BETAFOAM™ Renue
A Sustainable, Lower Density, Cavity Sealing
Technology for Automotive NVH
MATT ASHER
The Dow Chemical Company
438 Building
Midland, MI 48667
ALLAN JAMES
Dow Automotive Systems
1250 Harmon Road
Auburn Hills, MI 48326
ALI EL-KHATIB
Dow Automotive Systems
SAEED SIAVOSHANI
LMS
1250 Harmon Road
Auburn Hills, MI 48326
5755 New King Court
Troy, MI 48098
ABSTRACT
The noise, vibration, and harshness (NVH) performance of a vehicle is a major selling point in
today’s competitive automotive marketplace. The NVH performance of a vehicle’s passenger
compartment is a qualitative and quantitative assessment of the sounds associated with the powertrain
and external factors. Channels that are part of a vehicle’s finished body (pillars, rockers, etc.) are some
of the routes that transfer sound energy to the passenger compartment of a vehicle. Automotive
original equipment manufacturers (OEMs) have used various technology approaches to improve the
overall NVH performance of a vehicle. Sealing open cavities with polyurethane foam is one of these
solutions. BETAFOAM™ is a polyurethane technology that has been used by OEMs for NVH
improvement since 1995.
As OEMs look to new polyurethane technologies, sustainable chemistry is something that the
marketplace is asking for. Additionally, light weighting is a well known driver that OEMs are seeking
due to pending fuel economy standards. BETAFOAM™ Renue is a new cavity filling technology that
satisfies both of these drivers with the incorporation of > 25% renewable content coupled with a
reduction in density of 30% over traditional BETAFOAM™.
This paper will describe BETAFOAM™ Renue. It will also introduce a system level insertion loss
methodology, developed by Dow Automotive Systems, that is more appropriate for assessing NVH
performance for automotive applications.
INTRODUCTION / CHEMISTRY
Dow Automotive Systems is a major polyurethane supplier into the automotive marketplace.
BETAFOAM™ was first launched in 1995 as a means to reduce passenger cabin noise. The ability of
a polyurethane foam to effectively seal complex cavity shapes is a desired property for improved
acoustics. The polyurethane system is injected as a cavity, then reacts quickly to seal the intricate
space.
®™Trademark of The Dow Chemical Company ("Dow") or an affiliated company of Dow
PHOTOGRAPH 1. BETAFOAM™ Renue effectively sealing a Pillar
Dow’s relationships with OEMs give us insight into technology trends that they are seeking.
Sustainable technologies are recognized by OEMs as an aspect that some consumers use as a barometer
for vehicle purchase. Because of this, OEMs are encouraging polyurethane suppliers to consider the
development of sustainable solutions. Additionally, aggressive fuel economy standards are causing
OEMs to look at light weighting technologies in all areas, polyurethane foams being no exception. To
be truly successful, a polyurethane system must also have improved performance / physical properties
to accompany the incorporation of sustainable content. This paper will focus on the impact that
renewable content has on the final acoustic properties of lower density BETAFOAM™ Renue (1.4
pounds per cubic foot / pcf) while effectively maintaining other key properties such as reactivity.
Polyurethane chemistry is based on the reaction of isocyanates (-N=C=O) with an active hydroxyl
group (a polyol for example R-OH). A typical polyurethane foam contains both soft and hard
segments. The soft segment is typically comprised of the flexible polyol backbone. The hard segment
is made from diisocyanates and chain extenders. (Chain extenders are low molecular weight hydroxyl
or amine terminated compounds).
The full formulation of the system, including cell openers,
catalysts, etc., influences the balance of properties for a particular application.
The system that is discussed in this paper is based on a pre-polymer isocyanate. Pre-polymers (Part
A) are oligomeric liquid intermediates. An excess of either isocyanate or alcohol is enabled to react so
that the final pre-polymer is still in liquid form and contains reactive functional groups.
®™Trademark of The Dow Chemical Company ("Dow") or an affiliated company of Dow
Figure 1. General Pre-polymer reaction (MDI in excess)
The benefits of the pre-polymer approach for polyurethane in this application are many. An MDIprepolymer has lower “free” MDI, in the unreacted state, which eliminates the need for full ventilation
/ down draft booth during application; BETAFOAM™ only requires local ventilation. The prepolymer approach enables an easier means of controlling the reactivity of the foam since all of the
polyol is “pre-reacted” with the isocyanate. This leaves only the blowing reaction with water to
complete the formation of the foam. (See Figure 2). Additionally, the polyurethane reaction is
exothermic; using a pre-polymer lowers the heat generated during the final reaction, leading to better
quality foam. This particular formulation reacts to a temperature of < 90 °C (assuming raw materials
starting at room temperature). Pre-polymers also enable lower pressure (i.e. less expensive) dispense
systems to be used.
