High-rigidity high-precision cylindrical grinding wheel spindle

Abstract

This invention proposes a high-rigidity, high-precision external cylindrical grinding wheel spindle, comprising a housing, a spindle sleeve installed within the housing, and a shaft core rotatably installed within the spindle sleeve, the shaft core being supported by a front bearing assembly and a rear bearing assembly. It also includes a preload structure for applying and adjusting axial preload to the front bearing assembly, thereby enhancing the system rigidity of the shaft core. This invention improves the system rigidity of the grinding spindle by employing a four-section angular contact ball bearing layout at the front end of the spindle, combined with precision grinding of inner and outer spacers or thermal expansion compensation sleeves. This allows the spindle to withstand greater grinding forces and directly guarantees the highest rotational accuracy at the working end. The rear end of the spindle adopts a floating bearing assembly design, which eliminates destructive thermal stress and protects the preset precision preload state of the front bearing assembly, thus ensuring that the spindle maintains high precision throughout the entire temperature rise process.

Description

Technical Field

[0001] This utility model relates to the field of grinding spindle structure, and in particular to a high-rigidity and high-precision external cylindrical grinding wheel spindle. Background Technology

[0002] The rigidity and precision of the external cylindrical grinding wheel spindle directly affect the final quality of the workpiece. Traditional rolling bearing spindles have their preload fixed at the factory. If this static preload is set too low, the spindle will lack rigidity, making it prone to vibration marks during machining; if the preload is set too high, the bearing will generate excessive frictional heat, leading to thermal deformation of the spindle, compromising machining accuracy, and accelerating bearing wear.

[0003] Especially during the entire working cycle from cold start to thermal equilibrium, the various components of the spindle system (spindle, bearings, housing) experience uneven thermal expansion due to differences in materials and distance from the heat source. This causes the initially set optimal preload to drift. Typically, the spindle core heats up the fastest, and its axial elongation reduces the preload of the front bearing assembly, leading to a decrease in spindle rigidity during operation. This significantly affects the stability of the grinding process and the quality of the workpiece. Utility Model Content

[0004] This invention aims to solve the problem of how to maintain optimal or near-optimal rigidity of a spindle throughout its operating temperature range. It proposes a high-rigidity, high-precision external cylindrical grinding wheel spindle, comprising a housing, a spindle sleeve mounted within the housing, and a shaft core rotatably mounted within the spindle sleeve. The shaft core is supported by a front bearing assembly and a rear bearing assembly. It also includes a preload structure for applying and adjusting axial preload to the front bearing assembly to enhance the system rigidity of the shaft core.

[0005] Preferably, the front bearing assembly is used to support the front end of the shaft core and includes a four-row angular contact ball bearing assembly; the four-row angular contact ball bearing assembly includes a first tandem bearing pair and a second tandem bearing pair, both of which are formed by two angular contact ball bearings with the same pressure line direction connected in series; the first tandem bearing pair and the second tandem bearing pair are arranged back to back; the preload structure is a spacer assembly, which is disposed between the first tandem bearing pair and the second tandem bearing pair, and the spacer assembly includes an inner spacer and an outer spacer, with a length difference between the axial lengths of the inner spacer and the outer spacer to generate a preset axial preload.

[0006] Preferably, the preload structure is a thermal expansion compensation sleeve, which is installed between the inner hole of the spindle sleeve and the outer ring of the front bearing assembly, and the thermal expansion coefficient of the material of the thermal expansion compensation sleeve is greater than that of the material of the spindle sleeve.

[0007] Furthermore, the thermal expansion compensation sleeve is made of aluminum alloy or copper alloy, and the spindle sleeve is made of cast iron or steel.

[0008] Furthermore, it also includes a forced cooling device integrated with the housing, which is a spiral liquid cooling channel surrounding the outer wall of the spindle sleeve for active temperature control of the area of ​​the front bearing assembly and / or the motor stator.

[0009] Furthermore, it also includes a non-contact air curtain sealing device located at the front end of the shaft core. This device includes an annular airtight cavity opened on the inner wall of the front end of the housing and an air cutting line on the outer circular surface of the shaft core that corresponds radially to the airtight cavity. The air cutting line and the airtight cavity are connected.

