Výrobcovia prírubových matíc DIN 6923 na mieru

Flange Head Nut vs. Standard Hex Nut with Washer: Quantifying the Differences in Bearing Stress Distribution and Embedment Resistance

Under high preload, the choice between a flange head nut and a standard hex nut with a flat washer significantly affects joint performance. While both configurations aim to increase bearing area and reduce surface stress, experimental data reveals substantial differences in how they distribute pressure and resist embedding into the joint material.

1. Contact Stress Comparison: Quantified Data

The following table presents contact stress data for flange head nuts, plain hex nuts, and hex nuts with washers, measured under identical preload conditions (75% of proof load).

Data source: Contact stress measurements from bolted joint design studies .

For a Grade 10.9 M16 fastener, the flange head nut produces a contact stress of approximately 39.9 ksi, compared to 94.3 ksi for a plain hex nut—a reduction of 57.7%. The hex nut with a washer achieves 33.4 ksi, representing a 64.6% reduction from the plain hex nut. For higher strength Grade 12.9 M22 fasteners, the plain hex nut generates 131 ksi, while the washer configuration reduces this to 50.8 ksi, a 61.2% reduction.

2. Bearing Stress Distribution: The Pressure Profile Difference

Peak stress reduction from flat washers, while significant, does not reach the level one would predict based solely on contact area. Testing on 1/2"-13 fasteners at 80% of proof load showed that a hardened flat washer reduced peak pressure by approximately 50%, while a flange head fastener provided load distribution that is more dependent on individual fastener geometry.

Contact area measurements using pressure-indicating film have revealed that the contact area under a flange head can vary from essentially the full face to a narrow band at the flange OD, or a ring near the clearance hole . This variation is due to the flange's taper and the stiffness of the nut body. For hex nuts with washers, the standard flat washer does not achieve the full stress reduction predicted by its outer diameter because the washer is not thick enough to uniformly distribute the load out to its OD . Thicker washers are more effective at distributing loads and reducing stress in both the washer and the joint members .

3. Embedment Resistance: Preventing Preload Loss

Embedment is the localized yielding or compression of the joint material beneath the nut bearing surface. It is a primary cause of early preload loss after tightening. Both the flange head nut and the hex nut with washer reduce embedment by lowering the contact stress at the bearing surface.

• Flange Head Nut: The integrated flange provides a larger bearing area that distributes pressure over a wider zone. This reduces the risk of the nut embedding into softer materials such as aluminum, thin sheet steel, or coated surfaces . The flange also prevents surface damage and reduces the risk of the nut pulling through the joint material .
• Hex Nut with Hardened Washer: A properly specified hardened washer can increase gasket or joint load by 30-50% compared to no washer, by preventing embedment and distributing the load more uniformly . It compensates for irregular surface conditions and reduces friction at the bearing surface .

4. Additional Performance Considerations

• Torque-Tension Relationship: The radius of the contact area influences the torque required to generate a given preload. When contact occurs at the outer diameter of the flange, the resistance moment is higher, and for the same input torque, less bolt tension is generated. Tests have shown that the difference between inner-diameter and outer-diameter contact can reduce tension by 10-15% .
• Anti-Vibration Performance: Serrated flange nuts (often called whiz nuts) incorporate teeth on the bearing face that bite into the mating surface, providing a mechanical locking action that resists loosening under vibration . Smooth flange nuts do not offer this locking effect.
• Surface Damage: Serrated flange nuts can damage painted, anodised, or soft surfaces. For finished or cosmetic applications, smooth flange nuts or standard hex nuts with washers are preferred .

5. Manufacturing and Quality Perspective

Consistent flange geometry and controlled manufacturing tolerances are essential to achieving the load distribution benefits of flange head nuts. Zhejiang Chance & Union Import and Export Co., Ltd. (Chance & Union) is a family-owned enterprise under SEA Monies Metal Co., Ltd., inheriting 20 years of family experience and quality heritage in metal manufacturing. Relying on Shengzhao Metal's strong production capacity and supply chain advantages, we specialize in the R&D, production and global sales of high-quality metal products. Adhering to the family's pursuit of precision, rigorous working attitude and long-term commitment, we deliver stable and reliable products and services to customers across the globe.

