On Fri, 28 Jul 2006 22:24:10 -0700, Howard Kveck
<
[email protected]> wrote:
>In article <[email protected]>, A Muzi <[email protected]>
>wrote:
>
>> David Kerber wrote:
>> > I would think that the biggest advantage of Ti as a chain/lock set would
>> > be its weight. You could get just as strong a chain for much less
>> > weight than a steel one. Or you could get significantly stronger and
>> > still have a somewhat lighter chain, though it would likely be
>> > significantly bulkier. After all, Ti is significantly stronger than
>> > steel on a weight basis, but not on a volume (size) basis.
>>
>> Step back and see the whole problem: Titanium cuts quite easily with a
>> hacksaw - much easier than steel.
>
> Well, that depends on the alloy and heat treat levels of the titanium and steel
>being compared, as well as the lubrication (if any) being used.
>
> Something to consider: Order some titanium (say CP) from a material supplier, and
>some steel (say 1018). If titanium is so easily cut, why are the cutting fees for it
>so much higher than when they cut your steel?
Dear Howard,
Because . . .
"Compared to steel, titanium alloys offer several advantages. Their
density is only about half that of steel, so parts made from them
weigh roughly half as much as steel parts. Yet their strength exceeds
steel's, and they have twice the elasticity. That makes them ideal for
applications that require flexible materials that don't crack or
rupture. Titanium alloys resist corrosion better than the best
stainless steels. And, like steel, titanium alloys can be readily cast
or forged and are widely available to the industrial market."
"There are drawbacks, however. Most titanium alloys are poor thermal
conductors. Heat generated during cutting doesn't dissipate through
the part and machine table, but tends to concentrate in the cutting
area. The high temperatures - 2000 deg. F in some cases - temper and
dull cutting edges. These dull edges generate even more heat, further
shortening tool life. Cutting temperatures can get so high that chips
sometimes burst into flames."
"Titanium alloys' elasticity, so beneficial to finished parts, makes
them especially difficult to machine. Under cutting pressures, the
"springy" materials move away from the tool. Consequently, the cutting
edges rub rather than cut, particularly when making light cuts. The
rubbing process generates more heat, compounding problems caused by
poor thermal conductivity."
"As a result of the normal cutting process, titanium alloys tend to
workharden. This is especially true when an inappropriate tool is
applied. Instead of cutting the part, the wrong tool "pushes" it,
straining the alloy. As the material moves away from the cutting edge
it deforms plastically rather than elastically. Plastic deformation
increases the material's strength - and, unfortunately, its hardness -
at the point of cut. As the alloy reaches a higher level of hardness
and strength, cutting speeds that were appropriate at the start of the
cut become excessive, and the tool wears dramatically."
"Many shops misunderstand these peculiarities, and take a
trial-and-error approach to machining titanium alloys. They spend
considerable sums on cutting tools, trying to find the ones that work.
Some have even gone out of business as a result. Other shops,
intimidated by the prospector ruining parts worth thousands of
dollars, avoid working with the materials altogether."
"Despite titanium alloys' reputation for toughness, they can be
machined successfully and cost-effectively. Those shops that have
taken the time to learn how to machine the materials, in fact,
consider them a 'piece of cake.'"
http://www.hanita.com/hanita_protected/hanita-art3.htm
Taking time to learn how to machine titanium means higher charges,
particularly since there's far less demand than for steel cutting.
Cheers,
Carl Fogel
