Kiln Alignment Analysis
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INTRODUCTION The kiln must be aligned so that flexing and distortion of the kiln shell are minimized and so that loads to the support bearings are properly shared. Flexing and distortion of the kiln shell vastly increases mechanical wear and can severely reduce refractory brick life. Poor load sharing amongst the support rollers leads to roller and bearing problems. Alignment means positioning the support rollers so that the flexing of the kiln shell is minimized. The starting point is to know how the rollers are holding the kiln with respect to a straight line. To do this, that is to measure alignment with the kiln in full operation, accurately and reliably, requires an innovative approach. Only Phillips’ Direct Method produces accurate and repeatable results without involving measurements to the tires and support rollers (their diameters and relative positions). Why should such measurements be avoided? Tires and rollers wear unevenly so the accuracy of measurement is always compromised. Doing this with the kiln in motion also compromises reliability and safety. This method determines the state of alignment by measurements directly to the shell. Hence the name “The Direct Method”. It is not encumbered by a rotating shell, it actually needs this movement to determine the shell’s centers of rotation. Alignment, based on measurements made directly to the moving shell to find the centers of rotation, is the heart of Phillips’ innovative approach and is the basis on which the patents were awarded. Now it is possible to align an operating kiln precisely.
Kiln Alignment Analysis – The Direct Method
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Why is alignment important? It is the starting point for any mechanical maintenance program for a rotary kiln. Without understanding alignment and the associated mechanical conditions of the kiln it is impossible to plan maintenance work effectively. The life of refractory is directly related to alignment of the kiln. Alignment measurement, which includes all the mechanical operating characteristics of the kiln, should be a preventive maintenance tool. Unfortunately it has mostly been used as a rectification procedure. Once the damage has been done to a kiln, alignment has lost most of its value as a preventative measure. Not using it as a preventive maintenance tool means the kiln will be running with less than optimum conditions. It often means that abnormal or high wear rates of kiln parts and premature refractory failure are accepted as normal. This means high operating costs and low kiln availability. Not using alignment as a preventive maintenance tool invites unpredicted kiln stoppages. It means the operator cannot fully rely on the mechanical operation of the kiln and that the costs of production will be higher than need be.
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This presentation is meant to highlight the single basic concept which makes this procedure completely different from the others. This key point is the basis on which all the patents have been awarded. We will not attempt to detail the procedure for alignment measurement. Many methods commonly in use are either not reliable or require the kiln to be shut down to get reliable measurements. The discussion here focuses on how alignment measurements can both be reliable and done with the kiln in full operation. This is The Direct Method. In order to understand the difference between The Direct Method and all other techniques let us look at the basic concept of alignment. No matter what alignment measurement techniques are used, the final step when all the calculations have been done, is to compare the position of the kiln to a straight line. We call this the reference line. Such a line is defined by the simplest of definitions in trigonometry as the shortest distance between two points.
Kiln Alignment Analysis – The Direct Method
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When we introduce a third point, its position can then be measured as a deviation from this line in two directions; Horizontal deviation and Vertical deviation.
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We can then extend that idea to consider a multiple of points. Once the reference line is defined by two points, then the position of the remaining points can be determined in horizontal and vertical deviation, from that line. This is a very simple idea. What must be considered and what is not straight forward is what are these points and how are their positions measured? The most important thing to realize is, that it is the accuracy with which these points are established that determines the accuracy of the alignment. The alignment therefore is only as good as the measurements used to establish the position of these points. Put even more emphatically, the accuracy of an alignment is only as accurate as its worst measurement.
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3 ways to do alignment: #1: Internal Alignment
Setting targets inside the kiln – NEW KILNS (Bore Sight Alignment)
All alignment measurement methods can be sorted into two groups; the internal alignment method and the external alignment method. The internal alignment method is an accurate way of measuring the shell position. This is the way a new kiln is installed. Most times a new kiln shell is too long to be transported to site in one piece. It is shipped in sections and these have to be assembled and welded into a straight tube. The method involves establishing physical centers at each of the supports using measurements made from the inside surface of the shell. Once having established these centers it is only a matter of viewing them, either by naked eye, or with a theodolite, or most recently using a laser, to see if they line up. With this very simple technique it is easy to established if all these points are in a straight line or not. This method is often referred to as the “bore sight alignment”.
