Guide to External Vibration. Our know-how for your applications

Transcription

1 Guide to External Vibration Our know-how for your applications

2 Basic knowledge Vibrators in Industry Atlas Copco external vibrators have wide and varied uses in most industries from mining to food. Vibrators solve many material handling problems and save money for industry through increased production and decreased labor costs. This brochure shows some of the most common applications for vibrators and suggests proper mounting locations for best results. Contents Basic knowledge... 2 Hopper discharging... 4 Form Vibration... 6 Vibrating Tables... 8 Screening Feeding Dust Collectors Circular vibration Linear vibration According to vibrator type, vibration is generated by: - the rotation of an eccentric shaft (circular vibration), - the reciprocating linear displacement of a weight (linear vibration). Note: the combination of two circular vibrations of same speed, intensity and opposite direction produces a linear vibration. Power sources There are electric and pneumatic vibrators. Vibrator types Electric vibrators: the shaft of an asynchronous motor bears eccentric weights at each end. Electric vibrators produce a circular vibration. Pneumatic vibrators producing circular vibration: compressed air flow rotates an eccentric weight in a circular chamber. Main categories: turbo-vibrators and ball-vibrators.

3 Power source selection Selection depends upon site power supply, safety, health regulation,working conditions a.s.o. Formulae for circular vibrations eccentric torque Mo = Po x ro Po = eccentric weight (kg) ro = rotation radius = distance between centre of gravity and rotation axis (cm) Mo = eccentric torque (kg x cm) Fc = Mo x 2 π n n = frequency (r.p.m.) Fc = centrifugal force (N) Working moment Mt = 2 x Mo Mt = working moment (kg x cm) Vibrator amplitude u = Mo x 10 Q Q = vibrating weight vibrator weight + load weight (kg) u = vibrator amplitude (mm) Total vibration amplitude s = 2 x u s = total amplitude (mm) Acceleration a = Fc Q a = acceleration (m/s 2 ) 2 Changing operating data R.p.m. and frequency of an electric vibrator are determined by the electric motor and inlet current specifications. Inlet current frequency (Hz) can generally be adjusted by changing the eccentric weight settings. Performances of pneumatic vibrators stated on data-sheets can continuously be changed according to air pressure and flow. Basic calculations The experience gives average and practical value for the acceleration to be applied to the load and calculation formulae for evaluation of the requested centrifugal force for the most important applications. The formulae hereafter mentioned lead to a rough evaluation of the requested vibrating equipment according to the installation and material data. They are valid for rigid structures only. Total amplitude s = 182,315 x Fc n 2 Q Electric motor nr. of pole pairs Speed (r.p.m.) n Fc = s x 0,559 x Q x n 9,81 1,000 s = total amplitude (mm) Fc = centrifugal force (N) Q = vibrating weight (kg) n = frequency (r. p.m.) For the classical applications, practical rules and calculation formulae have been established. They are summarized in the following pages. Important The recommendations and practical values hereafter mentioned have been established following real applications. All these indications lead to average solutions suitable for most of the current projects. They are not liable to engage Atlas Copco s responsability. Experience shows that a number of building details may influence the reactions of the structure under vibrations to a large extent. This is the reason why a thorough examination or a preliminary test of the structure is often recommended. ro 2 u S = 2 x u Guide to Vibration 3

