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Abstract. This research focus’ on the finding of the suitable amount of filler that need to use in formulation of this rubber bearing base isolation system. This study used the five formulation with the different amount of filler for every formulation. One formulation, the samples was been mold into three tests sample that were tensile, hardness and resilience. The samples need to be cured or vulcanized at 1500C for 23 minutes for every formulation. The filler used in this study was the carbon black filler with type N660. The tensile test was done to determine the ability of the sample in term of the elongation with the load at break. The hardness test, it was been done to determine the ability of the sample to resist load. This hardness was measured in the unit of IRHD. The resilience test was be done to determine the properties of the sample in term of rebound characteristics. The finding for this study was shows that, the high the loading of carbon black filler, the high the tensile strength of the sample and the high the hardness of the sample. In term of resilience, it was inversely proportional to the loading of the carbon black filler.
Rubber bearing was the new devices used to protect the high-rise building from collapse when the disaster such as the earthquake occurs. The rubber bearing used to absorb the vibration from any disaster. Even it cannot absorb the fully vibration, but at least, this devices can reduce the vibration and can avoid the failure to the building. As knowing, on this present day, the construction to the high-rise building very high in number. At the same time, the disaster increases day by day. This devices consists of stiffness bearing that was been installed on the foundation  .Besides that, the rubber bearing also known as vibrator isolators. This system was normally made from viscoelastic materials . This devices usually used in many application in order to minimize the vibration. Beside to be used on the high-rise building, this isolator also commonly used in the bridge design. Previous study said that, this isolator base system was produced from the combination of the rubber with the other materials to make it more realistic and improve the devices ability.
Recently, the used of the rubber bearing devices is known over the world. But the previous user of this devices found that the main materials that was used to produce this isolation devices showing many bad effect in the long time of use and also the devices was not give full satisfied character as been inspected . The common weakness of the rubber was the crosslink between the chain. This was been proof when it was been attack by the huge external force, the chain was made the crosslink broke up . The real commonly affect was the aging of the rubber itself. Due to this problem, this study was conducted to search for the solution so that this devices can be improve. Since this recent time, the disaster happens without inspected, so the improvement to this base isolation devices was important .
There were several types of base isolator system that has been used in the construction or building. The most famous of base isolation system were two types of rubber bearing that are high damping rubber bearing (HDRB) and lead rubber bearing (LRB) . Previous study shows that HDRB have ability to make up the time period shift and also the energy dissipation. In this rubber bearing the combine compounds are layer of the rubber and some steel plate that was bonded by the vulcanization. The base isolation system should achieve the viscous damping for about 10% so that it can be used as the high damping rubber bearing. There were two types of rubber bearing that were filed rubber bearing and the unfilled rubber bearing, filled rubber bearing and unfilled rubber bearing . Filled rubber bearing is a rubber compound with addition of the filler such as carbon or non-carbon filler. The example for the carbon filler was carbon black. This type of filler commonly used in the rubber compound. The non-carbon filler, the examples are silica and calcium carbonate. These fillers was be grouped as the whitening filler. The function of the filler was to change the properties of the rubber compound in the term of dynamic properties for the modulus and the hysteresis. Unfilled rubber bearing is the rubber compound without the addition of the filler. By using this unfilled rubber bearing, the application for the structure will be limited because there were many weakness since the filler can give more improvement to the application for the structure.
The main materials used to produce compound rubber bearing are natural rubber, filler carbon black, zinc oxide as activator, streacid acid as co-activator, antioxidant, and sulfur as a crosslink reagent. Natural rubber is a flexible and been used successfully in engineering requests for 150 years, and stay the preeminent elastomer for springs and mountings. Natural rubber was selected because it occupies a comparable locale alongside stare to rubber springs as spring steel does alongside metal springs Most of the times rubbery materials are utilized to manipulation and mitigate the unwanted level of vibration and surprise . In rubber industry, one of the important reinforcing filler is Silica (SiO2) . Nitrile rubber is the type of rubber that was commonly used in the production of the rubber compound. This type of rubber was being mixing with the natural to make this rubber bearing will be more good condition. This nitrile rubber (NBR) had been used for the past 50 years. Nitrile rubber is the type of rubber that was commonly used in the production of the rubber compound. This type of rubber was being mixing with the natural to make this rubber bearing will be more good condition. This nitrile rubber (NBR) had been used for the past 50 years .