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Once a kiln has gone into operation some preparation is necessary before an internal alignment can be made. Naturally this internal method requires the kiln to be shut down. Not only does the kiln need to be shut down but because this method requires free internal line of sight and the ability to make several turns of the kiln, no other work can be done on or in the kiln at this time. Recreating the centers also means drilling the coating and the bricks at several locations for each target so that measurements can be made from the kiln shell plate directly. If the kiln has a chain section, usually a target must also be located in it as well. This means tying back the chains so that the work can be done. In order to get reasonable results the centers need to be established using at least three kiln positions. The changes that take place when the kiln is heated to its operating condition must be estimated and factored into the results. Usually these considerations are ignored. If the shell is distorted from heat damage more measurements are needed for good results. To work with accuracy under these conditions with the limited time available is difficult. But the most difficult problem is to make the time available for the kiln alignment in the first place. All of these restrictions usually means that alignment measurement is not done on a routine basis but only when damage is already visible. The value of alignment measurement as a preventive maintenance tool is therefore lost and is then only used as a rectification procedure.
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Bore Sight Alignment: Fig A. Two targets are established each using a single post (4’’ [100mm] diameter pipe) welded to the shell. A small area of refractory must be removed to do this. Their position along the length of the kiln will be at the center of a support tire. A sighting scope or laser is set outside the kiln on the burner floor, the fire-hood having been pulled back to facilitate this. The scope is positioned such that the line of sight strikes both targets. This is the rough setting. The position of the target post is significant and should start at either 3 or 9 o’clock position. The position of the line of sight is marked on both targets. Fig B: The kiln is rotated approximately 90 degrees such that the target post is at or near bottom dead center. The targets are re-sighted and positions on both targets are again marked. Fig C: Rotate another 90 degrees so that the post position is approximately opposite to its original position (either 9 or 3 o’clock) and mark the positions a third time. Find the center of rotation per the next illustration. Fig D. Reposition the scope so that its line of sight is coincident with the centers of rotation on both targets.
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The Center of Rotation is established on each target based on the three positions of the shell. 1) Join points one to two and two to three. 2) Bisect lines 1-2 and 2-3 3) The intersect of the bisects is the center of rotation based on the three positions. For increased accuracy the procedure can be repeated. It should be noted that due to ovality effects in the upper half of the shell, the selected target positions must avoid have the post located in the upper half of the kiln.
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Bore Sight Alignment: Fig A. Two targets are established each using a single post (4’’ [100mm] diameter pipe) welded to the shell. A small area of refractory must be removed to do this. Their position along the length of the kiln will be at the center of a support tire. A sighting scope or laser is set outside the kiln on the burner floor, the fire-hood having been pulled back to facilitate this. The scope is positioned such that the line of sight strikes both targets. This is the rough setting. The position of the target post is significant and should start at either 3 or 9 o’clock position. The position of the line of sight is marked on both targets. Fig B: The kiln is rotated approximately 90 degrees such that the target post is at or near bottom dead center. The targets are re-sighted and positions on both targets are again marked. Fig C: Rotate another 90 degrees so that the post position is approximately opposite to its original position (either 9 or 3 o’clock) and mark the positions a third time. Find the center of rotation per the next illustration. Fig D. Reposition the scope so that its line of sight is coincident with the centers of rotation on both targets.
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With the external alignment method the kiln still needs to be shut down so scheduling problems still exist. But, with this method the harsh environment inside the kiln is avoided. Instead, the centers are established by a series of external measurements. These are usually the roller and tire diameters, the roller spacing and the tire to shell gap since the shell is not concentric with the tire. Although we do not have to work inside the kiln, these measurements are an additional handicap since they are not easy measurements to make accurately. The most difficult problem is the roller spacing since no easy reference surface is available to measure from. On some kilns, where the rollers and tires are badly worn, diameter measurements can also be a problem. It must be remembered that the accuracy of the final alignment is only as good as the worst measurement made. With kilns in poor mechanical condition, this type of alignment usually gives poor results. Since down-time is still required and since results are often poor, this method is not a popular preventive maintenance tool and is just a rectification tool.
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DIMENSION “H” MUST BE CONSTANT FOR EVERY OFFSET MEASUREMENT There are 8 triangles to calculate in order to establish the correct position of each bearing. The three sides of the triangles are: Side 1, the base line - these are our 8 off-set dimensions, a, b, c, d, e, f, g, & h Side 2, the vertical line -H - which is common for all of the offset dimensions above Side 3, the hypotenuse - which is sum of the roller radius and the tire radius associated with each of the offset dimensions. Since “H” must be the same for all, and the roller and tire diameters can be measured, then each of the offset dimensions can be calculated: Any base line where I and j are the correct combination of radii associated with each of the offsets:
(a to h ) = ( Ri + rj ) 2 − H 2
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In the mid ‘80’s the “hot kiln alignment” method was introduced to the industry. These hot kiln alignment methods are based on the conventional external principals but done while the kiln is hot and running. It was already difficult to get accurate results based on external geometric measurement and now it must be done with the kiln in full operation! It was only because of the introduction of the portable computer and the development of the laser equipped theodolite that this even became possible. It should be understood however, that although such measurements (on moving machinery) became possible through the development of new measurement tools nothing in principle had changed in the alignment method and the quality of the results certainly did not improve. At the same time a great deal of interest and enthusiasm in “hot kiln” measurement arose since for the first time alignment could emerge from a corrective technique to a preventive technique since it appeared that checking alignment would not compete with down-time and the kiln could be aligned to its operating conditions.
