Feature

OhioMet obtains Quality, Productivity, and Low Costs with Thermotech Furnace

Ohio Metallurgical Service, Inc. in Elyria, Ohio wanted a furnace for high quality vacuum tempering and for atmosphere processing utilizing a Nitrogen/Hydrogen atmosphere. Thermotech had the answer -- A high convection furnace with atmosphere and vacuum processing capabilities.

The Thermotech Vacuum Furnace (which is an atmosphere furnace) allows the heat treater to combine vacuum processing segments with atmosphere processing segments, unlike conventional vacuum furnaces (OhioMet uses Nitrogen and Hydrogen blended at the furnace [up to 6% Hydrogen] as a processing atmosphere). With a net heat input of 200 kW (the gas-fired heating elements have a 1.2 MM Btu/hr. input) the furnace heats very quickly. With a recirculated wind internally in the furnace, the parts heat more uniformly than under vacuum alone and faster. The unique hot wall design, combined with vacuum tight heating tubes and cooling tubes offers a low maintenance, high heat treat quality design with fast processing times.

Bright product is required at OhioMet. Both carbon and stainless steels are successfully heat treated.

The Thermotech furnace that OhioMet selected is for heat treating temperatures up to 1650°F. The furnace load size is 36" x 36" x 56". Load weights over 2,000 pounds are regularly treated. The furnace has been in continuous operation since September of 1997.

OhioMet's Thermotech Vacuum Furnace being Loaded.

5920 American Road, Toledo, Ohio 43612 419/729-2666

Design, Sizes, and Features

The Gas-Fired Vacuum Furnace Explained

Heating takes place by convective heat transfer, which is further assisted by the muffle which separates the heating tubes from the load, assuring proper recirculation and radiation "hot spot" minimization. This mode of heat transfer, heating by convection, is by far the most effective at low process temperatures (below 1100°F). Conventional, electrically heated vacuum furnaces heat with radiation only.

AMS (Aerospace Material Specification) 2750 requirements specify that an empty furnace must meet better than +/- 25°F for general heat treating, better than =/- 15°F for aging above 1025°F and better than +/- 10°F for aging in furnaces below 1025°F.

Repeated tests with Thermotech's designs have shown that the temperature uniformity requirements of AMS can easily be met. The Thermotech furnace operates consistently within the tighter +/- 10^oF specification at all temperature ranges.

Thermotech vacuum furnaces operate differently than standard vacuum furnaces. Vacuum is used to evacuate the furnace of impurities. Clean atmosphere is used to offer faster and more uniform heating. A high volume fan then helps to recirculate the hot gases through the load, and helps with the accelerated cooling. With the selection of the proper atmosphere, the Thermotech furnace has the capability to offer brighter surface finishes than conventional vacuum furnaces.

In a typical gas-fired vacuum furnace heat treat cycle the furnace is vacuum purged with a high volume vacuum pump. The furnace is then refilled with clean nitrogen and the heating cycle begins. The recirculation fan assures high rates of heat removal from the heating tubes and helps transfer the heat quickly and uniformly to the load. A small amount of hydrogen can be used to keep the parts extremely clean.

End of Heating Tube End of Large Cooling Tube

The air cooling tubes accelerate the cooling process and assure that low break out temperatures can be obtained. Cooling is again assisted by the recirculation fan. The heating tubes are U-shaped to increase heat input and heat transfer. Consumption of cooling water for the entire furnace operation is very small and can be reduced to almost negligable levels with a specially designed water cooling system that is offered as an option.

First Gas-Fired Hot-Wall Vacuum Furnace Design

Thermotech's Latest Vacuum Furnace