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Author Topic:   Separating Molded Parts from Mold

Powergroove803 posted 09-30-2014 10:24 AM ET (US)
I have made a carbon fiber tube on a steel mandrel. I used the grease-and-tape method to wrap the tube, so the carbon fiber tube will slide off. I understand that the carbon fiber shrinks with the epoxy resin, and this 80-inch tube is stuck. It moved about a foot before it locked down. I made another one that was about five-feet long, and it came off the same tube, albeit not very easily, but it did come off. I have read that [applying] dry ice down the steel mandrel may cause enough shrinkage to allow [the molded part] to come off. Anyone have any other ideas?
Jefecinco posted 09-30-2014 10:54 AM ET (US)
If dry ice is difficult to find. try a mixture of ordinary ice and acetone. I've been told the mixture will cool below 32-degrees-F. I've never tried it, but back in the day it was used for fuel line cooling to prevent vapor lock on race cars.
Butch
Plotman posted 09-30-2014 12:53 PM ET (US)
Steel isn't really a very good conductor of heat; witness blacksmiths holding a two-foot hunk of iron that is red hot on one end and cool enough to hold the other.
I would try running a heat gun over the carbon tube to get it to expand and then pulling. Heat will also increase the viscosity of the grease; cooling it will make it stickier.
Powergroove803 posted 09-30-2014 01:59 PM ET (US)
Jeff--I also heard of mixing dry ice with acteone for around -50-degrees-F. Plug both ends with a pinhole in one end to release gases. A heat gun would be quicker. I will try that first. Dry ice is now readily available at Publix and Kroger. I have been using it in my 150-quart cooler for a couple of years for four-day summer camping. [The mixture] will stay frozen solid even in 98-degrees. Unless you have a Yeti or equivalent cooler, you need to put some rubber or foam between the dry ice and the cooler or it will crack it. Also, leave the drain plug open to vent or you will have yourself a little explosion
SpongeBob posted 10-01-2014 12:53 PM ET (US)
I know this is after the fact, but if you had used mold release instead of grease it would be much easier to get off. Even Johnson's or any good paste will work as well.
Jeff
Powergroove803 posted 10-08-2014 04:09 PM ET (US)
I ended up cutting the tube lengthwise to remove it from the mandrel and then gluing it back together. Next time I will use the "lost wax" method, or wrap the mandrel in mylar strips lengthwise, then they can be removed from the ends individually until the part is freed.
[Deleted long sidebar on new topic, not related to separation of molded parts from their molds.--jimh]
Binkster posted 10-09-2014 07:25 AM ET (US)
I built a plug and a mold for a center console last year. When it came time to separate the part I laid up from the mold. I was able to get some separation by forcing a plastic spackling knife between the two parts and then took a garden hose and forced water into the space and the part(center console) floated free.
Rich
jimh posted 10-09-2014 08:58 AM ET (US)
[I have deleted these comments because the Powergroove803 contacted me via email and said my comments about molded parts offended him. I don't think my comments were of sufficiently acute insight that they cannot be deleted from the discusison, and I assure you at no time was my intention to offend Powergroove803. I leave the field of discussing how to separate a molded part from a male mold entirely to Powergroove803--jimh]
jimh posted 10-10-2014 12:49 AM ET (US)
Please explain the meaning of "the grease-and-tape method to wrap the tube." I tried to find some reference to the phrase "the grease-and-tape-method" but a GOOGLE search did not locate anything related to forming parts on a mandrel.
I suspect that many readers, just like I am, are not familiar with "the grease-and-tape method" and would benefit from an explanation.
I think the advice to heat the mandrel and its molded part has to be considered with some eye to the coefficient of linear expansion of the two materials. If the mandrel is steel and the molded part is carbon fiber, in order for heat to provide some loosening of the molded part from the mandrel, the molded part would have to expand faster than the mandrel. What is the coefficient of linear expansion of carbon fiber and steel? Which is going to expand faster? I believe that you can make an inference about which direction the temperature should be changed by comparing the coefficients of linear expansion.
