JP2016023685A - Cylindrical roller bearing for turbo refrigerator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a roller bearing for a free side bearing of a turbo refrigerator which can prevent the damage caused by skidding for a long time and is useful as a substitute of a combination angular ball bearing.SOLUTION: In a cylindrical roller bearing for a turbo refrigerator, a DLC film containing silicon is formed on an inner ring raceway surface, and the silicon concentration of an outermost surface of the DLC film is 1-17 atom%.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a cylindrical roller bearing used as a free side bearing of a turbo refrigerator.

  As shown in FIG. 3, in the centrifugal chiller, the rotating shaft is supported mainly by a combination angular ball bearing on both the fixed side and the free side (see, for example, Patent Documents 1 and 2). Cylindrical roller bearings are sometimes used as free-side bearings to absorb the expansion of the rotating shaft as temperature rises (see FIG. 4), but they are loaded in the case of a turbo refrigerator used at high speed rotation. The so-called skid, which increases the revolving slip depending on the radial load, may cause wear damage and seizure. Yes.

  However, when a combination angular contact ball bearing is used as the free-side bearing, there are disadvantages such as an increase in the size of the compressor and an increase in loss due to an increase in the number of bearing rows. If the clearance between the outer ring and the housing of the free-side bearing is too large, excessive leakage of the lubricating oil from the outer diameter of the outer ring spacer is excessive, and if it is too small, the outer ring and the housing are constrained, and the bearing is subjected to a load due to shaft extension. Setting is difficult because there is a possibility of early damage.

JP 2009-19601 A JP 2009-215931 A

  The present invention has been made in view of such a situation, and a cylindrical roller bearing that can prevent damage due to skidding for a long period of time and is useful as a substitute for a combined angular ball bearing for a free-side bearing of a turbo refrigerator. The purpose is to provide.

  In order to solve the above problems, the present invention is characterized in that a DLC film containing silicon is formed on the inner ring raceway surface, and the silicon concentration of the outermost surface of the DLC film is 1 to 17 atomic%. Provided is a cylindrical roller bearing for a turbo refrigerator.

  The cylindrical roller bearing of the present invention is formed by forming a DLC film containing a specific amount of silicon on the raceway surface of the inner ring, and since DLC film contains a predetermined amount of silicon while ensuring the slidability and hardness of the DLC film. The residual stress of the film is reduced and peeling is suppressed, and as a result, skid damage can be prevented for a long period of time, and it is extremely useful as a substitute for a combination angular contact ball bearing for a free side bearing of a turbo refrigerator.

It is sectional drawing which shows the cylindrical roller bearing for turbo refrigerators of this invention. It is a graph which shows the time-dependent change of the amount of peeling of the silicon-containing DLC film obtained in the Example. It is sectional drawing which shows the rotating shaft periphery of a turbo refrigerator, and shows the general case using a combination angular contact ball bearing as a free side bearing. It is sectional drawing which shows the other example of the periphery of the rotating shaft of a turbo refrigerator, and shows the case where a cylindrical roller bearing is used as a free side bearing.

  Hereinafter, the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a sectional view showing a cylindrical roller bearing for a turbo refrigerator according to the present invention. As shown in the figure, a plurality of cylindrical rollers 3 are held by a cage 4 between the inner ring 1 and the outer ring 2 so as to be freely rollable. In the present invention, a DLC film 10 containing silicon (hereinafter referred to as “silicon-containing DLC film”) 10 is formed on the inner ring raceway surface 1a.

  The general DLC film itself has the effect of improving the slidability and wear resistance. However, the inclusion of silicon further reduces the residual stress of the film as compared with the case of carbon alone. The peeling is suppressed and the durability is increased. However, if silicon is excessive on the outermost surface of the silicon-containing DLC film 10, the slidability and hardness inherent in the silicon-containing DLC film 10 are lowered, so that the silicon concentration on the outermost surface is 17 atomic% or less. On the other hand, in order to obtain the effect of reducing the residual stress due to silicon, the silicon concentration on the outermost surface needs to be 1 atomic% or more. Preferably, the silicon concentration at the outermost surface of silicon-containing DLC film 10 is 3 to 5 atomic%.

  As described above, the silicon concentration of the outermost surface of the silicon-containing DLC coating 10 is 1 to 17 atomic%, but the silicon concentration may be uniformly 1 to 17 atomic% throughout the coating, and the carbon concentration increases toward the surface. The gradient composition may be such that the ratio is larger than the ratio of silicon. In the case of the latter gradient composition, the effect of reducing the residual stress of the silicon-containing DLC film 10 and the improvement of improving the slidability and hardness can be obtained more effectively.

