How to Measure Parallel Twin Screw Barrel Wear?

Why should I inspect my screw?

Every plastic processor should include routine inspection of plasticizing components in their maintenance program. Using worn components can cause many issues including decreased throughput, increased energy usage, and even equipment damage.

The best maintenance programs have regularly scheduled inspections where components are measured. Over time these measurements help to create a wear profile identifying the lifespan of a component.

Knowing the expected lifespan of a Parallel Twin Screw Barrel allows for planned replacement and repair.

Why do screws wear?

There are many causes of component wear. Wear is categorized into three broad categories: abrasive, adhesive and corrosive.

Adhesive- wear caused by metal to metal contact; this is caused by improper alignment or incompatible geometries.

Corrosive- wear due to chemicals reacting with metal surfaces; release of gasses from degraded resin. Examples include PVC and fluorocarbons.

Other factors that affect wear include:

screw, barrel, drive alignment
uniformity of heating
resin type
screw/barrel materials
excessive back pressure
high screw speeds

Inspecting Your Screw

Before inspecting, remove all excess resin and place the screw on a clean, flat work surface. Start by examining the general condition of the screw. Look for damage, pitting or cracks. If available, use a granite table to check the straightness of screw by rolling it and looking for bowing. If bent, feeler gauges can be used to measure.

Use a micrometer to measure the following values:

Shank diameter
Screw Outer Diameter
Root Diameter (feed, metering)
Channel Depth (feed, metering)
Shank length
Flight Length
Flight Width
*Tip: Use a parallel test bar spanning two flights to measure the outer diameter of the screw. Image title

Measuring Your Barrel

Compared with the screw a barrel is relatively easy to measure. Using a bore gauge measure as far down each end of the barrel as possible. Record measurements to compare to original/last values.

Interpreting Values

After recording measurements compare them to previous values to track a component's wear over time. Doing this at standard intervals allows you to create a wear profile and be better prepared for component repair/replacement.