Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F27—FURNACES; KILNS; OVENS; RETORTS
  • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
  • F27D25/00—Devices or methods for removing incrustations, e.g. slag, metal deposits, dust; Devices or methods for preventing the adherence of slag
  • F27D25/001—Devices or methods for removing incrustations, e.g. slag, metal deposits, dust; Devices or methods for preventing the adherence of slag comprising breaking tools, e.g. hammers, drills, scrapers
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
  • B01F35/00—Accessories for mixers; Auxiliary operations or auxiliary devices; Parts or details of general application
  • B01F35/10—Maintenance of mixers
  • B01F35/145—Washing or cleaning mixers not provided for in other groups in this subclass; Inhibiting build-up of material on machine parts using other means
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J2/00—Processes or devices for granulating materials, e.g. fertilisers in general; Rendering particulate materials free flowing in general, e.g. making them hydrophobic
  • B01J2/12—Processes or devices for granulating materials, e.g. fertilisers in general; Rendering particulate materials free flowing in general, e.g. making them hydrophobic in rotating drums
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B1/00—Preliminary treatment of ores or scrap
  • C22B1/14—Agglomerating; Briquetting; Binding; Granulating
  • C22B1/24—Binding; Briquetting ; Granulating
  • C22B1/2406—Binding; Briquetting ; Granulating pelletizing
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F27—FURNACES; KILNS; OVENS; RETORTS
  • F27B—FURNACES, KILNS, OVENS OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
  • F27B7/00—Rotary-drum furnaces, i.e. horizontal or slightly inclined
  • F27B7/14—Rotary-drum furnaces, i.e. horizontal or slightly inclined with means for agitating or moving the charge
  • F27B7/18—Rotary-drum furnaces, i.e. horizontal or slightly inclined with means for agitating or moving the charge the means being movable within the drum
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F27—FURNACES; KILNS; OVENS; RETORTS
  • F27B—FURNACES, KILNS, OVENS OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
  • F27B7/00—Rotary-drum furnaces, i.e. horizontal or slightly inclined
  • F27B7/20—Details, accessories or equipment specially adapted for rotary-drum furnaces
  • F27B7/2075—Removing incrustations

Definitions

• This invention relates to devices such as mixing devices and balling devices, in which to a moving surface is continuously fed a fine grained particulate material which adheres to the surface and builds up a material layer on the surface, e.g. on the surface used for balling of a balling disc, balling cone or balling drum, or the inner surface of a rotating mixing drum.
• a scraping device is normally used which periodically or continuously is posi ⁇ tioned at a short distance from the surface on which the material layer is formed, thus limiting the growth of the material layer by scraping adhering particulate material away from the surface.
• scraping devices are known from the literature and reference can e.g. be made to the French patent specifications Nos. 1,182,677 and 1,395,161 as well as the U.S. patent specification No. 3,316,585. The disclosure of these patent specifications is included by reference.
• Two common types of such scraping devices are the reciprocating scraper device which is moving parallel to the surface in question and which may comprise a comb-like scraping instru ⁇ ment which is moved to and fro along the surface with the ' .material layer, e.g. in a balling disc or balling drum.
• a rotating scraping device e.g. comprising an elongated shaft equipped with scraping instruments in the shape of protrusions from the shaft.
• a common type of the latter comprises scraping instruments consisting of flanges which extend radially outwards from the.shaft and along the shaft in the axial direction. These * flanges may be arranged helically in the axial direction. This is described in the U.S. patent No. 3,316,585 referred to above.
• said device is usually rotated so that the scraping instru ⁇ ments move in a direction opposite to the direction of the moving scraped surface with the material layer.
• the relative movement between the scraping instruments and the scraped surface normally produces a periodically recurring pattern of scraping marks, which means a permanen regular pattern or surface relief of recesses and pro ⁇ tuberances in the scraped surface caused by the interaction of the scraping device.
• the material layer is very thin or comprises several layers with different composition of which only the surface layer is intended to be removed, severe disturbances may al be caused if the scraping device when vibrating engages underlying parts of the machine or removes material which i
• WI intended to form a permanent layer on the surface.
• the scraped surface may be the inner surface of a cylinder, e.g. a balling drum, and the scraping device may be a comb ⁇ like device which is reciprocated in the axial direction.
• the comb-like device often comprises teeth coated with tungsten carbide and separated by interspaces. These teeth can produce sinus-shaped intersecting tracks in the surface forming a pattern of rhomb- or diamond-shaped protrudements in the surface separated by said tracks.
• a periodically recurring pattern of scraping marks is formed which has more or less " distinct wave-shaped recesses with the crests of the waves pointing in the axial direction.
