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Selection and Installation of Bearings I. Basic Code for Rolling Bearings file:///C:/DOCUME%7E1/ADMINI%7E1/LOCALS%7E1/Temp/msohtml1/01/clip_image001.gif Bearing type code: 0 Angular contact ball bearing 1 Self-aligning ball bearing 2 Spherical roller bearing and spherical roller thrust bearing 3 Tapered roller bearing 4 Double row deep groove ball bearing 5 Thrust ball bearing 6 Single row deep groove ball bearing 7 Single row angular contact ball bearing 8 Cylindrical roller thrust bearing N Cylindrical roller bearing QJ Four-point contact ball bearing II. Classification of Bearings and Their Advantages and Disadvantages Bearings can be divided into two main categories: rolling bearings and sliding bearings. (1) Advantages and disadvantages of rolling bearings compared to sliding bearings: Advantages of rolling bearings: 1. Rolling bearings have a lower friction coefficient than sliding bearings, resulting in higher transmission efficiency. The friction coefficient of ordinary sliding bearings is 0.08–0.12, whereas that of rolling bearings is only 0.001–0.005; 2. Rolling bearings have been standardized, serialized, and generalized, making them suitable for mass production and supply, as well as easy to use and maintain ； 3. Rolling bearings are made of bearing steel and undergo heat treatment; as a result, they not only possess high mechanical properties and a long service life, but also help to save the expensive non-ferrous metals used in manufacturing sliding bearings. 4. The internal clearance in rolling bearings is very small, and the machining precision of their components is high, which enables them to operate with high precision. At the same time, the stiffness of the bearing can be increased by applying a preload. This is very important for precision machinery; 5. Certain rolling bearings can withstand both radial and axial loads, thereby simplifying the design of the bearing supports; 6. Due to their high efficiency in transmitting force and low heat generation, rolling bearings reduce the amount of lubricant needed, making maintenance simpler; 7. Rolling bearings can be easily installed in any orientation within a space. However, everything has two sides, and rolling bearings also have certain disadvantages, mainly: 1. Rolling bearings have a much lower capacity to bear loads compared to sliding bearings of the same volume; as a result, they have larger radial dimensions. Therefore, in applications subject to high loads and where a small radial dimension and a compact design are required (such as in internal combustion engine crankshaft bearings), sliding bearings are commonly used ； 2. Rolling bearings generate significant vibration and noise, especially toward the end of their useful life. Therefore, in applications that require high precision and where vibration is not tolerable, rolling bearings are not suitable; sliding bearings are generally a better choice in such cases. 3. Rolling bearings are particularly sensitive to foreign objects such as metal shavings; once such objects enter the bearing, it can result in intermittent severe vibration and noise, as well as premature damage. Furthermore, rolling bearings are also prone to premature failure due to metal inclusions and other impurities. Even without early damage, the lifespan of rolling bearings is limited to a certain extent. In short, the service life of rolling bearings is shorter than that of sliding bearings. However, compared to sliding bearings, rolling bearings have their own advantages and disadvantages, and are suitable for certain applications; therefore, they cannot completely replace each other. Yet, due to the outstanding advantages of rolling bearings, they have now become the primary type of bearing used in machinery, with their use becoming increasingly widespread. III. Classification of rolling bearings file:///C:/DOCUME%7E1/ADMINI%7E1/LOCALS%7E1/Temp/msohtml1/01/clip_image002.gif IV. How to select rolling bearings 1. Methods and steps for selection The proper selection of rolling bearings is crucial for ensuring that the main machine operates efficiently and has an extended service life ； It plays a very important role in enabling enterprises to shorten maintenance time, reduce maintenance costs, and improve the operational rate of machinery. Therefore, whether it is the design and manufacturing party or the maintenance and operating party, great attention must be paid when selecting rolling bearings. Generally speaking, the steps for selecting bearings can be summarized as follows: 1. Based on the operating conditions of the bearing (including the direction and type of load, speed, lubrication method, requirements regarding coaxiality, whether positioning is required or not, the installation and maintenance environment, ambient temperature, etc.), select the basic type of bearing, tolerance grade, and clearance ； 2. Based on the operating conditions, stress levels, and lifespan requirements of the bearing, the bearing model is determined through calculations; or the bearing model is selected according to the application requirements, after which its lifespan is verified ； 3. Verify the rated load and maximum speed of the selected bearing. The main factors considered when selecting a bearing are the maximum speed, the desired service life, and the load capacity. Other factors help determine the final design for the bearing’s type, structure, dimensions, tolerance grades, and clearance. 