Galvanic reaction Carbon on Aluminum how to prevent question

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Galvanic reaction Carbon on Aluminum how to prevent question

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JaWillis	JaWillis posted 10 Years Ago Topic Details
Group: Forum Members Posts: 8, Visits: 24	Any input on this would be appreciated Maybe you can help me. I will be extending a piece of aluminum tubing by first cutting the tubing then inserting a carbon fiber "ferrule" if you will, to extend the tubing. I will then wrap the splice with carbon fiber tape and resin. 1. What adhesive can I use at the insertion point to bond the aluminum tubing to the ferrule? Will it there be a galvanic response? 2. What do I put in between the carbon fiber wrap and the Aluminum to prevent galvanization? My third question is how to adhere your prefab carbon tubing to pre-preg carbon fiber? Example: a 42mm ID tubing which happens to be the exact size id of a bicycle Bottom Bracket PF30. (press fit 30). However I need to beef up the wall thickness by wrapping pre-preg around it, then compress and heat to cure. I am concerned there may be a delamination issue between the tubing and the pre-preg. Is there something I need to treat the tubing with prior to applying pre-preg? Thanks in advance for your help. Jim W
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20_rc51_00	20_rc51_00 posted 10 Years Ago HOT Post Details
Group: Forum Members Posts: 95, Visits: 548	I've asked similar questions. The recommendation is to have glass between the areas where carbon may be in contact with metals. I really wonder and doubt that bicycle manufacturers actually take this into consideration. There are many videos on youtube from worthy bike companies showing manuf processes where there is no evidence of metal components being insulated. As far as I'm aware I've only heard of aircraft manuf actually employing this. Come to think of it I can recall seeing supercar companies just bolting carbon bits to engine blocks etc.... so it makes you wonder....
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ajb100	ajb100 posted 10 Years Ago Post Details
Group: Forum Members Posts: 346, Visits: 4.4K	All you need to do is electrically insulate the two materials from eachother, be this using a layer of glass, or ensuring a solid adhesive joint. However there also needs to be an electrolyte present so as long as you ensure the joint is dry when bonded and water tight, then there should be no issue Edited 10 Years Ago by ajb100
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wozza	wozza posted 10 Years Ago Post Details
Group: Forum Members Posts: 688, Visits: 5.4K	I've repaired four carbon mountain bike frames up to now we're the issue has been the ally bottom bracket shells coming loose in the carbon tube. I think one of the main reasons has been the higher shock loads when landing jumps etc so this may not apply to road bikes. Carbon doesn't really accept press fit components like steel or ally does. and most adhesives require a 0.2-0.4mm clearance. Too tight a fit and most of the adhesive gets pushed out on assembly, ET515 works well. I reduced the size of the shells to give the required clearance on the lathe and then added some grooves with the Dremmel. This increases the bond area and provides a better mechanical fix as the grooves fill with adhesive. A bit like a splined shaft. The downside is because of the clearance you need to make a fixture to align the two shells in the tube until the adhesive cures. As said I wouldn't worry too much about galvanic corrosion. Carbon Copies Ltd
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JaWillis	JaWillis posted 10 Years Ago Post Details
Group: Forum Members Posts: 8, Visits: 24	Thanks for the input.
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JaWillis	JaWillis posted 10 Years Ago HOT Post Details
Group: Forum Members Posts: 8, Visits: 24	Wooza What are your thoughts on these types carbon frame designs. The headset is the integrated type and the BB is for a PF30. My thought is to build these features into my molds for the headtube and the BB. This is not for a mountain bike, its for a gravel road bike, basically road bike with bigger 38 size tires. Edited 10 Years Ago by JaWillis
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wozza	wozza posted 10 Years Ago HOT Post Details
Group: Forum Members Posts: 688, Visits: 5.4K	JaWillis (25/10/2014) Wooza What are your thoughts on these types carbon frame designs. The headset is the integrated type and the BB is for a PF30. My thought is to build these features into my molds for the headtube and the BB. This is not for a mountain bike, its for a gravel road bike, basically road bike with bigger 38 size tires. Hi, I am no expert on frame design but I do have a decent understanding of the engineering behind it. For years now manufactures have been trying to increase the stiffness of frames around the bottom bracket area. particularly on full suspension bikes where suspension pivots are often mounted. one way of doing this is to increase the size of the chain set shaft/tube. This however means external rather than internal bearings. This resulted in cartridge bearings being screwed into the ally/steel bottom tube. When composite frames began to be developed this caused a problem, machining the thread in the now carbon tube. Different manufactures tried different things resulting in the vast array of BB styles you see now. One method was the press fit style you mention. This method has a few issues, press fit requires extremely accurate machining and requires machining from both sides of the frame to produce the rebate for the shells. As the BB is often the datum point for any subsequent machining this means complex and expensive fixtures are required to hold the bare frames accurately in position which is costly. Also you can only really replace the press fit shells two or three times before the housings become oversize and the frame is effectively scrap. It also requires specialist tools so a trip to the bike shop is required. Trek used a slightly different approach, bonding ally cups into the frame and then the bearing shells fitted into these cups. This also means that the bottom tube only requires machining from one side, keeping costs down. The trade off is a little more weight. As for which is better I prefer the Trek method but that is just my opinion. I suppose much depends on what facilities you have access to machining wise, but either way it has to be extremely accurate. Hope that has helped and not confused things Warren Carbon Copies Ltd Edited 10 Years Ago by wozza
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AHA	AHA posted 9 Years Ago HOT Post Details
Group: Forum Members Posts: 6, Visits: 14	We use to smear all alu and titanium parts where it came into contact with the carbon with two part rubber sealant. It works a treat.
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FLD	FLD posted 9 Years Ago Post Details
Group: Forum Members Posts: 468, Visits: 2.7K	Does duralac work in this situation?
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