An Ode to a cracked frame
09-14-07, 09:45 PM
#51
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I know a guy who road a Merlin into the ground. Cracked a Ti frame. You want to talk about sharp edges. Ti leaves a nasty edge when it cracks - razor sharp.
09-14-07, 11:36 PM
#52
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09-15-07, 07:47 AM
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I think AL was a good material for bike manufacturers, it's cheap, fairly easy to work with and light weight, but I am not convinced it's a good material for bike riders, it's harsh riding, and does fail at welded joins, unless the welds are perfect and the heat treating (to add strength) is done perfectly, after the welding is complete. No matter what, the weakest point in any metal is the welded joint, and since Aluminum suffers from stress fracturing, it's most likely to fracture at a weld.
Now most sub $1000 frames come from China, and lately we have been seeing some big quality issues with Chinese manufacturing (just ask the folks at Mattel ), so maybe it's poor quality welds, or poor quality control at the Chinese contractor that welds the frames. This may not even be Treks fault, because, as typical in Asia you hire a company, they sub-contract out and you have no control over who they sub-contract out to.
Now most sub $1000 frames come from China, and lately we have been seeing some big quality issues with Chinese manufacturing (just ask the folks at Mattel ), so maybe it's poor quality welds, or poor quality control at the Chinese contractor that welds the frames. This may not even be Treks fault, because, as typical in Asia you hire a company, they sub-contract out and you have no control over who they sub-contract out to.
+1
As en engineer (controls - not mechanical) my experience (with making brackets, etc.) is that, if you make a part out of aluminum that formerly was made out of steel, you make the aluminum part 25% to 50% thicker than the steel part. This is just a rule of thumb, and applied to non-critical parts. But I think it points towards some critical properties of aluminum.
Aluminum is softer than steel, so to get the same strength you have to make the part beefier. When you make the part beefier (thicker) you tend to loose some elasticity - just because a thicker part is less springy than a thinner part. That's why an aluminum frame has a "harsher" ride than a steel frame, so the manufacturers have to make forks and seatstays out of something that's springier to get an acceptable ride - carbon fiber, which is lightweight but has also comes with real-world durability issues.
Aluminum is harder to weld than is steel, and when you add the additional thickness of the part you get weld-penetration issues.
Then you go to a foreign country to get it done - with little or no government or regulatory oversight and a slave labor workforce - and what do you get?
Another less-desirable property of aluminum is that, again because of it's softness, you can't tap it for threads.
Add the problems of joining carbon fiber parts to aluminum - glue.
Also, it's necessary to make certain parts of an aluminum/carbon fiber frame out of steel - things like the dropouts - because neither aluminum nor carbon fiber is very good at carrying the concentrated loads inherently seen at the dropouts. Again, you have to figure out how to attach these dissimilar materials together - usually glue again.
Of course we are really living in the period of infancy regarding these technologies. As time goes by, the industry will learn how to apply these materials. For no, give me steel.
09-15-07, 08:36 AM
#54
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+1
As en engineer (controls - not mechanical) my experience (with making brackets, etc.) is that, if you make a part out of aluminum that formerly was made out of steel, you make the aluminum part 25% to 50% thicker than the steel part. This is just a rule of thumb, and applied to non-critical parts. But I think it points towards some critical properties of aluminum.
Aluminum is softer than steel, so to get the same strength you have to make the part beefier. When you make the part beefier (thicker) you tend to loose some elasticity - just because a thicker part is less springy than a thinner part. That's why an aluminum frame has a "harsher" ride than a steel frame, so the manufacturers have to make forks and seatstays out of something that's springier to get an acceptable ride - carbon fiber, which is lightweight but has also comes with real-world durability issues.
Aluminum is harder to weld than is steel, and when you add the additional thickness of the part you get weld-penetration issues.
Then you go to a foreign country to get it done - with little or no government or regulatory oversight and a slave labor workforce - and what do you get?
Another less-desirable property of aluminum is that, again because of it's softness, you can't tap it for threads.
Add the problems of joining carbon fiber parts to aluminum - glue.
Also, it's necessary to make certain parts of an aluminum/carbon fiber frame out of steel - things like the dropouts - because neither aluminum nor carbon fiber is very good at carrying the concentrated loads inherently seen at the dropouts. Again, you have to figure out how to attach these dissimilar materials together - usually glue again.
Of course we are really living in the period of infancy regarding these technologies. As time goes by, the industry will learn how to apply these materials. For no, give me steel.
As en engineer (controls - not mechanical) my experience (with making brackets, etc.) is that, if you make a part out of aluminum that formerly was made out of steel, you make the aluminum part 25% to 50% thicker than the steel part. This is just a rule of thumb, and applied to non-critical parts. But I think it points towards some critical properties of aluminum.
Aluminum is softer than steel, so to get the same strength you have to make the part beefier. When you make the part beefier (thicker) you tend to loose some elasticity - just because a thicker part is less springy than a thinner part. That's why an aluminum frame has a "harsher" ride than a steel frame, so the manufacturers have to make forks and seatstays out of something that's springier to get an acceptable ride - carbon fiber, which is lightweight but has also comes with real-world durability issues.
Aluminum is harder to weld than is steel, and when you add the additional thickness of the part you get weld-penetration issues.
Then you go to a foreign country to get it done - with little or no government or regulatory oversight and a slave labor workforce - and what do you get?
Another less-desirable property of aluminum is that, again because of it's softness, you can't tap it for threads.
Add the problems of joining carbon fiber parts to aluminum - glue.
Also, it's necessary to make certain parts of an aluminum/carbon fiber frame out of steel - things like the dropouts - because neither aluminum nor carbon fiber is very good at carrying the concentrated loads inherently seen at the dropouts. Again, you have to figure out how to attach these dissimilar materials together - usually glue again.
Of course we are really living in the period of infancy regarding these technologies. As time goes by, the industry will learn how to apply these materials. For no, give me steel.
We start at Gang Wang Smelting, the alloy specification for 1kg of metal is 800g of aluminum, 80g of copper, 80g of zinc and 40g of magnesium. The metal coming out is 820g of aluminum, 79g of copper, 80g of zinc and 39g of magnesium. The metal is sent to the tube maker. The reason is that copper and magnesium are very expensive, and by cutting back a hair, they can save some money.
Ching Zin tubing is supposed to make the tube with a OD of 45mm and an ID of 40mm the OD is actually 44.9mm and the ID is 40.1mm leaving the metal .2mm too thin.
It goes to the Chang Zee the frame builder, to save money on fuel their heat treating oven is 5℃ cooler then it should be, the welders are told to not waste welding rod, so the weld is .4mm shallower then it should be to last. The frame goes to the bike builder, who uses slightly under specification packaging, the spacers between the rear dropouts are 2mm shorter then they should be. The shipping office guys were out drinking the night before, and are throwing boxes extra hard today into the containers, and not packing them as tight as they should be. The ship goes through a Typhoon, and while 10 bikes are ruined in the container, 175 more contain hidden damage.
While no one factor alone would lead to a failure, all of them combined lead to a cracked frame with less then 1000 km on it.