Binkster posted 10-10-2014 09:48 AM ET (US)
jimh, your comments sound reasonable to me, but I believe powergroove is traveling down a different road than the rest of the posters here. I'm no expert on mold building but I have some experience, molding boat parts. I myself have no idea what he is talking about, but I'm interested, maybe I can learn something.
rich
Powergroove803 posted 10-14-2014 03:39 PM ET (US)
http://www.oneoceankayaks.com/Wshophtm/carb_tubing.htm
Link to grease and tape method, Im sure thats not what you call it, but not sure it has a real name

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Author	Topic: Separating Molded Parts from Mold
Powergroove803	posted 09-30-2014 10:24 AM ET (US) I have made a carbon fiber tube on a steel mandrel. I used the grease-and-tape method to wrap the tube, so the carbon fiber tube will slide off. I understand that the carbon fiber shrinks with the epoxy resin, and this 80-inch tube is stuck. It moved about a foot before it locked down. I made another one that was about five-feet long, and it came off the same tube, albeit not very easily, but it did come off. I have read that [applying] dry ice down the steel mandrel may cause enough shrinkage to allow [the molded part] to come off. Anyone have any other ideas?
Jefecinco	posted 09-30-2014 10:54 AM ET (US) If dry ice is difficult to find. try a mixture of ordinary ice and acetone. I've been told the mixture will cool below 32-degrees-F. I've never tried it, but back in the day it was used for fuel line cooling to prevent vapor lock on race cars. Butch
Plotman	posted 09-30-2014 12:53 PM ET (US) Steel isn't really a very good conductor of heat; witness blacksmiths holding a two-foot hunk of iron that is red hot on one end and cool enough to hold the other. I would try running a heat gun over the carbon tube to get it to expand and then pulling. Heat will also increase the viscosity of the grease; cooling it will make it stickier.
Powergroove803	posted 09-30-2014 01:59 PM ET (US) Jeff--I also heard of mixing dry ice with acteone for around -50-degrees-F. Plug both ends with a pinhole in one end to release gases. A heat gun would be quicker. I will try that first. Dry ice is now readily available at Publix and Kroger. I have been using it in my 150-quart cooler for a couple of years for four-day summer camping. [The mixture] will stay frozen solid even in 98-degrees. Unless you have a Yeti or equivalent cooler, you need to put some rubber or foam between the dry ice and the cooler or it will crack it. Also, leave the drain plug open to vent or you will have yourself a little explosion
SpongeBob	posted 10-01-2014 12:53 PM ET (US) I know this is after the fact, but if you had used mold release instead of grease it would be much easier to get off. Even Johnson's or any good paste will work as well. Jeff
Powergroove803	posted 10-08-2014 04:09 PM ET (US) I ended up cutting the tube lengthwise to remove it from the mandrel and then gluing it back together. Next time I will use the "lost wax" method, or wrap the mandrel in mylar strips lengthwise, then they can be removed from the ends individually until the part is freed. [Deleted long sidebar on new topic, not related to separation of molded parts from their molds.--jimh]
Binkster	posted 10-09-2014 07:25 AM ET (US) I built a plug and a mold for a center console last year. When it came time to separate the part I laid up from the mold. I was able to get some separation by forcing a plastic spackling knife between the two parts and then took a garden hose and forced water into the space and the part(center console) floated free. Rich
jimh	posted 10-09-2014 08:58 AM ET (US) [I have deleted these comments because the Powergroove803 contacted me via email and said my comments about molded parts offended him. I don't think my comments were of sufficiently acute insight that they cannot be deleted from the discusison, and I assure you at no time was my intention to offend Powergroove803. I leave the field of discussing how to separate a molded part from a male mold entirely to Powergroove803--jimh]
jimh	posted 10-10-2014 12:49 AM ET (US) Please explain the meaning of "the grease-and-tape method to wrap the tube." I tried to find some reference to the phrase "the grease-and-tape-method" but a GOOGLE search did not locate anything related to forming parts on a mandrel. I suspect that many readers, just like I am, are not familiar with "the grease-and-tape method" and would benefit from an explanation. I think the advice to heat the mandrel and its molded part has to be considered with some eye to the coefficient of linear expansion of the two materials. If the mandrel is steel and the molded part is carbon fiber, in order for heat to provide some loosening of the molded part from the mandrel, the molded part would have to expand faster than the mandrel. What is the coefficient of linear expansion of carbon fiber and steel? Which is going to expand faster? I believe that you can make an inference about which direction the temperature should be changed by comparing the coefficients of linear expansion.
Binkster	posted 10-10-2014 09:48 AM ET (US) jimh, your comments sound reasonable to me, but I believe powergroove is traveling down a different road than the rest of the posters here. I'm no expert on mold building but I have some experience, molding boat parts. I myself have no idea what he is talking about, but I'm interested, maybe I can learn something. rich
Powergroove803	posted 10-14-2014 03:39 PM ET (US) http://www.oneoceankayaks.com/Wshophtm/carb_tubing.htm Link to grease and tape method, Im sure thats not what you call it, but not sure it has a real name