InfiniSpring® technology was implemented in a CASEMATE Business Finland research project involving an AGCO Power internal combustion engine-generator set, operated by Global Boiler Works Oy (GBW). The project, led by the University of Oulu, formed the basis of a Master’s Thesis by Benjamin Timonen, supervised by Antti Korpela (GBW).

Original Setup and Modification

The engine-generator set was originally rigidly mounted to the floor of a test container. As part of the CASEMATE project, InfiniSpring® springs were dimensioned and installed between the engine-generator set and the container floor to reduce vibration transmission to the surrounding structure.

Notably, the engine-generator set remained unmodified. The InfiniSpring® springs were added externally, making the upgrade both straightforward and non-invasive.

Spring Selection and Load Matching

• Engine-generator set weight: ~1100 kg
• Springs used: 10 × InfiniSpring® 8HS130
• Load capacity per spring: 100–130 kg
• Total supported load range: 1000–1300 kg

This configuration matched the system’s weight perfectly, ensuring optimal isolation performance.

Datasheet with standard spring sizes is available on our webpages: InfiniSpring Datasheet

Design and Simulation

• Design of mounting rails for spring installation
• Development of a simulation model using AVL Excite™
• Vibration measurements and comparison with simulation results

The simulation revealed the following rigid body natural frequencies for the isolated system:

Isolation Performance

The critical isolation frequency is calculated as:

f_c = √2 · f_N

For vertical natural frequency of 7.7 Hz:

f_c = √2 · 7.7 Hz ≈ 10.9 Hz (653 rpm)

This means the spring installation begins isolating vibrations above 653 rpm. Vibration tests were conducted at operational speeds between 1000 rpm (16.7 Hz) and 2000 rpm (33.3 Hz).

Transmissibility and Isolation Efficiency

Transmissibility (T) is calculated using:

T = √(1 + (2ζr)^2) / √((1 – r^2)^2 + (2ζr)^2)

Where:

• r = Ω / f_N
• ζ = 0.01

Example:

At 2000 rpm (33.3 Hz), vertical natural frequency = 7.7 Hz

r = 33.3 / 7.7 ≈ 4.325

T ≈ 0.057

F_T = T · F_0 = 0.057 · 100 N = 5.7 N

Isolation efficiency: (1 – T) · 100 = 94.3%

Excitation Orders and Isolation

At 2000 rpm, the engine generates excitations at half-order intervals. Below is a summary of vertical direction transmissibility and isolation percentages:

Installation Summary

• Spring selection: 10 × InfiniSpring® 8HS130 for 1100 kg
• Installation: Springs placed symmetrically around the center of gravity for balanced load distribution and optimal isolation

Customer Feedback

Marko Jokinen, CEO of GBW, noted a tangible improvement in vibration levels: “I could feel the difference between the original stiff installation and the resilient InfiniSpring® setup from my office next door.”

Future Development

Future improvements may include integrating spring geometries directly into the steel support frame, eliminating the need for separate spring components and simplifying installation.

The full MSc Thesis (in Finnish) is available via the University of Oulu portal:

Polttomoottorigeneraattorin värähtelynvaimennuksen asentaminen ja simulointi

CASEMATE project:

In English

In Finnish

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Figure 1. Koja Oy heating, ventilating and air conditioning (HVAC) system.

Antti saw the potential in the InfiniSpring® integration and the new fan unit design was targeted to utilize InfiniSpring®-springs. Antti designated Miska Karttunen, an excellent candidate from Tampere University of Technology for the job.

MSc Thesis Main Targets

• Designing new fan unit frame with integrated springs
• Optimizing fan unit frame stiffness and mass
• Minimizing structure borne noise (SBN) from fan unit
• Ensuring the ease of fan unit manufacturing and assembly
• Enabling easy maintenance for fan unit

New Fan Unit with Integrated Springs

The most important factor in vibration isolation is to ensure high vibration isolation performance. This means that structure borne noise (SBN) from the fan unit to surroundings is minimized by making the vibration isolation very soft. The high flexibility of InfiniSpring®-springs enables this.

