Oil Seal Assembly Guides

The Design of Shaft

Proper seal installation ensures sealing performance. How the seal is fitted is very important. The end of the shaft must be chamfered, corners must be rounded, free from burrs and sharp edges to protect seals from damage during assembly. The contact area for the sealing lip has a crucial effect on the sealing.

Material

Steel, casting iron, hard chrome coating, engineering plastic, etc.

Hardness

For slower circumferential speed (12 m/sec, hardness needs 60 HRC, hardening thickness >0.3 mm.

Roughness of Surface

The most often used method is plunge-cut grinding. This can ensure non-machine lead on the shaft. Too large roughness values cause premature wear and leakage. Too low a roughness value, the lubricant cannot reach the sealing edge. This will result in premature hardening and cause cracks at the sealing lip.

Recommended roughness value:

Ra = 0.2 ~0.8μm Rz = 1.0 ~5.0μm Rmax ≤ 6.3μm

At Operating Pressure > 1 bar

Ra = 0.2 ~0.4μm Rz = 1.0 ~3.0μm Rmax = 6.3μm

Shaft Diameter and Chamfer

Shaft Diameter (mm)	Tolerance range (h9) μ	Shaft Diameter (mm)	d
up to 6	- 30 ~0	up to 10	SD- 1.5
up to 10	-36 ~0	up to 20	SD- 2
up to 18	-43 ~0	up to 30	SD- 2.5
up to 30	-52 ~0	up to 40	SD- 3
up to 50	-62 ~0	up to 50	SD- 3.5
up to 80	-74 ~0	up to 70	SD- 4
up to 120	-87 ~0	up to 90	SD- 4.5
up to 180	-100 ~0	up to 140	SD- 5
up to 250	-115 ~0	up to 250	SD- 7
up to 315	-130 ~0	>250	SD- 11
up to 400	-140 ~0

Concentricity (Shaft to Bore Misalignment)

It is the distance that the center of shock rotation is from the center of the bore. Too large concentricity leads to uneven contact pressure on the ceiling lip. Thus the behavior of the sealing lip will wear on one side.

Dynamic Run-Out

The center of the shaft is twice the distance from and displaced from the actual center of rotation. Shaft run out should be avoided or kept within a minimum. At higher speeds, the sealing lip is at risk to follow the gap between the sealing edge and the shaft. Therefore, the bearing place should remain at the minimal level.

The Design of Bore

Steel and cast-iron provide good surfaces for both rubber covered and metal OD seals. Recommended roughness value:

For rubber covered seal: Ra = 1.6 ~ 6.3μm

Rz = 10 ~ 25μm

Rmax < 25μm

For metal OD seal: Ra = 0.8 ~ 3.2μm

Rz = 6.3 ~ 16μm

Rmax < 16μm

The lead corner, or entering edge of the bore should be chamfered and free of burrs.

Recommended angle: 15° ~ 20°

The depth of the housing chamfer is determined based on the following equations and figure below:

d1 = 8.5 * (seal width) d2 = (seal width)+0.3

Ex:

Seal Width = 10

d1 = 0.85 * 10 = 8.5 d2 = 10+0.3 = 10.3

For soft alloy (Aluminum) bore, rubber covered OD seals are recommended since they can better follow the thermal expansion.

If surface roughness is greater, paint sealant can be added to the metal OD seal. The oil seal sizes are in accordance with DIN3760 which provides suitable press fit for the bore tolerance ISO H8.

Bore Diameter and Seal O.D.

Bore Diameter (mm)	Tolerance Range (H8) μ
up to 6	0 to +18
up to 10	0 to +22
up to 18	0 to +27
up to 30	0 to +33
up to 50	0 to +39
up to 80	0 to +46
up to 120	0 to +54
up to 180	0 to +63
up to 250	0 to +72
up to 315	0 to +81
up to 400	0 to +89

Cautions on Assembly

Bore	The leading edge must be deburred. A rounded corner or chamfer should be provided.
Shaft	Remove surface nicks, burrs, grooves, and spiral machine leads.
Shaft End	Remove burrs or sharp edges. The shaft end should be chamfered in applications where the shaft enters the seal against the sealing lip.
Dimensions	Be sure that the shaft and bore diameters match those specified for the seal selected. Damage may have occurred prior to installation. A Seal sealing lip that is turned back, cut, or otherwise damaged should be replaced.
Seal Direction	Make sure that the new seal faces in the same direction as the original one. Generally, the lip faces the lubricant or the fluid to be retained.
Correct Tools	Press fitting tools should have an outside diameter of 0.3 mm smaller than the bore size. For the best results, the center of the tool should be open so the pressure is applied only at the outer edge.
Pre- lubricate	Before installation, wipe the sealing element with the lubricant being retained.
Proper Force	Use proper driving force, such as a soft-face tool, arbor press, or wood. Apply force evenly around the outer edge to avoid cocking the seal.

Assembly Illustration

The following pictures illustrate the correct and wrong assembly.