Furnace Temperature Calibration in Joliet

What Is Furnace Temperature Calibration

Furnace temperature calibration is the process of verifying and documenting the temperature accuracy, uniformity, and control system performance of industrial furnaces used in heat treating, aerospace processing, and metallurgical operations. Calibration is performed on vacuum furnaces, atmosphere furnaces, continuous furnaces, and specialty heat treating furnaces to ensure that actual temperatures within the qualified work zone match setpoint temperatures within specified tolerances. Furnaces typically operate at significantly higher temperatures than ovens — ranging up to 2400°F (1315°C) and beyond — requiring specialized instrumentation, noble metal thermocouples, and procedures adapted for extreme thermal environments.

Unlike industrial ovens, furnaces are distinguished by their use of controlled atmospheres — including endothermic, exothermic, nitrogen, hydrogen, and vacuum environments — and their primary role in aerospace and metallurgical applications where material properties are directly dependent on precise temperature control. Furnace calibration encompasses both Temperature Uniformity Surveys (TUS) and System Accuracy Tests (SAT), with additional requirements for atmosphere monitoring verification, vacuum integrity testing, and the use of radiation pyrometers in applications where contact thermocouples cannot be permanently installed.

Types of furnaces subject to calibration include vacuum furnaces (oil quench and gas quench), atmosphere furnaces (endothermic, exothermic, and nitrogen), continuous furnaces (mesh belt, pusher, and roller hearth), salt bath furnaces, and fluidized bed furnaces. Calibration is performed on-site at the facility where the furnace is installed and operated, using NIST-traceable reference standards and instrumentation appropriate for the furnace type and operating temperature range.

The Furnace Calibration Process

Step 1: Pre-Survey Assessment

Prior to performing any temperature measurements, a complete assessment of the furnace is conducted. The furnace's physical condition, heating elements, insulation, and structural integrity are inspected. The atmosphere system — including gas delivery, flow controls, and safety interlocks — is reviewed for proper operation. Control instrumentation, including controllers, recorders, and over-temperature safety devices, is identified and its calibration status is verified. For vacuum furnaces, a vacuum integrity check is performed to confirm that the vessel achieves and maintains the required vacuum level and that the leak rate is within specification. The qualified work zone dimensions are confirmed, and the number and placement of survey thermocouples are determined based on furnace volume and the requirements of the applicable specification.

Step 2: System Accuracy Test (SAT)

A System Accuracy Test is performed to verify the accuracy of the furnace's temperature sensing, control, and recording instruments. An SAT compares the readings of the furnace's installed sensors against NIST-traceable reference thermocouples placed at the same location within the furnace. For vacuum furnaces where thermocouples cannot be permanently installed through the vessel wall, radiation pyrometers or thermocouple feedthroughs are used to obtain reference measurements. The difference between the furnace's displayed temperature and the reference reading is recorded and evaluated against the allowable tolerances specified in AMS 2750H. SATs are required to be performed at regular intervals — typically monthly or quarterly — depending on the furnace classification and the applicable pyrometry specification.

Step 3: Temperature Uniformity Survey (TUS)

A Temperature Uniformity Survey measures the temperature distribution throughout the furnace's qualified work zone. NIST-traceable survey thermocouples are placed at specified locations within the work zone — typically at the corners and center of the usable volume. For vacuum furnaces, thermocouple feedthroughs or load thermocouples are used to introduce survey sensors into the sealed chamber. In atmosphere furnaces, the effects of atmosphere composition on thermocouple accuracy are considered, and appropriate thermocouple sheathing is selected to prevent degradation. At elevated temperature ranges, noble metal thermocouples (Type R, S, or B) are required to maintain measurement accuracy and thermocouple longevity.

The furnace is brought to each qualified operating temperature, and thermocouple readings are recorded at defined intervals once the furnace has stabilized. The range of temperature readings across all survey thermocouples at each setpoint is compared against the uniformity tolerance specified for the furnace's classification under AMS 2750H. The number of survey thermocouples required depends on the volume of the qualified work zone, with AMS 2750H specifying minimum counts based on work zone dimensions.

Step 4: Atmosphere Monitoring Verification

Atmosphere monitoring verification is a critical component of furnace calibration that addresses the controlled atmosphere systems unique to industrial furnaces. For endothermic atmosphere furnaces, carbon potential monitoring systems are verified against reference standards to ensure accurate control of carburizing and carbon restoration processes. Oxygen probe calibration is performed to confirm that in-situ oxygen sensors are providing accurate readings for atmosphere control. Dew point analyzers used to monitor atmosphere moisture content are verified against known reference points. For vacuum furnaces, leak rate testing is performed to document that the vessel maintains vacuum integrity within the limits specified by AMS 2750H and applicable customer requirements. All atmosphere monitoring verification results are documented and included in the calibration record.