4 Hopper discharging In handling bulk granular materials through hoppers ans silos the material often jams, bridges, rat-holes or sticks causing interruptions in proper outflow. These blockages generally cause stoppages throughout the entire plant. Substantial costs are incurred because of loss of production and increased labor required to clear the blockage. By means of vibrators, such problems can be solved easily and often quietly. Recommended vibrators Atlas Copco normal speed (3,000 r.p.m.) electric vibrators and Atlas Copco ball or roller pneumatic vibrators give best results. The required centrifugal force for promoting flow in bins and hoppers usually ranges from one twentieth to one tenth of the weight of material in the cone section. For example, a vibrator producing 2,500 N of centrifugal force is suitable for a hopper cone section containing 2,500 to 5,000 kg of material. Location One or several vibrators are required according to the size of the hopper. Fix the first one to the side with the smallest angle of inclination to the horizontal line; level: 1/3 of total height of conical part. Fit the vibrator horizontally on a 500-1,500 mm stiffener (4 channel iron). Clearance between the channel iron ends and hopper edges or hopper stiffeners must be 200 mm or more. The vibrator must be fastened with a safety wire. When several vibrators are fixed on the same hopper, the minimum vertical distance between two of them is 100 mm. On hoppers with rigid wall, the vibrator(s) must be fitted on vibrating surface(s), as shown on mounting sketch. Important Operate the vibrator only when emptying the hopper, otherwise the material will be packed intensively, causing considerable problem with discharging. Note: Air Blasters This device is fixed to the hopper wall and discharges high speed compressed air right into the material, turning it into a fluid state, and thus moving it. The complete installation is made of air inlet hoses, tanks which are fixed to the outer side of the hopper wall and discharge pipes going through the wall. Air blasters give the same results as vibrators. : 1/20 to 1/10 of weight of material in the cone section of the hopper. Recommended vibrators: normal speed (3,000 r.p.m.) electric vibrators. Fitting a Atlas Copco pneumatic or hydraulic vibrator on a truck improves discharging of materials (the vibrator is powered by the pneumatic or hydraulic circuit of the truck). A Atlas Copco pneumatic vibrator improves the emptying of a wagon. 4 Guide to Vibration

5 4 channel iron U (500-1,500 mm) Safety wire Bracket Motor vibrator Min. 2/3 (200 mm) Fig.1: Hopper cu feet (0,25-7 m 3 ). Position of the vibrator. 1/3 L 4 channel iron Safety wire 2/3 L L 2-5 ( mm) min. 2/3 (200 mm) 1/3 L Fig. 2: Hopper and silo> 250 cu feet (> 7 m 3 ). Position of the vibrators. 4 channel iron U-100 max. 6 (2,000 mm) Bolt Flat springs max. 6 (2,000 mm) min. 1/3 (100 mm) 2-5 (500-1,500 mm) Safety Wire Yoke 4 pcs hole should be done in the wall for vibration transmission Bracket Fig. 3: Hopper and silo of concrete or heavy sheet construction. Position of the vibrating device. Fig. 4: Hopper of wood construction. Position of the vibrator. Guide to Vibration 5

6 Form Vibration Vibration is widely used in the production of precast concrete elements, in order to obtain high strength, void free filling and good surfaces. The form can be placed on a vibrating source (vibrating table or trestle) or it can be equipped with vibrators. Forms for pipes, beams, single and double Ts, wall and floor sections are generally equipped with vibrators. Recommended vibrators For tables, trestles, beam forms and most other horizontal type forms Atlas Copco 3,000/6,000 r.p.m. electric vibrators and pneumatic vibrators are recommended. On vertical forms, high frequency pneumatic or electric vibrators are more suitable. Vertical pipe forms can be equipped with Atlas Copco 6,000 r.p.m. or high frequency electric or pneumatic vibrators. Rule of thumb: force requirement is one pound of centrifugal force for each pound of concrete (based on 3 inch slump). For drier concrete, more force is required. The calculation formula for a rough evaluation of the required centrifugal force is: Fc = K (M B), Fc = centrifugal force in N, M = form weight in kg, B = concrete weight in kg, K ~ = 5 for vertical forms (beams, walls) K ~ = 5 to 10 for horizontal forms, K ~ = 15 for vertical pipes. Required number of vibrators 1) Permanently fixed vibrators: each vibrating point is equipped with one vibrator. 2) Quick release type vibrators: the number of vibrators is lower than the total number of brackets (tunnel and long beam forms). 3) Precast concrete factory: each form is equipped with the required number of brackets. The required quantity of vibrators is: - the number of vibrators for the largest form, or - the number of vibrators for one casting. Location Horizontal forms : fix the vibrators on the stiffeners in a zig-zag formation. Minimum distance between 2 vibrators: l.5 m. If the form has several sections, each of them must get at least one vibrator. If the form width is more than 2.5 m, fix the vibrators on two rows - clearance between row of vibrators and form edge must be 14 of total width. If the form width is less than 2.5 m, fix the vibrators in the middle. On horizontal forms, the vibrators can be fixed on the long sides in order to facilitate mounting. On large forms for single or double Ts (height > 2m) fix the vibrators on two rows: 2/3 at the low level, 1/3 at the high level. Vertical forms: fix the vibrators on the stiffeners in a zigzag formation. Minimum distance between two vibrators: l.5 m. If the form height is more than 2.5 m, fix the vibrators on 2 rows, if it is more than 4 m, on 3 rows... : Fc = K (M B) Vertical forms: K ~ 5 Vertical pipe forms: K ~ 15 Horizontal forms: K ~ 5 to 10. Recommended vibrators: electric 3,000/6,000 r.p.m. for horizontal form - electric 6,000 r.p.m. or high frequency pneumatic vibrators for vertical forms. 6 Guide to Vibration

