Dr O

“The light at the end of the tunnel” — Monitoring Mesh Belt Furnaces

/ ATMOSPHERE AIR FURNACES TECHNICAL CONTENT, BRAZING TECHNICAL CONTENT, FEATURED NEWS, MANUFACTURING HEAT TREAT

OCAccording to "Dr. O" – Dr. Steve Offley, product marketing manager at PhoenixTM – temperature control of the heat treatment application is critical to the metallurgical and physical characteristics of the final product, and hence its ability to perform its intended function. Explore today's Technical Tuesday article to find the light at the end of your mesh belt furnace tunnel.

This article first appeared in Heat Treat Today’s February 2022 Air & Atmosphere Furnace Systems print edition.

Dr. Steve Offley, “Dr. O"
Product Marketing Manager
PhoenixTM

Introduction – The Need for Accurate Product Temperature Measurement

Even though modern furnaces are supplied with sophisticated control systems, they are still not always capable of truly giving an accurate picture of the actual product temperature as it passes through the process. Temperature sensors positioned along the furnace give a snapshot of what the environmental temperature is possibly zone by zone. Furnace controllers, as the name suggests, can give confidence that the process heating is performed in a controlled manner but will never give an accurate view of what the actual product temperature is. When monitoring, it is important to be able to distinguish between process and product.

The challenge to any process engineer is understanding how the product heating cycle relates to the operation of the furnace. A furnace environment may be well controlled, but very different product temperatures can be experienced with variation in key properties such as product material, size, shape, thermal mass, and position/orientation in the furnace. Infrared (IR) pyrometers and thermal imagers can provide surface temperature measurements only and require line of sight, so they limit the areas of the product that can be measured. Setup can sometimes be complex considering surface characteristics (emissivity) and process background/atmosphere compensation. As with air sensors, being fixed, typically IR sensors only give information at that specific furnace location which prevents accurate calculation of soak times at critical temperatures. Without additional information, soak times and temperatures may need to be extended well beyond the target to guarantee the heat treat process is completed with confidence with an obvious compromise to throughput and energy conservation.

Product Temperature Profiling

To fully understand the operational characteristics of the heat treat process it is necessary to measure both the environment and product temperature continuously as it travels through the process. Such technique provides what is referred to as a “temperature profile” which is basically a thermal fingerprint for that product in that furnace process. This thermal fingerprint will be unique but will allow understanding, control, optimization, and validation of the heat treat process.

Table 1. Table showing the numerous benefits of thru-process temperature monitoring over traditional trailing thermocouples methodology for a mesh belt furnace

Historically, trailing thermocouples have been the go-to technique for product temperature monitoring. A very long thermocouple is attached to the product in the furnace. The data logger measuring the live temperature reading is kept external to the furnace. Although possible for static batch processes, the technique has significant limitations in a continuous/semicontinuous process, especially mesh belt furnaces (See Table 1).

Fig 1. Robust multichannel data logger designed specifically for thru-process temperature profiling

In thru-process temperature profiling the data logger travels with the product through the furnace. The data logger (Figure 1) is protected by an enclosure, referred to as a thermal barrier, which keeps the logger at a safe operating temperature (Figure 2). Temperature readings recorded by the data logger from multiple short length thermocouples can be retrieved post run. Alternatively, if feasible, the data can be read in real time as the system passes through the furnace using a two-way radio frequency (RF) telemetry communication option. The resulting temperature profile graph (Figure 3) provides a comprehensive picture — product thermal fingerprint — of the thermal process.

Fig 2. Thermal barrier protecting the data logger safely entering the conveyor furnace during the temperature profile run. Barrier size is customized to suit process credentials.

Fig 3. Typical temperature profile recorded for an aluminum CAB brazing line giving a complete temperature history for a brazed radiator at different product locations.(1)

Monitoring Your Heat Treat Process Temperature at the Product Level

Applying thru-process temperature monitoring product temperature measurement can focus on the micro product level which at the end of the day is most important. Static control thermocouples give an environmental temperature of the furnace in a zone, but this only reflects the true temperature wherever the thermocouple is located. This may be some distance from the product and may give some bias to its position if located on one side of the furnace. The thru-process monitoring system allows simultaneous product and/or air temperature measurement directly at the mesh belt. Monitoring can be performed across the belt with thermocouple placement on and in the core of the product and can be made to identify areas of different thermal mass resulting in differing heating characteristics.

A useful strategy to use before looking at the product temperature is to thermally map the furnace. Thermocouples, connected to the data logger protected within the thermal barrier, are positioned across the mesh belt using a mount jig such as that shown in Figure 4. The jig guarantees reliable location of the measurement sensor run to run and adjustment means it can be adapted to different belt widths. Applying this principle, the thermal uniformity of air across the belt width through the entire furnace can be measured.

Fig 4. Thermocouple mount jig allowing accurate positioning of thermocouples (1) across the mesh belt width with adjustment to suit different belt dimensions (2).

Such data can be compared with zone control thermocouples to see what temperature differential the product may be experiencing at the belt level. Temperature imbalances across the belt and hot or cold spots along the process journey can be identified.

