Stay Ahead of the Curve with Advanced Controls Technology
By Jason Sanders and Jim Grann, Ipsen USA   

Perfecting your thermal processing operations is paramount to producing high-quality products. By mastering and maintaining control of your equipment, old and new, you can achieve this optimization, which ultimately leads to the ideal performance of your heat-treating equipment. This performance allows you to obtain and replicate desired results, as well as streamline your process, creating time and cost savings.

Advanced controls technology gives you the operational flexibility needed to measure and analyze your equipment and processes with ease. You can then use said analysis to refine and adjust the settings and parameters of your equipment to enhance your process. With advanced controls, this optimization is simple and also ensures less human error in the production process because it eliminates several manual processes, automating them for precise, repeatable control.  

Revitalizing older equipment with controls upgrades increases its capabilities and overall flexibility, keeping it up-to-date and in line with your current systems. One example of the benefits of an upgrade to an older system is that many older vacuum furnaces require a manual adjustment of the heating elements via trim pots. With a controls upgrade, one can monitor and adjust the heating elements through the industrial computer's graphical interface. By eliminating the need for manual adjustments, you rely on the Program Logic Controller (PLC), thus eliminating potential for human error.  

In addition to perfecting your process, some heat treaters may need to meet rigorous industry specifications like those in the Aerospace industry including, but not limited to, Nadcap and AMS 2750. Demands for compliance to industry-specific regulations have never been greater, but the trend toward more precise measurement and control is increasing even outside these specifications and regulations.

Assessing Your Needs
Before purchasing a furnace or upgrading an older one, the first step is assessing your process and production needs. There are many types of thermal processing equipment and you want to be sure you are investing in the proper furnace or upgrades.

Fig. 1. Ipsen representative tests a control panel layout prior to installation.

Vacuum furnace systems are divided into two categories: classification and instrumentation type. Furnace classification is ranked from Class One through Class Six. Class One applies the most stringent furnace requirements with the smallest range in temperature uniformity: ±5 °F (±3 °C), and Class Six applies the least restricted furnace requirements with a wide range in temperature uniformity: ±50 °F (±28 °C).

Some processes require the performance and temperature uniformity of a Class One furnace. Other processes are not so particular, meaning it's possible to get acceptable results from a furnace of a lower class. Your process and the results you desire determines which class of furnace will work best for you. Therefore, it is imperative to know what you are trying to achieve, the type of processes you will run and what type of parts you will be treating. Once you understand these objectives, you will be prepared to begin researching new equipment or upgrading your existing equipment. 

Fig. 2. Advanced controls technology mounted in an industrial control enclosure.

Potential Nadcap and AMS 2750 rev. E Compliance Pitfalls

A common misconception is that you can purchase a furnace that is AMS 2750E and Nadcap accredited. In actuality, end users are responsible for investing in a furnace that is capable of meeting the specifications they are trying to achieve. Then, they are required to operate, maintain and test the furnace to obtain certification. The equipment manufacturer cannot control how end users operate and maintain their furnace; that is up to the heat treater. For instance, AMS 2750 revision E outlines the furnace classes and the standards by which each class is determined, but a furnace, as shipped from the manufacturer, is not by itself AMS 2750E or Nadcap compliant. A furnace is only capable of being compliant since the onus of compliance is reliant on the end user's control and operation of the furnace, as well as the particular process variables and specifications they are attempting to meet.  

Advanced Controls Technology

When it comes to advanced controls technology, there are many options to consider, including instrumentation, software, data storage and monitoring systems. All of these features offer the intelligent, superior control needed to achieve peak performance from your equipment, both new and old.  

Instrumentation
Enhancing your instrumentation involves applying state-of-the-art technology that improves your measurement capabilities, which makes running and maintaining your equipment easier and more cost effective. 

