DN35CF-DN40CF (2.75″ OD) 316LN SS Standard ConFlat® (CF) UHV Flanges

Overview of ConFlat Flanges

ConFlat (CF) flanges are the go-to solution for high vacuum (HV) and ultra-high vacuum (UHV) systems. Widely adopted in scientific and industrial applications, CF flanges support a variety of instruments, gauges, accessories, and feedthroughs, making them highly versatile.

Blank (Blind) Flanges

Blank flanges, also known as blind flanges, are solid plate-like fittings used in vacuum systems. Their primary purpose is to close off unused ports or tubing sections in vacuum chambers. Additionally, they can be machined for customization, offering flexibility when creating bespoke components or fittings.

CF Flange Sealing Mechanism

The CF flange utilizes a knife-edge sealing mechanism, which is machined just below the flat surface of the flange. When the flange pair is bolted together, the knife-edges press into a soft metal gasket, forming concentric grooves. The gasket’s extruded metal fills surface imperfections, creating an exceptionally tight seal. This robust sealing system operates efficiently across a wide pressure range, from atmospheric pressure (760 torr/103 mbar) down to UHV levels of <1 x 10⁻¹³ torr (<1.3 x 10⁻¹³ mbar). The CF flange is also suitable for temperatures between -196°C and 450°C, depending on the material used.

Sizing Nomenclature

In North America, CF flange sizes are typically identified by their outside diameter (O.D.), while in Europe and Asia, sizing is often based on the nominal internal diameter (I.D.), which refers to the largest tube that can be welded to the bored flange.

Types of ConFlat Flanges

CF flanges are available in two main configurations:

• Fixed Flange: This design features a single piece where the bolt-hole orientation is fixed relative to the fitting. These are commonly used when specific alignment isn’t necessary.
• Rotatable Flange: Consisting of two parts—the inner weld ring and outer bolt ring—this flange design allows the outer ring to rotate freely around the inner weld ring. This feature enables easier alignment with mating flanges, especially in systems where bolt-hole orientation is critical.

Both fixed and rotatable flanges come in variations with clearance-holes or tapped holes, catering to different assembly needs.

Hole Options

• Clearance-Holes: These through-holes provide enough space for bolts to pass through both flanges, secured by nuts or plate nuts.
• Tapped Holes: Machined with imperial or metric threading, tapped holes allow a bolt to be fastened directly into the flange without the need for additional nuts or plate nuts. Care must be taken when selecting tapped flanges to ensure proper alignment with other components.

316LN Stainless Steel Features

For demanding environments, CF flanges made from 316LN stainless steel offer several advantages:

• Increased Hardness: With a Brinell Hardness of 170, 316LN stainless steel is more durable than the commonly used 304L. This makes it ideal for applications that require frequent disassembly and reassembly.
• Electro-slag Remelting (ESR): ESR improves the homogeneity of the metal’s grain structure, reducing macro segregation and enhancing the overall quality of the material.
• Low Magnetic Permeability: With a magnetic permeability (µ) of ≤1.005, 316LN is less magnetically active compared to 304L (µ = 1.03), making it better suited for applications where low magnetic interference is essential.

These characteristics make ConFlat flanges an essential component in high-performance vacuum systems, ensuring long-term reliability and precision.

Ordering Table