Steve Offley

All About the Quench and Keeping Cool: Thru-process Temp Monitoring and Gas Carburizing

/ ATMOSPHERE AIR FURNACES TECHNICAL CONTENT, AUTOMOTIVE HEAT TREAT TECHNICAL CONTENT, CARBURIZING, CARBURIZING TECHNICAL CONTENT, CONTROLS, CONTROLS TECHNICAL CONTENT, FEATURED NEWS, QUENCHING TECHNICAL CONTENT

The future of heat treating requires new manufacturing solutions like robotics that can work with modular design. Yet so also does temperature monitoring need to be seamless to know how effectively your components are being heat treated — especially through being quenched. In this Technical Tuesday, learn more about temperature monitoring through the quench process.

Gas Carburization

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Carburizing has rapidly become one of the most critical heat treatment processes employed in the manufacture of automotive components. Also referred to as case hardening, it provides necessary surface resistance to wear, while maintaining toughness and core strength essential for hardworking automotive parts.

Figure 1. Typical carburizing heat treat temperature profile showing the critical temperature/time steps: (i) carburization, (ii) quench, and (iii) temper. (Source: PhoenixTM)

The carburizing process is achieved by heat treating the product in a carbon rich environment (Figure 1), typically at a temperature of 1562°F–1922°F (850°C–1050°C). The temperature and process time significantly influence the depth of carbon diffusion and other related surface characteristics. Critical to the process is a rapid quenching of the product following the diffusion in which the temperature is rapidly decreased to generate the microstructure, giving the enhanced surface hardness while maintaining a soft and tough product core.

The outer surface becomes hard via the transformation from austenite to martensite while the core remains soft and tough as a ferritic and/or pearlitic microstructure. Normally, carburized microstructures following quench are further tempered at temperatures of about 356°F (180°C) to transform some of the brittle martensite into tempered martensite to enhance ductility and grindability.

Critical Process Temperature Control

As discussed, the success of carburization is dependent on accurate, repeatable control of the product temperature and time at that temperature through the complete heat treatment process. Important to the whole operation is the quench, in which the rate of cooling (product temperature change) is critical to achieve the desired changes in microstructure, creating the surface hardness. It is interesting that the success of the whole heat treat process can rest on a process step which is so short (minutes), in terms of the complete heat teat process (hours). Getting the quench correct is not only essential to achieve the desired metal microstructure, but also to ensure that the physical dimensions and shape of the product are maintained (no distortion/warping) and issues such as quench cracking are eliminated.

Obviously, as the quench is so critical to the whole heat treat process, the correct quench selection needs to be made to achieve the optimum properties with acceptable levels of dimensional change. Many different quenchants can be applied with differing quenching performances. The rate of heat transfer (quench rate) of quench media in general follows this order from slowest to quickest: air, salt, polymer, oil, caustic, and water.

Technology Challenges for Temperature Monitoring

When considering carburization from an industry standpoint, furnace heat treat technology generally falls into one of two camps, embracing either air quench (low pressure carburization) or oil quench (sealed gas carburization/LPC with integral or vacuum oil quench). Although each achieves the same end goal, the heat treat mechanisms and technologies employed are very different, as are the temperature monitoring challenges.

To achieve the desired carburized product, it is necessary to control and hence monitor the product temperature through the three phases of the heat treat process. Conventionally, product temperature monitoring would be attempted using the traditional trailing thermocouple method. For many modern heat treat processes including carburization, the trailing thermocouple method is difficult and often practically impossible.1 The movement of the product or product basket from stage to stage, often from one independent sealed chamber to another (lateral or vertical movement), makes the monitoring of the complete process a significant challenge.

With the industry driving toward fully automated manufacturing, furnace manufacturers are now offering the complete package with full robotic product loading that includes shuttle transfer systems and modular heat treat phases to process both complete product baskets and single piece operations. Although trailing thermocouples may allow individual stages in the process to be measured, they cannot provide monitoring of the complete heat treat journey. Testing is therefore not under true normal production conditions, and therefore is not an accurate record of what happens in normal day to day operation.

Figure 2 shows schematic diagrams of two typical carburizing furnace configurations that would not be possible to monitor using trailing thermocouples. The first shows a modular batch furnace system where the product basket is transferred between each static heat treat operation (preheat, carburizing furnace, cooling station, quench, quench wash, temper furnace) via a charge transfer cart. The second shows the same heat treat operation but performed in a continuous indexed pusher furnace configuration where the product basket moves sequentially through each heat treat operation in a semi-continuous flow.

