The good news is that these oils have a crazy high viscosity index, a result of the synthetic formula and additive package required for effective low temperature operation.Īrctic oils can have VI’s in the range of 150-200, and because VI is measured from 40-100° C, it is a good indicator of how the oil will perform when summer finally arrives. Unfortunately, “arctic” oils are not cheap, and no fleet manager wants to change the oil in their machines every spring because they’re running watery oil inappropriate for the summer. If even a quality 22 weight hydraulic oil can barely pour at -27° C, these arctic oils will still exit an upside down beaker at -60° C or colder! These oils often have the words “arctic” or “blue” in their names, but they’re always synthetic oils formulated to flow at extremely low temperatures. However, you can imagine this oil will be pretty thick and difficult to push at -20° C if at seven degrees colder, it’s barely able to be called a fluid.įor machines to be happy in conditions similar to the winter of 2013-2014, a different kind of oil should be used. A premium 22 cSt oil with a respectable VI of 100 might have a pour point of -27° C. With hydraulic oil, a viscosity index of 100 is considered excellent (although automotive engine oil VI numbers can approach 200).Ī caveat about viscosity index and cold temperatures-often, the oil chemistry specific to the creation of high viscosity index doesn’t always translate into a lower pour point, which is really what we’re concerned with in cold temperatures. The higher the viscosity index, the higher the resistance to change in viscosity. It is often measured by comparing the change in viscosity between 40° C and 100° C. Viscosity Index is a dimensionless number to describe an oil’s resistance to a change in viscosity when subjected to a change in temperature. So what will the viscosity of a 22 weight oil be at minus twenty? Well, it depends…. This fluid could be appropriate in most mobile applications, but we should first consider a 22 centistoke oil is rated so at 40° C, not -20° F. Half of the consideration is with rated viscosity, such as “22 weight” oil, which is considered to be a low viscosity fluid by most. The solution to cold weather viscosity problems is to choose appropriate hydraulic fluid. I sometimes see cold hydraulic systems with cylinders that retract slower than they extend because of the extra pressure drop created by flow intensification of cold oil. The thicker the oil, the harder it is to pump, and if plumbing distance is long with marginal diameter, a lot of energy can be lost to pumping, leaving little left over to perform work. Hydraulic fluid is highly susceptible to viscosity changes based on temperature, especially if the machine has been sitting idle in the cold. Regardless, even if the seals can hold up from November to March, they won’t make it any easier to pump that ketchup. Luckily, seal manufacturers make solutions for arctic conditions, such as low-temp Nitrile or Viton. Some concern in frigid temperature operation is with seal material, and whether the seal material can avoid becoming brittle. However, the concern is when these metal parts either rub against other metal parts, or the metal parts are attempting to push a fluid as thick as ketchup. Luckily most hydraulic parts are made from iron or steel, which tend to not care about ambient temperature. Thermal Conductivity (cal/cm.As one of the longest, coldest winters on record comes to an end (or doesn’t come to an end, in this case), I consider how all the hydraulic machines must have fared throughout the brutal outdoor conditions we’ve experienced in the past four months. Polydimethylsiloxanes, trimethylsiloxy-terminated: Properties Product code Refractive index, surface tension, density, and viscosity-temperature coefficients are strikingly flat. Fluids with viscosities ≥ 50 cSt have negligible vapor pressure.Īt viscosities > 1,000 cSt (correlating to molecular weights > 30,000), polymer chain entanglement occurs which results in leveling of physical property change vs. The fluids are thermally stable indefinitely at 150 ☌ in air. An important consequence of the low intermolecular forces in polysiloxanes is the highest permeability coefficients of any polymer for oxygen and nitrogen. This causes polymers to spread over their own adsorbed films. The liquid surface tension of polydimethylsiloxane is lower than the critical surface tension of wetting (24 dynes/cm). This results in one of the lowest glass transition temperatures of any polymer. Polydimethylsiloxane has virtually no energy barrier for rotation. Conventional silicone fluids are composed of polymer chains with unique flexibility. They are commercially produced in viscosities ranging from 0.65 to 20,000,000 cSt. Conventional fluids are the well-known general purpose silicones described in chemical notation as polydimethylsiloxanes.
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