Surface® Combustion’s classic gas nitriding hardening furnace and equipment starts with a high alloy retort. This high alloy retort contains the ammonia, nitrogen, hydrogen and hydrocarbon atmosphere required for the nitriding hardening process. This retort is traditionally vertically oriented and the furnace loading style is in the configuration of a bell or a pit style. The retort contains a loading hearth on the bottom or a loading ring for pieces that may be hung from the top.  The retort is installed in an electrically heated insulated chamber with a double sealed base or lid. For the pit style, the lid is hydraulically lifted and manually rotated. The double seal consists of a thermal rope seal and a rubberized inflatable gas tight seal.  Nitrogen, hydrogen, ammonia, methane, carbon dioxide and carbon monoxide are metered into the retort as required through precise mass flow controllers. Exiting gas is flared through an incinerator. The control of the process gas is tightly controlled in conjunction with the work to maintain a precise Kn factor (a nitriding potential).

Ferritic nitrocarburizing (FNC) can be performed in the same chamber also with different temperatures and different gas mixes.

Typical load sizes are from 36” to 60” diameter by 90” tall.

Insulations used in the hot zone are fiber. Heating elements are traditionally rod overbend style that are electrically isolated from the steel casing. The annulus between the hot zone and the outer surface of the retort may be purged with a constant flow air.

Cooling of the load from temperature consists of increasing the air flow as well as recirculating the internal atmosphere of nitrogen through a water cooled heat exchanger.

As an alternative furnace style for ferritic nitrocarburizing, a lift cover, carbottom, or  Allcase® furnace can perform to the same exacting specifications.

For black oxide coating equipment, our diverse product line can provide hydrothermal oxidation based black oxide by steam-bluing, wet nitrogen or gas nitriding. Surface’s proven experience with manufacturing black oxide capable equipment and dunk tanks is sure to impress and deliver consistent process results.