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  1. #1
    Join Date
    Sep 2005
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    Texas
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    2,793

    FOAM insulation for injection molding

    I'm working on a commercial warehouse with a room built inside for injection molding machines where dew point in critical. My question is do any of you guys have experience with insulating a room with open or closed cell foam where humidity is crucial?

    Thanks in advance

  2. #2
    Join Date
    Jan 2001
    Location
    Nebraska
    Posts
    319
    Sorry I don’t have a direct answer to your question, but only some comments and questions based on some molding shop experience many years ago.

    The molding shops I have been around were too large for it to be practical to try to control the building environment to a tight humidity level. Desiccant dryers were used to control the humidity of the material in the hoppers.

    Even if you control the environment, how are you bringing your plastic in? Do you have space and time to acclimate the material? If you are pumping the plastic from railroad cars, my guess is that you will end up with desiccant dryers to control the materials moisture content rather than trying to maintain the environment above dew point.

  3. #3
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    Sep 2005
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    Texas
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    this is actually a room built on the inside of a warehouse thats 50w x 80L X
    20H, they want to foam the walls and ceiling. I know very little about injection molding but they said the mold drum that is cooled with chiller water will condensate, this condensation effects the mold somehow so humidity is aways a concern

  4. #4
    Join Date
    Jan 2001
    Location
    Nebraska
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    319
    Closed cell insulation is going to be denser and tougher and will be a better vapor barrier. The down side is of course it will be more expensive.

    The thickness or R factor will have to be determined by running heat loads for the room and its heat producing machinery and the temperature and humidity of the warehouse portion, and considering the year around outdoor conditions of your area..

    Large tonnage,high cycling speed Injection molding machines generally present large heat gains in the area they are operating in, and require exhaust venting of some pretty noxious fumes, which can create a big demand for makeup air.

    I don’t know what type of climate you live in, if you have both winter and summer conditions You are probably going to find that at times you could help heat the warehouse if there was no insulation. At other times (if the warehouse is air conditioned) the more insulation you have the better off you would be so the R factor will end up being a compromise.

    If you are chilling the mold it does not sound like you are injecting one of the common polymers, could this be Aluminum or something like that?
    Is the mold chilled or do they use a chilling plate?
    Is the hopper throat chilled?
    Is the Hydraulic heat exchanger chilled?
    Does the chiller use a remote tower?

    .

  5. #5
    Join Date
    Sep 2005
    Location
    Texas
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    you are raising the kind of questions that I'll have to get some answers for. It has a 25 ton chiller connected now that serves the feed throat (5tons) and the mold cooling (20tons). This is a plastic bottle process. The off gasing was also a concern I had. The data says this machine has an average power usage of 129kw but I'm not sure if the chiller is dealing with some of this load since it is a seperate part of the system.

  6. #6
    Join Date
    Aug 2000
    Location
    Sandusky Ohio
    Posts
    298
    Use a closed cell spay on FIRE RETARDENT two part foam..

    DO NOT USE OPEN cell such as icelene, open cell insulation such as that allows moisture and mold to grow, no matter what the contractor tells you, and besides, its not very ridgid.

    If you use a fire rated foam it usually does not have to have any further covering for fire.

    You will need to put an air conditioning/dehumidification system in this unit. Design it for maximum humidity removal; possibly using a variable drive system which can be adjusted for slower speeds across the coil. I recommend the A/C unit be placed inside the room, maybe include a heater in it if they use a liquid in tanks for their 'foam', it must be kept at about 80 F or the foam will orange peal during curing, which means the bubbles explode and the foam shrinks.. I mean REALLY shrinks!! Also, put the A.C blower system INSIDE the conditioned room along with all the ducts, this prevents air duct leakage and prevents outside humidity from entering the structure. If people are in this room all the time then you may need to look at bringing in outside air to meet OSHA/EPA and state codes and don't forget a fire damper/fan turn off system as well. This can be done with the same unit or a separate one, conditioning the air before entering the room.

    BTW, injection molding does use chilled water on the higher density 'foams'. Hard plastic "IS" foam, its just injected at a higher temp/pressure and doesn't have an expanding agent such as R134a, (which is being outlawed and replaced with another expander in the next few months.)

    MAKE certain your heat gain includes the machines/ lights and people gain, also the building and floor.

    The water lines from the chiller to the mold may still condense, it all depends what the velocity is of the water and if they have any significant temp difference across the mold, these lines should be insulated no matter what.

    Make certain you include in your quote a thermostat with humidity control on it if your using a variable system, the system then can slow down to control humidity. Also be certain that they tell you what they want for temperature, this is why I suggested to include a back up heater during closed times, if they want to keep the humidity down but the room temp at 80, the unit will be oversized and you'll have tons of problems later.

    Sorry for the length of this reply and the date, I just came across it googling some foam information for one of my own jobs.

    Rich

  7. #7
    Join Date
    Aug 2000
    Location
    Sandusky Ohio
    Posts
    298
    PS,

    The chiller only makes the plastic stay at a certain temp and it chills the mold to do several things.

    1. The plastic solidifies in the mold, thus speeding up production
    2. The chilled water controls the time, this is critical or every piece would cure at a different rate and temperature and this causes the plastic to shrink differently, I've seen some bottles be bigger than the caps and others smaller!! A consistant mold temp provides consistant shrinkage of the plastic. Also, if you didn't have the chilled water and your injecting hid density Poly Carb in that mold at 455 to 550 degrees, the mold would just keep getting hoter and hotter, and the plastic could adhere to the mold.
    3. the chilled water creates the surface 'shine' on the plastic.
    4. If they degrease the clamp time they usually have to lower the chiller temp, and vice versa. If they don't then the plastics shrinkage will change.
    5. The chilled mold allows workers to be able to handle the product when the clamp drops the bottle
    6. The plastic shrinks even after packaging, with containers this can be BAD to have the plastic too hot, they will continue to shrink while inside one another and you won't be able to get them apart!!

    You show a Dallas Star, make certain you compute grains of moisture in your area for the worse time of the year and be certain to get the right sized equipment. Your supplier should be able to help, but I would get more than one person working on this.

    OH, the chiller doesn't care about heat coming off the unit into the room, don't even think of it as an enviroment controled unit! It only cares about the throat and the mold. your lucky its in a room now, just close the place off if you can. Do a 15, 30, 45 and 1 hour reading of Delta T of the room AND AND HUMIDITY rise during FULL operation. Then compute the volume, temp rise and humidity and you should be able to determine the perfect size a/c unit needed to do the job. This is the easiest way to do this unless you want to spend days in math and phone calls.

    Rich

  8. #8
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    Sep 2005
    Location
    Texas
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    2,793
    Thanks for your imput. My understanding of their problem was that the molds condensate during summer time production and cause the plastics to stick and this causes the production problem

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