Usage:
This article describes the two types of Duo-Cone seals which are now used in track rollers and idlers. Criteria for determining if seals can be reused, as well as assembly recommendations, are also included.
Conventional Duo-Cone seals, shown in Illustration 1, have two rubber toric rings located on the outside diameter of each of the seal rings. The two metal seal rings are made so that a narrow flat seal band is located near the outside diameter of the seal ring faces. This contact band is lapped to obtain a very smooth and flat surface. As the seals rotate against each other, the area of contact moves toward the inside diameter. When this happens, the seals become a "matched pair".
Illustration 1. Cross section of a conventional Duo-Cone seal.
The toric rings are used to seal between the seal ring and the ramp in the end collar as well as twist to "force" the seal rings together.
Inverted Duo-Cone seals, shown in Illustration 2, were developed to maintain low wear rates while allowing use of larger shafts. They have one rubber toric ring on the inside diameter of the shaft seal ring and a rubber O-ring seal located on the outside diameter of the retainer seal ring. The contact band on this seal wears from the inside diameter toward the outside diameter.
Illustration 2. Cross section of an inverted Duo-Cone seal.
Criteria For Determining If Seals Can Be Reused
An efficient and cost effective undercarriage reconditioning operation includes procedures to inspect used Duo-Cone seals during rebuild or repair to determine if they can be reused. The following criteria should be used in making this determination:
... The seals must have operated satisfactorily before disassembly, with no evidence of leakage.
... The contact band on conventional Duo-Cone seals must not be less than 3.17 mm (.125") from the inside diameter of the seal rings. See Illustration 3.
Illustration 3. Typical wear pattern on a conventional Duo-Cone seal.
... The contact band on inverted Duo-Cone seals must be not be less than 3.17 mm (.125") from the outside diameter of the seal rings. See Illustration 4.
Illustration 4. Typical wear pattern on an inverted Duo-Cone seal.
... The bright, polished contact band must be continuous and well-defined on the seal ring faces. See Illustration 5. Examine the contact band carefully in reflected light.
... There should be no continuous visible scratches, pits, chips or other imperfections on the contact band. If defects exist, either oil can leak out or the contact band can gall. If any imperfections are found, discard the mated seals.
... Rubber toric rings should always be replaced.
... Examine the seal ring ramp for polished (shiny) areas. This indicates that the rubber toric ring has been slipping on the ramp. If the ramp appears shiny, as shown in Illustration 6, discard the mated seals.
Illustration 6. Polished seal ring ramp - do not reuse.
Assembly Recommendations
... Always install the seals in pairs. That is, install two new seals together or install two seals that were previously assembled together.
... Make sure that ramps on the retainers, shafts, bushings, end collars and seal rings are dry and free of oil. Isopropyl alcohol must be used to clean these parts and lubricate the metal seal ring faces.
Illustration 5. Seal ring faces.
... Make sure that rubber toric rings and seal rings are free of oil. Toric rings must roll, not slide on ramps.
... Use the correct assembly tools to ensure correct seal assembly. (See Special Instruction Form SMHS8484 for correct tools.)
... Make sure that seals remain free of foreign material before and during assembly. Even a small piece of lint from a paper towel can hold seal ring faces apart and cause leakage.
... For assembly and installation procedures of conventional Duo-Cone seals, see Special Instruction Form SMHS8364.
... For assembly and installation procedures of inverted Duo-Cone seals, see Special Instruction Form SMHS8483.
For disassembly and assembly procedures of idlers and rollers, see Undercarriage Reconditioning Guide Bulletin No. MP-11.