Home Vinyl Asylum

Welcome Licorice Pizza (LP) lovers! Setup guides and Vinyl FAQ.

Re: 24 hour rule

This has been discussed many times and I've yet to hear any compelling evidence, let alone see the alleged 1970's photographs from an audio publication that supposedly spawned the 24 hour rule. Consider the following:

A. The generally accepted theory is that the vinyl softens and distorts at the contact point of the stylus, then cools so quickly that replaying the same groove over and over will never result in any appreciable length of that groove actually being in a semi-solid state. If that's true, then why does the record have to cool for 24 HOURS after playing it once?

B. The Vicat Softening Point of PVC is about 185 F. That is the point where the vinyl turns semi-solid.

Vicat Softening Point, definition from Wikipedia....

Vicat Softening Point is determination of the softening point for materials such as polyethylene, which have no definite melting point. It is taken as the temperature at which the specimen is penetrated to a depth of 1 mm by a flat-ended needle with a 1 sq. mm circular or square cross-section, under a 1000-gm load. Also known as Vicat Hardness.

Note the test conditions....a 1mm flat ended needle under a 1000 gram load! By the way, I have worked in the plastics industry for 35 years. I have witnessed Vicat and many other ASTM tests done on Thermoplastics.

Do you really think that the miniscule tracking force of a stylus tracking a groove can generate enough heat energy via friction to soften the vinyl?

C. Consider also the time factor involved. At the outer groove, the record is traveling at about 21 linear inches per second (at 33.3 rpm) in relation to the stylus. This rate gradually diminishes to about 7 linear inches per second at the inner groove. Even using the slower figure of 7 inches per second at the inner groove, the actual contact time for the stylus at any given point in the groove is absolutely momentary, about .004, or four thousandths of second to travel 1/32 of an inch. If my math is correct, is this enough time to friction heat the vinyl to 185 F? Even if it isn’t, you get the point. The answer is NO.

D. All thermoplastics have a certain amount of "memory." If you heat it and then apply a force to distort it, the plastic will tend to "draw back" towards its original shape if the distorting force is removed prior to cooling. However, it will NEVER, I repeat NEVER return to the exact shape it was prior to heating and distorting. If the theory behind the 24 hour rule were true, you would irreparably damage a record a little bit every time you played it. This damage would be accumulative and permanent.

If you want to try and prove this wrong, put one of your records in the direct sunlight for a couple of hours on a 90 degree day, balanced on top of a coffee mug. Then bring it inside, lay it on a flat surface and see if it returns to its original state after it cools. Let me know it works out.

Until I see scientific evidence to the contrary.....The 24 hour rule is utter bullshit.





This post is made possible by the generous support of people like you and our sponsors:
  Amplified Parts  


Follow Ups Full Thread
Follow Ups


You can not post to an archived thread.