Part B in this case is comprised of the remaining raw materials required to make polyurethane foam
when combined with the pre-polymer (Part A). Part B consists of water, a tertiary amine catalyst, an
odor inhibitor, and a thickener. The water in Part B reacts with the “free” isocyanate in Part A,
generating carbon dioxide gas. The carbon dioxide generated by this reaction causes the product to
expand (“blow”) during the foaming process.
Figure 2. Polyurethane Foam Reaction.
BETAFOAM™ Renue is a new polyurethane foam that contains > 25% renewable content. The
petroleum based plasticizer of traditional BETAFOAM™ has been replaced with a plasticizer derived
from agricultural feedstock. This particular plasticizer was chosen due to its inherent stability. Also,
this material has no hydroxyl functionality which enables it to more effectively reduce viscosity of the
prepolymer, see Table 1. This lower viscosity material is easier to process during delivery to the OEM
and foam application in the plant.
Another benefit of Renue is its 30% reduction in density compared to traditional BETAFOAM™ (1.4
vs 2.0 pcf). This reduction in density is enabled through an increase in available isocyanate
functionality of the unreacted Part A. This increase leads to more CO 2 when the isocyanate reacts with
water, see Figure 2. The increase in CO 2 results in a lower density foam. Renue also has an optimized
mix ratio for part A and B to minimize density without impacting foam quality.
®™Trademark of The Dow Chemical Company ("Dow") or an affiliated company of Dow
Reactive Properties
The reactivity of a polyurethane system is important to an automotive OEM. Generally, faster
reacting systems are preferred so that the cycle time of an assembly plant, typically measured in
vehicles per hour, is not negatively impacted. In order to be considered viable in an OEM production
setting, the reactivity of Renue has to be as good as or better (faster) than traditional BETAFOAM™.
For this paper, the reactivity of traditional BETAFOAM™ and Renue is assessed through gel and tack
free times; two commonly used ways to characterize the reactivity of a polyurethane system.
Gel time is defined as the time between the discharge of the foam ingredients from the mixing head
and the point at which the foam has developed enough gel strength to resist light impressions and is
dimensionally stable. The surface of the material is probed with a tongue depressor until gelling is
observed. At gel point there is no “string” detected as the tongue depressor is removed from the
surface. The gel time of BETAFOAM™ Renue is measured to be less than 3 seconds.
Tack free time is defined as the time between the beginning of the foam pour and the point at which
the outer skin of the foam mass loses its stickiness or adhesive quality. After gel time, the surface of
the foam is touched with the flat surface of the tongue depressor. The time at which the foam is no
longer removed by the tongue depressor determines tack free time. Based on the foam data for gel and
tack free time (5 sec & 15 seconds respectively) of the traditional BETAFOAM™, it was determined
that these indicators of reactivity must be minimized to achieve the desired fast froth performance. Fast
froth foam reactions provide quick foam expansion inside the cavity and minimize material leakage
from cavity. The tack free time of Renue is measured to be less than 7 seconds.
Table 1. Key Properties of traditional BETAFOAM™ and Renue
Traditional
Property
Renue
BETAFOAM™
Prepolymer
Viscosity at RT (cps)
Free Rise Density
(pcf)
Sustainable Content
in reacted Foam
Petroleum Based
Plasticizer
Volume Expansion
%
Gel Time (s)
Tack Free Time (s)
1280
4500
1.4
2.0
< 25%
None
None
Yes
4800%
3400%
3
5
7
15
EXPERIMENTAL METHODOLGY
The proper quantification of a cavity filler’s acoustic performance in an automotive application is
critical. The reduced density of Renue is certainly valued by OEMs, but this value is greatly
diminished if its ability to block noise from entering the passenger cabin is compromised.
Insertion loss (IL) is an expression that has been utilized to characterize the NVH performance of
these various fillers in vehicle cavities. By definition, IL is the difference of the sound pressure level
down-stream in a channel by inserting a cavity filler treatment as compared to an empty cavity for a
given noise source. Historically, insertion loss has been utilized to compare different muffler
technologies within the automotive exhaust system.
®™Trademark of The Dow Chemical Company ("Dow") or an affiliated company of Dow
Figure 3. Historical Application of Insertion Loss in Exhaust System
Recently, insertion loss has been used to characterize the NVH performance of various cavity filler
options. In this application, a single cavity with the dimension of 3 x 3 x 10 inches has been introduced
to describe the vehicle cavities such as A, B, C, or D pillars and the rockers. By placing this empty
cavity between two rooms (See Figure 4), one representing the source room and the other being the
receiver, the sound pressure level in the receiving room is measured while the sound is simulated by
white noise, generated from a speaker in the source room.