• the increased power consumption may cause a decreas of the rotation speed of the scraping device. If this decrease of the rotation speed is large enough, the scraping device will come out of phase with the pattern in the scrapi surface and thereby interfere with and remove the "crests of the waves", which are situated between the wave-shaped depression in the surface. After the removal of the vibra ⁇ tion sustaining pattern the vibrations rapidly cease, the power consumption of the scraping device decreases and the speed of the scraping device returns to the original speed, whereupon a vibration sustaining pattern is again developed.
• the invention is not limited to any such theoretica explanation of the origin of the vibrations or the surface pattern respectively or their mutual relations.
• This invention relates to a method for operating a rotating device into which a fine-grained particulate material is continuously fed and forms a material layer on a rotating surface in the device and in which the thickness of the material layer is limited with the aid of a scraping device with scraping instruments arranged at a certain distance fro the rotating surface, and which perform a periodical, guided e.g. rotating or reciprocating, movement relative to the
• OM scraped surface This movement relative to the scraped surface creates a periodically recurring pattern of scraping marks in the scraped surface, at which at constant speeds of the rotating surface and the * scraping device a vibration sustaining pattern may form and/or the scraping device may get into violent vibrations.
• the vibration sustaining pattern or the vibration sustaining pattern and simultaneously the periodically recurring pattern of scraping marks are destroyed periodically or continuously.
• the invention may be applied to a rotating scraping device of the type shown in the U.S. patent No. 3,316,585 mentioned above.
• a comparatively small change of the moving speed or frequency of the scraping device and/or the scraped surface and/or the size of the relative moving speed or frequency is often enough, e.g. depending on the dimensions of the device.
• a suitable value is at least 1 % speed variation, preferably at least 2.5 %, especially at least 5 % and in particular at least 10 %.
• the minimum speed variation could be chosen higher, for instance at least 15 % or at least 20 %.
• OMPI ting scraping device with a rotating shaft arranged in the axial direction in a drum shaped device for scraping the inner surface of the drum, e.g. a.balling drum.
• the upper limit of the speed variation can usually be chose at will, e.g. a speed reduction of up to 80 %, preferably 5 and for choice 40 or 25 %.
• the frequency of (the time interval between) the speed vari tions of the scraping device and/or the scraped surface is very important and depends on the process conditions. It i fundamental to choose a frequency which is suited to preven the formation of a vibration sustaining pattern, the genera tion of violent vibrations of the scraping device, increase of the power consumption of the scrape motor or surging of circulating load in a balling device.
• the time intervals between the speed variations of the scraping device should be chosen so long that a vibration sustaining pattern formed during a preceding period is remo to a sufficient extent along the entire part of the scraped surface affected by the scraping device. This may mean a time period corresponding to at least.1, 5,-10, 20 or 50 revolutions of the rotating scraped surface between the spe variations.
• the interval between the speed variations shou be so short that after the speed variation a new vibration sustaining pattern does not have time to develop to a disturbing level, i.e. to a level such that the violent vibrations or other disturbances described above occur by the interaction of the scraping device and the vibration sustaining pattern.
• a suitable upper limit of the time period between the speed variations may be 10 minutes, 5 minutes, 2 minutes, 1 minute, 45 seconds, 30 seconds, 15 seconds, to a certain extent depending on the dimensions an speed of the plant, the material to be treated and the electrical arrangements of the plant.
• OM may also vary and may e.g. be 1 second, 5 seconds, 15 seconds, 30 seconds or 1 minute, depending on the speeds mentioned above.
• this time period may vary.
• a common value is 20 seconds to 2 minutes.
• an increase of the charge in the device, e.g. a balling drum which is obtained when the speed of the scraping device is changed and is caused by an increase of the amount of material scraped off from the scraped surface, coincides in time with an increase of the circulating load caused by an increase of the charge in the drum obtained at a previous change of the speed of the scraping device.
• Such a coincidence in time may cause a gradual development of large variations of the circulating load.
• the time between the speed variations may also be varied continuously or stepwise, e.g. by periodically repeating two or more time intervals between the speed variations.
• a second scraping device may be arranged at the scraped surface so that this second scraping device removes the vibration sustaining pattern caused by the first scraping device to such ah extent that this pattern cannot force the scraping device to vibrate, especially with the resonance frequency.
• This can be achieved e.g. with a similar e.g. rotating scraping device, which rotates with somewhat different speed or in any other way creates a pattern of different shape, or with a stationary or reci- procating scraping * device which influences the peaks and/or the valleys in the pattern.
• This may also be achieved with two scraping devices, which synchronously produce the same periodically recurring pattern of scraping marks in the scraped surface but which have different resonance frequencies and in this way mutually remove the vibration sustaining pattern formed by the other scraping device.
