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Lifespan of a Screw and Barrel

It is quite challenging to predict how long a screw or barrel will last. Every barrel and screw is different because of the numerous factors that affect productivity. Excessive wear is the main factor in premature degradation, and wear issues lead to a reduction in production yield.

Wear starts as soon as the screw starts rotating inside the barrel. The barrel surface, the screw flights, or both may experience wear. The faster wear happens and the original clearances get smaller, the tougher the material being processed is, whether it’s an abrasive filler in the polymer being processed or “tramp” metal particles that shouldn’t be in the melt stream. Melting efficiency will decline as the clearances rise. Many operators typically modify screw speed, barrel temperature, backpressure, or any combination of those modifications to make up for declining melting efficiency at the initial settings.

Wear can occur during the molding process in three different ways:

Abrasion – A result of the resin’s fillers or its composition
Corrosive – Resulting from resin additives
Adhesive – As a result of excessive friction between the barrel and screw

Although the screw is intended to rotate freely in the barrel bore, it is likely to make casual contact with the bore under normal circumstances. Adhesion occurs when the screw becomes too close to the bore. The contact between screw and barrel may increase for a number of reasons, including:

  • A bent screw or barrel
  • A bent screw drive
  • Worn bearings on the screw drive
  • Misalignment between the center of the barrel and the center of the screw driver coupler
  • An over-torqued screw that causes the screw to deflect during rotation

Other factors that may cause adhesive wear include:

  • Rotating the screw without resin
  • Leaving the hopper empty and the screw rotating for a long time
  • The plastic is overheated or cooled beyond its proper molding temperature due to malfunctioning heater bands, thermocouples, or temperature controllers
  • Use hopper magnets and material inspection devices to remove any foreign objects from resin.

Factors affecting the  Life Expectancy of a Screw and Barrel?

The lifespan is determined by the person who buys a fresh screw and barrel. If the unit is bought only primarily on pricing, it is likely that its lifespan will be significantly shortened if the components are not made of the right steel grade for its use. Or, the life duration may be shortened if the screw design is improper for the application or cycle run.

The person who installs the barrel and screw has some influence over life. When installing the components, care must be given to avoid chipping or scratching them, over tightening bolts, etc. Used components should be checked for straightness on a dimensional level before being combined with fresh components. Many attractive-looking screws that were once part of worn-out barrels are now bent. You should anticipate a reduced lifespan from your new component if a new or rebuilt component is utilized in conjunction with an older or more worn-out component (s).

There are a lot of personnel in many molding operations with the power to alter the molding cycle (time, temperature, pressures).

Maximum wear on a Barrel, Screw, and/or Check Valve

Simply measuring your barrel and screw will not provide an answer to this topic, as some materials are more effective than others when molding with damaged components. Your lost output yield must be measured. It’s time to calculate the lost money if you can’t schedule around wear and you’re losing production yield. It’s just basic math. In relation to the price of a new unit, how much money are you losing in lost production yields?

Your components should have a long and fruitful life if you schedule your molding machine correctly, buy high-quality parts that fit the specifications of your process, and adhere to the other rules.