1. Type selection: Various types of rolling bearings have different characteristics and are suitable for different applications in various machines. When selecting a bearing type, the following factors should generally be considered. Under normal circumstances: thrust bearings and angular contact bearings are used when bearing thrust loads, ball bearings are typically employed in high-speed applications, while roller bearings are chosen when dealing with heavy radial loads. In short, the appropriate type should be selected from a variety of bearing products manufactured by different manufacturers. Several factors to consider when selecting bearings: (1) The space occupied by the bearing in the machinery and its location. In mechanical design, the dimensions of the shaft are determined first, and then rolling bearings are selected based on those shaft dimensions. Generally, ball bearings are used for the small shafts, while roller bearings are used for the large shafts. However, when the bearing is constrained in the diameter direction of the machine, needle bearings or ball or roller bearings from the ultra-light and extra-ultra-light series are selected ； When the axial position of the bearing in the machine is restricted, narrow or extra-narrow series of ball or roller bearings can be used. (2) The magnitude, direction, and nature of the load on the bearing. The load is the most important factor in selecting a bearing. Roller bearings are used to bear heavier loads, while ball bearings are used for lighter or moderate loads. Bearings made of carburized steel or quenched in bainite can withstand impact and vibration loads. In terms of the direction of the load, when a pure radial load is applied, deep groove ball bearings, cylindrical roller bearings, or needle bearings can be used. When subjected to a relatively small pure axial load, thrust ball bearings can be used ； Thrust roller bearings can be used when subjected to large pure axial loads. When bearings are subjected to combined radial and axial loads, angular contact ball bearings or tapered roller bearings are generally selected. For cantilever support structures, tapered roller bearings or angular contact ball bearings are commonly used, and they are employed in pairs. (3) Self-aligning capability of bearings: When the center line of the shaft differs from that of the bearing housing, resulting in an angular error, or when the shaft’s stiffness is low due to a large distance between its two supports, making it prone to bending or tilting under stress, self-aligning ball or roller bearings, as well as outer ball bearings with good self-aligning capabilities, can be used. Such bearings can maintain normal operation even when the shaft is slightly tilted or bent. (4) Bearing stiffness The bearing stiffness refers to the magnitude of the force required to cause a unit deformation in the bearing. The elastic deformation of rolling bearings is very small, and it can be ignored in most machines. However, in some machines, such as machine tool spindles, bearing stiffness is an important factor; in such cases, cylindrical and tapered roller bearings should generally be used. This is because in these two types of bearings, the rolling elements are in point contact with the raceways when carrying loads, resulting in poor rigidity. Furthermore, various types of bearings can also achieve an increase in supporting stiffness through preloading. In bearings such as angular contact ball bearings and tapered roller bearings, in order to prevent shaft vibration and increase support stiffness, a certain axial force is often applied in advance during installation to press them together. It should be noted here that the pre-tightening amount must not be too large. If it is too large, it will increase bearing friction and raise temperature, affecting the bearing’s service life. (5) Bearing speed: Each bearing model has its own maximum speed limit, which is determined by physical characteristics such as size, type, and structure. The maximum speed refers to the highest operating speed of the bearing (usually expressed in r/min); exceeding this limit can cause the bearing’s temperature to rise, the lubricant to dry out, and even lead to the bearing getting stuck. The pitch diameter D multiplied by the shaft’s rotational speed (in r/min) yields a critical speed factor (DN), which is very important when selecting the type and size of bearings. The product catalogs of most bearing manufacturers provide the maximum speed values for their products, and practice has shown that it is better to operate at speeds that are 90% below these maximum values. The maximum speed of lip-lubricated bearings is lower than that of oil-lubricated bearings, and the method of supplying oil to the bearings affects the maximum speed that can be achieved. For grease-lubricated bearings, their maximum speed is generally only 80% of the maximum speed achievable when such bearings are equipped with a high-quality recirculating oil system; whereas for oil-mist lubrication systems, the maximum speed is