Engineering Help Desk

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Procedure: Add your question to the bottom of the list, below.

Feel free to ask questions below or at the following volunteers talk page:

user:mirwin[1]

Questions:

Contents

[edit] How Can I Calculate the Stress of Saddle Clamp Bolts Supporting a Vertical Mast?

(Question moved to the bottom of page. StuRat 15:28, 12 September 2008 (UTC))

[edit] Where are the files I contributed six months ago?

Answer: Probably still at Wikibooks[2] or lost in the link maze locally. Only a few Custodians have been appointed and it will take a while to sort out the elements of the database being moved from Wikibooks to the new dedicated name spaces at permanent URL http://en.wikiversity.org. Please try a search either here or at Wikibooks.

[edit] Can I request special attention for the files I need to get started?

Answer: Yes. Request the files be transwiki'd here: http://en.wikiversity.org/wiki/Wikiversity:Import it may take a few hours as there are only a few appointed Custodians (synonmous with administrator, sysop).

[edit] Is any Free Engineering actually occurring at Wikiversity?

I am doing some at Lunar Boom Town. If you have some time ask me how and why I am developing pieces and I can give you some pointers to places where the data,tools,techniques, are starting to pool up and become self organizinng with emergent properties with growing participation. Some of the folks at googles sci.space.* groups can helpfully assess the potential and limitations inherent in distributed virtual companies. The eductainment is still being researched and developed .... need some effective data feedback and improving mechanisms. 70.110.62.240 19:40, 26 November 2007 (UTC)

[edit] Efficient Combuustion Needed

My parents will not allow me to have natural gas pipeline plumbed into the workshop areas I borrow and rent from them so I can operate a microfoundry for aluminum parts for engineering research and commercial network game opportunities I wish to pursue. Can sombody help me learn what some better or worse options might be? Mirwin 19:55, 26 November 2007 (UTC)

I suggest propane tanks. They are readily available for use with barbecue units. The 1900°C temp of a propane flame is more than enough to melt aluminum (which melts at around 660°C). However, aluminum fumes are toxic, so you will need a good exhaust fan and a smokestack so you release the fumes above the elevation where people might breathe them. This will also require that you locate in an area zoned for industrial usage. This type of activity would not be permitted in a residential area. Also, depending on the jurisdiction, special permits may be required, and "scrubbing" of the exhaust fumes may be expected to gain approval. The obvious fire hazard from using combustible gases will also likely bring about requirements for extra fire precautions, like sprinklers. StuRat 22:35, 26 November 2007 (UTC)
Excellent information StuRat! Thanks. I will investigate air scrubbers and local zoning requirements. It is possible there is some lower limit on size of activity that will allow a tiny quantity of tiny parts to be cast in a microfoundry. Point about air quality is still taken seriously by me and I will investigate options although 20 years ago in local high school no special precautions were taken in much larger pours other than an excellent ventilation system in a large volume shop area. Despite that shop training I retained no idea that aluminum fumes were toxic so I wish you to know that you have assisted me greatly here. Thanks again! Mirwin 19:58, 18 December 2007 (UTC)
You're welcome. See [3] for info on aluminum toxicity. StuRat 20:12, 8 January 2008 (UTC)

[edit] Where to put Polymer technology?

Hello Wikiversity - people! I just joint this project and I have already my first question. In Germany "Polymer Technology" is considered a part of "Mechanical engineering". But in the english speaking part of the world it is considered a part of "Material Science". At which Portal should I start working. There is already a speciality "Polymers" in "Materials science and engineering". But that is more about the chemistry of polymers. But the "engineering part of polymers" is another thing than "engineering with steel" as there are quite a few special topics to consider. This won't be a problem for the next few weeks, as there is enough to learn about wikiversity itself and there definitely is a lot of material I'll contribute to the chemical side of polymer technology. But still I would like to have some opinions on that one. Yours Akinom 13:25, 8 January 2008 (UTC)
UPs. I think I may have found the solution. The german "Kunststofftechnik" isn't "Polymer Technology" but "Polymer engineering". Sorry for that one. But there comes the next question. Is "Polymer engineering" considered a department in the "School of Engineering" or is a subdivision of "Mechanical engineering"? Akinom 13:25, 8 January 2008 (UTC)
I have an engineering degree from the US and would break it down like this:
Mechanical engineering: Engineering subjects which do not depend on the material.
Material science: Mechanical properties of materials.
Chemistry: Chemistry of materials.
So, polymer engineering would fall under materials science, in my opinion. I'd add links from the adjacent fields of chemistry and mechanical engineering, however, so everyone can find your material :-). StuRat 20:20, 8 January 2008 (UTC)

