Misplaced Pages

#392607

40-413: Prachatice is made up of the town parts of Prachatice I, Prachatice II and Staré Prachatice, and the villages of Kahov, Libínské Sedlo, Městská Lhotka, Oseky, Ostrov, Perlovice, Podolí, Stádla and Volovice. The name is derived from the old Slavic personal name Prachata. It meant "the village of Prachata's people". Prachatice is located about 34 kilometres (21 mi) west of České Budějovice . It lies in

80-457: A 40 mm bearing, grease should be replaced every 5000 working hours, while for a 100 mm bearing it should be replaced every 500 working hours. Lubrication can also be done with an oil, which has advantage of higher maximum load, but needs some way to keep oil in bearing, as it normally tends to run out of it. For oil lubrication it is recommended that for applications where oil does not become warmer than 50 °C , oil should be replaced once

120-504: A bearing that rotates (either axle hole or outer circumference) must be fixed, while for a part that does not rotate this is not necessary (so it can be allowed to slide). If a bearing is loaded axially, both sides must be fixed. If an axle has two bearings, and temperature varies, axle shrinks or expands, therefore it is not admissible for both bearings to be fixed on both their sides, since expansion of axle would exert axial forces that would destroy these bearings. Therefore, at least one of

160-511: A bearing to have its nominal lifespan at its nominal maximum load, it must be lubricated with a lubricant (oil or grease) that has at least the minimum dynamic viscosity (usually denoted with the Greek letter ν {\displaystyle \nu } ) recommended for that bearing. The recommended dynamic viscosity is inversely proportional to diameter of bearing. The recommended dynamic viscosity decreases with rotating frequency. As

200-432: A lifespan at least 5 times as long. The industry standard life calculation is based upon the work of Lundberg and Palmgren performed in 1947. The formula assumes the life to be limited by metal fatigue and that the life distribution can be described by a Weibull distribution . Many variations of the formula exist that include factors for material properties, lubrication, and loading. Factoring for loading may be viewed as

240-401: A rough indication: for less than 3000 RPM , recommended viscosity increases with factor 6 for a factor 10 decrease in speed, and for more than 3000 RPM , recommended viscosity decreases with factor 3 for a factor 10 increase in speed. For a bearing where average of outer diameter of bearing and diameter of axle hole is 50 mm , and that is rotating at 3000 RPM , recommended dynamic viscosity

280-403: A settlement was founded in the area of today's Staré Prachatice ("Old Prachatice") town part. In the second half of the 12th century, it was acquired by Vyšehrad Chapter . When the settlement ceased to suit its purpose, a new settlement was established near the old one at the end of the 13th century. In 1312, Prachatice was first referred to as a town. In 1323, King John of Bohemia confirmed to

320-422: A tacit admission that modern materials demonstrate a different relationship between load and life than Lundberg and Palmgren determined . If a bearing is not rotating, maximum load is determined by force that causes plastic deformation of elements or raceways. The indentations caused by the elements can concentrate stresses and generate cracks at the components. Maximum load for not or very slowly rotating bearings

360-410: A year, while for applications where oil does not become warmer than 100 °C , oil should be replaced 4 times per year. For car engines, oil becomes 100 °C but the engine has an oil filter to maintain oil quality; therefore, the oil is usually changed less frequently than the oil in bearings. If the bearing is used under oscillation, oil lubrication should be preferred. If grease lubrication

400-399: Is 12 mm /s . Note that dynamic viscosity of oil varies strongly with temperature: a temperature increase of 50–70 °C causes the viscosity to decrease by factor 10. If the viscosity of lubricant is higher than recommended, lifespan of bearing increases, roughly proportional to square root of viscosity. If the viscosity of the lubricant is lower than recommended, the lifespan of

440-474: Is a bearing with ceramic balls and metal races. The calculated life for a bearing is based on the load it carries and its operating speed. The industry standard usable bearing lifespan is inversely proportional to the bearing load cubed. Nominal maximum load of a bearing, is for a lifespan of 1 million rotations, which at 50 Hz (i.e., 3000 RPM) is a lifespan of 5.5 working hours. 90% of bearings of that type have at least that lifespan, and 50% of bearings have

SECTION 10

#1732780139393

480-417: Is called "static" maximum load. Also, if a bearing is not rotating, oscillating forces on the bearing can cause impact damage to the bearing race or the rolling elements, known as brinelling . A second lesser form called false brinelling occurs if the bearing only rotates across a short arc and pushes lubricant out away from the rolling elements. For a rotating bearing, the dynamic load capacity indicates

520-447: Is circa 50% of maximum radial load, but it also says that "light" and/or "small" bearings can take axial loads that are 25% of maximum radial load. For single-row edge-contact ball bearings, axial load can be about 2 times max radial load, and for cone-bearings maximum axial load is between 1 and 2 times maximum radial load. Often Conrad-style ball bearings will exhibit contact ellipse truncation under axial load. That means that either

