Cracked silicon bronze casting

[andrewpatrol]

I've gone and cracked the arm on my lower rudder pintle. I'm wondering can cast silicon bronze be welded?
thanks

[James McMullen]

Re: Cracked silicon bronze casting

Welding, brazing, or silver soldering silicon bronze is a bitch. Needs expensive tools and perfect technique. I'd just cast a new one, honestly. Easier.

[PeterSibley]

Re: Cracked silicon bronze casting

Did you crack the pin or the attachment end Andrew ? If it's the pin perhaps you could drill it out and use a length of 316 round in place ? That shouldn't be too difficult.

It might be worth asking your local welder if he has the right filler rods for his TIG , he may be able to do a repair but I have no idea of the difficulties of welding silicon bronze. Some of the other bronze alloys aren't too difficult.

[suzyj]

Re: Cracked silicon bronze casting

Welding, brazing, or silver soldering silicon bronze is a bitch. Needs expensive tools and perfect technique. I'd just cast a new one, honestly. Easier.

This surprises me. I wouldn't have called myself particularly talented with the torch, but when I've had reason to solder bronze it's been incredibly easy. Wets out no dramas. Much easier than stainless, which is a pig. I guess if the casting has a lot of inclusions in it that could be a problem though.

My approach would either be silver solder with 56% silver rod and LPG/oxygen, or else TIG with silicon bronze filler. There will be a bit of a line with the silver solder, as the filler is a tad lighter than bronze. If it's in a spot where people will see it, I'd go the TIG with bronze.

Indeed, PM me and I'll give you my address. Send it across to me and I'll solder it back together for ya.

[James McMullen]

Re: Cracked silicon bronze casting

How big a boat? How big are the working stresses? Is it an underwater fitting? (Mixing metals leads to galvanic corrosion) How corroded or worn was the part? Was there an inclusion or corrosion which caused it to fail in the first place? What alloy was it made from in the first place?

A fresh casting avoids a lot of questions about a part which if it fails underweigh will disable your boat's steering.

Of course if it's just a lil' thang, solder away, and don't worry.

[Canoeyawl]

Re: Cracked silicon bronze casting

I have mig welded lots of silicon bronze, several 50 lb spools, either spray arc or short arc, piece of cake.

[andrewpatrol]

Re: Cracked silicon bronze casting

James, it's a 22' Oughtred grey seal. I'm pricing a new one now for the reasons you state. Part is brand new. Stupid me forced arms to splay out to fit new keel. I thought an 1/8" couldn't hurt, but the casting thought otherwise. Expensive mistake. Being the rudder I'm leaning towards a newy otherwise it'll always be on my mind. You can see fitting in my thread " Oughtred grey seal" in building/repair #326.
Canoeyawl, does that include castings. I've emailed manufacturers to see what breed of bronze it actually is, I'm guessing silicon but could be phosphorous maybe, dunno
another factor is that this rudder is quite big maybe weighing 20 or 30 kg bouncing up and down on this lower fitting. Sure it's in water but but on the trailer???
i have another shipment coming from suppliers any way so I guess I've talked myself into just writing it off as an expensive f..k up

[Canoeyawl]

Re: Cracked silicon bronze casting

Mostly castings...

[PeterSibley]

Re: Cracked silicon bronze casting

Is it locally made Andrew? Foundries here love gunmetal unless the alloy is otherwise specified.

[suzyj]

Re: Cracked silicon bronze casting

How big a boat? How big are the working stresses? Is it an underwater fitting? (Mixing metals leads to galvanic corrosion) How corroded or worn was the part? Was there an inclusion or corrosion which caused it to fail in the first place? What alloy was it made from in the first place?

A fresh casting avoids a lot of questions about a part which if it fails underweigh will disable your boat's steering.

Of course if it's just a lil' thang, solder away, and don't worry.

Silver solder and silicon bronze are quite close together on the galvanic chart, with the bronze being a little more anodic than the silver solder, and hence offering corrosion protection to the filler.

I was perhaps a little modest in my first post. I have a fair bit of experience with brazing bicycles, which are a lot more fiddly than boat bronze. I wouldn't hesitate to solder it back together, and would be confident that the repaired casting would be every bit as strong as the original.

[andrewpatrol]

Re: Cracked silicon bronze casting

Peter, it's one of Classic Marine's from England.
we have decided to go with a new one being the lower fitting it'd be always be on my mind in a blow which is how I like to consider these problems, cos there's no-one there to come fish you out when the chips are down.
thanks for the input everyone especially Suzi for your kind offer.

[PeterSibley]

Re: Cracked silicon bronze casting

What ever makes you comfortable Andrew ! She's going to be a great boat .

[kc8pql]

Re: Cracked silicon bronze casting

we have decided to go with a new one being the lower fitting it'd be always be on my mind...

Wise decision I think.

[Jay Greer]

Re: Cracked silicon bronze casting

A wise decision. But I do have a question. That is, how do you know the fitting is silicone bronze? It is more likely a manganese casting which will take to tig or mig welding very well.
Jay

[andrewpatrol]

Re: Cracked silicon bronze casting

Jay, I'm not sure what breed of bronze it is, that was just a guess. I've done a rough calc of the postage from here to England plus the manufacturers quote for repair and it comes out about 20% less than a new one, so I think a new one definitely.