performance appraisal of a rubber-metal … · performance appraisal of a rubber-metal spring...

Journal for Technology of Plasticity, Vol. 39 (2014), Number 1

*Corresponding author’s email: [email protected]

PERFORMANCE APPRAISAL OF A RUBBER-METAL SPRING

Abhijit Mukhopadhyay, Suman Nihar

Mechanical Engineering Department, Jadavpur University, Kolkata-700032, India

ABSTRACT

Spring is an elastic element that deflects under the action of load and returns to its original shape when the load is removed. Rubber-metal springs are assemblies of rubber blocks and metal plates joined in series. The rubber and metal plates may joined by vulcanization or they may have only the free contacts. In this paper a free contact case has been considered. One of the most important properties of spring is that it can absorb shocks and vibrations. Rubber-metal springs are good shock absorber as they possess elastic and damping characteristics simultaneously. They can work individually or in combination with pure metal springs. Some of the most important applications of rubber-metal spring are observed in railway buffer springs, draw gear, buffer springs in elevator, air-craft landing gears and so on. The present paper researches on reducing hysteresis by using rubber- metal spring in place of metal spring. Data have been recorded to compute accumulated energy, released energy, absorbed energy and finally hysteresis. Experimental results show that hysteresis in rubber- metal spring is lower than that in pure metal spring. Keywords: Rubber metal spring, rubber, hysteresis, disc spring 1. INTRODUCTION Springs are very suitable mechanical components to absorb shock and vibrations. Conditions of high vibration and shock in automobiles, railway vehicles, heavy machinery, pipe suspension systems at power plants and steel plants are the common phenomenon in engineering. Springs are thus used to cope up with those problems. Rubber being an elastic medium is the most universal material used for vibration damping. Rubber elements also absorb considerable amount of overloads for a short time without suffering any damage. During dynamic loading rubber converts the absorbed energy into heat by internal molecular friction. This phenomenon is known as

30


damping and is continuous. This property is particularly helpful when shocks have to be reduced quickly. In rubber-metal spring, both rubber and metal plates are to be joined systematically. Such assembly of rubber and metal can be accomplished in various ways [1]. It is also possible to use disc springs or Belleville springs in place of metal plates. Disc springs give wide variety of load-deflection curves not readily obtainable with conventional forms of springs [2,9]. Several information on rubber metal springs are available in different literatures [3-9]. Present paper researches on the comparative studies of rubber-metal spring with pure metal spring. EN-19 and EPDM rubber have been utilized for the purpose. It is also needless to mention that research on shock absorbing capacity of rubber-metal spring is the most potential area in engineering. 2. RUBBER METAL SPRING Rubber-metal springs are conveniently used in road and railway transport vehicles. Over metal springs they have the advantage like reduced weight, reduced cost, improved absorbing and damping capacity of shocks and overloads. In railway vehicles rubber-metal springs are used as primary and secondary suspensions, elastic supports of aggregates, buffers and draw gear applications [10]. Rubber-metal springs at railway vehicles are used for primary and secondary suspensions and elastic supports of aggregates. A specific application of rubber-metal springs in railway vehicle is to maintain wagons connection in a train. This is known as the buffing and draws gear. The railway vehicle suspension represents an elastic connection between vehicle parts and it provides the stability and comfort during the ride as well as suppresses vibration and noise.

2.1 Buffing and draw gear of railway vehicle The buffer gear maintains mutual distances between railway vehicles in a train. Their properties are of the crucial influence on transferring and reducing impact loads by which stability and safeness of railroading and maneuver are affected. The draw gear of railway vehicle transfers the traction force from a locomotive to wagon in a train. The draw gears are subjected to change in very large axial force. Thus, the elasticity of the draw gear as well as its shock absorbing capacity is the important characteristics to be considered.

Fig.1- Draw gear with rubber-metal spring

31


3. RUBBER HYSTERESIS During the compression and subsequent load relaxation of any viscoelastic material an interesting phenomenon, hysteresis, is observed [11]. Figure 2 shows a typical load-elongation curve for rubber. The clockwise loop, formed in between loading and unloading path, indicates the hysteresis. Hysteresis is the energy dissipation capacity of rubber. By virtue of this characteristic rubber can absorb shock and damp vibration which enables rubber to be used beneficially in rubber-metal springs and other engineering applications where shock loading and vibration are prominent [10, 12].