Carbon black was the famous filler that been used as filler in the filled rubber bearing. There were several type of the carbon black such as N220 (ISAF black), N330 (HAF black), N550 (FEF black), N660 (GPF black) and MT (medium thermal) black. It can used to boost the mechanical and the dynamic properties of the NR. The modulus and the abrasion resistance also can be increase. Beside the carbon black filler, there was other type of filler that was commonly used in the industry. These types of fillers were known as non carbon filler that was consists of silica, calcium carbonate and magnesium silicate . Among of this non carbon filler, the commonly used was the silica. The differences between the silica and carbon black were in the term of level reinforcement. In order to avoid the rubbery polymer from slipping due to the application of stress the vulcanizing agent that function as the crosslinking is needed. This phenomenon was called as vulcanization. Based on the previous study, this process will increase the forces and at the same time will decrease the permanent deformation after force is remove. This process occurs by added crosslink to the polymer network. There were several type of materials can be acted as the cross linking reagent such as sulfur, metal oxide, and also the peroxide. The most commonly used of vulcanizing agent was the Sulfur. In 1839, the process of sulfur vulcanization of rubbers was invented by Charles Goodyear and as a result of his discovery the rubber industry was explosively developed to this day .
2. Methods of research
In this paper work, there were various types of materials had been used in this laboratory work. Due to the previous study done by the researcher, it showed that the main materials to produce this rubber isolation system compound are the natural rubber, nitrile rubber, carbon black (filler), sulfur and the zinc oxide. The other materials also had been added to improve the ability of the rubber compound itself. The natural rubber that was used is the fresh rubber from the factory after run through the process. The natural rubber used for this work was from the faculty of applied science that was produced by the Lembaga Getah Malaysia (LGM) that located at the Sungai Buloh Selangor. The natural rubber that was used in the sample was the type L. Meanwhile, the type for the nitrile rubber used was CBR.
Carbon black was the particle used in this rubber compound to be function as the filler. This carbon black was in the form of powder. There were various types of carbon black that commonly used for the rubber research. For this study, carbon black N660 was used.
Sulfur was used in this rubber compound due to its function as crosslink reagent. In the rubber compound formulation, the zinc oxide will act as activator. Besides that, this material will make the rubber compound more efficient. This zinc oxide can be in the powder form. The samples preparation for this work is from the mixture of the natural rubber and the other particle with different percentage of the carbon black filler. These samples had been vulcanized at temperature of 1500C. Five samples had been prepared for the testing of this project. To produce this rubber bearing, the materials on the table below had been used. Table 1 shows that, the formulation for the samples of this laboratory work.
Table 1. Formulation for samples
|No of sample||1||2||3||4||5|
|Natural Rubber (SMR L)||50||50||50||50||50|
|Nitrile Rubber (NBR medium ACN) (Krynac 833)||50||50||50||50||50|
|N660 (GPF black)||20||30||40||50||60|
In order to get the influence of the carbon black filler, several test need to be done. In this paper work, the rubber bearing sample was tested with three different tests that were tensile test, hardness test and the resilience test. The tensile test will start with the cutting the sample from compression machine into the dumbbell shape. This process was done by using the tensile sample cutter machine. After the sample been cut into the dumbbell shape, the centre and the thickness of the sample need to measure and labelled. After that, the sample needs to be attached at the tensile machine using the clipper. Then the test was run and stop immediately after the sample was cut up.
The rebound resilience was been held by used the sample with the circular shape. The sample was labelled with sample one and sample two. For every sample, the test was held for three times to get the average value for the rebound resilience result. This hardness test was held by using the hardness testing machine provide by the Faculty of Applied Science Uitm. This test was done by placed the sample on the hardness test machine. This test was done three times for every sample. The test was run on the center, right and left side of the sample to get the average hardness value for the sample.
3. Results and discussion
The tensile test was conducted by using five samples for every type of samples with different value of the carbon black filler. The result for this testing was analyze by the desktop that was connected to the machine itself. Figure 1 shows the result from the tensile test for the 80 g carbon black used in the sample formulation. The analysis result shows that the data for the highest elongation break for the sample was 681.27 % can withstand with the applied force of 217.78 N. Besides that, the testing result also shown the tensile strength for the sample used. The modulus for the sample at 100, 300 and 500 also being analyzed based on this tensile test machine. Figure 2 until 5 shows the result for the tensile test of 120 g until 240 g of carbon black filler. On Figure 2, it shows that the highest elongation break of sample was 726.50 % can withstand with the force of 190.89 N. From figure 3, it shows that the elongation of sample was 613.20 % that can withstand with force of 200.36 N. Meanwhile, figure 4 shows the elongation of sample was 638.97 % which can withstand with applied force of 160.15 N. Then, figure 5 shows the result of elongation for the formulation 5 with the elongation of 439.33 that can withstand with the force of 151.81.
