Tooling is normally fabricated with different methodology which are hot-runner type and standard normal type and that is according to the tooling DFM,also based on the tooling analysis versus cosmetic requirement。With utilizing hot-runner is able to get better feeding resin (plastic) & better resin melting in the mold-set.
To a standard mold-set (without hot-runner),that is to purge the barrel of the press and to keep the barrel of the machine full of the resin/color (2ndresin color) we want to purge 1st resin when adding the ultra purge, so that barrel will be able cleaned up entirely for next resin shot with no problem。
To a mold-set with hot-runner,the way to clean up barrel is same by using purging the barrel of press (or ultra press)。However,the 1st resin is still over there in the hot-runner and the 1st resin is not able entirely going out of hot-runner when using purge way,especially 1st resin residue on the undercut area of the hot-runner even using multiple times of purge,so that cosmetic issue will be occasionally happened on the 2nd resin of (new) product that is caused by the 1st resin residue。So, the solution in the industrial for using multiple colors of resin in a hot-runner mold-set is to keep using the mold-set,but needing extra set of hot-runner for the new color of resin。