In rotomolding production, mold structure selection is one of the most critical factors influencing both product quality and manufacturing efficiency. This is especially important in applications where product capacity ranges widely from 50L to 50000L. In such cases, differences in size, wall thickness and application scenarios require a systematic approach to mold selection rather than relying solely on experience.

For small rotomolded products within the 50L–300L range, the typical height is between 300–700mm and the weight ranges from 2–10kg. These products usually have shorter heating cycles and simpler material flow paths. As a result, heat transfer efficiency becomes a key factor. Aluminum molds are commonly used due to their superior thermal conductivity, which helps reduce heating time and improve production efficiency. In addition, the structure of small molds is relatively simple, and a one-piece design is generally sufficient.

When product capacity increases to 500L–2000L, the dimensions become significantly larger, with heights typically ranging from 600–1200mm and weights reaching 10–40kg. At this stage, mold design must balance heat transfer performance with structural strength. Since rotomolding involves continuous rotation during heating, insufficient structural support can lead to deformation. Therefore, reinforced ribs or modular mold structures are often introduced to improve rigidity and stability.

For large tanks in the 3000L–20000L range, mold dimensions often exceed 1500mm, with bottom diameters between 1500–2700mm and heights above 3000mm. In this size category, the focus of mold design shifts from heat transfer efficiency to structural integrity and process compatibility. Large molds are typically designed in segmented sections to facilitate transportation and installation. At the same time, rotation paths must be optimized to ensure even material distribution inside the mold cavity and to avoid material accumulation or shortages in specific areas.

Process parameters play an equally important role. During rotomolding, the heating temperature must be controlled within a tolerance of ±2°C to ensure consistent melting across the entire mold surface. Rotation speed is typically maintained between 3–12 rpm. The ratio between the major and minor axes directly affects the material flow pattern. For smaller products, higher rotation speeds can be used to shorten the cycle time. However, for large tanks, slower and more stable rotation is required to maintain uniform wall thickness.

Wall thickness is another key parameter in mold design. Small products usually have wall thicknesses of 3–5mm, medium products range from 5–8mm, and large tanks can reach 8–15mm. As wall thickness increases, cooling becomes more critical. Air cooling is generally sufficient for thin-walled products, while water cooling is preferred for thicker structures to minimize deformation caused by uneven cooling rates.

In practical applications, mold selection should follow a structured approach. First, determine the mold size range based on product capacity. Second, select the appropriate mold structure according to the height-to-diameter ratio. Third, design the mold strength and segmentation based on wall thickness requirements. Finally, match the mold with machine capability and heating method. This multi-parameter matching process ensures better product consistency and reduces production risks.

In conclusion, rotomolding mold selection is not simply a structural decision but a comprehensive engineering process involving materials, processing parameters and equipment compatibility. Only by considering the relationships between size, capacity and process conditions during the design stage can manufacturers achieve stable, efficient and controllable production outcomes.