Selecting Cooling Water Rotary Joints for Injection Molds
On turntable (vertical) injection molding machines, the mold rotates continuously, so cooling water must pass through a rotary joint to reach the mold channels. A water interruption or leakage means warped parts, longer cycle times, or water damage to the electrical area around the turntable. This article outlines how to specify a rotary joint for typical mold cooling duty.
Operating profile: low speed, multiple circuits, continuous duty
Turntable speeds on injection machines usually range from 1 to 10 RPM, far below lathe or centrifugal applications. A single mold, however, often needs several independent water circuits (core side, cavity side, plus slides), and machines run more than 20 hours per day. The key criteria are therefore multi-passage integration and long-term seal reliability rather than maximum speed. DEWEL double-circuit rotary joints integrate several independent water circuits in one housing, reducing piping complexity and potential leak points compared with stacked single-passage units.
Medium, temperature and pressure
Mold cooling water typically runs at 10-90 degrees C; with a mold temperature controller it can reach about 120 degrees C, at system pressures of 0.3-1.0 MPa. Size the temperature rating from the controller setpoint plus a 20 percent margin, and the pressure rating from the pump shutoff pressure. The DEWEL rotary joint range covers DN6-DN350 with pressure ratings up to 138 MPa; standard cooling water service is normally met with DN15-DN40 at a 1.6 MPa rating, leaving ample margin. See the double-circuit rotary joint product page for details.
Number of passages and structure
Two-plate molds generally need 2-4 circuits, which a double-circuit design covers. For complex molds or combined hydraulic supply, a multi-passage custom structure keeps the water and hydraulic circuits separated. When space at the turntable center is limited, a custom solution based on the machine drawings is advisable; see DEWEL custom rotary joints.
Seals and bearings
Cooling water has low lubricity, so resin-impregnated graphite against stainless steel sealing rings is recommended. Bearings should be paired angular-contact ball bearings with clearance compensation to absorb turntable alignment errors. DEWEL was founded in 2006 and manufactures in Tengzhou, Shandong, under an ISO 9001 certified quality system; seal pairs and bearings are pressure and air-leak tested by batch.
Installation and maintenance
Mount the housing fixed with only the rotating shaft turning, and connect the inlet through flexible hose so piping stress does not reach the sealing faces. Purge air before rotation and confirm zero leakage before engaging the turntable. Inspect the sealing faces every 500 running hours and install a 60-80 mesh filter to keep scale particles away from the seal pair. With proper selection and maintenance, a 12-month inspection-free interval is a realistic target for injection mold cooling service.