[0010] Furthermore, the rear bearing assembly is a floating support structure, with its inner bearing ring fixed to the shaft core in a tight fit manner, and its outer bearing ring and the inner hole of the rear flange having a clearance fit to compensate for the axial thermal expansion of the shaft core.

[0011] Compared with the prior art, the beneficial effects of this utility model include: 1. This utility model improves the system rigidity of the grinding spindle by employing a four-section angular contact ball bearing layout at the front end of the spindle, combined with precision grinding of inner and outer spacers or thermal expansion compensation sleeves. This allows the spindle to withstand greater grinding forces and directly ensures the highest rotational accuracy of the working end.

[0012] 2. The rear end of the spindle adopts a floating bearing assembly design, which protects the preset precision preload of the front bearing assembly by eliminating destructive thermal stress, thereby ensuring that the spindle maintains high precision throughout the entire temperature rise process.

[0013] 3. The forced cooling device actively stabilizes the working temperature of the spindle core, effectively suppressing thermal deformation caused by temperature rise and extending the overall service life of the spindle.

[0014] 4. The front end of the spindle system employs an air curtain seal structure. Its non-contact nature avoids the frictional heat and wear of traditional contact seals, while also forming a powerful air curtain barrier. This not only prevents the intrusion of cutting fluid and significantly extends bearing life, but also contributes to the thermal stability and accuracy maintenance of the entire system. Attached Figure Description

[0015] The disclosure of this utility model is illustrated with reference to the accompanying drawings. It should be understood that the drawings are for illustrative purposes only and are not intended to limit the scope of protection of this utility model. In the drawings, the same reference numerals are used to refer to the same parts. Wherein: Figure 1 This is a diagram of the spindle structure in Example 1.

[0016] Figure 2This is a structural diagram of the forced cooling device in Example 1 or 2.

[0017] Figure 3 This is a structural diagram of the air curtain sealing device in Example 1 or 2.

[0018] Figure 4 This is a diagram of the spindle structure in Example 2.

[0019] Labels in the diagram: 1. Housing; 2. Shaft core; 3. Front bearing assembly; 4. Rear bearing assembly; 5. Outer spacer; 6. Inner spacer; 7. Thermal expansion compensation sleeve; 8. Forced cooling device; 9. Air curtain sealing device; 91. Gas cutting line; 92. Airtight cavity; 10. Motor rotor; 11. Motor stator; 12. Main shaft sleeve; 13. Rear flange; 14. Locking nut. Detailed Implementation

[0020] It is readily understood that, based on the technical solution of this utility model, those skilled in the art can propose various interchangeable structural methods and implementations without altering the essential spirit of this utility model. Therefore, the following detailed embodiments and accompanying drawings are merely illustrative descriptions of the technical solution of this utility model and should not be considered as the entirety of this utility model or as limitations or restrictions on the technical solution of this utility model.

[0021] Example 1 Please see Figures 1-3 A high-rigidity, high-precision external cylindrical grinding wheel spindle includes a housing 1, a spindle sleeve 12 installed inside the housing 1, and a rotatable spindle core 2. The housing 1 is fixed to the bed of the grinding machine via a rear flange 13; this connection method is prior art and will not be described in detail. The spindle sleeve 12 is installed in the inner hole of the housing 1, and the two are fixed by an interference fit to ensure the rigidity and heat transfer efficiency of the combination; this connection method is also prior art. The spindle core 2 is located at the center of the spindle sleeve 12 and is rotatably supported by a front bearing assembly 3 and a rear bearing assembly 4. The front end of the spindle core 2 extends out of the housing 1 for mounting the grinding wheel disc; the method of mounting the grinding wheel disc is also prior art. The rear end of the spindle core 2 is fixedly connected to the motor rotor 10, and the motor stator 11 is fixed to the spindle sleeve 12; the connection method of the stator / rotor is prior art. The motor can be a built-in motor installed inside the housing 1 or an external motor mounted on the bed.

[0022] Preferably, the housing 1 and the spindle sleeve 12 are made of ductile iron material with excellent vibration absorption and stability, and the internal stress is eliminated by aging treatment.

[0023] Preferably, the shaft core 2 is made of high carbon chromium bearing steel and undergoes heat treatment and precision machining to obtain high hardness and high rotational accuracy.