Fig.2 - Typical hysteresis curve of rubber

An important consequence of the unique load-deflection properties of rubber-metal is its ability to store large amount of energy and to release most of the stored energy on retraction. However, the loading path and unloading path never coincides. Hence, there is a loss of energy (hysteresis) which appears as heat and can lead to a damaging rise of temperature in unfavorable circumstances. Thus, a study on the hysteresis of rubber-metal spring is very important and this is the purview of the present paper. 4. EXPERIMENTAL WORK The load -vs.- deflection curves of rubber-metal spring assemblies have been obtained from the compression and subsequent load relaxation data. Universal Testing Machine has been utilized for this purpose. During both cycles the characteristic “load–deflection” has been recorded. Accumulated work (the work of compression) and absorbed work (energy) has been evaluated from the recorded data.

4.1 Specimen of the experiment

(a) Disc spring: It has already been mentioned that disc spring is used in place of circular metal plates. Disc springs are conically-shaped, washer-type components designed to be axially loaded.

0 10 20 30 40 50 600

5

10

15

percentage deflection

load

(in k

n)

hysterisis curve

32


Disc springs can be statically loaded either continuously, intermittently or dynamically subjected to the load cycle. They can be used singly or in multiples, stacked parallel, in series or in a combination thereof. A Belleville spring consists of a conical disc and looks like a dinner plate without bottom [8,13]. EN-45 steel has been used as the disc spring material and has been supplied by Technomax Engineering Pvt. Ltd., Howrah, India. Desired hardness of these springs in Rockwell scale is 38 RC and modulus of elasticity is 209 GPa.

Fig.3 - Disc spring

(b) Rubber washer: EPDM rubber washer has been used for the experiment. The rubber sheet has been supplied by NEL, Kolkata, India. EPDM (ethylene propylene diene monomer) is a type of synthetic rubber and an elastomer. The hardness of the rubber sheet is 80Å. EPDM rubber is emerging as a dominant elastomer in several engineering applications. The main properties of EPDM rubber are its outstanding heat, ozone and weather resistance. The resistance to polar substances and steam are also good. It has excellent electrical insulating properties. EPDM rubber is also visco-elastic in nature, that is, it exhibits both viscous and elastic characteristics during deformation [10].

4.2 Experimental framework Using a Universal Testing Machine (UTM), deflections of the assembled rubber-metal spring have been measured against known load. The loads are static and compressive in nature. All the experiments have been conducted in dry condition. Two set of assemblies have been used: one is purely metallic assemblies and the other one is alternate arrangement of metal and rubber. The springs have been placed between two flat platens. Loads in Newton have been fixed at 2800N, 4600N, 5300N, 7500N, 8200N. Corresponding deflection of the springs against each level of fixed load have been recorded. The deflections have been measured in both loading and unloading conditions. The load has been applied axisymetrically on the specimen. The lower platen is fixed and the upper one is movable in vertical direction. A small dial gauge indicates the deflections of the spring. Figure 4 shows the arrangement used in such experimentation [14].

33


Fig. 4 - Load – Deflection measurement in UTM

Throughout the test run the load and displacement, that is, the reduction in height values of the specimen have been recorded. These data have been utilized later on to find out various important values of rubber-metal as well as pure metal springs.

4.3 Spring assembly This has already been stated in the previous section that two types of assemblies have been used. One is purely metal disc springs and other one is the combination of rubber washers and metal disc springs.

(a) Combination 1: In this combination metal disc springs have been arranged in series. The arrangement is shown in figure 5 (a).

(b) Combination 2: In this combination alternate layer of rubber washers have been placed in between metal disc. The arrangement is shown in figure 5(b).

a) b)

Fig.5- Series arrangements of (a) pure metal spring and (b) rubber-metal spring

34


5. RESULT AND ANALYSIS In combination 1, the data have been recorded at five specified loads during loading and unloading conditions.

Table 1- Load-Deflection data for combination 1

Load (N) Deflection

during loading (mm)

Deflection during

unloading (mm)

2800 2.47 3.75

4600 4.30 5.05 5300 5.07 6.00

7500 6.25 6.50

8200 6.75 6.75

Then, force (N) was plotted against deflection (mm) on x-y scatter graph. These variables are important for finding work because work is expressed in N-mm (Newton millimeters). Thus, points were plotted in MATLAB and to find lines of best fit and to integrate the function to find the amount of work needed for compression and decompression, and the difference in values will indicate the amount of energy lost by the rubber-metal spring.

