It is widely used in modern industry. However, its mechanical properties are relatively poor, the coefficient of linear expansion is larger, the shrinkage rate is high, the processing is difficult, the hardness is low, the wear resistance is poor, and the thermal conductivity is poor. These defects have limited its wide application to a certain extent. Therefore, modification of pure PTFE can improve its comprehensive performance and expand its application in various fields.
Here, the glass fiber and carbon fiber reinforced PTFE are prepared, and the main mechanical properties and damping properties of are tested. The reinforced PTFE material is coated on the surface of the rolling bearing, and the absorption effect is also tested. It is hoped that this study will provide a basis for the development of PTFE composites in the field of vibration reduction.
| 1. Performance test of PTFE composite |
|---|
| 1.1 Mechanical Properties Test |
| 1.2 Damping Loss Factor Test |
| 2. Molding and vibration absorption of PTFE bearings |
| 2.1 Molding of PTFE bearings |
| 2.2 Experiment on vibraages/tion absorption of PTFE bearings |
| 3. Conclusion |
Different PTFE materials are prepared according to different conditions and working conditions, including pure PTFE, PTFE filled with glass fiber, PTFE filled with carbon fiber and PEEK. The glass fiber and carbon fiber are mixed evenly in high-speed mixer after the silane coupling agent treatment, then it is sintered at 380℃. The mass fraction of glass fiber, carbon fiber and PTFE is shown as the following table.
The mechanical properties of the composites l are tested, and the results are shown in the following table.
(1) The tensile strength and elongation of the composites decreases significantly after the addition of glass fiber; the tensile strength of PTFE added to carbon fiber is only a little lower than pure PTFE, and the tensile strength of composites does not decrease too much. The addition of glass fiber will impede the slip of the PTFE macromolecule chain. Too much glass fiber seems to be the stress concentration of the composite material, which makes the micro crack easier to germinate, which leads to the decrease of tensile strength.
(2) With the addition of glass fiber, the modulus of elasticity of PTFE increases gradually. The glass fiber filled PTFE makes the material hardness and modulus of elasticity increase, which makes the rigidity and brittleness of the material increase, thus the elongation is reduced. The hardness of carbon fiber filled composite material decreases and rigidity and brittleness of the composites does not increase substantially.
(3) The compressive strength and compression modulus of pure PTFE are the smallest. The addition of glass fiber and carbon fiber can increase the compressive strength and compression modulus of the composites. When the PTFE composite material is filled with 20% glass fiber and 5% carbon fiber, the compression strength is the most obvious, the compression modulus is larger, and the compression performance is better.
The three kinds of composite materials were pressed into standard samples. The size of the sample was as follows: the length is 180mm, the width is 10mm, and the thickness is 2mm. The damping loss factor of material is tested by half power bandwidth method, and the loss factor can be calculated as follows:
Where η is the loss factor of the sample, dimensionless. △f0i is the half power bandwidth, the unit is Hz; f0i is the resonance frequency, the unit is Hz; i is the number of resonances, 1, 2, 3...
In this paper, the PTFE composite material is coated on the surface of the rolling bearing, and the high damping loss characteristics of the PTFE material is used to isolate the transmission of the vibration from the bearing to the bearing seat. The implementation process of PTFE bearing is shown as follows. First, Mould A and Mould B are connected through the bolt, when the position of the bearing is fixed, the PTFE composite material is added to the mold. Then the composite material is pressed and molded with the Mould C. Finally, the Mould C is taken out, the l Mould B is rotated from Mould A, and the assembled bearings and their polymer materials are taken out with special tools. The composite bearing product is shown as shown in the drawings.
The experiment is carried out on the small bearing test bench. The vibration of the common bearing and PTFE bearing is compared. The test results are as follows:
From table 4, we can see that, the vibration reduction effect of PTFE bearings is reflected in the high frequency section. The absorption effect of pure PTFE is poor, only about 1dB. The addition of glass fiber can greatly increase the vibration damping effect of high frequency section; and can increase the damping effect of low frequency section at the same time; the absorption reaches 17dB. The absorption of PTFE filling carbon fiber can achieve 5.6dB at high frequency, but it will amplify low-frequency vibration.
From the above picture, it can be seen that the absorption effect of PTFE filling glass fiber is mainly reflected in the frequency band above 315Hz, especially in the frequency section above 800Hz, and the effect of vibration absorption is above 10dB. In addition, PTFE filling glass fiber also has a good performance in the low frequency section, and also has the 3dB damping effect at the main excitation frequency of the system.
The modification of PTFE was enhanced by filling glass fiber and carbon fiber. The following conclusions can be obtained through experiment:
(1) The addition of glass fiber can greatly reduce the tensile strength, elongation and elastic modulus of the composites, and increase the compressive strength and compression modulus.
(2) The addition of carbon fiber can reduce the tensile strength of the composites slightly, and increase the elastic modulus, compressive strength and compression modulus of the composites.
(3) The addition of glass fiber and carbon fiber can increase the damping loss of composite materials.
(4) The glass fiber and carbon fiber reinforced PTFE bearing have a certain absorption effect at the high frequency section, and the glass fiber reinforced PTFE bearing has the best damping effect.
(5) Glass fiber reinforced PTFE composites with reasonable structure can be used as damping materials in the field of vibration reduction.