Step 5: Documentation and Certification

Upon completion of all calibration measurements, a comprehensive calibration report and certificate are issued. The report includes all thermocouple placement locations, as-found and as-left temperature readings at each survey point, calculated temperature uniformity at each setpoint, SAT results with deviations from reference standards, atmosphere monitoring verification results, vacuum leak rate test results (where applicable), identification of all NIST-traceable reference equipment used, and a statement of measurement uncertainty. All certificates are issued under the scope of an ISO/IEC 17025 accredited laboratory.

Compliance & Standards

AMS 2750H — Pyrometry

AMS 2750H is the primary pyrometry specification governing the calibration, testing, and documentation requirements for thermal processing equipment used in aerospace and other regulated industries. For furnaces, AMS 2750H defines specific requirements based on furnace type and operating temperature range, including higher instrumentation accuracy classes for vacuum furnaces, mandatory use of Type R, S, or B noble metal thermocouples for high-temperature applications exceeding the range of base metal thermocouples, and dedicated survey procedures for vacuum furnace environments where thermocouple installation and routing present unique challenges. Compliance with AMS 2750H is mandatory for heat treating furnaces serving the aerospace industry and is required by most Nadcap-accredited operations.

Nadcap — Heat Treating Accreditation

The National Aerospace and Defense Contractors Accreditation Program (Nadcap) heat treating accreditation specifically evaluates furnace pyrometry documentation, atmosphere control records, and vacuum furnace leak rate documentation. Nadcap auditors review temperature uniformity survey records, system accuracy test results, thermocouple usage logs, and atmosphere monitoring data to verify compliance with AMS 2750H and customer-specific pyrometry requirements. Demonstrated compliance with all furnace calibration and monitoring requirements is a prerequisite for maintaining Nadcap heat treating accreditation.

AMS 2759 — Heat Treatment of Steel Parts

AMS 2759 is the aerospace specification governing the heat treatment of steel parts, including hardening, tempering, stress relieving, and carburizing processes. AMS 2759 requires that all furnaces used for these processes be calibrated in accordance with AMS 2750H, with documented temperature uniformity surveys and system accuracy tests current at the time of processing. The specification establishes temperature tolerances and uniformity requirements specific to each heat treatment process, and furnace calibration records must demonstrate compliance with these requirements.

Additional Standards

• ISO/IEC 17025 — General requirements for the competence of testing and calibration laboratories
• ASTM E220 — Standard Test Method for Calibration of Thermocouples
• AMS 2769 — Heat Treatment of Parts, General Requirements
• CQI-9 — AIAG Special Process: Heat Treat System Assessment (automotive)
• MIL-H-6875 — Military Specification for Heat Treatment of Steel (military heat treatment)

Industry Applications

Aerospace Heat Treating

Furnace temperature calibration is performed at aerospace heat treating facilities where turbine blades, structural alloys, landing gear components, fasteners, and brazed assemblies are processed. Solution heat treatment, aging, and stress relieving of aerospace alloys require calibrated furnaces with documented temperature uniformity. Nadcap accreditation is mandatory for aerospace heat treating operations, and prime contractor flow-downs from Boeing, Airbus, GE Aviation, and Pratt & Whitney impose additional pyrometry and calibration requirements beyond the baseline AMS 2750H specification.

Commercial Heat Treating

Independent commercial heat treating facilities serve multiple industries and process a wide variety of materials and part geometries. Furnace calibration is performed for carburizing, nitriding, carbonitriding, induction hardening, and flame hardening operations. Commercial heat treaters are typically required to maintain current furnace calibration records to satisfy the quality requirements of multiple customers simultaneously, including aerospace, automotive, medical device, and energy sector specifications. Temperature uniformity surveys and system accuracy tests are scheduled to maintain continuous compliance across all customer requirements.

Metal Processing & Forging

Furnace calibration is performed at forging operations, sintering facilities, hot isostatic pressing (HIP) installations, metal injection molding (MIM) operations, and powder metallurgy plants. Temperature uniformity within the furnace work zone is critical for achieving consistent material properties — including density, grain structure, and mechanical strength — across production lots. Calibration ensures that thermal processing conditions remain within the tolerances required by material specifications and customer requirements.

Tool & Die Manufacturing

Furnace calibration is performed at tool and die manufacturing facilities where tool steels — including D2, H13, M2, and A2 — are heat treated through vacuum hardening, tempering sequences, and cryogenic processing cycles. Dimensional stability and hardness requirements for tooling components demand precise temperature control and documented uniformity throughout the furnace work zone. Calibration records are maintained to demonstrate that furnace conditions meet the temperature tolerances specified by tool steel manufacturers and end-use application requirements.

Furnace Temperature Calibration in Joliet

On-site furnace temperature calibration is performed at heat treating, aerospace, and metal processing facilities in Joliet and the surrounding Illinois area. Temperature uniformity surveys, system accuracy tests, and atmosphere monitoring verification are conducted by ISO/IEC 17025 accredited laboratories using NIST-traceable reference thermocouples and data acquisition equipment. All calibration certificates are issued on-site upon completion of the measurement work.

Facilities in Joliet, IL requiring furnace calibration for AMS 2750H, Nadcap, CQI-9, or customer-specific pyrometry requirements are served through Temperature Calibration Specialists. Standard and priority scheduling is available.