Furnace mapping can be further developed to satisfy either CQI-9/CQI-29 or AMS2750F pyrometry standards where a two-dimensional jig is constructed to perform the temperature uniformity survey (TUS).2 Employing the plane method, a frame jig is constructed to match the furnace work zone with the necessary number of thermocouples to satisfy the furnace cross section dimensions. Temperatures recorded over the working zone are compared to the desired TUS levels to ensure that they are within tolerance as defined in the standards.

Discover the True Root Cause of Your Furnace Problems

When it comes to product quality and process efficiency in any mesh belt furnace applications, temperature monitoring is only part of the story. Gaining an insight into what is physically happening in the product’s furnace journey can help you understand current issues or predict issues in the future, which can be corrected or prevented. To allow true root cause analysis of temperature related issues, it is sometimes necessary to “go to Gemba” and inspect what the product is experiencing, directly in the furnace. This is not always possible under true production conditions.

For a classic mesh belt furnace application such as controlled aluminum brazing (CAB), internal inspection of the furnace is not a quick and easy task. Operating at 1000°F, the cool down period is significant to allow engineers safe access for inspection and corrective action and then further delay to get the furnace back up to a stable operating temperature. Such maintenance action may mean one or two days lost production, from that line, which is obviously detrimental to productivity, meeting production schedules, satisfying key customers, and the bottom line.

In addition to process temperature problems there are many other production issues that can be faced relating to the furnace operation and safe reliable transfer of the product through the furnace. In the CAB process a day-to-day hazard is the build-up of flux debris. Flux materials used to remove oxides from the metal surface and allow successful brazing can accumulate within the internal void of the furnace. These materials are most problematic at the back end of the muffle section of the furnace where, due to the drop in temperature entering the cooling zone, materials condense out. Flux buildup can create many different process issues including:

  • Physical damage to the conveyor belt or support structure requiring expensive replacement
  • Reduction in belt lubricity creating jerky movement and causing unwanted product vibration
  • Lifting of the mesh belt creating an uneven transfer of products causing possible excessive product movement, clumping, or clashing
  • Reduction in inner furnace clearance creating possible product impingement issues and blockages

To prevent such problems, regular scheduled inspection and clean out of the furnace is necessary. This is not a pleasant, quick operation, and requires chipping away flux debris with pneumatic tools. Often requiring a furnace down time of 1 to 2 days, this task is only performed when essential. Leaving the clean-up operation too long can be catastrophic, causing dramatic deterioration in product quality or risk of mid-production run stoppages.

Figure 5. PhoenixTM Optical profiling ‘Optic’ System - Optical Profile View. System adaptable for both temperature and optical profiling.

Optical Profiling – The Efficient Alternative

Optical profiling is a new complementary technique to that of thru-process temperature profiling. The innovative technology allows for the first-time process engineers to view the inner workings of the furnace under normal production conditions. Traveling through the furnace with the products being processed, the optic system gives a product’s eye view of the entire heat treatment journey. A thermal barrier, similar in design to that used in temperature profiling, protects a compact video camera and torch that are used to record a video of what a product would see traveling through the furnace (Figure 5). The principle is just like your car’s dash cam, the only difference being that your journey is being performed in a furnace at up to 1000°F. The resulting video, “Optical Furnace Profile,” shows process engineers so much about how their process is operating without any need to stop, cool, and dismantle the furnace. This allows safe routine furnace inspection without any of the problems of costly lost production and days of furnace down time.

Summary

Monitoring your mesh belt furnace from a temperature and optical perspective allows you to fully understand what truly happens in that black box. Understanding leads to better control, which helps you get the optimal performance out of your heat treat process from a quality, productivity, and energy efficiency perspective.

Don’t get left in the dark. Consider the power of temperature and optical profiling which will literally provide a light at the end of your furnace tunnel!

References:

[1] Steve Offley, “Unveiling the Mystery of Your Al Brazing Furnace with ‘Thru-Process’ Temperature Profiling," Heat Treat Today Magazine, June 2020, p40.

[2] Steve Offley, “Applying ‘Thru-process’ Temperature Surveying To Meet the TUS Challenge of CQI-9.” HeatTreatToday.com. June, 2019. https://www.heattreattoday.com/heat-treat-news/automotive-heattreat-news/applying-thru-processtemperature-surveying-to-meet-thetus-challenges-of-cqi-9/

About the Author:

Dr. Steve Offley, “Dr. O,” has been the product marketing manager at PhoenixTM for the last 4 years after a career of over 25 years in temperature monitoring focusing on the heat treatment, paint, and general manufacturing industries. A key aspect of his role is the product management of the innovative PhoenixTM range of ‘thruprocess’ temperature and optical profiling and TUS monitoring system solutions.

For more information, contact Dr. O at Steve.Offley@phoenixTM.com.

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Unveiling the Mystery of Your Al Brazing Furnace with ‘Thru-Process’ Temperature Profiling

/ AUTOMOTIVE HEAT TREAT, BRAZING TECHNICAL CONTENT, FEATURED NEWS

Dr. Steve Offley, Product Market Manager, PhoenixTM

Knowing the precise temperature from within your continuous heat treat process is now possible. In this Heat Treat Today Technical Tuesday article, Steve Offley, “Dr. O,” Product Marketing Manager at PhoenixTM identifies how this innovative temperature profiling system can help you with your continuous aluminum brazing or other processes.