Later the cavity filling solution is either baked or chemically-injected into the cavity and again, the
same methodology is utilized to measure the sound pressure level at the receiver room. The difference
between the sound pressure level of the empty cavity measured at the receiver room and the sound
pressure level measured while the cavity is filled is called the insertion loss.
ANECHOIC
RECEIVING CHAMBER
CHANNEL TEST FIXTURE
TEST CHANNEL
REVERBERATION
ROOM
LOUDSPEAKER
RECEIVING MIC.
SOURCE MIC.
Figure 4. Layout of Insertion Loss Suite (Courtesy of Kolano and Saha Engineers, Inc.)
This method was recently introduced by the Society of Automotive Engineers as SAE J2486-10.
However, the SAE method has some shortcomings when applied for specifically automotive NVH
assessments in the vehicle. Some of these shortcomings are:
- The simplicity of the cavity – In reality, the vehicle cavities such as the A, B, C, or D pillars and
rockers are built with several sheet metal layers and do not demonstrate simple behavior as
multiple parallel cavities exist.
®™Trademark of The Dow Chemical Company ("Dow") or an affiliated company of Dow
-
-
The simple cavity test methodology does not represent the upstream and downstream boundary
conditions. In reality, the cross sections of the vehicle cavities before and after the baffle (or
cavity sealing polyurethane foam) are very similar to each other and do not represent large
volumes of rooms described in the SAE methodology.
The complexity of the sound propagation through the vehicle cavities are not represented truly
with the SAE test methodology.
Due to these reasons, a new test methodology has been developed by Dow Automotive Systems
to compliment the SAE testing technique to predict the insertion loss of cavity fillers within the
proper cavity “boundary conditions.”
TRUE VEHICLE CAVITY INSERTION LOSS – NEW TEST METHODOLOGY
Historically, the SAE test methodology was limited to be utilized for a simple channel configuration.
However, the new technique described in this report provides a holistic perspective of the cavity NVH
performance in relation to the actual vehicle cavities with the right upstream and down-stream
boundary conditions. The new technique complements the existing methods of cavity NVH
characterization at the total body-in-white (BIW) level. This is a more relevant method to validate that
the material solutions are effective to achieve the desired NVH performance.
One intent of this study is to introduce the new insertion loss technique and use it to compare the
acoustic performance of traditional polyurethane cavity filling foam (2.0 pcf) vs. lower density
BETAFOAM™ Renue (1.4 pcf). The new insertion loss is measured within the body-in-white at the
down-stream of the cavities, with and without the cavity filler solutions. To develop the new
methodology, a Sedan BIW was chosen as the test subject. The insertion loss was developed for two
different locations, one at the A pillar and the other at the rocker. Figure 5 shows a step-by-step
method of how the A pillar was put together by adding layers of sheet metal upon each other. At the
end of this process, a smoke machine was utilized to check for air leaks.
Figure 5. A-Pillar Layering Process
When it was observed that no leakage existed, a Point Acoustic Simulator (PAS) was placed at the
base of the A pillar to inject white noise at a frequency range of 100 Hz to 8 kHz. This noise simulates
the wind, powertrain, or other potential noise sources traveling into the A pillar during vehicle
operation. To monitor the down-stream and upstream sound pressure level within the A pillar, two
microphones were placed at the base and upstream of the A pillar.
®™Trademark of The Dow Chemical Company ("Dow") or an affiliated company of Dow
Figure 6. Microphone (
) and Source Locations (
)
Using the same layer-building process, this was repeated on the lower rocker at the driver’s side.
Figure 7 shows the step by step process and the microphones placement inside the rocker to monitor
the sound traveling during this test. Figure 8 shows the PAS located at the front-face of the rocker
during the NVH performance characterization.
Figure 7. Rocker Layer Building Process
Figure 8. Rocker Noise Characterization Test Setup
TESTING AND MEASUREMENT
The first step to measure the insertion loss/noise reduction of the A pillar and the lower rocker is to
measure the background noise of both cavities without any NVH treatment. The background noise and
the noise reduction of the rocker and A pillar are provided in Figures 9 and 10 in the third octave band.
Note: Background noise is the noise reduction while the noise source was off. No Treatment is
when the noise source is on, yet there is no treatment in the cavity. It is possible for noise reduction to
be negative (i.e. < 0 dB) because there is no noise source present and the downstream microphone can
read higher than the upstream microphone.