In the project new side beams were designed utilizing the 4HS35 integrated InfiniSpring®-springs. The beam is shown below in Figure 2.

Figure 2. Koja Oy fan unit side beam with integrated 4HS35 InfiniSpring®.

The developed fan unit with integrated springs has flexible spring installation natural frequencies below 10 Hz. Vibration attenuation percentage is above 85 % in whole operating frequency range. Meaning that high vibration isolation efficiency is achieved as a result of this.

With soft InfiniSpring®-springs, the fan frame required structural modifications. Koja Oy made the modifications with the help of finite element analyses and the fan design was modified to optimize fan structural resonance modes (fan elastic body modes) above operational frequencies. This led to improved overall vibration performance of the fan.

Koja Oy Benefits 

With soft springs high vibration isolation performance is achieved. Soft springs eliminate noise and vibration issues as fan loads are not transmitted through the soft springs to surroundings. Spring integration enables simplification of fan frame and separate vibration isolation elements are avoided. Also, the support structures for the vibration isolation elements can be avoided making the design simpler.

Remember this while Designing

It is important to manage the structural resonance modes of the actual product. In this case the fan elastic body modes. Critical elastic body resonance modes are preferably designed outside of the operational frequency range. Today, with the help of finite element analyses, structural designs can be optimized for soft springs, structural resonances avoided and top level vibrational performance guaranteed safely already during the design phase.

Here is a video introducing available InfiniSpring®-spring sizes.

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The test case fan is equipped with a 2.2 kW electric motor, which is controlled via variable-frequency drive. The motor nominal speed is 1440 rpm. The fan is used in air handling units and typically equipped with rubber elements. In this article InfiniSpring®-springs are dimensioned below the fan.

Fan weight

The fan weight was first measured to determine spring selection. Measurement results were taken below the existing rubber elements and measurement results are shown in Figure 1.

Figure 1. Weight measurement results for the fan.

Spring selection

The fan originally had four springs and four InfiniSpring®-springs were chosen to be used in the fan. Spring selection can be made with following steps:

• Calculating total mass: 17.0 kg + 17.0 kg + 23.0 kg + 23.0 kg = 80.0 kg
• Deciding required number of springs: 4
• Calculation load for one individual spring: 80 kg / 4 = 20 kg
• Choosing optimal spring based on the individual spring load: 3HS20 spring with nominal load range 15-20 kg according to Table 1 below (table is taken from the datasheet found on the Product page)

Table 1. Vertical nominal loads of a single spring from the datasheet.

Spring locations

Final step is to dimension springs symmetrically around the center of gravity in the fan axial direction. Fan motor axial direction is referred as X-direction in Figure 2. The zero-point location is also shown in Figure 2.

Figure 2. Fan equipped with original rubber elements.

First the centre of mass x-coordinate is calculated. After this the location for the motor end spring is chosen. In this case 65 mm from the end of the 584 mm long attachment aluminum bar is used, Figure 3. Spring locations from the zero-point location are then calculated as follows.

Calculation steps

• Calculating centre of mass x-coordinate:

• Deciding motor end spring location: 65 mm
• Calculating spring locations:

Figure 3. Spring locations

Fan with new springs

Fan with 3HS20 InfiniSpring® is shown below in Figure 4. Individual InfiniSpring® is shown in Figure 5. Optimal springs were selected for the fan and the fan is ready for operation. Safe operational speed ranges from 755 rpm upwards. Minimum operational speeds can be found from the Data Sheet and also shown in Table 1 above. Please see also a video below introducing the fan and InfiniSpring®-springs.

Figure 4. Fan equipped with 3HS20 InfiniSpring®

The post How to select InfiniSpring® for a fan? appeared first on InfiniSpring.

Test case fan is equipped with 3HS20 InfiniSpring®-springs and with a 2.2 kW electric motor, which is controlled via variable-frequency drive. Motor nominal speed is 1440 rpm. This article focuses on testing the fan with big unbalance to see which rigid body modes are harmful for the fan installation. A fan with a big impeller unbalance mass (extra bolt) is shown in Figure 1 below.

