Cooling System Design and Optimization for Thin-Wall Molds

Effective cooling channel design starts with three fundamental parameters: channel diameter, pitch (center-to-center spacing), and depth (distance from cavity surface). For thin-wall molds running on HWAMDA SPV5 machines, the standard guidelines are channel diameter of 8-12mm, pitch of 2.5-3.0 times the channel diameter, and depth of 1.5-2.0 times the channel diameter from the cavity surface. On an 8-cavity yogurt cup mold, this translates to 10mm diameter channels at 25-30mm pitch located 15-20mm from the cavity wall. Coolant flow must be turbulent (Reynolds number above 10,000) to achieve maximum heat transfer -- for a 10mm channel with water at 20 degrees C, this requires a flow velocity of at least 1.2 m/s, corresponding to approximately 5.7 L/min per circuit. Series cooling circuits connecting multiple cavities should be limited to 4 cavities per circuit to prevent excessive temperature rise -- inlet-to-outlet temperature differential should not exceed 3 degrees C. Parallel circuits provide more uniform cooling but require flow regulators on each branch to prevent preferential flow through low-resistance paths.

Beryllium copper (BeCu) alloy inserts provide thermal conductivity of 105-130 W/m-K -- approximately 4-5 times higher than H13 tool steel (24-28 W/m-K). BeCu inserts are strategically placed in thermal bottleneck areas: core tips of deep-draw containers, thin ribs, and areas where conventional cooling channels cannot be routed close enough to the cavity surface. For yogurt cup core tips on HWAMDA SPV5 molds, a BeCu insert of 15-20mm diameter at the core base reduces the core tip temperature from 50-55 degrees C to 32-38 degrees C, enabling a 0.3-0.4s cycle time reduction. BeCu hardness is limited to 38-42 HRC (Alloy C17200), which is lower than H13 at 48-52 HRC, so insert placement must avoid high-wear areas where the gate impingement flow directly contacts the surface. The material cost is approximately USD 80-120 per kg versus USD 8-12 per kg for H13, but insert volumes are typically small (50-200g per insert). For the best thermal performance, BeCu inserts should be shrink-fitted into the surrounding H13 steel with an interference fit of 0.02-0.03mm on diameter, ensuring intimate thermal contact without an air gap that would negate the conductivity advantage.

Precise coolant temperature control is essential for consistent part quality on multi-cavity thin-wall molds. HWAMDA SPV5 production lines typically require a dedicated mold temperature controller (MTC) for each mold half, with total cooling capacity of 30-80 kW depending on mold size and cycle time. For an 8-cavity yogurt cup mold producing 6g PP cups at 4.0s cycle, the heat load calculation is: 8 cavities x 6g x specific heat of PP (1.8 kJ/kg-K) x temperature differential (230 degrees C melt minus 40 degrees C eject) divided by 4.0s cycle = approximately 4.1 kW from the melt, plus frictional heating and hot runner losses, totaling 5-7 kW. Coolant inlet temperature should be 15-25 degrees C for PP thin-wall applications, controlled to plus or minus 0.5 degrees C. Running coolant below 12 degrees C risks condensation on the mold surface in humid environments, causing surface defects and corrosion. Flow rate through the mold should be 40-80 L/min total, distributed across 4-8 independent cooling circuits. Monitor inlet-outlet temperature differential -- variation exceeding 5 degrees C between circuits indicates blockage or flow restriction requiring immediate attention.

Achieving cycle times below 4.0 seconds on thin-wall PP containers requires combining multiple cooling technologies. The baseline approach for HWAMDA SPV5 yogurt cup lines running at 3.5-3.8s cycle time integrates: conformal-cooled cavity inserts with 4mm channel diameter at 3mm depth from the cavity surface, BeCu core tips with internal bubbler tubes, and chilled water at 12-15 degrees C with glycol anti-freeze mix (15-20 percent concentration to prevent condensation). Cooling water flow is maintained at 60-80 L/min with turbulent flow (Re above 12,000) in all circuits. The mold opens with the part still slightly warm (surface temperature 35-45 degrees C), relying on air cooling during the 0.3-0.5s ejection phase for final solidification. Part ejection temperature must be carefully tuned -- too hot causes deformation during SWITEK robot handling (grip force 2-5N per cup), while too cold extends cycle time unnecessarily. The INOVA controller's adaptive cooling function adjusts holding pressure switch-over based on cavity pressure sensor feedback, compensating for ambient temperature variations of plus or minus 5 degrees C throughout the day to maintain consistent part dimensions within plus or minus 0.05mm.