Does vinyl melt under stylus pressure?
G.Alexandrovich in Glen Ballou’s "Handbook for sound engineers": "It has been experimentally shown that with such high pressures and forces of friction between stylus and the vinyl, that the outer skin layer of the record material melts as the tip slides over the plastic and then refreezes almost as fast as it melted. It has been suggested that since the melting temperature of vinyl is about 480 °F (248 °C) that the same temperature exists in the contact area.”
US patent 5,389,281 to LAST: “The friction between stylus and the record may heat the vinyl locally to temperatures near the melting point.”
Van den Hul apparently measured tip temperatures to be 160 °C.
ld does presented calculations factoring in tracking force, coefficient of friction, coefficient of thermal conduction of vinyl, 100nm vinyl groove skin depth, specific gravity of vinyl, specific heat of vinyl, resulting in a temperature increase of 10 K.http://www.vinylengine.com/phpBB2/viewt ... c7f6550859
I had a look in the technical literature and didn’t find any evidence that confirms the melting of vinyl under stylus pressure nor did find any evidence that disproves it. I found the following papers that are of interest for this particular question:
Archard, “The temperature of rubbing surfaces”, Wear, vol. 2 (1958/59), p.438
Barlow, “A thermal size effect in friction tests”, Wear, vol. 11 (1968 ), p.229
Barlow, “Some observations on the frictional properties of vinyl”, Wear, vol. 20 (1972), p.151
Archard, “The temperature of rubbing bodies: part 2, the distribution of temperatures”, Wear, vol 128 (1988 ), p.1
Barlow, “The indentation and scratch hardness of plastics”, Transactions of the ASME/J. of engineering materials and technology 1973, paper 73-Mat-L
Hunt, “On stylus wear and surface noise in phonograph playback systems”, JAES 1955, p.2
Max, “Record stylus pressure”, JAES 1955, p.66
Barlow, “Limiting factors in gramophone reproduction”, JAES 1957, p.109
Barlow, “The limiting tracking weight of gramophone pickups for negligible groove damage”, JAES 1958, p.216
Flom et al., “The deformation of plastics with hard, spherical indentors”, JAES 1959, p.122
Walton, “Stylus mass and reproduction distortion”, JAES 1963, p.104
Bastiaans, “ Factors affecting the stylus/groove relationship in phonograph playback systems”, JAES 1967, p.389
White, “An experimental study of groove deformation in phonograph record”, JAES 1970, p.497
Barlow et al., “Groove deformation and distortion in records”, JAES 1978, p.498
Walton, “Gramophone record deformation””, Wireless World, July 1961, p.353
Walton, “Versatile stereophonic pickup”, Wireless World, August 1961, p.407
Walton, “Stylus mass and distortion”, Wireless World, April 1963, p.171
Barlow, “Groove deformation in gramophone records”, Wireless World, April 1964, p.160
Kerstens, “Mechanical phenomena in gramophone pick-ups at high audio frequencies”, Philips Technical Review, 1956/57, p.89
Jaeger, “Moving sources of heat and temperature at sliding contacts“, J. Proc: Royal Society of New South Wales, vol. 56 (1942), no. 3, p.203
Barlow (1968) measured temperatures on lead-antimony (hardness similar to that of vinyl) with iron and constantan indentors. He concludes that temperature rise in gramophone records is very small (Barlow 1972).
According to Archard (1958) one has to distinguish between slow and fast moving heat source, and in either case between elastic and plastic deformation, so temperature calculation apparently is not as straightforward as one might think.
Speed criterion: Whether the source is considered as slow or fast moving depends on dimensionless parameter L= Vaρc/2K (Jaeger 1942)
V= groove speed
a = radius of contact surface
ρ = density
c = specific heat
K = thermal conductivity
Fast : L>5
For each case the temperature is calculated by a different equation.
The area of the contact surface depends on whether groove deformation is elastic or plastic. According to Barlow (1964) commercial pickups of the time work well into the fully plastic range. Vinyl material used for records shows work-softening behaviour under static load (White 1970, Barlow 1972, Barlow 1973). Sliding indentation tests show fully elastic behaviour at sufficiently low loads (Barlow 1973, 1978). Tests performed in unmodulated grooves at tracking forces ranging from 4.6 mg to 4.6 g showed that even for small VTF where the groove was expected to behave elastically the measured stiffness did not match the stiffness elasticity theory predicts (White 1970). White: “it is probably justified to conclude that groove deformation is incorrectly described by classical elasticity theory even at the lowest tracking forces for which no data were taken.”
According to Bastiaans (1967) the penetration into the convex groove wall is deeper than into the concave wall.
Is it possible that work-softening/plastic deformation (for which there is evidence, e.g. in Walton 1961, Walton 1963 ) has been (mis-) interpreted as melting?
In any case, the conclusion seems to be that what actually happens depends on stylus load, stylus size, effective stylus mass. The available evidence also clearly confirms the principle benefits of low effective stylus mass and low stylus load.
These days I’m crunching numbers only when absolutely necessary for my work (on average about once in 10 years), so if any of the expert crunchers around here wants to give it a go, drop me a PM and I send copies of the papers.