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The maximum speeds that rotational bearings can support also vary, generally performance is defined in terms of the product 'DN' where D is the diameter (often in mm) of the bearing and N is the rotation rate in revolutions per minute.
 
== Historija i razvoj ==
 
An early type of linear bearing was an arrangement of tree trunks laid down under sleds. This technology may date as far back as the construction of the [[Pyramids of Giza]], though there is no definitive evidence. Modern linear bearings use a similar principle, sometimes with balls in place of rollers.
 
The first plain and rolling-element bearings were [[wood]], but [[ceramic]], [[sapphire]] or [[glass]] can be used, and [[steel]], [[bronze]], other metals, and plastic (e.g., [[nylon]], [[polyoxymethylene]], [[teflon]], and [[UHMWPE]]) are all common today. Indeed, stone was even used in various forms. Think of the "jeweled pocket watch", which incorporated stones to reduce frictional loads, and allow a smoother running watch. Of course, with older, mechanical timepieces, the smoother the operating properties, then the higher the accuracy and value. Wooden bearings can still be seen today in old water mills where the water has implications for cooling and lubrication.
 
Rotary bearings are required for many applications, from heavy-duty use in vehicle axles and machine shafts, to precision clock parts. The simplest rotary bearing is the '''sleeve bearing''', which is just a cylinder inserted between the wheel and its axle. This was followed by the '''roller bearing''', in which the sleeve was replaced by a number of cylindrical rollers. Each roller behaves as an individual [[wheel]]. The first practical caged-roller bearing was invented in the mid-1740s by [[horology|horologist]] [[John Harrison]] for his H3 marine timekeeper. This used the bearing for a very limited oscillating motion but Harrison also used a similar bearing in a truly rotary application in a contemporaneous regulator clock.
 
An early example of a wooden ball bearing (see [[rolling-element bearing]]), supporting a rotating table, was retrieved from the remains of the [[Roman Republic|Roman]] [[Nemi ships]] in [[Lake Nemi]], [[Italy]]. The wrecks were dated to [[40 AD]]. [[Leonardo da Vinci]] is said to have described a type of ball bearing around the year [[1500]]. One of the issues with ball bearings is that they can rub against each other, causing additional friction, but this can be prevented by enclosing the balls in a cage. The captured, or caged, ball bearing was originally described by [[Galileo Galilei|Galileo]] in the [[1600]]s. The mounting of bearings into a set was not accomplished for many years after that. The first patent for a ball race was by [[Philip Vaughan]] of [[Carmarthen]] in [[1794]].
 
[[Friedrich Fischer]]'s idea from the year 1883 for milling and grinding balls of equal size and exact roundness by means of a suitable production machine formed the foundation for creation of an independent bearing industry.
[[Datoteka:Tapered steering head bearings.jpg|thumb|Tapered steering head bearings for a [[motorcycle]]]]
The modern, self-aligning design of ball bearing is attributed to [[Sven Wingquist]] of the [[SKF]] ball-bearing manufacturer in [[1907]].
 
[[Henry Timken]], a 19th century visionary and innovator in carriage manufacturing, patented the tapered roller bearing, in 1898. The following year, he formed a company to produce his innovation. Through a century, the company grew to make bearings of all types, specialty steel and an array of related products and services.
 
[[The Timken Company]] (Sale $4,973.4M, 2006), The [[SKF]] company($6,195.1M, 2005), the [[Schaeffler Group]] (Private), the [[NSK]] company($5,344.5M, 2006), and the [[NTN]] Bearing company($3,697.8M, 2006) are now the largest bearing manufacturers in the world.
 
== Također pogledajte ==
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