|11-25-2004 11:13 PM|
|email@example.com||Did I answer them or do you need some more clarification?|
|11-25-2004 11:00 PM|
|DYNOMITE||Willy thanx for the reply but i asked a couple simple questions that i still dont understand n/m|
|11-25-2004 10:48 PM|
Sorry, I am assuming everyone knows the process. Once the prototype is exactly what I wanted, I primed and painted it with some high quality one-step catalyzed paint. It was just a can of reject paint (color, not quality) I got really cheap at my supplier. Once it was well hardened, I color sanded and polished it to perfection. Then I waxed it 3 or 4 times with mold release wax. Do NOT use auto wax use mold relaease wax. Now it was ready to pull a mold off of.
Look closely at the orange female mold picture and you will see there are three parting lines and three parts to the mold that are bolted together through flanges with 1/4" bolts. The mold was made off the green prototype in three pieces. The two bottom pieces split to release the stem and the top piece sits on top of the other two. I started making the mold by building 1" wide dams using common modeling clay. I rolled the clay into hot dog sized rolls then flattened it with a roller. Then I stuck and molded the clay to the prototype until I had the negative of a flange for one of the three mold pieces. Next I sprayed on a coat of PVA which is a mold release film that dries very fast. It is just like a coat of cellophane that doesn't stick to resin or the waxed surface so the part pops right off after the resin sets. I could have left off the PVA step since the wax does a great job by itself and the PVA leaves a less than perfect surface but it is good insurance after spending a couple of weeks making athe prototype.
Since this first layup was of a mold piece that would receive rough service I painted on a couple of heavy coats of tooling gel coat and let it set. Tooling gel is a very rugged coating and usually comes in orange so when you paint on the gel color you will use for the final part, white in my example, it is very easy to see if you have a complete coating. Once the orange gel set but was still a little sticky, I laminated on 4 layers of heavy fiberglass mat and resin and let that set. Once hardened, I formed clay dams for the second piece of the mold and laid it up the same way. Finally I did the third section. When all the laminating was done, I drilled the bolt holes in the flanges so the mold could be reassembled after it was popped off the prototype.
I took the three mold pieces off and cleaned up the rough edges with a sanding disk on my grinder and now it was ready to make parts. I bolted the two bottom halves of the mold together and laid up that half of the final part using white gel coat and only 3 layers of mat. I laid up the top half of the part in that part of the mold.
Once these two parts hardened, I unbolted the two bottom mold halves and popped them off the part. I took the top half part out of it's mold. All that was left to do was to grind the rough edges of the parts so they would mate and finally epoxy them together at the gray line you see in the photo of the white finished part with the lights installed. Now it is ready to block sand with 320 and paint!
I say again, if you go read the educational sections of the links I posted above all this is explained in detail.
|11-25-2004 07:44 PM|
|DYNOMITE||Willys?, is the green stuff paint and clear or gelcoat?did you put the white gelcoat inside the mold and the white popped out on that part?dumb question but im lost ,did you put the glass inside that mold?just seems like tight working space to get as perfect as you did,thanx|
|11-23-2004 07:20 PM|
|mmartin1872||i remember one day when i first got interested in the "composite" side of aircraft, i was working at a helicopter repair shop out here, and this guy i worked with mixed up a batch of polyester resin in a plastic cup... he mixed it up so hot it melted through the cup, caught fire, and lit up the front of the helicopter where he was doing the repair.. It made for an interesting day.. Mind you this is the same guy that when he started working at the shop we told him the hangar doors where on the clapper and he had to stand over by the side of the door and clap to get the door open.. he stood there clapping.. came back said "it's not working" we said "you have to clap louder because of all the rivet guns going off the clapper isn't that sensitive." well he stood there for another couple of minutes clapping... we laughed.. went to the door where he was standing... and pulled the chain to open the door. (which is where we sent him... i didn't really think he'd take us seriously about the clapper).. i should rephrase that "one of the guys in the shop said "it's on the clapper" the rest of us just agreed. (i'd like to take credit for it... but i just cant )|
|11-23-2004 11:59 AM|
Your question brings out an interesting point about polyester resins in general. Since they are thermosetting rather than chemically cross linked, there is no precise recipe for how much catalyst to add. On cold days you can double your usual MEKP dose and it will not set, seemingly for days. On the other hand, on a typical Bakersfield summer day when it is 140F in my shop, I have had a tuna can of about 4oz of resin gel with only two drops of MEKP while I was still stirring it!
It's all a matter of time and temperature. A thin layup on a cold day will set but you really need to tip up the MEKP bottle. And as you point out, some parts seem to never harden. A friend of mine ordered a 1-piece tilt nose for his '42 Willys from a well known manufacturer clear across the country. Part looked great when it came in. We set it upside down on a couple of saw horses so we could install the tilt mechanism on the underside. When we turned it back over, there were two 2X4 shaped dents at least 1/4" deep across the hood! One would think a commercial part like this would be fully cured. We mounted it on the pickup frame and cowl so it would keep it's shape and let it sit in the sun for a couple of days. The gel coat was black so it got plenty hot and cured rock solid with the extra heat. The dents popped back out pretty well and only needed a slight skim of bondo to repair.
