Thread: what size solid brake line

Originally Posted by chazza

I think the work-hardening "issue" is a bit of a Furphy, given that steel and aluminium brake tube can also work-harden. .........
Cheers Charlie

I think that it is a bit of a furphy in that work hardening is very rarely a problem - I have seen copper brake lines used many times over the years, and have never seen this as a problem. On the other hand, I have seen copper fuel lines work harden and crack on quite a few occasions - perhaps because they are larger diameter than brake lines. But copper is certainly a lot more easily work hardened than most grades of steel, particularly those used for tubing of any kind, and also work hardens much more readily than most aluminium alloys, although I have had no experience with aluminium brake pipes.

John

Originally Posted by dullbird

what do you guys mean when referring to work hardening? a hardening of the metal causing fatigue/cracks perhaps?

Some, perhaps most, metals, when subjected to repeated deformation have the structure of the crystals that make up the metal modified in a way that makes them harder and at the same time more brittle. The increased hardness is rarely a problem (but see the comment below) but the increased brittleness is, as it can bring the amount of deformation into the range that results in fatigue cracking with relatively few cycles, even though this is not a problem with the original properties of the metal.

There are two metals in common use where work hardening is very pronounced. The first of these is copper. This was first discovered in prehistory where copper was the first metal used, and it was found that repeated hammering hardened the cutting edge of tools and weapons. Apart from brake lines, it is also a problem with electrical wiring and is the reason that all wiring in vehicles is made with very fine individual strands - it is not just so they can be bent during installation.

The second metal is most grades of stainless steel. For this reason, the use of stainless steel must be avoided in ant place where it is subject to vibration and carrying a heavy load. If it is absolutely necessary to use stainless, then it is necessary to use a design that minimises the cyclic deformation, so that it is bad practice to replace carbon steel bolts with stainless, especially in critical or high load positions. A further effect is to make stainless steel difficult to machine, as the work hardening makes the surface harder than most cutting tools unless every cut is deeper than the depth of hardening created by the previous cut.

John