Optimization of release consistency of EVA/PVC shoe soles: reducing drawing and sticking defects

# EVA/PVC shoe sole demolding consistency case: two weeks to reduce drawing stickiness and reduce rework

# Project overview

• Industry/Scenario: EVA/PVC sole molding and foaming
• Production method: Single shift continuous production
• Core Goal: Reduce stringiness, stickiness and incomplete edges, and improve batch consistency

# Initial questions

Customers have three types of problems in sole production:

1. Drawing and stickiness are combined, which affects the appearance and demoulding stability.
2. Edge integrity fluctuates, rework and picking costs rise
3. Parameter drift between shifts, more obvious when EVA and PVC are produced alternately

# Live baseline (before optimization)

• Defective appearance rate: about 4.0%~5.0%
• Rework ratio: about 10%
• Stability performance: Fluctuations are obvious after switching across materials, and batch consistency is insufficient.

Statistical caliber: daily production line reports for a single shift for two consecutive weeks, based on the customer’s current appearance and rework standards.

# Diagnostic Process (Days 1-3)

First check the materials, and then reconstruct the parameter window:

1. Compare the defect differences between EVA and PVC under the same parameters
2. Record spray coverage versus edge integrity
3. Examine the impact of dilution ratio fluctuations on the risk of stickiness
4. Unify shift handover parameter records to reduce human drift

Diagnostic Conclusion

• The main problem is not the failure of a single release agent, but the parameter mismatch caused by sharing windows across materials.
• EVA and PVC have different process sensitive points and need to be managed in separate windows.

# Implementation Plan (Days 4-10)

• Option A (material window): Establish EVA and PVC parameter intervals respectively
• Scheme B (Coverage and Dilution): Fixed coverage and dilution ratio to reduce on-site drift
• Plan C (Team Collaboration): Execute shift handover parameter locking and review

Establish SOP simultaneously:

• First piece confirmation per shift (edge ​​integrity + tackiness risk)
• Random inspection of key defect points every 2 hours
• Abnormal troubleshooting sequence: Material window → Coverage → Dilution ratio → Clear mold status

# Two-week results (trial production stage)

• Defective appearance rate: reduced from about 4.0% to 5.0% to 1.8% to 2.6%
• Rework ratio: reduced from about 10% to 5%~7%
• Consistency performance: Fluctuations converge after cross-material switching, and shift stability is improved

# Reusable experience

1. The sole scene should adhere to “windows according to materials” to avoid sharing parameters.
2. Stabilize the coverage and dilution ratio first, and then optimize the efficiency to make it easier to reduce rework.
3. The dual indicator evaluation of “appearance defective rate + rework ratio” is closer to the true cost.

# Applicable boundary description

The results of this case are based on the current mold status, sole structure, temperature and humidity conditions and rhythm. Under different formula systems, pattern complexity and quality standards, it is recommended to verify the sample first and then import the whole line.

# Consulting advice

Material type, tempo, current defect distribution and rework data can be provided, and we can provide an initial parameter window suggestion that can be implemented.