Definition: Plant: meaning a facilities / operation where manufacturing is occurring. Cooling: 1) free of heat 2) capable of lowering temperature. System: an assemblage or combination of things or parts forming a complex or unitary whole: a cooling system Piping: a hallow cylinder used for the conveyance of water, steam, gas etc.
In the previous section the fluid has been cooled and then piped to the area of the machine, and or other process equipment. This section covers the piping on the machine to the mold and or the extruder blow molder etc. that needs this fluid. This piping may also be to thermulator, or chillers located at the machine.
Plumbing on the machine may be set from the equipment manufacture and most may say this is adequate for the operation. One need to evaluate what is happening and where the fluid is being used. Sometimes the piping plumbing is left to the manufacturing plant which than adds the pipes, hoses and T's to accommodate all that is necessary.
As stated previously some machines of the hydraulic type require a good amount of water flow to cool the hydraulic fluid via the heat exchanger. This is usually from the tower, and the fluid is control by a solenoid valve which opens and closes to try and maintain a constant temperature to the hydraulic fluid. Thus on this circuit the water flow can fluctuate. This may in fact be the same circuit one is using for the mold and the throat of the machine. In that case the fluid rate to the other two points is now not constant; this may have an effect on the cooling of the mold. The throat on the machine is capable of handling this inconsistency. Remember that throat cooling is calculated at ˝ to 1 ton up to 3 inch diameter of screw, and hydraulics require 1/10 ton per 1 HP all at 3 gal per minute (10 degree F delta). Thus a 10 HP equipped machine would require a minimum of 6 gallon per minute flow. Thus if a 1 inch line were attached to the machine to feed all 3 components there is only 5 gpm left for the mold given schedule 80 pipe at 11 gpm maximum flow.
On some machines the manufacture has included a manifold located on the platens to supply fluid and fluid return to the cooling system of choice. What size piping has been used for this system? What is required by the mold?
An example of an issue was a large press of 1500ton which had a mold which used a flood type system for cooling of the tool. This means there was a large diameter connection for water to and from the mold and all individual circuits were than incorporated within the mold itself. On the B side of the tool the supply lines from the machine manufacture were ˝ the size of the line for the mold. Thus in this case it was not able to meet the flow required by the mold.
The long term fix was to increase the supply lines on the machine itself which than resulted in a faster cycle time due to being able to take heat away by more efficient cooling. (proper flow)
The machine manifold is a distribution point of fluid flow to the mold. These types of systems can be purchased with the machine or added later so as to supply a connection to flexible tubing or hoses which than attach to the mold fitting and circuits. In many cases it has been observed that the piping supplying the manifold is of a reduced size as compared to the fitting for this on the manifold. This can be seen by the use of reducer fittings in the manifold and or end of the pipe.
It should be noted that in many cases the flow of fluid is calculated for these manifolds based on area. Thus the area of the supply inlet equals the total area of the fitting connection on the manifold. If anything the supply side should be bigger than that of the fitting connectors so as to maintain a higher supply and pressure to the mold. In many designs one observes this as the number of outlets one may purchase can range from a few to many, meaning the fewer shall have higher flow rates while the many shall have minimum of design.
On the return side the manifolds are the same as supply, if for any reason a restriction of flow is necessary it is on this side that the restriction should be placed, decreasing any flow into the mold by limiting its output.
The two simple checks one can make at the manifolds to the mold is to check temperature of the manifold supply versus return; are they different and by how much and to check pressure of both to calculate that there is a Delta P (supply higher than return) thus showing that there is flow.
What has to be remembered is the water or our fluids choose the path of least resistance. If for example on the manifold different diameters of hoses are attached and different lengths are used (exaggerated) than flow through each circuit may be different. Further a manifold is creating a parallel flow system.
The design above is for a manifold (typically used in pairs one for supply and one for return). Though many designs and configuration most look at the area of supply / return and compare to area total of the ports. Another aspect is that this design is a parallel flow meaning that each port runs a separate circuit, thus when the main inlet is flowing at say 12 gallons per minute than each port may if balanced support 2 gallons per minute of flow. But if for example one of the ports has some restriction than the flow are reduced to that port and fluid flow increases through the other ports, now creating an imbalance in flow.
SL Silvey
11092012.01
