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SOLIDCast UNIT 44: Cooling Channels in Permanent Mold Casting

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When you have a model displayed in SOLIDCast and you select Model… Materials List, then select the Mold Materials tab, you are displaying the selection of materials can be used in a model other than the casting alloy. These are the Mold Materials. There are various types of Mold Materials which can be represented in a model. The type of material is indicated by the selection labeled Material Type on the screen, which has a small arrow next to it. If you click on this arrow, you will see a list of different material types which are available to use for materials in the mold. One of these is the Cooling Channel.

A Cooling Channel is typically used in a permanent mold die. This is a channel or area in the die where a fluid is passed, which is assumed to have a constant temperature, for the sake of cooling that area of the die. The Cooling Channel type of material allows this channel to be turned ON or OFF at various times during the process.

If you have a cooling channel in your die which is continually on (it is not turned off during the process), then instead of using the Cooling Channel type of material, you can use the Constant Temperature type of material. A Constant Temperature material is maintained at the given temperature throughout the entire simulation; it is never turned on or off.

If the cooling channel in your process cycles on and off during the process, then you should use the Cooling Channel material type. This type of mold material allows the cooling channel to be controlled in two ways:

1. The first method of turning the Cooling Channel on and off is through the use of a timer. In this case, the system allows you to specify a Start Time and a Stop Time, in minutes. These are measured from the start of each cycle, i.e., from the start of pouring. Before the Start Time, the cooling channel is not active, i.e., it is turned OFF. After the Start Time and before the Stop Time, the cooling channel is ON, and then after the Stop Time the cooling channel is OFF again. This is repeated for each cycle of a permanent mold simulation.

2. The second method of turning the Cooling Channel on and off is through the use of a thermocouple which is placed at a certain (x,y,z) location in the model. In this method, a High Limit (or a Low Limit) can be specified for operation of the channel. If a High Limit is specified, then the cooling channel starts out turned OFF, and the system monitors the temperature reading of a thermocouple at the given (x,y,z) location in the model. Once the thermocouple registers a temperature above a given Set Temperature, then the cooling channel is turned ON. If the thermocouple reading drops below the Set Temperature, then the cooling channel is turned OFF. This type of control acts continuously throughout the simulation. (Note: There is also a setting called Low Limit, which will turn the channel ON when temperature drops BELOW a given Set Point, and OFF when the temperature rises above the Set Point. The Low Limit control is typically used to control a heating element rather than a cooling channel).

As an example, suppose that you have a cooling channel in a die, such that water runs through the channel. You place a thermocouple at a specific position in the die such that its location is at X = 165 mm, Y = 0 mm and Z = 102 mm. If the temperature recorded by this thermocouple goes above 345 C, then you want the cooling channel to be turned ON. Once the temperature drops below 345 C, then the cooling channel should be turned OFF.

In order to simulate this condition, you must be able to specify the temperature of the water in the cooling channel, and also the heat transfer coefficient at the inside surface of the channel (the fluid HTC).

Some typical values for a water cooling channel might be:

Temperature: 60º C (140º F)
Heat Transfer Coefficient: 1532 W-m² /º K (270 BTU/Hr-Ft² – ºF)

Typical values for an air cooling channel might be:

Temperature: 32º C (90º F)
Heat Transfer Coefficient: 142 W-m² / º K (25 BTU/Hr-Ft² – ºF)

These values would be in effect ONLY while the cooling channel is turned ON. When the channel is turned OFF, it has little or no effect on the heat transfer in the die.

In order to create a material to use to simulate this cooling channel, you would select Model… Materials List and then enter the following data for the material at the bottom portion of the window:

Name: Cooling Channel 1
Type: Cooling Channel
Initial Temp: 38º C (See Note 1 below)
Thrm Cond: 17 W/M- ºK (See Note 1 below)
Spc Ht: 837 J/Kg-º K (See Note 1 below)
Dens: 6400 Kg/M³ (See Note 1 below)
Cooling Channel Type: High Limit
Temperature ON: 60º C
HT Coeff. when ON: 1532 W-m² /º K
Temperature Set Point: 345 ºC
X: 165 mm
Y: 0 mm
Z: 102 mm
(Note 1: Thermal Conductivity, Specific Heat, Density and Initial Temperature are properties which are NOT USED for cooling channel type of materials. Therefore, you can enter any data into these fields.)

Now, click on the button labeled “Add to List”. This action will create a cooling channel material in the “Materials in List” box on the screen, with the properties as specified. Please note that this only creates a material; in order to actually use a cooling channel in the model, it is necessary to actually create a shape in the model, and to designate its material type as being the cooling channel material type which is on the mold material list. There is no limit to the number of shapes which can be created using this material type. For example, if you have four channels in a mold and they all have the same properties (they are all controlled the same way, and have the same temperature and HTC when ON), then they can all be designated as this type of cooling channel material.

You can create up to 8 different types of cooling channel material in a single model. This means that you can vary the types of control, the temperature when ON and the HTC when ON up to eight different ways in a model. Typically, we would name these something like CC1, CC2, CC3, etc. As mentioned, there is no limit on the number of shapes that can be created in the model with each cooling channel material type.

Whenever there is one or more cooling channel material listed in the Mold Materials for a model that is designated either as a High Limit or a Low Limit type of control, and a simulation is run, a file is created which contains the time and temperature data for the readings from that thermocouple. This file is named tcdata.tmp, and can be found in the folder that contains the simulation result data. This is a text file that can be imported into programs such as Microsoft Excel for viewing or plotting.

One important note is that a time/temperature data file will be created in the simulation result file, even if there is no cooling channel shape in the model, as long as a cooling channel material (either High Limit or Low Limit type) is listed in the mold material list for a model. This allows the user to place from 1 to 8 thermocouples in a model, without requiring that any cooling channels actually exist in the model.

By default, a thermocouple time/temperature data file creates an entry for every time step in a simulation. If you have a large simulation with many cycles, this can create a very large file with many thousands of entries. There is a method by which the number of time/temperature entries can be reduced. It is possible to create a small text file called $tcinc.500 in the SOLIDCast installation folder (this folder is normally c:\Program Files\SOLIDCast). This $tcinc.500 file can be created with NotePad or any other Windows program that can create a text file. This file should contain a number. For example, suppose that the file $tcinc.500 exists and contains the number 10. This means that any time/temperature data will be written only every 10 time steps instead of every time step. By using this method, the amount of time/temperature data can be reduced by a factor of 10. If the file $tcinc.500 exists and contains the number 100, then data will be written to the tcdata.tmp file every 100 time steps. If $tcinc.500 does not exist, the system writes time/temperature data every time step.

For calculating the surface heat transfer coefficients inside cooling channels, we have the HTC Calculator utility. This program can calculate HTC’s for air and water cooling channels, given the flow rate and the channel diameter. The calculated value would then be used when creating a cooling channel type of material, under the “HT Coeff. when ON” entry.

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