560-500: Is located on the railway line Číčenice – Nové Údolí . The town hosts the Golden Salt Path Celebrations every year with a rich cultural program. The historic centre is formed by Velké Square and adjoining streets, and is delimited by the remains of the town walls. Due to the stagnation of economic life in the 17th and 18th centuries, Prachatice have many Renaissance buildings, some of then reconstructed in

600-541: Is necessary, the composition should be adapted to the parameters that occur. Greases with a high bleeding rate and low base oil viscosity should be preferred if possible. Most bearings are meant for supporting loads perpendicular to axle ("radial loads"). Whether they can also bear axial loads, and if so, how much, depends on the type of bearing. Thrust bearings (commonly found on lazy susans ) are specifically designed for axial loads. For single-row deep-groove ball bearings, SKF's documentation says that maximum axial load

640-443: Is normally held within the bearing releasing the lubricant oil as it is compressed by the balls. It provides a protective barrier for the bearing metal from the environment, but has disadvantages that this grease must be replaced periodically, and maximum load of bearing decreases (because if bearing gets too warm, grease melts and runs out of bearing). Time between grease replacements decreases very strongly with diameter of bearing: for

680-656: The Bohemian Forest Foothills . The highest point is the Libín mountain at 1,093 m (3,586 ft) above sea level. The stream of Živný potok flows through the town. The Blanice River flows along the northwestern municipal border. Prachatice was founded with the beginning of trade on the Golden Trail, an important salt trade route beginning in Passau , Bavaria . Probably in the 9th or 10th century,

720-627: The Empire style . Since 1981, the historic core of the town has been protected as an urban monument reservation . One of the main landmarks of the town centre is the Old Town Hall, a Renaissance building from 1570–1571. The New Town Hall was built in pseudo-Renaissance style in 1903. The Church of Saint James the Great near the square is the largest building in the historic centre. It is a late Gothic building first mentioned in 1359. Its final form

760-467: The 16th century, trade on the trail reached its peak and the town prospered. The Rosenbergs controlled Prachatice until 1601 when Peter Vok of Rosenberg , the last member of the family, sold the town to Emperor Rudolf II who would again make it a royal town in 1609. It remained firmly under royal control until the Bohemian Revolt during which it sided with the rebels. However, in 1620, the town

800-497: The ID of the outer ring is large enough, or the OD of the inner ring is small enough, so as to reduce the area of contact between the balls and raceway. When this is the case, it can significantly increase the stresses in the bearing, often invalidating rules of thumb regarding relationships between radial and axial load capacity. With construction types other than Conrad, one can further decrease

840-505: The balls and transmit the loads through the balls. In most applications, one race is stationary and the other is attached to the rotating assembly (e.g., a hub or shaft). As one of the bearing races rotates it causes the balls to rotate as well. Because the balls are rolling, they have a much lower coefficient of friction than if two flat surfaces were sliding against each other. Ball bearings tend to have lower load capacity for their size than other kinds of rolling-element bearings due to

SECTION 20

#1732780139393

880-499: The bearing (where width is measured in direction of axle). Bearings have static load ratings. These are based on not exceeding a certain amount of plastic deformation in the raceway. These ratings may be exceeded by a large amount for certain applications. For a bearing to operate properly, it needs to be lubricated. In most cases the lubricant is based on elastohydrodynamic effect (by oil or grease) but working at extreme temperatures dry lubricated bearings are also available. For

920-439: The bearing decreases, and by how much depends on which type of oil being used. For oils with EP ('extreme pressure') additives, the lifespan is proportional to the square root of dynamic viscosity, just as it was for too high viscosity, while for ordinary oils lifespan is proportional to the square of the viscosity if a lower-than-recommended viscosity is used. Lubrication can be done with a grease, which has advantages that grease

960-568: The bearings must be able to slide. A 'freely sliding fit' is one where there is at least a 4 μm clearance, presumably because surface-roughness of a surface made on a lathe is normally between 1.6 and 3.2 μm. Bearings can withstand their maximum load only if the mating parts are properly sized. Bearing manufacturers supply tolerances for the fit of the shaft and the housing so that this can be achieved. The material and hardness may also be specified. Fittings that are not allowed to slip are made to diameters that prevent slipping and consequently

1000-411: The cage that holds the rolling elements at equal distances, due to the rolling elements trying to all slide together at the location of highest sideways torque. If the cage collapses or breaks apart, the rolling elements group together, the inner ring loses support, and may pop out of the center. In general, maximum load on a ball bearing is proportional to outer diameter of the bearing times the width of

1040-661: The center-lines of rotation of these bearings are not the same, then large forces are exerted on the bearing, which may destroy it. Some very small amount of misalignment is acceptable, and how much depends on type of bearing. For bearings that are specifically made to be 'self-aligning', acceptable misalignment is between 1.5 and 3 degrees of arc. Bearings that are not designed to be self-aligning can accept misalignment of only 2–10 minutes of arc (0.033-0.166 degrees) . In general, ball bearings are used in most applications that involve moving parts. Some of these applications have specific features and requirements: The ball size increases as

