fiberglass molding

Discussion in 'Fiberglass and Composite Boat Building' started by Guest, Apr 12, 2002.

  1. Guest

    Guest Guest

    We are looking at building boats and we recently toured a facility that produces fiberglass hoods for arge trucks, ie. kenworth, peterbuilt etc. I had been told that the process was very similar to that of boats. But they did something I hadn't seen before. They sent the hoods through a curing oven at 120 degrees after they were laid up in the mold, then theypulled the hoods out of the molds and put them through another "post-curing" oven at 220 degrees for about 30 minutes. This confused me because I had been told that you can not have too hot of temperatures or your gelcoat will blister. If that is a concern why would they heat it in an oven? they all came out good, but why do they put the pieces in an oven, because I have seen others that do not use an oven at all. Any clarification on this would be greatly appreciated. We would be building in a very hot location so i had been trying to figure out how I can cool the work area so that I don't have problems with my gelcoat. The temperature is about 110 degrees in the summer so it will be expensive to cool if I have to. I would prefer not to cool if I don't have to. But If I do need to cool, during what parts of the process is it necessary? thanks
  2. duluthboats
    Joined: Mar 2002
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    duluthboats Senior Dreamer

    All resins are not the same. You should work with your supplier to get the right one for your conditions. With that hot a temp I would be worried about working time while you do your layup.
  3. Jeff
    Joined: Jun 2001
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    Location: Great Lakes

    Jeff Moderator

    “There are a number of epoxies that are formulated as "room temperature cure" products. These products do not require post cure to achieve acceptable physical properties, but may benefit from exposure to a higher temperature cure. The improved properties can range from higher heat resistance to higher toughness as measured by Izod impact testing. Properties are enhanced because elevated temperatures allow the epoxy's resin and hardener molecules to continue cross-linking to a higher degree of cure.

    Even low temperature post cures of 110°F for several hours can produce dramatic results for some epoxy products. An example would be PRO- SET® 125 resin and 226 hardener. This combination has a tensile strength of 7,960 psi when cured at room temperature for two weeks. After exposure to 110°F for eight hours, the tensile strength improves to 10,592 psi. That's a 33% improvement. The flexural strength for the 125/226 combination is 12,760 psi for room temperature cure and 18,087 psi for samples post cured at 110°F, a 41% gain. An additional benefit to post curing a part is that the thermal properties increase along with the mechanical properties. This translates to better resistance to print through once the part is in service and better stability at elevated use temperatures. In many cases, very good room temperature cured properties are improved dramatically with exposure to a little heat and time through post curing"


    Post Cure Basics by Tom Pawlak, Technical Services Gougeon Brothers, Inc

    Building Post Cure Ovens

    from SP Systems

    As far as the 220 degree oven, it would be critical to use the correct gelcoat (if a gelcoat is used (?) and resin for the job - epoxy and gelcoat suppliers will be happy to help you select the right resin for the job at hand.

    And as Gary said, if your working temperatures are as high as 110 degrees, you will need to use a slow-cure hardner.
  4. Guest

    Guest Guest

    cooling the molds before Gelcoat?

    Thank you Jeff and Gary, your info helps out a ton. One other thing that they did that I didn't understand is that they put the molds in an air conditioned room before the gelcoat was applied. They said that they did it to prevent problems in the gelcoat. Is this necessary? What happens if you don't do it? if you must do it then what is the optimal temperature for gelcoat? what temperature is too high for gelcoat to be done without problems and finally do you have to use air conditioners or can you use a swamp cooler? Does the humidity of a swamp cooler cause problems in the lay-up process? Thank you again for all of your help!
  5. duluthboats
    Joined: Mar 2002
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    duluthboats Senior Dreamer

    I'm sure the air conditioning is for humidity control. A swamp cooler wouldn't do much to help that. I don't know about your conditions. Here in MN the humidity is almost always high. The composite shop at work is air conditioned to keep the humidity below 60%.
  6. Scott Dryden

    Scott Dryden Guest

    mechanical designer

    Dear Sir,

    I have designed all types of marine vessels mostly fiberglass.
    The temperature in Vancouver B.C. does reach 110 degrees,however in my experiance humidity / in some cases heat, can cause problems.
    Proper air flow will correct most any problem reguardless of 110 degrees.

    I would strongly discourage baking your frp mould parts.

    Especially for a frp hull.

    Sounds like these truck mfgs. are the Burger King ofthe fiberglass industry they certainly could save themselves alot of trouble if they used an infusion system on these molds........ and not sacrifice productivity........

    The company that I work for has just expanded their fiberglass layup
    and fairing building. A state of the art facility,it includes dust extraction and a few other toys.

    I'd be happy to send you some pictures. Need an e-mail

    contact me at

    Scott Dryden
    Westbay Sonship Yachts
  7. rxcomposite
    Joined: Jan 2005
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    rxcomposite Senior Member

    Post Curing


    There are two reasons why the laminate is heated after layup or after it is pulled out of the mold.

    1. To speed up the production process or more specifically, to reduce the turn around time of the mold. Room temperature cured resins takes about 24 hours to set properly and achieve an acceptable hardness. Heating the part after lay up while it is in the mold reduces the time the part stays on the mold so that the mold can be used for the second batch.
    2. Heating the part after it is pulled out of the mold improves its physical characteristic and ensures that the part will no longer warp even when exposed to high heat of the sun. It is a sort of insurance that the part will not deform.

    Air conditioning the room and not the mold itself is a process used to standardize production process. Fact is, even humidity is controlled. Resins are temperature sensisitive and you may find that you may have to add or subtract the MEKP depending on the temperature.

    Very dry atmosphere may cause static electricity and may ignite the volatiles emitted by the resin. Very humid room may cause the resin not to cure properly. Resins are hygroscopic and absorb moisture from the air. Too much moisture and the resin will not cure properly.

    I think what you have seen is a controlled enviroment composite room. I have worked in an aircraft factory and a boatbuilding yard and both plants have the same controlled enviroment.

  8. fiberglass_rest
    Joined: Feb 2005
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    Location: Gainesville,Mo

    fiberglass_rest Fiberglass Restoration

    Fiberglass~Gell Coats~Flakes~Resin do's and don'ts

    I was just looking thew reading,and well my husban can give you all the answers you'll ever neede-mail add,
  9. Ssor
    Joined: Jan 2005
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    Location: Bel Air, Md

    Ssor Senior Member

    We mustn't overlook the heat of the engine, these were truck hoods for very large diesel engine systems. I'm sure the resin systems were chosen for heat resistant characteristics.
    Last edited: Feb 19, 2005

  10. boat182
    Joined: Jun 2005
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    boat182 Junior Member

    I am closing down my boat company. Would you be interested in purchasing the company or assets? Contact me to discuss the details.

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