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Servo-Electric Unscrewing Devices

Precision-Controlled Demolding of Threads

Servo-electric unscrewing units developed by Servomold and sold by its sister company i-mold support precision-controlled, gentle demolding of threads in injection molded parts. Krallmann, a German toolmaker, has integrated five such systems into a mold which Festo Polymer uses to produce the complex housing for the DB Mini pneumatic maintenance unit for its parent company, Festo.

Five female threads and multiple undercuts make demolding of the housing for a pneumatic maintenance device (top) a challenge. Servo-electric unscrewing units (bottom) provided an elegant solution for this task  (© Servomold)

Hendrik Sanio, project manager at Krallmann, cites the reasons why servo-electric unscrewing devices were given preference over their hydraulical counterparts: "The respective unscrewing torques can be individually monitored and controlled, and the threads can be demolded at the optimum speed in each case. The servo-electric unit requires less mounting space and yields shorter cycle times than a hydraulic solution. In addition, there is no risk of contamination by leaking oil."

Festo Polymer produces the cube-shaped housing with an edge length of some 40 mm from a high-strength, high-modulus glass-fiber-reinforced polyamide (PA66-GF50). Its five female threads have diameters of 1/8 ", 1/4 " and 36 mm and are between 12 and 22 mm long. In line with the positions of these threads, four of the associated unscrewing spindles are arranged at 90° angles to each other, in parallel with the parting surface, on the ejector side of the single-cavity mold. A fifth spindle moves parallel with the ejector set in the central machine axis.

Servomold selected and dimensioned the five unscrewing units to match the torques which were found to range from 6 to 33 Nm. They are controlled by a mobile SRS-8.6 rack-type controller which is capable of handling up to six servo motors. This adapts the individual speeds so that all five liquid-cooled threaded cores reach their respective limit positions simultaneously when they are screwed in. The SRS also monitors the torque of each servo unit and emits corresponding signals when preset threshold values are reached.

The servo motors are equipped with resolver-type encoders whose zero positions are individually referenced on the clamped, preheated mold in each case. The mold is thus protected from possible damage during closing, because in everyday operation the control unit of the molding machine will issue start clearance only when the SRS reports that these reference points have been reached.

Company profile

Festo Polymer GmbH

Hasseler Straße 60
DE 66386 Sankt Ingbert
Tel.: 06894 591-0

i-mold GmbH & Co. KG

Gewerbepark Gräsig 72
DE 64711 Erbach

Krallmann Holding u. Verwaltungs GmbH

Siemensstr. 24
DE 32120 Hiddenhausen
Tel.: 05223 989-0
Fax: 05223 989200

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