Today, there are more furnace control choices and options available than ever before. With the continued improvement and advancement of controller features, the end user has much to consider when choosing a control system for a new furnace or retrofitting existing equipment. From everyday operation to long-term data storage and system complexity, costs will vary as much as one can imagine in functionality. This article focuses on a few examples with some features of the most commonly requested systems implemented on furnaces today.
Common control systems
The most common, popular scheme for furnace controls includes implementing an Allen-Bradley PLC and PanelView Plus operator interface to control process and cycle functions. Industry standards, reliability and familiarity with the hardware and software give a level of comfort to end users, as well as original equipment manufacturers (OEMs). This approach also allows for the greatest flexibility in furnace options to be added to the control system. More often than not, no two furnaces are exactly alike. A control system that provides the most flexible interface to the furnace functions becomes the most "operator" friendly and easy to use.
In addition to the OEM supplied systems using off-the-shelf hardware and software, there are dedicated controls suppliers to choose from that are geared toward the heat treating industry. There are a variety of advantages to each supplier's products including a compact line with internet interface technology; a wide line of oxygen probes, single loop temperature and carbon controllers; as well as multi-loop process controllers.
Controllers have a limited lifespan due to component failure or planned obsolescence. It is not uncommon for a furnace to outlive its controls many times over. As control systems age, replacement components become harder and more expensive to get from vendors. Companies also have to compete for market share by pushing the latest and greatest and obsoleting the old. As seen in the home computer market, electronics continually advance and obsolescence is inevitable. With new features and improvements in technology, the benefits of new controls eventually float to the surface and a choice has to be made. Users must ask themselves what is the best, most reliable system they can get that will maximize the return on their investment?
Standardizing controls
Surface Combustion has standardized on nonproprietary Allen-Bradley hardware based on the above rationale. The most common example is the PLC/CASEmate®, which is the control system for the Surface Allcase® batch integral quench furnace. It is an evolution of Surface's original proprietary CASEmate process controller, and includes both process and automatic furnace cycle control. The operator interface provides an easy to use functionality with the familiar layout of the traditional CASEmate controller. An operator can easily adjust to the four-segment recipe and recognizable screen layout. The color touch screen provides quick access to make changes and jump from screen to screen.
In addition to the furnace controller, it becomes advantageous to add a Supervisory System such as Surface's Heat Treat Management (HTM™) software to work with the furnace controllers. By networking all of the controllers to a computer on a supervisor's desk or on the plant floor, load scheduling, viewing current furnace conditions and permanent data storage can enhance the efficiency of furnace line operation. Loads can be created in HTM software and scheduled for a particular furnace. When the load is ready to be run in the furnace, the operator simply enters the load identification number and the correct cycle recipe is run. After a load is completed, a report can be generated identifying the part and the actual process data during the cycle. Other than just the specific load data, reports for furnace utilization, total pieces run and production in pounds per hour can be generated to help recognize efficiencies in production.
Case studies
Specialty Heat Treating Inc. is a commercial heat treater specializing in high quality, precision vacuum processing, as well as quality conventional atmosphere processing. Specialty also offers special handling, parts washing and sorting services and also specializes in stainless steel, as well as tool and alloy steels. Specialty, with facilities in Grand Rapids and Holland, Mich. and Elkhart, Ind. has a variety of Surface's proprietary furnace controllers including CASEmate, TEMPmate®, Autocarb® and DATAVAC® on Allcase, vacuum and temper furnaces. The controllers are all networked to Surface's Trend Alarm Log (TAL™) software package. When Specialty recently decided to start replacing units on existing furnaces, it was time for a choice to be made. With multiple furnace lines at different plant locations, updating all the units had to be considered in steps. Both existing and new controllers are connected to the Surface network for communication to the TAL software. The TAL software has been indispensable for identifying furnace problems and troubleshooting those "unexplainable events in the night". The system provides permanent data storage for retrieval at a later date. If process information is required for a load that was run, a historical graph can be generated for that time. If the load identification number feature is enabled, process information for that load can be retrieved by simply searching by the ID number assigned.
National Metal Processing (Richmond, Ky.) has been performing commercial heat treating services since 1969. National Metal specializes in high volume automotive commercial heat treating services and other manufacturing sectors. National Metal recently installed an Allcase line to compliment its existing batch and vacuum equipment. The new furnace line at NMP is outfitted with the latest furnace controls. The Allcase batch integral quench furnaces along with the Uni-DRAW® and P/M Uni-DRAW batch tempering furnaces are outfitted with PLC based controllers. The Uni-DRAW, P/M Uni-DRAW and Allcase furnaces are networked via Ethernet to a central supervisory computer with the HTM and TAL software packages.
National Metal Processing also uses a bar coding option with HTM. Loads are scheduled with the parts and desired recipes in HTM and a load card is printed out and queues a load of parts to be built by an operator. The load card travels through the heat treat shop with the load of parts. A barcode on the load card is scanned at the Allcase and P/M Uni-DRAW furnaces. At that time, the controller downloads the part and recipe information from the HTM computer. The operator quickly verifies the process control number on the screen and runs the cycle. If the number of parts is different, the operator can edit the part count field for the actual number being processed in that load. Ideally, the bar coding feature is a tool to improve operational efficiency and prevent operator error, and the risk of running the wrong cycle in the wrong furnace is eliminated. Parts can be assigned to be processed in certain furnaces, and once the load card is generated, the HTM computer is in charge of the recipe being run. The operator's job is to get the load into the furnace, scan the load card, initiate the cycle and remove the load to get it to the next step of the process. The HTM/TAL software package utilizing bar code entry adds another level of control to ensure error-free processing.
In addition to conventional atmosphere batch integral quench furnace control, Surface provides a similar system using the PLC and PanelView Plus for vacuum equipment. The vacuum equipment can be configured to be either single chamber, two chamber or three chamber batch systems. All functions are controlled including cooling rate, quench temperature (if applicable) and transfer time. Likewise, vacuum tempering equipment can be controlled by PLC TEMPmate controls or Multipoint TEMPmate systems. All systems likewise link into the network computer.
These examples include some of the most common solutions to control systems having a networked supervisory computer. Another level of complexity can be added to the above systems for complete automation of a batch integral quench line to increase efficiency and productivity and reduce process errors. Automation can be defined to include a few or all furnace functions into one system. In the discussion, automation is defined as the complete heat treat cycle through a batch integral quench furnace line from the time a load is assembled to the time it is disassembled. As noted above with the HTM supervisory system, a load is created at the computer to be processed, and the operator builds the load, enters it into the system and places it on a charge table. There is no load card to travel with the load. The system takes care of moving the load to the correct furnace, loading the recipe into the controller and cycling the furnace. After processing the load through the line, it is left on the discharge table for an operator to disassemble. All process data is stored in the supervisory computer or on a central server, and reports can be viewed and printed for a particular part or load as desired.
Considering all of the above, the goal is to plan and choose a system that ultimately meets the needs of day-to-day operation of your facility. Ask yourself, what features are the most important to your operation and how much can you afford? The more advanced a system that is required, the greater the initial investment. The return is ease of use, elimination of operator errors, and making the heat treat as efficient as possible. IH