making roof molds

[rbrown7713]

Here are some pictures of how I made these roof molds.  I don't have complete procedures on the Superliner roof mold, but the Amfleet roof mold is the same procedure.  One thing to consider is whether to use  urethane rubber or silicon.  Here are the pluses and minuses.  With urethane I used a silicone spray for mold release and It is hard to remove the silicone spray off of your part for painting, that is a minus.  You may use an oil base release, and is more easily removed for painting. Urethane is cheaper.  If you use silicone, you will pay more, but produces a better mold.   If you are pouring a urethane plastic part with a urethane rubber, than it is suggested that you use a silicone based release, hence the problem of removing the release from your part for painting, very difficult.  In the first picture the pattern is laid on the bottom of the mold enclosure and has to be sealed because the void under the roof can allow the mold material to leak into the void and ruin the mold.  You have to glue the roof to the mold enclosure and then run a silicone seal around the mold to prevent any seepage, or the professional method is to fill the entire void with clay and that is the secure method to prevent any mold material getting into the void.  The first part of the mold is only poured half way up the walls of the enclosure to allow room for the second part of the mold.  When the first half of the mold is cured, it is removed from the enclosure, cleaned up, turned over, and at this time respray the mold and part with release.  Reinstall the part, and then it is time to make the second part of the mold.  I used dowelling across the top mold, I think 5/16", so that when pouring the part, the top mold does not sag, it stays where it should be.  These dowels are CAed to the sides of the enclosure and when top is cured they come off of the sides when the mold is removed.  You then remove the pattern and you are ready to make a part.  The part is poured with the molds in the enclosure to keep them straight.  On one end of the enclosure, the end is cut down to the top of the bottom mold to allow excess plastic to run out.  Pouring of plastic.  You pour your plastic more starting at the left, and then insert the top mold, rolling it along to the right, squeezing the plastic toward the right and running out of the mold.   I pour my parts on granite, not worrying about the run off of plastic, because on granite, the plastic just pops off when cured.  Follow the directions for mixing the rubber and plastic.  You will note dowels in the bottom of the enclosure, and they, when poured, will serve as alignment tools to keep the two parts of the mold straight.  After the fist part of the mold is poured, these will be popped off of the bottom of the enclosure to allow for a flat surface when turning over the mold. That is about it and whatever I left out, you can ask me and I will answer.   Remember, these pictures are of making the mold and when getting ready to make the part, at the right end, the wall is cut down to the top of the bottom part of the mold to allow excess plastic to run out like last picture. Bob.