Torsional vibrator for testing plastics materials

Claim 1

A torsional vibrator for testing a test piece of plastics material, comprising a first loading clamp for retention of one end of the plastics test piece, a disc type flywheel having a central axis of vibration, a second loading clamp rigidly connected to said disc type flywheel for gripping the other end of the plastics test piece, a temperature box for enclosing the plastics test piece, the plastics test piece, said disc type flywheel and said second loading clamp comprising a torsion pendulum, a device for exciting torsional vibrations of said torsion pendulum, said device including at least one periodically excited fixed solenoid and at least one armature fixed to said disc type flywheel in front of and spaced from the solenoid, and means for measuring the duration of the vibration or frequency of the torsion pendulum vibrations, said means including a fixed luminescent diode, a first aperture formed in said disc type flywheel at the rim thereof, a fixed second aperture and a fixed photo-electric device, the illumination area of the luminescent diode and the lightsensitive area of the photo-electric device at least corresponding to the opening of the first aperture, and said photo-electric device positioned on the opposite side of said disc type flywheel from said luminescent diode to be half illuminated by the luminescent diode through the first and second apertures when the disc type flywheel is in its rest position.