SCHWING Fluidized Bed Heat Treatment
Fluidized solid beds have certain properties which are of decisive importance in practice.
The ease of operation, constant temperature and rapid exchange of heat, combined with the clean and
nonpolluting process help to reduce operating times and therefore offer substantial economic advantages.
The fluidized bed furnace is a retort furnace which uses the properties of a fluidized medium.
The retort is filled with fine-grained aluminum oxide (Al2O3). A uniform flow of fluidizing gas enters the
retort through the gas-permeable diffusion plate at the bottom, and sets the particles of the medium in
suspended motion (fluidized bed).
At the same time the fluidizing gas determines the retort atmosphere.
The fluidized medium is physically similar to a liquid. In addition the fluidization ensures uniform temperature
conditions throughout the furnace.
Rapid heating-up and uniform temperatures ensure accelerated operation and excellent heat treatment quality.
The same furnace can be used for varying heat treatment processes by changing only the temperature
setting and atmosphere mixture. Aluminum oxide, as an inert medium, guarantees the rapid transfer of heat,
the fluidizing gas and the temperature determine the type of heat treatment.
A comparison with other conventional heat treatment processes clearly demonstrates the major cost ad
The main elements of the furnace are the retort and the heating system.
The retort is heated either electrically or by gas. At the bottom is a gas-permeable diffusion plate, through
which a uniform flow of fluidizing gas enters the retort and fluidizes the aluminum oxide.
Special insulation prevents unnecessary heat loss. The furnace is loaded from above with baskets, loading
racks or individual parts or components.
Fluidized bed furnaces for neutral hardening, annealing etc. can, with the addition of a gas mixing facility,
also be used for thermochemical heat treatment processes such as carburizing, carbonitriding, nitriding or
For example, after a carburizing process, the furnace can be converted into a furnace for neutral hardening
by pressing a single button.
The rapid gas exchange in the retort allows the two processes to follow each other with practically no delay.
Fluidized bed furnaces are available in a wide range of sizes with nominal temperatures scaled accordingly.
The fluidized bed
As fluidized beds are made up of solids there is no danger of them freezing.
Aluminum oxide in the retort can be heated from minus temperatures to over 1300¡É.
The high thermal conductivity means short heat-up times, uniform temperature conditions,
and short process cycles.
7. Diffusion plate
8. Fulidizing gas
1) The fluidized bed 2) The fluidized bed 3) The fluidized bed
Fluidized bed furnaces operate with no environmental pollution.
The fluidized bed medium is nonreactive, non-toxic.
There is no danger of an explosion, even if water enters the hot medium.
When inflammable gases are used (e.g. carburizing gas) a special control system monitors the entire
Design, efficiency and safety are based on the experience gained in the construction of over 4.500
fluidized bed systems.
The same furnace can be used for the most varied heat treatment processes.
Annealing, hardening, tempering, martempering, solution annealing, secondary hardening, pre-heating,
carburizing, carbonitriding, nitriding, nitrocarburizing.
The products to be treated may all be from series production or different parts of a tool room shop.
In neutral heat treatment, pure nitrogen is used as the fluidizing gas, while carburizing is done in
a controlled atmosphere, e.g. with a mixture of methanol and nitrogen.
The fluidized bed is a future-orientated, innovative technology already conforming with the environmental
protection regulations which are becoming increasingly necessary - because calls for a clean environment
will make no exception for hardening plants.
When the costs of hardening per unit of weight are considered, the financial advantages compared to
other methods become quite clear.
The uniform temperature conditions in the fluidized bed and the high rate of heat transfer shorten
the process times.
The universal operation of the fluidized bed system allows a high level of plant utilization.
That means investment costs for fluidized bed systems can be amortized relatively quickly. Modern
microprocessor technology controls the process in the fluidized bed furnace - at the same time,
it monitors the consumption of energy in the plant.
In line with production needs, operation can be fully automatic.
The use of the latest technology combined with a well thought-out technical concept means that
only minimum service and maintenance is required to operate the furnace.
Further positive features are the short repair and down times.
Present furnace dimensions are 250 dia x 400 mm for small series, laboratory systems up to 1000 mm
dia. x 1500 mm for large production systems.
In addition continuously operating furnaces are in operation with a retort length of 10 m. e.g. for wire
Fast, uncomplicated Fluidized bed hardening, Simple loading of the Hardening a broach
gas exchange particularly suitable furnace for precision
The demands made on the properties of heat-treated components are high and constantly rising.
The required properties must be achieved as uniformly as possible not only in each individual component,
but also in an entire batch. Therefore, heat treatment plants must meet the highest demands.
Fluidized bed furnaces from Schwing's program fulfil all requirements.
Before you decide on an new hardening plant check whether it has the following characteristics :
- Extremely high temperature uniformity throughout the retort.
- No destortion in hardening thanks to uniform heating-up and cooling-down.
- Avoidance of unnecessary carburization or partial decarburization due the absolutely inert atmosphere.
- Defined carburizing atmospheres through carbon level control.
- Recording of atmospheres and temperatures
- Corrosion resistance through nitrocarburizing treatment with subsequent oxidation.
- Fully automatic process through microprocessor control.
1) Cross-section of a carbonitrided component
2) Controlled carburization in methanol / nitrogen atmosphere Ck 15, 930¡É, 1h
3) Ck 15,930¡É, 4h
4) White layer of a nitrocarburized sinter component
5) Sample testing in the materials laboratory
6) Computer optized carburizing process