Operating costs are one of the primary concerns for every manufacturer looking for ways to increase their bottom-line revenues, and for producers of critical parts like forgings there is a constant effort to identify, contain, and minimize operating costs. In forging operations, billet and bloom heating is an essential process, one that must be optimized in order to maintain process efficiency.
The main cost considerations in forging are billet and/or bloom reheating, labor, and maintenance. The evaluation of the forging process should be total cost of ownership (TCO), taking into account both the capital investment and ongoing costs associated with the operation. In an ever-more competitive global environment for both closed-die and open-die forgings, automation combined with synchronous flow manufacturing offers forgers the opportunity to drive down costs. Such techniques combined with improved and more fuel-efficient combustion systems, and higher order Supervisory Control (SCADA)/Level II Automation, will create an environment of lowest TCO, and allow a U.S.-based forger to competed effectively with forging suppliers from India and China. While we recognize that open die Ingot Forging plays a significant role in the overall forging business, this article will concentrate on the potential for automation in the Reheating of Billets and Blooms with application to both closed and open die forge shops.
Heating as a Continuous Process
In forging operations, automation systems that manage loading and unloading of batch and continuous forging furnaces may incorporate flexible loading schemes that accommodate a range of billet and bloom sizes, reducing fuel consumption, maintenance and labor costs. By integrating these systems to create a continuous manufacturing process, losses in time and temperature can be minimized.
The design of an automated furnace cell must address several critical factors, but the method for conveying billets and/or blooms through the furnace is the main consideration. There are numerous methods of continuous conveyance for billets and blooms in forging reheating applications, including walking beam/walking hearth, rotary furnaces, pusher furnaces, and slot furnaces.
Rotary furnaces have proven to be a very reliable, rugged way to heat multiple billet and/or bloom sizes. Incorporating a dedicated robot into a rotary furnace cell will optimize loading in a way that is repeatable and accurate. This produces programmed movement within the cell that can be optimized further for transfer speed and cycle time.
Continuous heating usually involves a larger furnace system designed to incorporate a customer’s current or future product mix. Often, a continuous furnace can replace multiple batch furnaces to reduce the amount of labor required to tend each furnace. Automated loading and unloading, with billet de-bundling systems and integrated robotics, will reduce further the manual labor requirements.
Similarly, a continuous furnace system will reduce the amount of fuel required to process the same amount of product that would be processed in multiple batch systems. Some of the efficiencies that can be achieved by continuous heating are easy to recognize.
By design, a continuous furnace is engineered to achieve greater fuel efficiency in comparison to a “slug-fed” batch furnace. Some of the efficiencies that can be achieved by a continuous furnace system are easy to recognize: Door opening losses can be minimized, for example, and the thermal recovery time to reestablish the optimal heating temperature is much less of a factor and results in net savings in energy consumption.