Rolling bearings

Abstract

This invention provides a rolling bearing equipped with a cage that offers enhanced lubricity, wear resistance, and impact resistance at low temperatures, enabling a longer service life and making it particularly useful for liquefied gas pumps. [Solution] The rolling bearing comprises at least an inner ring, an outer ring, rolling elements, and a cage, the cage being made of a resin composition, and 50% or more, preferably 60-100% by mass, of the total resin component being ultra-high molecular weight polyethylene. Furthermore, the above rolling bearing is useful for liquefied gas pumps.

Description

Technical Field

[0001] The present invention relates to a rolling bearing, and more particularly to a rolling bearing provided with a specific cage and suitable for a liquefied gas pump.

Background Art

[0002] In order to transport gases such as natural gas, the gas is liquefied and pumped by a liquefied gas pump. Fig. 1 shows an example of a liquefied gas pump. The illustrated liquefied gas pump includes a housing 21, a main shaft 23 inserted inside the housing 21, and, for example, two rolling bearings 10, 10 interposed between the housing 21 and the main shaft 23 and arranged at an axial interval. The outer rings of the rolling bearings 10, 10 are mounted inside the housing 21, and the inner rings are fitted to the main shaft 23. The main shaft 23 is rotatably supported with respect to the housing 21 by the rolling bearings 10, 10. An impeller 25 for pumping liquefied gas is provided near one end of the main shaft 23, and a motor 27 (having a stator and a rotor) for rotationally driving the main shaft 23 is provided near the other end.

[0003] In addition, in a liquefied gas pump, the rolling bearings 10, 10 are immersed in the liquefied gas, and the liquefied gas functions as a lubricant. However, since the liquefied gas has a low viscosity, its lubricity is poor. Further, the boiling point (at 1 atm) of the liquefied gas falls within a low temperature region (1°C or lower) or an extremely low temperature (-30°C or lower) region. For example, liquid nitrogen is about -196°C, liquid oxygen is about -183°C, liquefied methane gas is about -164°C, and liquefied butane gas is about +1°C. Therefore, as the rolling bearings 10, 10, cages made of a resin composition containing a fluororesin such as PTFE (polytetrafluoroethylene) as a resin component and blended with a solid lubricant for enhancing lubricity and a fibrous filler for reinforcement are widely used (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004] [Patent Document 1] Japanese Patent Publication No. 2016-75386 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] In recent years, there has been an increasing demand for longer lifespan in rolling bearings for liquefied gas pumps. To achieve this, there is a strong need for cages to have improved lubricity, wear resistance, and impact resistance at low temperatures. Therefore, the present invention aims to provide a rolling bearing that has a cage with improved lubricity, wear resistance, and impact resistance at low temperatures, enabling a longer lifespan and being particularly useful for liquefied gas pumps. [Means for solving the problem]

[0006] The above objective of the present invention is achieved by the following configuration [1] relating to a rolling bearing.

[0007] [1] A rolling bearing comprising at least an inner ring, an outer ring, rolling elements and a cage, A rolling bearing characterized in that the cage is made of a resin composition, and 50% or more by mass of the total amount of resin components is ultra-high molecular weight polyethylene.

[0008] Furthermore, preferred embodiments of the present invention relating to rolling bearings are described in the following [2] to [4].

[0009] [2] The rolling bearing according to [1], wherein the ultra-high molecular weight polyethylene is 60 to 100% by mass of the total amount of the resin components. [3] The rolling bearing according to [1], wherein the cage is made of only the ultra-high molecular weight polyethylene. [4] A rolling bearing described in any one of [1] to [3] for use in a liquefied gas pump. [Effects of the Invention]

[0010] The rolling bearing of the present invention has a cage made of a resin composition, and more than 50% by mass of the total resin component (i.e., the main component) is ultra-high molecular weight polyethylene. As a result, the lubricity, wear resistance, and impact resistance of the cage at low temperatures are further enhanced, leading to a longer lifespan, and it is particularly useful for liquefied gas pumps. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a cross-sectional view showing a liquefied gas submerged pump, which is an example of a liquefied gas pump. [Modes for carrying out the invention]

[0012] One embodiment of the present invention is described below. This embodiment is merely an example of the present invention, and the present invention is not limited to this embodiment. Furthermore, various modifications or improvements can be made to this embodiment, and such modified or improved forms may also be included in the present invention.

[0013] In the present invention, as long as the cage is made of a resin composition containing 50% by mass or more of ultra-high molecular weight polyethylene, there are no restrictions on the type or composition of the rolling bearing itself. For example, assuming that the rolling bearing is immersed in liquefied gas as a rolling bearing for a liquefied gas pump, the inner and outer rings constituting the rolling bearing can be made of sub-zero treated steel, such as stainless steel, high-speed tool steel, bearing steel, or carburized steel. The rolling elements can be made of sub-zero treated steel or ceramic, and as steel, the above-mentioned stainless steel, high-speed tool steel, bearing steel, or carburized steel can be used.

[0014] As described above, the retainer is made of a resin composition, and at least 50% by mass of the total resin component is ultra-high molecular weight polyethylene. Preferably, the weight-average molecular weight of the ultra-high molecular weight polyethylene is 1 million or more. If the weight-average molecular weight is less than 1 million, the effects of improving lubricity, wear resistance, and impact resistance at low temperatures may not be obtained. Furthermore, while there are no particular restrictions on the upper limit of the weight-average molecular weight of ultra-high molecular weight polyethylene, it is usually 20 million.