FIGURE 1. Five samples of 20pphr (80g) carbon black filler FIGURE 2. Five samples of 30pphr (120g) carbon black filler
FIGURE 3. Five samples of 40pphr (160g) carbon black filler FIGURE 4. Five samples of 50pphr (200g) carbon black filler
FIGURE 5. Five samples of 60pphr (240g) carbon black filler
Comparison the effect of different carbon black loading due to the stress at 100%( M100), 300%(M300) and 500%(M500)
Figure 6 and 7 show that the effect of filler loading to the stress of M100 and M300. It shows that, loading or amount of carbon black filler 60 pphr was the optimum value which gives the high stress to the rubber bearing sample. Beside the 60 pphr of carbon black filler, it shows that the 50 pphr carbon black filler is the best option if compare to the 20 pphr, 30 pphr and 40 pphr itself. Based on the Figure 6, the high loading of black filler that was 60pphr had highest value of stress that was 4.69. Meanwhile, the lesser loading of carbon black filler was the lowest stress was 1.71. Three of sample that were 30pphr, 40pphr and 50pphrt the value for the stress was 1.78, 3.18 and 2.83 respectively. Figure 7, the high loading of black filler was 60pphr had highest value of stress, which was 12.39. Meanwhile, the lesser loading of carbon black filler was the lowest stress was 5.14. Three of sample that were 30pphr, 40pphr and 50pphrt the value for the stress was 5.75, 9.77 and 8.73 respectively.
FIGURE 6. Effect of filler loading to the stress at 100% FIGURE 7. Effect of filler loading to the stress at 300%
Figure 8 shows that the effect of filler loading to the stress of M300. It shows that, loading or amount of carbon black filler 60 pphr was not applicable for modulus 500 to the rubber bearing sample. Beside the 60 pphr of carbon black filler, it shows that the 50 pphr carbon black filler is the best option if compare to the 20 pphr, 30 pphr and 40 pphr itself. Based on the Figure 8, the highest loading of black filler that was 60pphr, there was no stress modulus.
Meanwhile, the lesser loading of carbon black filler was the lowest stress, 12.64. Other three samples that were 30pphr, 40pphr and 50pphrt showed the value for the stress was 12.68, 17.89, and 15.43 respectively. From the result, it shows the data for sample of 50 pphr might be some mistake since the modulus should be increase by the increasing of the carbon back filler. This might happen because of some mistake during producing this sample.
FIGURE 8. Effect of filler loading to the stress at 500%
Comparison the effect of the carbon black filler to the elongation @ break and load at break
Based on the graph below, we can see that, the increasing in the carbon black filler will caused the decreasing of elongation or breaking the rubber bearing sample. This was happen because when the rubber content in the mixture was decrease, it will reduce in the elasticity of the sample. One of the rubber properties was elastic. So, when the volume was decrease and replace with the filler, the elasticity of sample will reduce directly. For this 20 pphr (80 g) of carbon black, the results show the average for the elongation can be stand by the sample was 628.57 % from the actual length of sample at average load of 199.4 N. The length of the elongation was inversely proportional to the load of break.
For the 30 pphr carbon black sample, the elongation of break was 635.63 % with the load of break 185.32 N. If compare to the 20 pphr sample, the 30 pphr sample result not applicable since the result of elongation should be less than 20 pphr sample. Then for the 40 pphr carbon black, the elongation of break and the load of break were 547.70 % and 197.53 N respectively. Meanwhile, for the 50 pphr the elongation was 587.43 % and load at break was 174.44 N. Lastly, for 60 pphr of carbon black, the elongation was 416.80 % with load of break at150.83 N. The elongation of the sample was corresponding to the force applied to the sample during the testing. From the graph above, the elongation for the 50 pphr of filler was high than 40 pphr, but it should be otherwise. This was happen maybe during the producing of sample; incorrect of weighing of filler might happen.
