| Electronics > Projects, Designs, and Technical Stuff |
| really proper way to apply thermal compound? |
| << < (10/14) > >> |
| coppercone2:
I developed a theory. The thermal paste is rather abrasive. If you get it into your thread then it will mess with your torque readings. You can't tighten the thread right unless its cleaned and maybe oiled (bit better). If you put gobs of thermal grease over a part that can get into a torque sensitive adjustment screw it might prevent you from clamping. It should not be an issue with overhead springs though. Maybe this is how it all started? It seems like you can do it to a TO-220 easily. Keep in mind standard bolts (not metrological or special use) come in 5 grades of tolerances and probably surface finish (but this is not controlled as well), and I don't know how threads are listed. If the thread is really ratty and unpolished chances are you will compress a asparity of the metal, which will yield over time and actually reduce spring force. Also even if you tighten by extension you can have some stuff creep out of the threads if it gets in there after a while or from evaporation and cause the torque to change. Also the derivation of torque from rotation requires stable known geometry as a constant I believe to be applicable to bolts. I might check this later This is why you never use ratty old sealant on nice pipe threads I think. Also, you use teflon tape. Its pretty slippery stuff. Its not aluminum oxide impregnated rough tape. If you take something rusty apart its a good idea to use new bolts but if not be sure to brush them good to derust and give a slight polish and then lubricate and clean out the thread hole. For small bolts you can kinda wing it by taking a pair of wire cutters to a dremel brush to make a smaller dremel brush. But properly you would wanna use a rethreading tool, or re-tap the hole with a bigger size (re-threader / thread cleaner) is different then a new tap.. or if you need the same size drill a bigger hole and insert a heli spring thread insert. |
| Mr. Scram:
--- Quote from: coppercone2 on December 13, 2018, 08:32:29 pm ---I developed a theory. The thermal paste is rather abrasive. If you get it into your thread then it will mess with your torque readings. You can't tighten the thread right unless its cleaned and maybe oiled (bit better). If you put gobs of thermal grease over a part that can get into a torque sensitive adjustment screw it might prevent you from clamping. It should not be an issue with overhead springs though. Maybe this is how it all started? It seems like you can do it to a TO-220 easily. Keep in mind standard bolts (not metrological or special use) come in 5 grades of tolerances and probably surface finish (but this is not controlled as well), and I don't know how threads are listed. If the thread is really ratty and unpolished chances are you will compress a asparity of the metal, which will yield over time and actually reduce spring force. Also even if you tighten by extension you can have some stuff creep out of the threads if it gets in there after a while or from evaporation and cause the torque to change. Also the derivation of torque from rotation requires stable known geometry as a constant I believe to be applicable to bolts. I might check this later This is why you never use ratty old sealant on nice pipe threads I think. Also, you use teflon tape. Its pretty slippery stuff. Its not aluminum oxide impregnated rough tape. --- End quote --- Why are you suddenly going off on a tangent about threads and spring force? |
| coppercone2:
--- Quote from: Mr. Scram on December 13, 2018, 08:37:41 pm --- --- Quote from: coppercone2 on December 13, 2018, 08:32:29 pm ---I developed a theory. Maybe this is how it all started? It seems like you can do it to a TO-220 easily. ] --- End quote --- Why are you suddenly going off on a tangent about threads and spring force? --- End quote --- I don't know why you don't understand the context but to explain it in clear detail: 1) There is some crap about using too much thermal grease being bad other then non economic 2) there is a claim insufficient mounting pressure is a result 3) there is a claim this is non sense because it should work and mechanically cannot be explained 4) a partial explanation is offered by the mounting geometry of certain packages being susceptible to contamination if excessive thermal grease is used 5) there is a detailed explanation about the functioning of bolts and screws for those that did not read very boring literature about proper screw function (going off about) yea im 'going off' maybe try to follow the discussion? I noticed that people who are not mechanical engineers, and most engineers in general that I spoke to, don't really appreciate the mis behavior of threads from contamination. Plenty of people think "yea its real tight that means its good". but idk do you say that to your wife when she complains you left your socks on the floor? 'shes going off' ............ ::) |
| james_s:
--- Quote from: wraper on December 13, 2018, 08:12:47 pm --- --- Quote from: james_s on December 13, 2018, 07:44:57 pm ---Too much paste makes a huge mess all over everything, and in the case of power transistors I've replaced failed transistors that had so much paste that they weren't sitting flat on the heatsink. --- End quote --- If transistors were not sitting flat, it's certainly not because of the amount of the thermal paste. But because they were not mounted properly or were not tightened as should. --- Quote ---I repaired something that was malfunctioning due to conductive paste oozing out on the leads. --- End quote --- You need to buy that crap specially. And those are not even among the best in regards of thermal conductivity of modern thermal pastes. --- End quote --- I didn't mount them, I just cleaned up the mess. These were arcade vector monitors with big TO-3 transistors that screw into flimsy stamped frame sockets. |
| fsr:
I just use an old credit card to spread the paste over the entire contact surface. It takes some time, but won't make a mess with the paste when tightening, and seems to work without problems. |
| Navigation |
| Message Index |
| Next page |
| Previous page |