• the vibration frequency of the scraping device at the periodically occurring violent vibrations usually coincides with the resonance frequency of the scraping device.
• Said frequency may vary depending upon e. the weight of the scraping device with adhering fine parti ⁇ culate material.
• the scraping device wi suitable means to vibrate with a frequency which is differe from the resonance frequency.
• the scraping device may thus be designed so that its resonance frequency or enforced frequency lies sufficiently far below or above the frequenc of a disturbance which may be expected to arise because of the pattern forming effect of the scraping device on the scraped surface, which in turn, as mentioned above, depends the geometrical shape of the scraping device and the speed the scraping instruments and the scraped surface.
• the variation of the speed of the scraping device may be achieved i several ways e.g. with an engine preferably hydraulic or electric, with stepwise or continuously variable speed, e.g.
• the ' speed variation may also be achieved by a mecha ⁇ nical or hydraulic gear, for instance a planetary gear box or a belt gear box with variable diameter pulleys.
• the speed variation may also be achieved by interrupting the power supply to one or more phases for longer or shorter time periods.
• the vibrations are reduced or eliminated so that the risk of fatique failures is reduced and noise nuisance is avoided.
• the surging in the circulating load is reduced or eliminated.
• Figure 1 is a schematic section through a balling drum of t type which is described in the U.S. patent No. 3,316,585.
• Figure 2 is a graph which shows vibrations, scraper motor power consumption and main motor power consumption as a function of the time.
• Figure 3 is a graph which shows .scraper motor power con- sumption, size of the vibrations, circulating load, new fee rate and the rotary speed of the scraper all as a function time, as well as
• Figure 4 is a graph which shows the vibration amplitude, th scraper motor power consumption and the main drive motor po consumption as a function of time.
• FIG. 1 shows schematically a section through a balling device according to the U.S. patent mentioned above.
• a driven drum 1 rotating with the speed W, rpm rests on rolle 2.
• the drum 1 there is a layer 3 of fine particulate material originating from a tumbling charge 4 of fine parti culate material and seed balls.
• the layer 3 in the drum should have a certain inner diamete R obtained by scraping the layer 3 with a scraping device 5 with a driven shaft 6 which is counter-rotating to the drum with a speed of W rpm and is provided with a pair of longi tudinal flanges 7 serving as scraping instruments, the outer ends of which when rotating are shaping the surface of the layer 3 and are describing an orbit with the radius r around the shaft 6.
• the flanges 7 may also be regarded as describing an involute curve in relation to the drum and cut out a series of wave-shaped traces 8 with axially extending wave crests 9 in the surface.
• Such traces corresponding to the movement of a pair of flanges are shown in Figure 1 represented by a circle arc with a radius R .
• the shape of the traces depends on several factors, such as the relationships W between the rotary speeds wa and W * c._ and the radius R of the layer 3, which in turn depends on the "radius r of the scraping device as well as the distance S between the centres of the drum 1 and the scraper shaft 6.
• the number of scraping instruments on and their distribution around the circumference of the rotating shaft 6 also influences the geometrically calculable and virtual shape of the trace formed in the layer 3 of the drum.
• W comprises an integral number and possibly a decimal, of which the integral number shows the number of trace cycles made by the scraper in the rotating surface during one full revolution of the surface. From the decimal it can be concluded how far from hitting its old track (made during the immediately preceding revolution of the scraped surface) the scraping device is at that revolution of the scraping device which corresponds to the integral number. For various values on this decimal Fp (W) it is possible to calculate the number of revolutions N of a rotating surface which will pass before the scraping device hits its old track.
• FIGS 2, 3 and 4 show recorder graphs for a balling drum with a rotating scraping device.
• These experiments compris the balling of iron ore concentrate on a balling drum with rotating scraping device, basically of the type described i the U.S. patent mentioned above.
• the drum diameter was 3.6 m, the length 9 m and the speed 12 rpm.
• the diameter o the scraping device was 680 mm with four flanges at 90° interspace.
• the vibrations were measured in horizontal direction on the support of the scraping device at the bearing at the feed end.
• the rotary speed of the scraping device could be changed with a motor power frequency converter.
• Figure 2 shows a graph recorded when operating the balling device described above at constant scraper speed, 98 rpm.
• Curve a in the figure shows the vibration amplitude in mm
• curve b the power consumption of the scraping device in kW
• curve c the power consumption of the balling drum in kW as a function of the time.
• Figure 2 shows that after a vibration peak has declined, the scraping device will work steadily for a certain period, after which a new vibration peak will appear. This phenomenon is usually regular ' , with very regular time intervals between the vibration peaks. Simultaneously it is recorded that the power consumption fo the scraping device during the calm periods rises slowly.
