Worm gears operate under difficult conditions, presenting unique lubrication demands. They serve as speed reducers in many different industries and applications. This article addresses how effectively lubricated worm gears affect worm gear performance. Worm gears are used in various industries and machinery applications. They are unique in their ability to achieve large speed reductions in a compact space. They can transmit high loads at high-speed ratios. Ratios of up to and higher are normally achieved.
Non-throated - a helical gear with a straight worm. Tooth contact is a single moving point on the worm drive. This leads to high unit loads and wear. Single-throated - has concave helical teeth which wrap around the worm. This leads to line contact, permitting higher loads without excessive wear. Double-throated - called a cone or hourglass. It has concave teeth both on the worm and helical gear. This increases from line contact area permitting increased loading and lower wear.
Worm drives are inefficient because the gears experience sliding rather than rolling contacts, leading to operating temperatures much higher than other gear types.
Due to the sideway sliding motion in worm gears, it is difficult to maintain a hydrodynamic oil wedge. This results in gears operating under boundary lubrication conditions.
They also require good thermal and oxidative stability. The types of oils most commonly used to lubricate worm gears are compounded mineral oils, EP mineral gear oils and synthetics.
Each has its own unique characteristics and all three types are used successfully. These lubricants have been used extensively in worm gears with great success in a wide variety of applications. Compounded gear oil is a mineral basestock with normal rust and oxidation inhibitors that is blended with four to six percent acidless tallow or synthetic fatty acid the compounding agent. The surface-active compounding agent gives these products excellent lubricity and prevents sliding wear in worm gears.
Many OEMs recommend compounded gear oils.
Compounded oils were initially used as steam cylinder lubricants because of their ability to adhere to cylinder walls in the presence of steam. Because compounded lubricants are difficult to use out of this temperature range, they are often replaced with EP gear oils for consolidation purposes.
In some cases, an 8A VG is used. Refer to the OEM for specific viscosity recommendations. EP mineral gear oils are used more extensively in worm gears. Under conditions of high pressure and temperature, the EP antiscuff additive reacts with the metal surface to form a soft, slippery chemical layer which prevents severe wear and welding. Previously, there was a concern that sulfur-phosphorous EP additives would react with the bronze gear. However, new EP additive technology used by most of the major lubricant suppliers has reduced the corrosive attack by utilizing nonactive sulfur.
EP lubricants work particularly well when shock loading occurs. EP gear oils also protect steel gears better than compounded gear oils. Typical recommendations are for both AGMA 7 and 8 viscosity grades.
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The Right Way to Lubricate Worm Gears
Gear box oils. Filter by. Product Category. Industrial oils. Equipment Type. Available with. High-quality lubricants certified to meet OEM cleanliness requirements. Apply Filter Cancel. Premium quality extreme pressure gear oils that perform under demanding conditions. High performance gear oils for industrial and marine applications.
Designed to deliver outstanding performance in steam and hydroelectric turbines. Gear oils designed to emulsify water in mining and construction applications.
Our Meropa gear oils are formulated to provide you with long equipment and oil life.
Watch now. Meropa family of gear oil products.Bar Mill 1 cooling bed reducer worm gearbox Steel plant Egypt. Situation An Egyptian steel plant operates a Bar Mill 1 cooling bed equipped with reducer worm gearboxes. Lubricated with a conventional mineral oil, the gearboxes were experiencing severe pitting in some of the wheel gear teeth, causing breakdowns to occur after just 1.
In an effort to reduce unscheduled downtime, the plant reached out to ExxonMobil engineers to identify a lubricant solution that could help improve equipment reliability.
Bar Mill 1 cooling bed reducer worm gearbox Steel plant Egypt Situation An Egyptian steel plant operates a Bar Mill 1 cooling bed equipped with reducer worm gearboxes.
Actual results can vary depending upon the type of equipment used and its maintenance, operating conditions and environment, and any prior lubricant used.
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Average rating: 5 out of 5 stars, based on 3 reviews 3 ratings. Average rating: 5 out of 5 stars, based on 1 reviews 1 ratings. Product Title Valvoline? Reduced Price. Product Title 9 pack Super tech 80w gear oil, 1 qt. Product Title Lucas Oil 32oz. Heavy Duty 80W Gear Oil. Email address. Please enter a valid email address. Mobile apps. Walmart Services. Get to Know Us. Customer Service. In The Spotlight.Of all the different types of gear configurations, worm gear systems are considered some of the most problematic because they present unique lubrication challenges due to their distinct design.
To overcome these challenges, you must understand not only the complexities of worm gears but also which qualities to take into account when choosing a worm gear lubricant.
A worm gear is a non-parallel, non-intersecting axis design consisting primarily of two gear elements: the worm, which is the driving gear in the shape of a spiral or screw, and the worm gear or worm wheel, which is the driven gear in the shape of a common spur gear. Technically, the entire worm gear system should be called a worm drive or worm gearset to avoid confusion. The worm always drives the worm wheel. This design characteristic is due to the extreme helical angle, which is nearly 90 degrees.