Hygrometer (Dew Point Analyzer)
Installing a hygrometer upgrade on a furnace affords users the ability to monitor the moisture content in the process gas. Its design allows the flexibility to operate and monitor precisely under various conditions. The hygrometer is mounted in an enclosure near the furnace backfill inlet to ensure the system receives an accurate sample. Many specifications mandate that the backfill and partial pressure gases are scrutinized before being exposed to the parts. In general, this is a best practice to prevent discoloration of your parts. Some customers choose to use the hygrometer for information only, but others choose to integrate it with their control system for a "go, no-go" condition, meaning, if it deems a no-go condition, the software sounds an alarm and, in some cases, prevents the gas from entering the vessel.

Fig. 3. Ipsen's hygrometer upgrade provides the flexibility to operate and monitor under many conditions.

Vacuum Gauge
Vacuum gauges provide end users with accurate and repeatable results. These gauges integrate easily into the furnace and have a modular design that allows for future expansion. The vacuum gauge measures the vacuum and partial pressure levels throughout the heat treatment cycle. Some industry specifications mandate the monitoring of vacuum levels prior to the start of a heat cycle or partial pressure range during the heat cycle, so end users need accurate representation of those levels. It is important to remember that selecting the proper vacuum gauge is critical to adhering to particular specifications.   

Digital Data Recorder
A digital data recorder adds advanced data collection, storage and reporting. Data collection and reporting have become one of the most critical parts of today's control systems. Many older control systems utilize paper chart recorders that record the run based on time intervals. These older systems require manual setup and finalization. They also have limited readability and storage capabilities.  

With an upgrade to the digital data recorder, paired with a software upgrade, the data is stored on the industrial computer, sent to a specified network location via an Ethernet connection or both. This ability gives the customer the required redundancy for critical data storage and, typically, helps to comply with most industry specifications.  

Comparatively, a new digital recording system is far easier to use than an analog paper recorder as it allows you to better track your results in order to refine your process and improve your quality throughput. Charting is made easier with the digital readout and it provides on-the-fly reports, as well as adjustable configuration of reports, depending on your needs.

Fig. 4. Ipsen's digital data recorder provides the end user with the flexibility and scalability of recording the most critical data, as well as optional touch screen capabilities.

AMS 2750 rev. E New Charting Requirements May Prove Challenging for Older Analog Paper Recorders

Section 3.2.1.1.1 of the AMS 2750 revision E states, "Temperature resolution requirements for chart recorders shall be in accordance with Table 4." This mandates the maximum amount of chart paper divisions per inch. The older paper analog print recorders are not typically configured to meet these new requirements, whereas the majority of newer digital recorders meet these standards and provide more accurate results.  

This change was specified in the previous revision, but the newest revision identifies a deadline, which means that - after the deadline passes - all recording devices not meeting the proper chart divisions may cause a violation impeding certification. Some have argued that they can create a dual-scale charting system that prints out the analog results onto their older, existing chart paper. Unfortunately, this could severely complicate matters because, once the cycle is complete, an operator is required to sign off on the report. If, after several months, the operator who signed the report is asked by a Nadcap auditor to explain how he validated the cycle in order to sign off on it, the dual-scaled chart may cause more complexity and challenge than is desired.

Software Control Upgrades
Software upgrades are often teamed up with equipment modifications in an effort to provide better functionality and measurement. Often these upgrades are referred to, in the more general sense, as control upgrades because they are typically whole system upgrades that may include PLC, cabinet-mounted industrial computers and monitors, recipe development and storage capabilities, in-process recipe editing, real-time and historical data trending and/or process-cycle reporting.  

As mentioned earlier, these software control upgrades reduce the possibility of human error by automating adjustments that, in the past, required manual action. For instance, if you are running partial pressure and vacuum processes in the same furnace with different load configurations, switching from one to the other makes it tougher to monitor and refine your production processes. New software options now allow you to save your settings for future reference. Then, when the operator chooses to run partial pressure or vacuum, the system is intuitive and automatically selects the proper parameters for running that particular process. This allows for greater flexibility by providing a very simple method for switching production in and out of the equipment.

