Plastic Colander Injection Mold

Plastic colanders are essential kitchen tools used for draining fruits, vegetables, and pasta. The mold design for single-color colanders must address several specific requirements: uniform wall thickness, precise drainage hole formation, and efficient cooling.

Drainage Hole Formation

The drainage holes in a colander are typically arranged in a circular or grid pattern across the bowl surface. These holes must be cleanly formed without burrs or flash. The hole geometry—including diameter, spacing, and edge finish—is determined by the cavity and core design. For colanders with intricate hole patterns, the mold may require side-core actions or slide mechanisms to achieve the desired hole geometry. The parting line location must be carefully chosen to ensure that holes are formed cleanly and that the part can be ejected without damage. Typical hole diameters range from 3 mm to 8 mm depending on the application, with hole spacing determined by structural requirements.

Uniform Wall Thickness

Maintaining uniform wall thickness is essential to ensure consistent cooling and prevent warpage. Uneven wall thickness leads to differential shrinkage, which can cause the colander to deform after ejection. For bowl-shaped products with curved surfaces, wall thickness is typically maintained between 2.0 mm and 3.5 mm. CAE mold flow analysis is commonly used to identify areas of uneven thickness and optimize the design before mold manufacturing begins.

Cooling System Design

Cooling efficiency is critical in colander mold design. The bowl-shaped geometry with varying depths presents cooling challenges, as deeper sections retain heat longer than shallower areas. Modern colander molds incorporate cooling channels placed close to the molding surface. By positioning cooling lines near the cavity and core surfaces, the cooling process is accelerated, reducing cycle time and improving part quality. Typical cooling channel diameters range from 8 mm to 12 mm, with channel spacing of 30 mm to 50 mm depending on the part geometry. Cycle time for colander production typically ranges from 25 to 45 seconds.

Gate Design and Melt Flow

The gate location significantly affects the filling pattern and part quality. For round or oval colanders, a central gate at the bottom of the bowl allows the melt front to advance uniformly toward the rim. For larger colanders, multiple gates or fan gates may be used to ensure balanced filling. The gate design must also consider the ease of degating—whether manual trimming or automatic degating is employed. Common gate types for colander molds include pin gates, submarine gates, and edge gates.

Mold Steel Selection

The mold steel for colander production must withstand repeated injection cycles while maintaining precision. Common steel grades include:

P20 (pre-hardened, HRC 28-32): suitable for medium-volume production

718H (pre-hardened, HRC 33-38): offers improved wear resistance for higher volumes

S136 (stainless, HRC 48-52): provides corrosion resistance and high polishability for food-contact applications
For high-volume production, the cavity and core may be manufactured from higher-grade steels and subjected to nitriding or PVD coating to extend mold life.

Ejection System

Given the bowl shape of colanders, the ejection system must be carefully designed. Ejector pins are typically arranged around the perimeter and base of the part to ensure balanced ejection forces. For deeper colanders, ejector sleeves or air-assisted ejection may be employed to prevent part deformation during demolding.