Manufacturing Process

The purpose of this paper is to establish the appropriate heat treatment process for a worm gear. This paper provides the details of worm gear which have high strength and corrosion resistance. The selected material is heated in an atmosphere containing certain elements that will alter the composition, micro-structure and properties of their surface. A hard high-carbon surface is produced, with typical hardness ranging from 30 to 62 HRC if using 8620 Steel. In order to increase the service life of a worm gear, selecting material and heat treatment process is critical. The worm gear has to have excellent wearing resistance because it contacts with driven gear, while rotating at a high speed. This paper demonstrates that heat treatment process enhances all of these desirable properties.

FURNACE ATMOSPHERE
The first step in establishing and maintaining the process atmosphere. Therefore furnace atmosphere optimization becomes a very important aspect of achieving components of the highest quality. To setup the furnace you must:

Calibrating of the furnace controllers.
Setting the proper conditions for the furnace.
Setting the proper temperature settings.
Setting the proper atmosphere flows.
Setting the proper furnace load.

Pre-Heat Zone: This section is designed to prepare the parts for the high heat zone by pre-heating and removing lubricant. Pre-heating the specimen Mock carburized at 925°C (1700°F) for 8 hrs. Therefore the furnace atmosphere should produce oxidizing conditions for AISI 8620 Steel.
Hot Zone: Annealing Heat to 820 oC - 850 oC, holds until temperature is uniform throughout the section. Carburize at 900 oC - 925 oC, holding for sufficient time to develop the required case depth and carbon content, followed by a suitable hardening and tempering cycle to optimize case and core properties. The moisture content or dew point must be low enough to reduce metal oxides.
Cooling Zone: The main function of the atmosphere in the cooling zone is to cool down the components in a protective medium. Cool from carburizing temperature to room temperature, re-heat to 820 oC - 840 oC and hold until temperature is uniform throughout the section and quench in oil.
Temper immediately at 150°C - 200°C will improve the toughness of the case with minimal effect on its hardness and reduce the possibility of grinding cracks.
With these basic instruments furnace operators can analyze their equipment:

a. Temperature measurement
b. Hydrogen analyzer
c. Oxygen analyzer
d. Dew Point analyzer
e. Independent read-outs
f. Data logging.
e. Recording the information.