[0015] The resins other than ultra-high molecular weight polyethylene in the above resin components are preferably polyamide resins, polyimide resins, polyphenylene sulfide resins (PPS), and polyether ether ketone resins (PEEK), and may also be mixtures of two or more types.

[0016] The resin component consists of ultra-high molecular weight polyethylene accounting for 50% by mass or more, with the remainder being the other resins mentioned above. However, the higher the proportion of ultra-high molecular weight polyethylene, the better the lubricity, wear resistance, and impact resistance at low temperatures. Therefore, 60% by mass or more is preferred, 75% by mass or more is more preferred, 90% by mass or more is even more preferred, 95% by mass or more is even more preferred, and 100% by mass (i.e., the retainer is made solely of ultra-high molecular weight polyethylene) is particularly preferred.

[0017] Furthermore, the resin composition may contain a solid lubricant to enhance lubricity and a fibrous filler for reinforcement. The type of solid lubricant is not particularly limited, but examples include graphite, hexagonal boron nitride, fluoromica, melamine cyanurate, graphite fluoride, molybdenum disulfide, and tungsten disulfide. The type of fibrous filler is not particularly limited, but examples include aluminum borate whiskers, potassium titanate whiskers, carbon whiskers, graphite whiskers, silicon carbide whiskers, silicon nitride whiskers, alumina whiskers, carbon fibers, silica fibers, and glass fibers.

[0018] In addition, depending on the purpose, various compounding agents such as heat stabilizers, light stabilizers, antioxidants, plasticizers, lubricants, colorants, flame retardants, ultraviolet absorbers, antistatic agents, antifungal agents, carbon black, inorganic fillers such as talc, and neutron shielding agents, which are usually added and mixed with polyolefins, may be blended within a range that does not impair the object of the present invention.

[0019] Note that the blending amounts of the above-mentioned solid lubricants, fibrous fillers, and various compounding agents in the resin composition are each the necessary amounts. However, as shown in the examples described later, it is particularly preferable that the cage consists of only ultra-high molecular weight polyethylene, that is, the cage is made of only ultra-high molecular weight polyethylene.

[0020] To manufacture the cage, since 50% by mass or more of the total amount of the resin component is ultra-high molecular weight polyethylene, it has poor fluidity and it is difficult to manufacture it by injection molding like a general resin cage. Therefore, in the present invention, it is appropriate to manufacture the cage by cutting.

Examples

[0021] Hereinafter, the present invention will be further described with reference to examples.

[0022] (Examples 1 to 3, Comparative Example 1) As shown in Table 1, in Example 1, a test piece consisting of 100% by mass of ultra-high molecular weight polyethylene was produced. Also, in Example 2, a test piece consisting of 90% by mass of ultra-high molecular weight polyethylene and 10% by mass of an inorganic filler was produced. Further, in Example 3, a test piece consisting of 95% by mass of ultra-high molecular weight polyethylene and 5% by mass of a reinforcing material was produced.

[0023] Also, in Comparative Example 1, a test piece consisting of "PB1211" manufactured by AGC Inc. (80% by mass of PTFE, 15% by mass of glass fiber, 5% by mass of molybdenum disulfide (MoS2)) was produced.

[0024] All test specimens were 40 mm wide x 40 mm long x 4 mm thick. A SUS440C stainless steel ball (φ6.35 mm) was placed on the test specimen, and a ball-on-disk friction and wear test was performed. The test was conducted under liquid nitrogen conditions, with the following sliding conditions: load: 20 N, rotation radius: 11.4 mm, rotation speed: 50 rpm, and test time: 60 minutes. After the test, the wear volume of the test specimen was measured using a CCI (optical interference microscope: Taylor Hobson). Here, the wear volume represents the amount of wear due to sliding, and a smaller wear volume indicates better wear resistance. The ratio of the wear volume of the example to the wear volume of comparative example 1 was calculated as the "wear volume ratio".

[0025] The results are shown in Table 1, and it can be seen that each example (Examples 1-3) using ultra-high molecular weight polyethylene as the resin component exhibits superior abrasion characteristics compared to Comparative Example 1, which uses PTFE as the resin component.

[0026] [Table 1]

[0027] Furthermore, the Izod impact values ​​(kJ / m²) under liquid nitrogen were measured for the test specimens of Examples 1-3 and Comparative Example 1. 2 The following measurements were taken. The results are shown in Table 2, and it can be seen that each example using ultra-high molecular weight polyethylene as the resin component is superior to Comparative Example 1, which uses PTFE as the resin component, in terms of impact resistance at extremely low temperatures. In particular, the test piece of Example 1, which uses only ultra-high molecular weight polyethylene (ultra-high molecular weight polyethylene: 100% by mass), is outstanding.

[0028] [Table 2]

[0029] As is clear from the results of the above examples, rolling bearings equipped with a cage made of ultra-high molecular weight polyethylene as the resin component are suitable for use in liquefied gas pumps because they have excellent wear resistance and impact resistance at extremely low temperatures. [Explanation of Symbols]

[0030] 10 Rolling bearings 21 Housing 23 Main axis 25 Impeller 27 Motor

Claims

1. In a rolling bearing comprising at least an inner ring, an outer ring, rolling elements, and a cage, A rolling bearing characterized in that the cage is made of a resin composition, and 50% or more by mass of the total amount of resin components is ultra-high molecular weight polyethylene.

2. The rolling bearing according to claim 1, wherein the ultra-high molecular weight polyethylene is 60 to 100% by mass of the total amount of the resin components.

3. The rolling bearing according to claim 1, wherein the retainer is made solely of the ultra-high molecular weight polyethylene.

4. A rolling bearing according to any one of claims 1 to 3, for use in a liquefied gas pump.

Images