usually 50% higher than that of similar basic lubrication systems. (6) The design and structure of the cage also affect the bearing’s maximum speed, as there is a sliding contact between the rolling elements and the cage surface. Using a costly, well-designed cage made of high-quality, low-friction materials not only separates the rolling elements but also helps maintain the lubricating oil film in the sliding contact area. However, inexpensive retainers such as stamping retainers can usually only keep the rolling elements separated. Therefore, they suffer from accident-prone and troublesome sliding contact, resulting in a lower limit speed. Generally, in applications operating at high speeds, deep groove ball bearings, angular contact bearings, and cylindrical roller bearings are preferred ； In applications operating at lower speeds, tapered roller bearings can be used. The maximum speed limit for tapered roller bearings is generally about 65% of that for deep groove ball bearings, 70% for cylindrical roller bearings, and 60% for angular contact ball bearings. Thrust ball bearings have a low maximum speed and can only be used in applications with lower speeds. For bearings of the same type, the smaller the size, the higher the allowable rotational speed. When selecting bearings, care should be taken to ensure that the actual rotational speed is below the limit speed. (7) Bearing play and axial displacement: Usually, a shaft is supported by two bearings at a certain distance apart. To accommodate the varying degrees of thermal expansion affecting the shaft and the housing, one bearing should be fixed axially during installation, while the other should allow it to move along the shaft (i.e., serve as a floating support), in order to prevent jamming caused by the expansion or contraction of the shaft. For floating bearings, cylindrical roller bearings and needle bearings with no ribs on the inner or outer ring are usually chosen, mainly because the internal structure of such bearings allows for appropriate axial movement between the shaft and the housing. At this time, a tight fit can be used between the inner ring and the shaft, as well as between the outer ring and the housing hole. When non-separable bearings are used as floating supports, such as deep groove ball bearings or self-aligning roller bearings, it is necessary during installation to allow a loose fit between the outer ring and the housing bore, or between the inner ring and the shaft, so that free axial movement is possible. Tapered roller bearings, self-aligning roller bearings, and deep groove ball bearings are essentially of the positioning type; when used for non-positioning purposes, they are installed with a loose fit. All thrust roller bearings are positioning-type bearings. (8) Facilitates the installation and removal of bearings. When selecting a bearing type, it is also necessary to consider thoroughly whether its installation and removal are easy, especially for large and extra-large bearings. Commonly used angular contact ball bearings, tapered roller bearings, cylindrical roller bearings, and needle roller bearings with separable outer rings are easy to install and remove, as their inner and outer rings can be mounted on the shaft or in the holes of the housing separately. In addition, self-aligning roller bearings, double-row cylindrical roller bearings, and self-aligning ball bearings with a conical bore in the inner diameter and set screws are also relatively easy to install and remove. (9) Clearance selection: Clearance is an important factor for the proper operation of rolling bearings, and it is divided into axial clearance and radial clearance. Choosing the appropriate clearance allows the load to be distributed evenly among the bearing rollers ； It can restrict the axial and radial displacement of the shaft (or housing), ensuring the rotational accuracy of the shaft ； Enables the bearing to operate properly at specified temperatures ； Reducing vibration and noise helps to increase the lifespan of bearings. Therefore, when selecting bearings, it is necessary to choose the appropriate bearing clearance. a. The so-called clearance refers to the maximum amount of movement of one ring while the other ring remains fixed, either radially or axially. Generally speaking, the greater the radial clearance, the greater the axial clearance, and vice versa. b. The function of the clearance — is to ensure the proper operation of the rolling elements and proper lubrication, as well as to compensate for the thermal expansion of the shaft. If the clearance is too large, the number of rolling elements under load during operation decreases while the load on each individual rolling element increases, which reduces rotational accuracy and lifespan and causes vibration and noise. Too small a clearance exacerbates wear and heating, thereby reducing the bearing’s lifespan as well. c. When selecting the bearing clearance, the following factors should be considered: 1. The operating conditions of the bearing, such as load, temperature, speed, etc ； 2. Requirements for the performance of bearings (rotational accuracy, friction torque, vibration, noise) ； 3. The reduced bearing clearance is caused by an interference fit between the bearing and the shaft as well