JPH025545B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cooling structure for a rotating shaft that is designed to efficiently dissipate heat from a rotating shaft that rotates at high speed, and is particularly suitable for being incorporated into a spindle of a machine tool.

An increase in the temperature of the rolling bearing of the spindle of a machine tool may deteriorate the machining accuracy of the workpiece due to the accompanying thermal deformation, and in some cases may cause seizing of the rolling bearing itself. Therefore, as a method to reduce the temperature rise of the bearing, a method has been adopted in which a very small amount of grease is sealed in the bearing to reduce the amount of heat generated by the bearing due to the large deformation rate that the grease undergoes at the rolling contact part of the bearing. .

However, as spindles in machine tools have become faster in recent years, it has become necessary to further reduce the heat generated by bearings in order to ensure machining accuracy. Cooling methods using fluids are increasingly being used. As shown in FIG. 1, which shows the spindle cooling structure of such a conventional machine tool, a spindle 1 is rotatably supported by a housing 3 via a number of bearings 2.
In the housing 3 located around the housing 3, there is an oil groove provided with an oil filler port 4 through which cooling oil is supplied and an oil drain port 5 through which the cooling oil that has become hot due to heat exchange between the bearing 2 is discharged. 6 is formed. Generally, since the outer ring of the bearing 2 is in contact with the housing 3, it generally has better heat dissipation properties and a lower temperature than the inner ring. However, in the above-mentioned cooling structure, the temperature of the outer ring tends to be lower than that of the inner ring, and as a result, the outer ring contracts while the inner ring of the bearing expands, resulting in excessive preload on the rolling elements of the bearing, which can lead to seizure. Ta.

Since the spindle is often equipped with part of the tool changer, it is difficult to route heat pipes or cooling fluid inside the spindle. Therefore, cooling the outer periphery of the spindle may be considered to improve heat dissipation on the inner ring side of the bearing, but the heat generated from the bearing needs to be taken away from the outer periphery of the rotating shaft via the inner ring of the bearing. Since the thermal resistance between the cooling fluid and the bearing is large, in order to increase the cooling efficiency, the cooling temperature must be sufficiently lowered and the temperature gradient of the heat flow path must be increased. However, when the temperature of the cooling heat is lowered, the inside of the housing, where the flow path for transporting and collecting the coolant to the rotating shaft is formed, is also cooled, causing thermal deformation of the housing and hindering the rotation of the rotating shaft. This reduces accuracy and induces axial displacement, which manifests as poor machining accuracy of the workpiece, for example, in the main spindle of a machine tool.

Generally, in machine tool spindles, etc., thermal displacement of the rotating shaft and housing is suppressed for the purpose of improving machining accuracy, and it is necessary to change the cooling capacity of the coolant depending on the rotation speed of the rotating shaft. However, even when trying to control the cooling capacity of the rotating shaft by controlling the temperature of the coolant, there is a problem with responsiveness.For example, when performing a quick start that rapidly rotates at high speed, it is necessary to control the expansion of the temperature difference between the inner and outer rings of the bearing. In some cases, the bearings were not sufficiently effective, leading to seizure of the bearings.

The present invention focuses on the Peltier effect, in which heat is absorbed or generated at the junction of two metals when a current is passed through a circuit made of a combination of two metals. In view of this, it is an object of the present invention to provide a cooling structure that is highly efficient and has excellent heat dissipation properties.

The configuration of the rotating shaft cooling structure of the present invention that achieves this objective is such that the rotating shaft is rotatably supported by a housing via a bearing, has a thermoelectric element, and has a heat generating part on the outer circumferential side and a heat absorbing part on the inner circumferential side. A cylindrical cooling device is fixed to the inner circumferential wall of the housing near the bearing so as to surround the rotating shaft with a gap therebetween, and absorb heat generated by the bearing through the rotating shaft. The cooling device is characterized in that a cooling means facing the heat generating portion on the outer peripheral side of the cooling device is provided between the cooling device and the housing.

Hereinafter, an embodiment in which a rotating shaft cooling structure according to the present invention is incorporated into a spindle of a machine tool that can rotate at high speed will be described in detail with reference to FIGS. 2 to 5. The second part representing the overall structure of this example
As shown in the figure, a drawbar 13 for fixing and releasing a tool from the spindle 12 is installed in the spindle 12, which has a tapered hole 11 formed at its tip into which a tool (not shown) is fitted. It is attached so that it can be moved freely along the The spindle 12 is rotatably supported by a housing 16 via a pair of front and rear bearings 14 and 15, and these bearings 14 and 15 are connected to the spindle 12 and the housing 16 by bearing holders 17 and 18 and nuts 19 and 20, respectively. It is fixed between.

