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.
In part VII the mold was the described as the heat exchanger and it was discussed about fittings and whether or not there was serial flow or parallel flow within the system.
To continue with the flow channels within the mold and inserts placed into the mold to be cooled the size and placement is critical to cooling. The diameter of the cooling channels within the mold as with water lines and fittings must be sized correct.
While it is known that to calculate Reynolds numbers for turbulent flow is important, within the mold we can have areas which change flow rate and do not even realize it. These areas can be due to inserts where water is to flow around both sides of the inserts, bubblers, fountains, and other products and designs to provide cooling flow paths to the mold.
The simplest way to explain this is the area of the water line must be maintained and not allowed to change in area / volume. Thus for example if the water line is 10 mm in diameter that than means we have an area of 78.54 square mm. If the flow though this line is 5 liters per minute, than anytime we increase the area the flow shall decrease (in that space) and correspondingly anytime we decrease the flow channel the rate at that point shall increase. (Note we are disregarding pressure drops at this point, but they are critical too)
Thus if we have an insert placed in the tool which has a channel for cooling going around the base of the insert and the tool maker cuts it to be the same area as the water line, the flow is the same. But wait where is the exit, if the flow is in at one point and out at another and goes completely around and out close to the entrance we are good. But as are most of the cases we go into the channel and then split the flow so that it flows in 2 paths to go out opposite the entrance; than with channels cut identical to water line area we have decrease the flow around the insert. Thus with decrease flow we now may not have turbulent flow and the heat exchange rate shall decrease.
Using the example above for a 10mm line at 5 liters per minute flow, if we now flow around both sides of an insert by splitting the flow the flow on either side is now only 2.5 liters per minute due to two flows.
The above shows the flow of fluid into an insert in a mold. As is shown by the arrows the fluid now flows around both sides of the insert, thus the volume of this area must be ˝ that of the inlet and out let to maintain flow. If it is the same volume as the inlet than the flow rate is ˝ of what flows into the insert due to it being split in half per each side. If it is larger than flow it further decreases its flow in this area.
This same phenomenon occurs when using a bubbler and or baffle. The area of flow into the void is one area and that of flow out is different, usually greater thus the rate of flow is now lower and one goes from having a good cooling flow which equates to turbulent flow to now having a lower flow rate and having laminar flow.
The bubbler is the use of a small diameter pipe into a drilled hole which transmits fluid into the tip of the hole and then flows out down the sides of the hole, again area calculation is necessary. Sometimes with bubblers it is the tip of the hole that is important and not the whole of the insert, but in most cases it is the whole of the insert which needs to be cooled. Pressure drop with bubblers may be an issue to be aware of.
The baffle is another way to cool and these in the past have been and still are brass. The major issue has always been that the baffles bend or lean over thus decreasing the flow channel. Further fit has been an issue since if we do not seal than there is by-pass flow of fluid and cooling effect is limited. The use of plastic baffles with a sealing edge has been successful in many cases.
A link to see the effects as stated by a manufacture is as follows:
DME: https://na.dmecompany.com/Catalog/CatalogListing.aspxCatalogId=DSO&CatalogDetailId=203
Baffles come in both straight and spiral.
Bubblers come in various types and styles this one is a calculated one in that flow in and flow out are properly sized by design. Some may use just a tube in which cases, the hole diameter size to tube diameter must be calculated.
Understand that there are many issues in play here, such as pressure drops, types of plumbing within the mold and supply return lines which can also influence what goes on inside the mold. The processor must be aware of the tool design so as to plumb the tool correctly.
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16102012.01
