Worn screw, still processing

When should a screw or barrel should be replaced?

Keeping a bad component in production flushes dollars down the drain with every part because of reduced recovery output and quality defects, but so does unnecessarily replacing a screw that’s only 50% worn.

Understand the causes, signs and factors of wear, and know what to look for and when your components have “gone bad.”



Wear: Cause and Effects

As screws and barrels begin to wear, material will start to get lost over the flight OD during recovery due to increasingly excessive clearance with the barrel. This clearance will initially reduce recovery output and increase shot recovery times. As this wear continues, the “lost” material will build up a heat history, which leads to burning and degradation, negatively impacting part quality.

As degradation continues, corrosive gases also cause screw deterioration, little-by-little, resulting in more opportunity for material hang-ups and even more burning. Screw to barrel clearance becomes more critical as you move from the feed port to the discharge end, meaning you can have a great deal more clearance in your feed section than you can in your metering zone before experiencing any issues.

What to Look For

A good guideline to use is 0.015” total clearance in the metering section, 0.025” in the transition section, and 0.035” in the feed section. Once the wear on your components reaches these clearances, it’s probably a good idea to begin monitoring your process output and predicting when components will eventually need replacement. Much like the car you drive, many miles can sometimes be driven when the low fuel light comes on. Unfortunately, sometimes you can run out of gas! MSI is here to help ensure you’re never stranded.

Is Replacement Needed?

Bottom line? Two crucial factors should determine whether a screw or barrel are in need of replacement: shot recovery time and part quality. Once cycle times impact costs or rejects increase due to unacceptable quality, it’s time to consider component replacement. In addition, tips can wear on both the check ring OD and the front seat, causing cushion control issues and the need for replacement. If you are not running your components until these issues begin to surface, you’re not getting your money’s worth! After all, screws can start looking really ugly long before output and quality issues surface.

Monitoring Components for Wear

So – do you have the personnel and time to inspect, measure, and monitor your process data to assure you’re getting the most from all your components? Most don’t and many more recognize that they don’t have to by relying on the professionals at Molders Services.

Consider the kind of precision information revealed in one of MSI’s inspection reports. For example, several sections display zone-by-zone wear on a screw and barrel, and on the check ring OD, as well as the total clearance between the screw and barrel. Extensive comments sections include expert observations and recommendations. Compare this information with your existing process data to determine which components are causing issues and whether they are significant enough warrant replacement.

Don’t leave productivity and performance to chance. Call us. That’s why we’re here for you.