[0024] The shaft core 2 is supported by a front bearing assembly 3 and a rear bearing assembly 4. The front bearing assembly 3 is mounted at the front end of the shaft core 2. Specifically, four high-precision angular contact ball bearings are mounted on the journal of the shaft core 2 with their inner rings tightly fitted, while their outer rings are mounted in the inner hole of the spindle sleeve 12 with clearance fit. The four bearings are installed in a configuration where two pairs of tandem bearings are mounted back-to-back (DB). That is, the pressure lines of the two tandem pairs diverge outwards, forming a wide support base. Between the two tandem bearing pairs, a set of precision-fitted inner and outer spacers is also provided.

[0025] Specifically, four high-precision angular contact ball bearings, pointing from the grinding wheel end to the end of the housing 1, are designated as first angular contact ball bearing 3a, second angular contact ball bearing 3b, third angular contact ball bearing 3c, and fourth angular contact ball bearing 3d. The first and second angular contact ball bearings 3a and 3b form a first tandem pair; the third and fourth angular contact ball bearings 3c and 3d form a second tandem pair. Between the second angular contact ball bearing 3b and the third angular contact ball bearing 3c, a pair of precision-machined inner spacer 6 and outer spacer 5 are provided. The inner spacer 6 is located between the inner rings of the second angular contact ball bearing 3b and the third angular contact ball bearing 3c, and the outer spacer 5 is located between the outer rings of the second angular contact ball bearing 3b and the third angular contact ball bearing 3c. By controlling the axial length L1 of the inner spacer 6 to be slightly smaller than the axial length L2 of the outer spacer 5, when the entire bearing assembly is axially compressed by the locking nut 14, this length difference ΔL (ΔL=L2-L1) will be converted into a constant and precise axial preload. This preload ensures that the steel balls inside the bearing always maintain elastic contact with the raceway, eliminating bearing clearance and thus giving the spindle system excellent dynamic stiffness and rotational accuracy.

[0026] Lock nut 14 is used to connect the front flange and housing 1, and this connection method is existing technology.

[0027] The rear bearing assembly 4 comprises two high-precision angular contact ball bearings arranged back-to-back, mounted on the journal at the rear end of the shaft core 2. Their inner rings are still tightly fitted to the shaft core 2, while their outer rings are clearance-fitted with the inner bore of the rear flange 13, forming a floating support. The rear bearing assembly 4 primarily provides radial support, and its floating design allows the shaft core 2 to expand and contract axially when heated as a whole, without generating destructive thermal stress between the front and rear bearing assemblies, ensuring the stability and lifespan of the entire bearing system. This configuration gives the front end of the shaft core 2 extremely high radial and axial load-bearing capacity and excellent resistance to overturning moments.

[0028] It's important to understand that when the spindle starts working, both the motor rotor 10 and the spindle core 2 will heat up simultaneously. Because they are tightly connected as a whole, heat will be conducted between them, and their temperature rise trends will be synchronized. Therefore, they will not experience asynchronous deformation due to uneven heating.

[0029] Furthermore, this embodiment includes a forced cooling device 8, which is a spiral liquid cooling channel integrally formed on the outer wall of the spindle sleeve 12 and the motor stator 11. This channel surrounds the critical heat-generating areas where the front bearing assembly 3 and the motor stator 11 are located. By introducing a constant-temperature coolant, the heat generated during spindle operation is actively and efficiently carried away, stabilizing the temperature of the entire spindle system within a preset, ideal operating range. This not only prevents thermal deformation caused by spindle overheating but also ensures that the thermal self-compensation device can operate within its most effective temperature range.

[0030] Furthermore, this embodiment includes a non-contact air curtain sealing device 9 disposed at the front end of the spindle, comprising an airtight cavity (92) and at least one gas cutting line 91.

[0031] The gas cutting line 91 is one or more precision micro-grooves formed on the outer circular surface of the shaft core 2, corresponding radially to the airtight cavity 92. Its groove shape can be V-shaped or U-shaped. Axially, the gas cutting line 91 is located on the side of the shaft core 2 closer to the external environment. When high-pressure gas flows outward from the airtight cavity 92 through the tiny gap between the shaft core 2 and the housing 1, the special groove structure of the gas cutting line 91 creates a throttling and acceleration effect on the airflow, thus forming a high-speed, stable annular airflow. This high-speed airflow forms an air curtain that can cut and block intruding external cutting fluid, grinding dust, and other contaminants with powerful kinetic energy.

