Flange Design

If you are talking about rectangular HVAC sheetmetal ducting, how I interpret your ducting - If not, please be more specific.

Design to SMACNA's "HVAC Duct Construction Standards--Metal and Flexible";

There are no real calculations to perform. The details (bolt size, flange size, ......) are all prescribed according to the "Reinforcement Class"

Note also that your question of "flange" is very vague; there are many styles of "flanges" - please, hopefully it is legible, see the picture below:

Thanks for the table and sorry if the question is too general.I am now designing a system(in Solid Works,design table to be exact) that need user to key-in only the value and done with the design.So, for flanges,I need to know the calculation,so that I can customize the dimension.Anyways,thanks for the table Xmech.Or do you have any other ideas for me to simplifies the design table?

Like I said, there are no real calculations - you would just have to build a look-up database of all the information in the SMACNA standard to determine the specified reinforcement spacings, flange sizes, support spacing, duct sizing, design pressure, ducting thickness, ...................

You will need to get a hold of the standard - there is A LOT of information,

If you can't justify/find the money:

http://www.smacna.org/bookstore/index.cfm?fuseaction=search_results&topicID=4&cfid=10419832&cftoken=10297664

Maybe a local library has it - or a trades institution.

This is the simple ducting that I am talking about.For this simple duct,I need to simplified the flange dimension,so that the end user just need to key-in the ducting size and the flange will automaticly be build by solid works.Hope that my intension to have the flange calculation is understandable.

The critical variables you are missing, besides width and height of duct, are:

• pressure
• length (between flanges/supports)
• thickness of sheetmetal
• required insulation - sound deadening
  

Are those variable as well?

There is a way to solve your problem without computations. If you consider the standards they have at base a computation and a similitude. For instance the flange thickness is related to the bolt and distance between bolts and so on. So if you take the dimensions in the standards and build up the relations between main parameters and the other you obtain the similitude laws and you have only to give the nominal dimension and the whole will be drawn accordingly. this can be called reverse engineering.

Does this means I have to use scaling?

You may call it scaling I call it similitude. Because some dimensions are not only on scale.

Thanks mate! that really helps.

The duct is only for a blower with 2500 cfm.

The length of the duct will be key-in by user.

The thickness of the duct will be key-in by user.

There will be no insulation.

The pressure in the duct is not more than 8.7 miliBar.