"vey" <[email hidden]> wrote in message
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Quoted message said:Quoted message said:
How Forgings compare to Castings (quote from
http://www.forging.org/facts/faq3.htm
Quoted message said:Quoted message said:):
That said, many items are forged, but don't say that they are. I would
think that just about all the stems you will meet would be forged, but I
am sure that there are exceptions if they are particularly old.
It can be hard to tell the difference between forged and cast stems.
Most lower cost aluminum alloy stems were/are made from castings.
The Japanese companies SR and Nitto both produced cast aluminum stems.
Only their premium models were forged.
Same thing goes for most European producers. While almost all Italian 3TTT
quill style stems were forged, I think that some of their early cheap
stems were cast. Phillipe stems from France were mostly cast but a few of
their top end stems were forged. Same with French Atax and British GB an
so on.
It was the cheap French stems from the Bike Boom era of the 1970s by Pivo,
AVA, Belleri and others that had a bad reputation for breaking although
I've seen the same problem in SR stems from the same time period.
Several differences between forged and cast bike stems:
In a forging the metal has been compressed and is more dense. It tends to
be more ductile and less likely to develop cracks from normal use or in an
accident.
Cheap poor quality castings can be brittle and crack easily from stress
because of the grain structure of the metal and possible flaws in the
castings.
Castings can be less expensive to produce because they are "near net
sized" and can require less machining and finishing. That's why they've
been used so much for inexpensive bike stems.
Modern casting techniques have resulted in much better quality aluminum
castings. I checked out a lot of threadless stems over the past year. Of
the 100 or so that I looked at most of them appear to have been made from
castings.
Aluminum is either forged at room temperature (cold forged) or heated to
200°F to 800°F (95°C to 430°C)
Many bike stems are touted as being cold forged. Sugino and other Japanese
companies used to claim that their products were "melt forged" - injection
molded castings.
Actual strength and hardness of aluminum depends more on the alloy
composition and subsequent heat treatment than the manufacturing process.
There are a lot of critical aerospace and automotive parts made of cast
aluminum.
I prefer forged aluminum stems myself. Back in the 1970s I had 3 cast
stems break off while riding and it's not a comfortable feeling holding a
set of bars in the air while trying to stop the bike. Two of the events
were while road testing cheap French Bike Boom bikes, the 3rd time was
with a Belleri stem on my own 1973 Gitane Super Corsa. They all failed at
the splits for the wedge cone at the bottom of the quill.
After that I switched to Cinelli and 3TTT forged stems.
Here's some links to sites about aluminum forging:
http://www.aluminum.org/Content/NavigationMenu/The_Industry/-Forgings/Forgings.htm
http://www.metalpass.com/metaldoc/paper.aspx?docID=296