7 3 1,000 mm 5-8 1,500-2,500 mm 5-8 1,500-2,500 mm 3 1,000 mm 5-8 1,500-2,500 mm 5-8 1,500-2,500 mm Fig. 5: Vertical form for pipes. Position of the vibrators. Fig. 6: Vertical form: Position of the vibrators ,000 mm 5-8 1,500-2,500 mm ,000 mm 5-8 1,500-2,500 mm 5-8 1,500-2,500 mm Fig. 7: Horizontal form: Position of the vibrators. Fig. 8: Form for columns and beams. Position of the vibrators. Guide to Vibration 7

8 Vibrating Tables and Trestles for Form Vibration Vibrating tables and trestles are widely used in the production of precast concrete elements. The form is placed on the vibrating table or trestle and filled with concrete. The vibrations compact the concrete in a short time. Recommended vibrators Atlas Copco normal speed electric vibrators are most of the time used for this kind of applications. However, Atlas Copco high and low speed electric vibrators as well as pneumatic vibrators are suitable. The formula hereafter gives a rough evaluation of the required centrifugal force. - loose form Fc = K (Mt M B) - fixed form Fc = K (Mt + M B) I-profile with transversal stiffenings Rubber support Fc = centrifugal force in N Mt = weight of the vibrating part of the table or trestle (including vibrators) in kg M = weight of form in kg B = weight of concrete in the form in kg K = factor depending on concrete mix and form rigidity (average values: from 20 to 40). Fig. 9: Vibrating trestle with circular vibration. Position of the vibrator. Location In the case of circular vibration, the vibrator is fixed under the table plate or the trestle right under its centre of gravity. For linear vibrations, 2 identical electric vibrators must be fixed parallel to the vertical plan of symetry and at the same distance from the centre of gravity of the table or trestle. They must rotate towards each other (applications: light and small products casting). Table sheet Rubber support Frame Fig.10: Vibrating table with circular vibration. Position of the vibrator. : - Loose form Fc = K (Mt M B) - Fixed form Fc = K (Mt + M B) K ~ 20 to 40 Recommended vibrators: normal or high speed electric vibrators, pneumatic vibrators. 8 Guide to Vibration

9 Vibrating Tables: other applications In addition to concrete precast industry applications, vibrating tables are widely used in a large number of activities for compacting bulk materials in containers and drums. Vibration leads to reduced handling, freight and spillage costs. It helps increasing production through high speed automated filling, weighing and packaging operations. In the casting industry, vibrating tables are used for moulding and coring sand compaction. During vibration, bulk materials are turned to a fluid state practically without internal friction. The particles are moved, and air escapes as they rearrange themselves closer to each other. This usually occurs within a few seconds and leads to compaction ratios from 10 to 50%. The grid-top vibrating table is widely used in modern, automated, high capacity filling lines; this table has vertical supports that raise between roller conveyor rolls, thus lifting and isolating the container during vibration cycle. Tables can also be used for discharging containers and drums as well as for shake and fatigue testing of electronic and machine assemblies and many products and instruments. Within a few seconds, a vibrating table simulates the behaviour of goods on a crosscountry trip by rail, truck or air, thus enabling to check the accuracy of circuitry or reliability of assembly. Jolting of sheets of paper, veener sheets, nesting and orienting of various manufactured items are some other applications of vibrating tables. Recommended vibrators According to their size and applications, vibrating tables can be equipped with one or two Atlas Copco pneumatic, low or normal speed electric vibrators or one pneumatic piston vibrator. The calculation formula for a rough evaluation of the required centrifugal force is: - loose load Fc = K (Mt + 0,25 C) - fixed load Fc = K (Mt + C) Fc = centrifugal force in N. Mt = weight of the vibrating part of the table (including vibrators) in kg. C = weight of the load in kg. K = factor depending on application: moulding and coring sand compaction K ~ 30, bulk materials compaction K from 20 to 30, fatigue tests of components K ~ 100. Location See page 8. Table sheet Table sheet Rubber support Frame Rubber support Frame Fig.11: Vibrating table with circular vibration. Position of the vibrator. Fig.12: Vibrating table with vertical linear vibration. Alternative position of the vibrators. : - Loose load Fc = K (Mt + 0,25 C) - Fixed load Fc = K (Mt + C) K ~ 20 to 100 according to application. Recommended vibrators: Normal speed (3,000 r.p.m.), electric vibrators. Guide to Vibration 9