This article appeared in the edition June 2020 edition of Heat Treat Today’s Automotive Heat Treating magazine.

In the automotive industry, aluminium brazing is key to many of the manufacturing processes used to produce radiators, condensers, evaporators, etc. The quality of the brazing process is important to the performance and product life for its intended function. A critical requirement of the brazing process is the optimization and control of the product temperatures during the complete brazing process. A valuable tool to achieve such requirements is the use of ‘Thru-process’ temperature profiling as a direct alternative to the traditional trailing thermocouples as discussed in the following article. Obtaining the product temperature profile through the brazing furnace gives you a picture of the product/process DNA.

The Basic Brazing Principle and its Temperature Dependence

Aluminium brazing employs the principle of joining aluminium metal parts by means of a thinly clad soldering ‘filler’ alloy, whose melting point is lower than the base/parent metal.

As part of the brazing process, control of the product temperature is critical to achieve selective melting of the filler alloy 1076°F-1148°F (580°C -620°C) to allow it to flow and fill the joints between the parent metal substrate without risk of melting the substrate itself. Often the difference between the melting points of the two materials is small, so accurate temperature monitoring through the entire furnace is critical to the success of the brazing process.

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PhoenixTM works with major automotive radiator manufacturer customizing a brazing barrier solution to meet their specific application needs.

PhoenixTM was approached by a major automotive radiator manufacturer in the USA. The manufacturer had a specific need for a reliable CAB brazing monitoring system that would withstand heavy use, approximately 45 runs per week. The two companies collaborated to design a unique barrier solution which was adopted for standard profiling use.

“The new barrier is great; the operators love them. All those design iterations paid off.”

It is estimated that barriers supplied back in 2014, which have seen routine use over five years and are still operational, have accumulated in excess of 2,500 successful profile runs without damage or any wear problems.  Over the same period, many conventionally designed barriers have been scrapped due to HF acid damage of cloth and microporous insulation. The customer for this reason has now standardized the TS08 design for all their CAB profiling activity.

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Critical Challenges of the Brazing Process

The system enters the continuous aluminum brazing furnace with product being monitored.

Prior to any brazing process, it is important that the substrate surface is prepared correctly to allow the brazing process to work correctly. Surface preparation before brazing may involve thermal degreasing where the substrate temperature is elevated to drive off lubricants. A second more important procedure is the removal of any surface oxide layer to allow wetting, and therefore flow of the brazing filler alloy over the parent substrate. Unfortunately, aluminium is easily oxidized and the resulting aluminium oxide (Al2O3) prevents such wetting processes. Therefore, prior to brazing, the oxide layer needs to be eliminated. In most cases, cleaning of the substrate layer is achieved by the application of a corrosive flux, which in a molten state, dissolves the oxide layer.

A data logger with 10 thermocouple channels.

The type of flux used must be matched to the application substrate and filler alloy composition. A common brazing process used today is that of the Nocolok Process® in which the flux is potassium fluoroaluminate K 1-3 AlF4-6, a white powder deposit.

For the reasons discussed above, elimination of oxygen - and especially water - from the brazing process is a critical requirement, so the furnace is generally run under a nitrogen atmosphere (Controlled Atmosphere Brazing ‘CAB’ Oxygen < 100 ppm, Humidity < -40°F /-40°C). The design and construction of monitoring systems needs to be carefully considered, as discussed later, to ensure that the furnace atmosphere is not contaminated (by oxygen and water), in any way.

Design Principles and Challenges of a "thru-process" Brazing Furnace Monitoring System

The ‘thru-process’ profiling system concept is based on the principle of sending a data logger through the brazing furnace which is protected from the heat and harsh brazing environment by a thermal barrier. Multiple thermocouples connected to the product test piece (radiator), which are connected directly to the data logger, measure the product temperature (and furnace) as it travels through the furnace storing the information in the data logger memory. The resulting temperature profile can be reviewed, analyzed, and a validation report generated. As the system is compact and travels with the product, there is no need to use the cumbersome and potentially hazardous challenge of feeding (and retrieving) long thermocouples through the furnace, as required in the use of traditional trailing thermocouples.

Innovative Thermal Barrier Design

The thermal barrier has the job of providing thermal protection to the data logger. Although this is the case for aluminium brazing, the barrier also needs to be designed in such a way as to avoid damage to itself from potentially hostile corrosive chemicals generated in the furnace, and prevent contamination of the CAB atmosphere from barrier outgassing materials.

Traditionally, thermal barriers are manufactured employing micro-porous block insulation wrapped in high-temperature glass cloth. During use, moisture trapped in the insulation block is released within the barrier cavity where it can form hydrofluoric (HF) acid in combination with chemicals in the brazing flux. Over only a short period of time, the highly corrosive HF acid can cause significant damage to both the barrier cloth and insulation. This compromises the integrity of the barrier, reduces its thermal performance, and potentially creates a dust contamination risk to the process.

