Tips for Replacing Wear Parts of Plastic Recycling Equipment: How to Replace Blades, Filters, and Sealing Rings for Longer Service Life

In the operation of plastic recycling production lines, blades, filters, and sealing rings are high-frequency wear parts. Their replacement frequency and quality directly affect equipment efficiency, recycled material quality, and operating costs. Many enterprises experience over 30% reduction in wear part lifespan due to improper replacement methods, which may even cause equipment failures. This article details scientific replacement techniques for these three core wear parts to help extend part lifespan and reduce maintenance costs.

I. Crusher Blades: "Alignment" and "Balance" Are Key to Replacement, Extending Lifespan by 50%

Crusher blades (for single-shaft/twin-shaft crushers) are core components for breaking waste plastics. After long-term shearing of hard plastics, they are prone to edge wear and chipping and require regular replacement. Improper replacement methods (e.g., uneven blade clearance, misalignment during installation) can lead to unevenly broken particles and even accelerated wear of the knife shaft.

1. Preparation Before Replacement: Confirm Model and Inspect Component Status

• Confirm blade model: Crushers use blades of different materials, sizes, and edge angles. Strictly match the equipment model to avoid knife shaft jamming caused by mixed use.

• Inspect the knife shaft and blade holder:  Before replacement, clean residual plastic from the knife shaft surface and check if the blade holder is deformed or worn. 

2. Core Replacement Techniques: Three Steps for "Precise Installation"

• Step 1: Align the blade edge direction
       Single-shaft crusher blades must be installed in the "spiral direction", while twin-shaft crusher blades must ensure "staggered engagement" between the blades of the two shafts. Reversed installation will reduce crushing efficiency by 50% and cause blade chipping.

• Step 2: Control blade clearance
       After installation, use a feeler gauge to check the clearance between the moving blade and fixed blade:

• For flexible materials (films, woven bags): Control clearance at 0.2-0.5mm;

• For hard materials (thick-walled plastics, rigid parts): Adjust clearance to 0.5-1mm.
        Excessive clearance leads to unbroken large pieces, while insufficient clearance accelerates edge wear.

• Step 3: Dynamic balance test
       After installing the blades, manually rotate the knife shaft to check for jamming or imbalance. If imbalance occurs, verify whether the blades have the same weight or if their installation positions are symmetrical. For twin-shaft crushers, the total weight difference between the blades of the two shafts must not exceed 5g—otherwise, severe vibration will occur after startup, damaging the bearings.

3. Post-Replacement Maintenance: Key to Extending Lifespan

• After installing new blades, run the machine without load for 10 minutes to check if the knife shaft rotates smoothly. Feed materials only if there is no abnormal noise.

• Avoid feeding hard impurities (e.g., metal, stones) during initial operation. Install a magnetic separator at the feed inlet to prevent edge chipping.

• Check the blade fixing bolts weekly. Tighten them according to the equipment manual to prevent blade displacement due to loosening.

II. Extruder Filters: "Timing" and "Operation" Are Key to Replacement, Avoiding Melt Leakage

Extruder filters filter impurities (e.g., metal shavings, unmelted particles) from molten plastic. Long-term use causes clogging, leading to increased melt pressure and reduced productivity. Improper replacement (e.g., prolonged shutdown, filter misalignment) can cause material degradation and abnormal equipment pressure.

1. Determine Replacement Timing: Don't Ignore These 3 Signals

• Excessive melt pressure: When the die pressure exceeds 10% of the set value and remains high for 10 minutes, the filter is clogged.

• Product surface defects: Scratches, black spots on extruded pipes/granules, or holes in films may indicate filter damage and impurity contamination.

• Reduced productivity: If hourly output decreases by over 10% compared to normal levels at the same screw speed,  check for filter clogging.

2. Core Replacement Techniques: "Non-Shutdown Operation" with Twin-Station Screen Changers (Mainstream Solution)

• Step 1: Preheat the backup filter
       Place the new filter (usually 2-3 layers stacked: fine mesh inner layer +  coarse mesh outer layer) into the standby station of the screen changer. Preheat it to the same temperature as the extruder's homogenization section. This avoids melt solidification and clogging caused by cold filters contacting high-temperature melt.

