Definition: Plant: meaning a facilities / operation where manufacturing is occurring. Cooling: 1) free of heat 2) capable of lowering temperature. Mold: 1) form used to shape molten or plastic materials usually a negative of finished design.
The molds function is to act as a form number one, but number two it is a heat exchanger. What is meant by this is that we place hot molten plastic into a mold and then transfer the heat out of the plastic thus allowing it to become solid, stiff, into a shape, etc... The rate of cooling is critical to the finished part, and is based on: thickness of plastic material, distance water lines are from surface of cavity, materials used for mold construction, fluid flow, and temperature of fluid.
The water or cooling fluid that has been plumbed to the machine and its manifold and or a thermulator or chiller now has to supply the mold. As previously shown (part VI) most of these manifolds are of a parallel type meaning that flow is to a large reservoir and then to the individual lines. The question now is how is the mold designed for cooling? How many lines and fittings are there on the mold? Are all the diameters internally within the mold the same size? Are the cavities cooled in parallel or series? Are the hoses and fittings to be used equal in size, diameter and flowability of fluid?
Yes many questions and in many cases the processor finds more in's and out's on the mold than what is supplied by the manifolds, this than leads to a series being created by use of the hoses and loops.
The key or most important point is that the mold cooling rate applied to the plastic part need be uniform. This may in fact lead one to loop, (place into a series) a circuit or two on the mold. This may lead to use of a thermulator not to increase temperature but to increase pressure and flow to a line or circuit within the mold that is of series or of a smaller diameter within due to part/product design. This use allows for additional flow/pressure needed to cool that area, hopefully at the same rate other areas of the part are cooling.
Fittings;
These are what are used to screw into the mold and manifold which than allow for quick or hose connection between the two (Quick Disconnects). In some plants a self-closing fitting may be employed thus preventing fluid from leaking when taken off. Self-closing/sealing are a great thing to keep the area dry, but they are a pressure and flow reducer when in use, due to design and restrictions within.
As can be seen from the above a non-valve fitting (one that does not seal off) has less pressure drop as compared to valved. This does not mean one cannot use these, what it means is one must have the pressure and flow to compensate for the use of these types of fittings. It is also important to realize the use of 90 degree angle fittings, or 45 degree angel fittings all have loses which are not seen in a straight fitting. Again, if enough pressure and flow exist than there is not an issue, but if one were to run a minimum of flow and pressure than there definitely is an issue.
What length of hose is one using? If one were to use long and short segments of hose to plumb the mold from the manifold, than the length needs to be documented and tested. In some cases the length can have a detrimental effect on flow, this due to the pressure drop one sees based on diameter and length. Again one has to understand what one has to start with, and whether the system is capable or not.
Series flow is when water goes through a series of cooling paths. This is either cooling multiple cavities in a sequence or the possibility of looping lines on the mold to form a series path on the mold. Basically as the fluid flows it heats up thus the temperature at the start is not what it is at the end, or worst case is that the series degrades the flow due to extended length thus the GPM is not what is expected.
Parallel flow is similar to a manifold in that all flow is parallel to each other, supposedly all the same. One may by looping water lines in this example create a series flow within the mold. This is done unintentionally when the number of lines on a mold exceeds those present in a manifold which now allows the processor to choose which shall be looped and placed into a series, which may this time be different than next time if instructions, diagrams, or photos are not used for the set-up sheet.
SL Silvey
28092012.01
