Spring head screw assembly

Abstract

The present invention relates to a spring-head screw assembly (8) comprising a spring-head screw (10) having a head (12), the head (12) having a tapered skirt (14) that widens toward a free end of a threaded shank (16), the shank (16) being adjacent to the head (12), wherein the spring-head screw assembly (8) has a washer (30) located in an unthreaded portion (18) of the shank (16) having a bolt diameter (d0) between the threaded portion (20) of the skirt (14) and the shank (16), the inner surface (22) of the skirt being at a radius (R) U ) transitions to the rod section, the inner surface (22) and the support plane (E) A The contact angle (α) is formed by the supporting plane (E). A The end of the skirt (14) facing the screw is defined and is orthogonal to the screw axis. A feature of the invention is that the shank has a cylindrical region with a bolt diameter between the supporting plane and the radius transitioning to the skirt.

Description

Technical Field

[0001] This invention relates to a spring head screw assembly. Background Technology

[0002] In the prior art, for example in DE102016100446A1, spring-head screws are known to have a tapered skirt in the form of a disc spring extending from the screw head, which widens toward the free end of the spring-head screw. The inner surface of the tapered skirt transitions to the threaded shank by a radius. The end of the skirt facing the free end of the screw has a contact area, which in particular forms a support plane orthogonal to the screw axis. The inner surface of the tapered skirt forms a contact angle α with the support plane.

[0003] This type of screw is used to secure clamping components to lower components whose thickness decreases over time, in which case the spring head is used to maintain the preload.

[0004] In particular, when subjected to temperature changes, some materials will undergo significant creep deformation under the preload applied in each case.

[0005] A drawback of the existing design is the risk of defective screw connections where the washer can become stuck. When exposed to temperatures, for example, above 80°C to approximately 160°C, for an extended period while in a tightened state, the preload will decrease over time to below the minimum permissible value. Summary of the Invention

[0006] This invention is based in particular on the understanding that creep deformation occurs especially in the high contact pressure region of the clamping component.

[0007] The object of this invention is to provide a spring head screw assembly that improves the retention of preload when exposed to higher temperatures and achieves greater assembly safety.

[0008] In a known manner, a spring-head screw assembly includes a spring-head screw having a tapered skirt extending from the head in the form of a disc spring, the skirt widening towards the free end of the spring-head screw. The inner surface of the tapered skirt transitions to the threaded shank by a radius. At the end of the skirt facing the free end of the screw, the skirt has a contact area that specifically forms a support plane, particularly orthogonal to the screw axis. The inner surface of the tapered skirt forms a contact angle α with the support plane.

[0009] The present invention provides a washer positioned between the threaded portion of the rod and the skirt of the spring-head screw, with the rod passing through the washer. Therefore, in the assembled state, the washer is located between the retained component and the skirt.

[0010] The function of the gasket is to reduce the contact force exerted by the skirt on the assembly. For the same preload, this reduces the magnitude of creep deformation of the clamped component.

[0011] The washer is preferably held in a fixed position at the unthreaded portion of the shank, which is located between the head and the threaded portion of the shank and has the bolt diameter. The inner diameter of the washer is preferably between the outer diameter of the screw thread and the bolt diameter.

[0012] The screw of the present invention is designed such that the shank has a cylindrical region between the radius of the supporting plane and the region transitioning to the skirt, the cylindrical region having a diameter that is in particular equal to the bolt diameter.

[0013] When the washer only contacts the skirt, the washer surface facing the screw head will be on the support plane.

[0014] The presence of a cylindrical region between the support plane and the rod transition reduces the likelihood that the rod transition (with a radius) between the rod and the skirt will abut against the washer when the spring head screw is screwed in (even if the desired preload of the skirt has not yet been reached), which can increase the process-limited screwing torque.

[0015] According to the invention, the cylindrical region between the support plane and the rod transition allows the screw to be tightened at a larger screw-in angle without the rod transition abutting against the washer. This allows for more reliable utilization of the elastic spring travel of the skirt.

[0016] In this way, for example, the inner diameter of the washer can be made only slightly larger than the diameter of the shank, as required for coil-wound retaining washers, without negatively impacting the screw-in angle. For washer inner diameters with a larger tolerance compared to the shank diameter, this also significantly reduces the likelihood of blockage between the shank transition and the washer in cases of washer misalignment.