• Step 2: Rapidly switch stations
       Close the screen changer's feed valve (if equipped) and rotate th switching handle (twin-station screen changers are usually manual or pneumatic) to push the standby station to the working position. Complete the process within 30 seconds to reduce melt residence time and avoid degradation.

• Step 3: Clean the old filter and sealing surface
       After removing the old filter, clean the screen changer's sealing surface with a brass brush (avoid steel wire brushes to prevent scratches). Check if the gasket is deformed or damaged—replace it if necessary to prevent melt leakage.

3. Extend Filter Lifespan: 2 Pre-Measures

• Raw material pretreatment: Install a "magnetic separator + vibrating screen" at the extruder feed inlet to filter metal impurities and large foreign objects, reducing filter clogging frequency.

• Graded filtration: Use two-stage filtration ("coarse + fine")—e.g., 60-mesh filter for large impurities (first stage) and 120-mesh filter for fine filtration (second stage)—to avoid overloading a single filter.

III. Equipment Sealing Rings: "Selection" and "Sealing" Are Key to Replacement, Preventing Leakage

Sealing rings are widely used in washing line tanks, extruder flanges, and granulator pelletizing chambers to seal liquids (washing water) or gases (high-temperature melt volatiles). Common materials include nitrile rubber (NBR), fluororubber (FKM), and Teflon (PTFE). Long-term use causes aging and deformation, leading to water or material leakage.

1. Key Selection Principle: 3 Materials for 3 Scenarios

• Washing line tanks (normal temperature, alkaline environment): Choose NBR sealing rings. They are alkali-resistant, water-resistant, suitable for -40℃-120℃, and cost-effective.

• Extruder flanges (high temperature, oily environment): Choose FKM sealing rings. They resist temperatures (-20℃-260℃), oil, and molten plastic corrosion, suitable for processing PE, PP, PET, etc.

• Pelletizing chambers (water cooling, high-speed friction): Choose PTFE sealing rings. They are wear-resistant, water-resistant, suitable for -200℃-260℃, and ideal for underwater pelletizers.

2. Core Replacement Techniques: Two Steps for "Cleaning + Tightening"

• Step 1: Thoroughly clean the sealing surface
       After removing the old sealing ring, wipe the equipment's sealing surface with alcohol or acetone to remove residual plastic, oil, and aged adhesive. Ensure no scratches or protrusions—sand the surface smooth if scratches exceed 0.2mm.

• Step 2: Correct      installation and tightening
       Apply a thin layer of "food-grade grease" (for washing lines) or "high-temperature grease" (for extruders) to the new sealing ring to avoid scratches during installation.
       Ensure the ring is fully seated in the sealing groove (no offset or distortion). Tighten the bolts evenly: use the diagonal sequence and tighten in 3 steps (increase torque by 1/3 each time). Follow the equipment manual for final torque to prevent leakage due to uneven pressure.

3. Extend Sealing Ring Lifespan: 2 Usage Habits

• Avoid over-temperature use: For example, NBR sealing rings cannot be used above 120℃ (accelerates aging). Strictly follow the material's temperature range.

• Regular inspection and maintenance: Check sealing rings in high-frequency use areas weekly. Replace them immediately if deformation, hardening, or cracks are found to prevent minor leaks from  worsening.

IV. General Principles for Wear Part Replacement: Remember These 3 "Don'ts"

1. Don't mix models: Blades, filters, and sealing rings must match the original equipment specifications. For example, a 0.5mm difference in blade thickness may cause knife shaft imbalance, and a 1mm difference in sealing ring diameter may lead to leakage.

2. Don't skip pretreatment: Clean component surfaces and inspect related parts (e.g., blade holders for blades, sealing surfaces for rings) before replacement to avoid "faulty installation."

3. Don't omit test runs: After replacement, run the equipment under no-load or light load for 10-30 minutes. Confirm no abnormalities (e.g., noise, leakage) before normal production.

Mastering scientific wear part replacement techniques not only extends part lifespan but also reduces equipment downtime, improving the stability and economic efficiency of plastic recycling production lines.