Description: The present invention relates to high-pressure composite pressure vessels, specifically Type IV cylinders, and more particularly to an improved end boss design with anti-rotation features to enhance assembly integrity and operational safety.

Background of the Invention:
Type IV composite cylinders are widely used in CNG or hydrogen storage and transportation. These cylinders typically consist of a polymeric liner overwrapped with a composite material, and metallic end bosses that serve as interfaces for valves and pressure fittings.
During valve assembly, particularly while torquing, the end boss may rotate or shift slightly, leading to misalignment, potential thread damage, and compromised sealing. This rotation is often exacerbated by the smooth cylindrical interface between the boss and liner.
 
Prior Art Potentially Relevant
1. US 8397938 B2 – Clamped liner boss connection
This patent teaches a pressure vessel boss system where an inner boss has a “liner channel” and is clamped to a vessel liner, with an outer boss secured over it. It addresses sealing and mechanical locking between boss and liner but does not disclose machined face cuts or flats on the boss neck for anti rotation during valve torquing

2. US 2016/0348845 A1 – Boss assembly with locking notches
Describes a boss assembly for composite vessels where the outer shell locks into notches and reverse draft cuts. These features hold the wrapping shell and boss together mechanically. However, it doesn't mention axial face cuts or engagement of flats in the neck for torque resistance during valve installation
3. EP 3 814 674 B1) – Ribbed boss connector with anti rotation elements
These documents describe bosses featuring interspaced radial ribs or protrusions on the outer neck (between 2 and 10 rib elements) that create mechanical interference to reduce rotational movement relative to the composite laminate. The ribs may be circular, polygonal, serrated, or contoured and serve an anti rotation function. These ribs act somewhat like your face cut equivalents, though arranged as protrusions rather than flat machined surfaces
4. Recent Analysis (MDPI, 2024) of Type IV boss geometry
Publications such as Meng et al. and research on Type IV cylinder boss structures highlight the influence of boss shape and liner dimensions on stress distribution and sealing reliability. None explicitly describe flat face cuts for anti rotation, focusing instead on geometry, liner thickness, stress analysis, or angled stop platforms (e.g., Toyota’s 65° inclination stop rotate platform)

Summary of the Invention:

To address the above challenges, the present invention introduces a novel design feature: face cuts on the outer diameter of the neck portion of the end boss, specifically located adjacent to the flange. These opposite face cuts act as anti-rotation elements, engaging with corresponding locking or grip features in the liner or assembly tooling to prevent unintended rotation during torquing of the valve.
This innovation provides a mechanically interlocked interface that stabilizes the end boss during assembly, ensuring a more secure torque application, minimizing stress on threads, and ultimately enhancing the structural integrity and leak-proof performance of the Type IV cylinder.
Brief Description of the Drawings:
Figure 1 illustrates a front view of the end boss with clearly marked face cuts on the neck region (highlighted in blue ellipses). These face cuts are symmetrically positioned to enable grip and resist rotational forces during assembly.
Detailed Description of the Invention:

Referring to Figure 1, the metallic end boss includes a flanged portion that interfaces with the polymeric liner. Just adjacent to this flange, on the outer diameter of the neck, two face cuts are machined on opposite sides.
These face cuts provide the following advantages:
1. Anti-Rotation Locking: The cuts allow engagement with a complementary tool or liner feature to hold the boss steady while torque is applied to the valve.

