This is a customizable spring. Not as durable as a steel one, but functional. You can use the customizer to change its dimensions, as well as elastic properties. Feel free to experiment. I opted for this pseudo washer design because I thought a spiral will be less sturdy and wanted a design without rotational tension, so that the spring doesn't have to support more than vertical forces. Parameter election is critical for each type of spring. You can lead to High elastic springs to sturdy low compression springs. Do your proof but remember these are plastic springs and its elastic, thermal, or hardness properties are very dependant of the material used to print them. In general this plastic springs will have a low compression ratio and poor shock resistance due to its plastic composition, but anyway you could make a proof with semiflex like materials, I didn't check out that yet, this will produce mild force springs but shock proof ones...
Also remember that low temperatures will increase a lot the fragility of the plastic.
At print time I recommend to print them horizontal with buildplate support only to alleviate bridge generation and ease of suport removal. Anyway printing it vertically if you can will make a better and more suitable structure for the spring.
Hint: Those unusable prints you may produce, you can give it to your mother as hair curlers, but warn her about not using a hair dryer with those... ;-)
(UPDATE 04-APR-2019) Removed customizer support. Too many public funny tests, hiding the original idea. Just use OpenSCAD from now.