■ Load capacity calculation
◇ Cylidrncal bushes, flange bushes
P= F / d×L (N/mm²)
F=Load (N)
d=Shaft (mm²)
L=Bearing Length (mm²)
◇ Thrust washer
P= 4F / π(D2-d2) (N/mm²)
F=Load (N)
D=Washer OD(mm²)
d=Washer ID(mm²)
As the factor of clearance, bushes chamfer, oil groove ect, The actually load ( Pact) is higher than theory of calculation(Pmean).

■ Maximum surface static load
The actual dynamic load is usually less than the maximum surface static load recommended in the data sheet. Due to the clearance exists between the shaft and bearings, the actual working surface area are not the same as the projected area of the bearing, The working area is depended on the clearance between the shaft and the bearing. The value in the datasheet is valid when the shalt is less than 0.01m/s. The value could also be applicable for a short run (shorter than 3 minutes) condition.

■ The load, temperature and speed
The load capacity will be decreased along with the temperature increase. Load capacity may sharply decrease when the operating temperature is higher than the recommended maximum temperature (Graph 7). The load capacity will be decreased along with the speed increase. Speed increase will result into a temperature increase that decreases the load capacity.

There is a limited temperature range that EP Series bearings could be used. The lowest temperature is the one the material will become brittle under that value (Graph 10) and the highest temperature is the one the bearing material wear resistance feature will start to change (Graph 9). If the bearings are used under the conditions of alternatively changing high and low temperature, the bearing feature will be considerably affected and thus shorten the bearing service life.

PV is the product of the specific bearing load P and the sliding speed V. It is a very important design data for the bearing application. The PV value is inverse proportional to the bearing sevice life ( Graph 12).So it is recommended to consider a lower design PV value during the bearing the bearing selection.

Commonly the bearings are not continuously running during most of the applications. The short time operation period (less than 10 minutes) does not allow the bearing reach the highest limited operation temperature so that the limited PV value will increase because during the stop period, the heat generated by the friction will be reduced. Graph 13 shows the intermittent operation correction factor y1 for different stop and operate period.

Although EP bearings are normally designed for the dry operation, it has good the general lubricant such as oil or grease. The initial oil or grease lubricating will improve the starting performance of the bearings and therefore achieves a shorter run-in time. At the same time, the using of lubricants considerably improves the loading capability of the bearings because the lubricants will reduce the temperature increasing during the operation so that the loading capability of the bearings is improved. Graph 14 shows the PV correction factor y2 for different lubricants are used.

As the bearings wear resistance affected by many factors, it is difficult to accurately describe bearing wear and life span. Through numerous experiments we can conclude that the main factors affect the anti-wear property are the load, moving method, speed, roughness of mating surfaces, ambient temperature and dust and type of the outside lubricating medium, etc. When the load, speed and temperature increase, the wear resistance of bearings gradually reduced; when there is outside lubrication medium, the wear resistance could be doubled; SAVI recommend the roughness of axis to be Ra0.2 - Ra0.8. If the shaft is too rough or too smooth, it might increase the wear. Although there is no special restriction on the using of shaft material for the EP series bearings, SAVI recommend the use of hard chrome plated shaft material. The recommended shaft hardness is over HRC35 in order to avoid the initial wear off on the shaft.

Bearings used for outdoor equipments are constantly exposed to different critical environment. Anti-UV property is one of the most important indexes of a variety of bearing materials to resist UV-ray damage. EP Series plastic bearing UV-resistance reference (Graph 16).

EP series plastic bearings are usually used under the conditions where chemical media exist. Therefore the chemical resistance feature is very important for such a critical application. The existing chemical media may cause deep changes to the performance of the bearing material depending on the different conditions such as the chemical kinds, temperature, and the contacting period to the bearing materials as well as the load and operation speed. Sometimes chemical medium act as an effective lubricant and thus will extend the service life of bearings. Resistant to virtually all chemical media (Graph 16).

■ Housing: The bearing housing and the fitting tools must be kept clean during the assembling. A chamfer of 250 0n the housing should be ensured for an easy assembling. A stepped press pin is recommended to be used for the assembling. The inner diameter of the EP series product is measured after the bushing is fitted into the H7 housing.

Graph 17: Assembly example

■ Shaft: There is no critical requirement for the shaft material but chrome plated shaft is recommended for better operation. Rounded chamfer is required on the shaft for easy assembling. SAVI recommend the shaft roughness to be in the range of Ra0.2-0.8. Please refer to Graph 15 for the relation between the surface roughness and bearing friction coefficient(Graph :1 9).
EP series products are designed according to IS0 3547 Standard(Graph 18). Although the EP bearings are designed for self-lubricating purpose, but the initial lubricating helps the assembling and the future operation of the bearings.

Graph 19: Friction coefficient & surface roughness

■ Adhesive agent: EP series plastic bearing assembly generally needn't use glue, in case the glue is necessary, please consider the used glue can also work properly at the required temperature. Relative testing is recommended in this case.