This testing was done in a semi-anechoic room that was built in a production laboratory environment.
®™Trademark of The Dow Chemical Company ("Dow") or an affiliated company of Dow
During the course of this paper, the authors describe the outcome of the test both on the basis of NR
and IL to demonstrate that these values can be extracted from the raw acoustic data generated. It
should be mentioned that both NR and IL follow the same trend during the testing.
Figure 9. Background Noise and Noise Reduction of Empty Rocker
Figure 10. Background Noise and Noise Reduction of A Pillar
One of the objectives was to measure the insertion loss (through noise reduction) of traditional
BETAFOAM™ and Renue (2.0 and 1.4 pcf) to determine if the reduced density of Renue had any
negative impact on acoustic performance. First, the cavity was tested empty then the cavities were
filled with 2 pcf material (indicated by blue line). Later, the foam was cleaned and replaced with 1.4
pcf foam (indicated by black line). Figures 11 & 12 provide the noise reduction at the A pillar and
rocker locations.
®™Trademark of The Dow Chemical Company ("Dow") or an affiliated company of Dow
Figure 11. PU Foam (2.0 and 1.4 pcf) Noise Reduction at A Pillar
Figure 12. PU Foam (2.0 and 1.4 pcf) Noise Reduction at Rocker
According to Figures 11 and 12, the lower density Renue provide very similar noise reduction
performance as traditional BETAFOAM™. Both provide 35-42 dB of noise reduction.
Figures 13 and 14 below show similar insertion loss data provide the insertion of loss of Rocker and
A Pillar (removing the background noise and noise reduction without treatment). Similar insertion loss
results are achieved with both traditional BETAFOAM™ and lower density Renue.
®™Trademark of The Dow Chemical Company ("Dow") or an affiliated company of Dow
Figure 13. PU Foam (2.0 and 1.4 pcf) Insertion Loss at A Pillar
Figure 14. PU Foam (2.0 and 1.4 pcf) Insertion Loss at Rocker
CONCLUSION
BETAFOAM™ Renue has effectively incorporated >25% sustainable content into a cavity sealing
polyurethane foam. Renue has also improved other properties, lower density and faster reactivity, that
are critical to an automotive OEM.
The new methodology utilized in this study not only compares the noise reduction of different cavity
filler solutions, but also the insertion loss performance. The data obtained from this paper indicates
that both polyurethane cavity filler solutions provide an average of 35-42 dB noise reduction
performance. It also indicates that the noise reduction performance of both traditional BETAFOAM™
and Renue are very similar. In other words, the reduced density of the Renue does not negatively
impact the acoustic performance when compared to higher density material. Finally, the new testing
methodology provides the noise reduction and the insertion loss of the cavity fillers in a proper
boundary condition within the true body-in-white and is an enhancement methodology to the SAE
cavity filler insertion loss test procedure.
®™Trademark of The Dow Chemical Company ("Dow") or an affiliated company of Dow
FOR ADDITIONAL INFORMATION
1.
Goldman, Al and Lilley, K., “NVH Improvement with Two-Component Polyurethane Foam.”
Proceedings of the Automotive Body Interior and Safety Systems, International Body Engineering
Conference, pp. 22-27 (1994).
2. Otto, D.J., and Hanley, J.L., “From Art to Science: A New Acoustic Baffle Material,” SAE paper
951245, for P-291. Proceedings of the 1995 SAE Noise and Vibration Conference, Traverse City,
MI, pp 95-101, May 1995.
3. Saha, Pranab and Myers, R.D., “Evaluating Acoustical Performance of Expandable Sealant
Materials,” SAE paper 930336, SAE International Congress and Exposition, Detroit, MI, March
1993.
4. Saha, Pranab and Myers, R.D., “The Need of a Standardized Acoustical Evaluation Method for
Cavity Fillers,” Proceedings of the Automotive Body Interior and Safety Systems, International
Body Engineering Congress, pp. 166-181, 1995.
5. Visintainer, Anthony and Saha, Pranab, “Acoustical Study of Cavity Fillers for Vehicle
Applications.” SAE paper 971931. SAE Noise and Vibration Conference, Traverse City, MI, May
1997.
6. Laboratory Measurement of the Airborne Sound Barrier Performance of Automotive Material and
Assemblies, SAE J1400, May 1989.
7. Pearson, Brad A., “New Low MDI Polyurethane Foam System for Acoustical Barrier Applications
in the Automotive Industry.” SAE paper 1999-01-1671. SAE Noise and Vibration Conference and
Exposition, Traverse City, MI, May 1999.
