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Screw joint analysis ensures correct fastening torque parameters

Almost everyone has used one – a lip balm stick that gives relief to cracked and dry lips. Twist the balm out of the practical rotating sleeve; apply balm onto the lips, done! What appears so easy can actually prove to be a brain-teaser for industrial production.
What happens if problems arise in the assembly of the lip balm’s plastic components? What if waste is produced time and again in the screw assembly of the lip balm casing? The error analysis on site may take weeks, or even months. This is when a detailed screw joint analysis from the screwdriving specialists pays off.
In his laboratory for screw joint analysis, application engineer Rudolf Schmidbauer is holding three plastic parts in his hands: the casing, the piston, and the spindle for the lip balm. During assembly, the piston is first inserted into the casing. It is actually the second step that leads to most problems. This is what the company DEPRAG SCHULZ GMBH & CO is now about to examine carefully by means of the screw joint analysis ordered by the client: the spindle is screwed into the preset threaded hole of the piston until the snap-on connection to the casing closes. At the same time, the piston is inserted into the deepest position in the casing. The next step in the factory would be the filling of the assembled plastic tube with the lip balm and - sealing the tube.
But the question which really matters for the DEPRAG screw joint analysis is: Which is the ideal torque for the screw assembly of the plastic spindle into the pistons? And which rotation speed should be applied? What type of screwdriving tool best fits the task? Rudolf Schmidbauer explains: “In order to find out the best way to screw together a component, I have got to destroy it. I have to consciously apply excessive torque until screws or components are overstressed. Only in so doing, is it possible to determine the overload torque.”

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