[0017] The present invention increases the spring area of ​​the head of the spring-head screw, thereby improving the retention of preload when exposed to high temperatures.

[0018] Preferably, the transition from the radius to the rod and skirt can be a tangential transition. This has the advantage of achieving uniform pressure distribution in the skirt while reducing the notch effect, thus providing higher dynamic safety.

[0019] On the supporting plane, the skirt forms a supporting inner diameter D. KA The annular surface. The unthreaded portion of the rod has a bolt diameter d0.

[0020] In another preferred embodiment of the invention, the radius of the transition portion from the rod to the inner surface of the skirt can be less than tan(α). coefficient (D KA-d0) / 2, where the coefficient is less than 0.5, and preferably 0.2-0.4.

[0021] The radius of the transition section of the rod therefore satisfies the following formula: R U <tan(α) coefficient (D KA -d0) / 2 | coefficient < 0.5.

[0022] Preferably, the inner diameter of the washer is less than 1.07 times the diameter of the unthreaded portion of the shank between the threaded portion of the head and the shank.

[0023] In another preferred embodiment, the contact angle α is 20°–40°, particularly 28°–32°. This provides the advantage of providing a sufficient rotation angle window for assembly under the desired preload.

[0024] In another advantageous embodiment, the thickness of the skirt is approximately 5%-25% of the inner diameter of the support. The thickness of the skirt can be used to adjust the range of preload that can be generated.

[0025] In another aspect, the present invention provides a method for automatically assembling the spring-head screw of the present invention. According to the present invention, the spring-head screw is tightened until a predetermined torque is reached, and once the torque is detected, the spring-head screw is further tightened by a predetermined rotation angle.

[0026] The predetermined angle is at least 180°, and the predetermined torque is preferably higher than the screwing torque defined for each application but lower than the torque required to achieve plastic deformation of the skirt.

[0027] The plastic deformation zones in each application can be easily detected because in the initial plastic deformation zone, the increase in torque tends to plateau significantly. The torque curve at the screw-in angle remains stable until the skirt is fully plastically deformed, and the torque increases sharply again as the screw-in angle increases.

[0028] The predetermined torque is preferably between the torque required for plastic deformation and the screwing torque defined for each application.

[0029] In the method of assembling spring head screws of the type described above, the spring head screws are used to connect the clamping component to be installed and the lower component, the clamping component being made of a material that exhibits significant creep behavior when subjected to various preloads and exposed to corresponding temperatures, and the spring head screws being inserted into the lower component.

[0030] In another aspect of the invention, the invention relates to a component connection comprising, as described above, a spring-head screw assembly containing a spring-head screw and a washer, a lower component into which the spring-head screw is screwed, and a clamping member located between the washer and the lower component, the clamping member being held in place between the washer and the lower component layer under preload.

[0031] The fact that the edge area of ​​the skirt abuts against the washer significantly reduces the local stress transmission through the skirt to the clamping component, which significantly reduces the creep of the clamping component material, and thus reduces the creep deformation of the clamping component.

[0032] Even when the component connection is used within the temperature range allowed by the intended use of the component connection, the thickness of the clamping component will still reduce the maximum creep distance due to creep deformation under the preload applied by the spring head.

[0033] Therefore, the spring head screw assembly, especially the spring head screw, is sized such that the spring travel stored in the elastic deformation of the spring head and the elongation of the screw stored in the elongation of the shank produce a total travel greater than the maximum creep distance within the temperature allowable range.

[0034] This allows for a stored spring travel, ensuring that the preload can be reliably applied to the clamping components even if creep occurs. Therefore, for the same preload and screw diameter, the total travel exceeds the elongation of a standard screw.

[0035] Preferably, the difference between the total stroke and the maximum creep distance within a given time corresponds to the spring stroke applied to the component at the minimum preload. This can be achieved by appropriately designing the dimensions of the washers and skirts.

[0036] The minimum preload is predetermined relative to the specific application and component connection.

[0037] The spring-head screw and washer are made of, for example, steel, and the clamping parts are preferably copper clamping parts.

