Control System Improves Heat-Treating Precision
IIT Research Institute's (IITRI) Thermal Processing Center (Chicago) is a unified technology center capable of performing manufacturing research and development projects for aerospace precision-gear and similar industries. The research and development facility wanted to upgrade its process control to a tighter control system that was capable of data tracking and security and that was more reliable and accurate than the one that was in place. Data collection and analysis is key to subsequent commercial implementation of the developed technology at IITRI's heat-treating facility.
The IITRI project involved upgrading process-control equipment on several furnaces, a gas generator and a cryogenic treatment unit-control equipment that was state-of-the art just a few years ago according to IITRI heat treating facility manager Joseph Shenosky. IITRI's objectives included:
- Improving temperature and process control
- Installing and using the best available technology for present and future R&D projects
- Providing process recipe and set-point scheduler functions
- Developing a control algorithm using real-time gas analysis data
- Having the capability to meet future customers' thermal processing requirements
IITRI's goal upon completion of the project was to have a showcase environment to help perform and sell R&D projects to prospective customers in both the government and commercial arenas.
To meet IITRI's stringent requirements, the control system had to have the following capabilities:
- The hardware and software system had to be compatible with the facility's existing plant floor equipment
- The improved control schemes had to reuse existing sensors and actuators
- The control equipment had to provide unlimited data storage and access to variables both during and after project completion
- Data had to be accessible in spreadsheet and trend format with back-up on a mirror hard drive, on CD-RW and as hard copy for client and internal use
- Process data and variables had to be accessible from offices in Chicago and remotely over the Internet via modem
- The system had to have data security functions to restrict access to sensitive information
- The software had to be operator-friendly for configuration and customization
- The equipment had to have the ability to integrate other measurement and testing equipment into a common database and control scheme
The control-upgrade plan selected by IITRI was that of Thermal Control Systems Inc., (Thercon) of Monee, Ill., a furnace designer and systems integrator in the heat-treating industry. The initial plan specified the incorporation of Honeywell UMC800 multiloop process controllers, Honeywell UDC3300 single-loop controllers, Honeywell VRX180 paperless data recorders, a multigas analyzer and a computer station. IITRI later changed its requirement for the gas analyzer, preferring to incorporate a laser gas analyzer developed by Atmosphere Recovery Inc., (ARI) of Plymouth, Minn., for use in monitoring heat treating process and control applications. ARI's analyzer is capable of simultaneously analyzing eight different gases relevant to the carburizing/ carbonitriting heat treating process. Thercon developed a scheme to integrate the laser gas analyzer into UMC800 multiloop controller. The modular control approach permits upgrading PC software and individual control instruments at a later date without affecting the integrity of the overall system.
The primary goal of the project was to provide a control system having local PID control at each furnace and networking capabilities that permitted interface and data acquisition from the PC station. The UMC800 multiloop controller having set-point recipe capabilities was selected for its ability to perform process control on multiple furnaces with up to 16 PID loops of control. All IITRI's furnaces and its gas generator use multiple control loops for temperature and process gas control. The UMC800 also is capable of providing loop control of the process control gas valves.
The UMC's Control Builder graphic programming software, alarms, diagnostics, set-point scheduling, data acquisition and many other features made it the preferred choice for use in the process-control application. The UMC Local Operator Interface allows for local control through preformatted display screens, which makes it easy for the operators to use. The Operator Interface also has a disk drive that allows for redundant backup of process data and provides the ability to quickly upload/download the configuration program. In addition, the laser gas analyzer could be integrated into the UMC800's carbon control algorithm.
For temperature control on the temper furnaces and cryogenic treatment unit, the Honeywell UDC controllers were selected together with new logic control for all control functions. These controllers provide up to two loops of control, alarms, local operator interface and set-point programming. All of IITRI's existing furnace sensors and actuators were reused.
IITRI's customers require certification of all heat-treating equipment. The VRX180 paperless recorder including an LCD video display was selected to record process data. The recorder is used on a moveable cart with plug-in jacks to an Ethernet connection at any of the control equipment. The recorder provides operator interface and network interface for up to 24 thermocouples during temperature uniformity surveys of the heat-treating equipment. The paperless recorder provides the benefit of eliminating the need change paper and pens regularly, as all the data is saved on an integral disk drive. The information on the disk is saved in an encrypted format to ensure secure and tamper-proof information.
The IITRI project presented several programming challenges. The facility's equipment came from various vendors having different addressing and communications protocols. It was imperative that all of the heat-treating equipment could operate independently, so if any individual piece of equipment failed, the rest of the controllers would continue to operate without interruption. The human-machine interface (HMI) software had to have the capability of communicating (read/ write) with the OPC server, instruments and valves. Because IITRI is a research and development facility, the software and instrumentation also had to have the capability to be reconfigured to perform customized testing. The process-control scheme that was installed addressed these challenges while allowing for simplified future expansion of the control scheme.
The control system upgrade has resulted in increased control accuracy and temperature uniformity. IITRI's integral quench furnace is now capable of uniformity in the range of I3?F (I1.5C) at operating temperatures between 1400 and 1700F (760 and 930C). IITRI's facility manager noted that a uniformity of I10F (I5.5C) is considered to be precision heat treating, so the I3F uniformity being achieved using the new control system offers "better-than-precision" heat treating.
IITRI can now test traditional and nontraditional process gas mixtures. Simple reconfiguration of the UMC 800's control algorithm permits running tests to exactly match a customer's requirements. The laser gas analyzer provides precise and rapid analysis of eight process gases to accuracy levels of less than 0.25% of full scale. Infrared and other methods of process gas analysis do not match the real-time gas analysis capabilities of the laser gas analysis (LGA). LGA also permits implementation of advanced real-time control schemes.
The accompanying Citect data acquisition software and programming configuration permits collecting virtually unlimited data on all variables relating to the heat treating of particular loads. The data can be recorded and compiled in any format that meets IITRI's or its customers' requirements. All current and historical process data can be accessed and analyzed from either the PC station in Chicago or remotely via the Internet.
The upgrade also allows IITRI to develop production procedures to minimize process cycle times and maximize metallurgical properties.
The UDC3300 controllers were field-upgraded to incorporate Honeywell's Health-Watch diagnostic software. The software increases productivity and reduces downtime and maintenance costs by triggering an alarm in the controller when it detects a problem with the process, thereby avoiding a shutdown.
For more information: Contact Fred Vodde, Honeywell Control Products, 1100 Virginia Dr., Fort Washington, PA 19034; tel: 215-641-3798; fax: 215-641-3599; e-mail: firstname.lastname@example.org