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Must pay attention to the basic item in storage of the grease

14th December 2013 Bearing Technology 0 Comments

When the grease rubs against others to lubricate in the bearing on the part, it is the solid friction that substituted with its internal friction between the friction surfaces of parts. So, the degree of viscosity of the grease has very great influence in using the mechanical power consumption of the grease. If the grease used is relatively large in viscosity, obviously there will be more friction losses.

The degree of viscosity of grease, with cutting the properties of changing rapidly, make it have special adaptability while using on the machinery that the speed often change. When the speed is high, require the degree of viscosity of lubricant to be low, the structural damage of grease is aggravated at this moment, the fiber orients, it happens that the degree of viscosity becomes low. The degree of viscosity of grease, with cutting the change of the speed basically accord with the mechanical rotational speed to change the requirements for degree of viscosity of lubricant.

Cutting the speed with grease degree of viscosity and start of the friction part that is being lubricated when being very small are having very great relations. Because grease cut degree of viscosity loud hour such as speed, at this moment if the degree of viscosity of the grease passes the conference and increases starting resistance. Especially increase in the degree of viscosity of the lower grease of low temperature, will make low-temperature start influenced even more, even cause the difficulty. In fact when machinery is started, it is much greater to overcome the grease and cut the force ratio that the resistance to flow of hour of the speed is being required overcome the strength with required breakdown point. For example, some lithium lipoprotein is not greater than 686 in 40 ℃ shear stress limit. 5Pa7gf/ cm2 ,And it is in 2 at the same temperature. The resistance to flow is 2452Pa 25gf/cm2 5s-1 hour ,Therefore, the low degree of viscosity when cuts the speed at the low temperature of grease is of great impact to the low-temperature starting performance of the grease. The grease that used to the low temperature or wide temperature range needs to stipulate its low-temperature degree of viscosity.

First, maintainability of temperature and oil film of backfalling

The grease is covered on the metal surface, hinder external air and aqueous vapor and metallic value from connecting and keeping in touch, therefore has protected the metal surface. If the cover makes the grease not adhere to the metal surface and backfall again for the change of the ambient temperature, then the grease is equal to not playing a role in protecting. Backfall temperature represent grease to vertical the intersection of metal surface and adherent highest temperature extreme. The landing temperature of the grease is decided by drop point, surface ability, looks state and degree of viscosity – temperature coefficient of the grease, and the coating thickness on the metal surface.

The surface of the ordinary soft steel keeps in touch with water, air at the room temperature, will get rusty in 10min soon. Spreading and protecting can delay the time to get rusty with the grease. The thicker the oil film is, seeing through the more slowly of oxygen and aqueous vapor. The greater the density of the oil film is, the lower breathability is. At a stationary temperature, determine the weight of even oil film on every unit area, named the oil film maintainability. Sector standard SH/ T0334- 92 lubricates leaf fat membrane maintainability mensuration.

Second, antirusting

Because its good adherence of grease, can keep the sufficient adipose membrane on the metal surface, isolate the aqueous vapor, air, acid and corrode the metal surface with the corrosivity gas or liquid through the adipose membrane, therefore the grease can make the metal surface not corroded more than the lubricating oil. However, the grease has breathability in the formative adipose membrane of metal surface. Generally speaking, the thicker the adipose membrane is, the more slowly air and agricultural air are crossed far. Similarly, the greater the density of the adipose membrane is, the lower breathability is.

Find the characteristic test method of antirusting of grease has the following aspects:

1. It is the grease shielding property mensuration that the trade marks difficult SH/ T0333- 92, suitable for determining the grease prevents the ability of the metal corrosion when the humidity increase.

2. National standard GB/ T2361- 92 antirust the intersection of oil and the intersection of damp heat test and the intersection of side and Shen, suitable for high-temperature high wet condition determine, antirust oil to metallic characteristic of antirusting.

3. National standard GB/ T5018- 85 is that the grease defend the cut-and-try method of the corrosivity, suitable for determining that coats with defending corrosion behavior of the toper roller bearing of the grease in moist condition. This method consulted ASTMD1742 it was made that ” the grease defends the test method of the corrosivity “.

Third, antisepticizing

Thickening agent and base oil of the grease are not corroded metallically. Make the grease produce the corrosive reason numerously, it is mainly caused by oxidizing and producing the acid material. Generally speaking, too much free organic acid, alkali will cause corrosion. Whether the corrosion test has corrosive action on metal to measure the grease. There are several kinds of methods to determine, experimental condition is different too, but at certain temperatures and test periods, observe allochromasis at the foil metal or produce speckle, come, judge the intersection of grease and caustic magnitude. The measuring method has trade border that allows SH/ T033l- 92 grease to corrode the cut-and-try method, SH/ T0080- 91 oil corrosivity cut-and-try method and GB/ T7326-87 grease steel sheet of antirusting corrode the cut-and-try method. Among them GB/ T7326- 87 employs the most extensively, is divided into two kinds A laws and B laws. The condition generally chosen is 100 ℃, 24h. Take out the sheet copper after the test finishes, after washing, first law is to test the sheet copper to compare with standard color disc of copper corrosion, confirm the corrosive rank. Second law is whether the sheet copper of the check test changes color. This method can only be suitable for determining the corrosivity to the sheet copper of lubricating grease. First law is to adopt ASTMD4048 ” grease steel sheet etched foil process ” equivalently, and second law is to adopt JISK2220- 1984.5.5 ” cut-and-try method of copper corrosion ” to make and purchase equivalently.

Fourth, water-resistance

The water-resistance of the grease can represent the hydroscopicity of the grease under the atmospheric damp condition. Require the grease not to have ability to absorb moisture in storing and using. After grease absorb water, will make it take pharmaceutical, dissolve and change the structure and reduce the drop point not to wither, cause corrosion. Thus reduce protective action. Some grease, such as some compound calcium base grease, harden because of moisture absorbed in the atmosphere, lose the lubricated ability of the grease progressively, influence in-service use.

A water-resistance that mainly depends on thickening agent of water resistant of the grease and emulsifying properties, the hydrocarbyl thickening agent such as the earth wax The water-resistance is good, difficult to absorb water, difficult to emulsify. The sodium soap adjusts and melts the water-resistance difference of pharmaceutical, easy to absorb water, will also be dissolved by water.

Sector standard SH/ T0109- 92 is that the water resistant of grease drench characteristic mensuration.

In addition, still use and lengthen the awl out going degree mensuration of the job in GB/ T269- 91. Add 10% water into working device, enter the change of the scale value after 100,000 times of work with the awl to weigh the water-resistance of the grease. U.S.A. has ASTMD4049 grease water resistant spraying mensuration, in order that while evaluating water spray lipoprotein kind, adhesive capacity to the metal surface of lubricating grease.

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