Drop Bottom Furnaces: The Traditional Powerhouse of Aluminum Heat Treatment

In our previous blog, we explored the science behind solution heat treating aluminum and how a precise balance between time and temperature is required to achieve optimal aluminum alloy properties. In this next installment of our blog series, we will focus on the traditional powerhouse of aluminum heat treatment: the drop bottom furnace. We will explore how they operate, the advantages, and what to consider when choosing a drop bottom furnace. 

The Drop Bottom Furnace: A Tried-and-True Design

One of the most traditional pieces of equipment for solution heat treatment is the drop bottom furnace. This workhorse of the industry boasts a simple yet powerful design that consists of an elevated furnace with a door at the bottom (or two opposing doors) and a quench tank that sits beneath the furnace on a movable platform.

How Drop Bottom Furnaces Work

1. Loading: The aluminum parts, often loaded in baskets or on a grid, are lifted into the furnace chamber through the bottom doors using a hoist system that runs vertically through the roof of the furnace.
2. Heating: Once the load is raised into the chamber, the furnace is sealed, and the heating process begins. Precise temperature control is crucial, as discussed in our previous blog.
3. Quenching: Once the optimal temperature and soak time are reached, the bottom doors rapidly open, and the load is quickly lowered into the quench tank below. The goal is to achieve a fast, controlled quench.

The Need for Speed: The Advantage of Drop Bottom Furnaces

The primary advantage of drop bottom furnaces is their exceptional quench speed. Quench time is the interval from the moment the furnace doors open to when the load is fully submerged in the quench tank. This rapid quench, often achieved in as little as 5-10 seconds, is essential for maintaining the part temperature until it is submerged.

Key Features When Choosing a Drop Bottom Furnace

Selecting the right drop bottom furnace for your aluminum solution heat treatment process impacts the quality of your finished parts and your operational efficiency. Let's explore some key features to consider during your selection process:

• Temperature Range and Uniformity: Make sure the furnace can achieve the required temperature range for your specific aluminum alloys. Pay close attention to temperature uniformity specifications – tighter uniformity means more consistent heat treatment across your entire load. The furnace manufacturer should test and validate the results prior to shipment.
• Quench Speed and Delay: Be sure the furnace has the proper quench delay (time from when the door starts to open until the load is fully submerged) for the loads you are processing. Thicker cross-sections such as heavy castings, can generally tolerate a longer quench delay (15 to 20 seconds or longer), while thinner materials such as aluminum sheets, require 5 to 7 seconds. 
• Heating Options: Consider your facility's infrastructure and choose a furnace with a heating method that aligns with your needs – electric, direct gas-fired, or indirect gas-fired. Some alloys require that no products of combustion, which are created by industrial burners, come in contact with the load. If that is the case, you will need an electric heated, or indirect gas fired design (where the burner fires through a heat exchanger).
• Control and Automation: Drop bottom furnace manufacturers offer sophisticated controls and automation capabilities. Look for features like programmable temperature controllers, data acquisition systems, and even fully automated operation for maximum control and efficiency.
• Industrial IoT: The leading furnaces manufacturers will offer an industrial IoT system for your equipment, to allow real-time remote problem diagnosis, and preventative maintenance.
• Quench Tank Design: The quench tank plays a significant role in the process. Consider factors like tank agitation, capacity, and the ability to add cooling, heating, or filtration systems as needed. Due to the extreme weight of a loaded tank, they often use rail car wheels and travel on railroad tracks.
• Construction and Durability: Choose a furnace built with high-quality materials and robust construction to ensure longevity and reliability. Features like a stainless steel interior and maintenance-free door seals can significantly reduce downtime and maintenance costs. Avoid furnace interiors with exposed insulation, as it can absorb steam during the quenching operation and degrade over time. The interior should be cladded with sheet metal.
• Compliance and Safety: Ensure the furnace meets all required industry standards and safety regulations, such as NFPA86, NFPA 79, and the mil specs that apply to your material, such as AMS2750, AMS-2770, MIL-H-6088, and others.
• Customization Options: Every heat treatment operation is unique, so it is important to consider the availability of customization options, such as load baskets, auxiliary hoist, catwalks and ladders, polymer quenching systems, and more, to tailor the furnace to your specific needs.
• Manufacturer Reputation and Support: Choose a reputable manufacturer with a proven track record in the industry. Excellent customer service and technical support can be invaluable throughout the lifespan of your furnace. Make sure they have their own field service personnel, and offer installations, service, and repair.

By carefully considering these features, you can select a drop bottom furnace that meets your specific requirements, delivers exceptional performance, and helps you achieve consistent, high-quality results.

Wisconsin Oven Drop Bottom Furnaces: Reliability & Performance

With a focus on innovation, durability, and customization, Wisconsin Oven's drop bottom furnaces are an excellent choice for a wide range of aluminum heat treatment applications. Whether you're processing extrusions, sheet metal, castings, or other components, our drop bottom furnaces offer the precision, performance, and reliability you need to achieve superior results. Contact us to learn more about our drop bottom furnaces. Interested in seeing a Wisconsin Oven Drop Bottom Furnace in operation? Click the link below:

Our Next Blog: The Modern Alternative: Horizontal Quench Systems

While drop bottom furnaces are reliable workhorses, they do have drawbacks in terms of space requirements and upfront cost. In our next blog post, we'll cover the modern alternative: horizontal quench systems. Stay tuned!