Air trapped in the micro-porous insulation block and within the barrier cavity during heating can expand and escape from the barrier into the furnace. Obviously, being made up of 21% Oxygen (O2 (g)), the air will contaminate the CAB environment, and potentially create a risk of aluminium oxide formation resulting in wetting/brazing problems.

To eliminate the damage to barriers, extend operational life expectancy, and minimize outgassing of air (O2(g)) or moisture, PhoenixTM developed a unique new TS08 specifically for the demands of CAB brazing.

As shown in figure 1, the logger draw loading mechanism significantly reduces the amount of insulation cloth that is exposed to the aggressive flux. Prior to supply, the insulation block is preheated in a high vacuum and back flushed with nitrogen (N2(g)) to drive out any air trapped in the porous insulation structure. For processes where any air outgassing is a significant contamination risk, it is possible, with specific barrier configurations, for customers to purge the small barrier cavity of any remaining air with a supply of low-pressure Nitrogen (N2(g)).

Figure 1: The brazing barrier is designed to give low height thermal protection to the data logger. Designed with front loading logger tray and metal construction to limit exposure of insulation and cloth materials to corrosive HF. Available with nitrogen purge facility option to remove any risk of O2 (g) outgassing into the furnace.

  1. PhoenixTM Datalogger with 6, 10 or 20 Channels
  2. Front loading logger tray with encapsulated thermal insulation protecting from HF
  3. Thermal breaks reduce heat conduction to logger
  4. Heat sinks provide additional thermal protection employing phase change technology
  5. Mineral Insulated Thermocouple inserted into radiator fins
  6. Rear barrier optional Nitrogen feed nozzle for pre-run purging of insulation and barrier cavity of air (02(g))

Unveiling the Mystery of your Brazing Furnace with a ‘thru-process’ Temperature Profile Trace

The key temperature transitions/phase of the brazing process are clearly shown on a typical temperature profile as in figure 2.

Figure 2. Thru-process temperature profile of a typical CAB brazing furnace showing critical temperature transitions.

Thermal profile graph displayed in the Thermal View Plus software package.

The brazing system is supplied with Thermal View Plus software, which is designed to provide full analysis and reporting tools for monitoring the brazing process against the monitoring requirements detailed in Table 1.

Below in Table 1 is a summary of the target temperature transitions in the CAB brazing process, the impact on process, and possibly, the quality of the brazed final product.

The PhoenixTM brazing system is supplied with Thermal View Plus software, which is designed to provide full analysis and reporting tools for monitoring the brazing process against the monitoring requirements detailed in Table 1.

Table 1. Critical monitoring requirements for the CAB brazing process.

Overview

The PhoenixTM ‘Thru-process’ brazing system provides a rugged, reliable, and clean solution for performing product temperature profiling of Automotive CAB brazing furnaces. Providing the means to Understand, Control, Optimize and Certify the brazing heat treat process.

 

About the author: Steve Offley, “Dr. O,” the product marketing manager at Phoenix TM, is an experienced global marketing manager with a demonstrated history of working in the industrial temperature monitoring industry over the last 25 years.

For more information, contact Steve at Steve.Offley@phoenixtm.com.

 

 

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Applying “Thru-Process” Temperature Surveying To Meet the TUS Challenges of CQI-9

/ AUTOMOTIVE HEAT TREAT, AUTOMOTIVE HEAT TREAT NEWS, FEATURED NEWS, THERMOCOUPLES TECHNICAL CONTENT

Dr. Steve Offley, a.k.a. “Dr. O”

Sponsored content

In the modern automotive manufacturing industry, CQI-9 HTSA (AIAG) has become a key part of driving process and product quality in heat treatment applications. The standard has a broad scope and covers many different aspects of common heat treatment processes (see Process Tables A-H in the standard) and monitoring requirements used. A critical part of the standard is the requirement to perform a temperature uniformity surveys (TUS) in order to validate the temperature uniformity of the qualified work zones and operating temperature ranges of furnaces or ovens used. In this Heat Treat Product Spotlight, Dr. Steve Offley, a.k.a. “Dr. O”, Product Marketing Manager with PhoenixTM, discusses the challenges of performing a TUS on continuous furnace types and one possible solution his company offers.

CQI-9 Heat Treat System Assessment

A critical part of the CQI-9 HTSA (AIAG) standard is the requirement to perform temperature uniformity surveys (TUSs). The TUS is performed to validate the temperature uniformity characteristics of the qualified work zones and operating temperature ranges of furnaces or ovens used. (See Figure 1.)

Fig 1: Schematic showing TUS principle. Thermocouple measurement from the field test instrument, of the furnace’s actual operational temperature, against a setpoint to check that it is within tolerance. Setpoints and tolerances are defined in CQI-9 Process Tables A-H to match each heat treat process.

The “Thru-Process” TUS Principle

Traditionally, TUSs are performed by using a field test instrument (chart recorder or static data logger) external to the furnace with thermocouples trailing into the furnace heating chamber. This technique has many limitations, especially when the product transfer is continuous such as in a pusher or conveyor-type furnace. The trailing thermocouple method is often labor-intensive, potentially unsafe, and can create compromises to the TUS data being collected (e.g., number of measurement points possible, thermocouple damage, and physical snagging of the thermocouple in the furnace).

