Rapid Temperature Cycling
Extend robot strokes to allow for the auto-packing of parts. Climate control so people won’t leave and the molds in the factory sweat all summer plus summer/winter process parameters stay the same. Tie water temp controllers into the press. I’d put chiller and tower to the injection molding machines for the best cooling choice for that resin/part. Stay with one brand of press and controller.
Rapid Temperature Cycling Injection Molding
Rapid Temperature Cycling, (also referred to as Rapid Heat Cycle Molding or Vario-thermal Molding) will enable you to heat the surface of the injection mold to 200C.
The technology uses Saturated Steam to heat the injection mold and Tower Water to cool the injection mold. At the end of the cooling cycle, Compressed Air is blown through the injection mold cooling channels to remove the water. Steam at up to 235C is then flowed through the cooling channels to heat the surface of the injection mold PRIOR to plastic injection, the steam is subsequently removed by Compressed Air followed by cooling water to remove the heat from the plastic.
Compression Molding Pros and Cons
1, Labor: A whole line would require only two people (the whole line is compounded by the compression molding machine, folding, slitting, and lining (EVA) machines).
2, Maintenance: The compression molding and other line machines have different. But in my opinion, easier maintenance. The mold centenarian is also easier due to you deal with every cavity separately, no frame, no plates.
3, Quality: The compression molding machines have a per-unit quality inspection online, discarding any off specs closure from the production line. That is not possible using the injection molding process. Also, the closures have minimum stress compared with injection molding.
4, Raw materials: The common resin is PP, it’s better to use a lower melt flow index but the range suitable for this process is wider than the required for injection molding.
5, Productivity: At the end of the line you will have a bigger and better production with compression molding compared, similar cavitation molds using injection molding. A usual rotary machine may have 64 cavities and its products may be as high as 60 MM caps/month.
6, Costs: Also at the end of the month your production costs will be lower using compression molding compared with Injection.
7, Market: Most Soft drinks producers and water bottlers around the world know and trust in compression molded closures.
Injection Molding and Temperature
Based on the grade you are using, check for the coefficient of linear thermal expansion (CLTE). It will depend on which stage your weld lines are formed. If you have a high molecular weight material and the weld area is during the initial stages of fill. The weld strength may be good in both climates. If your weld area is towards the end of fill, a grade higher elongation property might help. If you face the problem in an assembly, you have to check the CLTE of both the matching surfaces. Without having the complete details, it would be difficult to provide an appropriate solution.
The mold temperature and melt temperature may be the same irrespective of climate
When you are molding a part, the mold temperature and melt temperature may be the same irrespective of climate. So the environment at molding is uniform (assuming that the material is pre-dried if it has moisture). If moisture is present, the weld strength would be low and at the same time. You will notice surface defects. The molecular chain would break and the material strength would below. As good as low molecular weight material. The stresses developed due to climate change can cause problems.
Thus, you have to analyze the problem whether it is in an individual part or in an assembly. Ambient temperatures and R.H. WILL influence the precise conditions that the material experiences as it makes its way through the tool. I’m confident that if the tool was fitted with thermocouples just near to the mold surface near to the weld-line location, also with a melt temperature sensor (Kistler and others offer these, even combined with pressure transducer function: another useful parameter to monitor for this purpose). Also near the weld-lines, you would see differences, even with exactly the same barrel temperature and cooling medium settings.
For clarity, it’s arguably better to refer to ambient air conditions (temperature and R.H.).Than “climate change” as this latter may trigger very different thoughts amongst some readers! Good points about the location of the weld-line (early or late in the flow path). But as this is fixed and material is fixed, the variables under scrutiny here are surely related to the ambient environment only.