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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Comet suspension
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<blockquote data-quote="Martyn Goodwin" data-source="post: 77714" data-attributes="member: 2433"><p>Following information appeared in 2014 in an Australian section newsletter:</p><p></p><p>The fork blades, part FF40 are made from L40 alloy material which is an old British specification superseded by HE15 which is similar to AS1866-1977 grade 2014.</p><p></p><p>For straightening or welding first anneal at 360 to 400 degrees centigrade. Solution heat treat at 505 to 515 degrees centigrade for 2 hours. Quench in boiling water then straighten within 30 minutes.</p><p></p><p>Precipitation harden at 155 to 185 degrees centigrade for 5 hours and furnace cool. This will restore the original hardness of 72 Rockwell B.”</p><p></p><p>In case anyone is interested in what the above steps are designed to do, first, "solution heat treating" doesn't involve putting the Girdraulic in a bubbling cauldron of some solution. It refers to holding the Al (aluminium) at a high enough temperature to allow all of the alloying element(s) responsible for hardening it -- primarily Cu (copper) in this case -- to go into solid solution in the Al. If the Girduraulics are made of L40 the Cu content is <4.0%, and if they are RR56 it's 2.1%. This is the same as putting so much salt in a cup of room temperature water that some is still left as a solid at the bottom of the cup after as much salt as possible has dissolved. This is a "saturated solution" at that temperature. Heating the Al (or salt water) to a higher temperature and holding it there long enough allows additional Cu (or salt) to go into solution.</p><p></p><p>Since Cu diffuses fairly slowly in the Al, quenching it doesn't give the excess Cu time to precipitate, resulting in a "supersaturated solution" of the Cu once the Al is back at room temperature. However, since the solution is supersaturated, even at room temperature the Cu atoms would (very) slowly diffuse through the Al, bump into other Cu atoms, and precipitate as microscopic Cu inclusions. These Cu inclusions pin the movement of dislocations in the Al. A soft metal is one in which dislocations move easily, and a hard metal is one in which they move with difficulty, so L40 and RR56 are "precipitate hardened" alloys.</p></blockquote><p></p>
[QUOTE="Martyn Goodwin, post: 77714, member: 2433"] Following information appeared in 2014 in an Australian section newsletter: The fork blades, part FF40 are made from L40 alloy material which is an old British specification superseded by HE15 which is similar to AS1866-1977 grade 2014. For straightening or welding first anneal at 360 to 400 degrees centigrade. Solution heat treat at 505 to 515 degrees centigrade for 2 hours. Quench in boiling water then straighten within 30 minutes. Precipitation harden at 155 to 185 degrees centigrade for 5 hours and furnace cool. This will restore the original hardness of 72 Rockwell B.” In case anyone is interested in what the above steps are designed to do, first, "solution heat treating" doesn't involve putting the Girdraulic in a bubbling cauldron of some solution. It refers to holding the Al (aluminium) at a high enough temperature to allow all of the alloying element(s) responsible for hardening it -- primarily Cu (copper) in this case -- to go into solid solution in the Al. If the Girduraulics are made of L40 the Cu content is <4.0%, and if they are RR56 it's 2.1%. This is the same as putting so much salt in a cup of room temperature water that some is still left as a solid at the bottom of the cup after as much salt as possible has dissolved. This is a "saturated solution" at that temperature. Heating the Al (or salt water) to a higher temperature and holding it there long enough allows additional Cu (or salt) to go into solution. Since Cu diffuses fairly slowly in the Al, quenching it doesn't give the excess Cu time to precipitate, resulting in a "supersaturated solution" of the Cu once the Al is back at room temperature. However, since the solution is supersaturated, even at room temperature the Cu atoms would (very) slowly diffuse through the Al, bump into other Cu atoms, and precipitate as microscopic Cu inclusions. These Cu inclusions pin the movement of dislocations in the Al. A soft metal is one in which dislocations move easily, and a hard metal is one in which they move with difficulty, so L40 and RR56 are "precipitate hardened" alloys. [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
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