"The future is in plastics" they used to say...but those were the businessmen. Invented by Chemists, created by Chemical Engineers and mass Manufactured by Mechanical and Industrial engineers, I would indeed go so far as to create a branch of engineering called Polymer Engineering and to add it to the template. The information you have may be most suitable to Chemistry (science behind it) or Chemical Engineering (how to make it), Industrial Engineering (plastics in a larger scope), Mechanical Engineering (ways to use it), and/or Materials Science (how it behaves as a material). A good curriculum for a Polymers Engineer would include all of these courses. -71.159.31.220 04:01, 19 February 2008 (UTC)

[edit] Relating flow rate of compressed gas to pressure

Hi, folks. How much information is needed to find (even to within about 20%) the flow rate of a tank of gas compressed at a given pressure? Specifically, given a tank of 0.4m^3 helium compressed to 16500 kPa, is it possible to work out (on paper) what pressure to regulate it down to in order to achieve an initial flow rate of 15 lpm? Would I need to know the area of the narrowest part of the outlet? Thank you, Lsterling 06:56, 14 July 2008 (UTC)

Yes, you would need to know the cross sectional area of the narrowest restriction, but also the shape of that opening. A circular opening should allow for faster flow than a narrow slit of the same cross sectional area, for example. You would also need to know the type of fluid (helium, in this case) and pressure in the tank (16500 kPa, in this case) and the pressure in the target container. Other factors, like the fluid temperature, and the smoothness, length, and straightness of the connection hose, would have a minor effect (perhaps less than 20%) on the flow rate. You did use the term "initial flow rate", so it sounds like you already understand that the flow rate would decrease as the pressure in the tank decreases and (possibly) the pressure in the target container increases. The volume of the tank doesn't actually matter for finding the initial flow rate, but it will affect how quickly the pressure in the tank drops, which, in turn, affects how quickly the flow rate decreases. Similarly, the volume of the target container will also matter. Note that, for a flexible target container, like a balloon, a more complex relationship will exist between the quantity of gas and the back-pressure/flow rate. StuRat 22:52, 14 July 2008 (UTC)
Thanks, StuRat. (question moved to the bottom...) Lsterling 03:52, 24 October 2008 (UTC)

[edit] How Can I Calculate the Stress of Saddle Clamp Bolts Supporting a Vertical Mast?

I need to calculate the stress of a saddle clamp bolt supporting a vertical mast to the side of a building.

For a vertical cantilever mast, such as an antenna or flag pole, force due to wind pressure on the antenna or flag will cause a moment around the mast base. The moment can be calculated by multiplying the force on the mast by the distance from the base to the force.

M = FL

The stress on the mast at the base can be calculated by dividing the moment around the base by the section modulus of the mast.

\sigma=\frac{M}{I}

I am dealing with a slightly different situation as shown in this diagram.

Image:Vertical-tube-and-saddle-clamp.png

The upper saddle clamp has two bolts holding the mast to the building. To calculate the stress in a single bolt, can I simply substitute the section modulus of the bolt?

There is a reason why I ask this question for a single bolt -- not two bolts. When the force on the mast is such that it loads the bolts in tension, it's reasonable to expect each to carry about half of the load. When the force on the mast is such that is loads the bolts in shear, this may not be the case. The bolts do not fit precisely into the saddle clamp. It's possible that one bolt would need to deform before both bolts are carrying the load. Therefore, I think the conservative approach is to consider the load in shear of a single bolt.

Anyway, can I simply use the section modulus of the bolt to calculate the stress in the bolt in this scenario?

--xquercus 10:43, 12 September 2008 (UTC)

I'd agree that you need to do your calculations as if a single bolt is present. See my diagrams below:
IF MAST IS VIEWED AS RIGID
--------------------------
 \ <- wind     wind ->/
  \                  / 
   \  +-+           /+-+
    \ | |          / | |
     \| |         /  | |
      +-+            +-+

IF MAST IS VIEWED AS FLEXIBLE
-----------------------------
  \ <- wind      wind ->/
   \                   / 
    \ +-+             /+-+
     || |             || |
     || |             || |
      +-+              +-+
So, if the mast is viewed as rigid, then, depending on the wind direction, most of the forces will apply either to the top or bottom bolt. If the mast is viewed as flexible, then the majority of the forces will always apply to the top bolt. In any scenario, we can't assume that the forces are distributed evenly. Therefore, I'd do the calculations for each bolt assuming that it's the only bolt. Otherwise, the bolt carrying the majority of the forces may fail, causing all the forces to apply to the second bolt, which may then fail as well.
Now, as for the question about using the section modulus of the bolt to determine if it will shear; yes, that seems reasonable, when the bolt is under a shear load. However, with different loads on the bolt it may fail in different ways. The head of the bolt may break off or the threads of the bolt (or material into which the bolt is screwed) may also strip. Vibrations and/or a twisting load may also cause the bolt to unscrew over time, so it may be best to weld the bolt in place or at least use an adhesive ("thread lock") to prevent this. StuRat 15:47, 12 September 2008 (UTC)
Thank you for your comments. I want to make sure I understand your comments and I may not have been clear. Each saddle clamp shown in the diagram has two hex bolts connecting the clamp and mast to the side of the building. When I refer to a single bolt, I am referring to a single hex bolt. The diagram above includes two sets of clamps, for a total of four bolts, as this is how I plan to do my installation. The following diagram includes a single clamp with a total of two hex bolts.