Fig. 5. Screenshot of real-time software trend

The software upgrade also performs a similar action when dealing with the utilization of either argon or nitrogen gas for different part processing. There is a specific density change between these gases as argon is heavier. You cannot calibrate and tune your machine for nitrogen and then run argon gas, or vice versa, and expect the system to display correct vacuum readings. However, there is software available that knows which gas is being selected for partial pressure or backfill and automatically calculates the math to give you real-time data.  

Another great new software feature is that the systems are now capable of tracking 32 data points, all of which are selectable by the user. When the system is switched on, it automatically begins logging data to populate the trend screens, alarm history and user login information. Users can toggle between real-time and historical information at any point in time. This information is also capable of being retrieved by date and then displayed on screen or printed.  

Pairing this software control upgrade with a digital data recorder provides an extra level of redundancy when needed or required. This pairing helps ensure the data is not lost. Historical files can be transferred to a compact flash card or a networked hard drive via an Ethernet connection. All files created are read-only files that cannot be altered without detection, which is becoming extremely important in the Aerospace and Pharmaceutical industries, as well as other market sectors.  

Supervisory Control and Data Acquisition (SCADA) Systems
Upgrading to incorporate a SCADA system provides the means to view furnace data and operational settings for multiple furnaces at the same time on a single display. As an alternative to physically going to each individual furnace to retrieve information, all of the data is sent to the SCADA system via an Ethernet connection. This gives the end user the flexibility of collecting and reporting the data in one central location. This functionality allows for more efficient reporting. SCADA systems provide more robust monitoring and reporting; however, they do not define your production process.  

Fig. 6. Ipsen's SCADA system provides users with the ability to view furnace data and operational settings for multiple furnaces at the same time on a single display.

Effects of Partial Pressure on SAT and TUS

One perceived issue AMS 2750 has yet to address is that end users may be running parts in partial pressure and not always in a vacuum environment; however, AMS 2750 only outlines the requirements for vacuum. The concern is that the results of your SAT and TUS can vary widely depending on whether or not you are conducting them in vacuum or partial pressure. If end users are charged with emulating the production environment for SAT and TUS, one must take into consideration the effects of partial pressure if it is utilized in the production cycle.  

There are many uses and benefits of partial pressure, but there is one particular side effect that is of great concern: the gas's ability to transfer heat and its ability to negate the insulation factor of the hot zone. When high partial pressures are selected during a production cycle, the gas's ability to negate the insulating properties of the hot zone results in the need to increase the temperatures of the heating elements so as to maintain the required set points, which increase even more so during ramping. The end user never sees an issue as the furnace ramps normally, reaches set point normally and soaks out accordingly. Though, depending on the particular hot zone configuration (e.g., all metal has greater losses), the actual parts may see significantly elevated surface temperatures during the ramping or soaking modes of the cycle. Based on physics, the heating elements are always hotter than any set point temperature while ramping or at a soaked condition.  

Different gas pressures and different gas selections (e.g., nitrogen, argon, hydrogen, helium) affect the amount of heat loss, which may greatly vary. The greater the heat losses, the higher the percentage of heating power output must be to maintain the set points. One should give great consideration to the fact that, if you run your production cycles in partial pressure, you may wish to consider running your SAT and TUS in partial pressure as well. The reasoning behind this is based on the possibility of the parts being exposed to far greater radiation, which is due to the higher percentages of power being utilized to compensate the gas's effect on heat loss from the hot zone. In order to properly measure the results, you would need to run testing in both vacuum and partial pressure. You may find a vast difference in the results, which is mainly due to the thermal dynamics caused by the heat loss and greater element watt densities.  