1080-504: The details below. Request from 172.68.168.226 via cp1108 cp1108, Varnish XID 195715431 Upstream caches: cp1108 int Error: 429, Too Many Requests at Thu, 28 Nov 2024 07:48:59 GMT Ball bearing A ball bearing is a type of rolling-element bearing that uses balls to maintain the separation between the bearing races . The purpose of a ball bearing is to reduce rotational friction and support radial and axial loads. It achieves this by using at least two races to contain

1120-464: The first modern recorded patent on ball bearings was awarded to Philip Vaughan , a Welsh inventor and ironmaster who created the first design for a ball bearing in Carmarthen in 1794. His was the first modern ball-bearing design, with the ball running along a groove in the axle assembly. Jules Suriray , a Parisian bicycle mechanic , designed the first radial style ball bearing in 1869, which

1160-470: The load to which the bearing endures 1,000,000 cycles. If a bearing is rotating, but experiences heavy load that lasts shorter than one revolution, static max load must be used in computations, since the bearing does not rotate during the maximum load. If a sideways torque is applied to a deep groove radial bearing, an uneven force in the shape of an ellipse is applied on the outer ring by the rolling elements, concentrating in two regions on opposite sides of

1200-408: The mating surfaces cannot be brought into position without force. For small bearings this is best done with a press because tapping with a hammer damages both bearing and shaft, while for large bearings the necessary forces are so great that there is no alternative to heating one part before fitting, so that thermal expansion allows a temporary sliding fit. If a shaft is supported by two bearings, and

1240-481: The outer ring ID and increase the inner ring OD to guard against this. If both axial and radial loads are present, they can be added vectorially, to result in the total load on bearing, which in combination with nominal maximum load can be used to predict lifespan. However, in order to correctly predict the rating life of ball bearings the ISO/TS 16281 should be used with the help of a calculation software. The part of

Prachatice - Misplaced Pages Continue

1280-399: The outer ring. If the outer ring is not strong enough, or if it is not sufficiently braced by the supporting structure, the outer ring will deform into an oval shape from the sideways torque stress, until the gap is large enough for the rolling elements to escape. The inner ring then pops out and the bearing structurally collapses. A sideways torque on a radial bearing also applies pressure to

1320-441: The second half of the 17th century, trade on the Golden Trail declined and never revived. The town and the whole Krumlov manor changed hands again in 1719, following the death of Princess Marie Arnoštka of Eggenberg and came under the control of the affluent Schwarzenberg family . The weak political and economic situation affected the condition of the houses. Old ones were not reconstructed, and new ones were not built. Until 1918,

1360-468: The smaller contact area between the balls and races. However, they can tolerate some misalignment of the inner and outer races. Common ball bearing designs include angular contact, axial, deep-groove, and preloaded pairs. The balls in ball bearings can also be configured in various ways. Ball bearings are used in a wide range of applications, some of which include skateboards and centrifugal pumps. Although bearings had been developed since ancient times,

1400-623: The town of Prachatice the right to use the trade route to Passau and to collect customs duties there. Prachatice was fully completed in the 3rd quarter of the 14th century. During the Hussite Wars in the 15th century, Prachatice was attacked twice, It was eventually conquered by the Hussites , who killed most of the population. In 1436, after the end of the conflict, Prachatice was granted the status of royal town by King Sigismund , and all its old privileges were confirmed. Only one year later,

1440-490: The town was offered as collateral to Jan Smil of Krems , but it fell under the control of the Rosenberg family for a short period following Smil's execution in 1439 at Český Krumlov . Oldřich II of Rosenberg sold the town almost immediately after the execution, but it again became property of the family in 1501. In the second half of the 15th century, the number of inhabitants increased, and new houses had to be built. In

1480-622: The town was part of Austria-Hungary , in the district of the same name, one of the 94 Bezirkshauptmannschaften in Bohemia . After 1945, the German population was expelled as a result of World War II. There are no large industrial companies. The largest employer based in the town is the hospital. The largest industrial employers are the companies of InTiCa Systems (manufacturer of electronic components) and Reinfurt-ČR (manufacturer of ball bearings ), both with more than 250 employees. Prachatice

1520-537: Was achieved by reconstructions between 1505 and 1513. Dolní Gate ("Lower Gate"; also called Písecká ) is a preserved element of stone town fortifications, which comes from the first half of the 15th century. The gate is from around 1527 and creates the entrance to the historic centre. Prachatice is twinned with: Blanice (Otava) Too Many Requests If you report this error to the Wikimedia System Administrators, please include

1560-678: Was reconquered and connected to the Krumlov manor. After the Battle of White Mountain , Prachatice lost its royal town status and privileges and became the property of the Eggenberg family though the emperor's troops remained in the town throughout the remainder of the Thirty Years' War . Later in the war, the town was conquered by the Swedish army , and another large ransom was demanded. In

1600-455: Was then fitted to the winning bicycle ridden by James Moore in the world's first bicycle road race, Paris-Rouen , in November 1869. There are several common designs of ball bearing, each offering various performance trade-offs. They can be made from many different materials, including stainless steel , chrome steel , and ceramic ( silicon nitride , Si 3 N 4 ). A hybrid ball bearing

#392607