Figure 1. Fan impeller with big unbalance mass.

Completed Test

The fan was tested with a big unbalance mass in different rigid body mode (flexible installation natural mode) resonances by setting the motor speed to measure natural mode frequency of the flexible installation. In practice the fan speed was set first to fan longitudinal mode frequency 4.5 Hz (270 rpm) and fan vibration levels were checked. After this, the speed was raised to fan transversal mode frequency 4.75 Hz (285 rpm) and again fan vibration levels were checked. This was continued all the way up to the last natural mode. In total there are always six degrees of motion (3 translation degrees of freedom and 3 rotating degrees). Below are shown six tested rigid body natural modes and their frequencies.

Test with big unbalance

The test revealed that only transversal and vertical natural modes are excited with big unbalance. Other rigid body natural modes are not excited. Below is a video showing the fan is speeded up from 0 Hz to vertical mode 9.5 Hz (570 rpm) with a very big impeller unbalance. The fan vertical rigid body mode is excited heavily in the vertical direction.

With InfiniSpring® vertical rigid body mode always has a higher natural frequency compared to transversal rigid body mode. Due to this, the vertical rigid body mode defines the minimum operating frequency for the fan. For the fan that was tested, the vertical rigid body mode is 9.5 Hz (570 rpm) and transversal rigid body mode is 4.75 Hz (285 rpm).

Conclusions

Based on the test transversal and vertical rigid body modes for the fan are excited with big unbalance. They are therefore the most harmful rigid body modes. Other rigid body modes are not excited.

Vertical rigid body mode frequency is always higher than transversal mode frequency. Due to this, the vertical rigid body mode frequency is used for dimensioning InfiniSpring®-springs for a fan, and it also defines the fan minimum operating frequency.

Datasheet values can be used to define minimum operating frequency. The datasheet defines the minimum rotational speed, e.g. 3HS20 InfiniSpring® is for rotational speeds above 755 rpm (12.6 Hz). The rpm value can be found from the datasheet.

P.S. In this case, the fan can be operated safely in a speed range from 755 rpm up to the speed allowed by the fan or motor.

P.P.S. With the balanced fan, none of the rigid body modes were excited and it was safe to operate the fan from 0 rpm upwards.

The post Which frequencies are harmful for fan installations and what is fan’s minimum operating frequency? appeared first on InfiniSpring.

The test case fan is equipped with 3HS20 InfiniSpring®-springs and a 2.2 kW electric motor, which is controlled via variable-frequency drive. The motor nominal speed is 1440 rpm. The fan is used in air handling units and typically equipped with rubber elements. This article focuses on validating InfiniSpring®-spring selection based on the fan weight data. Fan with 3HS20 InfiniSpring® is shown in Figure 1 below.

Datasheet Data for 3HS20 Spring

According to technical datasheet 3HS20 spring is for nominal load ranges between 15-20 kg and for rotational speeds above 755 rpm. Maximum vertical natural frequency is less than 11.7 Hz, Table 1 below.

Table 1. Maximum vertical natural frequencies when using nominal load range.

Natural Frequency Validations

The vertical natural frequency was measured to validate the limit value 11.7 Hz. The measured vertical natural frequency result is shown below in Table 2 together with the datasheet limit value.

Table 2. Measured vertical natural frequency.

In order to comply with the data sheet value, the measured value needs to be below the datasheet frequency 11.7 Hz for vertical natural mode. Based on the 9.5 Hz measurement result we are clearly on a safe side. It is to be noted that the test case fan 3HS20 InfiniSpring® is for a load range of 15-20 kg and the spring load is 20 kg. This means that 15 kg spring load would give vertical natural frequency of approximately 10.5 Hz and the result would be safe with lower load.

Conclusions

Based on the measurement the vertical mode frequency for the test case fan 3HS20 InfiniSpring® is from 9.5 Hz to 10.5 Hz and vertical mode frequency is always safely below the datasheet value 11.7 Hz. Weight data can be used very safely for the spring selection.

Fan and InfiniSpring®-springs introduced below.

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