Yopa Prawatya

Laboratory bench for the characterization of triboelectric properties of polymers

The use of polymers as materials for sliding machine components is due to their low cost, ease of manufacturing, as well as appropriate mechanical and thermal properties. The aim of this paper is to present the experimental bench designed for the study of the triboelectric charge generated in sliding conformal contacts between flat polymer materials. The experiments were performed with 4-mm-thick samples of polystyrene and 5-mm-thick samples of poly-vinyl-chloride.The normal contact force can be adjusted using an appropriate control system and measured by a force sensor (± 50 N). The translational back-and-forth motion of the samples is produced by a crank-shaft system that generates a sinusoidal translational speed profile, with amplitudes between 12 and 50 mm/s, for strokes of 36 to 60 mm. The distribution of charge at the surface of the samples is measured by the capacitive probe of an electrostatic voltmeter (± 10 kV). The experiments pointed out that this bench enables the evaluation of the non-uniformity of the electric charge accumulated on the sliding bodies and the study of the correlations that might exists between this charge and the external forces applied to the contact.

Influence of surface roughness on the tribo-electric process for a sliding contact between polymeric plate materials

Polymers are used in many industrial applications due to their good mechanical and thermal properties. Studies have shown that electrical insulators, such as the polymers, are generating electrostatic charge by frictional contact. This tribo-charging effect influences de sliding conditions, and the level of charge depends of several factors. The aim of this paper is to validate two paradigms: (I) the electrostatic charge increases with contact pressure; (II) the level of charge is influenced by the number of contact points on the surface. The tribocharging experiments were carried out with samples cut from two polymers: Acrylonitrile-Butadiene-Styrene, 5 mm x 15mm x100 mm, roughness: Ra = 0.4 µm; and Polyvinyl Chloride, 5 mm x 50 mm x 180 mm, with various roughness values: Ra = 3-12 µm and RSm = 150-350 µm. The modification of asperity density was accompanied by changes in the electric potential measured at the surface of the PVC samples. Thus, its average value V increased from -0.33 to -0.85 kV, and its maximum value Vmax, from -1.56 to -4.83 kV.

Surface-Electric-Potential Characteristics of Tribo- and Corona-Charged Polymers: A Comparative Study

The ability of polymers to acquire and retain electrostatic charges is valued in designing new equipment like electrostatic separators, electret filters, and powder coating devices. Several recent studies have pointed out the beneficial effect of electric charges on the lubricated contacts. The aim of this paper is to compare two physical mechanisms of electric charging of polymers: 1) triboelectric effect; and 2) corona discharge. The experiments are performed with 5-mm-thick samples of Acrylonitrile-butadiene-styrene, poly-vinyl-chloride, and polypropylene. The cartography of the electric potential is made using the induction probe of an electrostatic voltmeter. The tribocharging is done by back and forth movement of two polymer plates in conformal contact with each other (speed: 7 to 30 mm/s; constant normal force: 10 N). Uniform corona charging is performed by moving the sample in the space charge zone generated by a wire-type high-voltage electrode used in a triode configuration with the potential of the grid electrode set at 1 and 2 kV. The electric potential at the surface of tribocharged polymers is less uniform, but decays slower than that of corona-charged samples.

Comparison between the surface-electric-potential characteristics of tribo- and corona-charged polymers

The ability of polymers to acquire and retain electrostatic charges is valued in designing new equipment like electrostatic separators, electret filters and powder coating devices. Several recent studies have pointed out the beneficial effect of electric charges on the lubricated contacts. The aim of this paper is to compare two physical mechanisms of electric charging of polymers: triboelectric effect and corona discharge. The experiments are performed with 5-mm-thick samples of polystyrene (PS), poly-vinyl-chloride (PVC) and polypropylene (PP). The cartography of the electric potential is made using the capacitive probe of an electrostatic voltmeter. The tribocharging is done by back and forth movement of two polymer plates in conformal contact with each other (speed: 7 to 30 mm/s; constant normal force: 2 N). Uniform corona charging is performed by moving the sample in the space charge zone generated by a wire-type high-voltage electrode, used in a triode configuration, with the potential of the grid electrode set at 0.5 kV, 1 kV and 2 kV. The electric potential at the surface of tribo-charged polymers is less uniform and decays faster than that of corona-charged samples.

Statistical process control of the tribocharging of polymer slabs in frictional sliding contact

Besides the nature and condition of the surfaces in contact, several factors influence the triboelectric charging of polymer slabs in frictional sliding contact: pressure load and relative velocity between the two bodies, number of friction cycles, ambient temperature and humidity. This paper is aimed at pointing out the peculiarities of the statistic control of such a process. Thirty experiments were performed for the optimal combination of factor values (i.e., normal force: 10 N; sliding speed: 55 mm/s; number of sliding cycles: 10) that maximize the absolute value of the average potential at the surface of the tribocharged materials: 1600 kV. The capability index calculated from the experimental data was satisfactory and two Shewart charts were established for the statistical control of the process. Two out-of-control situations were simulated, in order to test the efficiency of the charts.

Optimization of continuous triboelectrification process for polymeric materials in dry contact

Triboelectrification (i.e., generation of electric charge by friction between two materials) is a complex process. Besides the nature and condition of the surfaces in contact, several factors can have an influence on charge generation: pressure load and relative velocity between the two bodies, number of friction cycles, ambient temperature and humidity, condition and type of material surface. This paper aims at demonstrating that associating the experimental response surface methodology and genetic algorithms is an effective technique for the optimisation of triboelectrification process. The quadratic model derived from the experiments is used in a genetic algorithm program to find the optimal combination of factor values (10 sliding cycles; normal force: 10 N; sliding speed: 55 mm/s) that maximize the average potential at the surface of the tribocharged materials: -1633 V. A final experiment confirmed the prediction of the genetic algorithm. The conclusions of this experimental study can be applied to the optimisation of industrial triboelectrification processes, and contribute to the reduction of the related maintenance, energy and raw-material costs.

Triboelectrical charge generated by frictional sliding contact between polymeric materials

The polymers used regularly in mechanical assemblies are brought up in relative sliding. The electrostatic charges generated in these functional conditions are merely known. Many factors are involved in the triboelectric charging process: normal load, the sliding velocity. The aim of this paper is to analyse the influence of these factors in the repartition and evolution of the electric potential at the surface in contact. The tribocharging experiments are carried out with samples cut from three polymers: sample A (5 mm x 15 mm x100 mm) from Acrylonitrile Butadiene Styrene (ABS) or Polypropylene (PP), and sample B (5 mm x 50 mm x 180 mm) from Polyvinyl Chloride (PVC). The normal load is set to four values in the range 2 to 14 N, and the sliding velocity is varied between 70 and 122 mm/s. The results point out that the variation of relative velocity between samples is not changing the average potential for the sample B. The surface potential has a linear increase with the normal load.