as the housing holes ； 4. When the bearing is in operation, the temperature difference between the inner and outer rings causes the bearing clearance to decrease ； 5. The difference in expansion coefficients between the shaft and the housing materials causes the bearing clearance to decrease or increase. Based on practical experience, the most suitable operating clearance for ball bearings is close to zero ； Roller bearings should maintain a small amount of operating clearance. In components that require good rigidity, bearings allow a certain amount of preload. It should be specifically noted here that A refers to the so-called operating clearance – the clearance of the bearing during operation. During operation, the inner ring experiences the greatest temperature rise and the most thermal expansion, which results in a reduction of the bearing’s clearance ； At the same time, due to the load, elastic deformation occurs at the contact point between the rolling elements and the raceways, which increases the bearing clearance. Whether the operating clearance of the bearing is greater or smaller than the installation clearance depends on the combined effect of these two factors. B. Installation clearance 2 }& c5 C4 h+N# D/ x6 X! ?, N: Also known as fit clearance, it is the clearance that exists in a bearing when it has been installed on the shaft and bearing housing but has not yet started to operate. Due to interference fitting, either the inner ring expands, the outer ring contracts, or both, which results in an installation clearance that is smaller than the original clearance. C. There is another type of clearance called the original clearance, which refers to the clearance of the bearing in its free state before installation. The original clearance is determined by the manufacturing process and assembly carried out by the factory. The original clearance is greater than the installed clearance. Our choice of clearance is mainly to select an appropriate operating clearance. For standard deep groove ball bearings, the radial internal clearance (in um), bearing nominal inner diameter d (in mm), and radial internal clearances C2, C0, C3, C4, C5 are as follows: above, below, minimum, maximum, minimum, maximum, minimum, maximum, minimum, maximum. 2.5, 6, 0, 7, 2, 13; 8, 23, 14, 29, 20, 37; 6, 10, 0, 7, 2, 13; 8, 23, 14, 29, 20, 37; 10, 18, 0, 9, 3, 18; 11, 25, 18, 33, 25, 45; 18, 24, 0, 10, 5, 20; 13, 28, 20, 36, 28, 48; 24, 30, 1, 11, 5, 20; 13, 28, 23, 41, 30, 53; 30, 40, 1, 11, 6, 20; 15, 33, 28, 46, 40, 64; 40, 50, 1, 11, 6, 23; 18, 36, 30, 51, 45, 73; 50, 65, 1, 15, 8, 28; 23, 43, 38, 61, 55, 90; 65, 80, 1, 15, 10, 30; 25, 51, 46, 71, 65, 105. **The clearance values specified by standards are divided into three groups: the basic group (C0 group), the low-clearance auxiliary group (C2 group), and the high-clearance auxiliary groups (C3, C4, C5 groups).** When making a choice, under normal operating conditions, it is advisable to opt for the basic group first, so that the bearing can obtain an appropriate operating clearance. When the basic group cannot meet the usage requirements, the auxiliary group clearance should be selected. The large clearance auxiliary group is suitable for applications where the bearing fits tightly with the shaft and the housing bore, where there is a significant temperature difference between the inner and outer rings of the bearing, where deep groove ball bearings need to withstand high axial loads or have their self-aligning properties improved, as well as in situations where it is necessary to increase the maximum operating speed and reduce the bearing’s friction torque ； The low clearance auxiliary group is suitable for applications that require high rotational precision, strict control over the axial displacement of the housing holes, and reduced vibration and noise. 0 j. b- ~5 L0 B5 |- V6 }% J# p# u; o. V. Inspection of clearance: The inspection of clearance is divided into two types: radial clearance inspection and axial clearance inspection. (1) The methods for checking radial clearance are as follows: ‘G5 Y: F. j$ Q) p* N” ?* {' T—I. Sensory method: 1. Rotate the bearing by hand; it should turn smoothly and effortlessly, without any sticking. 5 z& K3 B- g/ s: h. w Chemical Technology Forum – Giving roses to others leaves a pleasant fragrance behind. 2. By shaking the outer ring of the bearing, even if the radial clearance is only 0.01 mm, the axial displacement of the highest point on the bearing is still 0.10~0.15 mm. This method is specifically designed for single-row radial ball bearings. & W* M9 S) ?* f, }; d" x Chemical Engineering Technology Forum – Giving roses brings fragrance to one’s own hands. II. Measurement methods & J- K+ m0 D; _$z } r- rbbs.**.net 1. Use a feeler gauge to check the area of the rolling bearing that is under maximum load; insert the feeler gauge between the roller that is 180° from this area and the outer (or inner) ring. The thickness of the feeler gauge that fits appropriately represents the radial clearance of the bearing. This method is widely used in self-aligning bearings and cylindrical roller bearings. 