Suggestions for seal selection and installation

1. Prior to installation

1.1. Pay attention to bore surface when disassembly of the used seal

Bore surfaces not to be damaged while disassembly of used seal. If applicable, a hole can be drilled to back surface of the seal and than the seal can be pulled out with a bolt.

1.2. Pay attention to seal selection

1.2.1. Before fitting, individual seals should be examined thoroughly to ensure that the lip is not scratched or damaged, that the garter spring is correctly located and that the seal is clean and dust free. For visual defects please refer to Appendix 1.

1.2.2. When fitting, an oil seal must be fitted whose arrow points in the direction of rotation of the shaft. In SKT sealtype designation;

(SOL) indicates that seal should be used at counter clockwise rotating of the shaft.

(SAG) indicates that seal should be used at clockwise rotating of the shaft.

1.2.3. In sealing, media where pressure is more than 0.5 bar, seals with reinforced profile should be used. These seals have a "B" letter code in SKT seal type designation. In some special applications back-up rings can be used.

Figure 9: Application of standard seals with back-up ring in pressurised media.

1.2.4. Material selection of sealing lip depends on the media (fluid type, temperature of sealing lip, vibration, eccentricity, etc.) and the working conditions. Refer to Appendix 2 for selection of material for specified rotational speed and shaft diameter.

1.2.5. Silicone rubber requires special attention and should be handled gently.

1.3. Rotary shaft seals should be taken out from the packaging by hand, only. The use of sharp tools should not be attempted.

1.4. The shaft should be machined according to h11 tolerances. Refer to below table.

All dimensions are in mm.

Table 5

The shaft should have a surface hardness of 45-55 HRC. If the media is dusty or the surface speed is more than 4 m/s, then the surface hardness should be at least 55 HRC.

The shaft surface should be ground to a roughness of Ra=0.2-0.8 µm, Rz=1-5 µm, Rmax= 6.3 µm. ( for reciprocating shafts Rz<1 µm, for silicone seals Rz= 1-2 µm.)

Spiral grooves can be generated on a shaft surface during the finishing operation. This condition, known as SHAFT LEAD, can cause leakage. The surface of the shaft where seal works should be plunged grinded.

The contact surface of the shaft to seal should be clean and free from rust.

If the seal is to be mounted over the shaft by the front face first, the shaft end should be chamfered and the corners should be free from burrs. If the seal is to be inserted over the shaft by the back face first, the shaft end will be rounded. (See below figure)

Figure 10

Table 6

If the shaft cannot be machined as required, or if splices or keyways exists on the shaft end, a special cap will have to be used. The cap should be chamfered or rounded and freed from burrs.

Figure 11

Runout deviation or dynamic eccentricity of the shaft should be avoided as far as possible. Eccentricity tolerance of shaft axis relative to bore axis is shown below graphic.

Figure 12

At high revolutions the danger exist that the sealing lip, as a result of inertia, can no longer follow the shaft. The inevitable increase in the seal gap between the sealing edge and the shaft results in leakage after a certain level of enlargement. For this reason radial shaft seal must be located in the immediate vicinity of the bearing and the bearing play must be minimised. Permissible values for runout are given below graph.

Figure 13

1.5. The bore should be machined according to ISO H8 tolerances. Refer to below table.

Bore diameter(D)	Tolerances	Bore diameter(D)	Tolerances
1-3	+0.014 -0.000	50-80	+00.016 -0.000
3-6	+0.018 -0.000	80-120	+0.054 -0.000
6-10	+0.022 -0.000	120-180	+0.063 -0.000
10-18	+0.027 -0.000	180-250	+0.072 -0.000
18-30	+0.033 -0.000	250-315	+0.081 -0.000
30-50	+0.039 -0.000	315-400	+0.081 -0.000

Table 7: All dimensions are in mm.

The roughness of the bore should be Ra = 1.6-6.3 µm, Rz=10-20 µm, Rmax=25 µm.

Recommended chamfer dimensions on the bore are shown in below table. SKT advises initially machining of the chamfer and then the bore.

Table 8, Figure 14 (Ref =DIN 3760, September 1996)

2. Important points in seal installation

2.1. The front face (or the garter spring) of the seal should be faced the medium to be sealed.

2.2. Minimum wear at optimum sealing capability can only be experienced when the sealing lip is sufficiently lubricated. The sealing lips, outside surface of seal and the shaft should be lubricated lightly with fluid to be sealed. If the dust lip is to contact to the shaft, the grease should be applied between the two lips.

