Traditional independent casting equipment relies entirely on manual operation. Fatigue, unstable mold positioning and ambient temperature fluctuation will continuously interfere with feeding accuracy, leading to off-spec weight and uneven foam density when output rises sharply.

Figure 2: Typical Defects Caused by Uncontrolled Density Drift

The integrated production line is not simple equipment splicing, consisting of four core linked modules:

1. Raw Material Storage & Temperature Control: Jacketed material tanks and continuous agitators stabilize raw material viscosity via constant temperature adjustment.
2. Precision Metering & Mixing: Servo drive metering pump + high-shear mixing head to guarantee uniform component blending.
3. Conveying & Positioning: Rotary disc line for shoe soles, linear track for large-size PU parts with submillimeter mold positioning accuracy.
4. Central PLC Control: Real-time linkage of pump speed, injection stroke and track moving speed in millisecond level.

Figure 3: Haifeng Automated Rotary Disc Production Line for Shoe Soles

Figure 4: Servo Motor Precision Metering System for ±0.5% Ratio Accuracy

3.1 Production Problem

A footwear factory adopted open-loop single machines: at 20℃ morning, each sole feeds 50g standard material; ambient rises to 32℃ in afternoon, polyol viscosity drops, actual feeding reaches 54g without parameter correction. Excessive material causes flash; low viscosity insufficient feed leads to toe voids, scrap rate above 12%.

3.2 Haifeng Closed-Loop Solution

Install Coriolis mass flow sensor before mixing head, detecting actual material flow 100 times per second. Once flow deviates from set value, PLC instantly adjusts servo motor speed to amend output in real time, locking single-piece feeding tolerance within ±0.5g all day long.

Figure 5: Coriolis Mass Flow Meter for Real-Time Flow Correction

3.3 Actual Effect

Batch density difference drops below 2%, scrap rate reduced from over 12% to under 1%.

Even precise flow control fails without matched line speed:

• Too fast track → uneven material distribution inside mold
• Too slow track → raw material cures before filling, inner void occurs

Automatic line uses distributed sensors to lock injection only after mold is fully positioned; curing channel running speed matches foaming cycle to ensure standardized solidification.

Upgrading from discrete single equipment to integrated automatic conveyor production line is a core production reform for shoe manufacturers to eliminate density drift and cut scrap loss.

Haifeng Polyurethane Machinery provides customized whole-plant layout, equipment matching and after-sale technical service according to customer's output and product specification. If you suffer from unstable sole density and high reject rate, contact us for free production line evaluation.