2. Use a dial indicator for inspection: first zero the dial indicator, then lift the outer ring of the bearing; the reading on the dial indicator represents the radial play of the bearing. III. Lead wire method: Select an appropriate lead wire and insert it between the two rolling elements; then rotate the inner and outer rings so that the rolling elements press against the lead wire. Remove the lead wire and use a caliper to measure the portion of it that has been compressed by the rolling elements – the value read off is the clearance of that bearing. (II) The method for checking the axial clearance is as follows: d7 g6 W" ~9 D8 Z) x*ebbs.**.net1. 1. The tactile method & O. `$ f8 J' w+ / v – This involves using fingers to check the axial clearance of rolling bearings, and it is used in cases where the shaft end is exposed. When the shaft end is sealed or cannot be inspected with fingers for other reasons, it is possible to check whether the shaft rotates smoothly. 2. Measurement method 5 _; m `$ E&_bbs.**.net (1) Use a feeler gauge for inspection; the procedure is the same as that used to check radial clearance, but the axial clearance should be given by the formula c = λ / (2sinβ), where c represents axial clearance in mm ； λ —— gauge thickness, mm ； β —— bearing cone angle, (°). / w5 |% z+ @9 c% R (2) Use a dial indicator to check this; by moving the shaft with a crowbar to its two extreme positions, the difference in the readings taken with the dial indicator represents the axial play of the bearing. However, the force applied to the lever should not be too great, otherwise the housing will undergo elastic deformation; even if the deformation is small, it still affects the accuracy of the measured axial clearance. VI. Characteristics of various bearings: 1. Self-aligning roller bearings: Primarily used to bear radial loads; they can also handle moderate axial loads. They have a high capacity to bear radial loads and excellent self-aligning properties. They can operate with an angular deviation between the inner and outer rings of no more than 2.5°. The inner ring of these bearings can move axially, allowing for adjustment of the radial clearance. Mounted on retaining rings, they are suitable for use on shafts without shoulders, as well as in situations where frequent installation and removal of bearings are required. 2. Stainless steel bearings: Stainless steel bearings are characterized by high precision, low noise, corrosion resistance, resistance to acids and alkalis, non-magnetism, and high temperature tolerance. 3. Oil-impregnated bearings: Under variable load conditions, the friction factor, temperature rise, and vibration levels are all higher than under static load conditions. The friction factor of oil-impregnated bearings is lower than that of ordinary bearings, but the vibration characteristics are the opposite; when in operation, oil-impregnated bearings exhibit better tribological properties than ordinary bearings, whereas ordinary bearings have superior vibration characteristics. 4. Spherical bearing: It consists of a spherical bearing with seals on both sides and a bearing housing that is cast (or made by stamping steel plates). The internal structure of an outer spherical bearing is the same as that of a deep groove ball bearing, but the outer ring of this type of bearing has a spherically truncated outer surface that fits with the concave spherical surface of the bearing housing, allowing for automatic self-centering. Typically, set screws, eccentric sleeves, or retaining rings are used to fix the inner ring of such bearings to the shaft, so that it rotates together with the shaft. Bearings with housings have a compact design and are easy to install and remove, making them suitable for simple support applications. 5. Needle bearings: They can withstand radial loads, have a small outer diameter, and are particularly suitable for structures where the radial installation dimensions are limited. 6. Thrust ball bearings: They can only withstand axial loads in one direction, restricting axial movement in that direction; their maximum rotational speed is low. Dual-direction thrust ball bearings can handle axial loads in both directions, limiting axial movement in both directions as well, with a low maximum rotational speed. 7. Tapered roller bearings: They can withstand both radial and axial loads, with radial loads being the predominant type. Bearings with a larger taper angle can handle axial loads as well as radial loads; under radial load, an additional axial force is generated. Therefore, they are usually used in pairs. They can withstand radial loads, but when used alone, an external axial force must be greater than this additional axial force. 8. Angular contact ball bearings: They can withstand both radial loads and unidirectional axial loads, as well as pure axial loads. The capacity to handle axial loads is determined by the contact angle α (the standard contact angles are 15°, 30°, and 40°), and this capacity increases as the contact angle increases. It has a high maximum rotational speed; when a pair of bearings is mounted on the shaft relative to each other, it can restrict axial movement in both directions. They are generally used in pairs, and in the separate-type design, the inner and outer rings can be mounted separately, making them suitable for locations where installation conditions are limited. 