Development of a Polyurethane Engine Cover Using the Spray Method

Today, reducing emissions and noise in vehicles is among the top priorities for automotive manufacturers. Acoustic comfort is a quality parameter that determines customer preferences as end users, while noise is also a form of pollution that negatively affects human health. With this approach, all components inside the vehicle must have good noise absorption capability to achieve the desired acoustic performance throughout the vehicle. Numerous parts inside the vehicle cause noise, such as doors, engines, seats, and more. Considering that the engine is one of the parts generating the most noise in a vehicle, it is a critical expectation that the engine hood component on the motor has high noise absorption capability. The purpose of using an engine hood is to dampen the noise caused by the vehicle engine and provide aesthetic appearance. Within the scope of this work, an engine hood, an important component for the automotive industry, was produced using the spray polyurethane application method. The objective of the study is to make the produced engine hood lighter than its counterparts, provide higher acoustic performance, and obtain products with better thermal performance. In this context, the product obtained after the current study; its properties were examined and its acoustic performance was tested.

1. Introduction

With the development of technology in the automotive sector, the expected properties from materials are changing and the demand for innovative materials is increasing day by day. For automobile manufacturers, especially in recent years when internal combustion engines are being replaced by electric motors, different properties such as acoustic performance and thermal performance have gained importance in addition to lightness. With the decreasing engine noise, sounds that were previously not heard but existed in the vehicle are beginning to emerge, which will create a need for automobile parts with better acoustic performance, light weight, and ideal strength values. While meeting the expected properties of parts in vehicles, keeping material costs low is an expectation for automotive industry manufacturers. Accordingly, the use of plastic materials instead of traditional materials reduces product costs as well as production costs. Recently, engineering plastics and their combinations, as well as composite materials, are being preferred by taking on critical tasks for critical parts in vehicles. Polyurethane, an engineering plastic that has found significant use in many sectors for many years, is becoming increasingly in demand as applications where lightness takes center stage in vehicles increase. Polyurethane; due to its ease of forming in terms of mouldability, is an important polymer material for producers of different types of products. Polyurethane, obtained from the reaction of a polyol, an alcohol containing two or more hydroxyl (-OH) groups, with isocyanates containing multiple reactive -NCO groups; is used in many different fields such as textiles, medical, and automotive sectors. Within the automotive sector, polyurethane is preferred in many different parts such as interior trim components, NVH parts, steering wheels, armrests, gear knobs, sun visors, and more. The production of the engine hood component inside the vehicle using the spray polyurethane method would be a different approach as a product that is light and has good mechanical properties with high acoustic performance both inside and outside the vehicle.

2. Material and Method

Within the scope of this study; an engine hood was produced using the spray polyurethane production method and its properties were examined. Currently produced engine hoods are single-component or two-component products. In two-component products, the skin is generally a plastic surface followed by felt or sponge to complete production. Within the scope of this study, a two-layer engine hood is obtained with different forms of a single material. Since both the polyurethane skin structure applied via spray application and the polyurethane sponge structure are produced together in the same mold, the method does not require assembly operations. The engine hood, whose technical drawings are given in Figure 1, has high sound and heat insulation as well as good vibration damping values.

The production method consists of two stages:

1) Application of Spray to Mold Surface: Polyurethane spray material containing polyol and isocyanate as base raw materials at 750 g/dm3 is applied homogeneously to the mold with the aid of a robot arm at a specific thickness of 1.75 ± 0.25 mm. 2) Application of Polyurethane Sponge: Flame-retardant sponge at ≤60 g/dm3 is injected onto the mold on which spray has been applied. By adding the second component to the product in this way, the total density of the product is reduced. However, improvement in mechanical properties can be achieved at the same time. Figure 2 shows a cross-sectional image of the product.

3. Findings and Discussion

The spray engine hood produced during this study; was compared with a single-component polyurethane engine hood currently in production and sales. Surface images of engine hoods taken from a Leica brand stereo microscope are given in Figure 3. When examining the images in Figure 3, image a shows pores that are close together and closed, but image b draws attention to gaps between the pores. Since these gaps between the pores prevent the progression of noise, it is expected that the product produced with the spray polyurethane application method will have good acoustic performance. To determine the acoustic performance of the aforementioned products, tests were conducted in accordance with ISO 10524-2 standards using a Type 4206 Impedance Tube System (50 Hz – 6.4 kHz). Test results are shown in Figure 4. The graph in Figure 4 shows the change in the sound absorption capability of engine hoods at increasing frequency values. As seen in the graph, the noise damping values of the engine hood produced with the spray application method show superiority over existing engine hoods. Testing of the spray polyurethane engine hood under hot and cold humidity conditions and simultaneously on-vehicle testing are continuing.

4. Conclusions

Within the scope of this study, a dual-layer engine hood using two different forms of polyurethane with both skin surface and sponge structure made of polyurethane was successfully produced using the spray polyurethane method. Compared to its existing counterparts, the newly produced product; is 20% lighter, due to its porous structure has better acoustic performance, and due to its light weight will consume less energy on the vehicle and therefore can be said to be indirectly more efficient. Based on the findings obtained, it is evident that introducing new approaches to material production methods, moving away from conventional methods, will produce positive results.

Note

The developed product; is supported by Tubitak under the 1501 Industrial R&D Projects Support Program with project number 3151086.   Ebru Barut R&D Engineer and Materials Senior Engineer Pimsa Otomotiv A.Ş.           Cem Yiğit R&D Director Pimsa Otomotiv A.Ş.       Ömür Seyman General Manager Deputy Pimsa Otomotiv A.Ş.           Emre Gürtaş Powertrain Integration Specialist       References 1. Mugutkar, H. and Swetha, D., (2015). ''Static and Modal Analysis of Engine Cover for Different Materials'', International Journal of Scientific and Research Publications, Volume 5, Issue 9, ISSN 2250-3153. 2. Siano, D. ve ark., (2016). ''Automotive Materials: An Experimental Investigation of an Engine Bay Acoustic Performances'', 71st Conference of the Italian Thermal Machines Engineering Association, Turin, Italy. 3. Ibarra, D., (2016). ''Characterization of the Noise Reduction of Engine Hood: Experimental Method'', International Journal of Innovative Research in Technology & Science, Volume 4, Number 5, ISSN: 2321-1156. 4. Siano, D. et al. ''Experimental Acoustic Measurements in Far Field and Near Field Conditions: Characterization of a Beauty Engine Cover'', Recent Advances in Fluid Mechanics and Thermal Engineering, Napoli, Italy. 5. Akaydın, O. et al, (2013). ''Determination of Acoustic Properties of Noise Control Elements with Impedance Tube'', 10th National Acoustics Congress Yıldız Technical University Auditorium, Istanbul.