[0032] The airtight cavity 92 is an annular groove formed on the inner wall of the front end of the housing 1. This groove forms a complete 360-degree annular chamber and is connected to an external clean compressed air source through an air supply port (not shown in the figure). The airtight cavity 92 is used to receive and store compressed air from the external air source, effectively buffering pressure fluctuations of the air source and ensuring that the pressure is evenly distributed along the entire circumference of the shaft core 2. The airtight cavity 92 and the gas cutting line 91 are connected and cooperate to form a reliable air curtain.

[0033] Example 2 Please see Figures 2-4The spindle base structure in this embodiment is similar to that in Embodiment 1, including a housing 1, a spindle sleeve 12 installed inside the housing 1, and a rotatable spindle core 2. The housing 1 is fixed to the bed of the grinding machine via a rear flange 13. The spindle sleeve 12 is installed in the inner hole of the housing 1, and the two are fixed by an interference fit to ensure the rigidity and heat transfer efficiency of the combination. The spindle core 2 is located at the center of the spindle sleeve 12 and is rotatably supported by a front bearing assembly 3 and a rear bearing assembly 4. The front end of the spindle core 2 extends out of the housing 1 for mounting the grinding wheel, and the rear end of the spindle core 2 is fixedly connected to the motor rotor 10. The motor stator 11 is fixed to the spindle sleeve 12. The connection method of the stator and rotor is existing technology. Its core difference and innovation lies in the inclusion of a thermal expansion compensation sleeve 7.

[0034] The thermal expansion compensation sleeve 7 is a precision-machined metal ring sleeve that is tightly installed between the inner bore of the spindle sleeve 12 and the outer ring of the outermost bearing of the front bearing assembly 3, separating the bearing outer ring from the inner wall of the spindle sleeve 12. The key to this device lies in the choice of materials: the thermal expansion compensation sleeve 7 uses a material with a high coefficient of thermal expansion, such as 6061 aluminum alloy; while the spindle sleeve 12 uses a material with a low coefficient of thermal expansion, such as cast iron. Utilizing the difference between the high coefficient of thermal expansion of the thermal expansion compensation sleeve 7 and the low coefficient of thermal expansion of the spindle sleeve 12, when the spindle temperature rises, the restricted radial expansion is converted into an increase in axial preload. This increase automatically compensates for the decrease in preload caused by the thermal expansion of the spindle, achieving dynamic adaptive enhancement of rigidity.

[0035] It is known that the thermal expansion compensation sleeve 7 can be directly applied to the front bearing assembly 3 containing four angular contact ball bearings in Example 1, or it can be applied to other situations, such as the front bearing assembly 3 composed of two angular contact ball bearings.

[0036] The working principle of this embodiment is as follows: Initial state (cold state): When assembling at room temperature, a small initial preload is applied by the locking nut 14 at the front end. This force is only used to eliminate bearing clearance and ensure that the spindle can start smoothly.

[0037] Operating state (hot state): When the spindle rotates at high speed, the front bearing assembly 3 and the built-in motor stator 11 become the main heat sources, causing the spindle system temperature to rise. Since the coefficient of thermal expansion of the thermal expansion compensation sleeve 7 is significantly greater than that of the spindle sleeve 12, under the same temperature rise ΔT, the free radial expansion tendency of the thermal expansion compensation sleeve 7 is much greater than the radial expansion of the inner hole of the spindle sleeve 12.

[0038] Self-compensation effect: Because the thermal expansion compensation sleeve 7 is constrained by the spindle sleeve 12, its radial thermal expansion is hindered. According to Poisson's effect and the principles of material mechanics, this restricted radial expansion is converted into a huge axial compressive stress. This compressive stress is transmitted through the outer ring of the bearing, applying an additional axial preload ΔF to the angular contact ball bearing, which increases with temperature. This ΔF can effectively compensate for or even exceed the preload loss caused by the thermal expansion of the spindle core 2 itself, thereby achieving a dynamic adaptive compensation effect for the spindle rigidity during operation.

[0039] The advantages of this utility model are: 1. This utility model improves the system rigidity of the grinding spindle by employing a four-section angular contact ball bearing layout at the front end of the spindle, combined with precision grinding of inner and outer spacers or thermal expansion compensation sleeves. This allows the spindle to withstand greater grinding forces and directly ensures the highest rotational accuracy of the working end.

