Defining the Application
Type 1 Open Gear Drives
Type 1 open gear drives consist of an actuator and a rack system used to transmit power. This type of open gearing is primarily used on the cable hoist drums, swing motion drives, mechanical boom lifts, shuttle transfer units and in the hoist and drag drives of mining shovels, draglines and excavators. These open gears can be bidirectional in motion, and in most applications the tooth geometry, surface finish, pitch line and intermittent loads cause them to operate in thin lubrication film or boundary lubrication condition. Type 1 gears are typically spur-type gears.
The primary functions of a lubricant used on a Type 1 open gear drive is to act as a friction-reducing interface between the meshing gear tooth surfaces and as a cushion against shock loads. If the open gear lubricant is able to provide these characteristics and contaminants and wear debris do not exceed moderate levels, the open gear lubricant can significantly increase the life of the open gearing.
Type 2 Open Gear Drives
Type 2 open gear drives typically consist of an actuator, pinion and a gear or a series of connecting gears used to transmit continuous loads. They are normally used to power stationary or semi-stationary equipment such as kilns, grinding mills, rotary furnaces, dryers, debarkers, rubber mills, paper mills and finishing mills.
Type 2 open gear drives typically operate at or near their design limits and are often exposed to abrasive contaminants and wear debris. They usually consist of single helical and double helical-type gears.
Open Gear Lubricant Requirements and Industry Standards
Open gearing applications, particularly those associated with ball mill and finishing mill applications, are considered some of the most difficult applications a lubricant can encounter. Generally, these types of open gears operate at low pitch line velocities and/or under heavy loads. However, more recent designs on equipment require open gearing to transmit increasingly higher loads. Because of these considerations, an open gear lubricant must possess the following characteristics and properties:
The AGMA 9005-D94 and AGMA 9005-E02 stipulate the use of residual compounds 14R and 15R for open gearing when the open gear lubricant is applied by intermittent application methods, where the pitchline velocity does not exceed 7.5 meters per second (1,500 feet/minute). The stated viscosities for 14R and 15R are 428.5 to 857.0 and 857.0 to 1,714 cSt at 100oC respectively.
In addition to the AGMA specifications, different OEMs of mining machinery and open gearing units have their own benchmark tests and specifications. Falk specifies that an open gear lubricant must have a minimum viscosity of 857 cSt at 100oC, while Sevedala specifies the open gear lubricants have a minimum viscosity of 150 cSt at 100oC. The remaining OEM requirements for mining machinery are outlined in Table 2.¹
Types of Open Gear Lubricants
Currently, the lubricants used by both Type 1 and Type 2 open gears consist of the following: