Sealing of the bearing space is very important, because damaging materials which can be found in the bearing environment influence it and often can cause its breakdown. Sealing also has an opposite function – it prevents the lubricant leaking out of the bearing and arrangement space. That is why sealing must always be designed with regard to operating conditions of machines or equipments, arrangement design, lubricating method, maintenance possibility and economic questions concerning production and utilization.
Non-Contact Sealing
Between non-rotating and rotating parts there is only a narrow gap when using this sealing. It is filled with grease. Using this sealing, wear of components from friction does not occur and that is why this sealing can be used for the highest rotational speeds and for high operating temperatures. Examples of a gap sealing are in Pict. 1.
Another very effective sealing is the labyrinth sealing which can improve the sealing effect by a greater number of labyrinths or prolongation of sealing gaps. Examples – see Pict. 2.
Rubber Sealing
Rubbing sealing is created of elastic or soft, but sufficiently impermiable material, which is inserted between the rotating and firm part. Such a sealing is usually cheap and is suitable for various designs. The disadvantage is the sliding friction of the contacting surfaces, and therefore there is limited utilization for high rotational speeds. Sealing with a felt ring is the simplest (Pict. 3). It is suitable for operating temperature -40° to +160°C and for peripheral speeds to 7 m.s-1 and sliding
surface roughness max. Ra = 0,16, hardness min. 45 HRC or hard chromium plating. Dimensions of the felt rings are given by corresponding national standards.
A very wide-spread way of sealing is sealing with shaft washers (Pict. 4). Radial shaft seal washers are made of rubber or other suitable plastic reinforced by steel sheet reinforcement. According to the material used they are suitable for operating temperature from -30° to +160°C. Permissible peripheral speed depends on sliding surface roughness:
- to 2 m.s-1 is roughness max. Ra = 0.8
- to 4 m.s-1 is roughness max. Ra = 0.4
- to 12 m.s-1 is roughness max. Ra = 0.2
Except for mentioned most commonly used sealing rings there are rubbing sealing designs which use the just formed sealing rings made of rubber, plastic, etc., or special spring rings. This sealing is chosen either for applications with high requirements on bearing space sealing (great environment pollution, high temperature, chemical substance influence), or for economic reasons by mass or series production. Examples – see Pict. 5.
Combined Sealing
Increase sealing effect can be reached by non-contact and rubbing sealing combination. Such a sealing is recommended for wet and polluted environment. Example – see Pict. 6.