10 Screening Screening is another field of application for vibrators. Vibrating screens are mainly used in: - sorting material by size into different fractions (gravel and crushed aggregates for instance); - check screening (removing of core lumps and alien materials from moulding sand); - dewatering (twig and bark dewatering in the pulp and paper industry; dewatering of vegetables). Recommended vibrators Atlas Copco standard (3,000 r.p.m.) vibrators usually give best results. Required frequency is in inverse proportion with screen cloth opening (the larger the opening, the lower the r.p.m.). Note: Vibration amplitude The screen cloth opening size fixes the amplitude of vibration: the larger the opening, the greater the amplitude of the screen. With a cloth opening of 1 mm for instance, the amplitude should be 0.5 mm; it should be 2.5 mm for an opening of 30 mm and 6.5 mm for an opening of 100 mm. The centrifugal force and amplitude of the vibrators depend on cloth opening size and type of vibration. The rule of thumb for an inclined screen with a circular vibration is: the required centrifugal force must be 3 to 4 times the total weight of the screen (including the vibrators). For all screening installations, the manufacturer s recommendations are very useful. Location A vibrating screen consists of a frame, one or more screen clothes, a vibration unit and a spring mounting or suspension. The vibration unit is made of 1 or 2 vibrators. If the screen is equipped with one motor vibrator, (circular vibration), the screen must be declined 10o or more in order to promote a good flow of material on the screen cloth. If the screen is equipped with 2 identical vibrators (linear vibration), it may be horizontal. The vibrators must be positioned 45 o in relation to the screen so that the line of action of the vibration passes through the centre of gravity of the screen (including the vibration unit). According to the application, the 2 vibrators can be mounted either above, under or on each side* of the screen. The 2 vibrators must rotate towards each other. Note: Before fixing the vibrator(s) on a vibrating structure such as a screen, check that the suspension system is correctly installed and take the dynamic reactions of the structure into consideration. * In this case, distance between the vibrators makes synchronisation more difficult. : 3 to 4 times the total weight of thescreen (including the vibrators). Recommended vibrators: standard (3,000 r.p.m.). 10 Guide to Vibration

11 Spring suspension Screen cloth 10 Fig. 13: Vibrating screen with circular vibration. Position of the vibrator. Anchor plate Stiffenings Spring suspension or spring support Screen cloth 45 Fig. 14: Vibrating screen with linear vibration. Alternative position of the vibrators. Guide to Vibration 11

