Understanding Drop Bottom Furnaces

When it comes to industrial heat treatment furnaces, drop bottom furnaces offer a unique design and functionality well-suited for certain applications.

Also known as a drop hearth furnace, this type of furnace allows the hearth or flat surface that the materials rest on to literally drop down, facilitating easy loading and unloading of large or heavy workpieces. In this blog post, we’ll explore what makes drop bottom furnaces distinct and the advantages they provide.

Drop Bottom Furnace Design

The key defining feature of a drop bottom furnace is the movable, dropping hearth in the heating chamber. The hearth is suspended and supported by a frame that allows it to hinge down, opening up the furnace chamber for loading from the top using an overhead crane or other materials handling equipment.

The dropping hearth is counterbalanced and can swing down to create a clear opening for charging the furnace. Once loaded, the hearth swings back up and re-seals against the furnace casing to contain the heating chamber. The furnace can then ramp up to the desired heat treatment temperature using gas, electric, or fuel-fired heating methods, just like any other industrial oven or furnace design.

After the heating cycle is complete and the load has soaked at temperature for the required dwell time, the load can be easily removed by again dropping the hearth and using an overhead crane or specialized equipment to lift out the treated parts from the top of the open chamber.  

Applications for Drop Bottom Furnaces

The ability to easily load and unload heavy, awkwardly-shaped, or extremely large parts from the top of the furnace makes drop bottom designs ideal for heat treating the following types of workpieces and materials:

– Large castings, forgings, and formed parts

– Long shafts, cylinders, pipes, and rods  

– Bulky tool and machine components

– Hot stamping dies and tooling

– Heating heavy metal billets for forging or rolling

– Stress relieving large fabricated weldments and structures

Drop bottom furnaces are commonly used for heat treatment processes like normalizing, annealing, tempering, solution heat treatment, age hardening, and stress relieving. They allow heating large loads uniformly from all sides. Certain drop hearth furnace designs can even tilt the hearth at an angle to drain off liquids or molten materials.

Key Advantages of Drop Hearth Furnaces  

In addition to the inherent advantage of simplified top loading and unloading, drop bottom furnaces provide several other benefits including:

Safety – Top loading eliminates the need for furnace operators to reach into a hot chamber, reducing burns and injuries. Heavy loads are handled with cranes rather than manually lifted.  

Floor Space Savings – The furnace footprint only needs to accommodate the hearth size since loading is done vertically from above. This can save valuable floor space compared to front-loading furnace designs.

Uniform Heating – Heating is applied evenly from all sides of the load on the hearth, allowing consistent heat treatment results.   

Large Capacity – Because of the open top loading design, drop bottom furnaces can easily handle extremely large and heavy loads with ample hearth space. Capacities from 5 tons up to 100+ tons are available.

Whether it’s heat treating massive steel castings, age hardening aluminum parts, or stress relieving large weldments, drop bottom furnaces offer an effective heating solution tailored to processing heavy, oversized workpieces safely and uniformly. Their vertical top loading functionality is a major advantage for many industrial heat treatment applications.