Reusing Bronze knock on sail hanks

[davidmh]

It is quite easy to gently ease the claw up and sideways to allow the hank to be removed from the sail, and you can then replace the grommet. However when I replace the hank the claw somtimes snaps off meaning I have to replace the hank at £6-7 a time. would heating up the claw make it more malleable, and hence less likely to fracture. Has anyone found a successful way to do it,

Regards
David MH

 

[vyv_cox]

You can anneal bronze and some other copper alloys by heating to dull red followed by quenching in water.

 

[VicS]

You can anneal bronze and some other copper alloys by heating to dull red followed by quenching in water.

I did not think quenching was necessary ????

It might be convenient to cool an object quickly but a small item like a sail hank is not going to remain hot for long.
Quenching a large object might limit the time for excessive grain growth but that wont apply to a small object that cools naturally fairly quickly

 

[vyv_cox]

It isn't something I am very familiar with but I am finding many references like this:

'The alloy of copper and tin has the peculiar property that, whereas steel becomes hard through cooling, this mixture, when cooled suddenly, becomes noticeably soft and more malleable. The alloy is heated to a dark-red heat, or, in the case of thin articles, to the melting point of lead, and then plunged in cold water. The alloy may be hammered without splitting or breaking.'

But I also find quite a few that don't seem to mention quenching. It seems that annealing temperature is the more important factor.

 

[doug748]

It is quite easy to gently ease the claw up and sideways to allow the hank to be removed from the sail, and you can then replace the grommet. However when I replace the hank the claw somtimes snaps off meaning I have to replace the hank at £6-7 a time. would heating up the claw make it more malleable, and hence less likely to fracture. Has anyone found a successful way to do it,

Regards
David MH

I don't think you have anything to lose by trying it. I have just had a go and, whilst noticeably softer, it broke anyway. It was visibly necked on the inside of the claw so it may have been damaged as it was taken off. So best to do it before removal if you can.

I used a gas blowlamp, to redish heat, on the claw, and then quench.

 

[VicS]

It isn't something I am very familiar with but I am finding many references like this:

'The alloy of copper and tin has the peculiar property that, whereas steel becomes hard through cooling, this mixture, when cooled suddenly, becomes noticeably soft and more malleable. The alloy is heated to a dark-red heat, or, in the case of thin articles, to the melting point of lead, and then plunged in cold water. The alloy may be hammered without splitting or breaking.'

But I also find quite a few that don't seem to mention quenching. It seems that annealing temperature is the more important factor.

The reason quenching is not necessary is that copper has only one crystal structure, unlike iron which changes betweem the relatively soft BCC and the hard FCC structure at 910C. With steel you quench to capture the hard FCC structure or cool slowly to allow the BCC structure to form.

The only reasons to quench copper alloys is for convenience or in the case of large items to prevent excessive grain growth. The latter, together with the annealing temperature, is particularly important with α-brasses which are prone to excessive grain growth recognizable by an "orange peel" effect on the surface.

The metallurgy of bronzes is somewhat more complex than brasses but AFAIK the same applies.

 

[vyv_cox]

The reason quenching is not necessary is that copper has only one crystal structure, unlike iron which changes betweem the relatively soft BCC and the hard FCC structure at 910C. With steel you quench to capture the hard FCC structure or cool slowly to allow the BCC structure to form.

The only reasons to quench copper alloys is for convenience or in the case of large items to prevent excessive grain growth. The latter, together with the annealing temperature, is particularly important with α-brasses which are prone to excessive grain growth recognizable by an "orange peel" effect on the surface.

The metallurgy of bronzes is somewhat more complex than brasses but AFAIK the same applies.

Yes, I agree, but the quote above, and many others, comes from practical people who have done it. The one above comes from a cymbal manufacturer.

 

[Rum Run]

What affect would annealing temperatures have on the plunger spring? Presumably they are stainless but I stand to be corrected.

 

[vyv_cox]

What affect would annealing temperatures have on the plunger spring? Presumably they are stainless but I stand to be corrected.

Difficult to say without knowing the composition. Most unlikely to be 300 series stainless but could possibly be 400 series. There are quite a few copper alloy spring materials, so yet another variable. Best advice might be to just heat the claw end and quench as quickly as possible.

 

[davidmh]

Thanks for all the input from the metallurgists, I will have a go and see if it stop the claws breaking

David MH

 

[doug748]

What affect would annealing temperatures have on the plunger spring? Presumably they are stainless but I stand to be corrected.

When I tried it the spring still sprung but I did follow vyv-cox's advice and concentrated my fire on the prong itself.


I have always quenched but, as someone said, as a workshop convenience. The other practical consideration is pickling, which can be speeded up greatly by quenching in 5% sulphuric acid solution. * The item comes out dead clean and much time is saved.

* This is of course a digression from the olden days of mufflers and clogs, before the Health and Safety. I am not suggesting it for the OP's project.