You know I have done many copper heatsinks using a copper plumbing end cap, then cutting up flat copper sheet to drop in the end cap and using solder to bind. Well I found something I guess I never thought of and that is "copper shot", to use for bullion casting.
I stumbled upon it on ebay here. 8 ounces of .999 pure copper shot for $7.77 free ship. (USA) Well if you ever bought copper fittings or copper sheet, you know that copper shot is relatively cheap and 8oz of it would fill several P60 sized heatsinks. The other nice thing is that the shot will fill the copper end cap better and pack tighter, so - more copper, less solder, better heat transfer.
I bought some and recieved it within 4 days. It's just as it was pictured.
I saw this thread about using copper shot to fill the pill to increase mass and improve heat-sinking performance.
I hope this is in the same vein of thought
So I understand mass improves heat transfer.
Back in my days in trade school, (welding), we learned that copper gained heat very well, but the description as to why was poor. I thought we used copper as a weld backer to prevent blowing holes in some welds due to over heating.
1st, can someone explain why copper is so good, and 2nd, why not just fill the pill part way with lead? Wouldn’t that transfer heat away from the LED too?
True, but not entirely. Submerge the cap in water so that the majority of it is submerged, and just the open end sticks above the water line. Melt copper pipe/shot/whatever and then pour into the cap. The liquid copper will fill the void perfectly, but the cooling provided by the water will not allow the cap to melt.
If I recall correctly, the melting point of copper is above 1000 °C. You wouldn't be able to melt a significant amount of it without professional equipment...
If anyone does this, PLEASE, video tape it! wooo ho hooo !
I think that it will be very difficult to get a decent pour, with the moisture making steam, and the pill being WAY to cold to get any control. The molten metal will cool to fast, you want the metal to cool slowly to produce a homogenous pour, one piece, from top to bottom.
Thanks for the help Old Lumens, but I’m almost embarrassed at my lack of understanding. I looked at the chart in the link and it might as well been ancient hieroglyphics, I couldn’t find anything that I could understand.
I know “number don’t lie”, but I need to know which language they are “not lying in”
If you use the copper shot you should try to smash it into the copper cap to create flat spots on the individual balls to increase contact surface area and to allow slightly more of the shot to be used before sealing it with solder.
True, you would have different grains in the final metal, but since this is for heatsinking and not for use in a structure or electrical conduction that shouldn’t impact the performance too much.
Water going through a thin pipe will flow slowly. If it goes through a big fat pipe, it will flow abundantly. Even if it flows from the same container.
As far as heat is concerned, lead and tin are thin pipes. Copper is a big fat pipe.
Higher thermal conductivity equals easier transfer of heat.
Just look in the third colum (Thermal Conductivity) and remember that Silver is the best in that chart, so consider the number for Silver (235) as best and you are wanting something that is as close to 235 as you can get. The higher the number, the better. Copper is excellent, Gold is good and everything else is varying degrees of poor to lousy. Solder conducts electricity ok, but it doesn't conduct heat very well. (lead/Tin in the chart are very low numbers).
Aluminum is just a trade off of price and availability versus some thermal conductivity. It's all about the money and availability. Aluminum is readily available and relatively cheap, but middle of the road for thermal conductivity. Hope that helps.
I don’t have a lathe, but apparently aluminum is also easier to machine. It is also available in a wide variety of shapes and sizes but since no lathe I use plumbing bits. Thanks for the hot tip. Mmm. Flattening the shot sounds like a good idea as well(smooth jaw vice?);more surface area and less solder.