12 Feeding Flow of bulk materials from hoppers and silos is another handling problem in industry. Vibrating feeders promote a regular flow of material to conveyors, crushers, mills and other processing equipments. The shape of the hopper discharge opening has a significant influence on flow performance. The opening design must allow the pressure of material to be absorbed by the hopper. If not, a column of material will remain on the feeder, and more powerful vibrarors will be necessary. Recommended vibrators Atlas Copco low speed and normal speed vibrators give the best results the higher the feeder capacity, the lower the vibrator frequency. Electric vibrators (3,000 r.p.m.) are recommended when an accurate regulation of the flow is required. The required centrifugal force depends upon the feeder size. The average value is 4 to 7 times the total weight of the installation. Location The main parts of a feeder are a trough, spring suspension elements and one or two vibrators. If the feeder is equipped with one motor vibrator, it must be declined 15 at least. The vibrator is fixed under the trough so that the line of action of the vibration passes through the centre of gravity of the feeder. When equipped with 2 identical motor vibrators, feeders are designed to work horizontally. When installed in series, they allow long distance material transport. Furthermore a treatment can be applied during transportation (heating, cooling, dust cleaning... ). The two Atlas Copco motor vibrators must be fixed 25 to the horizontal, and the line of action of the vibration must pass through the centre of gravity of the feeder. Note: Material introduction on feeders. The material flow intake must be as constant as possible in order to obtain a good feeder efficiency. Any material build-up from hopper on the intake side of the feeder will reduce transport capacity. In a number of applications, vibration does not move materials or products; it keeps flow regular and prevents installation stoppage by clogging or blockage. Small Atlas Copco pneumatic vibrators are often used for this purpose: they work intermittently, and their control is either manual or automatic by sequence. The drawings hereafter show some usual applications. Vibrating feeders equipped with Atlas Copco normal speed electric vibrator. : Fc = K (Mc C). K ~ 40 to 70 according to application. Recommended vibrators: Normal speed (3,000 r.p.m.) vibrators. 12 Guide to Vibration

13 15 Spring suspension One Atlas Copco ball vibrator improves efficiency of this tin transportation system. Anchor plate Channel iron Fig.l5: Vibrating chute. Position of the vibrator. Working intermittently, a Atlas Copco pneumatic vibrator promotes a regular material flow in this pipe. Spring suspension or rubber support Stiffening Anchor plate Fig.16: Conveyor with linear vibration. Alternative position of the vibrators. One Atlas Copco ball vibrator avoids bottle blockage on this conveyor. Guide to Vibration 13

14 Dust Collectors Dust collectors help lowering air pollution level and improving working conditions. Vibration is required for 2 kinds of dust collectors: the fabric filter-bag type and the electrostatic precipitator. In the first type, all the dust is collected by the filter bags which must be cleaned at regular intervals. For this purpose, the vibraror shakes the bags intermittently and the dust falls from the bags into hoppers positioned below. Furthermore, vibrarors are often used to improve dust discharge and removal from collecting hoppers. In electrostatic precipitarors, the vibrarors are used to shake both wire and plate frame, thus moving the dust particles they hold. The dust falls into hoppers. In this case too, vibrators are often used to help dust removal from collecting hoppers during cleaning cycles. Recommended vibrators Atlas Copco normal speed electric vibrators (3,000 r.p.m.) are recommended for this application. The required centrifugal force is between 3 and 4 times the vibrating weight (i.e. filter elements + frame). Location A dust collector is made of an air-proof box including a hopper at its lower side and in which the collecting elements are suspended. All the filter elements are mounted on a common frame and stretched by springs. The vibrator is fixed on a channel iron which is mounted on the frame upper part. 4 channel iron should be positioned on the angle iron frame Motor vibrator Angle iron Spring suspension Note: For effectively clearing, the filter bags should be stretched Fig.17: Dust separator with filter bags. Fig.18: Dust separator with filter sheets. : 3 to 4 times the vibrating weight. Recommended vibrators: normal speed (3,000 r.p.m.) electric vibrators. 14 Guide to Vibration

15 Atlas Copco Vibration Electric Vibrators Pneumatic Vibrators Normal speed, ER type High speed, ER 7is type Turbo, EP type Ball, EB type Mould vibration Concrete Sand Materials compaction Discharging Hoppers and silos Dessanding Cleaning Filters Transportation Feeders and Conveyors Screening Screens Vibrators have many applications which fall outside the categories previously mentioned. This booklet can be used as a guide for quite a number of such cases. For suspended or spring mounted structures, choose the most similar listed application: tables, trestles, screens or feeders. In the same way, recommended Atlas Copco vibrators for bins, forms, hoppers are suitable for fixed structutes such as pipes, chutes... Guide to Vibration 15

16 Copyright Construction Tools GmbH, Essen, Germany. We reserve the right to change specifications without notice Photos and illustrations do not always show standard versions of machines. The above information is a general description only, is not guaranteed and contains no warranties of any kind. Committed to sustainable productivity We stand by our responsibilities towards our customers, towards the environment and the people around us. We make performance stand the test of time. This is what we call Sustainable Productivity.