Fig 2: PhoenixTM thermal barrier being loaded into a batch furnace with a survey frame as part of the TUS process.

The “Thru-Process” TUS principle overcomes the problems of trailing thermocouples as the multi-channel data logger (field test instrument) travels into and through the heat treat process protected by a thermal barrier (Figure 2). The short thermocouples are fixed to the TUS frame. Temperature data is then transmitted live to a monitoring PC running TUS analysis software, via a 2-way RF telemetry link.

Data Logger Options

To comply with CQI-9, field test equipment needs to be calibrated every 12 months minimum, against a primary or secondary standard. The data logger accuracy needs to be a minimum +/-0.6 °C (+/-1.0 °F) or +/-0.1% (TABLE 3.2.1).

Fig 3: PhoenixTM PTM1220 20 Channel IP67 data logger comes calibrated to UKAS ISO/IEC17025 as an option with an onboard calibration data file allowing direct data logger correction factors to be applied automatically to TUS data.

The data logger shown in Figure 3 has been designed specifically to meet the CQI-9 TUS requirements offering a +/- (0.5°F (0.3°C) accuracy (K & N). Models ranging from 6 to 20 channels can be provided with a variety of noble and base metal thermocouple options (types K, N, R, S, B) to suit measurement temperature and accuracy demands (AMS2750E and CQI-9).

Mixed thermocouple inputs can be provided to support the process specific requirements and also allow the use of the data logger to perform system accuracy testing (SAT) to complement the TUS.

Innovative Thermal Barrier Design

Fig 4: “Octagonal” thermal barrier fitted to product/survey tray.

CQI-9 covers a wide range of thermal heat treatment processes and as such the thermal protection for the data logger will vary significantly. A comprehensive range of thermal barrier solutions can be provided to meet specific process temperature requirements and space limitations. Figure 4 shows a unique octagonal thermal barrier designed to fit within the boundaries of the product tray/survey frame used to perform a TUS using the “plane method” (See “Thermocouple Measurement Positions (TUS)” below in this article.). The design ensures maximum thermal performance within the confines of a restricted product tray/basket.

Live Radio TUS Communication

Fig 5: Schematic of LwMesh 2-way RF Telemetry communication link from data logger TUS measurement back to an external computer.

The data logger is available with a unique 2-way wireless RF system option allowing live monitoring of temperatures as the system travels through the furnace. Analysis of process data at each TUS level can be done live allowing full efficient control of the TUS process. Furthermore, if necessary, by using the RF system, it is possible to communicate with the logger installed in the barrier to reset/download at any point pre-, during, and post-TUS. In many processes, there will be locations where it is physically impossible to transmit a strong RF signal. With conventional systems, this results in process data gaps. For the system shown in Figure 2, this is prevented using a unique fully automatic “catch up” feature.

Any data that is missed will be sent when the RF signal is re-established, guaranteeing 100% data transfer.

Thermocouple Options (TUS)

In accordance with the CQI-9 standard (Tables 3.1.3 / 3.1.5), thermocouples supplied with the data logger, whether expendable or nonexpendable, meet the specification requirements of accuracy +/-2.0°F (+/-1.1°C) or 0.4%. Calibration certificates can be offered to allow the creation of thermocouple correction factor files to be generated and automatically applied to the TUS data within the PhoenixTM Thermal View Survey Software. Care must be taken by the operator to ensure that usage of thermocouples complies with the recommended TUS life expectancies and repeat calibration frequencies. Before first use, thermocouples must be calibrated with a working temperature range interval not greater than 250°F (150°C). Replacement or recalibration of noble metal (B, R or S) thermocouples is required every 2 years. For non-expendable base metal (K, N, J, E), thermocouples replacement should be after 180 uses <1796°F (980°C) or 90 uses >1796°F (980°C). For expendable base metal (K, N, J, E), thermocouples replacement should be after 15 uses <1796°F (980°C) or 1 use >1796°F (980°C). Note that base metal thermocouples should not be recalibrated.

Thermocouple Measurement Positions (TUS)

To perform the TUS survey, a TUS frame needs to be constructed to locate the thermocouples over the standard work zone to match the form of the furnace. The TUS may be performed in either an empty furnace in which case thermocouples should be securely fixed as shown in Figure 6. A heat sink (thermal mass fixed to thermocouple tip) can be used to create a thermal load to match the normal product heating characteristics. Alternatively, the thermocouples should be buried in the load/filled product basket. See Figure 6 to see schematics of TUS Frames for a box and cylindrical batch furnace with CQI-9-quoted number of thermocouples required to match void volume (Volumetric Method Table 3.4.1).

Fig 6: TUS Thermocouple Test Rigs. Required number of thermocouples: 1) Work Volume < 0.1 m³ (3 ft³) = 5; 2) Work Volume 0.1 to 8.5 m³ (3 to 300 ft³) = 9; 3) Work Volume > 8.5 m³ one thermocouple for every 3 m³ (105 ft³). (Click on the images for larger display.)

