Case Study: Innovative Injection Mold Design for a 115mm PVC Tee Fitting

• Product Type: 3-Way Pipe Fitting (Tee) with Hub/Socket Ends
• Material: Rigid PVC (Polyvinyl Chloride)
• Internal Diameter (ID): 115mm
• Port Configuration: 2 x Inline Straight Hub Ports, 1 x Lateral Curved Hub Port
• Core Actuation System: Direct-Drive Hydraulic Oil Cylinders
• Specialized Mechanism: Horseshoe-Shaped Moving Slider with a Slant Top Slot
• Tooling Versatility: Modular Core/Cavity Inserts (Convertible to 4-Way Cross)

Before evaluating the mold structure, it is essential to contextualize the material behavior of PVC. PVC degrades quickly if overheated or subjected to excessive shear stress, liberating corrosive hydrochloric acid (HCl) gas. Therefore, the mold flow paths must be exceptionally smooth, and the internal cooling channels must maintain strict thermal equilibrium.

Furthermore, a hub end requires absolute dimensional accuracy to guarantee leak-free joints in field applications. The shrinkage of a 115mm large-diameter PVC fitting generates tremendous wrapping force (clamping friction) onto the internal steel cores during the cooling phase. Demolding a curved port under these conditions without causing scuffing, whitening, or structural deformation requires a highly sophisticated mechanical trajectory.

The foundational layout of the mold prioritizes robustness and minimal maintenance. The three primary internal cores are directly driven by independent, heavy-duty hydraulic oil cylinders. This hydraulic setup ensures high clamping force resistance and uniform, linear extraction forces, which are critical for stripping large-diameter components off the steel elements.

The defining innovation of this mold lies in the demolding sequence of the lateral curved hub port. Traditional linear sliders cannot clear a curved internal radius without cutting into the plastic part wall. To solve this, our engineering team developed a custom horseshoe-shaped moving slider (horseshoe core).

1. Linear Pulling Force to Slant Slot Engagement to Core Wrapping Force to Instantaneous Inward Swing to Undercut Clearance to Safe Linear Extraction
2. The Slant Slot Design: A precision-machined diagonal/slant guide slot is integrated into the top section of the horseshoe core assembly.
3. Utilizing the Material Wrapping Force: When the hydraulic cylinder begins its backward stroke, it does not immediately pull the entire mechanism out linearly. Instead, the high wrapping/clamping force exerted by the cooling PVC part onto the core acts as a temporary anchor.
4. Instantaneous Pivoting Motion: As the cylinder pulls against this resistance, the mechanical force is redirected through the top slant slot, causing the horseshoe slider to instantly swing and pivot inward along the radial path of the port's arc.
5. Interference-Free Retraction: This instantaneous rotation effectively shrinks the core’s cross-sectional envelope, completely disengaging it from the internal geometry. It prevents any mechanical interference with the upper and lower straight cores. Once the undercut is cleared, the slider retracts smoothly out of the cavity along a linear path.

To maximize tool longevity and prevent part deformation, the mechanical cycle follows a strict, automated sequence:

• Phase 1: Injection and Cooling. The polymer melt solidifies, and the part contracts around the cores.
• Phase 2: Lateral Core Extraction. The lateral hydraulic cylinder fires first. The horseshoe slider executes its instantaneous swing motion to clear the curved undercut and completely retracts from the side port.
• Phase 3: Straight Core Extraction. The top and bottom hydraulic cylinders actuate simultaneously, pulling the straight-through inline cores cleanly out of the part.
• Phase 4: The mechanical ejector system pushes the finished 115mm PVC tee out of the cavity.

In modern industrial manufacturing, capital expenditure (CapEx) optimization is paramount. To maximize the asset's Return on Investment (ROI), this mold base was engineered with a highly flexible, modular architecture.

The tool is capable of producing both 3-Way Tees and 4-Way Cross Pipe Fittings. The mold block features a dedicated pocket at the opposite side of the branch port that accepts interchangeable inserts.

This swap-out process can be performed directly on the injection molding machine without dismantling the entire mold base, allowing manufacturers to respond dynamically to changing market demands with zero secondary tooling development costs.

Molding a 115mm PVC tee fitting with a curved lateral port demonstrates how smart mechanical kinematics can simplify complex manufacturing hurdles. By pairing a robust hydraulic layout with an innovative horseshoe swinging slider, this tool delivers high-velocity cycle times, zero cosmetic defects on sealing surfaces, and exceptional multi-part versatility.