How to Read the Back of a Gsar
What Is a Worm Gear?
A worm gear is a gear consisting of a shaft with a spiral thread that engages with and drives a toothed bike. Worm gears are an old style of gear, and a version of 1 of the half-dozen simple machines. Basically, a worm gear is a screw butted up confronting what looks like a standard spur gear with slightly angled and curved teeth.
It changes the rotational movement by 90 degrees, and the plane of movement besides changes due to the position of the worm on the worm bike (or simply "the cycle"). They are typically comprised of a steel worm and a brass wheel.
How Worm Gears Work
An electrical motor or engine applies rotational power via to the worm. The worm rotates confronting the wheel, and the screw face pushes on the teeth of the bike. The bicycle is pushed confronting the load.
Worm Gear Uses
There are a few reasons why ane would cull a worm gear over a standard gear.
The first 1 is the high reduction ratio. A worm gear can have a massive reduction ratio with little endeavour - all one must practice is add circumference to the bicycle. Thus yous tin use it to either greatly increase torque or greatly reduce speed. Information technology will typically take multiple reductions of a conventional gearset to achieve the same reduction level of a single worm gear - meaning users of worm gears have fewer moving parts and fewer places for failure.
A second reason to apply a worm gear is the inability to reverse the management of power. Because of the friction between the worm and the wheel, it is virtually impossible for a bike with force applied to it to commencement the worm moving.
On a standard gear, the input and output tin exist turned independently once plenty force is applied. This necessitates adding a backstop to a standard gearbox, further increasing the complication of the gear set.
Why Not to Use Worm Gears
There is i especially glaring reason why ane would non choose a worm gear over a standard gear: lubrication. The movement between the worm and the bike gear faces is entirely sliding. There is no rolling component to the tooth contact or interaction. This makes them relatively hard to lubricate.
The lubricants required are usually very high viscosity (ISO 320 and greater) and thus are difficult to filter, and the lubricants required are typically specialized in what they exercise, requiring a product to be on-site specifically for that type of equipment.
Worm Gear Lubrication
The primary problem with a worm gear is how it transfers power. It is a benefaction and a expletive at the same fourth dimension. The spiral motility allows huge amounts of reduction in a comparatively pocket-size amount of infinite for what is required if a standard helical gear were used.
This screw motion also causes an incredibly problematic condition to be the master mode of power transfer. This is commonly known equally sliding friction or sliding wear.
With a typical gear set the power is transferred at the superlative load point on the tooth (known equally the noon or pitchline), at to the lowest degree in a rolling wear condition. Sliding occurs on either side of the apex, just the velocity is relatively depression.
With a worm gear, sliding movement is the just transfer of power. Equally the worm slides across the molar of the bicycle, information technology slowly rubs off the lubricant pic, until in that location is no lubricant film left, and equally a event, the worm rubs at the metallic of the wheel in a purlieus lubrication regime. When the worm surface leaves the wheel surface, it picks upwards more lubricant, and starts the process once again on the side by side revolution.
The rolling friction on a typical gear tooth requires piffling in the style of lubricant film to make full in the spaces and split up the two components. Considering sliding occurs on either side of the gear tooth apex, a slightly higher viscosity of lubricant than is strictly needed for rolling wearable is required to overcome that load. The sliding occurs at a relatively depression velocity.
The worm on a worm set gear turns, and while turning, it crushes against the load that is imposed on the wheel. The simply way to prevent the worm from touching the bike is to have a flick thickness large enough to non have the entire tooth surface wiped off before that role of the worm is out of the load zone.
This scenario requires a special kind of lubricant. Not only volition it will have to be a relatively high viscosity lubricant (and the higher the load or temperature, the higher the viscosity must exist), information technology must have some way to help overcome the sliding status present.
Read The Right Way to Lubricate Worm Gears to learn more on this topic.
Viscosity
Viscosity is the major factor in preventing the worm from touching the wheel in a worm gear set. While the load and size of gearing determines the required lubricant, an ISO 460 or ISO 680 is fairly common, and an ISO 1000 is not unheard of. If y'all've ever tried to filter this range of viscosity, you know it is problematic considering it is likely that none of the filters or pumps y'all have on-site will exist the proper size or rating to function properly.
Therefore, you would likely demand to get a specific pump and filter for this type of unit of measurement. A lubricant that viscous requires a tedious operating pump to prevent the lubricant from activating the filter bypass. It will as well require a large surface expanse filter to allow the lubricant to flow through.
