Hot Dip Molding
Dip Molding or dip coating of plastisols consists of forming a plastisol part on a male mold. If the dip process is used to mold a part for another substrate, the part is stripped from the mold, as in the case of post caps or slide on grips. This process is used in a variety of products such tool handles, hooks, park and recreational furniture and hog flooring. In dip coating, the formed plastisol part is left on the substrate. Hot dip coating, are available in a variety of finishes, including glossy, textured, and foam.
This process is used for tool handles, wire racks, and miscellaneous parts. Used when coating metal parts or making parts (caps) to be put on to other substrates that cant withstand the heat. Hot dips are available in a variety of finishes, including glossy, textured, and foam.
1. Parts need to be clean and free of grease, dirt, or any other contaminate.
3. Preheat metal items in an oven between 350° to 500°F.
4. When the metal mold is hot or up to temperature, immerse the part into the plastisol.
5. Allow the part to stay immersed in the plastisol 15-45 seconds depending on thickness desired. Thickness is controlled by the preheat temperature, the immersion time, and the viscosity of the plastisol. After about 45 seconds the part no longer has the heat capacity left to continue gaining thickness on the part.
6. Withdraw the part at a rate of 1 inch per every 1 to 10 seconds. Make the withdrawal smooth or parts will have a wavy surface.
7. Allow part to drip. For no drip parts see NO DRIP HOT DIP.
8. Suspend in an oven set between 365° and 450° F for 5 to 10 minutes to cure. Plastisol is completely cured when it reaches a temperature about 360°F. Other processing times and temperatures may be needed if special properties such as texture or foaming applies.
9. Parts can be air or water cooled. If the parts are foam they must be air cooled so the cells don't collapse.
Dripping can be avoided by inverting the article when the dripping is complete before the part goes into the oven. Another method that is used is touching the drip with a small piece of paper or cardboard to remove the drip.
1. Plastisol Burning, Discoloring, or Sagging Cure temperature and /or time too long. If burned on outside and not cured inside, preheat temperature is too low. Adjust cure cycle to prevent burn, sagging, or discoloration.
2. Voids on the surface Air entrapment in the plastisol during processing. Try dipping at different angles, or take part out of plastisol at a slower rate to avoid air entrapment. If this doesn't work let plastisol sit overnight before continuing, or deaerate it.
3. Voids at surface going all the way to the metal Dipping process too fast, or dipping at the wrong angle.
4. Uneven surface or globs on finished product Gel particles in dip tank, can be recirculated to break up particles during dipping process.