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Mechanical Engineering

G B Reid MIMechE, SIMarEST

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G B Reid MIMechE, SIMarEST last won the day on December 19 2019

G B Reid MIMechE, SIMarEST had the most liked content!


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    Benfleet, England
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    [NOTE: No longer SIMarEST, but connot remove!] Mechanical engineering "generalist", experience in Design (industrial, mechanical, aerospace grade components), Rail, Underground, defence, process flow optimisation, Project Engineering and Mechanical Systems 3D CAD user (various) since 1992. Electrical design installation and verification.

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  1. Hi Pablo Alas, I have no first hand experience with the Jominy, so I will not comment on this. (I only comment where I have knowledge or first hand experience...) That said, on the other, yes, use the figures for the 100mm, if incorrect, the error will be on the "safe" side. Bruce
  2. Hi AliceIn....apologies for the delay, just read your message! ALWAYS err on the side of caution and use the lowest value unless absolutely sure! Warmest wishes Bruce
  3. That's a loaded question...(please excuse the pun!)...it depends! If you are building a structure subject to repeated loading, or safety critical, you should use the yield...NOT the UTS. If you are designing fastners, the UTS is more relvant...but then again, if subjected to vibration or "impulse" loading, again the Yield becomes far more important. It is not a straight forward answer to what seems a simple question. The differring UTS values are generally due to the heat-sink aspect of the material undergoing heat treatment. Basically when an item is hardened (quenching for steels). The item is heated up passed the crystalisation temperaure and then quenched in either oil or water. This takes the heat out of the material so quickly that the crystal-growth is restricted and they remain small. The thicker the item, the more heat remains within the material allowing the crystals to grow to larger (unwanted) sizes....basically for hardness, smaller crystals are better (in steels al least - be careful...other metlaic materials differ quite significantly!) I would always err on the side of caution and use the lowest value. This is especially the case for a shaft...the hardening may only affect the surface! For the diagram....for me there is insufficient detail to answer the question....there would be accompanying information to expain further what it is showing...the only answer I can give is that it is two differing samples! (although...as I think about it further, it is possible my previous answer may actually be helpful here!)
  4. Just to expand a little on Dudley's answer... Professional thread dies are adjustable and used alongside wire gauges to determine the true size of the cut thread. These are NOT the same as the units readily available for hobby engineers. Basically the wire gauges engage with the thread INSIDE the cut thread and are measured across the cut thread....measuring the effective thread size. They can be adjusted to ensure that the thread is correct at the final size. Hope this helps! Bruce
  5. Its worth just trying out a standard thermal expansion coefficient calculation. (You have not stated the material that you are measuring) Take the material thermal expansion coefficient of the material you are working with and calculate its diameter for 30 degrees C...then calculate the same for 60 degrees C...I think you'll find a good correlation. Then just use the 60 degree figure for your measurements. Hope this helsp
  6. With any motor, the power is from P = IV The power (in Watts) used is proportional to the voltage (in Volts) AND the Current (in Amps).....If you up your voltage, the ampage should drop significalty...as you've experimentally discovered, if the voltage is too low, the ability to supply a sufficient current (ampage) becomes the limiting factor. New (DC) motors are rated for a no load speed at a specific VOLTAGE...the current increases subject to the load to match the power requirements...and CRITICALLY the wire requirements are rated on CURRENT. If you run your motor at too low a voltage, your wires will overheat - both externally and internally - the varnish will evaporate from the winding wires inside the motor and the motor will either burnout through a resulting internal shortcircuit or catch fire! Hope this helps I shan't - at the moment - expand further as your experimentally discovering lots on your own which is by far the best way to learn....but I'll be happy to look again for additional questions. Good luck!
  7. Okay...enough is enough...my turn! Assuming the chain links form a cyclic and therefore have a natural load-spread between both legs and no stress concentration: Stress = F/A Stress = 75 000 000 N/m^2, F = 50 000 N A = 50 000 / 75 000 000 = 0.000 667 m^2 for both legs A = (pi r^2)/2 per leg so r = root (0.000 333 / Pi) = 0.010 301 m d = 2r = 0.020 601 m = 20.601 mm - always round to the safety side....so: Therefore use 21mm dia stock minimum!
  8. I'd agree with DrD....that said, ball-bearings are inappropriate in this application....I'd use taper roller as it has both an axial and radial component of force, otherwise - due to the mass of air, mass of the assembly and the resultant action - you will have premature bearing failure!