  The silicon-containing DLC film 10 preferably contains hydrogen in addition to silicon. Although C—H bond and Si—H bond are mixed by hydrogen, since Si—H bond has low binding energy, uncombined hydrogen atoms are positively bonded to silicon atoms and do not contain hydrogen. As a result, the residual stress of the film becomes smaller.

  In order to form such a silicon-containing DLC film 10, sputtering may be performed in a vacuum using a carbon target and a silicon target. When hydrogen is further contained, sputtering is performed in a hydrocarbon gas atmosphere such as methane gas using a carbon target and a silicon target. Sputtering can be performed using, for example, a magnetron sputtering apparatus. In the case of a gradient composition, the voltage applied to the carbon target during film formation is gradually increased while the voltage applied to the silicon target is gradually decreased.

  In addition, it is preferable to control the temperature of the inner ring raceway surface 1a to 150 to 180 ° C. during film formation. If it is less than 150 ° C., the film formation efficiency is poor, and if it exceeds 180 ° C., silicon tends to be formed in a crystalline state. On the other hand, the volume expansion of the DLC film 10 can be suppressed by setting the temperature range to 150 to 180 ° C. Moreover, the hardness reduction of the steel material which comprises the inner ring | wheel 1 is prevented, and the adhesiveness of the inner ring raceway surface 1a and the DLC film 10 becomes favorable.

  The film thickness of the silicon-containing DLC film 10 is preferably 0.8 to 1.6 μm. If the film thickness is less than 0.8 μm, the durability of the film is not sufficient, and if it exceeds 1.6 μm, the residual stress of the film is too large and sufficient adhesion cannot be obtained, and the film tends to peel off from the inner ring raceway surface 1a. In order to obtain such a film thickness, the sputtering time may be adjusted.

  Moreover, it is preferable that the silicon-containing DLC film 10 has a Young's modulus of 150 to 200 GPa. When the Young's modulus is less than 150 GPa, the hardness of the DLC film 10 is not sufficient, and when it exceeds 200 GPa, the inner ring raceway surface 1a is difficult to deform and easily peels off in a high load environment.

  Further, the DLC film 10 may be formed through a metal intermediate layer such as chromium.

  In the present invention, there is no limitation except that the silicon-containing DLC film 10 is formed on the inner ring raceway surface 1a as described above, and the materials and lubricants of the inner and outer rings may be known ones.

  The present invention will be further described below with reference to examples, but the present invention is not limited thereto.

  The inner ring of a general cylindrical roller bearing (nominal number “NU307”) for a turbo refrigerator was mounted on a magnetron sputtering apparatus. The magnetron sputtering apparatus was provided with a carbon target and a silicon target, and a silicon-containing DLC film was formed on the inner ring raceway surface at a temperature of 180 ° C. in a vacuum. At that time, the voltage applied to the carbon target was gradually increased, and the voltage applied to the silicon target was gradually decreased, so that the gradient composition was obtained so that the silicon concentration on the outermost surface was 3 to 6 atomic%. And the bearing was assembled using the inner ring | wheel in which the silicon-containing DLC film was formed, and it was set as the test bearing A.

  For comparison, the same cylindrical roller bearing composed of an inner ring without forming a film and having an exposed inner ring raceway surface was used as a test bearing B.

  Durability tests were conducted using the test bearings A and B at the PV values and sliding speeds shown in Table 1. The PV value and sliding speed are ratios relative to the skid generation limit value. The durability was evaluated by the time until the skid damage occurred (durability time).

  The results are shown in Table 1. In test bearing B, skid damage occurred after 30 hours, while in test bearing A with a silicon-containing DLC film, there was no sign of skid damage even after 480 hours. I couldn't see it. Moreover, about the test bearing A, the peeling amount (area ratio of the area | region where the film has peeled with respect to the total area of a film | membrane) was calculated | required for every predetermined time, but as shown in FIG. Further, there is a sufficient margin with respect to the limit value of 30%, which is considered to have a practical effect on the amount of peeling.

  Thus, it was confirmed that the effect of preventing skidding damage can be maintained over a long period of time by forming the silicon-containing DLC film on the inner ring raceway surface as in the present invention.

DESCRIPTION OF SYMBOLS 1 Inner ring 1a Inner ring raceway surface 2 Outer ring 3 Cylindrical roller 4 Cage 10 Silicon-containing DLC film

Claims (1)

  A cylindrical roller bearing for a turbo refrigerator, wherein a DLC film containing silicon is formed on an inner ring raceway surface, and a silicon concentration of an outermost surface of the DLC film is 1 to 17 atomic%.

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