Fig. 7.1, 7.2. PhoenixTM system showing 9 Point TUS survey rig and Thermal View Software TUS frame library file showing as part of TUS report exactly where thermocouples are positioned. (Click on the images for larger display.)

 

For continuous conveyorized furnaces, it is recommended that an alternative thermocouple test rig is employed called the “plane method”. Since the system travels through the furnace it is only necessary to monitor the temperature uniformity over a 2-dimensional plane/slice of the furnace (Figure 8). The required number and location of thermocouples are shown in Table 1 (CQI-9 Table 3.4.2).

(Click on the images for larger display.)

Table 1: Required thermocouples and locations for differing work zones (Plane Method)

(1) 2 Thermocouples within 50 mm work zone corners 1 Thermocouple center. (2) 4 Thermocouples within 50 mm work zone corners. Rest symmetrically distributed.

“Thru-Process” Temperature Uniformity Survey (TUS) Data Analysis and Reporting

Operating the PhoenixTM System with RF Telemetry, TUS data is transferred from the furnace directly back to the monitoring PC where, at each survey level, temperature stabilization and temperature overshoot can be monitored live, with thermocouple and logger correction factors applied. The Thermal View Survey software generates TUS reports which comply with the requirements of AMS2750E/CQI-9 standards.

As defined in CQI-9 (Section 3.4) for furnace with an operating temperature range ≤ 305°F (170°C), one setpoint temperature (TUS level) within the operating temperature range is required. If the operating temperature of the qualified work zone is greater than 305°F (170°C), then the minimum and maximum temperatures of the operating temperatures range shall be tested.

The TUS levels can be automatically set up in the TUS analysis software. Figure 9 shows both the TUS level file and TUS levels applied against the TUS survey trace.

Fig. 9.1

Fig. 9.2

Fig 9.1, 9.2 PhoenixTM Thermal View Survey Software showing TUS Level set-up and application to TUS trace.

Within CQI-9, there is a very prescriptive list of what should be contained in the TUS report (Section 3.4.9).

To comply with all said requirements, the software package provides a comprehensive reporting package as shown below.

Fig 10.1, 10.2, 10.3.  TUS Report showing a TUS profile at three set survey temperatures (graphical and numerical data). The probe map shows exactly where each thermocouple is located and easy trace identification. A detailed TUS report is generated, meeting full CQI-9 reporting requirements. (Click on the images for larger display.)

Overview

The PhoenixTM Thru-Process TUS System provides a versatile solution for performing product temperature profiling and furnace surveying in industrial heat treatment meeting all TUS requirements of CQI-9 within the automotive manufacturing industry, providing the means to understand, control, optimize and certify the heat treat process.

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Temperature Monitoring and Surveying Solutions for Carburizing Auto Components: AMS2750E and CQI-9 Temperature Uniformity Surveys

/ AUTOMOTIVE HEAT TREAT, CARBURIZING TECHNICAL CONTENT, FEATURED NEWS

Dr. Steve Offley (“Dr. O”), Product Marketing Manager PhoenixTM

This is the final installment in a 4-part series by Dr. Steve Offley (“Dr. O”) on the technical challenges of monitoring low-pressure carburizing (LPC) furnaces. The previous articles explained the LPC process and explored general monitoring needs and challenges (part 1), the use of data loggers in thru-process temperature monitoring (part 2), and the thermal design challenge (part 3). In this segment, Dr. O discusses AMS2750E and CQI-9 Temperature Uniformity Surveys. You can find Part 1 here, Part 2 here, and Part 3 here. 

A significant challenge for many heat treaters is the need to provide products certified to either AMS27150 (aerospace) or CQI-9 (automotive). To achieve this accreditation, furnace Temperature Uniformity Surveys (TUS) must be performed at regular intervals to prove that the furnace set-point temperatures are both accurate and stable over the working volume of the furnace. Historically, the furnace survey has been performed with great difficulty trailing thermocouples into the heat zone. Although it’s possible in a batch process when considering a semi-batch or continuous process, this is a significant technical challenge with considerable compromises as summarized below.

Trailing Thermocouple TUS Process Steps

Figure 1. Typical TUS thermocouple. Positions — 9 point survey. Furnace void corners and center

  • TUS is often carried out using long or ‘trailing’ thermocouples that exit through the furnace door.
  • Furnace often needs to be cooled, then de-gassed so TUS frame can be set up in the furnace.
  • Thermocouples are then led out through the furnace door and connected to a data logger or chart recorder.
  • The furnace is then heated to surveying temperatures.
  • The survey is then carried out, after which furnace is cooled, and thermocouples are removed.

 

Disadvantages of Traditional TUS Process

  • Lots of furnace downtime may be involved (can be up to 24 hours).
  • Thermocouples have to exit the furnace door.
    • This may involve “wedging” the door up, or “grooving” out the hearth to get thermocouples out.
    • Or thermocouples may get caught in the furnace door.
  • A significant amount of the technician’s time is taken up preparing report.

