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15th Jan 2009, 10:46 PM #1Intermediate Member
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- Feb 2008
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- Melbourne
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- 35
Cast Iron - Braze or Silver Solder?
Hi,
I need to replace a broken tooth on a cast iron cog in my old Hercus lathe. I intend to mill a slot where the tooth was and insert a piece of cast iron the same width as the original tooth into the slot, then either braze or silver solder it in. I can get some bits from an old cast iron bath to use for the new tooth. Any suggestions on the preferred method?
I have oxy and have been using it (as an amateur) for over 40 years. I have both plain bronze and nickel-bronze rods and can get silver solder. Which of these would be easiest and/or adequate? If sliver solder is the go, what %?
From reading other posts here regarding welding CI I understand that preheating is important. What other tricks of the trade are important when brazing CI?
Buncha
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16th Jan 2009, 12:50 AM #2
Braze , I always found tinning flux to work well . Best of luck , cause cast iron is a b1tch to play with
Ashore
The trouble with life is there's no background music.
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16th Jan 2009, 03:14 PM #3Member
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- Nov 2008
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- Canada
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- 57
I have seen teeth repairs done just by building up with the brazing rod and machining the new tooth out of the brass. I understand they hold up very well.
Darrell
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18th Jan 2009, 09:24 PM #4
Brazing for my money
Use Tobin Bronze braze rods
Grahame
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26th Jan 2009, 10:08 PM #5Intermediate Member
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- Feb 2008
- Location
- Melbourne
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- 35
Thanks guys, brazing it is
I've had a practice on an old cast iron gear, so I'm ready for the real thing now.
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27th Jan 2009, 07:48 PM #6
Gidday )
Read this ....................... haven't seen it put better
http://www.weldingtipsandtricks.com/...cast-iron.html
Hope u get from it what i have
Regards LukeJust Do The Best You Can With What You HAve At The Time
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28th Jan 2009, 11:02 PM #7
One way is to drill and tap holes along the length of the broken tooth ,then screw threaded pins into the threaded holes ,Then use them as a base to build up with brazing .
Have done this type of repair a few times on big industrial press gears that take a pounding day in day out .
Preheat if you are going to attempt arc or mig welding, bury and cool slowly in a lime box or very dry sand .
Kev."Outside of a dog a book is man's best friend ,inside a dog it's too dark to read"
Groucho Marx
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22nd Feb 2009, 09:04 PM #8Novice
- Join Date
- Feb 2009
- Location
- Port Macquarie
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- 10
Nickel Bronze tooth
Hey Buncha,
The best way to repair the lost tooth is to build up the area with Nickel Bronze and then machine the new tooth.
Nickel Bronze is designed for this purpose and in many ways is much better than the cast iron and much easier than trying to use a piece of cast iron as a replacement. Cast iron is tricky material and can come in many forms and hardnesses from soft gray to hard white and black heart. Your gear will be made from gray cast iron and can easily be prepared to take the Nickel Bronze build up.
You will need some copper and brass flux (303), File the surface where the bronze is to be built up. Don't grind the area as the grinding action spreads the graphite from the cast iron across the surface and intergranular penetration won't take place and the tooth could release from the gear.
Preheat the whole gear prior to braze welding to a temperature where some flux when sprinkled on the area to be brazed changes to a liquid.
Be careful not to overheat the area and the flame should be applied and removed frequently when building up the area, the reason being that 1) the bronze will run out of the area, 2) overheated bronze will fume indicating that the properties are being burnt out of the bronze 3) overheating the cast iron prior to welding will oxidise the surface of the cast iron and intergranular penetration won't take place. I have alwaays found great success repairing gear teeth using this method. Contact me if I can be of any further help. Regards Ted.
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23rd Feb 2009, 10:04 AM #9Intermediate Member
- Join Date
- Feb 2008
- Location
- Melbourne
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- 35
Hi Ted,
Thanks for that. I heated the gear in the oven to 270 C (lovely smell of hot oil in the kitchen ) then used nickel bronze as you suggested. After it was cool I cut a slot either side of it, then filed the tooth profile on. Before starting I had made a profile gauge by putting a blob of Polybond bog over three good teeth. I used this as I was filing to check position and profile. Once it looked good with that I got the mating gear and ran it over the repaired area by hand to see if I could feel any problems. It was fine, so I reassembled it to the lathe. It ran perfectly with no change in the gear noise as the new tooth was engaged.
Thanks to all for their advice.
Buncha
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