Table 2- Deflections in loading and unloading for combination 2

Load (N) Deflection in loading (mm)

Deflection in unloading

(mm) 2800 7.00 7.50

4600 8.00 8.50

5300 9.00 10.00

7500 11.25 11.50

8200 12.00 12.00 The graph (Fig.6) represents the recorded data. The graph contains points (taken off of the raw data), and then a line of best fit. One line represents the compression process, the other, relaxation. Both lines of best fit are third order polynomial functions, which will be used to find work. Experimental points of loading and unloading were fitted in a third order polynomial equation and high correlation factor ensures its adequacy.

The lines of best fit are as follows:

Compression: 1585.56 322.19 53.32 6.79 (1)

Decompression: 36365.65 24152.85 4978.75 352.89 (2)

35


Fig.6 - Load deflection curve for combination 1

Both fits are >99% accurate in regards to the raw data. This means that the average variance between data points and the line of best is less that a 1% offset. Therefore, the line of best fit can be considered to be a direct representation of the data collected.

Table 3 - Calculated values for Combination 1

Accumulated work (N-mm)

Released Work

(N-mm)

Absorbed Work

(N-mm)

Hysteresis (%)

21802.29 14126.26 7676.03 35.20

Similarly, in combination 2, data have been taken at five specified loads in both loading and unloading and points have been plotted in MATLAB and to find lines of best fit and to integrate the function to find the amount of work needed for compression and decompression and the difference in values indicate the amount of energy lost by the rubber-metal spring. Experimental points of loading and unloading (Fig.7) have been fitted in a third order polynomial and high correlation factor ensures its adequacy.

Fig.7 - Load deflection curve for combination 2

36


The lines of best fits are as follows:

Compression:y 42459.38 13093.35x 1235.04x 41.34x (3)

Decompresn: 108771 34371.8 3510.96 121.67 (4)

Table 4 - Calculated values for Combination 2

Accumulated work

(N-mm)

Released Work

(N-mm)

Absorbed Work (N-

mm)

Hysteresis (%)

28952.65 24501.53 4451.12 15.37

When rubber-metal specimen is compressed and then allowed to release subsequently it is observed that a fraction of energy which was put into the compressive specimen during loading is not recovered upon release of load. The energy required to change the original shape of the specimen that is the strain energy is obtained from the area under the compression (loading) curve. Similarly energy released during relaxation (unloading) is also obtained from the area under the unloading curve. The difference gives the amount of hysteresis.

Table 5 - Comparison between Combination 1 & 2

Combination 1 2

Hysteresis (%) 35.20 15.37

Comparing combination 1 and 2, one can see the difference of hysteresis. The hysteresis in combination 2 is lower than combination 1. As, combination 1 is consists of ten metal disc springs (arranged in series) and combination 2 is consists of rubber and metal that is why hysteresis in combination 2 is lower than that of combination 1. 6. CONCLUSION Graphs have been plotted with the experimental data of applied compressive load and corresponding deflection of springs. Curves for both the loading as well as unloading paths have been obtained in this manner. MATLAB codes have been developed for the purpose and the equations of the corresponding curves have also been obtained. The equations have been used for the computation of accumulated work, released work, work absorbed and the hysteresis. The correlation coefficients in each case were very high (more than 99%), which indicates the acceptability of the experimental data. It has been observed that the hysteresis in rubber-metal spring is lower than that of metal spring. Hysteresis may lead to damaging rise in temperature and is not favorable in various applications. Thus, rubber-metal springs are suitable owing to their low hysteresis over metal springs.

37


MISCELLANIOUS

Acknowledgement: The authors are thankful to the faculty members, laboratory staff members and the students of Mechanical Engineering department, Jadavpur University, Kolkata, who at any point of time and at any capacity extended their co-operation towards this research work. The authors are also thankful to National Engineering Ltd.(Rubber), Technomax Engineering pvt. ltd. and IRC Industrial Research & Consultancy pvt. ltd. for providing the samples and extending co-operation in conducting experiments in their laboratory. REFERENCES [1] Stamenkovic, D., Milosevic, M.: Friction at Rubber –Metal Springs. Proceedings of the

11th. International Conference on Tribology (SERBIATRIB-’09), University of Belgrade, Faculty of Mechanical Engineering, Belgrade, Serbia, 13-15 May , 2009, pp. 215-219,

[2] Working manual of Key Bellevilles Inc, http://www.keybellevilles.com, pp. 1-53.

