Views:2 Author:Site Editor Publish Time: 2018-05-26 Origin:Site
Troubleshooting Mold Temperature Control
Mold-temperature control is just one of many process elements that can affect the quality of an injection molded part. Even within that relatively narrow slice of molding technology, the number of different variables is almost innumerable. We will limit scope of this article, therefore, to some of the basic causes of three different classes of quality problems: problems that appear during start-up, problems that appear suddenly, and problems that develop over time.
We will assume that we are dealing only with cold-sprue molds, as hot-runner systems only add more variables to an already complex subject. We will also assume that the injection molding machine is correctly set up, that cooling times and overall cycle times are reasonable, and that the resin is properly heated prior to injection. In other words, we will assume that any quality problems observed are related to mold temperature.
In a perfect world, anyone running a particular mold would know what the mold designer set as the ideal temperature and flow rate for the cooling water. In reality, operators and setup personnel don’t always know these settings and/or something changes so that it is necessary to re-establish them by trial and error.
Quality problems related to heat transfer in the mold tend to arise from improper polymer flow in the tool due to over-cooling or under-cooling. The latter condition would apply when parts are not completely solidified and therefore stick in the mold or deform after being ejected from the mold. Over-cooling may be suspected when some or all of the mold cavities do not fill properly. Surface detail may not be perfectly replicated or, worse, parts may be incomplete (short shots). Shrinkage or warpage could result from over- or under-cooling or could be due to uneven cooling.