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With the outercvjoint or shaft rubbing the buffers

2017-07-17 16:04:50 | 日記
Figure 4 details one alternative which includes a bolted aluminum wheel retaining plate on the end of the shaft. However, the degree of hazard in these situations dictates that extraordinary precautions to more securely prevent such shifting are in order, so further methods of attachment or restraint are required.



The AMCA standard provides the system designer with a uniform way to specify the system requirements and provides fan manufacturers with general guidelines. Steps must also be taken to assure that the impeller, bearings, and shaft are adequately attached and/or restrained to prevent a lateral or axial shift in these components.html. The remainder of the fan components are furnished in their standard material, usually mild steel. Practically speaking, it is not possible to predict a safe length of time, because there may be other ferrous components within the fan airstream which could be torn or jarred loose by the rubbing or striking of the wheel or shaft, and such loose ferrous objects could create a spark.
4) The use of aluminum or aluminum alloys in the presence of steel which has been allowed to rust requires special consideration. Research by the U. Fans with any type of SRC are only intended to minimize the potential that any two or more fan components might generate sparks within the airstream by rubbing or striking during operation.AMCA Standard requires construction that will not permit a wheel and/or shaft to shift due to some malfunction during operation. A fan design which requires an inlet cone is usually furnished with an aluminum cone to act as the buffer on one side. The build-up of foreign material or rust, the potential deterioration due to abrasion or corrosion, or the accidental shifting of any fan part could lead to further hazards of potential ignition or explosion. The user or specifier must exercise caution in selecting this type so that the safety of the installation is not compromised for the sake of initial cost. A spark-resistant buffer is added around the housing opening through which the shaft passes as shown in Figure 2.

AMCA Type C Spark Resistant Construction requires the fan shall be so constructed that a shift of the impeller or shaft will not permit two ferrous parts of the fan to rub or strike.com/products/index.

Aluminum is the most frequently used alloy due to its low cost.com/contact. However, the severity of a hazard that calls for AIRSTREAM TYPE SRC dictates that the fan should be closely monitored and shut down immediately upon such an occurrence. Spark-resistant construction also does not protect against ignition of explosive gases caused by catastrophic failure or from any airstream material that may be present in a system.The use of the above Standard in no way implies a guarantee of safety for any level of spark resistance.

It should be noted that:No bearings, drive components, or electrical devices shall be placed in the air or gas stream unless they are constructed or enclosed in such a manner that failure of that component cannot ignite the surrounding gas stream. In applications where such maintenance is not possible, an SRC method that places steel in the airstream is not recommended.


In AMCA Type B Spark Resistant Construction the fan shall have a nonferrous impeller and nonferrous ring about the opening through which the shaft passes. The Air Movement and Control Association (AMCA) established a standard set of Classifications for Spark-Resistant Construction.
For this Standard, nonferrous material shall be any material with less than 5% iron or any other material with demonstrated ability to be spark resistant.

A fan furnished with AIRSTREAM TYPE SRC should provide the greatest degree of spark resistance. Steps must also be taken to assure that the impeller, bearings, and shaft are adequately attached and/or restrained to prevent a lateral or axial shift in these components.ventilating. For most purposes, the fan manufacturer uses more readily available alloys that are considered nominally nonferrous and which have strength and work properties suited to fan construction.

Regardless of which classification is chosen, airborne foreign or tramp particles could either strike each other, or strike one of the components of the fan, causing a spark. The system designer is in the best position to weigh the alternatives and specify the required fan equipment. The precise method will vary by fan size and type. If allowed to operate, the rubbing or striking of these fan components will generate frictional heat, quickly deteriorate, and eventually catastrophically fail.

Moving explosive or flammable gas streams through fans requires the utmost care in system design and equipment selection. The BUFFER TYPE SRC is intended to provide a low cost alternative for non-critical applications.

A major limitation is the practical availability of truly nonferrous alloys that really can be used in fan construction. In the event that two or more fan components in the airstream rub or strike together, a properly maintained fan should be able to continue in operation for some reasonable period of time, without producing a spark. High speed fans will tend to wear away buffers more rapidly than slower speed fans, and thus BUFFER TYPE SRC should be used with caution on high speed fans.
As with the WHEEL TYPE SRC, fans furnished with BUFFER TYPE SRC should not continue to operate for any length of time with the outercvjoint or shaft rubbing the buffers. Protection against SRC does not eliminate the potential for spark generation.



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