Re-manufacturing and Service Exchange of Viscous Vibration Dampers

We provide re-manufacturing and service exchange of viscous vibration dampers from Hasse & Wrede, STE, Holset, Simpson, Metaldyne and WSK.

Description and Application hints for Viscous Torsional Vibration Dampers

Introduction

Torsional vibrations in piston-engine crankshafts are generated by the crank throws, which convert linear reciprocating piston movement into rotational movement. The vibration amplitudes superimposed on uniform rotation of the shaft can reach levels, both in the zones of resonance and on their flanks, which ge­nerate unacceptable stresses or at the very least undesirable noise.

The viscous damper has proved successful for many years in reducing crankshaft loads. It operates independently of the en­gine's lubricating-oil circuit and needs no maintenance or ad­justment throughout its working life.

Construction

The damper consists of a totally-enclosed housing (1) with cover (2) and the inertia ring (3). The inertia ring (3) is located radially and axially in the housing by the plain bearings (4), which also ensure the necessary internal clearance. Gaps (5) between the housing and the ring are filled with a high-viscosity silicone fluid. Two extraction plugs (6) provide the opportunity of testing the silicone fluid without having to dismantle the damper.

Function

The viscous damper provides the necessary torsional vibration damping effect by resilient, damped coupling of the secondary to the primary mass. If the crankshaft rotates uniformly without torsional vibration the inertia ring in the housing is driven round without any slippage occurring. However, as soon as even slight superimposed vibration amplitudes occur, relative move­ment takes place between the housing (primary mass) and the ring (secondary mass). This generates alternating shear stres­ses in the silicone film. The sum of these stresses over the entire gap surface results in a "damping" moment. The damper is operative throughout the engine's speed range and takes ef­fect at all orders of harmonics.

The vibration energy generated by the combustion and inertial forces acting on the crankshaft is converted by the damper into an equivalent quantity of heat. This heat is dissipated by the surface of the housing. If the cooling effect thus obtained is in­adequate, additional oil or air cooling has to be provided.

The working temperature of the damper should not exceed 95°C. It is permissible to run the damper at higher temperatures but this may lead to a reduced life time.

Silicone fluid

A characteristic feature of the viscous damper is the high-vis­cosity silicone fluid it contains. The viscosities normally em­ployed in dampers range from 80.000 to 500.000mm²/s. Silicone fluid is completely transparent when new. The loss in viscosity due to operation at increased temperatures is less in silicone fluid than in, say, mineral oil; the viscosi­ty in fact varies in accordance with the speed of deformation, and for this reason silicone fluids are referred to as being of the "non-Newtonian" type.

Damper life

Due to the large number of applications for viscous dampers in engine systems, the differing stresses to which such dampers are subjected and the variations in operating conditions, it is impossible to give more than a general guide as to when dam­pers should be replaced. Based on experience gathered to date and on the assumption that the damper exhibits no external mechanical damage, dampers which have been subjected to normal loads should achieve the following life spans between overhauls:

a) Dampers on motor vehicle engines 500.000 km

b) Industrial, locomotive and marine applications 20,000 service hours

(speeds exceeding 600 1/min)

c) Other industrial and marine applications 30,000 to 50,000 service hours

(speeds up to 600 1/min)

It is possible to increase the above mentioned periods when the proper function of the damper is checked in regular intervals by measuring the viscosity of the silicone fluid inside the damper. Two extraction plugs on the damper housing provide the oppor­tunity to extract fluid samples (see chapter "Taking a silicone oil sample"). The first sample should be taken after 10,000 hours (application b) resp. 30.000 hours (application c).

Taking a silicone oil sample

Viscous dampers equipped with extraction plugs provide the opportunity of testing the viscosity of the sili­cone oil inside the damper without having to dismantle it. Corre­sponding to the condition of the silicone oil an approximate as­sessment of the damper efficiency is possible. A silicone oil sample should be extracted as follows:

- After engine stops let damper cool down to nearly 40°C (i.e. 100°F)

- Rotate the damper to bring one of the extraction plugs (6) to optimum position.

Prepare the sample container (10) by removing one of its caps (11).

- Unscrew and remove the extraction plug (6) and replace it by the sample container (10). If meeting at the inertia ring (3) unscrew the container one revolution.

- Remove the second cap from the sample container and wait until silicone fluid (5) begins to flow out from the free end. Depending on the silicone viscosity this process needs a certain amount of time. If possible it can be speeded up by means of

1) turning the damper until the sample container is under­neath the crankshaft,

2) temporarily removing the second extraction plug, too

- As soon as the silicone fluid begins to flow, shut the sample container by the cap. Remove the container from the damper casing, wipe off the sealing face round the extraction hole and screw in the plugs together with new sealing washers (7). Now close the second side of the container.

- Tighten both extraction plugs with thumb and forefinger then turn them further for 45° (about 20 Nm=2 kpm=170 lb ins torque).

- Seal both plugs by caulking their grooves.

- Send the sample container complete with the damper type, serial number, engine and operation data to our address:

AVM Diesel (F.E.) Pte Ltd

Blk 27 Tuas Ave 13 #01-23

Singapore 638993

The quantity of silicone oil removed is so small that up to 10 such samples can be taken without risk.

The viscosity of the silicone oil sample is best measured by the damper manufacturer, who can assess the approximate condi­tion of the damper after analyzing the sample. The damper ma­nufacturer will also indicate the operating period after which a fresh sample should be tested.

If it is impracticable to submit samples to the damper manufac­turer, some other suitable laboratory can be asked to determine the viscosity of the oil. We recommend the use of a rotation vis­cometer with cone and plate sensor system and contact con­trol.

Damper overhauls

Viscous torsional vibration dampers with either a bolted or a welded cover can be reconditioned “as new".

General hints

The viscous damper should be treated with the same care as any other moving part of the engine. Mechanical damage to the thin-walled damper housing can adversely affect damper efficiency and can lead to unacceptable stresses in crankshaft and transmission elements. If the general vibrations in the engine system rise at any speed within the normal speed range with the engine in operation, this can be caused by a reduction in damper efficiency and the damper should then be exchanged and investigated at the ear­liest opportunity. In identical engine systems dampers are fully interchangeable. It should be noted however, that when dampers are fitted to two or more systems it will become necessary to check the damper running time in each case.

The damper surface can be cleaned with any commercially available cleansing medium.