Figure 2.1. Modular batch furnace system (Source: PhoenixTM)
Figure 2.2. Continuous pusher furnace schematic (Source: PhoenixTM)

Thru-process temperature monitoring as a technique overcomes such technical restrictions. The data logger is protected by a specially designed thermal barrier, therefore, can travel with the product through each stage of the process measuring the product/process temperature with short, localized thermocouples that will not hinder travel. The careful design and construction of the monitoring system is important to address the specific challenges that different heat treat technology brings including modular batch and continuous pusher furnace designs (Figure 2).2

The following section will focus specifically on monitoring challenges of the sealed gas carburizing process with integral oil quench. Technical challenges of the alternative low pressure carburizing technology with high pressure gas quench have previously been discussed in an earlier publication.3

Monitoring Challenges of Sealed Gas Carburization — Oil Quench

Figure 3. “Thru-process” temperature monitoring system for use in a sealed carburizing furnace with integral oil quench — (3.1) Monitoring system entering furnace with thermocouple fixed to automotive gears, product test pieces (3.2) System exiting oil quench tank (3.3) System inserted into wash tank with product basket (Source: PhoenixTM)

Presently, the most common traditional method of gas carburizing for automotive steels is often referred to as sealed gas carburizing. In this method, the parts are surrounded by an endothermic gas atmosphere. Carbon is generated by the Boudouard reaction during the carburization process, typically at 1562°F–1832°F (850°C –1000°C). Despite the dramatic appearance of a sealed gas carburizing furnace, with its characteristic belching flames (Figure 3), from a monitoring perspective, the most challenging aspect of the process is not the heating, but the oil quench cooling. For such furnace technology, the historic limitation of “thru-process” temperature profiling has been the need to bypass the oil quench and wash stations, missing a critical process step from the monitoring operation. Obviously, passing a conventional hot barrier through an oil quench creates potential risk of both system damage from oil ingress and barrier distortion, as well as general process safety. However, the need to bypass the quench in certain furnace configurations by removing the hot system from the confined furnace space could create significant operational challenges, from an access and safety perspective.

Monitoring of the quench is important as ageing of the oil results in decomposition (thermal cracking), oxidation, and contamination (e.g. water) of the oil, all of which degrade the viscosity, heat transfer characteristics, and quench efficiency. Control of physical oil temperature and agitation rates is also key to oil quench performance. Quench monitoring allows economic oil replacement schedules to be set, without risk to process performance and product quality.

Figure 4. “Thru-process” temperature monitoring system oil quench compatible thermal barrier design: (1) Robust outer structural frame keeping insulation and inner barrier secure; (2) Internal thermal barrier — completely sealed with integral microporous insulation protecting data logger; (3) Mineral insulated thermocouples sealed in internal thermal barrier with oil tight compression fitting; (4) Multi-channel high temperature data logger; and (5) Sacrificial insulation blocks replaced after each run. (Source: PhoenixTM)

To address the process challenges, a unique thermal barrier design has been developed that both protects the data logger in the furnace (typically three hours at 1697°F/925°C) and also protects during transfer through the oil quench (typically 15 mins) and final wash station (Figure 3). The key to the barrier design is the encasement of a sealed inner barrier with its own thermal protection with blocks of high-grade sacrificial insulation contained in a robust outer structural frame (Figure 4).

Quench Cooling Phases

Monitoring the oil quench in carburization gives the operator a unique insight into the product’s specific cooling characteristics, which can be critical to allow optimal product loading and process understanding and optimization. From a scientific perspective, the quench temperature profile trace, although only a couple of minutes in duration, is complex and unique. From a zoomed in quench trace (Figure 5) taken from a complete carburizing profile run, the three unique heat transfer phases making up the oil quench cool curve can be clearly identified:

Figure 5. Oil quench temperature profile for different locations on an automotive gear test piece shows the three distinct heat transfer phases: (1) film boiling “vapor blanket”, (2) nucleate boiling, and (3) convective heat transfer. (Source: PhoenixTM)
  1. Film boiling “vapor Blanket”: The oil quenchant creates a layer of vapor (Leidenfrost phenomenon) covering the metal surface. Cooling in this stage is a function of conduction through the vapor envelope. Slow cool rate since the vapor blanket acts as an insulator.
  2. Nucleate boiling: As the part cools, the vapor blanket collapses and nucleate boiling results. Heat transfer is fastest during this phase, typically two orders of magnitude higher than in film boiling.
  3. Convective heat transfer: When the part temperature drops below the oil boiling point. the cooling rate slows significantly. The cooling rate is exponentially dependent on the oil’s viscosity.

