company news about Service Life of Screws and Dies in Twin screw floating fish feed production machines

In commercial fish feed production, the service life of wear parts is measured in operating hours rather than months. High-quality nitrided screw segments (38CrMoAl) typically last between 2,000 and 4,000 hours, while bimetallic or tungsten carbide-coated screws can exceed 6,000 hours. Die plates generally have a shorter lifespan of 800 to 1,500 hours due to the intense pressure at the discharge point. These intervals can decrease by 50% if the raw material has a high ash/silica content or if moisture levels are kept below 18%.

1. Screw Segment Lifespan by Material Type

The "screw" in a Twin-Screw floating Fish Feed Extruder is a modular assembly. Different sections wear at different rates, with the compression and discharge zones bearing the most stress.

2. Why Die Plates Wear Faster Than Screws

The die plate is the "bottleneck" of the entire system.

• High Velocity: Material is forced through tiny holes (as small as 0.6mm) at high speeds, creating extreme friction.

• Thermal Shock: The die plate sits at the boundary between the 150°C barrel and the ambient air, leading to microscopic metal fatigue over time.

• Pellet Size Impact: Small dies (0.8mm - 2mm) wear much faster than large dies (6mm - 10mm) because the total surface area of friction is significantly higher.

3. Top 3 Factors That "Kill" Your Wear Parts

A. Silica & Ash Content (The "Sand" Factor)

If your raw materials (like rice bran or low-grade fish meal) have not been properly cleaned, they contain microscopic silica.

• Impact: This acts as an industrial abrasive, grinding down the screw flighting until the clearance between the screw and barrel exceeds 1.5mm, at which point the Twin screw floating fish feed pellet making machine loses pressure and floating pellets begin to sink.

B. Specific Mechanical Energy (SME) & Moisture

Low moisture (<20%) increases the internal friction (SME).

• Impact: While this helps with "cooking," it generates excessive heat that can soften the nitrided layer of the metal, causing the screw edges to round off prematurely.

C. Corrosive Ingredients

Recipes with high salt content or acidic additives can cause pitting corrosion on the screw surfaces.

• Prevention: Always purge the machine with a high-starch material (corn flour) before shutdown to remove corrosive residues.

4. Maintenance ROI: When to Replace vs. Wait?

Using worn parts is a "hidden cost."

• The 10% Rule: When screw wear reduces your hourly output by 10%, the electricity cost per ton of feed increases to the point where it is cheaper to buy new screws than to continue running the old ones.

• Preventive Replacement: Replacing a die plate before it fails ensures pellet uniformity, which is critical for maintaining your brand's reputation in the market.

5. FAQ: 

Q: How often should I replace my Twin screw floating fish feed pellet extruder machine screws?
A: For a standard 8-hour shift, 5 days a week, expect to replace segments every 12 to 18 months. However, you should measure the screw-to-barrel clearance every month; if it exceeds 2% of the screw diameter, replacement is necessary to maintain floating quality.

Q: Why is my floating feed suddenly sinking?
A: This is the #1 symptom of screw wear. As the screw flights wear down, material "leaks" backward over the flights instead of being pushed forward. This loss of pressure prevents the pellets from expanding, making them too dense to float.

Q: Can I resurface or weld worn extruder screws?
A: It is not recommended for twin-screw systems. Welding can warp the shaft and destroy the precise intermeshing tolerances. It is much more cost-effective to replace modular screw segments.

Q: Does adding steam conditioning extend screw life?
A: Yes. Steam softens the raw materials and provides "thermal lubrication." Properly conditioned material (85°C+) is much less abrasive than cold, dry powder, potentially extending screw life by 30%.

Q: How do I clean a blocked die plate without damaging it?
A: Never use a hardened steel drill bit. Use a copper or brass pin or an ultrasonic cleaner. Scratches inside the die holes from steel tools will cause future blockages and irregular pellet surfaces.