Process Control & Instrumentation
FEATURE | Process Control & Instrumentation

Increasing Efficiency with Advanced Controls

July 1, 2014
Trans

Ever-increasing competition continues to push manufacturers to find new ways for reducing costs without sacrificing quality. Manufacturers (including heat treaters) in low-cost regions, which were once also associated with lower quality, have increasingly adopted newer technologies and equipment in an effort to make themselves more competitive. With improved and lower-cost heat treating available in such regions, one of the hurdles to relocating other manufacturing processes to these locations is eliminated, thus placing additional stress on domestic manufacturers. As “free-trade zones” expand, additional cost pressures are placed on heat treaters.

 

In order to be more competitive, heat treaters need new tools to reduce operating costs without sacrificing – preferably improving – product quality. Traditional tools continue to improve and maintain efficient and quality heat treating; tools like recipe controllers, “carbon” probes and gas analyzers. But these are well understood, and improvements garnered with their use are incremental. In a review of potential savings technologies, we identify two – namely advanced gas handling and new process modeling tools – that can provide significant cost-savings and product improvement opportunities.

 

Advanced Gas Handling Systems

For years, handling of protective gases used in atmosphere heat treating was done with manually controlled valves and simple rotameters. In many parts of the world, this is still quite common, particularly in Southeast Asia. Over time, heat treaters have migrated to digital controls and have extended this to flow controls where both the reading of a flow meter and the adjustment of a gas control valve are done digitally. This allows the treatment process to be more tightly controlled, resulting in higher quality and more reproducible parts. It can also reduce gas consumption by ensuring that gas-flow values are not incorrectly set or modified by an untrained operator. Today, we see the use of these digital flow meters, along with the advantages they provide, growing rapidly in emerging manufacturing markets.

    The next generation of gas handling builds on the advantages of digital meters by incorporating new features aimed at both reducing consumption of gas and providing better information about gas usage on specific furnaces.

    UPC’s “Valve-Tronic Plus” takes a traditional digital rotameter and adds a sophisticated computer, complete with a built-in web server and mathematical routines that make the meter far more accurate than traditional digital meters (Fig. 1). By means of either MODBUS/TCP communications or simply by logging in to the meter using a standard web browser, the user now has access to the meter parameters and a variety of features that are not possible on traditional digital meters (Fig. 2). For example, this new generation of meters uses its computer to provide a built-in gas totalizer that can tell the user exactly how much has flowed through this meter since the last reset of gas flow. This can even be converted to a monetary value, so a user could, for instance, log how much money the gas for each furnace costs per week.

    Building on similar concepts, the “AccuBlender” is a new system for endothermic gas generators that can automatically change the amount of gas being produced in response to demand changes from the furnaces (Fig. 3). Using a pressure transducer, the AccuBlender senses any rise or drop in generator output pressure caused by decreased or increased demand at the furnaces and modifies the amount of gas being produced to match demand (Fig. 4). This means that the amount of excess gas being burned off is minimized to that required to maintain positive pressure at the furnace.

 

Advanced Modeling

Hardware isn’t the only way to save money and improve product quality. Computer modeling has been used extensively in manufacturing and in heat treating. Carburizing, in particular, has been modeled by many people with varying degrees of success. The idea here is relatively simple. If one can use a computer to model their parts and process, they can develop a process to provide the correct surface chemistry without having to run test parts.

    In practice, modeling for carburizing has been a mixed bag because the part geometry and surface condition play such a large role in the diffusion process. However, these are often poorly accounted for by simple computer models.

    Newer modeling tools now allow part geometry and customized alloy compositions to be included in the modeling process. As such, the accuracy of these models – and the resultant savings from a better process and less testing – is greatly improved (Fig. 5).

    The very latest software for atmosphere heat treating adds something that has been desperately needed. Over the last decade the use of carburizing has waned somewhat in favor of nitriding, which allows materials to achieve performance on par with carburized parts with significantly less part distortion in certain applications.

    Nitrocarburizing is becoming more popular since it allows the use of low-alloy carbon steels for applications where parts are typically carburized. Both nitriding and nitrocarburizing have typically been “art forms” for processing because detailed models and understanding were limited and existed in only a few companies and people. Until recently, process modeling had limited availability for nitriding.

    Along with carburizing and nitriding, the latest models also accurately predict low-pressure carburizing and carbonitriding, two processes that have had limited availability of modeling tools until now (Fig. 6).

 

Online Modeling

Probably the most important outcome of modeling is when it can be adapted for online use. Online means changes can be made in the controller that is actively controlling the process in real time. No process achieves its recipe parameters exactly: there is overshoot, slower-than-expected ramps, furnace upsets, etc. What online modeling can do is constantly update the model for the part as it is being treated with input from thermocouples and sensors in the furnace (Fig. 7). What this means to the operator is that when the process deviates, the online model can predict the impact on the parts and then modify the process on-the-fly to compensate for the deviation. It can essentially be used for “feed-forward” control of the process in response to actual conditions.

 

Conclusion

The ever-increasing need to produce higher-quality parts with lower costs requires newer tools to reduce waste and optimize processes. By using advanced gas-handling systems, heat treaters can reduce waste and get a handle on each furnace’s gas consumption. Using process modeling for carburizing, nitriding and carbonitriding can help users develop more efficient processes. By moving them “online,” such models could be used to actively manage the process, always ensuring optimal process time, parameters and part quality. IH

 

For more information:  Yvonne H. Boltz, vice president, United Process Controls, 8904 Beckett Road, West Chester, OH 45069; tel: 513-772-1000; fax: 513-326-7090; e-mail: yvonne.boltz@group-upc.com; web: www.group-upc..com

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