From a heat treat perspective, the quench step relative to the whole process (hours) is quick (seconds), but it is probably the most critical to the performance of the metallurgical phase transitions and achieving the desired core microstructure of the product without risk of distortion. By being able to monitor the quench step, the process can be validated for different products with differing size, form, and thermal mass. As shown in Figure 6, the quench curve profile over the three heat transfer phases is very different for two different automotive gear sizes.

Figure 6. Oil quench temperature profile for different automotive gear sizes (20MnCr5 case hardening steel) with different thermal masses: Passenger Car Gear (2.2 lbs) and Commercial Vehicle Gear (17.6 lbs) (Source: PhoenixTM)

Summary

As discussed in this article, one of the key process performance factors associated with gas carburization is the control and monitoring of the product quench step. Employing an oil quench, the measurement of such operation is now very feasible as part of heat treat monitoring. Innovations in thru-process temperature profiling technology offer specific system designs to meet the respective application challenges.

References

[1] Dr. Steve Offley, “The light at the end of the tunnel – Monitoring Mesh Belt Furnaces,” Heat Treat Today, February 2022, https://www.heattreattoday.com/processes/brazing/brazing-technical-content/the-light-at-the-end-of-the-tunnel-monitoring-mesh-belt-furnaces/.

[2] Michael Mouilleseaux, “Heat Treat Radio #102: Lunch & Learn, Batch IQ Vs. Continuous Pusher, Part 1,” interviewed by Doug Glenn, Heat Treat Radio, October 26, 2023, audio, https://www.heattreattoday.com/media-category/heat-treat-radio/heat-treat-radio-102-102-lunch-learn-batch-iq-vs-continuous-pusher-part-1/.

[3] Dr. Steve Offley, “Discover the DNA of Automotive Heat Treat: Thru-process Temperature Monitoring,” Heat Treat Today, August 2023, https://www.heattreattoday.com/discover-the-dna-of-automotive-heat-treat-thru-process-temperature-monitoring/.

About the Author

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

Dr. Steve Offley, “Dr. O,” has been the product marketing manager at PhoenixTM for the last five 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 thru-process temperature and optical profiling and TUS monitoring system solutions.

For more information: Contact Steve at Steve.Offley@phoenixtm.com.

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“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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Amazon Gift Card Winners Announced for Leaders in Aerospace Heat Treat LinkedIn Group

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Heat Treat Today recently announced the launch of the Leaders in Aerospace Heat Treat LinkedIn Group and with it was a month-long event encouraging readers to join the group and comment on any of the posts during the month of April.

Leaders in Aerospace Heat Treat LinkedIn Group  (click here) provides a professional-level space where heat treaters from the aerospace industry can discuss issues and ideas. Heat Treat Today is regularly providing content related to the group, keeping members current on the latest technologies, products, processes, and discussions. If you’re a heat treat leader in the aerospace industry, you should be in this group.

As a special welcome to founding members of the Leaders in Aerospace Heat Treat LinkedIn Group, Heat Treat Today conducted a drawing for three winners, each to receive a $100 Amazon gift cards, open to anyone who joined the group AND commented on any of the posts during the month of April.

The three winners have been notified and they are:

  • Gary Berwick, Sales Engineer at Dry Coolers, Inc.
  • Steve Offley, Product Marketing Manager at Phoenix Temperature Measurement
  • Ellen Conway Merrill, Vice President at DELTA H TECHNOLOGIES, LLC

Each will receive a $100 Amazon gift card.

This new professional space was launched on the heels of releasing our inaugural Leaders in Aerospace Heat Treat monthly e-newsletter and the new Aerospace Heat Treat special print/digital edition (click here for digital).

To join the LinkedIn group:

Go to your LinkedIn account, sign in and search for “Leaders in Aerospace Heat Treat.” Join the group and connect with other leaders in aerospace heat treat.

For more information about the Leaders in Aerospace Heat Treat monthly e-newsletter, contact Doug Glenn at doug@heattreattoday.com.

Amazon Gift Card Winners Announced for Leaders in Aerospace Heat Treat LinkedIn Group 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.

 

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

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