Leveraging the factory's robust R&D and production capabilities, we specialize in high-strength rivets, bolts, nuts, washers, pins, screws, and various non-standard custom parts. Our product range covers materials including stainless steel, alloy steel, aluminum alloy, copper, and special alloys, utilizing processes such as cold heading, hot forging, and CNC machining. Our products are exported to over 25 countries, serving more than 200 clients.

Chance & Union is committed to seamlessly connecting "Manufactured in China" with the international market, providing global customers with one-stop fastening solutions from R&D to mass production through professional technology and exceptional quality.

6. Frequently Asked Questions (FAQ)

• Q1: Does a flange head nut completely replace the need for a hardened washer?
  A: In most applications, yes, because the flange provides a larger bearing area and distributes the load effectively. However, for very soft materials, slotted holes, or where the joint surface is irregular, a hardened washer may still be necessary to prevent embedding and ensure uniform load distribution. Zhejiang Chance & Union Import and Export Co., Ltd. (Chance & Union) can recommend the appropriate configuration based on your specific joint design and material.
• Q2: Why does the contact stress data show a hex nut with a washer performing better than a flange head nut for some sizes?
  A: The data reflects contact stress at the bearing surface. A properly sized hardened washer can sometimes distribute the load more effectively than the flange of a nut, particularly if the flange geometry does not create full-face contact. The standard flat washer, when used with a bolt, has been observed to distribute stress more uniformly than the flange in certain tests. Zhejiang Chance & Union Import and Export Co., Ltd. (Chance & Union) can provide specific recommendations and product data for your application.
• Q3: What is the main performance difference between a serrated flange nut and a smooth flange nut?
  A: Serrated flange nuts provide a mechanical locking action by biting into the mating surface, which resists loosening under vibration. Smooth flange nuts distribute load without marking the surface and are used where surface finish must be preserved. Zhejiang Chance & Union Import and Export Co., Ltd. (Chance & Union) offers both types and can advise on the best choice for your assembly conditions.

DIN 6923 Flange Nut vs. DIN 934 Hex Nut with Washer: How Do Flange Diameter and Run-out Tolerance Affect Preload Retention via Contact Stress and Embedment Resistance?

The selection between a DIN 6923 flange nut and a DIN 934 hex nut with a separate washer is a critical decision in bolted joint design. While both configurations aim to distribute bearing stress and resist embedment, their geometric and tolerance differences lead to quantifiable differences in contact stress distribution and, consequently, preload retention. This article examines how the flange outer diameter (dw) and run-out tolerance of the DIN 6923 nut translate into distinct mechanical behaviors.

1. Dimensional Comparison: DIN 6923 Flange Nut vs. DIN 934 Hex Nut with Washer

The integrated flange of the DIN 6923 nut provides a defined, consistent bearing surface geometry. In contrast, the DIN 934 nut relies on a separate washer, introducing additional tolerances and assembly variability. The following table compares key bearing surface dimensions for M10 and M16 sizes.

Data source: DIN 6923 dimensions from Westfield Fasteners .

2. Contact Stress Distribution: What the Research Shows

Experimental and FEM research has revealed important characteristics of bearing pressure distribution under flange nuts.

• Non-Uniform Radial Distribution: Three-dimensional photoelastic experiments have shown that the pressure distribution on the bearing surface of hexagonal flange nuts is not uniform. The pressure concentrates at the inner part of the flange, while the pressure at the outer part reduces to nearly zero . This means the effective load-bearing area is smaller than the full flange area suggests.
• Asymmetrical Distribution: The same research demonstrates that the stress distribution in the bolted joint and the pressure distribution on the bearing surface of the flange nut are axially asymmetrical, corresponding to the asymmetrical shape of the threaded part . This asymmetry contributes to the loosening mechanism.
• Flange Geometry Effects: Elasto-plastic FEM analysis has confirmed that flange thickness and flange slope angle substantially influence both contact stress distribution and permanent set (embedment) at the bearing surface . A well-designed flange geometry can mitigate the concentration of stress at the inner edge.

