The deterioration of mineral oils for quenching was studied under the same procedure as described in the 1st report (The Deterioration of Fatty Oils: Tetsu-to-Hagane No. 2, Feb. 1954 p. 103-111). The properties of mineral oils vary with the blowing with air as follows:
(1) The quenching ability of mineral oils increases at the beginning and then decreases slowly with the blowing time, and the time required to cool from 700° to 350°C is given approximately as a function of the blowing time by the following formula:
The changes of cooling ability with the blowing time abovementioned are attributed to the rise of the characteristic temperature in cooling process, at which vapour film breaks down, due to the formation of polar substances with the blowing time and the rise of the beginning temperature of the convection stage due to the increase of the amount of polymerized product. the τmin offers a criterion for the life of oil and the ρmax gives a degree of variation of cooling ability during the deterioration of oil.
(2) The viscosity increases with the blowing time:
The amount of sludge increases with the blowing time:
The specific gravity increases with the blowing time:
The flash point decreases with the blowing time:
The acid value increases with the blowing time:
The iodine value decreases and the saponification value increases with the blowing time.
(3) When oil is highly refined, the t0, the τmin and the αF are larger and the ρmax, αη, αS, αG and αA are smaller respectvely, that is, highly refined oil is more stable.
(4) Lighter oil is more stable than heavier oil, but this difference of stability becomes smaller according to better refining.
(5) Highly refined naphthenic oil is stable as paraffinic oil.
(6) Among a series of mineral oils produced from identical crude oil, the larger the iodine value and the more the residual carbon, the deterioration of oil is the more rapid.
(7) It is observed that the τmin becomes larger for higher temperature of oil in the measurement of cooling curves at various temperatures below 100°C with a same oil.
(8) The t0, the τmin and the αS of mineral oil are larger and the αη and αG are smaller than those of fatty oil. Then, the deterioration of mineral oil is much slower than that of fatty oil.
(9) The deterioration of mineral oil containing fatty oil is more rapid than that of straight mineral oil.
(10) Quenching oil must be evaluated synthetically with values of the t0, τmin, ρmax, αη, αS, etc. Note:
t: Time required to cool from 700° to 350°C for oil blown with air, sec.
t0: Time required to cool from 700°C to 350°C for fresh oil, sec.
tmin: Minimun value of t, sec.
ρmax: Curvature at the point of t=tmin on the curve.
η: Viscosity of oil blown with air, Redwood, sec.
η0: Viscosity of fresh oil.
S: Amount of sludge of oil blown with air, mg/10g.
S0: Amount of sludge of fresh oil.
G: Specific gravity of oil blown with air.
G0: Specific gravity of fresh oil.
F: Flash point of oil blown with air, °C.
F0: Flash point of fresh oil.
A: Acid value of oil blown with air.
A0: Acid value of fresh oil.
τ: Blowing time, hr.
τmin: Blowing time for the minimum value of t, hr.
c, b, αη, αS, αG, αF and αA: the constants.