AMS 2750 Pyrometry, the most important furnace calibration document for the entire heat treatment community, especially those doing heat treatment for the aviation, space and defense industries, has been used since April 1980. It has undergone a total of 6 revisions over time. The last AMS 2750E we used was published in 2012. In this article, I will compare the old version "E" and the new version AMS 2750F.
Why is AMS 2750 so important?
We need calibration and therefore pyrometry to understand how long the raw material or part we are heat-treating remains at the required temperature in the furnace, whether that temperature is really the desired temperature (SAT), and whether the parts in each region of the heat-treatment furnace (TUS) are exposed to similar temperatures. . For this reason, it is mandatory for every heat processor to use this standard.
In a PRI training I attended, the instructor was also a NADCAP heat treating auditor who had conducted over 350 inspections, and he said that the standard that caused the most nonconformance in his inspections was AMS 2750. Understanding and applying this important standard is essential for sustainable heat treatment quality.
Now let's take a look at the changes brought by AMS 2750F.
Definitions
There is no major change in the definitions in general, the term sensor is now used more clearly instead of thermocouple. While some new definitions have been added, some have been removed. I have written them one by one below.
Newly added definitions
Adjustment, autoclave, batch furnace, bias or input shift, radiation survey sensor, refrigeration equipment, comparison SAT, alternate SAT, wireless transmitter, zener voltage reference
Extracted definitions
Dead band, elapsed usage time, failure of survey thermocouple, grounded junction, monitoring instrument, monitoring sensor, sheathed-thermocouple assembly
There is a change in the tables of AMS 2750!
What I like most is that the tables are no longer at the end of the standard, but right behind the page they are first referenced to.
Table 1: Sensors and their calibrations (Table 1 in AMS 2750E)
While AMS 2750E has different maximum permitted error for each SAT, TUS, control, recording and charge sensor (thermocouple) in different furnace classes (class 1&2 and class 3&6), AMS 2750F has the same calibration for all furnace classes. It demands sensitivity.
To give an example, in the old standard, a type S control, the recording sensor should have an accuracy of ±4°F or ±2.2°C or ±0.75% for class 3 to 6 ovens, whereas in the AMS 2750F these values are ±1 % for all classes. °F or ±0.6°C or ±0.1%
This means that the sensors will now work much sharper. Naturally, we will need to purchase more sensitive sensors and our costs will increase.Table 2: Sensor and extension cable/connector (Table 2 on AMS 2750E)
I can say that there is no practical change in this table. Connector colors suitable for the cable have been added.
Reduced reuse counts for some sensors in AMS 2750F.
Table 5: Sensor reuse and calibration (Figure 1 on AMS 2750E)
While AMS 2750E uses a U formula for sensor life, no relevant formulation is used in the new standard, but direct usage numbers are specified. Since I can't write them all here, I'll use an example,
An "expandable" N type TUS sensor will have a single use if used 10 times between 260-650°C or 3 months (whichever comes first) above 650°C . The upper temperature for single use used to be 980°C. This will result in fewer uses.
Table 7: Instrument and instrument calibration (Table 3 in AMS 2750E)
The only change that caught my eye in this table is that the measurement sensitivities (resolution) of the oven instruments in the AMS 2750F are not changed in fahrenheit, but are rearranged as celcius. 0.6°C was requested for Class 1&2 and 1.7°C was requested for Class 3-6.
Table 8: Recording instrument resolution requirement (Table 4 in AMS 2750E)
There is no change in this table.
Table 9: Recording instrument pressure range and recording speed requirement (AMS 2750E Table5)
While the maximum recording interval in the old standard was 15 minutes, AMS 2750F reduced this time to 10 minutes. I believe that these periods will not put a strain on the recording instruments of today's furnaces in our country, but old furnaces abroad will need to make some changes.
This title contains surprises!
Table 12: Instrumentation type requirements (AMS 2750E Figure 3)
This table introduces a new type of instrumentation. Its name is " D+ "
In addition to the usual D type, it is required that there be a recording sensor for each control zone, located at least 76mm away from the control sensor, and that this sensor be of a different type.
Tables 14 and 15, which determine furnace class, instrument type and system accuracy test (SAT) range for raw material and part heat treatments, have undergone a single numerical change.
The maximum allowable SAT difference upper limit for class 6 furnaces was previously 1.0%, but this value is no longer available (N/A). In other words, SATs will be harder for class 6 bakeries. In the past , an oven operating at 1000 °C could operate with a SAT error of ±10°C, but now this value can reach a maximum of ±5.6°C.
The maximum permitted adjusted offset in the relevant table of the old standard (Table 6) was also removed from this table in F and moved to the TUS tables (18 and 19) with the name change "maximum permitted offset".
AMS 2750F Tables 18 and 19 specify the requirements for Temperature Uniformity Investigation (TUS). There is no change in values compared to the old version. The newly defined D+ instrumentation has taken its place in the table. Another ease of application added to these tables is that the maximum permitted offset values are displayed in the same table.
AMS 2750 Figure 1 presents the numbers and locations of TUS sensors as a drawing. There was no such drawing sampling in the C and D versions I worked with before. I think it's pretty self-explanatory. CQI-9 was using such a drawing, and it is a good decision for AMS to switch to it.
Temperature uniformity probe (TUS) sensor error
This issue has frequently been a problem for AMS 2750 implementers, and TUS has to be restarted due to a sensor that stopped sending signals at an unexpected moment. AMS 2750F has not made any changes in this regard. He turned the numbers, which used to be in plain text, into two separate tables. (tables 23 and 24) This will provide us with ease of use.
I tried to explain AMS 2750F, the latest version of AMS 2750, one of the most important documents of the AMS series, which was increased from 43 pages to 54 pages, in terms of tables and changes. I hope it was useful for you. You can contact me for your questions and suggestions for changes on the subject.
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