The current state of the art for industrial heat-treatment furnaces and related ancillary equipment (quench equipment, atmosphere generators, etc.) traces much of its origins to World War I, where the demands for high-volume equipment necessitated larger batch and continuous furnace systems. As furnace manufacturers met those needs, the basis for much of the field empirical data was established, leading to sizing standards for each manufacturer. The biggest risk for any equipment manufacturer is to either oversize or undersize the furnace/quenching system. The former leads to excessive estimates that will almost certainly result in a lost contract. The latter produces equipment that does not meet the needs of the customer – a completely unacceptable outcome. Furnace manufacturers are being asked to meet ever-tightening requirements in a number of areas, and the general factors that are driving those changes are as follows:
- Production capacity
- Temperature uniformity
- Mechanical properties
- Level II automation with plant interface
- Reduced energy consumption
- Part dimensional stability
- Shortened processing time
Production CapacityWhen Can-Eng (manufacturer) entered into the mesh-belt hardening-furnace business in the late 1980s the equipment capacity of competitive rotary retort/shaker equipment and Japanese-supplied mesh-belt furnaces was in the order of 500 lbs/hour. In addition to the low production capacity, there were other drawbacks including part damage. Almost immediately, the manufacturer identified the need for higher-volume equipment, and the first commercial systems sold by the firm were 1,500 lbs/hour. More recently, Can-Eng has supplied equipment that meets 8,000 lbs/hour of neutral harden, quench and temper capacity. This is a 16-fold production-capability increase in the past 20 years. As one would expect, equipment does not scale up in a linear fashion, and the advances required to achieve the current norms for high-volume output required significant design development.
Temperature UniformityIt would appear there is a continuing trend towards tighter temperature uniformity both on heat up, soaking (holding at temperature) and quenching. For many automotive aluminum customers, temperature uniformity of +/-5°F or better is now required, with some specifications as tight as +/-3°F. While there may be some debate in terms of the validity of these requirements, the trend is driven largely by Six Sigma programs, and this has put increasing pressure on furnace manufacturers to achieve the stated uniformity.
Mechanical PropertiesA developing trend is for end-users to ask for mechanical properties guarantees. There is some real jeopardy for the furnace manufacturer since many variables are outside of our control, including chemical composition (hardenability), cleanliness (inclusions), grain size, part design and manufacturing methods. Nevertheless, in some circumstances this is becoming a new reality.
Level II Automation with Plant InterfaceFor most installations, the days of a stand-alone furnace operating in a customer’s facility are essentially a thing of the past. Increasingly, customers want Level II automation systems that have the capability for recipe control, part tracking, process history, scheduling, alarm and maintenance notification. In addition, many customers are asking for the Level II automation system to be interfaced with their plant-management system (SAP, other). These systems alone allow the end-user to optimize their facility, increasing throughput and minimizing gaps between different lots/recipes (Fig. 1).
Reduced Energy ConsumptionWith rising gas prices and increased offshore competition from low cost countries, the demands on fuel-savings technology has never been more attractive. In the past seven years alone, projects that were once unattractive for auto-recuperative or regenerative burners now meet acceptable ROI targets. In addition, conventional processing methods such as products processed in energy-consuming baskets have led to the development of “basketless” heat-treatment systems.
These are some of the challenges that the industry is facing today, and the following will describe some practical development tools to optimize the heat-treatment process.
There are a number of computer-modeling programs available today that cover a broad range of applications, including FEA (finite element analysis), CFD (computational fluid dynamics) and heat transfer. As one would expect, the results of the model are only as good as the parameters used to calibrate it along with any supporting field data available. Can-Eng has utilized CFD modeling to our benefit on a number of jobs where the placement of baffles was critical to ensuring good fluid flow in quenching applications.
The introduction of AutoCAD some 20 years back was a vast improvement over the old board drawings and resulted in fewer interferences and errors. The latest advances in drawing technology gives our engineers the ability to draw the equipment entirely in 3-D, with direct estimates for steel weights developed from the model. Two-dimensional views are developed from the 3-D model and sent to the shop for manufacturing. Models can be directly downloaded to the shop CNC equipment so that manufacturing can proceed entirely from the electronic version. The ability to set the equipment up in 3-D gives us the possibility to further investigate both furnace and part interferences at the design stage, eliminating such problems without costly rework.
Thermocouples attached to parts do a good job at indicating local part temperature conditions. Unfortunately, there is a practical limit to the number of T/Cs that can be run on a given furnace load, and there are also some cost limitations as well. One of the newer tools that is available is thermal imaging, which is based on infrared imaging of a furnace load. The manufacturer has found this technology to be particularly useful in precision air quenching scenarios to demonstrate the uniformity of quench on a real-time basis.
Empirical Field Data
While the addition of modeling tools coupled with 3-D drawing has been a real improvement in furnace-system design, there is still no substitute for actual field data. Fortunately, Can-Eng has done numerous surveys on operating equipment to ensure that the customer requirements will be met. Very often this involves thermocouples embedded into parts traveling through the furnace linked to a data logger or directly coupled with a Datapaq unit that is protected from the furnace environment. Figure 8 gives actual field data from a furnace installation. Very often this data is utilized to calibrate some of the computer-modeling programs the company is using.
As discussed, Can-Eng has recognized the need for tighter customer specifications combined with higher-volume production needs, resulting in the implementation of higher-order engineering tools that allow for better furnace equipment. These tools, combined with a large inventory of empirical field data, ensure that the designs the company produces meet or exceed customer expectations on all committed deliverables. IH
For more information:Michael K. Klauck, P.Eng., is product manager – custom equipment and Tim Donofrio is product manager – aluminum equipment for Can-Eng Furnaces Ltd., P.O. Box 235, Niagara Falls, N.Y. 14302; tel: 905-356-1327; fax: 905-356-1817; email: email@example.com; web: www.can-eng.com
Additional related information may be found by searching for these (and other) key words/terms via BNP Media SEARCH at www.industrialheating.com: mesh belt furnace, Level II, rotary retort, Six Sigma, thermal imaging, data logger