1、 Core preparation before processing
Material confirmation and pretreatment: Confirm that the flange material meets the requirements and perform appropriate stress relief treatment to prevent deformation during subsequent processing or use.
Detailed benchmark positioning: It is necessary to use the center circle or back of the bolt hole of the flange as an accurate benchmark for clamping, and confirm that the sealing surface is perpendicular and concentric with the center of the bolt hole after processing. This is a prerequisite for ensuring even force distribution during installation.
2、 Key control points during the processing
Surface roughness: This is the soul of the sealing surface.
The roughness value must strictly meet the standard (such as Ra 3.2~12.5 μ m, depending on the type and standard of the gasket). Being too rough can cause the gasket to be embedded too deeply, making it difficult to disassemble and prone to damage; If it is too smooth, it may reduce friction and cause the gasket to slip under pressure.
The direction of the pattern should be concentric circles (naturally formed by turning). This continuous concentric circular pattern can effectively hinder the radial leakage of the medium, creating a "labyrinth seal" effect. Radial or intermittent knife marks are strictly prohibited.
Flatness and flatness: The sealing surface needs to be a geometric plane.
Prevent "convexity" or "concavity": A slight "convexity" may cause only the middle circle to make contact, resulting in concentrated clamping force; A slight 'concave' will cause the inner and outer rings to come into contact and the middle to be suspended. Both will greatly reduce the sealing effect.
After processing, flat plates or optical flat crystals need to be used for testing to confirm that the flatness error within the entire sealing ring range is within the standard allowable range.
Sealing ring tightness:
For RF flanges, it is necessary to confirm that the width of the sealing ring at the top of the protrusion is consistent and the edges are clear without collapse.
For concave convex surfaces (MF/FM) and mortise and tenon surfaces (T/G), it is necessary to strictly control the fitting size, scale, and angle of the concave convex grooves. When processing, pairing processing should be preferred to confirm tight fit and even gaps.
3、 Details after completion
Thoroughly clean and protect:
After processing, it is necessary to thoroughly remove chips, oil stains, burrs, and any small particles on the sealing surface. A hard particle that is difficult to see with the naked eye may cause uneven indentation on the gasket, leading to leakage.
Immediately take protective measures, such as applying anti rust oil (to be removed before subsequent installation) or installing protective covers, to prevent collisions, scratches, and rust during transportation and storage.
Hardness matching: For high pressure or special working conditions, it is necessary to consider the matching of sealing surface hardness and gasket hardness. Sometimes surface hardening treatment is applied to the sealing surface (such as welding hard alloy, chrome plating, etc.) to improve its resistance to abrasion and erosion, and to confirm that its hardness is slightly higher than that of the gasket to prevent the gasket material from being embedded in the flange surface.
Microscopic defect inspection: For required applications such as nuclear power and high-risk chemicals, the sealing surface needs to undergo penetration testing (PT) after processing to confirm the absence of small cracks, pores, or slag inclusions.
4、 Systematic thinking to enhance sealing performance
Matching principle: The sealing surface form needs to match the gasket type. For example, wrapping gaskets require a hard and smooth sealing surface; Rubber gaskets can adapt to slightly rough surfaces. No matter how meticulous the processing is, if the selection is wrong, it will be of no use.
Collaborative consideration of bolt tightening: Detailed sealing surfaces require the correct bolt tightening sequence and torque. Uneven pre tightening force can cause flange deflection, making it difficult for the sealing surface to evenly press the gasket. The tightening principle of "cross symmetry and step-by-step increase" should be followed.
Adaptability consideration of working conditions: Before processing, the system working conditions should be taken into account.
High temperature working conditions: The coefficient of thermal expansion of the material needs to be considered, and sometimes it is necessary to intentionally process extremely small "concavities" to reach a flat surface in the hot state.
Cyclic load condition: requires high surface flatness and hardness to resist relaxation caused by alternating stress.