[0040] 2. The rear end of the spindle adopts a floating bearing assembly design, which protects the preset precision preload of the front bearing assembly by eliminating destructive thermal stress, thereby ensuring that the spindle maintains high precision throughout the entire temperature rise process.

[0041] 3. The forced cooling device 8 actively stabilizes the working temperature of the spindle core 2, effectively suppressing thermal deformation of the spindle core 2 caused by temperature rise and extending the overall service life of the spindle.

[0042] 4. The front end of the spindle system employs an air curtain seal structure 9. Its non-contact nature avoids the frictional heat and wear of traditional contact seals, while also forming a powerful air curtain barrier. This not only prevents the intrusion of cutting fluid and significantly extends bearing life, but also contributes to the thermal stability and accuracy maintenance of the entire system.

[0043] The technical scope of this utility model is not limited to the content described above. Those skilled in the art can make various modifications and variations to the above embodiments without departing from the technical concept of this utility model, and all such modifications and variations should fall within the protection scope of this utility model.

Claims

1. A high-rigidity, high-precision external cylindrical grinding wheel spindle, characterized in that, include: The housing (1), the spindle sleeve (12) installed inside the housing (1), and the shaft core (2) rotatably installed inside the spindle sleeve (12), the shaft core (2) being supported by a front bearing assembly (3) and a rear bearing assembly (4); It also includes a preload structure for applying and adjusting axial preload to the front bearing assembly (3) to improve the system rigidity of the shaft core (2).

2. The high-rigidity, high-precision external cylindrical grinding wheel spindle according to claim 1, characterized in that, The front bearing assembly (3) is used to support the front end of the shaft core (2) and includes a four-row angular contact ball bearing assembly; The four-row angular contact ball bearing assembly includes a first tandem bearing pair and a second tandem bearing pair. Both the first tandem bearing pair and the second tandem bearing pair are composed of two angular contact ball bearings connected in series with the same pressure line direction. The first tandem bearing pair and the second tandem bearing pair are arranged back to back. The preload structure is a spacer assembly, which is located between the first tandem bearing pair and the second tandem bearing pair. The spacer assembly includes an inner spacer (6) and an outer spacer (5). The axial lengths of the inner spacer (6) and the outer spacer (5) have a length difference to generate a preset axial preload.

3. The high-rigidity, high-precision external cylindrical grinding wheel spindle according to claim 1, characterized in that, The preload structure is a thermal expansion compensation sleeve (7), which is installed between the inner hole of the main shaft sleeve (12) and the outer ring of the front bearing assembly (3), and the thermal expansion coefficient of the material of the thermal expansion compensation sleeve (7) is greater than that of the material of the main shaft sleeve (12).

4. A high-rigidity, high-precision external cylindrical grinding wheel spindle according to claim 3, characterized in that, The thermal expansion compensation sleeve (7) is made of aluminum alloy or copper alloy, and the spindle sleeve (12) is made of cast iron or steel.

5. A high-rigidity, high-precision external cylindrical grinding wheel spindle according to claim 2 or 3, characterized in that, It also includes a forced cooling device (8) integrated with the housing (1), the forced cooling device (8) being a spiral liquid cooling channel surrounding the outer wall of the main shaft sleeve (12) for active temperature control of the area of ​​the front bearing assembly (3) and / or the motor stator (11).

6. A high-rigidity, high-precision external cylindrical grinding wheel spindle according to claim 2 or 3, characterized in that, It also includes a non-contact air curtain sealing device (9) set at the front end of the shaft core (2). The device includes an annular airtight cavity (92) opened on the inner wall of the front end of the housing (1) and an gas cutting line (91) set on the outer circular surface of the shaft core (2) that is radially corresponding to the airtight cavity (92). The gas cutting line (91) and the airtight cavity (92) are connected.

7. A high-rigidity, high-precision external cylindrical grinding wheel spindle according to claim 2 or 3, characterized in that, The rear bearing assembly (4) is a floating support structure. Its inner bearing ring is fixed to the shaft core (2) in a tight fit manner, and its outer bearing ring is clearance fit with the inner hole of the rear flange (13) to compensate for the axial thermal elongation of the shaft core (2).

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