Lubricant Types to Await For
One lubricant blazon ordinarily used with worm gears is mineral-based, compounded gear oils. In that location are no additives that can be put into a lubricant that tin make it overcome sliding habiliment indefinitely, but the natural or synthetic fatty condiment combination in compounded gear oils results in practiced lubricity, providing an extra measure of protection from metallic-to-metallic contact.
Another lubricant type commonly used with worm gears is mineral-based, industrial extreme pressure level (EP) gear oils. There are some issues with this type of lubricant if you are using a worm gear with a yellowish metal (contumely) component. Even so, if you lot have relatively depression operating temperatures or no yellowish metallic nowadays on the gear tooth surfaces, this lubricant works well.
Polyalphaolefin (PAO) gear lubricants piece of work well in worm gear applications considering they naturally have good lubricity properties. With a PAO gear oil, it is necessary to sentinel the condiment package, because these tin can have EP additives. A standard-duty antiwear (AW) fortified gear oil will typically exist acceptable, but bank check that the properties are uniform with well-nigh metals.
The author recommends to closely picket the wear metals in oil analysis testing to brand certain that the AW parcel isn't so reactive as to cause significant leaching from the brass. The effect should exist far less than what would exist seen with EP even in a worst-case scenario for AW reactivity, simply it can show up in metals testing. If you demand a lubricant that can handle higher- or lower-than-typical temperatures, a suitable PAO-based product is likely available.
Polyalkylene glycols (PAG), a fourth type of lubricant, are condign more common. These lubricants have excellent lubricity backdrop, and practise not contain the waxes that cause low-temperature issues with many mineral lubricants, making them an excellent depression-temperature choice. Caution must be taken when using PAG oils because they are not compatible with mineral oils, and some seals and paints.
Metallurgy of Worm Gears
The about common worm gears are made with a brass wheel and a steel worm. This is because the brass cycle is typically easier to replace than the worm itself. The wheel is made out of brass because it is designed to be sacrificial.
In the event that the two surfaces come into contact, the worm is marginally safe from wearable because the wheel is softer, and therefore, virtually of the article of clothing occurs on the bicycle. Oil assay reports on this type of unit most e'er bear witness some level of copper and low levels of iron - as a result of the sacrificial bike.
This brass bike throws another trouble into the lubrication equation for worm gears. If a sulfur-phosphorous EP gear oil is put into the sump of a worm gear with a brass wheel, and the temperature is high enough, the EP additive will activate. In normal steel gears, this activation produces a sparse layer of oxidation on the surface that helps to protect the gear tooth from shock loads and other farthermost mechanical conditions.
On the brass surface notwithstanding, the activation of the EP condiment results in meaning corrosion from the sulfur. In a short corporeality of time, yous tin can lose a significant portion of the load surface of the wheel and cause major impairment.
Other Materials
Some of the less common materials establish in worm gear sets include:
Steel worm and steel worm wheel - This application does not accept the EP complications of brass gearing, only there is no room for error built into a gearbox like this. Repairs on worm gear sets with this combination of metal are typically more costly and more fourth dimension consuming than with a brass/steel worm gear set. This is because the cloth transfer associated with failure makes both the worm and the bicycle unusable in the rebuild.
Contumely worm and brass worm wheel - This awarding is most likely found in moderate to light load situations considering the brass can just concur up to a lower amount of load. Lubricant selection on this metallic combination is flexible considering of the lighter load, simply one must still consider the additive restrictions regarding EP because of the yellow metal.
Plastic on metal, on plastic, and other similar combinations - This is typically found in relatively light load applications, such as robotics and automotive components. The lubricant option depends on the plastic in use, considering many plastic varieties react to the hydrocarbons in regular lubricant, and thus will crave silicon-based or other nonreactive lubricants.
Although a worm gear will always have a few complications compared to a standard gear prepare, it can easily be an effective and reliable piece of equipment. With a little attention to setup and lubricant selection, worm gears can provide reliable service besides as any other type of gear set.
Related Reading
Ray Thibault. "Lubrication of Worm Gears." Machinery Lubrication magazine. May-June 2001.
Source: https://www.machinerylubrication.com/Read/1080/worm-gears
Post a Comment for "How to Read the Back of a Gsar"