Applying the “Thru-Process” approach to TUS, the measurement system is transferred into the furnace with the survey frame allowing the setup process to be done quickly, safely, and repeatable. (See Figure 2)

Figure 2. PhoenixTM System loaded into a furnace as part of a TUS frame. Thermocouples pre-fitted to the 8 vertices of the cube frame and center. Furnace ambient temperature recorded either with a virgin exposed junction thermocouple (typical MI) or with heat sink damper fitted.

Operating the system with RF telemetry, TUS data is transferred directly from the furnace back to the monitoring PC where at each survey level temperature stabilization and temperature overshoot can be monitored live with TC and logger correction factors applied. The Thermal View Software is developed to ensure that the final TUS report complies fully to the AMS2750E/CQI-9 standards.

Figure 3. PhoenixTM Thermal View Survey Software showing a TUS profile at three set survey temperatures. The probe map shows exactly where each probe is located and easy trace identification. Detailed TUS report generated with efficiency.

Features incorporated into the Thermal View Software to provide full TUS capability include the following:

TUS Level Library – Set-up TUS level templates for quick efficient survey level specification (Survey Temp °F, Tolerance °F, Stabilization, and Survey Times)

TUS Frames Library – Show clearly exact TUS frame construction and probe location using Frame Library Templates – Frame Center and 8 Vertices.

Logger Correction File – Create a logger correction file to compensate TUS readings automatically from the logger’s internal calibration file.

Thermocouple Correction File – Create the thermocouple correction file and use to compensate TUS readings directly.

TUS Result Table & Graph View – For each TUS temperature level, see from the graph or TUS table instantaneously full survey results.

Furnace Class Reporting – Report the specified furnace class at each temperature level.

 

 

Overview

The PhoenixTM Temperature Profiling System provides a versatile solution for both performing product temperature profiling and furnace TUS in industrial heat treatment. It is designed specifically for the technical challenges of low-pressure carburizing (LPC) whether implementing either high-pressure gas quench or oil quench methodology, providing the means to Understand, Control, Optimize and Certify the LPC Furnace and guarantee product quality and process operation efficiency and certification.

 

Temperature Monitoring and Surveying Solutions for Carburizing Auto Components: AMS2750E and CQI-9 Temperature Uniformity Surveys Read More »

Temperature Monitoring and Surveying Solutions for Carburizing Auto Components: Thermal Barrier Design

/ AUTOMOTIVE HEAT TREAT, AUTOMOTIVE HEAT TREAT NEWS, CARBURIZING TECHNICAL CONTENT, FEATURED NEWS, INSULATION TECHNICAL CONTENT

This is the third in a 4-part series by Dr. Steve Offley (“Dr. O”) on the technical challenges of monitoring low-pressure carburizing (LPC) furnaces. The previous articles explained the LPC process and explored general monitoring needs and challenges (part 1) and the use of data loggers in thru-process temperature monitoring (part 2). In this segment, Dr. O discusses the thermal barrier with a detailed overview of the thermal barrier design for both LPC with gas or oil quench. You can find Part 1 here and Part 2 here. 

Low-Pressure Carburizing (LPC) with High-Pressure Gas Quench – the Design Challenge

A range of thermal barriers is available to cover the different carburizing process specifications. As shown in Figure 1 the performance needs to be matched to temperature, pressure and obviously space limitations in the LPC chamber.

 

Fig 1: Thermal Barrier Designed Specifically for LPC with Gas Quench.

(i) TS02-130 low height barrier designed for space limiting LPC furnaces with low-performance gas quenches (<1 bar). Only 130 mm/5.1-inch high so ideal for small parts. Available with Quench Deflector kit. (0.9 hours at 1740°F/950°C).

(ii) Open barrier showing PTM1220 logger installed within phase change heatsink.

(iii) TS02-350 High-Performance LPC barrier fitted with quench deflector capable of withstanding 20 bar N2 quench. (350 mm/13.8-inch WOQD 4.5 hours at 1740°F /950°C).

(iv) Quench Deflect Kit showing that lid supported on its own support legs so pressure not applied to barrier lid.

The barrier design is made to allow robust operation run after run, where conditions are demanding in terms of material warpage.

Some of the key design features are listed below.

I. Barrier – Reinforced 310 SS strengthened and reinforced at critical points to minimize distortion (>1000°C / 1832°F HT or ultra HT microporous insulation to reduce shrinkage issues)

II. Close-pitched Cu-plated rivets (less carbon pick up) reducing barrier wall warpage

III. High-temperature heavy duty robust and distortion resistant catches. No thread seizure issue.

IV. Barrier lid expansion plate reduces distortion from rapid temperature changes.

V. Phase change heat sink providing additional thermal protection in barrier cavity.

VI.  Dual probe exits for 20 probes with replaceable wear strips. (low-cost maintenance)

LPC or Continuous Carburizing with Oil Quench – the Design Challenge

Although commonly used in carburizing, oil quenches have historically been impossible to monitor. In most situations, monitoring equipment has been necessarily removed from the process between carburizing and quenching steps to prevent equipment damage and potential process safety issues. As the quench is a critical part of the complete carburizing process, many companies have longed for a means by which they can monitor and control their quench hardening process. Such information is critical to avoid part distortion and allow full optimization of hardening operation.

