Hello everybody. For this entry, I would like to share this contribution prepared by Jason Dervish. If you have interesting information related to heat treatment, do not hesitate to contact me (firstname.lastname@example.org) We will be happy to review and publish every value added article with the TTM community.
Minimising downtime and reducing costs with a Hot Box TUS
A temperature uniformity survey (TUS) is a test during which a calibrated field test instrument such as a data logger and calibrated thermocouples are used to measure temperature variation in furnaces prior to and after temperature stabilisation. Today industries such as aerospace and automotive manufacturers require all furnaces in which parts are heat treated and subsequently incorporated into the final product to be surveyed according to a strict specification. Suppliers to the aerospace industry comply to the AMS2750E specification and in the automotive industry suppliers comply to CQI-9. Surveys are generally carried out at set time periods or after any major repair work or maintenance has been carried out on the furnace.
Thermocouples fixed to a survey frame measure the extremities of the working volume of the furnace. Often the furnace needs to be cooled and de-gassed so the survey frame and probes can be installed. The thermocouples are then connected to a data logger which is traditionally located externally to the furnace. The probes or “trailing” thermocouples are generally long and exit through the furnace door. Following the set-up, the furnace is then heated to the surveying temperatures.
This method of surveying furnaces presents some challenges:
- For continuous furnaces, the use of cumbersome “trailing” thermocouples could be an issue if the furnace has atmosphere locks as the locks could damage the probes
- Furnace downtime is required to survey the furnace
- Several hours could be necessary for the technician to prepare the TUS report
It is now possible to perform a TUS in a more efficient manner. This involves an in-process “hot box” temperature surveying system which can be loaded into the furnace with the survey frame. The system includes:
- A data logger to collect the survey temperature data
- A thermal barrier or “hot box” to protect the logger from the ambient heat inside the furnace
- Software to analyse the collected data and prepare the survey report
- Radio frequency (RF) telemetry to transmit the date in real time directly from inside the furnace during the survey.
The set-up of the system is straight-forward: thermocouples are fixed to the survey frame and the data logger is reset using dedicated software before being placed in the protective thermal barrier. The complete “hot box” system is then positioned in a survey basket or frame and is charged as a normal load, without the need to cool or de-gas the furnace. This method eliminates cumbersome “trailing” thermocouples. Optional wireless telemetry allows real-time data collection enabling the operator to monitor the survey and view any potential temperature overshoots as they occur.
Surveying continuous furnaces using a “Hot Box” system has the potential to realize substantial savings. Precious furnace time can be allocated mainly to the heat treating of parts and technicians’ time can be freed up for other activities. Overall, a “Hot Box” system minimizes downtime and reduces costs.