TUS in praxis
As I wrote in the last blog, periodically doing SAT and TUS is a obligation. But it costs money, and a lot of it, so we have to answer a few questions. Do we want to do it ourselves or with external suppliers?
The problem with an external solution is the price, the time mismatch between our needs and the supplier’s time, and in the case of Nadcap, the supplier’s qualifications. In aerospace manufacturing, everything is controlled and supervised by everyone. Thus, in order for someone to be able to perform activities according to AMS 2750G, he must be trained, and the trainer must be authorized. But there is a solution via PRI, e.g. here:
https://p-r-i.org/news/approved-training-provider-for-pyrometry/
If the acquisition value of the data logger is CZK 1 million and we depreciate it over 5 years, we have an annual cost of CZK 200,000, even if the device will lie in a closet. However, external TUS will cost us approx. 50 thousand CZK per furnace, and with a frequency of 1x a year we must have at least 4 furnaces that we will validate according to CQI-9, or one furnace under Nadcap with the obligation of TUS 1x every 3 months so that we are on the same amount.
It is also possible not to do it, but there are fields where our inaction will lead to collapse. Not so long ago, I visited a company working for aircraft production, with the obligation to meet deadlines according to AMS 2750G. The technician who took care of these measurements and who was qualified for it had left, they had a lot of furnaces in the hall without which production would have stopped, and since some measurement operations require a weekly interval, the company was close to collapse. How to get out of it?
All that remains is for us to carry out these measurements ourselves. If we don’t have the appropriate 1 million for a datalogger, we can just buy at least a 9-channel digital recorder, e.g. Eurothem 6000 series, and start. But it only works sometimes
https://thermalprocessing.com/increased-productivity-combining-cc-fixturing-and-lpc/
https://www.kaybrazing.com/brazing-articles/1000974-temperature-uniformity-survey-tus-fixturing.html
If we have a two or more-chamber oven, we have a problem. The measuring fixture with the thermocouples outside the furnace cannot be moved. In the case of Ipsen TQF7 furnaces, this was solved by inserting the measuring fixture with sufficiently long thermocouples, up to 3 m long, into the heating chamber through the loading door, which was then carefully closed so as not to damage the thermocouples and the measurement was carried out. It works as a workaround, but it’s terrible to work with.
A better solution is a Phoenix data logger with or without a Bluetooth signal. It does not need any wires outside the furnace and is sent to the furnace in the usual way, on the base grid as a standard charge. It either stores the data in its memory or sends it online via the Bluetooth interface. We mustn’t just forget that it can’t be immersed in an oil quenching bath when pulling out the furnace, or we have to get a version that can survive immersion in oil
Such a device with a Bluetooth signal can even be used as part of furnace temperature control during annealing or tempering processes, when it can theoretically replace the Tc thermocouple and function within a conditional delay as a signal to start the countdown.
This data logger is also an ideal device for measuring TUS in ECM Flex furnaces. The fuxture with the measuring box goes into the vacuum tunnel and gradually transports the measuring system to the individual chambers that we need to measure.
Of course, a data logger is not the only thing we need to have to make the system work. We must also have a data logger linked to higher standards, a thermocouple control system, qualified personnel, complete documentability and traceability, etc. But if we devote time and money to all of this, we are sure that our furnaces will do what is expected of them.
But there are also other, almost ingenious solutions. One of them is owned by TAV Vacuum Furnaces. When I first saw it, I was really excited. Simple and intelligent. You press a button and everything is done automatically. If you need several hours of preparation for a normal TUS, then everything can be done here in just minutes, without having to install or connect anything.
If you are interested in more, please contact me personally. I will be happy to connect you with experts from TAV Vacuum Furnaces and we will offer you a solution. It should be noted, however, that they can only be purchased with a new furnace, for already installed devices, reconstruction is not possible, or at least very difficult.
Jiří Stanislav
June 11, 2023