When designing a quench system (thermal barrier) the following important considerations need to be taken into account.

  • Data logger must be safe working temperature and dry (oil-free) throughout the process.
  • The internal pressure of the sealed system needs to be minimized.
  • The complexity of the operation and any distortion needs to be minimized.
  • Cost per trial has to be realistic to make it a viable proposition.

To address the challenges of the oil quench, PhoenixTM developed a radical new barrier design concept summarized in Figure 2 below. This design has successfully been applied to many different oil quench processes providing protection through the complete carburizing furnace, oil quench and part wash cycles.

Fig 2: Oil Quench Barrier Design Concept Schematic

(i) Sacrificial replaceable insulation block replaced each run.

(ii) Robust outer structural frame keeping insulation and inner barrier secure.

(iii) Internal completely sealed thermal barrier.

(iv) Thermocouples exit through water/oil tight compression fittings.

In the next and final installment in this series, Dr. O will address AMS2750E and CQI-9 Temperature Uniformity Surveys, which often prove to be challenging for many heat treaters. "To achieve this accreditation, Furnace Temperature Uniformity Surveys (TUS) must be performed at regular intervals to prove that the furnace set-point temperatures are both accurate and stable over the working volume of the furnace. Historically the furnace survey has been performed with great difficulty trailing thermocouples into the heat zone. Although possible in a batch process when considering a semi-batch or continuous process this is a significant technical challenge with considerable compromises." Stay tuned for the next article in the series of Temperature Monitoring and Surveying Solutions for Carburizing Auto Components.

Temperature Monitoring and Surveying Solutions for Carburizing Auto Components: Thermal Barrier Design Read More »

Temperature Monitoring and Surveying Solutions for Carburizing Auto Components: The Data Logger

/ AUTOMOTIVE HEAT TREAT, AUTOMOTIVE HEAT TREAT NEWS, CARBURIZING TECHNICAL CONTENT, FEATURED NEWS

This is the second in a 4-part series by Dr. Steve Offley (“Dr. O”), Product Marketing Manager at PhoenixTM, on the technical challenges of monitoring low-pressure carburizing (LPC) furnaces. The previous article explained the LPC process and explored general monitoring needs and challenges. In this segment, Dr. O talks about the data logger and its monitoring capabilities. 

The Range of the PhoenixTM Data Logger

Figure 1: PhoenixTM PTM1220 20-Channel IP67 Datalogger

A data logger, an electronic device that records data over time or in relation to locatio, can be useful in a variety of configurations and modified to suit the specific demands of the process being monitored. A range of models are on the market. At PhoenixTM they include 6 to 20 channels with a variety of thermocouple options (types K, N, R, S, B) to suit measurement temperature and accuracy demands (AMS2750 & CQI-9). Provided with Bluetooth wireless connection for short-range localized download and reset (direct from within the barrier) the logger memory of 3.8M allows even the longest processes to be measured with the highest resolution to deliver the detail you need. An optional unique 2-way telemetry package offers live real-time logger control and process monitoring with the benefits detailed in a later section.

 

Live Radio Communication

Figure 3: Schematic of RF telemetry real-time monitoring network

The logger is available with a unique 2-way RF system option allowing live monitoring of temperatures as the system travels through the carburizing processes. Furthermore, if necessary using the RF system it is possible to communicate with the logger, installed in the barrier, to reset/download at any point pre, during and post-run.

Provided with a high performance “Lwmesh” networking protocol the RF signal can be transmitted through a series of routers linked back to the main coordinator connected to the monitoring PC. The routers are located at convenient points in the process, positioned to maximize signal reception. Being wirelessly connected they eliminate the inconvenience of routing communication cables or providing external power as needed on other commercial RF systems.

In many processes, there will be locations where it is physically impossible to transmit a strong RF signal. In carburizing obviously within the oil quench, the RF signal is not capable of escaping when the system is submerged. With conventional systems, this results in process data gaps. For the PhoenixTM system, this is prevented using a unique fully automatic ‘catch up’ feature. Any data that is missed will be sent when the RF signal is re-established post-quench guaranteeing in most applications 100% thru-process data review.

Thru-Process Data Analysis and Temperature Uniformity Surveys (TUS)

Figure 3: Thermal view SW displaying the temperature profile from a carburizing with gas quench process

In thru-process temperature monitoring, the data logger collects raw process data directly from the product or furnace as it follows the standard production flow. To understand the data to allow process control and optimization, a Thermal View software analysis is used.

Using a range of analysis tools, the engineer can interpret the raw data. Key analysis calculations can be performed such as:

  • Max / Min — Check maximum and minimum product temperature over whole product or product basket through phases of process carburizing, diffusion and quench.
  • Time @Temp — Confirm that the soak time above required carburizing temperature is sufficient for correct carbon diffusion and surface properties.
  • Temperature Slopes —Measure the quench rate of the product to ensure that the hardening process is performed correctly.

 

Next up in the series: Designing an Innovative Thermal Barrier — The carburizing process by its nature is very demanding when considering protection of the datalogger from high temperatures and rapid temperature and pressure changes experienced in either the gas or oil quench.

 

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