Furnace Calibration(Temperature Uniformity Survey)

Contents

• AMS 2750 E Standard

• Temperature Uniformity Survey

• Need of TUS

• Furnace Class and their uniformity

• Sensor requirement

• Methodology

• TUS applications

• SAT(System Accuracy Test)

• Calibration Report

The AMS 2750 E (Aerospace Material Specifications) is a standard for the processing of materials in aviation and aerospace industry which has been increasingly applied in the automotive industry as well. The standard describes in detail the requirements for thermal processing systems:

Temperature uniformity in the useful space• Instrumentation (specification of the measurement and control instruments)• Inspection cycles of temperature sensors including documentation of the inspection

cycles• Inspections of system precision

Adherence to the standard's rules is necessary to ensure that the required quality standard of the components to be manufactured can be reproduced in serial production. For this reason, extensive and repeated inspections as well instrument testing, including the relevant documentation, are required.

AMS 2750E Standard

The standard defines the way heat treatment must be performed and more precisely:

The use of furnaces, sensors and other instruments:• Different furnace classes• Different types of authorized sensors• Different levels of instrumentation (number of sensors)• Different types of calibration instruments

The test and control means:Two regular and frequent obligatory tests:TUS - Temperature Uniformity SurveySAT - System Accuracy TestThe frequency of SAT and TUS is defined according to the furnace class and the level of instrumentation

Temperature Uniformity Survey

TUS: Temperature Uniformity SurveyObjective:Determine the work zone of a furnace

Method:• Measure the furnace temperature variation with

individually monitored thermocouples inside the furnace before and after temperature stabilization.

• Compare the result with the authorized deviation from set-point.

• Apply the test standards set in AMS 2750 for calibration frequency and accuracy.

= Acquisition of temperature from differentsensors over a certain period of time

Need of TUS

• The purpose of the uniformity survey is to determine the range of

temperatures present at different locations in the furnace under

normal operating conditions standards.

• It will cater the needs for uniform heating inside the furnace to

match the product quality as well as process parameters.

Furnace Class & their Uniformity

Furnace Class

TemperatureUniformity (°C)

TemperatureUniformity (°F)

1 ±3 ±5

2 ±6 ±103 ±8 ±154 ±10 ±205 ±14 ±256 ±24 ±50

Sensor required in differentsize of furnaces

Work Space Volume Less

than

3 Ft3

(0.085m3)

225 Ft3

(6.4m3)300 Ft3

(8.6m3)400 Ft3

(11m3)600 Ft3

(17m3)800 Ft3

(23m3)1000 Ft3

(28m3)2000 Ft3

(57m3)3000 Ft3

(85m3)4000 Ft3

(113m3)

No. of Sensorsclass 1 & 2 5 9 14 16 19 21 23 30 35 40

No. of Sensorsclass 3 to 6 5 9 12 13 14 15 16 20 23 25

1. Arrangement of the sensors• The flexible thermocouples are placed at the corner of the working space of the

furnace plus one standard thermocouple to determine the reference temperature in the geometric center.

• At least three temperature set point should be selected generally at 5% , 50%, and 95% of temperature operation.

2. Preliminary test and conditionsEnsure that both the controller and recorder instrumentation are functioning correctly and are they calibrated.• Oven should be kept as it is for 1 hour.• Leakage should be checked from different points of furnace.

Methodology

Temperature Uniformity reflects the quality of oven design regarding isolation, location of the heaters and air circulation patterns. Temperature uniformity can be evaluated by surveying the temperature within the oven in steps of rising temperature.Following parameters to be determined from the data obtained by temperature uniformity survey:Temperature Gradient: difference between the highest and lowest average temperature value of the temperature sensors in oven, after stability.

Temperature fluctuation: measure of the variation of temperature on location inside of the oven chamber in a period time after achieving stability.

Temperature Drift: the difference between the highest and the lowest oven temperature recorded during a long period of time (48 hour or more) of continuous operation without alteration to the thermostat setting shall not exceed 1°C at 100°C setting point.

Reproducibility of Oven temperature: the initial oven temperature shall be regained to within 1°C after the oven has been switched off, and again switched on after 6 hours for 2 hours, without any alteration to the thermostat setting.

Temperature Uniformity

For Furnaces volumes greater than 4000 ft.³ (113 m³) use the appropriate class formula to calculate number of sensors:

• Classes 1 & 2 :

•

• Classes 3 to 6 :

• Vacuum Furnace

• Continuous Belt Furnace

• Forging Furnace

• Batch Furnace

• Rotary Furnace

We Can Perform a TUS on

• System Accuracy Test, commonly referred to as an SAT, is another critically important and often required test.

• System Accuracy Tests are performed to determine the error within the temperature control system (temperature control device/lead wire/thermocouple).

• Regardless of the application, knowing the error that exists in your temperature control system allows for more consistent control of quality.

Objective:• Control and certification of the accuracy of data acquisition and control of the

system over time.Method:• Comparison in situ of data recorded with data read on the calibration

instrument in order to define temperature gradients and check if they are acceptable.= Localized test of accuracy

System Accuracy Test (SAT)

Calibration Report

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