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AMCA Standard requires construction that will not permit a wheel andor shaft to shift due to some malfunction during operation. If two ponents are allowed to shift and rub against each other for any length of time nike air max 2016 homme , either sparks or frictional heat could bee a hazard in an explosive or flammable gas stream. Normally, standard procedures of fastening the wheel to the shaft and locking the shaft in the bearings are sufficient. 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. AMCA Standard requires construction that will not permit a wheel andor shaft to shift due to some malfunction during operation. If two ponents are allowed to shift and rub against each other for any length of time, either sparks or frictional heat could bee a hazard in an explosive or flammable gas stream. Normally nike air max 2016 prix , standard procedures of fastening the wheel to the shaft and locking the shaft in the bearings are sufficient. 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. The fan manufacturer must still develop unique designs to deal with the physical and practical limitations of fan equipment when developing construction methods to ply with AMCA. Fan applications with airstreams of explosive or flammable particles or gases require spark-resistant system ponents for the safe handling of such airstreams. This includes ponents such as ductwork, dampers, filter devices chaussure nike air max solde , heating or cooling coils, and fans. This article presents practical considerations and methods of providing fans with varying types of Spark-Resistant Construction (SRC). The Air Movement and Control Association (AMCA) established a standard set of Classifications for Spark-Resistant Construction. AMCA Type A Spark Resistant Construction requires all parts of the fan in contact with the air or gas being handled shall be made of nonferrous material. Steps must also be taken to assure that the impeller, bearings, and shaft are adequately attached andor restrained to prevent a lateral or axial shift in these ponents. 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. Ferrous hubs, shafts chaussure nike air max pas cher , and hardware are allowed, provided construction is such that a shift of impeller or shaft will not permit two ferrous parts of the fan to rub or strike. Steps must also be taken to assure that the impeller, bearings, and shaft are adequately attached andor restrained to prevent a lateral or axial shift in these ponents. 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. It should be noted that: 1) No bearings, drive ponents nike air max bleu marine homme , 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 ponent cannot ignite the surrounding gas stream. 2) The user shall electrically ground all fan parts. 3) 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. 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.S. Bureau of Mines and others has shown that aluminum impellers rubbing on rusty steel may cause high-intensity sparking. The use of the above Standard in no way implies a guarantee of safety for any level of spark resistance. “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.” A major limitation is the practical availability of truly “nonferrous” alloys that really can be used in fan construction. There are certain alloys or noble metals than are truly nonferrous, alloys that contain no iron, but for the most part they are extremely expensive andor difficult to obtain in forms and strengths necessary for fan construction. 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. Aluminum is the most frequently used alloy due to its low cost. However nike air max bleu marine femme , as pointed out in the AMCA Standard, when aluminum is in close proximity to steel, careful maintenance programs are necessary to prevent rust, because aluminum rubbing against rusty steel can cause high-intensity sparking. In applications where such maintenance is not possible, an SRC method that places steel in the airstream is not remended. Regardless of which classification is chosen nike air max bleu marine pas cher , airborne foreign or “tramp” particles could either strike each other, or strike one of the ponents of the fan, causing a spark. Protection against SRC does not eliminate the potential for spark generation. Fans with any type of SRC are only intended to minimize the potential that any two or more fan ponents might generate sparks within the airstream by rubbing or striking during operation. No type of SRC can be guaranteed to eliminate the possibility of generating a spark, nor would any SRC type preclude sparks resulting from any foreign influence such as airborne materials striking each other. A fan furnished with AIRSTREAM TYPE SRC should provide the greatest degree of spark I hav.
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| Beitrag vom 09.03.2016 - 09:01 |
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