Dosing Accuracy Drifting? It's Not about the Motor, These Three Parts Are Wearing Out Over Time

The accuracy of a screw doser directly determines whether your formula is on point. After about a year of running, operators often notice that the actual output no longer matches the set value, set for 50 kg, but only 48 kg comes out. You check the variable frequency drive and the motor—both are fine. At this point, you need to pull the screw out and see exactly where the material is slipping through.

The first place to check is the outer edge of the screw flight

There's an extremely small clearance between the flight edge and the barrel wallabout 0.1 to 0.3 mm when new. As material moves through the screw, it continuously wears down the flight edges and the clearance gradually increases. Once the clearance exceeds the particle size of the material, some material will just tumble around in the screw channel instead of being pushed forward, and the actual feed rate naturally drops. Use a caliper to measure the outer diameter of the flight and compare it with the factory specs. You'll see exactly how much wear has occurred.

The second place to check is the inner wall of the barrel

The barrel wall also gets thinner over time, the inner diameter increasesand so does the annular gap between the barrel and the screw. Barrel wear is often even worse than flight wear, because the material continuously rubs against the barrel wall throughout the entire conveying process. Use an inside micrometer to measure the barrel's inner diameter and confirm whether it's still within the allowable tolerance.

The third place to check is the bearings and shaft seal

Worn bearings cause radial runout in the main shaft, making the screw run off-center inside the barrel. The clearance is larger on one side and smaller on the other. On the tight side, you might get metal-to-metal contact; on the loose side, material flows back in large amounts. A worn shaft seal allows material to leak out along the shaft, which is both wasteful and messy. Listen for any unusual rubbing noises or increased vibration during operation. This is the most straightforward way to tell if the bearings are worn.

All three of these wear points are gradual. Regularly measure and record the dataand schedule maintenance or replacement before accuracy drops too far out of spec. It's far less hassle than waiting until your product assays come back out of tolerance and then trying to track down the problem.