The worm drive resembles the design of the crossed helical gear configuration, except the gear teeth on the worm of a worm drive will circle around the circumference of the worm at least once. Since the worm may have as little as one tooth that spirals radially around the helix, the number of teeth on the worm is more appropriately identified by the number of starts or threads.
There are three categories of worm drive designs that describe the degree to which the gears mesh together: non-throated non-envelopingsingle-throated single-enveloping and double-throated double-enveloping or globoidal.
Non-throated or non-enveloping is the most basic design in which the worm and worm wheel are both cylindrical in shape. This allows for simplistic manufacturing, but the limited contact zone of a single point on one or two gear teeth can become problematic. In single-throated or single-enveloping designs, one of the gear elements most commonly the worm wheel has concave helical teeth for contour or envelopment of the gear teeth onto the worm.
This enables the contacting zone to increase to a line. Double-throated double-enveloping or globoidal designs not only have concave helical teeth on the worm wheel, but the worm is also shaped like an hourglass so the two gear elements wrap around each other during motion. This results in nearly eight times more contact area in the shape of a radial band with three or more teeth in contact.
As the contact surface area increases, the torque capacity, load-holding ability shock load resistance and durability are improved.
Enveloping gear designs also have a lower anticipated wear rate as a result of the load distribution. Worm drive manufacturers attempt to optimize this contact relationship between the two gear elements for improved reliability. Worm drive designs have one major drawback: the relative motion between the mating teeth of the two elements is almost entirely sliding. This poses a significant challenge because the lubricant is continually scraped aside.
The sliding friction losses result in elevated temperatures and inadequate hydrodynamic pressure development. Consequently, wear debris generation can increase. In many cases, the higher temperatures will be the limiting factor on the worm drive before the loading limitations are reached. The load distribution of enveloping gear designs can lessen this problem, but the challenge still persists. Also, because of the sliding nature of the worm drive, metals with a low coefficient of friction are generally used.
The worm wheel typically contains yellow metals, while the worm is usually made of steel. This results in more favorable wear characteristics, better loading ability and less heat generation not found in other metal combinations.
Yellow metals like bronze that are used on the worm wheel can present unique lubrication challenges when selecting a compatible additive package. With this metallurgical combination, it is also expected that the worm wheel act sacrificially in comparison to the worm due to the relative effort and costs in worm drive rebuilds. Gearing designs and materials have been modernized through the years to achieve better load-carrying capability, higher torque conversions and improved longevity.
Sophisticated testing platforms and computerized methods have provided a better understanding of common worm drive failure modes and offered clues for optimizing the solutions. Lubricants are no exception to these enhancements for worm drives. Generally speaking, a high-quality worm drive lubricant will have low friction, high oxidation resistance, good anti-wear protection and high viscosity index. While using lubricants formulated with mineral oil is quite common within worm drives, employing synthetic base oils generally results in improved gear efficiency and lower operating temperatures.
Figure 5 illustrates lubricant life and oil change interval expectations for polyalphaolefins PAOspolyalkylene glycols PAGs and mineral oils over a range of oil sump temperatures. This is supported by the Arrhenius Rate Rule, which states that for every increase of 10 degrees C in the average oil temperature, the chemical reactions double. Figure 6 specifies the improved efficiency when choosing a synthetic over a mineral oil, particularly PAGs, which have an inherently low coefficient of friction.This oil withstands the heavy loads found in gear boxes.
Viscosity is the thickness of an oil. The higher the grade, the thicker the oil, and the less it flows. Mineral oil is derived from petroleum and is usually more economical than synthetic oil. Synthetic oil lasts longer than mineral oil and withstands a wider range of temperatures.
Semisynthetic oil, a blend of mineral and synthetic oils, balances low cost with long-lasting performance. Oil with zinc neutralizes acid and is a good replacement for leaded oil. Mobil oil can be used with worm gears. Mobilgear XP prevents corrosion, even in the presence of salt water, so it's good for marine applications.
This oil withstands the heavy loads found in gears and gear-drive systems. Use it in food-processing and preparation areas. It's NSF registered H1 for use in areas where there is the possibility of incidental food contact. Mineral oil is derived from petroleum and is more economical than synthetic oil. For use in worm gears, this oil stands up to high pressure.
It is NSF registered H1 for incidental food contact. Oil in a pail has an FZG load stage rating greater than or equal to 12, designating it as a high-pressure oil. Wear-resistant properties keep hydraulic pumps and equipment working, even in high-pressure systems. Reduce wear on rings, cylinders, and other moving parts in most major manufacturers' air compressors.
This oil is chemically inert and long lasting with an indefinite shelf life. Use this oil in food-processing and preparation areas. Formulated to reduce friction and wear, this oil ensures smooth, uniform motion of slides, tracks, and ways.
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