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Screw Testing?

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Topic: Screw Testing?

rarmada
Member

Posts: 1
From:
Registered: Jul 2004

posted July 01, 2004 02:11 PM

How can I meassure or test my injection molding machine´s screws?

How can I know when is time to change my screws?

Thanks
Axel

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Tom C
Moderator

Posts: 345
From:Brodheadsville, PA USA
Registered: Jun 2001

posted July 03, 2004 05:33 PM

Screw flight to barrel clearance is the most important criteria for determining if the screw and/or barrel is worn out. Low output and surging are indicators, but can be sourced by other problems.

Check the screw outer diameter and the barrel inner diameters. The tools for this are avaiable from the sponsor of this web site;
www.feedscrews.com

Initally (as new) the clearance on one side of the screw is typically 0.001 x diamter. Mid life is typically when the clearance reaches 0.002 x diameter, and worn out is over 0.004 x diameter.

Also check the screw for cracked and missing flights. Screw roots can also wear badly.

A good factor to monitor in injection molding for screw/barrel wear is screw recovery time. It will increase as the screw wears.

Tom Cunninham
Extrusion Technical Services.

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