|11-23-2004 11:42 AM|
|mrcleanr6||ok, i guess i stand corrected. i myself have also gone to get my resin and found it hard in the can six months later. what throws in the curve ball is i have worked on boats that have left the factory 15 years ago and come back for some work to be done and found a soft layup. i'm not talking gooey here, just not hardened to the degree it should be. i assumed it was the same when i found it hard in the can. hard, yes but maybe not as hard as it should be like if it were catalyzed properly. who knows, i guess thats why they had chemical engineers running around, to figure crap like that out. whatever, i'm glad i know now. one more thought. if it takes heat to kick off the resin and the promoter and mekp generate that heat then why does a thin layer of glass and resin or even gelcoat kick off when it doesn't have enough thickness to build any heat? you can lay glass outside at 55deg. and the resin wont get more than a degree or two over that and still get hard. it will take a little while but it will happen. just something else that made me think there was more than heat having an effect.|
|11-23-2004 09:35 AM|
Willys I don't mean that sort of "turned off", I just mean bored to tears. I just wanted to say I am not bored that is for sure. No, this is beautiful, sure there are differences of opinion, that is no big deal.
Post the facts as you know it and let the reader decide. That is all you can do with stuff like this, it works very well.
|11-23-2004 09:31 AM|
|firstname.lastname@example.org||I hope too many people aren't turned off by this thread. I think it is an example of what is great about this site - lots of info and opinion which makes us all more informed. I haven't seen anything that is remotely offensive so far.|
|11-23-2004 09:21 AM|
I know a lot of people are turned off by this discussion, I am enjoying the heck out of it. I have never studied chemistry or science and really love the subject.
I know everyone is different but I think knowing the technology a little helps you work with these products so much better. I know I had been painting almost 20 years when I took the paint rep job and they started training me on the products. That training INSTANTLY made me a better painter. And over the years it made a HUGE difference. I am ashamed of some of the "quality" paint jobs I thought I did prior to the education I got from S-W.
What I have learned on this thread and others on this forum WILL help me in future fiberglass projects. I thank you guys a lot.
This is not saying to stop, if you have more bring it on.
|11-23-2004 08:59 AM|
"As has been mentioned, given enough time an unsaturated polyester resin will set by itself. This rate of polymerisation is too slow for practical purposes and therefore catalysts and accelerators are used to achieve the polymerisation of the resin within a practical time period."
and from a company that manufactures resins,
"Polyester resins are called "thermosetting" plastic resins because heat causes them to set up and cure. Actually they will set up and cure all by themselves if left in the can for 3 to 18 months depending on the type of resin;
Most projects have to proceed at a faster pace so we add a catalyst to the resin to obtain a much shorter set and cure time. The most common catalyst is MethylEthylKetonePeroxide or M.E.K.P. for short.
MEKP reacts with other chemicals (promoters) that have been added previously to the resin. The oxidation reaction generates internal heat and causes the resin to begin setting up."
And from my garage I could have offered several exhibits of cans of rock hard gel coat and polyester primer but I to$$ed 'em!
|11-22-2004 07:01 PM|
The stuff I use comes with a matched pump set, one pump of can A to one pump of can B -- and we always do it one at a time in case we lose count.. cause we lost count once and didn't like the pain.....
|11-22-2004 06:41 PM|
[QUOTE]Originally posted by email@example.com
[B]I can attest to that! I don't know how many $$ quarts of polyester gel coat I have forgotten and left in my shop over the 100F summers here in B'field only to open them to find a rock solid paper weight inside. They completely solidified over time w/ medium environmental temperature w/o catalyst. Conversely, I have a two bottle epoxy resin tablet top coating that I have had in the shop for at least 8 years and both bottle are still liquid and I assume still reactive.
I have never used the vinyl ester resin mentioned previously in this thread but I understand it is even more environmentally reactive and is made only in small batches, on-order because it auto-polymerizes so readily.
yes, this is true. the shelf life of polyesters changes greatly with temp. but polyester wont catalyze alone with just heat, there is a little more to the equasion than that. i'm not a chemist, just an end user that works with the stuff every day and done alot of expierementing so i am sure there are some gaps in my info. the mekp and cobalt have to play a big factor in the curing other than generating heat. as i said before that resins are available unpromoted. this is the main reason for that. when unpromoted the resin will never harden and will have a very long shelf life. i have even seen some resins where the cobalt has been substituted for a uv promoter. when run under uv light the stuff kicks in about 10 seconds. i have also seen fiberglass parts made where not enough mekp has been used and the layup is still somewhat soft after 15 years of sitting in the summer sun. if either you or barry have any other info to the specifics of any of this then please feel free.
|11-22-2004 04:31 PM|
What people don't understand there are many markets and many companies that blend this stuff.
It is not a matter of buying an epoxy resin and its ready to go.
It may be blended with another or many other resins than solvents added depending on that companies market.
No two companies come up with the same thing. I'm automotive and just knew car body builders had to be using an epoxy, wrong
that what I get for reaching to an area I'm not involved with.
There are 120-123 epoxy manufacturers the last I knew just in the USA.
Here is the kicker, try to find a suggested formula to make one from scratch. I don't think there is such a thing in any book or on line.
It would be about impossible to have a standard formula.
Automotive is a good example, try to use the Dupont activator in the PPG epoxy. Theoretically it should work but most likely not.
|11-22-2004 04:12 PM|
|mmartin1872||I myself was talking from the aviation side of resins which is where my training is from.. So my text books most likely are very biased towards the "specialty epoxy resins" I guess. From what i can tell, I must not be as informed about this subject as i once thought i was|
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