Melting Bronze

Steamman3

New member
Hello all. I'm hoping someone on here an help me. I work part time in a machine shop and today I was melting some bronze to make a new bearing for a large surface grinder we have. I have been using my home made propane furnace for a couple years now. The problem is figuring out how much raw material one needs to cast a blank for the new bearing. The old bearing weighs 17 pounds so I assumed I would need at least 20 pounds of raw bronze melted to make this blank. Wrong! I ended up with a little more than half of what was needed for the part. I haven't taken the part out of the mold yet so I don't know exactly how much the blank does weigh. It doesn't really matter because the molten bronze only filled the mold up half way to the top. This is a open top mold. It is a cylinder mold 4" in dia. and 10" high with a 1-1/2 pipe in the center to create the starting point of the bore of the bearing. I hope this makes sense. Question is how much raw material do I need to cast a cylinder 4" in dia and 10" long with a 1-1/2" hole thru the center? Thank you, Jim in Pa.
 

neonman

New member
108 cu. in. is correct as I calculate it. Looking at a couple of sources for weights of metals, bronze comes in about 541 pounds per cubic foot. 108/1728 * 541 = 33.8 pounds of bronze.
 

Pete Spaco

New member
Maybe a small point, but, are you using 1 1/2" pipe or are you using a piece of pipe that is 1 1/2" in OD?
1 1/2" water pipe has an OD of 1.900 inches.

Pete Stanaitis
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JoeCB

Subscriber
Your problem is simply that you didn't consider that the cast bearing is (and has to be) significantly larger than the finished bearing that you weighed at 17 #. Calculate the total volume of the proposed rough cast part that will have larger OD , smaller ID and longer than the original part and go from there. The difference in weight will be left in chips on the lathe bed.

Joe B
 

LCJudge

Subscriber
Your problem is simply that you didn't consider that the cast bearing is (and has to be) significantly larger than the finished bearing that you weighed at 17 #. Calculate the total volume of the proposed rough cast part that will have larger OD , smaller ID and longer than the original part and go from there. The difference in weight will be left in chips on the lathe bed.

Joe B

And in sprues, risers, parting seam waste and as you mentioned, all those chips left on the lathe, mill and so on.
 

Pete Spaco

New member
I notice that, when smarter guys than I do bronze casting, they usually add some amount of tin and or zinc into the melt. That, apparently is to make up for oxidation or evaporation of those metals. Maybe that is something you might look into if those bearings are used in critical applications.

Pete Stanaitis
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Andrew Mackey

Moderator
I seem to remember that when casting brass and cast iron, the mold has to be made 10% oversized to account for the metal shrinkage after it cools. if you just re-cast the old bearing, the result will be undersized for your needs.
 

Steamman3

New member
Thanks for all the helpful suggestions. Looks like I need to make a larger crucible and hope it fits in my forge. I'm going to melt 34# of bronze and design a new mold. I'll let you all know what happens in a couple weeks.

Jim in Pa
 

Tony Leonard

New member
Hello,

Since I sell bronze and cast iron bar stock, I am curious why you would rather melt the bronze rather than to buy tube bar stock and machine from that? I stock SAE660/CDA 932 bronze tube stock in 4" OD x 1.50" ID. The OD is cast oversize and the ID is cast undersize to finish to these nominal sizes. The weight for a 10" long tube is 38 lbs. I am just curious why you would rather make the bronze tube than to buy one ready to machine?
 

Steamman3

New member
Buy it ready cast? Guys, that would take all the fun out of it! Where's your sense of adventure? Are we all getting lazy:shrug:

Jim in Pa
 

Steamman3

New member
I notice that, when smarter guys than I do bronze casting, they usually add some amount of tin and or zinc into the melt. That, apparently is to make up for oxidation or evaporation of those metals. Maybe that is something you might look into if those bearings are used in critical applications.

Pete Stanaitis
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Hello Pete,

Since you obviously have more experience in casting than I do, can you recommend a method for making a core for my casting, keeping in mind this will be an open top mold. Thank you,
 

Tony Leonard

New member
A high leaded tin bronze mix will give you better wear properties and some insurance against galling or your hard parts wearing. You always want the bearing to wear, not the hard parts. Just my 2 cents worth.
 
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