Executive Summary
Architectural patch fittings are essential structural metal components designed to clamp, pivot, and secure frameless toughened glass panels in modern commercial and residential entrance systems. By transferring structural loads from cantilevered glass assemblies directly to floor, ceiling, and transom supports, patch fittings create clean, minimal glass facades. This article details material metallurgy, cutout geometries, component classification, and structural design considerations.
1. Material Metallurgy and Structural Components
Patch fittings clamp onto toughened safety glass panels without requiring structural adhesives. Performance relies on mechanical clamping friction, engineered internal gaskets, and precision metal castings.
Structural Composition
Outer Decorative Covers: Stainless steel (AISI 304 / AISI 316), solid brass, or anodized aluminum alloy, available in satin, mirror polished, PVD gold, or powder-coated matte black finishes.
Internal Core Bodies: High-pressure die-cast aluminum alloy or forged zinc alloy providing high tensile strength and resistance to mechanical fatigue.
Gaskets and Interlayers: High-density vulcanized rubber, PVC, or aluminum shims. These prevent direct metal-to-glass contact and distribute clamping forces uniformly to eliminate point-load stress concentrations.
2. Classification of Standard Patch Fitting Configurations
Modern glass entrances rely on standardized patch fitting profiles recognized across the architectural hardware industry:
PT 10 (Bottom Patch): Clamps to the bottom corner of the glass door leaf, connecting directly to the floor spring or pivot spindle.
PT 20 (Top Patch): Connects the upper corner of the door leaf to top pivots, side connectors, or overpanels.
PT 30 (Overpanel Patch): Mounts to fixed overpanels and transom glass to receive the top pivot pin of a PT 20 fitting.
PT 40 (Patch with Fin Fitting): Integrates side glass panels, overpanels, and structural glass fins for large frameless entrances.
Patch Locks (US 10 / US 20): Specialized lock housing patches fitted with euro-profile cylinders or thumb-turns installed at the base or vertical edge of glass doors.
3. Glass Preparation, Machining, and Structural Load Limits
Frameless patch fitting systems require precise glass preparation. All drilling, cutting, and corner notches must occur prior to the thermal glass toughening process.
Cutout Specifications & Hole Tolerances
Glass Type: Must utilize Toughened Safety Glass (TSG) or Laminated Toughened Glass with standard thicknesses ranging from $10\text{mm}$ to $15\text{mm}$.
Cutout Radii: Corner cutouts must incorporate smooth internal radii (minimum $R \ge 5\text{mm}$) to prevent stress concentration and cracking during heat treatment and operational usage.
Tightening Torque: Clamping bolts must be torqued precisely using torque wrenches (typically $12\text{--}15\text{ Nm}$) to maintain adequate friction without crushing internal interlayers.