[0038] Spring-head screw assemblies are used, for example, to connect a clamping component providing removable electrical contact to a second component providing electrical contact. Maintaining preload thus also allows for reliable contact over a wide temperature range. The second component can consist of the lower component or another clamping component.

[0039] The proposed method and the spring head screw assembly of the present invention can reliably achieve the component connection of the present invention, which can maintain the preload very well under the influence of temperature. Attached Figure Description

[0040] Other advantages, features and possible applications of the present invention will become apparent from the following description in conjunction with the embodiments shown in the accompanying drawings.

[0041] In the attached diagram: Figure 1 This is a cross-sectional view of the spring head screw assembly according to the present invention, and Figure 2 The component connection according to the present invention includes a spring head screw assembly, a clamping component, and a lower component. Detailed Implementation

[0042] Figure 1 The spring-head screw assembly 8 of the present invention is shown, comprising a spring-head screw 10 having a head 12, the head 12 having a skirt 14 extending in a tapered shape in the form of a disc spring. The skirt 14 forms a support plane E facing the free end of the spring-head screw 10. A Support plane E A It is basically orthogonal to the screw axis A.

[0043] The tapered skirt 14 is on the supporting plane E A The inner diameter is formed, denoted as the supporting inner diameter D. KA .

[0044] The spring-head screw 10 also includes a shank 16 with an unthreaded portion 18 at the end facing the head 12, the diameter of which is referred to as the bolt diameter d0. In the direction of the free end of the screw 10, opposite to the head 12, the shank 16 has a threaded portion 20 with an outer diameter d0. A Larger than bolt diameter d0, inner diameter d K It is usually smaller than the bolt diameter d0.

[0045] The spring head screw assembly 8 of the present invention further includes a retaining washer 30, which is wound around the shank 16 of the spring head screw 10. The inner diameter D of the washer 30 is... i Therefore, the outer diameter d of the threaded portion 20 of the rod portion 16 is greater than that of the threaded portion A It is small, but larger than the bolt diameter d0.

[0046] In the spring head screw 10 of the present invention, the unthreaded portion 18 of the shank 16 has a radius R U Transitioning to skirt 14, the other unthreaded portions 18 of rod 16 are on support plane E. A With radius R U Between these points, this section has a bolt diameter d0.

[0047] The advantage of this is that, during tightening, the center of gravity of the head of the spring-loaded screw 10 shifts towards the washer 30 due to the spring travel of the skirt 14, preventing the washer 30 from abutting against the widened rod transition portion from the rod 16 to the skirt 14 in the longer cylindrical region in the axial direction. This increases the range in which the spring-loaded screw 10 can be used with the washer 30 in the elastic region.

[0048] In this design, the inner surface of the skirt 14 and the supporting plane E are represented. AThe contact angle α between them is 30°.

[0049] The radius R of the lower profile of the head U Represented as (D) KA -d0) / 2 tan(α=30°) The coefficient is approximately 0.3 in this embodiment.

[0050] radius R U The tangential transition extends to the rod section 16 and the skirt section 14.

[0051] This ensures that the axial displacement of the center of gravity of the head 12 in the screwing direction does not prematurely cause the transition from the rod to the head to abut against the washer 30, which would increase the process limiting torque.

[0052] This allows for better consideration of creep under preload, especially the creep of clamping components, and also improves the retention of preload.

[0053] Figure 2 An assembly connection 40 is shown, comprising a spring-headed screw 10 of the present invention with a washer 30 and a lower component 44, the spring-headed screw 10 being screwed into the lower component 44, and a clamping component 42 being clamped between the washer 30 and the lower component 44, the skirt 14 of the spring-headed screw 10 applying a preload force to the clamping component 42. In embodiments of the invention, the clamping component 42 exhibits higher creep behavior than the lower component 44 under the influence of temperature. Multiple clamping components may also be clamped between the washer 30 and the lower component 44.

[0054] In the design of component connection 40, the components are matched to each other in such a way that, under predetermined operating conditions—namely, preload, temperature profile, and time—the spring-head screw compensates for the creep of the clamping component, ensuring that it still has a certain spring travel. The spring-head screw thus applies a minimum preload force to the clamping component 42.