  9. Marin; NEVER feel ashamed for attempting something and making an error....being ashamed should be left to those who do not try - and I include myself in that (ie I have not tried and that IS shameful!!!). I've been an Engineer now for 30 years, and the one thing I can say without fear of contradiction is you NEVER learn anything from getting things right...that just generates hubris...it reassures that the calculations are done correctly, but that can occur without the deepened understanding needed to be successful in the field! Celebrate mistakes, especially if you learn from them! And to tackle my "Shame": Using the H7/u6 details on the quoted text (reference docs not available) Generally on a "nominal" 120mm dia shaft, allow for a "runout" of 0.1, so all dimensions should be a minimum of the runout on both sides (120 - (0.1*2)) = 119.8 - ie the maximum diameter of the shaft MUST be below this value. Therefore assuming a "base" of 119.6mm to allow for the +.166 of the shaft... Therefore shaft at u6 = 119.744 - 119.766 (on a "base" of 119.6mm - +.144+.166) Hole on H7 = 119.6 - 119.635 (on a "base" of 119.6 - +0.000/+.0.035) It's definitely an interference fit...now, where did I leave the nitrogen...? I may be wrong; I look forward to Saurabh's answers! Warmest wishes! Bruce
  10. There are a couple of different types of "Eco Cooler" design....one utilising water - sometimes known as an evaporative cooler works by taking advantage of the energy of evaporation of water....basically as water (or any liquid for that matter ) evaporates, it absorbs a certain amount of energy... If this utilises natural airflow through an opened window, it will have the effect of cooling the air enterring, but will increaee the humidity within. The other form (inverted cones) takes advantages of the ideal gas laws...it effectively forces a minor pressure drop in the air which reduces the air temperature, but this may not be sufficient to actually notice. Both of these do work to some degree, however if utilising a powered driver there will be energy consumed there. The best form of heating/cooling is that of a "heat pump" which moves heat from one area to another and only "cost" is the power to do so...they can have an energy multipier effect - sometimes of as much as 8x - where for a power input of - say - 1000 Watts - a heating/cooling effect of 8000Watts can be achieved.
  11. Just perusing the answers to this quiz...I find them...well....."interesting" answers to say the least and...er.."worryingly" consistent. If the shaft starts at 120mm you need to think on the maximum size of the shaft available....are you going to spray-weld the shaft to increase its size...before you even begin? If you look at the question it states the SHAFT diameter is 120mm....
  12. Balaji, you have rounded down - ie to the "unsafe" side. In fasteners of any kind, you would always round up...always "enhance" safety, not detract from it.
  13. I may no t be understanding you r question properly, but it looks like you may be misunderstanding what the "static pressure" actually is.... When the flow increases through an enclose space - be it pipe or venturi - the presure reduces proportionally to the velocity of the flow. Basically, the faster the flow rate, the lower the pressure is. This flow rate presure (was historically....there are now sensors that can....)/(is) difficult to measure directly, so there's a "trick" that can be used to infer - with a very high degree of accuracy - the velocity of the fluid - be it gas or liquid - in the pipe....that is the measurement of the static pressure. Effectively, the static pressure is the pressure to which the internal flow presure drops. This is from memory, so I may get it upside down, but it still works anyway as it is a ratio of proportionality....it's: rho1/v1 = rho2/v2 The static presure measurement is the measurement of the rho(1 or 2). It's basically the mass flow calculation at two different speeds for the same mass...rho = m/v This then becomes rho1/v1 = m and rho2/v2 = m and, as m is the same, rho1/v1 = rho2/v2 Therefore, if the flow velocity increases, the pressure drops - this is measured by a static tube measuring hte drop in the static pressure as a result of the change in velocity - so therefore any change in velocity DOES affect the static pressure. Hope this helps
  14. Now this is entirely theoretical!! It may be possible to use "arc-spatter" to advantage. (My welder's knackered at the moment so I cannot try it to see...) If a (semi-sacrificial) earthed-point is located immediately proud of a MIG-tip, and the power and gas-flow ramped up to "silly levels", the spatter from the feed wire "should" spray on to the target metal. It will likely take some fine tuning, but - despite the increased use of gas - it may be a workable solution. Basically, the "earthed-point" will spark the arc...if the power is high enough, the metal should near-vapourise, forming a fine spray, being easily blown - by the shielding gas - onto the workpiece where it will solidify. If it works, it's an oxygen free solution. Please do feed-back if this works - good luck! My thoughts and best wishes are with all in India at the moment....and indeed all who have been either directly or indirectly affected by this terrible disease wherever they are in the world!
  15. Hi there "Alwayslearning"! I've had a similar error in the past using ANSYS (or may have been NASTRAN...?)...when I gave up after banging my head against the wall for about two days, I got on to the Technical support guys... ...it turned out in my case that it was a migrogap between two edges (where there should not have been a gap). This resulted in the model be discontinuous from the analysis perspective. The model was redrawn and the problem solved. Hope this helps.
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