| 摘要 |
A flexible piston rod for an injection device, which piston has the form of a helical spring made up from a number of narrowly adjacent turns of windings. These turns provide an external thread, which thread fits into the internal thread of a nut element. When the nut element is rotated the piston rod is advanced forward, which movement is used to displace a piston inside a cartridge containing a fluid to be expelled. In order to prevent the piston rod from rotating when the nut element is rotated, the helical spring making up the piston rod is provided with a longitudinal spine, which is located at a peripheral area of the helical spring. The spine can either be a mechanical removal of a part of the out-turned area of each winding, or it can be a reduction or removal of an initial tension in a longitudinal area of the helical spring.
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