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

Vibration Isolation OverviewSession 3Examples

Choosing the right part

Example

• • FIRESTONE INDUSTRIAL PRODUCTS COMPANY

Airmount Example # ISO 1

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.


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.


Step 1 –

Determine the load at each mounting point

(69 kN + 27 kN)4

24 kN

Airmount Example Problem


Selection Guide



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

3 16,72 416 2,494 22,90 534 2,415 28,97 651 2,366 35,62 774 2,327 41,65 890 2,31

113Dynamic Characteristics at 125 mm Design Height

(Required for Airmount Isolator design only)

Gauge Pressure

(Bar)

Load (kN)

Spring Rate

(kN/m)

Natura l Frequency

(Hz)

3 18,07 416 2,394 24,76 529 2,315 31,33 646 2,276 38,72 771 2,237 45,44 887 2,20

113-1Dynamic Characteristics at 140 mm Design Height


Gauge Pressure

(Bar)

Load (kN)

Spring Rate

(kN/m)

Natura l Frequency

(Hz)


Natural Frequency


ƒn ≈ 1,76 Hz ƒn ≈ 1,61 Hz

3 14,67 200 1,844 20,23 262 1,795 25,85 318 1,756 31,99 375 1,717 37,38 430 1,69

21Dynamic Characteristics at 240 mm Design Height


Gauge Pressure

(Bar)

Load (kN)

Spring Rate

(kN/m)

Natura l Frequency

(Hz)

3 16,48 183 1,664 22,69 238 1,625 28,70 289 1,586 35,33 340 1,557 41,34 390 1,53

21-2Dynamic Characteristics at 265 mm Design Height


Gauge Pressure

(Bar)

Load (kN)

Spring Rate

(kN/m)

Natura l Frequency

(Hz)


Isolation Effectiveness

21-2

21

113-1

113


Step 3 – • Determine design height



Recommended Airmount Design Height 125 mm


Comparing Isolators

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

Why is Style 21 a better isolator than Style 113?


Comparing Isolators

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

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

2. 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


Increasing Isolation %

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

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

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


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.



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

• The Reservoir should have a flow path with Minimal Restrictions


Airmount Placement

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


Plumbing

• Individual captured-air springs• Three point regulated system• Three point leveled system


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


3 Point Leveled System

Technigram No. 107Valve part numbers on pg 25 of EMDG

MarshMellow Isolation Problem


MarshMellow Example #M1

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.


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.


Step 2 –

Determine the load at each mounting point– For MarshMellows, it is necessary to

determine both minimum and maximum load conditions

kN

kNkN5.15

4

2240

kN

kN10

4

40

Maximum Minimum

MarshMellow Example Problem


Step 2 –

Determine MarshMellow load capabilitiesMinimum 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 0176 MarshMellow requires 10,22 kN for 15% compression – Our minimum load is 10 kN which provides only 12% compression

The 0187 MarshMellow will be at its maximum compression of

27.5% at 14,58 kN – Our maximum load is 15,5 kN which

creates 29% compression


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.

%5.7%100 FreeHeight

StrokeStrain



Selection Guide – Stroke

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

accommodate the stroke requirement



Step 4 –

Determine Isolation Effectiveness

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


Natural Frequency


3,17 Hz2,93 Hz


Isolation Effectiveness

0190

0122


Application Example # M2 – You work on this one

• 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


Each MarshMellow

Min Load = 3,76 kN

Max Load = 4,90 kN


Application Example # ISO 2

• Precision Grinder = 1150 kg• 4 Mounting Points• Isolate from other

equipment in plant (assume 10 Hz)

• Select Airmount that provides Maximum Isolation


Isolation Mounts

• Air Spring• Marsh Mellow• Steel Coil• Rubber• Wire rope• Thin pads


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INITIAL COST

ISOLATION EFFICIENCY

PERFORMANCE LONGEVITY

OVERLOAD CAPACITYPRODUCT LINE RANGELATERAL STABILITYSOUND TRANSMISSIONCORROSION RESISTANCEFAILURE CONSEQUENCES

Isolation Mounts

RATING:

BEST WORST


Questions?

Quiz Time

The End(of this presentation)

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