• curve d represents the scraper motor power con- sumption in kW
• curve e the vibration magnitude as mm/s RMS at 7.5 Hz
• curve f the circulating load in tph returned from from the discharge end of the drum to the feed end
• curve g the feed rate to the balling drum in tph iron ore concentrate
• curve h the rotary speed of the scraper in rpm
• curve k represents the vibration amplitude in mm
• curve 1 the scraper motor power consumption in kW
• curve m the scraper speed in rpm, all as a function of time plotted along the vertical axis.
• Figure 3 shows that during the time period 0 - 55 minutes the scraper speed was constant. During this time ⁇ period there were pronounced peak values in the scraper motor power con ⁇ sumption, scraper vibrations and the circulating load.
• the curves show that one can easily establish the existence of periodical disturbances which present peak values twice or more as large as the mean variation of respective parameters during the period therebetween, e.g. the peak values Al, A2 of the vibration amplitude and a significantly smaller vibration amplitude B therebetween.
• the curves also show that in the period 55 minutes to 1 h and 36 minutes the speed of the scraper periodically alternated between 95 and 100 rpm, during which time the parameters mentioned above varied within close limits and with peak and mean values far below the peak values during the preceding time period.
• Figure 4 represents another test where the size of the vibr tions, scraper motor power consumption and the scraper spee were recorded.
• Curve k shows that when the scraper operate at constant speed, there are periodical vibration peaks wit an amplitude of -4.0 mm. During those periods when the spe as indicated by curve m alternated between 95 and 100 rpm, the vibrations amounted to only about -0.3 mm. At the time 80 minutes a vibration peak E started to develop. Then the speed was.changed as indicated at point F of curve m. The vibration peak then declined immediately.
• Curve 1 shows that there are pronounced peaks in the scrape motor power consumption of about 12 kW in connection with the vibration peaks. During periods with periodically alternating speed the scraper motor power consumption fluctuated between 5 and 7 kW. These fluctuations are directly connected to the alternations of scraper speed.
• the preferred embodiment of the invention is illustrated on Figures 1, 3 and 4 and comprises a balling drum with a O rotating scraper, the rotary speed of which is periodically changed with such a size of the speed variation and such a short interval between the speed variations that the develop ⁇ ment of vibrations of the scraping device with vibration amplitudes considerably exceeding the normal vibration 5 amplitudes is prevented.
• the size of the speed variation should be. limited to the lowest possible figure which gives the desired effect in order to reduce disturbances caused by the acceleration and retardation of the scraping device.
• the invention is industrially utilizable when operating a rotating device into which a fine-grained particulate material is continuously fed and forms a deposition on a rotating 5 surface in the device the thickness of said deposition being controlled with a scraping device arranged at a. certain distance from the rotating surface with scraping instruments, which perform a periodical, guided, e.g. rotating or reci ⁇ procating, movement in relation to the scraped surface and 0 during this movement in relation to the scraped surface form a periodically recurring pattern of scraping marks in the scraped surface, at which at constant speed of the rotating surface and the scraping device there may develop a vibration sustaining pattern and/or violent vibrations of the scraping 5 device.
• a scraping device arranged at a. certain distance from the rotating surface with scraping instruments, which perform a periodical, guided, e.g. rotating or reci ⁇ procating, movement in relation to the scraped surface and 0 during this movement in relation to the scraped surface form a periodically recurring pattern of scrap
• Examples of such devices are mixing devices and balling devices, in which a moving surface is continuously fed with a
• OMPI fine-grained particulate material which adheres on and buil up a material layer on the surface, e.g. the surface used for balling of a balling disc, balling cone, or balling dru or the inner surface of a rotating mixing drum.
• a scraping device is normally used which is periodically or continuously positioned at a short distance from the surface on which the material layer is formed, and in this way restricts the growth of the coating thickness b scraping accumulated material from said surface.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Organic Chemistry (AREA)
• Environmental & Geological Engineering (AREA)
• Geology (AREA)
• Manufacturing & Machinery (AREA)
• Geochemistry & Mineralogy (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• General Life Sciences & Earth Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Centrifugal Separators (AREA)
• Crushing And Grinding (AREA)

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Citations (8)

• 1977
  • 1977-09-15 SE SE7710372A patent/SE7710372L/sv unknown
• 1978
  • 1978-09-15 GB GB7934866A patent/GB2037175A/en not_active Withdrawn
  • 1978-09-15 WO PCT/SE1978/000044 patent/WO1979000148A1/en unknown
• 1979
  • 1979-03-27 EP EP78900120A patent/EP0006911A1/en not_active Withdrawn

Patent Citations (8)

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