On the other hand, a cylindrical cooling device 21 is provided on the inner circumferential wall of the housing 16 between these bearings 14 and 15, and surrounds the spindle 12 with a small gap from the outer circumferential surface of the spindle 12. As shown in FIG. 3, which is an enlarged view of 21, and FIG. bismuth telluride 2
3 are arranged alternately through resin plates 24, and cylindrical internal copper plates 25 and external copper plates 26, which are partitioned every other by the resin plates 24, are connected to the inner circumferential surface of the N-type bismuth telluride 22 and P Type of bismuth telluride 2
It is in contact with the outer peripheral surface of No. 3. These are resin plates 2
Resin flange 27 made of epoxy resin, tetrafluoroethylene resin, etc. with low thermal conductivity and electrical conductivity similar to 4.
These inner and outer peripheral surfaces are covered with an insulating layer 28 made of ceramic or the like with relatively good thermal conductivity.
It is coated with. As shown in FIG. 5, which shows a cross section in the direction of the − arrow in FIG. 4, the internal copper plate 25
A lead wire 29 led from the outside of the housing 16 is electrically connected to both ends of the housing 16, and the inner copper plate at the right end in FIG. 25 is connected to a positive potential, and the leftmost internal copper plate 25 is connected to a negative potential. In this example, N-type bismuth telluride 22 and P-type bismuth telluride 23 are used as thermoelectric elements, but other PN junction elements etc. can be used arbitrarily as long as they have a Peltier effect. It is possible.

An oil groove 32 is formed between the outer periphery of the cooling device 21 and the housing 16, which communicates with a cooling oil supply path 30 through which cooling oil is supplied and a cooling oil discharge path 31 through which the cooling oil is discharged. The cooling oil flowing through this oil groove 32 cools the external copper plate 26 which becomes hot. In this embodiment, the cooling device 21
Although cooling oil is flowed around the cooling means, it is of course possible to use other known cooling means.

Therefore, when electricity is applied to the N-type bismuth telluride 22 and the P-type bismuth telluride 23 via the internal copper plate 25 and the external copper plate 26, an endothermic action occurs in the internal copper plate 25 due to the Peltier effect, causing the spindle 12 to rotate at high speed. Since the spindle 12 and the bearings 14, 15 absorb heat from On the other hand, in parallel with this, the external copper plate 26 generates heat, but the cooling oil flowing through the oil groove 32 causes the external copper plate 26 to generate heat.
The external copper plate 26 is cooled and the high temperature cooling oil is led out of the housing 16 from the cooling oil discharge path 31. In other words, some of the frictional heat between the inner and outer rings of the bearings 14 and 15 and the rotating body is transferred to the spindle through the inner rings of the bearings 14 and 15.
The heat transferred to the spindle 12 and the internal copper plate 25
The heat is absorbed into the internal copper plate 25 which has an endothermic effect through a minute air gap between the oil grooves 32 and the external copper plate 26 generates heat.
It is cooled by the cooling oil flowing through it, so no heat builds up. On the other hand, the heat transmitted to the housing 16 via the outer rings of the bearings 14 and 15 is cooled by the natural heat radiation of the housing itself in contact with the atmosphere and the cooling oil flowing in the oil groove 32, resulting in the temperature of the inner and outer rings of the bearings 14 and 15. In addition to reducing the difference, the cooling of the external copper plate 26 itself increases the heat absorption efficiency of the internal copper plate 25.
Cooling of the spindle 12 and bearings 14, 15 is further promoted.

As described above, according to the rotating shaft cooling structure of the present invention, the spindle rotating at high speed is surrounded by a cooling device having a thermoelectric element, and the heat of the spindle is absorbed by the cooling means using the Peltier effect. Since the heat dissipation from the inner ring side of the bearing is good and the thermal response is excellent, the temperature difference between the inner and outer rings of the bearing will not increase even in the case of high-speed rotation due to a sudden start-up of the rotating shaft such as a quick start or cold start. is suppressed and seizure of the bearing can be prevented. In addition, even if the temperature of the coolant that cools the heat generating part of the thermoelectric element is kept equal to room temperature, the temperature of the heat absorbing part of the thermoelectric element can be sufficiently lowered, so the temperature gradient between it and the heat generating part of the bearing can be increased. This ensures sufficient cooling capacity. Furthermore, since the rotating shaft itself is directly cooled, there is almost no adverse thermal effect on the housing, etc., and the cooling capacity of the cooling device is controlled based on the amount of heat generated according to the rotation speed of the rotating shaft. By doing so,
Thermal displacement at the tip of the rotating shaft is extremely small (e.g.
15 micrometers or less). For example, when the present invention is applied to the main axis of a machine tool, this is extremely advantageous in stabilizing and increasing the machining accuracy of the workpiece.

[Brief explanation of drawings]

Fig. 1 is a sectional view schematically showing a conventional spindle cooling structure, Fig. 2 is a sectional view showing a schematic structure of an embodiment in which the present invention is applied to a spindle of a machine tool, and Fig. 3 is a sectional view of the cooling device. An enlarged sectional view of a part of the detailed structure, Figure 4 is a sectional view taken in the direction of the arrow.
Fig. 5 is a cross-sectional view taken along the arrow, and the reference numbers in the figure are: 12 is the spindle, 14, 15 are the bearings, 16 is the housing, 21 is the cooling device, 22 is N type bismuth telluride, 23 is P type of bismuth telluride,
24 is a resin plate, 25 is an internal copper plate, 26 is an external copper plate, 29 is a lead wire, 30 is a cooling oil supply section, 31
3 is a cooling oil discharge path, and 32 is an oil groove.

Claims (1)

[Claims] 1. On a rotating shaft that is rotatably supported by a housing via a bearing, a cylindrical cooling device having a thermoelectric element and having a heat generating part on the outer circumference and a heat absorbing part on the inner circumference is connected to the rotating shaft. The cooling device is fixed to the inner circumferential wall of the housing near the bearing so as to surround it with a gap therebetween, and absorbs heat generated by the bearing via the rotating shaft. A cooling structure for a rotating shaft, characterized in that it is provided between a device and the housing.