For a standard hex nut with a washer, the contact pressure is also non-uniform, but the presence of a separate washer introduces additional variables: the washer may not be perfectly centered, and its deformation under load can affect the pressure profile.

3. Embedment and Preload Retention

Embedment—the localized plastic deformation of the bearing surface under the nut or washer—is a primary cause of preload loss after tightening.

• DIN 6923 Flange Nut: The larger bearing area of the flange nut reduces the contact stress for a given preload, thereby reducing the depth of embedment. However, because pressure concentrates near the inner edge of the flange, the stress reduction is less than a simple area ratio calculation would suggest. The use of a serrated flange (with teeth) can improve locking by biting into the mating surface, but this also increases surface damage and may reduce the reusability of the connection.
• DIN 934 Hex Nut with Washer: A properly specified hardened washer can increase joint load by 30-50% compared to no washer, by preventing embedment and distributing the load more uniformly . However, the effectiveness depends on the washer's hardness, thickness, and alignment. A washer that is too thin will not distribute the load out to its OD, negating some of the benefit.

4. Manufacturing and Quality Perspective

Consistent flange geometry and controlled manufacturing tolerances are essential to achieving the load distribution benefits of flange head nuts. Zhejiang Chance & Union Import and Export Co., Ltd. (Chance & Union) is a family-owned enterprise under SEA Monies Metal Co., Ltd., inheriting 20 years of family experience and quality heritage in metal manufacturing. Relying on Shengzhao Metal's strong production capacity and supply chain advantages, we specialize in the R&D, production and global sales of high-quality metal products. Adhering to the family's pursuit of precision, rigorous working attitude and long-term commitment, we deliver stable and reliable products and services to customers across the globe.

Leveraging the factory's robust R&D and production capabilities, we specialize in high-strength rivets, bolts, nuts, washers, pins, screws, and various non-standard custom parts. Our product range covers materials including stainless steel, alloy steel, aluminum alloy, copper, and special alloys, utilizing processes such as cold heading, hot forging, and CNC machining. Our products are exported to over 25 countries, serving more than 200 clients.

Chance & Union is committed to seamlessly connecting "Manufactured in China" with the international market, providing global customers with one-stop fastening solutions from R&D to mass production through professional technology and exceptional quality.

5. Frequently Asked Questions (FAQ)

• Q1: Does a DIN 6923 flange nut completely replace the need for a hardened washer?
  A: Yes, in most applications. The integral flange provides a larger bearing surface and distributes the load effectively. However, for very soft materials, slotted holes, or where the joint surface is irregular, a hardened washer may still be necessary to prevent embedding and ensure uniform load distribution. Zhejiang Chance & Union Import and Export Co., Ltd. (Chance & Union) can recommend the appropriate configuration based on your specific joint design and material.
• Q2: Why is the contact stress under a flange nut not uniformly distributed across the entire flange?
  A: Photoelastic experiments have shown that pressure concentrates at the inner part of the flange, while the pressure at the outer part is reduced to near zero . This is due to the stiffness of the nut body and the geometry of the flange. Zhejiang Chance & Union Import and Export Co., Ltd. (Chance & Union) ensures precise flange geometry to optimize load distribution.
• Q3: What is the effect of flange slope angle on preload retention?
  A: Elasto-plastic FEM analysis has shown that the flange slope angle substantially influences both contact stress distribution and permanent set at the bearing surface . An optimized flange slope angle helps to distribute the load more uniformly, reducing stress concentrations and the associated embedding that causes preload loss. Zhejiang Chance & Union Import and Export Co., Ltd. (Chance & Union) can provide guidance on optimal flange geometry for your specific application.