1 Introduction
Regardless of the quenching of the workpiece, the most basic requirement for the quenching oil is the stability of the quenching oil performance, especially the cooling performance of the quenching oil. Quenching oil is a multi-component polymer organic compound that is constantly changing, so on-site management of quenching oil is very important. There are many technical indicators for quenching oil, such as physical and chemical indicators, cooling performance indicators, antioxidant performance indicators, bright performance indicators, and saturated vapor pressure. In the field is mainly to control the cooling performance of quenching oil. According to the provisions of SH 0564 "Heat Treatment Oil": characteristic temperature, cooling time of 800-400 ° C and cooling time of 800-300 ° C. The first two are the high temperature zone cooling performance of the quenching oil, and the latter one is the low temperature zone cooling performance of the quenching oil. According to SH 0564 "Heat Treatment Oil", the cooling performance of quenching oil is specified in Table 1:
Item Characteristic temperature °C
Cooling time not less than 800-400 ° C, s, (80 ° C)
Cooling time not greater than 800-300 ° C, s, (80 ° C)
Not more than the characteristic temperature °C is not lower than 800-400 ° C cooling time, s, (120 ° C)
Not more than the characteristic temperature °C is not lower than 800-400 ° C cooling time, s, (160 ° C)
Ordinary quenching oil 520 5.0
Quick Quenching Oil 600 4.0
Speeding quenching oil 585 6.0
Fast Bright Quenching Oil 600 4.5
No. 1 vacuum quenching oil 600 5.5
2 vacuum quenching oil 585 7.5
No. 1 isothermal quenching oil 600 5.0
No. 2 isothermal quenching oil 600 5.0 600 6.0
Table 1 quenching oil cooling performance (SH 0564)
2 meaning of quenching oil technical indicators
The physical and chemical indicators of quenching oil, such as kinematic viscosity, open flash point, moisture, etc., can be tested by oil companies. China has adopted the internationally accepted 40 ° C or 100 ° C kinematic viscosity.
An important indicator of kinematic viscosity heat treatment oil, its change reflects the degree of aging of quenching oil. We use the viscosity ratio to indicate.
Viscosity ratio = viscosity of service oil / viscosity of new oil The ratio of the kinematic viscosity (40 ° C 100 ° C) of the service oil to the kinematic viscosity of the new oil is recommended to be no more than 1.3.
The kinematic viscosity of domestic quenching oil is 15-40 mm2 / s (40 ° C) for cold oil and 15-50 mm 2 / s (100 ° C) for hot oil.
Flash point of the opening: The temperature at which the oil is heated under standard conditions, the mixture of vapor and air of the oil and the open flame, which begins to flash and immediately extinguish, is called the flash point. The quenching oil uses an open flash point, and the closed flash point is generally 10-40 ° C lower than the open flash point. Flash point is a safe indicator of heat treated oil. Since the quenching oil is directly in contact with the red hot workpiece and is in contact with the air (non-protective atmosphere quenching), the maximum use temperature of the heat treatment oil in China should be at least 80 ° C lower than the flash point of the opening, so as to ensure the safe operation of the quenching process.
The water content of the base oil of the moisture heat treatment oil is very low in the refining process, only a few to several tens of ppm (parts per million). The water in the heat treatment oil may come from many aspects such as air, mixing during oil preparation, water leakage from the cooler, and the like. The moisture of the quenching oil required for the brightness should be controlled to be absent. In general, the moisture of other quenching oils should not be greater than the trace (0.03%).
Carbon residue: The oil is heated under conditions that do not pass into the air, causing it to evaporate, decompose and coke. After the burned gas is discharged, the remaining residue of the charred carbon residue is expressed by mass percentage. The main substances that form carbon residue are asphaltenes, colloids, polycyclic aromatic hydrocarbons and unstable compounds in oil. When there are many sulfur, oxygen and nitrogen compounds, the residual carbon is high. Therefore, the size of the residual carbon of the oil can indicate the depth of refining of the oil, and the degree of coking and coking under thermal oxidation conditions. In general, the more additives are added to the heat-treated oil, the more residual carbon it has. The residual carbon of the quenching oil is generally controlled at 0.1-0.7%.
Thermal oxidation stability: At present, China adopts the petrochemical industry standard SH/T0219 "heat treatment oil thermal oxidation stability determination method". The main point of the method is: in a 300 ml oil sample, a copper wire and a wire are used as a catalyst, and 10 l/h of dry air is introduced into the sample, and after continuous oxidation at 165 ° C for 24 hours, the following definition is obtained. Viscosity ratio and residual carbon increase.
