Worm Gearbox Lubrication
The basic problem with a worm gearbox is how it converts power. The spiral motion permits huge values of reduction in a relatively small amount of space for what is needed if a standard helical gear was employed.
This spiral movement also causes an incredibly problematic state to be the primary mode of power conversion. This is usually introduced as sliding wear or sliding friction.
With a common gear arrangement, the power is moved at the peak load section on the tooth (introduced as the pitch line or apex), at least in a rolling wear state. Sliding happens on either part of the apex, but the velocity is comparatively low.
With a worm gear reducer, the sliding output is the only transfer of energy. As the worm moves across the wheel tooth, it slowly wears out the lubricant layer until there is no lubricant layer left, and as a result, the worm wears away at the metal of the wheel in a boundary lubrication section. When the worm surface leaves the top of the wheel, it picks up more lubricant and begins the procedure over again on the next revolution.
The rolling friction on a common gear tooth needs little in the way of a lubricant layer to fill in the places and separate the two sections. Since sliding happens on either part of the apex of the gear tooth, a slightly greater viscosity of lubricant than is strictly required for rolling wear is needed to prevail over that load. The sliding happens at a comparatively low velocity.
The worm on a gear set turns, and once turning, it crushes against the force that is imposed on the gear. The only method to prevent the worm from touching the top of the wheel is to have a layer thickness large enough not to have the total tooth surface wiped off before that section of the worm is out of the power zone.
This scenario needs a particular kind of lubricant. Not only will it have to be a comparatively great viscosity lubricant (and the larger the temperature or load, the greater the viscosity must be), it should have some method to help prevail over the sliding condition present.
What are the main Lubrication Oil Types？
One lubricant form typically utilized with worm gearboxes is the mineral-based, multiplex gear oils. There are no extra materials that can be put into a lubricant that can prevail over sliding wear indefinitely, but the synthetic or natural fatty additive combination in multiplex gear oils results in good lubricity, providing an additional measure of protection from metal-to-metal touching.
Another lubricant type typically employed in worm gears is mineral oil, industrial Extreme Pressure (EP) type of gear oils. There are some difficulties with this form of lubricants if you are using a worm gear with a component that is yellow metal (brass). However, if you have comparatively low-performing temperatures or no yellow metal existing on the gear tooth surfaces, this lubricant operates well.
Polyalphaolefin (PAO) lubrication oil operates properly in worm gear applications since they have good lubricity features generally. It is essential to watch the additive package with a PAO gear oil since these can have EP additives. A normal-duty antiwear (AW) fortified gear oil will be admissible commonly, but check that the features are compatible with most metals.
Many manufacturers recommend precisely watch the wear metals in oil analysis checking to make sure that the AW arrangement isn’t so reactive as to cause considerable leaching from the brass. The result must be far less than what would be detected with EP even in a worst-case situation for AW reactivity, but it can show up in metals checking. If you require a lubricant that can tolerate lower or higher than usual temperatures, an appropriate PAO based lubrication oil is likely available.
Polyalkylene Glycols (PAG), the fourth form of lubrication, is becoming more usual. It has perfect lubricity features and do not include the waxes that cause low-temperature issues with several mineral lubricants, making them a perfect low temperature option. Caution should be taken when employing PAG oils since they are not matchable with mineral oils and some paints and seals.
Viscosity
Viscosity is the basic feature in preventing the worm from touching the wheel in a gear arrangement. Whereas the size and load of gearing specify the needed lubricant, an ISO 680 or ISO 460 is justly common, and an ISO 1000 is not unheard of. If you’ve ever tried to control this level of viscosity, you learn it is difficult because it is probably that none of the pumps or filters you have on-site will be the appropriate size or rating to perform exactly.
As a result, you would probably require to get a special filter and pump for this form of unit. A viscous lubricant needs a slow working pump to prevent the lubricant from activating the bypass of the filter. It will also need a great surface area filter to allow the lubricant to flow properly.
