Process Temperature Monitoring For Investment Casting Shells

The Need for TempCHEKs

Ceramic materials undergo certain changes when heated in a kiln. These changes are essential for developing specific properties that make the use of a ceramic material desirable.

For investment casting shells, the shell is capable of withstanding the subsequent stresses applied when coming in contact with molten metal during a pour. For developing the most robust shell, controlling the heating cycle is a critical variable in the development of shell strength and resistance to cracking or fracturing.

TempCHEK can measure energy input into to the firing process, which is commonly referred to as heat work (the combined effect of time and temperature). If the element of time is ignored in temperature measurement, an essential part of the energy equation is left out.

TempCHEK is a highly sensitive shrinkage device, made of ceramic materials similar to the ceramic material being fired and hence it reacts to heatwork in the same manner.

The TempCHEK has been developed by Orton so it can be used to measure the heatwork within the kiln by precise measurement of its shrinkage. This shrinkage measurement can be a representation of the success or failure to reach a desired fired property.

One main benefit of TempCHEK is that in spite of electronics and technology being quite advanced, we do not know whether the last calibration was done accurately or whether the system is presently accurate. One may not know the condition of the kiln between calibrations and whether a calibration is in order.

However with a TempChek, these do not change over time and are not subject to drift. One can rely on them to report the amount of heat work performed on a load independent of electronic data. They can also be placed directly where the cores are fired, not in a stationary position within the kiln wall or roof.

Applications

Verification of Uniformity and Consistency of Heatwork Delivery within Ware

An essential part of a comprehensive quality assurance system is to verify the firing of the product. The regular use of TempChek can provide key process feedback, essential to the system control for verifying the consistent and uniform delivery of thermal energy required to mature a product.

TempCHEKs offer verification of heatwork delivery without disrupting the firing process. Using TempCHEKs on a routine basis and recording the results using Orton’s proprietary TempCHEK-Trakker software offers an easy-to-use record of kiln performance with minimum operator time commitment.

The process is simple and very user friendly. The process is as follows:

  • Determine where to place the TempCHEKs
  • Develop a numbering scheme to identify each location
  • Using a ceramic marking pencil, mark each TempCHEK and place it within the designated location
  • Once the load with the TempCHEKs exits the kiln retrieve the TempCHEKs
  • Using the Orton Desktop Gauge, measure each TempChek and send the measurement to your computer hosting the TempCHEK-Trakker software (cable or wireless).
  • Make sure the TempCHEK-Trakker software is utilizing the calibration data for the batch of TempCHEKs you are reading; the batch number of the TempCHEK is etched into the surface of each TempCHEK so there is certainty of using the correct batch calibration data.

The TempCHEK-Trakker software will create a table of data and a graphical display of the data as shown in Figure 1. The addition of upper and lower control limits provide a “quick look” to determine if any location is outside the expected temperature range. S

ince the size of the TempCHEK correlates to the temperature it is also possible to compare size rather than convert to a temperature since the firing profile has a significant influence on the final size of the TempCHEK.

Figure 1. XYZ Shell Kiln 1

Figure 2. Orton TempCHEK with software

Synchronization of Thermal Processing Between Kilns

Even two identical kilns do not always operate in the same way, but it is desirable to get uniform product from all production kilns that are firing the same product.

Regardless of controller settings, there is no guarantee that the heatwork delivery will be equal between two kilns. By using TempCHEKs in each kiln and comparing results, one can see if and how much difference there is in the thermal energy being delivered to the product by each kiln.

Adjusting the firing profile of the errant kiln will synchronize the heatwork delivery and insure uniform thermal processing.

The same approach can be applied between a laboratory kiln and a production kiln. By adjusting the laboratory kiln profile to yield the same heatwork as the production kiln laboratory development work will be much more likely to repeat when scaling up to production.

About Orton Ceramic Foundation

The Standard Pyrometric Cone Company was established in 1896 by Dr. Edward Orton Jr., the first Chairman of the Ceramic Engineering Department at The Ohio State University. With creation of the Edward Orton Jr. Ceramic Foundation after his death in 1932, the primary focus became providing products to assist and enhance high temperature processing of ceramics and other materials.

Today Orton provides Pyrometric Devices, Thermoanalytical Instruments, and Material Testing to more than 70 countries worldwide.

This information has been sourced, reviewed and adapted from materials provided by Orton Ceramic Foundation.

For more information on this source, please visit Orton Ceramic Foundation.

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