2. Assembly Efficiency: Reduces risk of misalignment or cross-threading during installation.

3. Structural Reliability: Ensures secure torqueing without transferring rotational stress to the liner.

4. Enhanced Safety: Maintains consistent thread engagement and seal performance, reducing the chance of gas leakage.
The face cuts can be flat, elliptical, or customized based on specific engagement tooling but are positioned precisely opposite to each other to maintain balance and ensure symmetrical load distribution during torqueing.
The present invention provides an innovative enhancement to the end boss design of Type IV composite pressure vessels, particularly suited for CNG (Compressed Natural Gas) applications. These cylinders typically comprise a lightweight polymeric liner, overwrapped with carbon fiber or glass fiber composite layers, and terminated at both ends with metallic end bosses that allow for valve connection and pressure containment.
The end boss serves as a critical interface component, generally made of aluminum, stainless steel, or brass, and is threaded to accept standard valves or other fittings. During the final stage of cylinder assembly, valves are torqued into the end boss, requiring the boss to remain stationary to ensure correct alignment, thread integrity, and sealing.
However, due to the cylindrical geometry of the end boss neck, it often lacks features that can resist the rotational force (torque) applied during valve installation. If the end boss rotates slightly within the liner or composite shell during this stage, it may lead to:
● Thread misalignment,

● Damage to sealing surfaces,

● Stress concentration at the liner interface,
● Long-term leakage or valve failure.

To address this, the invention introduces precision-machined face cuts on two diametrically opposite sides of the outer diameter of the end boss neck, situated just below or adjacent to the flanged section.
Design Features:
● The face cuts are flat or slightly concave planar sections machined into the circular cross-section of the boss.

● Each cut spans approximately 90°–120° arc length and reduces the local diameter in that region, creating a gripping surface or flat face.

● The depth and width of the cut are optimized to retain mechanical strength while providing sufficient surface area for engagement.
Functional Purpose:
● These face cuts are designed to engage with mechanical features in either:

○ A custom torque fixture/tool, which clamps onto the flats and holds the boss static during valve torquing;

○ Or with corresponding anti-rotation features molded into the liner itself during manufacturing.

● The flat surfaces resist torsional forces by creating a positive mechanical lock, preventing relative rotation between the end boss and the liner or external tool during valve installation.
Assembly Process:
1. The end boss is inserted into the molded polymeric liner and bonded using standard techniques (e.g., interference fit, adhesive bonding, or co-molding).

2. During valve installation, a torque fixture is placed over the boss, and its jaws or clamping teeth engage directly with the face cut regions.

3. As torque is applied to the valve, the fixture ensures zero rotation of the boss, maintaining precise thread engagement and axial alignment.
Advantages of the Invention:
1. Prevents rotation of the end boss during valve torquing, thereby protecting threads and seals.

2. Improves assembly accuracy, reducing error rates in high-volume cylinder production.

3. Enhances safety and performance by ensuring consistent torque application and reducing potential gas leak points.
4. No major redesign of the end boss geometry is required — only localized modifications to the neck portion.

5. Compatible with existing liner materials and composite overwrapping processes.

6. Facilitates non-destructive torque control, without requiring adhesive reinforcement or rotation-stopping adhesives.
Possible Variations and Embodiments:
● The number of face cuts may vary (2, 3, or 4), although a symmetrical two-face configuration is preferred for balance.

● The face cuts may be shallow keyways, flat milled surfaces, or machined dovetails, depending on tool design.

● Additional indexing features such as notches or locking tabs may be incorporated to align with robotic torque tools.

● The design can be adapted for both male and female end boss threads and for various standard valve sizes (e.g., 1.125-12 UNF 12B parallel threads).

● The face cuts can be used in composite cylinders for other gases like hydrogen, oxygen, or specialty industrial gases where secure torqueing is essential.
, Claims:1. A Type IV composite cylinder comprising:

○ a polymeric liner;

○ a metallic end boss with a flange and a neck;

○ wherein the outer diameter of the neck, located adjacent to the flange, features face cuts on two opposite ends to prevent rotation during valve torquing.

2. The cylinder of claim 1, wherein the face cuts are shaped to engage with liner features or tooling elements to provide anti-rotation locking during assembly.

3. The cylinder of claim 1, wherein the face cuts improve torque transmission efficiency and reduce stress on the threaded portion of the end boss.

4. The cylinder of claim 1, wherein the end boss and liner interface achieves enhanced sealing integrity through the use of said face cuts.