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Molding a Part with Rotational Molding |
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The actual molding of a part using rotational molding is complex to set up but then straightforward once the rotation, cook time and cooling cycle are established. Think of it as making a new recipe. |
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- First you need to figure out how much plastic to use. This is done by calculating the exterior surface of the part and the desired wall thickness. If you also know the density of the plastic you are going to use, you can calculate how many pounds of resin you need in the mold. This is known as the "Shot Weight".
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- Next you need to figure the rotation ratio for the mold. The machine arm is usually designated as the major axis and the plate is usually the minor axis. A ratio of 4:1 is considered the best ratio for a globe and is a good starting point. The actual speed is largely the result of your resin selection.
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- The next item up is the oven temperature. This will be specified by the type of resin you are using.
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- Once you have the shot weight, rotation ratio and oven temperature, you can complete the cooking cycle by deciding how long to cook the part. There are process tools like Rotologs that can assist in determining the length of cook time that is required.
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- When the part is cooked and ready to take out of the oven , it is a molten gel covering the inside of the mold. A cooling cycle will allow the part to cool and shrink inside the mold.
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