Mathematical dependences are derived for determining air-cleaning efficiency as a function of the number of filter material regeneration cycles. Filter material with the optimum physicomechanical properties was determined based on an evaluation of regeneration and cleaning efficiency.As dust accumulates on filter elements, their maximum productivity and air-cleaning efficiency indexes and the reliability of the filter elements worsen.Dust removal and dust separation in filters take place on movement of dust-laden gas through the filter material, which is the basic working element in filtration units. For this reason, the productivity, air resistance, cleaning efficiency, and reliability of operation of the filter are greatly dependent on correct selection of the material.To increase the lifetime of filter materials and improve the filtration process, it is necessary to periodically regenerate the filter elements. Regeneration of filter elements consists of applying loads to the dust-laden filter material, which breaks up and separates the dust layer from the material. The most effective method of regeneration is the combination of mechanical shaking and pulsed blowing.We investigated the filtration properties of multiply, regenerable nonwoven bag filter materials of three types, where the linen-weave fabric shell material made of polyester fibres serves as the strengthening element. All samples of the filter bags had a diameter of 260 mm and a height of 400 mm. Their characteristics are reported in Table 1.Standard methods and instruments were basically used to determine the most important characteristics of the filter materials the porosity, thickness, breaking load, elongation at break, and rigidity. The thickness and porosity of the materials were determined with methods developed in the Laboratory of Filtration Systems at the Scientific Auto and Tractor Institute (SATI).The essence of the method of determining the porosity (Π, %) of regenerable nonwoven filter materials consisted of measuring the volume of liquid displaced by the fibres of the materials, and its porosity was calculated for known thickness of the material with the following equation in consideration of the abovewhere m d is the weight of the dry sample, g; m is the weight of the wet sample, g; ρ l is the volume density of the liquid, g/cm 3 ; V is the volume of liquid displaced by the sample, cm 3 . The higher the porosity of the samples, the lower the required excess pressure for separating dust and the more the pressure loss decreased. The results of measuring the physicomechanical properties of the filter materials are reported in Table 2.The filtering and regeneration properties of the filter materials were investigated on a bench unit for testing air cleaners according to GOST 800274.
The conditions of testing sewing thread do not correspond to the conditions of testing lap-sewn fabrics, which makes it difficult to predict their properties. For designing lap-sewn fabrics with given strength properties, the breaking load of sewing thread should be measured at a stretching rate of 100 mm/min.In measuring the breaking load of lap-sewn fabric, the strength indexes of the fabric as a whole are determined by testing samples. To successfully design lap-sewn fabrics with given strength properties, it is important to perform tests with standard methods. Respecting the extension rate provided by the standard is one condition for obtaining reliable and comparable results in tests. How important this parameter is can be judged by the results of testing the three kinds of lap-sewn fabrics represented in Fig. 1. The characteristics of these fabrics are reported in Table 1.As Fig. 1 shows, increasing the extension rate of the samples from 100 mm/min (standard rate [1]) to 200 mm/min significantly increases the breaking load both in the longitudinal and in the transverse direction. Nonrespect of the extension rate provided by the standard makes it impossible to objectively compare different lap-sewn fabrics.Lap-sewn fabric consists of lap fibres and the sewing thread securing it. The strength of the fabric is determined by the strength and interaction of the structural elements it contains. To effectively control the strength properties of lap-sewn cloth, it is necessary to have information on the role of the individual structural elements. This primarily relates to the sewing thread, since it absorbs the basic load when lap-sewn fabrics are stretched.Since the fabric consists of two structural elements, its overall breaking load can be expressed as the sum of two constituents:where P f is the breaking load of the lap-sewn fabric, daN; P t , P l are the breaking load provided by the sewing thread and lap fibres, daN.The indexes of the breaking load of the thread are given in the corresponding standards and technical documentation. However, it is necessary to note the testing conditions in which the results were obtained. There are no unified testing conditions for the different types of thread. GOST 6611.0-73 [2] recommends establishing the thread extension rate calculated so that the duration of the test before the thread breaks would be 10±1 sec. The extension rate for cotton yarn with approximately 9% elongation at break is 300 mm/min. These testing conditions are undoubtedly reflected in the results obtained.To confirm this conclusion, we tested the basic types of sewing thread used in production of nonwovens at a different stretching rate. Table 2 shows that an increase in the extension rate is accompanied by a significant change in the breaking load of the sewing thread. It should be noted that the extension rate affects the breaking load of sewing thread of different types to a different degree: for cotton yarn and polyester thread, this index increases by 10 and 4%, it decreases by 7% for polypropylen...
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