FIGURE 9. Effect of filler loading to the elongation at break FIGURE 10. Effect of filler loading to the load to break sample
Effect of the carbon black loading due to the tensile strength
The graph below shows that the values of the tensile strength decrease by the increase in the filler amount in the sample formulation. Based on the theory of the research, the tensile strength graph should be in the S- curve graph. From the graph, the highest tensile strength for the sample was at 20 pphr carbon black with the value of 21.04 MPa. Meanwhile, the lowest tensile strength for the sample was at 60 pphr with the 15.49 MPa. The optimum value of tensile strength was at carbon black loading of 40 pphr that was 19.74 MPa. The other two samples that were at 30 pphr and 50 pphr got the tensile strength of 18.89 MPa and 17.82 MPa respectively. The values for the 20 pphr of carbon black filler should be lower than 30 pphr carbon black filler. The result for the 20 pphr of carbon black filler has some mistake. The 40 pphr carbon black filler was the optimum loading to get the better tensile strength for the rubber bearing samples.
FIGURE 11. Effect of carbon black loading to the tensile strength
Due to the ASTM, hardness was measured based on specified condition as the resistance to surface indentation. The test was done by taking the average of measure on three place to the sample that were at centre, right and left side of the sample. The test was being conducted based on the ISO 48 as a guideline. Figure 12 shows the best loading of the carbon black can be used as filler in the rubber bearing formulation was 60 phr. The hardness value for this 60 pphr carbon black was 81.83 for sample 1 and 81.67 for sample 2. The lowest hardness was the 20 phr of carbon black sample that was 47.17 for sample 1 and 47.5 for sample 2.Meanwhile the median hardness is 70.5 and 72.37 respectively for the sample with 40 pphr of carbon black for sample 1 and sample 2.
For the sample of 30 pphr the hardness was 51.5 and 51.83 for the sample 1 and sample 2 respectively. Then for the 50 pphr for sample 1 and sample 2, the value of hardness was 66.0 and 67.67 respectively. Besides that, the bar chart also shows the hardness of the rubber bearing increase when the carbon black filler increase, but at 50 pphr the hardness of the rubber bearing decrease. Based on the previous study, the hardness of rubber bearing wills increase by increase the loading of the filler.
Figure 12. Bar chart for hardness
This test was run due to the ISO 4662. The result for this test can be calculated based on the following formula:
Rebound resilience (%) = [ 1- cos (θ – σ2)]/[1-cos (Ф-σ1)] x 100
Where: θ = rebound angle, Ф = angle of drop (45), σ1, σ2 the damping correction for rebound and drop angle respectively.
For this project, the study was just to determine the effect of the filler loading to the rebound properties. Based on the previous study, the resilience of the rubber bearing should be inversely proportional to the filler loading. This was because the high the loading of filler, the high the damping of the rubber bearing. Based, on the bar chart below, the resilience value for the 20 pphr carbon black was 57.93 % for sample 1 and 57.59 % for sample 2.
The lowest resilience was the 600 pphr of carbon black sample that was 35.56 % for sample 1 and 38.76 % for sample 2. Meanwhile the median resilience was for the sample with 40 pphr of carbon black that was for sample 1 and sample 2 with 46.36 % and 47.46 % respectively. For the sample of 50 pphr the resilience was 43.75 and 41.24 % for the sample 1 and sample 2 respectively. Then for the 30 pphr for sample 1 and sample 2, the value of resilience was 52.04 % and 49.79 % respectively. Due to the bar chart, the result was satisfied the theory from the previous study. The lower loading of filler was give the high resilience compares to the high loading of filler.
Figure 13. Bar Chart for Resilience Result
From the result, it can conclude that the highest loading of carbon black filler used in the rubber bearing formulation give the good effect to the sample as base isolation system in the tensile strength, hardness and rebound resilience. Based on the graph of the tensile strength, the final data for the 20 pphr sample might be wrong because it was high than other samples. This was might because the mistaken during weighing the materials of the formulation.
Besides that, for the hardness result, the hardness of the sample increase directly proportional due to the carbon black filler loading but, due to the graph of the hardness, at carbon black loading 50 pphr, the hardness was decreased. That should not be to happen. That might had been some mistake to the sample. The mistake that possible can be was the exchanges of the sample during the compressing stages.
For the last result of this study, the graph shows that the resilience results decrease by the increasing of the carbon black filler. The lower carbon black filler that was 20 pphr give the high percentage of the rebound resilience that was around 60 % compare to the high loading of carbon black filler that was give around 40 % rebounded resilience. From this result, it can be conclude that, the high loading of filler give high damping to the sample.
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