Are you in the know when it comes to the recent revisions to AMS 2750 rev. E?
October 9, 2013
Did you know that AMS 2750 rev. E has new charting requirements that may prove challenging for older analog paper recorders?
Section 188.8.131.52.1 of AMS 2750E states that, “Temperature resolution requirements for chart recorders shall be in accordance with Table 4.” This mandates the maximum amount of chart paper divisions per inch. The older paper analog print recorders are not typically configured to meet these new requirements, but most newer digital recorders can meet them and provide more accurate results overall.
This change was specified in revision D, but in revision E a deadline has been identified. This means that all recording devices not meeting the proper chart divisions after the deadline passes may cause a violation, impeding certification. Some have argued that they can create a dual-scale charting system for printing out the analog results onto their older, existing chart paper. Unfortunately, this could severely complicate matters because an operator is required to sign off on the report once the cycle is complete. If after several months the operator who signed the chart is asked by a Nadcap auditor to explain how he validated the cycle in order to sign off on it, the dual-scaled chart may cause more complexity and challenge than desired.
Now you can run your TUS with a load or a survey fixture.
AMS 2750 rev. E, section 184.108.40.206 allows for either the use of a standard nine-point fixture method, which is acceptable for most customers, or – for those with complex geometry parts, special processes or unique load configurations – TUS can be done using a test load to truly emulate the production environment.
Heat sinks are now allowed as a viable option during TUS.
AMS 2750 rev. E, section 2.2.24 now states that heat sinks can be used during a TUS. Section 220.127.116.11 defines minimum and maximum parameters for acceptable heat-sink diameters.
Heat sinks allow for a far better emulation of the production environment because, similar to production parts, the heat sink will not reflect high and low PID (proportional integral derivative) fluctuations. When used properly, heat sinks merely serve as optical filters, averaging devices that accurately depict the production environment of the parts.
AMS 2750 rev. E requires that you keep all thermocouple correction factors (error deviations) on hand for data conversion.
Section 18.104.22.168.6 requires that you must be able to provide the correction factors for each calibration temperature. Ipsen’s control software has an intuitive screen where users can enter the correction factors for all of their work thermocouples and control thermocouples so that the printed and historical data being recorded is automatically corrected, enabling users to store and print real-time data.
Type-K thermocouples are no longer accepted as resident SAT thermocouples.
AMS 2750E, section 22.214.171.124.1.1 outlines that when an SAT is required in order to validate control thermocouples of type S or R, a resident thermocouple of type B or N is allowed. Type-K thermocouples are no longer accepted as resident SAT thermocouples if operating above 500°F. It is important to also consider the maximum operating temperature of the furnace, noting that any cleanup cycles that run above 2400°F will compromise a type-N thermocouple. Many customers utilize a type-B thermocouple as the resident SAT thermocouple, eliminating the need to verify temperature conditions as with the type N.
For non-resident thermocouples, type K is still acceptable for SAT use. Figure 1 of AMS 2750E clarifies SAT and TUS sensor timetables and notes a few changes from the previous revision (AMS 2750D). Additionally, Footnote 1 below Figure 1 makes mention of the insertion depths of type-K or type-E SAT thermocouples being equal to or greater than any previous use each time an SAT is run. Many continue to utilize type-K thermocouples as non-resident for SATs and then discard them after one use, which means that immersion depths do not need to be recorded/tracked. Others utilize a type-N expendable non-resident SAT thermocouple since there is no issue with recording the insertion depth. The length of use is solely based on times at temperatures as mandated within AMS 2750E.
Process items never before covered by AMS 2750 have been added to the new revision.
General new additions to the AMS 2750 specification now include oil quench, deep-freezing and salt-bath systems. If you are using these processes, be sure to check the new revision to be sure you are compliant.