2.3. A satisfactory assembly can only be achieved with a force fit device and a suitably shaped installation tool. Hammers should not be used for installation. Strict attention must be paid to the fact that the oil seals are not placed in oblique position to the bore, since after forcing it in, the seal can no longer be aligned and will then remain in a tilted position. Refer to below figure

Figure 15

2.4. The garter spring is designed according to Engineering Specifications and the garter spring's length should not be changed.

2.5. It is vital that the pressing force applied, is uniformly distributed to the periphery and as close as possible to the outside diameter. SKT advises an installation tool diameter of 0.5 mm smaller than the bore diameter. Pay attention not to apply excessive deforming force.

Refer to below figure.

Figure 16

2.6. The shaft surface should be clean and smooth

2.7. A special installation tool should be used to align seal and shaft according to bore, when the shaft has to be installed before the seal installation.

Figure 17

The above figure shows proper installation method and tool, to be used at installation of an extended lip seal (ex: L1C or L3C) where fits front-side up.

Seal should be installed perpendicular to bore axis. Refer to below figure where the front face of bore is machined, it should be used as a reference surface.

Figure 18

Refer to below figure for installation method of seal where seal bottoms on machined more bottom.

Figure 19

Refer to below figure for installation method of seal tool through bore where installation tool bottoms on shaft.

Figure 20

2.8. Refer to below figure for installation method of seal where fits side-up.

Figure 21

Figure 22

Figure 23

2.9. Refer to below figure for installing seal elements which slide over splices, keyways or holes.

Figure 24

Installation tools should be free of burrs, nicks and should be carefully handled.

2.10. If a machine element has to be tight fit over the shaft surface where the seal will operate, the shaft should be machined down to 0.2 mm under the shaft diameter.

Figure 25

2.11. Assembly must be carried out, with the outer surface lightly oiled, with fixed speed and force. This facilitates the assembly, increases the tightness of the sealing point and prevents the oil seal from springing back after being forced in.

2.12. If elastomeric seals have to be assembled at low temperatures, flexibility of sealing lip maybe restored by placing the seal for 10 to 15 minute in a clean, compatible fluid at a temperature not to be exceed 50°C .

2.13. In case of replacement, a new seal shall always be used. Do not use the old seal.

The sealing lip of the new seal shall not be allowed to engage with the previous track of rotation; it shall be shifted to the fluid side. This can be achieved by fitting spacers or exchanging the shaft bushes or the race rings or by varying the depth to which the seal is pressed into the bore.

Fitting check list

Be careful during dismount of the old seal. Do not give any damage to the bore!

Before mounting, examine the seal carefully!

Is there any extra pressure? Then use seals for pressuried media!

Is the rubber material of the seal, suitable for the working media?

Take out seal from its' package by hand, only.Do not use sharp objects!

Let the label be on the package till the last seal picked-up !

Let the edge of the shaft smooth and clean. Is there any sharpness' ?

Shaft surface, at which the seal will work, shall be free of burrs, scrap and scale!

Use sleeves to protect seal from key slots!

Does the dimension of the housing match to the seals' ?

Let the mounting of the seal in true direction:The spring of the seal should be faced to oil side!

Let the lip of the seal or outside diameter of the shaft be oiled before mounting!

Mount the seal with a mounting tool!

Do not hit the seal with hammer!

Do not shorten the original garter spring!

Let the shaft axis and seal axis be paralleled, while mounting!

If reverse-mounting should be attempted, take care not to deform the seal!

Let the outside diameter of the shaft be oiled and then mount the seal within continuos and steady motion!

Before mounting, wait till the seal temperature achieves to room temperature!

Never use the old seal!

Appendix 1

Molded single lip seal defects type

Figure 26

Knife trimmed dual lip seal defect types

Figure 27

Table 9: Guide to the significance of visual radial lip variations (Ref: SAE J946 OCT91)

Appendix 2: Selection of suitable material for rotary shaft seals

Figure 28: The permissable shaft RPM under athmospheric pressure conditions for various seal materials with good heat dissipation and appropriate lubrication. (DIN 3760)

Example: For a shaft of 50 mm diameter rotating at 4000 RPM, the surface speed is 10.5 m/s. If the type of medium to be sealed and the operating temperature allow, polyacrylic rubber can be chosen as the lip of material.

Sealing elements

• The importance of sealing elements

• General definitions of parts of seals for motor vehicles

• Nomenclature and basic types of SKT seals

• Sealing mechanism and seal life

• Suggestions for seal selection and installation

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SKT Yedek Parça ve Makina Sanayi ve Ticaret A.Ş.

Organize Sanayi Bölgesi, Yeşil Cad., No: 17, 16140 Bursa.
Phone: (+90 224) 2434100 - Fax: (+90 224) 2431424
E-mail: skt@skt.com.tr   URL: www.skt.com.tr

SKT A.Ş. is a company of Diniz Holding.

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