Image:Vertical-tube-single-clamp.png

I believe in the above diagram, the forces are a bit more complicated. For example, there may be some torsional forces in the bolts. Ignoring these forces, I believe when the bolts are in tension, we can reasonably expect the bolts to share the load. When the bolts are in shear, I don't believe the tolerances are close enough that the load will be shared evenly between the two hex bolts. Thus, a conservative maximum load should be determined by the strength of a single hex bolt in shear.
As an aside, I've seen a general rule that the strength of a bolt in shear can be estimated by taking 60% of the strength in tension. I haven't found an authoritative source on this but am certainly looking for one.
Thank you for reminding me of the potential failures at the head or threads. When doing my calculations, I've been using data from various ASTM standards which specify the yield strength of my bolts. I need to do a bit more reading to insure that the yield strength includes possible failure of the threads.
My particular project is the installation of a vertical mast on the side of my house to support amateur radio antennas. I'm going through the entire process of calculating the maximum wind surface area the saddle clamps and bolts can handle using the Telecommunications Industry Association models for wind loading. The impact of a failure in this particular system is negligible however I'm preparing to erect a number of cantilever and guyed lattice towers. This exercise is a step in the learning process so I can understand the tower manufacturer's specifications and (if needed) my PE's calculations. --xquercus 23:53, 12 September 2008 (UTC)
Thanks for the clarifications. I'm still unclear on the form of the mast itself, however. It appears to be cylindrical with no holes, in your diagrams, is this correct ? Your method seems good provided the bolts actually go through the mast, although there the mast itself will be considerably weakened by the holes, if the holes were drilled for this purpose, the mast now being subject to corrosion. It's difficult to tell if this is what was meant from the diagram. If they only go on either side of the mast and rely on friction with the clamp to keep the mast from sliding downward, then that would be a far weaker design. Perhaps the best method of all would be if the top pair of bolts went on either side of the mast (to preserve the strength of the mast where it will experience the strongest forces) and the bottom pair of bolts went through the mast (to support it):
      |     |
+-----+-----+-----+
| / \ |     | / \ |
| \_/ |     | \_/ |
+-----+-----+-----+
      |  M  |
      |  a  |
      |  s  |
      |  t  |
      |     |
      | / \ |
      | \_/ |
      |     |
      | / \ |
      | \_/ |
      |     |
      +-----+
A comment on the final rotation of the bolts: The bottom pair is in a good orientation, but it would be best if the upper pair were rotated so that the flats are parallel to the sides of the mast. This will prevent the corners of the bolts from putting unwanted force concentrations on the bracket. Since it may be difficult to control the final rotation of the bolt heads, using circular washers between the bolt heads and bracket may be a better way to accomplish this. Ensure that the washers are wider than the corners of the bolt heads.
One last question, what material do the bolts screw into ? Beware that this material itself may fail, in that the bolts may strip out of it, or a piece of the material may break off, or the material may crack, or the entire piece may break off of the building (for example, if a bolt is screwed into a brick). If possible, arrange it so that each bolt screws into a different object, to distribute the forces widely. Attaching to the frame of the building would be the best way to go.
Beware that certain combinations of metals cause corrosion since one material acts as an anode and the other as a cathode. If you are near salt-water, special precautions will be needed for dealing with salt-water spray. Painting the bracket, bolts, washers, and mast (near the holes) with an outdoor paint may help to slow failure due to corrosion. Also, be sure to use hardware rated for outdoor use. The antenna mast will also need to be grounded to protect the house from lightning strikes. StuRat 10:09, 13 September 2008 (UTC)

[edit] Helium flow rate compared to argon

I'm trying to control a helium (97%, air 3%) tank using a flowmeter calibrated for argon. From rough experiments it seems that the helium is flowing at about 2.5x the marked rate. Is there a general theoretical reason that would confirm or correct this number, or would it depend largely on the specific configuration of the equipment? (Or maybe this is a chemistry question?) Cheers, Lsterling 03:52, 24 October 2008 (UTC)

I'd say experimental methods are probably the best way to establish the different flow rates. Differences will be caused by the atomic masses of the elements, the radius of the atoms (which depends on the electron configuration), what molecules they form (monoatomic or diatomic, for example), any charge they have, etc. You could theoretically combine all this info together to come up with a flow rate, but it sounds like more work than the experimental method, to me. StuRat 02:16, 28 October 2008 (UTC)
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