When purchasing a used fully automatic double-line T-shirt bag making machine, the core principle is to "avoid pitfalls" rather than simply "find a bargain." Given your location in the Wenzhou plastics machinery industrial cluster, it's highly recommended to prioritize searching for machines locally (e.g., in Ruian, Pingyang) from dealers with physical premises or from factories upgrading their equipment, as this facilitates on-site inspection. Here are the 5 Critical Checkpoints you must adhere to:
1. First, Verify Identity: Machine Type & Material Compatibility
• Confirm it's a genuine "double-line" unit: Ensure the machine is an original double-line design (with two independent pulling systems and two sets of cutting blades). Be wary of "fake double-line" machines cobbled together from two single-line units, as their synchronization is often poor.
• Strictly check "biodegradable" adaptability: If you plan to produce biodegradable bags (PBAT/PLA), you must verify the machine's temperature control precision. Biodegradable film has a low melting point (approx. 110–130°C). Older machines with imprecise temperature control easily burn through the film or fail to seal properly. Prioritize models equipped with servo motors and PLC temperature control.
• Check brand and age: Give priority to mainstream local brands from Ruian (e.g., Zhengbang, Gaofeng, Hualian, etc.) for easier parts sourcing. Avoid older relay-controlled machines over 8–10 years old unless the price is extremely low.
2. On-site Inspection: Focus on Wear in the "Heart" of the Machine
You must conduct a test run with film (at least 30 minutes), focusing on:
• Heater block and punch die: Observe if the bottom seal is even and free of burn marks. Check if the handle holes are punched cleanly. Manually feel the bearings on the heater block frame; significant wobble or abnormal noise indicates severe spindle wear, which is costly to repair.
• Electrical and drive systems: Open the electrical cabinet. Check the brand of the PLC and touchscreen (lower-end domestic brands have higher failure rates). Listen for smooth operation of servo motors (if equipped); older stepper motors are prone to losing steps (causing inconsistent bag lengths).
• Defect rate test: Produce 100 bags consecutively during the test and count the defects. If the defect rate exceeds 3% for a used machine, it's essentially buying "scrap metal."
3. Calculate "Hidden Costs": Purchase Price ≠ Total Investment
• List of consumable/wear parts: Request current photos of the heater blocks, cutting blades, punch dies, and rubber rollers. Replacing these worn parts can cost thousands, a factor that must be deducted from your offer price.
• Retrofitting costs: If the machine lacks automatic web guiding, automatic counting, or stacking, adding these features later may cost an additional 10,000 – 20,000 RMB.
• Price reference: Based on configuration (servo/stepper, presence of automatic roll change), the reasonable price range for a used double-line machine is typically 30,000 – 80,000 RMB. Machines priced below 20,000 RMB are usually problematic.
4. Leverage Geographic Advantage: Secure Local After-sales Service
• Avoid "no-name" sellers: Only consider used equipment dealers with fixed premises or physical stores. In the Wenzhou/Ruian area, it's easy to find manufacturers dealing in used machines. They can often provide limited warranties of 3–6 months.
• Spare parts inventory: Confirm if the seller has technical drawings for the heater blocks and dies for that model, or can provide spare parts quickly. Sourcing parts from afar for a broken-down machine leads to significant downtime losses.
5. Transaction Red Lines: Documentation and Contract
• Request documentation: You must obtain the electrical circuit diagrams, a backup of the PLC program, and the operation manual. The worst-case scenario for used equipment is losing the PLC program, which can render the machine useless.
• Contract terms: The contract should clearly state "payment after successful on-site test run with material" and specify performance guarantees like "ensuring synchronized double-line operation and firm sealing." Verbal promises are worthless.
⚠️ Special Reminder (For Wenzhou Buyers)
If you primarily produce small garbage/shopping bags and don't have strict biodegradable requirements, prioritize machines retired by local Ruian factories during upgrades. These are often well-maintained, and local technicians are familiar with repairs. If producing high-end biodegradable bags, carefully consider buying used. Investing in a new machine might be more prudent (temperature control stability is critical).
If you have specific bag dimensions (width × length) or a budget range, I can help you assess which used configurations offer better value.
