Worm gear and worm are a type of gear, often used to transmit motion and power between two interlocking shafts, and are widely applied in various motion and power transmission devices, such as worm gear and worm reducers.
Types of Lubricating Oil for Worm Gears and Worms
At present, the lubricating oils used for worm gears and worms include the following types:
Mineral-based gear oil:
One type is the special lubricating oil for worm gears and worm wheels. This type of gear oil is added with fat additives to provide lubrication for the sliding between the teeth of worm gears and worm wheels, reducing the friction between the tooth surfaces.
Another common type is mineral extreme pressure gear oil (EP), which contains sulfur and phosphorus extreme pressure additives. However, if this type of gear oil comes into contact with copper-containing components, it may cause corrosion. If this type of gear oil is used, it is fine when the temperature is low, but when the temperature is high, it will cause corrosion of copper-containing components. If the gears in contact with the oil do not contain copper, this type of gear oil can be used.
Synthetic gear oils: Mainly include PAO and PAG.
PAO (Polyalphaolefin), also known as polyalphaolefin, has excellent lubricity and is therefore very suitable for applications involving a lot of sliding friction, such as worm gears and worm gears. Similarly, when choosing this type of synthetic oil, remember to check if there are sulfur-phosphorus type extreme pressure additives in the composition.
- PAG (Polyalkylene glycols) polyether synthetic oil also has excellent performance and is gradually becoming popular. The characteristic of PAG is that it is particularly lubricated and completely free of paraffin. At low temperatures, paraffin wax solidifies. The poor fluidity of many mineral oils at low temperatures is due to wax formation. Therefore, PAG synthetic gear oil has excellent low-temperature performance. The main issue with using PAG gear oil is compatibility (whether PAG is compatible with seals, coatings, etc.) When switching to PAG gear oil, is it compatible with the original oil?
Case Analysis
Let’s discuss the selection of worm gear lubricating oil based on the problems that occurred in the worm gear and worm gearbox of a wet grinding machine we once served in a certain enterprise.
Equipment Condition:
The company has 12 wet grinding machines, which are made in the UK and put into use in January 2007. They basically operate 24 hours a day.
The gearbox is driven by worm gear and worm, with a power of 350kw. The input speed of the reducer is 1480r/min, and the output shaft speed is 109r/min. It is equipped with a water cooling system, so the oil temperature will not be too high, and the surrounding environment does not involve water vapor. High-temperature and high-humidity conditions can be disregarded.
Since its commissioning, Mobil SHC320 has been in use.
The equipment has been operating normally all the time.
Problems encountered during lubrication: Pitting corrosion was found in the internal components during the maintenance in April 2009.
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Key Points for Selecting Oil Products
Due to the particularity of the worm gear and worm structure
When the rotation direction of the worm gear is at a right Angle to the rotation direction of the worm wheel that transmits power, and the two tooth surfaces mesh and come into contact, it is almost entirely a sliding contact. High sliding force generates a large amount of friction, so the temperature during the operation of worm gear gearboxes is often higher than that of spur gears and helical gears. Moreover, as the worm gear and worm are vertical, it is relatively difficult to form an oil film on the worm. Therefore, the lubricating oil needs to have good adhesion and excellent lubrication and load-bearing capacity. And it does not contain sulfur and phosphorus type additives. In view of the special circumstances of the equipment, the oil products we select need to meet the following conditions:
It has a relatively high viscosity index to ensure that the viscosity of the oil does not change much under certain