Changing the extrusion die on a fruit net machine is one of the most common changeover tasks in a foam-net workshop, yet it is also where beginners make costly mistakes. A fruit net machine die head is not a single piece-it is a circular rotating die assembly made of a die body, an inner mandrel (which sets strand count: 4/6/8 ribs), an outer die ring, and a breaker/screen pack. Swapping it correctly means respecting heat, pressure, and torque order, not just unbolting and rebolting.
1. Safe Shutdown First
Stop the screw, kill the butane pump, and purge the barrel with clean LDPE for 3–5 minutes to clear foaming agent. Engage LOTO (Lockout-Tagout) on the main breaker-never work on a hot die head with live power. Let the die cool to 60–80 °C: warm enough that residual PE is soft, cool enough that you will not burn your hands or distort the mandrel.
2. Relieve Flange Bolts in Cross Pattern
The die connects to the extruder barrel via a heated flange. Loosen the flange bolts evenly in a cross (star) pattern, half a turn at a time. Never remove one bolt fully first-uneven release warps the die face and causes melt leakage on restart. Support the die head with a hoist or die cart rated for its weight (a 75-type rotary die head is 40–80 kg).
3. Pull the Mandrel and Outer Ring
Once the flange is free, slide the inner mandrel out the front (some fruit net machine models use a threaded mandrel-unscrew, do not pry). Remove the outer die ring and the screen pack/breather plate behind it. Photograph and label every part in disassembly order; the radial slit orientation on the mandrel must match the die ring groove on reassembly or the mesh will be asymmetric.
4. Clean Before Swapping
Even if you are fitting a new die, clean the barrel nose and breaker plate face with a brass scraper or copper gauze-never steel tools, which scratch the polished flow surfaces and seed carbon buildup. Wipe with lint-free cloth and isopropyl alcohol. Inspect old mandrel slits for carbon; if switching strand count (say 6→8 rib), confirm the new mandrel's OD matches the die ring ID.
5. Fit the New Die Set
Mount the new breaker plate, then the outer die ring, then slide the new mandrel in until its shoulder seats flush. Apply high-temperature anti-seize to bolt threads only (never on sealing faces). Torque flange bolts in cross pattern to the manufacturer's spec (typically 80–120 N·m on a 75-type fruit net machine); uneven torque distorts the die and leaks melt at 180–200 °C.
6. Preheat and Purge
Close LOTO, restore power, and preheat the die zone gradually-ramp at 3–5 °C/min to the set point (die head ~180–200 °C). Do not spin the rotary die motor until the head is at temperature. Start screw at low rpm (5–8 r/min), open butane after stable melt pressure, and run scrap net for 10–15 minutes. Measure tube diameter on the sizing sleeve; if off-spec, adjust haul-off VFD, not the die bolts.
Common Pitfalls
Cold die start → mandrel seizes in the ring, shears the drive pin.
Steel screwdriver on die lips → permanent scratch, forever marks the net.
Guessing torque → leaks, then fire risk from butane at the flange.
No photo before disassembly → mandrel slit clocking wrong, diamond mesh skews.
A die swap on a fruit net machine takes a trained operator 45–90 minutes including cooldown and restart. Log the die serial, mandrel rib count, torque value, and preheat time for every change-repeatability is what keeps mesh density stable across SKUs.