES Centrifuges, fans, screw conveyors, and hammer mills.
The remainder of this part of ISO 21940 focuses on moderate susceptibility classification machines (type II). For evaluation of low susceptibility or high susceptibility machines, a correction factor can be applied to adjust the sensitivity range. Table 1 shows correction factors that are applied to the sensitivity values (see Clause 5) based on machine susceptibility type (see 4.2 to 4.4).ISO 21940-31 pdf download.

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