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limiting energy transfer between mold and environment
Definitions: mold. 1) A hallow form or matrix into which a plastic material is placed and which imparts to the material its final shape as a finished article. 2) To impart shape to a plastic mass by means of confining cavity or matrix. Insulation Plates: 1) A plate of material which impedes thermal conductance, 2) a material which insulates
In many ways since the mold is a heat exchanger it is not always only exchanging heat from the mold and plastics but also the mold and the machine. As stated previously the mold is an assembly of precision ground plates which when combined can produce a product. This tool/mold/mould is placed into a machine clamping system which must also be precision so that it opens and closes said tool correctly and is allowed to apply pressure uniformly to the mold.
The issue arises when a mold temperature is over/under room temperature and some might only say 150°F and above, but in truth one must know the machine, mold and time of operation. The issue is that as in electronics the contact area of the mold to the platen lets the platen act as a heat sink, heat source, thus robbing the tool of heat or cooling, and dependent on location of source of heat or cool from the platen may be adsorbed more in one direction than the other.
** The concept of the insulation plate is to insulate, both from heat transfer to a platen and platen heat to mold when running cooler. The benefits are in isolation of the mold so that it may be controlled more accurately and more economically, in that additional heat or cold is not called for when heating or cooling other components of the process such as the press platens, air and or other contact points to the mold.
When applying heat to a mold, what this means in a sense is that instead of heating the mold cavities one may be heating up the platens and then in order the tie bars and machine frame. If one cannot place ones' hand onto a platen while in operation and keeping it there for a period of time because it is too hot than insulation from the molds may be required. This is where insulation plates are used, thus a layer of material which impedes the flow of heat, and also where it is sometimes helpful to cool the top clamp plate.
Note* heating up of platens causes them to thermally expand, and in so doing creates an issues with tie bars parallelism, length and clamp tonnage (toggle press), and abnormal wear and tear on a press and possibly a mold. All one has to do is look at thermal expansion numbers for steel to understand the possibly variations that may occur.
An example of thermal expansion would be a platen which is bolted to a press frame and tie bars spacing is 24" by 24". When the A platen is heated from room temperature to say 180F, the spacing would than increase by 0.017" and would not be uniform as the platen is bolted to the frame and that area cannot expand as freely as the top of the platen. The expansion than creates a non-parallelism with tie bars as the 3rd platen is still at room temperature.
Below is a copy of data from a supplier of insulating materials.
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Maximum service temperature
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Thermal conductivity
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Coefficient of Thermal Conductivity Across thickness
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Coefficient of Thermal Conductivity across Surface
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425°F
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1.8 BTU-in/hr-ft²-°F
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7.02 x 10ˉˢ in/in/°F
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1.10 x 10ˉˢ in/in/F
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550°F
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1.9 BTU-in/hr-ft²-°F
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6.43 x 10ˉˢ in/in/°F
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1.24 x 10ˉˢ in/in/F
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The use of the insulator plates is to reduce the rate of thermal transfer from the mold, to the platen (both hot & cold). They do not totally prevent heat transfer but reduce the rate of transfer, and in short run jobs do an excellent job. In long run jobs they still work and everyone uses them. In long running production run there is still though at a slower rate the heating up or transfer of heat to platens which may need to be considered, for the wear and tear of a machine and or quality of the production.
Concerns;
The insulating materials have a maximum use temperature, and they need to be resistant to moisture and oil adsorption such as what is to be found in a molding plant. The calculation for performance can be reviewed in the sheet above under "Thermal conductivity" (transfer rate of heat energy through) is based on a 1" thick piece of insulation. When in fact most insulation is between 0.250" or 0.500" thickness the rate is going to be higher.
The compression properties of the insulating material are very critical in that when molding, high pressures are used to clamp the tool. Thus the material must be uniform and allow for these pressures and not break down.
Life span is also an issue in that it is based on temperature and hours at temperature and over time the materials used for these insulation plates can break down and performance decreases.
Damage is another issue that can affect the performance of these plates if allowed to be chipped and or embedded with contaminates due to storage and transport. To isolate damage and or prevent these plates can sometimes be sandwiched between the Top clamp support plate and the main A plate, thus protecting from damage and allowing if need be cooling lines into a Top clamp plate which than isolates the platens from long run heat if heating the mold.
In conclusion to insulations plates it if important to understand that they isolate the mold, and impede heat transfer so that the mold (our factory) may achieve it desired temperature more quickly and in the process save monies in the way of energy reduction to our mold. The side benefits are that it allows the process to be stable and machine wear and tear to be less.
SLSilvey
240312014.01
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