9. Self-aligning ball bearings: These bearings come in two types – those with cylindrical bores and those with tapered bores. They are primarily designed to bear radial loads, while also being able to handle moderate axial loads. The axial displacement of the shaft (or housing) is limited within the range of the clearance provided by the bearing; they possess self-aligning capabilities, allowing them to function properly even when the inner and outer rings are tilted by up to 3° relative to each other. They are suitable for use in components where the coaxiality of the mounting holes cannot be guaranteed with precision. 10. Deep groove bearings: These bearings are mainly used to bear radial loads, but they can also handle moderate axial loads. The axial displacement of the shaft is limited within the axial clearance range, and the inner ring can be tilted by 8° to 15° relative to the outer ring. VII. How to determine the quality of bearings after use 1. Assessment of radial ball bearings: In a radial ball bearing in good technical condition, there should be no peeling or severe wear on the raceways of the inner and outer rings, and these raceways should appear as smooth, circular grooves ； All balls should remain round, with no spots, cracks, or peeling on their surface ； The cage is not loose, broken, or worn out. When holding the inner ring with one hand and using the other hand to gently push the outer ring to rotate quickly, the rotation should be smooth, with only a slight sound of the balls rolling on the tracks, and no vibration ； When stopping, the speed should be reduced gradually, and there should be no backward movement after stopping. In a normal radial ball bearing, the clearance between the inner and outer rings and the rolling elements is 0.005–0.010 mm; when the inner and outer rings are moved radially, no clearance should be felt. For used bearings, one can hold the inner ring and shake it axially a few times; if there is a noticeable noise coming from the outer ring and the balls, it indicates that the clearance between them exceeds 0.03 mm, and such bearings should not be used any longer. 2. Inspection of tapered roller bearings: After the bearings have been in use, it is necessary to check whether there is any peeling on the rolling elements and the inner ring raceway, whether the cage is too loose, whether the front and rear edges of the inner ring are intact, and whether there are any cracks in the outer ring raceway. After the inner ring and roller assembly are installed in the outer ring, the rollers should fall into the middle of the raceways, with a forward displacement of no more than 1.5 mm. If one of them fails, it cannot be used. 3. Inspection of self-aligning roller bearings and short cylindrical roller bearings: The outer rings of these bearings are separable. Under normal conditions, the inner and outer raceways as well as the rollers should be free of cracks, pitting, and deep wear marks ； The cage should be free from deformation and able to hold the rollers against the inner ring ； The fit clearance between the inner and outer raceways and the rollers should not exceed 0.06 mm. 4. Inspection of thrust ball bearings: Under normal conditions, there should be no flaking or severe wear on the two raceways, and the balls should be free from cracks and pitting ； The cage should be free of deformation, not touch the two raceway washers, and hold the balls tightly together. VIII. Bearing Installation The correct installation of bearings affects precision, lifespan, and performance. Therefore, installation must be carried out strictly in accordance with the operational standards, which generally include the following items: (1) Cleaning the bearings and components related to them; (2) Checking the dimensions and finish of these related components; (3) Installation; (4) Inspection after the bearings have been installed; (5) Applying lubricant. It is recommended to open the bearing packaging only just before installation. It is generally lubricated with grease; no cleaning is required, and the grease is simply filled in. Lubricated with lubricating oil, it generally does not need to be cleaned. However, bearings used in instruments or at high speeds should be cleaned with clean oil to remove the rust inhibitors applied to them. Bearings without rust inhibitors are prone to rusting, so they cannot be left unattended. Furthermore, bearings that have already been filled with grease are used directly without cleaning. The method of installing bearings varies depending on the bearing’s structure, fit, and operating conditions. Generally, since the shaft is the one that rotates, the inner ring requires an interference fit. Cylindrical hole bearings are usually pressed in using a press or installed by heat treatment. In the case of tapered holes, it can be installed directly on a tapered shaft or using a sleeve. When installing it into the housing, a clearance fit is generally used, with an interference fit on the outer ring; it is usually pressed in using a press, or a cold-shrink fitting method after cooling may also be employed. When dry ice is used as a coolant in applications involving cold shrink fitting, moisture in the air will condense on the surface of the bearings. Therefore, appropriate rust prevention measures are needed.