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Vibration Isolation Overview. Session 3 Examples. Choosing the right part Example.

Vibration Isolation Overview

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- Session 3
- Examples

Isolate a vibrating screen which weighs a total of 69 kN, preferably with ONE isolator at each corner. The additional material load on the machine is 27 kN. The vibrating mechanism is rotating at a speed of 17 Hz with a total stroke of 19 mm.

Airmount Example # ISO 1

Design Parameter Sheet

Step 1 – Review the Airmount Design Parameter Sheet. This will help remind you of all of the questions you should ask, and get the information you would need to get help from your Firestone representative.

(69 kN + 27 kN)

24 kN

4

Airmount Example Problem

Step 1 –

Determine the load at each mounting point

Selection Guide

Airmount Example Problem

Step 2 –

- Determine isolation effectiveness
- natural and forced frequency

Natural Frequency

Natural Frequency can be found in the Dynamic Characteristics table on each data sheet

ƒn ≈ 2,40 Hz

ƒn ≈ 2,32 Hz

Natural Frequency

Natural Frequency can be found in the Dynamic Characteristics table on each data sheet

ƒn ≈ 1,76 Hz

ƒn ≈ 1,61 Hz

Isolation Effectiveness

21-2

21

113-1

113

Airmount Example Problem

Step 3 –

- Determine design height

Recommended Airmount Design Height 125 mm

Style 113Style 113-1

- Isolation = 97,25% - Isolation = 97.75%

- Design Height = 125 mm- Design Height = 140 mm

- List Price = €249,87 - List Price = €281,31

Style 21Style 21-2

- Isolation = 98.5% - Isolation = 99%

- Design Height = 240 mm - Design Height = 265 mm

- List Price = €221,13 - List Price = €321,74

Comparing Isolators

Two parameters affect the natural frequency of air springs!!!!!!!!!

The rate of change of the internal volume as a function of deflection, which causes a change in pressure

The rate of change of the effective area of the air spring as a function of deflection which causes a change in load carrying capacity at a constant pressure

Comparing Isolators

By extension there are two things you can do to decrease the natural frequency of air springs (improve isolation)

Reduce the rate of change of the internal volume as a function of deflection

Reduce the rate of change of the effective area of the air spring as a function of deflection

Increasing Isolation %

Comparing Isolators

To change the rate of change of effective area, just use a longer part. For instance use a 21 instead of a 113

To change the rate of change of volume (pressure), you can also use a longer part since it will have more volume, however

You can also add a reservoir tank to further reduce the rate of change of the volume.

Increasing Isolation %

Rule Of Thumb - Maximum Reservoir size = 3 x Spring Internal Volume

The Reservoir should have a flow path with Minimal Restrictions

Increasing Isolation %

Ideally, Airmount should be in the same plane as the center of gravity

Rule of Thumb - The smallest distance between Airmounts should be twice the vertical height to the center of gravity

Airmount Placement

Individual captured-air springs

Three point regulated system

Three point leveled system

Plumbing

Captive Air Inflation

Tank valves are used to individually inflate air springs for isolation applications. However, due to air permeation, you need to regularly inspect the pressure to insure that your system is working to it’s potential.

3 Point Regulated System

Technigram No. 107

Valve part numbers on pg 25 of EMDG

3 Point Leveled System

Isolate a vibrating screen which weighs a total of 40 kN, preferably with ONE isolator at each corner. The additional material load on the machine is 22 kN. The vibrating mechanism is rotating at a speed of 20 Hz with a total stroke of 13 mm.

MarshMellow Example #M1

Design Parameter Sheet

Step 1 – Review the MarshMellow Design Parameter Sheet. This will help remind you of all of the questions you should ask, and get the information you would need to get help from your Firestone representative.

MarshMellow Example Problem

Step 2 –

Determine the load at each mounting point

- For MarshMellows, it is necessary to determine both minimum and maximum load conditions

Maximum

Minimum

MarshMellow Example Problem

Step 2 –

Determine MarshMellow load capabilities

Minimum Load

- MarshMellows must have at least 15% compression to be an effective isolator, therefore, there is a minimum amount of load required to be on the spring at all times
Maximum Load

- MarshMellows are a solid mount so there is a limitation to the energy input to the spring before it will fail from heat build up, therefore, there is a maximum amount of load for which it is rated

Selection Guide – Load

The 0187 MarshMellow will be at its maximum compression of 27.5% at 14,58 kN – Our maximum load is 15,5 kNwhich creates 29% compression

The 0176 MarshMellow requires 10,22 kNfor 15% compression – Our minimum load is 10 kNwhich provides only 12% compression

MarshMellow Example Problem

Step 3 –

Determine MarshMellow stroke capabilities

MarshMellows are a solid mount and therefore can survive only a defined amount of movement. The amount of movement allowed is a function of:

However, you don’t need to worry about this calculation since we have taken care of this in the selection charts.

Selection Guide – Stroke

The 0200 MarshMellow can carry the load for our application but cannot accommodate the stroke requirement

MarshMellow Example Problem

Step 4 –

Determine Isolation Effectiveness

What do we know about the relationship between natural frequency and isolation effectiveness?

Natural Frequency

Natural Frequency can be found in the Dynamic Characteristics table on each data sheet

2,93 Hz

3,17 Hz

Isolation Effectiveness

0190

0122

Vibrating Screen:

Machine Weight = 2300 kg

Material Weight = 700 kg

6 Mounting Points

Operating at 12 Hz

Throw of 10 mm

Customer requested at least 90% isolation

Select MarshMellow that provides Maximum Isolation

Application Example # M2 – You work on this one

Each MarshMellow

Min Load = 3,76 kN

Max Load = 4,90 kN

Precision Grinder = 1150 kg

4 Mounting Points

Isolate from other equipment in plant (assume 10 Hz)

Select Airmount that provides Maximum Isolation

Application Example # ISO 2

Air Spring

Marsh Mellow

Steel Coil

Rubber

Wire rope

Thin pads

Isolation Mounts

BEST

WORST

Isolation Mounts

RATING:

- Quiz Time

The End

(of this presentation)