[0055] For example, the clamping component 42 is in electrical contact with the lower component 44.

[0056] For example, the spring-head screw 10 and washer 30 are made of steel, and the clamping part 42 is made of copper.

[0057] Washer 30 is held securely on spring head screw 10, making it easy to install.

Claims

1. A spring-head screw assembly (8) comprising a spring-head screw (10) having a head (12) having a tapered skirt (14) that widens toward a free end of a threaded shank (16), the shank (16) being adjacent to the head (12), wherein, The spring head screw assembly (8) has a washer (30) located in the unthreaded portion (18) of the shank (16) having a bolt diameter (d0) between the threaded portion (20) of the skirt (14) and the threaded portion (20) of the shank (16), the inner surface (22) of the skirt (14) being at a radius (R). U The inner surface (22) transitions to the rod portion (16), where the inner surface (22) meets the support plane (E). A The contact angle (α) is formed by the supporting plane (E). A The shank (14) is defined by the end of the skirt (14) facing the screw and orthogonal to the screw axis, characterized in that the shank (16) is in the support plane (E A ) and the radius (R) of the transition to the skirt (14). U There is a cylindrical area with a bolt diameter (d0) between them.

2. The spring-head screw assembly according to claim 1, characterized in that, The washer (30) has a hole with an inner diameter (D) i The outer diameter (d) of the threaded portion (20) of the adjacent rod portion (16) is smaller than that of the adjacent rod portion (16). A ).

3. The spring-head screw assembly according to claim 1, characterized in that, The radius (R) U ) Tangential transition to the rod (16).

4. The spring-head screw assembly according to claim 3, characterized in that, The radius (R) U ) Tangentially transitions to the inner surface (22) of the skirt (14).

5. The spring head screw assembly according to any one of claims 1 to 4, characterized in that, The skirt (14) is on the supporting plane (E) A Define the inner diameter of the support (D) KA The radius (R) U ) less than (D KA -d0) / 2 tan(α) Coefficients, where the coefficient is less than 0.

5.

6. The spring-head screw assembly according to claim 5, characterized in that, The coefficient is 0.2-0.

4.

7. The spring head screw assembly according to any one of claims 1 to 4, characterized in that, The inner diameter (D) of the washer (30) i It is less than 1.07 times the bolt diameter (d0).

8. The spring head screw assembly according to any one of claims 1 to 4, characterized in that, The contact angle (α) is 20°-40°.

9. The spring-head screw assembly according to any one of claims 1 to 4, characterized in that, The skirt (14) is on the supporting plane (E) A Define the inner diameter of the support (D) KA The thickness of the skirt (14) is equal to the inner diameter of the support (D). KA 5%-25%.

10. The spring-head screw assembly according to any one of claims 1 to 4, characterized in that, The washer (30) is fixedly mounted to the spring head screw (10).

11. A method for automatically assembling the spring head screw assembly (8) according to any one of the preceding claims, characterized in that, Insert the spring head screw (10) into the clamping member (42) and fix it to the lower member (44) located below the clamping member (42). Tighten the spring head screw (10) until a predetermined torque is reached, and once the torque is detected, further tighten the spring head screw (10) by a predetermined rotation angle.

12. The method according to claim 11, characterized in that, The predetermined rotation angle is at least 180°.

13. A connecting assembly comprising a spring-head screw assembly (8) according to claim 1, a lower part (44) therein into which the spring-head screw (10) is screwed, and a clamping part (42) located between the spring-head screw (10) and the lower part (44), wherein, when exposed to a predetermined temperature and subjected to a predetermined contact pressure, the thickness of the clamping part (42) in the area abutting against the surface of the washer (30) reduces the creep distance, and the spring-head screw (10) is designed such that, once the screw is tightened, the sum of the elongation of the shank (16) and the spring travel of the skirt (14) exceeds the length of the creep distance.

14. The connection component according to claim 13, characterized in that, Prepared using the method of claim 11.

15. The connection component according to claim 13, characterized in that, The spring head screw assembly is made of steel, and the clamping component is made of copper.

16. The spring-head screw assembly according to claim 8, characterized in that, The contact angle (α) is 28°-32°.

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