This modernized basketless rotary-hearth furnace is based on similar design characteristics as its predecessor but integrates multiple carousel levels as a means of increasing the system capacity.
Basketless Heat Treatment System (BHTS)The patent-pending BHTS can be oriented in a side-by-side layout to accomplish both the solution treatment and artificial aging processes. A major advantage of this arrangement is that individual aluminum products can be placed into the rotary systems, eliminating any need for part-conveying baskets. A flexible robotic handling system transfers the product in a singular part-flow manner from the charging table and into one of the various solution-furnace carousel levels. Castings are appropriately positioned within the carousel and placed into the furnace. The carousel ensures each part is properly supported and receives uniform recirculating airflow during rapid ramping and soaking stages of the processes (Fig. 1).
Furnace Design Characteristics
A centrally located, axial-flow fan recirculates large volumes of heated process air to each carousel level. A distribution baffle directs high-velocity forced convection air through the work chamber and back into a plenum, where it is reheated and reintroduced into the work chamber. The carousel is supported by a base that rotates within the cylindrical shell.
Designed and manufactured to support product families of similar geometry, the carousel is easily modified to process different products. Product features are carefully considered during the design of the furnace system to ensure they are properly supported to prevent damage or distortion. The carousel design integrates a structural frame capable of supporting the product’s mass at processing temperature. The base is fitted with an easily accessible drive system that provides the carousel rotation external to the hot chamber. Communications between the drive and carousel sensors control each rotational position, ensuring accurate part positioning.
Each hearth level is accessible via an independently operated door system. Door opening and closing, carousel rotation and robotic handling are all controlled and verified via a central programmable processor (Fig. 2). Inspection of the system is provided via access doors positioned in the upper and lower shell sections. In cases where residual foundry sand remains within the casting prior to heat treating, a simple sand collection and discharge process has been integrated into the system. Singular part flow simplifies quenching so that the system is smaller and can be mounted at floor level, eliminating the need for foundation pits and ancillary facilities.
Quench System Improvements
Furnace designers have typically struggled with the development of uniform quenching systems for integration with conventional batch or roller-hearth heat-treatment systems. This is largely due to the dense loading practices observed, variations in loading consistency, basket misalignments and limitations in delivering the quench media in a uniform and reliable method. Development engineers understood that quenching of aluminum engine castings is one of the most critical processing steps and a dominant area for the creation of residual stresses. This understanding led to the development of an improved quench system that could be integrated with their current BHTS. The objective was to design a system that provides improved quenching uniformity and flexibility for processing various components.
Following the development testing, new quench methods were made available to manufacturers of cast engine blocks and cylinder heads. These new methods offer a combination of benefits over traditional technologies. The primary improvements include the individual part quenching of castings for both conventional basket applications and basketless processing methods. As a result of the individual-casting quenching capability, significant quenching uniformity improvements were realized across the casting’s various sections. This is achieved through independently controlled and monitored quench distribution nozzles. These quenching systems integrate in-situ process monitoring and closed-loop feedback to ensure the uniform distribution of quench media.
Quench systems for integration with BHTS provide added benefits over conventional basket-type quench systems. The most significant benefit relates to the reduction of system size. This is accomplished by the piece-by-piece handling of castings through a more efficiently sized system. In general, a BHTS-style quench system can be floor mounted, eliminating the need for costly pits and added infrastructure. The recirculating, heating and cooling systems are sized more efficiently for continuous steady-state operation versus the mass loading associated with basket-type quench systems. The quench-media temperature can be controlled within a tighter band, improving the part-to-part uniformity, which contributes to improvements in product quality CpK values.
The integration of these new quench developments has created a number of new opportunities for further improvements to the quenching-system designs. These new concepts are opening doors for the development of hybrid quenching technologies that provide gradient quenching using a combination of quench medium.
System BenefitsEnergy Consumption, CO2 is Reduced
Eliminating baskets has greatly reduced electrical usage and energy consumption required to process parts. Manufacturers have experienced a 40% minimum reduction in fuel consumption when compared to similar solution-treated and aged components processed in a conventional roller-hearth system. As a result of reduced fuel consumption, CO2 emissions are also reduced.
Savings on Spare Parts and Maintenance Requirements
The simplified part conveyance concept reduces the drive system’s quantity and complexity when compared to maintenance-intensive roller- and chain-conveying systems employing internal moving components. Part positioning within the system is held constant through the use of external conveyance, eliminating part movement within the furnace. The reduction in conveyance, recirculation and burner components reduce the spares inventory as well as operator and maintenance involvement. Recent systems have demonstrated a 75% reduction in mechanical component requirements when compared to roller-hearth or chain-conveyor heat-treatment systems.
Greater Uniformity and Enhanced Quality
Single-part processing has improved product quality by reducing the temperature profile spread over densely loaded basket systems and by optimizing quenching. Through improved quenching uniformity of part-geometry castings, mechanical property Cpk results are improved by 10-20%.
Improved Process Times
Another equally important benefit of single-part processing is the reduction in cycle times. Individual-casting handling reduces the time required to bring parts to solution and aging temperatures. These process improvements allow manufacturers the ability to better tune their process to provide the optimal combination of cycle time and productivity. Testing has demonstrated that reduced heat-up profiles have been reduced up to 20%.
Reduced Expansion Costs
Manufacturers no longer have to provide a long linear system to achieve the same soak time required to process aluminum castings. The cylindrical and compact design of the BHTS has reduced floor-space expansion costs and reduced furnace volume by up to 30% over a conventional roller-hearth layout.
Quenching Flexibility, Consistency and Efficiency
The system allows for different quenching media to be employed depending upon the required outcome. Engine blocks and cylinder heads can be processed with the integration of water, precision air quenching and hybrid quenching. Quenching-system efficiencies are improved through the development of smaller systems that run at steady-state conditions versus batch systems that are cyclic and prone to variation.
Lastly, work in process (WIP) inventories can be reduced, enhancing lean-manufacturing processing. Manufacturers of aluminum castings and formed products now have an alternative when evaluating new capacity requirements. The improved efficiencies of the BHTS can greatly assist manufacturers to overcome industrial competition and ensure profitability.
ConclusionsManufacturers of mass-produced cast-aluminum engine blocks and cylinder heads can take advantage of the quality and cost benefit improvements that can be realized through the use of new basketless heat-treating and quench technologies. Can-Eng Furnaces has commissioned multiple systems for manufacturers of high-volume aluminium-intensive automotive products. These users are exploiting the numerous benefits of this efficient Basketless Heat Treatment System over conventional linear roller- or chain-conveying systems.IH
For more information:Contact Tim Donofrio, product manager, Can-Eng Furnaces International Limited, 6800 Montrose Road, Niagara Falls, ON Canada L2E 6V5; tel: 905-356-1327; fax: 905-356-1817; e-mail: tdonof firstname.lastname@example.org; web: www.can-eng.com
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