Shaft diameter must correspond to h11 tolerance group conditions specified in ISO 286-2.
Tabloyu incelemek için sağa kaydırın.
|Shaft Nominal Diameter (mm)|
For general applications, shafts made of carbon steel (SAE-AISI 1035 or 1045) is convenient for applications. When cast iron and carbide coated shafts are preferred, it should be ensured that there are no deep pores on the surface. In water-containing or corrosive environments, generally the materials can be preferred such as brass or stainless steel etc.
In rotary shaft seals, primary sealing lip material (generally rubber) is considerably softer than shaft material (generally steel). However, relatively hard particulates (carbon, graphite, silica, etc.) in the lip material and the friction between the shaft and the seal lip, even if there is sufficient lubricant in the system, abrasion occurs on the shaft surface over time. Level of this abrasion depends essentially on the shaft speed, dirt in the oil, seal lip material and the structure of the shaft material. Surface hardness of metal shafts should be at least 45 HRC. In dusty and dirty environments and with rotating shafts faster than 4 m/s, the minimum hardness should be 55 HRC. For surface hardening, heat treatment depth should be applied at least 0,30 mm.
The surface roughness values of shafts are critical to the performance of the seals. If the surface roughness is too high, the seal lip will is abraded faster than expected and premature leakage occurs. If the roughness is too low, the abrasive band that is desired to be formed with first work on the lip cannot be formed or occurs late. Absence of the abrasive band delays the formation of the microscopic oil film, which is the main component of the sealing mechanism. During this period, premature leaks occur. The surface roughness of the rotating shafts according to the fluid pressure recommended for the following roughness values:
|p ≤ 1 bar (µm)||p > 1 bar (µm)|
|Rz||1,0 – 5,0||1,0 - 3,0|
|Ra||0,2 – 0,8||0,2 - 0,4|
In addition to these values, there should be no traces of spiral machining on the shaft surface. Best way to achieve this is to grind the shaft after machining. It should be noted that thin or microscopic spiral traces on the surface can do useful work in relation to the direction of the shaft rotation, or when the shaft rotates in opposite direction, it can also do harmful work with supporting oil pumping from inside to outside.
To prevent damage to the rotating shaft seal during installation, entry parts of the shaft should be chamfered. No sharp surface should be left on the corners where it is chamfered, and should be free from burrs and rounded. If mounting from the rear surface of the rotary shaft seal, the shaft end must be rounded.
|10 - 20||1,00|
|20 - 30||1,25|
|40 - 50||1,75|
|50 - 70||2,00|
|70 - 90||2,25|
|90 - 140||2,50|
|140 - 250||3,50|
Dynamic shaft misalignment
The difference (offset) between the axis of rotation and the geometric axis of the rotation shaft is referred to as the dynamic shaft misalignment, or general name as ‘runout’ in the industry. Bearing gap can be caused by an unbalanced load, oscitation of shaft or machining errors. Especially at high rotational speeds, in case of high runout, seal lip cannot follow the shaft at the same speed. Because of the sudden expansion between the seal lip and the shaft surface, the microscopic oil film in this region degenerates and the seal leaks. The permissible dynamic misalignment depends on the seal lip geometry, lip material, shaft diameter, rotational speed, temperature and other ambient conditions, but as a simple reference, the permissible dynamic misalignment values for conventional seal designs are shown in the graph.
You can see the basic rubber types recommended for different shaft diameters according to the shaft speed in the corresponding graph. In the area under each curve, rubber based recipes defined in that curve may be used.
The propositions in the graph are prepared based on high friction, heat and temperature resistance. In a real application, material selection is based on variables such as chemical content of the fluid used in a system, outdoor temperature, humidity, vapor, and gas in the system should be taken into consideration.