Viscosity ratio = viscosity after oxidation / viscosity before oxidation Increase in residual carbon = residual carbon after oxidation / residual carbon before oxidation Generally, the viscosity ratio of the heat-treated oil and the added value of residual carbon are controlled to 1.5 or less at the time of shipment.
Cooling performance At present, China has two test standards, SH/T0220 and JB/T7951 (the standard is equivalent to ISO 9950). Most of the test quenching oils use SH/T0220, and most of the water-based quenching media are tested with ISO 9950. Test quenching oil with ISO 9950, it seems a bit slow: test water-based quenching medium with SH / T0220, it seems a bit too sensitive. Cooling performance index of quenching oil using SH/T0220 The cooling mechanism of quenching oil is divided into three cooling stages, which are:
The first stage is the vapor film stage, which is the film boiling stage. A vapor film is formed around the workpiece, and cooling at this stage is slow because heat transfer is performed by the vapor film by radiation and conduction. The stability and durability of this uniform film depends on the base oil of the quenching oil, the additives, the temperature of the quenching oil and the degree of agitation.
The second stage is the nuclear boiling phase. The stable film eventually ruptures, and the quenching oil comes into contact with the hot metal, causing nuclear boiling and high heat removal efficiency. At this stage, heat is removed as latent heat of steam. At this stage, the cooling effect is best, and the maximum cooling rate and the maximum cooling rate are at this stage. The intersection of the first phase and the second phase is called the characteristic temperature. The time to reach the characteristic temperature is called the characteristic temperature second, which is referred to as the special temperature second. The high viscosity base oil has a high characteristic temperature, and the low viscosity base oil has a low characteristic temperature. The effect of the refrigerant in the high temperature zone is mainly to increase the characteristic temperature and move the cooling curve to the upper left, which not only greatly improves the cooling capacity of the high temperature zone, but also increases the cooling capacity of the low temperature zone accordingly. The indicators for assessing the cooling capacity of the high temperature zone are mainly the characteristic temperature and the cooling time of 800-400 °C. The higher the characteristic temperature, the shorter the cooling time, the better the cooling capacity in the high temperature zone. According to SH 0564, the average cooling rate of 800-400 ° C, ordinary quenching oil should be greater than 80 ° C / s, fast quenching oil should be greater than 100 ° C / s. , ultra-speed quenching oil, the average cooling rate of 800-300 ° C should be greater than 84 ° C / s.
The third stage is the convection stage, ie the no-boiling stage. The slowest phase of cooling, which is related to heat transfer and convective heat transfer in the liquid. At this stage, the viscosity of the quenching oil is important. The low-temperature zone of the high-viscosity base oil has poor cooling ability, and the low-temperature zone of the low-viscosity base oil has good cooling ability. The indicator for assessing the cooling capacity of the low temperature zone is mainly the cooling time of the characteristic temperature of 800-300 °C. The higher the characteristic temperature, the shorter the cooling time of 800-300 ° C, the better the comprehensive cooling capacity of the low temperature zone. Of course, the main reason is the length of the cooling time. The main function of the cryogen in the low temperature zone is to shorten the cooling time of 800-300 ° C. Generally, the quenching oil enters the convection phase from 350 ° C. That is to say, the cooling after 300 ° C is very slow, it is oil quenching. advantage.
3 quenching oil service life
The service life of quenching oil can be defined as the longest time to meet the quenching requirements of the workpiece during quenching. Oils without additives, for example, 32 mechanical oils, 15 mechanical oils, have a longer life than quenching oils to which additives are added. The more functional quenching oil, for example, the fast bright quenching oil, the isothermal grading quenching oil, relatively speaking, the life is shorter. In the actual operation of the heat treatment workshop, there is a very difficult problem: the standard for replacing the quenching oil. We present a set of data in Table 2 as a reference.
Item viscosity than opening flash point Moisture Brightness Characteristic temperature 800-400°C 800-300°C
The replacement index value reaches 1.3, lower than the standard 20 °C, greater than 0.5%, lower than the standard level 1, lower than the standard, 20 °C, greater than the standard, 0.3 seconds, and more than the standard 0.5 second. One of the above items should be considered, and the cooling performance and Brightness properties can be adjusted with additives.
4 Summary Above we have some basic knowledge about heat treatment oil, hoping to help the use and management of heat treatment oil.