Although AMS 2750 has yet to define a solution, hopefully, the committees in charge of reviewing the specification will address this in the future. We believe a best practice in this situation is to perform a SAT and TUS for both vacuum and partial pressure and save the proper adjustments in the control system. Then, you would switch between hard vacuum and partial pressure cycles all within one furnace, depending on your load configurations, without the risk of overheating parts. Ipsen's advanced controls systems are currently designed to accommodate for these and similar changes. Call us for more details at 800.727.7625.

Putting it All Together
Optimizing your thermal processing equipment starts by, first, understanding your process and production needs. Then, you need to research the proper furnace type to meet those needs. Finally, it is important to be informed about the advanced controls technology available so you are able to make an informed decision on how you will measure, operate and analyze your equipment; thus, allowing you to best determine how to refine your process and meet the requirements of any applicable industry specifications. The controls upgrades in this article merely scrape the surface of the options available. Streamline your processes today to stay ahead of the curve and save critical time and money by taking advantage of our customizable systems, all of which can be tailored to provide the necessary solutions and meet your specific objectives. To learn more about the advanced controls options available to you, see Engineered Components or call Nathan Durham at +1.815.332.2582 for a quote today.

Fig. 7. Ipsen representative updating a customer's custom control cabinet.

Are You in the Know When it Comes to the Recent Revisions to AMS 2750 rev. E?  

Now you can run your TUS with a load or a survey fixture.   

AMS 2750 revision E, section 3.5.10.1 allows for either the use of a standard nine-point fixture method, which is acceptable for most customers, or, for those with complex geometry parts, special processes or unique load configurations, TUS can be done using a test load to truly emulate the production environment.   

Heat sinks are now allowed as a viable option during TUS.  

AMS 2750 revision E, section 2.2.24 now states that heat sinks can be used during a TUS. Section 3.5.10.1 defines minimum and maximum parameters for acceptable heat sink diameters.   Heat sinks allow for a far better emulation of the production environment because, like the heat sink, the parts will not reflect high and low PID (Proportional Integral Derivative) fluctuations. When used properly, heat sinks merely serve as optical filters, averaging devices that accurately depict the production environment of the parts.  

AMS 2750 revision E requires that you keep all thermocouple correction factors (error deviations) on hand for data conversion.   

Section 3.1.2.2.6 requires that, for each calibration temperature, you must be able to provide the correction factors. Ipsen's control software has an intuitive screen where users can enter the correction factors for all of their work thermocouples and control thermocouples so that the printed and historical data being recorded is automatically corrected, enabling users to store and print real-time data.

Type K thermocouples are no longer accepted as resident SAT thermocouples.

AMS 2750 revision E, section 3.4.5.2.1.1 outlines that when a SAT is required in order to validate control thermocouples of type S or R, a resident thermocouple of type B or N is allowed. Type K thermocouples are no longer accepted as resident SAT thermocouples if operating above 500° F. It is important to also consider the maximum operating temperature of the furnace, noting that any cleanup cycles that run above 2,400° F will compromise a type N thermocouple. Many customers utilize a type B thermocouple as the resident SAT thermocouple eliminating the need to verify temperature conditions as with the type N.  

For non-resident thermocouples, type K is still acceptable for SAT use. Figure 1 of AMS 2750 revision E clarifies SAT and TUS sensor time tables and notes a few changes from the previous revision, D, of AMS 2750. Additionally, Footnote 1 below Figure 1 makes mention of the insertion depths of type K or E SAT thermocouples being equal to or greater than any previous use each time an SAT is run. Many continue to utilize type K thermocouples as non-resident for SATs and then discard them after one use as not to have to record and track immersion depths. Others utilize a type N expendable non-resident SAT thermocouple since there is no issue with recording the insertion depth; the length of use is solely based on times at temperatures as mandated within AMS 2750 revision E.  

Process items never before covered by AMS 2750 have been added to the new revision. 

General new additions to the AMS 2750 specification now include oil quench, deep-freezing and salt bath systems. If you are using these processes, be sure to check the new revision to be sure you are compliant.

Download the Advanced Controls technical paper (PDF)