8. Billotto, Frank; El-Khatib, Ali; Lekovic, Huzeir and Pearson, Brad. “A New 1:1 Low MDI
Acoustical Roam System for Cavity Sealing Applications.” SAE paper 05NVC-162. SAE Noise
and Vibration Conference, Traverse City, MI, May 2005.
9. Weber, Philip and Hopton, Gregory W., “Characterizing the In Vehicle Performance of Expandable
Sealants Used as Acoustic Baffles.” SAE paper 1687, SAE International Congress and Exposition,
Detroit, MI, March 1999.
10. Siavoshani, Saeed J., “Evaluation of Cavity Fillers to Improve Vehicle NVH Comfort Quality.”
SAE paper 2008-01-0566, SAE International Congress and Exposition, Detroit, MI, March 2008.
11. Siavoshani, Saeed J., “NVH Experimental Evaluation of Vehicle Cavity Fillers to Improve Vehicle
NVH Comfort Noise.” SAE Noise and Vibration Conference, Chicago, IL, May 2009.
12. Siavoshani, Saeed J., “ACOUSTOMIZE™ - A Method to Evaluate Cavity Fillers NVH and Sealing
Performance.” SAE Noise and Vibration Conference, Grand Rapids, MI, May 2011.
®™Trademark of The Dow Chemical Company ("Dow") or an affiliated company of Dow
BIOGRAPHIES
Matt Asher
Matt Asher is currently the Technical Service and Development Leader for
Performance Solutions in North America. In this role, Matt is responsible for the
technical success and integration of the Performance Solutions portfolio in the NA
marketplace. This portfolio includes polyurethane foams, elastomers, brake fluids
and compressor lubricants. Matt began his career with the Dow Chemical
Company in 2001 working in Glass Bonding TS&D. In 2008, Matt was the
Technical Leader for the Automotive Fluids and Lubricants group. He assumed
his current role in 2011. Prior to 2001, Matt worked for PPG Industries, Inc.
where he developed automotive topcoat technologies. He has a Bachelor of
Science degree in Chemistry from Indiana University-Bloomington.
Allan James
Allan James works for Dow Automotive Systems as the market manager for
composites development in North America. Prior to his current role, Allan worked
in the automotive polyurethane development and implementation spanning many
applications. He began his career with the Dow Chemical Company in 1981 in
Research and Development. In 1990, he joined Dow Automotive working with
polyurethanes, epoxy resins, and vinyl esters. He has authored a number of papers
and patents with respect to thermosetting materials and automotive applications.
Allan serves as the vice-chair of the Society of Automotive Engineers (SAE) VOC
Committee. Allan has a bachelor of Engineering Science degree in Chemical
Engineering from the University of Western Ontario.
Ali El-Khatib
Ali El-Khatib is a Technical Service and Development Specialist for Dow
Automotive Systems. Ali’s focus has been in the area of cavity filling, acoustic
foam. Ali has led the formulation development of multiple BETAFOAM™
technologies, including Renue and BETAFOAM™ SR. Ali holds a Bachelors
degree in Chemical Engineering from the University of Detroit Mercy and a
Masters in Material Science and Engineering from Wayne State University.
Saeed Siavoshani
Dr. Saeed J. Siavoshani is currently a Technical Program Manager for LMS, A
Siemens Company and an adjunct professor at the University of Detroit Mercy. In
addition Dr. Siavoshani serves as the Chief Industry Advisor for SAE Professional
Development Seminars and Academies. Over the past two decades, he has worked
for the Dow Chemical company, General Motors Corporation and Ford Motor
Company as an NVH technical specialist. During his career, Dr. Siavoshani has
also worked on composite projects related to offshore oil and gas, infrastructures,
and pressure vessels and automotive systems including powertrain, body structure,
exhaust/induction systems as well as the interior and exterior of the vehicle. He has
also been instrumental in the development of new technology, notably the integrated Front of
Dashboard concept and Acoustomize, a unique method of analyzing and offering solutions to
automotive noise problems. He has also worked in the area of thermoforming utilizing electromagnetic field technology. Dr. Siavoshani has helped to build the infrastructure for the electric
vehicle battery pack including thermal management as well as reducing the weight of the overall
battery. He has been granted several patents and was presented the SAE Forest R. McFarland Award
in 2012 for distinction in professional development and education. Dr. Siavoshani has a M.S. in
Mechanical Engineering from Wayne State University and a Ph.D. in Mechanical Engineering from
Oakland University.
®™Trademark of The Dow Chemical Company ("Dow") or an affiliated company of Dow