[3] Luo, Rk., Wu, Wx.: Fatigue failure analysis of anti-vibration rubber spring. Engineering Failure Analysis, Vol. 13, 2006. pp. 110–116.

[4] Mars, W.V., Fatemi, A.: A literature survey on fatigue analysis approaches for rubber, International Journal of Fatigue, Vol. 24, 2002, pp. 949–961.

[5] Persson, B.N.J.: On the theory of rubber friction”, Surface Science 401, 1998, pp. 445–454.

[6] Milkovic, D., Simic, G., Lucanin, V.: Experimental and analytical determination of rubber-metal springs elements characteristics. University of Belgrade, Railway Engineering Department, Belgrade, Serbia.

[7] Langa, M., Ouakka, A: Suspension Coil Spring and Rubber Insulators: Towards a Methodology of Global Design. Allevard Rejna Autosuspention-Sogeti Group, Research and Technology Development Center, Douai Cedex, France.

[8] Almen, J.O., Laszlo, A: The uniform-section disc spring. Trans ASME 58, 1936, pp. 305- 314,

[9] Dharan C.K.H., Bauman J.A.: Composite disc springs. Composites: Part A 38, 2007, pp. 2511-2516.

[10] Mukhopadhyay, A., Sarkar, M.: Flow behavior of EPDM rubber of different hardness values under axysymetric compressive load in dry working condition. Proceeding of the 12th International Conference on Tribology (SERBIATRIB’11), Faculty of Mechanical Engineering in Kragujevic, Serbia, 11-13 May 2011., pp. 56-64.

[11] Kalpakjian S., Schmid S.R.: Manufacturing Processes for Engineering Materials. 4th.Edition, Pearson Education,2009.

[12] http://www.madphysics.com/exp/hysteresis_and_rubber_bands.htm

[13] Bhandari, V.B.: Design of Machine Elements (2nd Edition). Tata McGraw-Hill Publishing Company Ltd, New Delhi, ISBN-13: 978-0-07-061141-2 (2008).

[14] Nihar S., Mukhopadhyay A., Nabi S.A.: Hysteresis in Rubber Metal Spring in Comparison with Steel Spring”, 4th. International & 25th. AIMTDR-2012, Dec. 14-16, 2012, Jadavpur University, Kolkata, pp. 210-215.

38


PROCENA KARAKTERISTIKA KOMBINOVANE GUMA-METAL OPRUGE

Abhijit Mukhopadhyay, Suman Nihar

Mechanical Engineering Department, Jadavpur University, Kolkata-700032, India

ABSTRACT

Opruga predstavlja elastični element koji se ugiba pod dejstvom opterećenja, odnosno vraća u svoj prvobitni položaj po njegovom uklanjanju. Sklop gumenih blokova i metalnih ploča spojenih u seriju čini tkz. guma-metal oprugu. Gumeni i metalne ploče mogu se spojiti vulkaniziranjem ili biti u slobodnom kontaktu. U ovom radu razmatran je slučaj opruge sa slobodnim kontaktom. Jedna od najvažnijih osobina opruga je da može da apsorbuje udarce i vibracije. Guma-metal opruge su dobri amortizeri pošto istovremeno poseduju elastične i prigušne karakteristike. Ove opruge mogu se koristiti kao pojedinačni elementi ili u kombinaciji sa čisto metalnim oprugama. Guma-metal opruge najčešće se primenjuju kao amortizeri i elementi vučno-odbojnog sklopa na železničkim vagonima, amortizeri kabina liftova, prigušni elementi sistema za sletanje aviona itd. Ovaj rad analizira mogućnost smanjenja veličine histerezisa pri eksploataciji opruga zamenom metalne opruge oprugom tipa guma-metal. Prilikom ispitivanja karakteristika obe vrste opruga, odgovarajući podaci su registrovani i korišćeni za proračun akumulirane energije, oslobođene energije, apsorbovane energiju i na kraju histerezisa. Eksperimentalni rezultati pokazuju da histerezis kod guma-metal opruge je niži nego za čistu metalu oprugu. Ključne reči: Guma metalni proleće, guma, histerezis, disk opruge.

performance appraisal of a rubber-metal … · performance appraisal of a rubber-metal spring...

Documents