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Here then is a summary of the conditions that have prevented the hot kiln alignment method from becoming an accurate, convenient and powerful preventive maintenance tool. In order to accurately establish the position of the centers, both the internal and external methods including the hot kiln alignment methods, have several physical problems to deal with. These are: shell eccentricity - the shell is not on the same center as the kiln tire. shell ovality - the shell undergoes continuous deflection during rotation. pitching - the shell may be moving from side to side because of a bent shell axis. permanent shell deformations - from refractory failure and heat damage. worn rollers’ and tires’ surfaces. no reliable surfaces on the kiln components to measure to.
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The key question must now be asked. How can The Direct Method overcome all these difficulties? It is simply this: To determine alignment, we do not measure the support components (tires or rollers) at all. Alignment measurement only involves monitoring shell position. The Direct Method does not consider the rotation of the kiln as an obstacle. It is the first method to recognize that rotation is a key to new information. The heretofore hot alignment methods simply considered rotation an obstacle to overcome. A body in rotation (the shell) has a center of rotation which is usually not the physical center of the body. It can be found without knowing the shape of the object. The object does not have to be round, and we need not know how it is supported. To find its center of rotation requires only that the rotary movement of the object, the kiln shell in our case, be monitored in three places around its periphery. If the points to be aligned are the centers of rotation rather than physical geometric centers of the shell then we are actually aligning the kiln to its true operating condition. To determine alignment, we do this without actually measuring any diameters or roller positions.
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Schematically represented by the heavy outline is a kiln shell in cross section. It is not round and it has some planetary motion because we assume it has a bent axis. Although the shell turns continuously only eight positions representing one rotation are shown by the dotted outlines. Three position monitors, displacement measurement lasers in this case, placed anywhere around the periphery of the shell continuously measure the shell position during rotation. Each laser simply sees the shell move back and forth in front of it. A computer frequently samples the readings. Since the relative position of the lasers with respect to each other is either fixed or otherwise known, the average shell position determined by their respective measurements yields three points P1, P2, and P3. Three points define a unique circle since only one circle can pass through them. The center of this circle is the center of rotation of the body being scanned. Since the shell is generally expected to be round it is tempting to think of this circle as being the shell. In principal it is not, because the “body” being scanned can be rectangular, triangular or any shape for that matter, and a “working circle” will still evolve with this method. A fixed frame of reference has also been selected within which the shell rotates. The position or location of this frame of reference only requires that the kiln shell be completely contained in it. Carefully placing an instrument at known locations within the reference grid allows the center of rotation as determined in the foregoing, to be located in real distances, x millimeters longitudinally, y millimeters laterally, and z millimeters in elevation. It is worth noting that there is a distinct difference between the center of rotation and the physical center of the shell. This difference may not be great but what is significant is that the center of rotation has been determined totally independently of the kiln supports. Additionally, the ease of getting these measurements and their accuracy and reliability are far superior than trying to measure the support components’ geometry in order to derive physical centers.
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The Apparatus A variety of laser scanning arrangements can be used to scan for the three positions at each cross section of the shell. Shown here is one configuration of the side shot set up. Shown is a single laser arrangement at an angle with a locating prism. This arrangement is most convenient for the largest kilns. It allows the exact location of the laser to be determined accurately. The prism mounted on the apparatus is used to optically locate the position of the entire apparatus within the reference frame or reference grid. Each laser scans the entire surface of the shell and reports its mean position. These three “means” combined with the ITS locations of the prism positions allows the computation of the center of rotation of the shell to the nearest millimeter in the axial, transverse and azimuth directions.
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Another arrangement is the bottom shot. The laser continuously scans the shell to track movement which is made up of both run-out and shell shape variations. This method requires that the shell be moving, preferably with the kiln in steady state, normal, operating conditions. Prior “hot alignment” methods could actually be performed with the kiln shut down since those measurements were not not sensitive to movement and only considered rotation as an additional obstacle to overcome. The direct method uses rotation as a new source of information to find the centers of rotation! Note too that the shell, not the kiln tires are being targeted. Consequently the size of the gap between the shell and the tire does not influence the determination of alignment. There is a good deal of flexibility in avoiding or working around obstructions with this method. Theoretically positions anywhere around the circumference can be selected.
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With the use of reference prisms located around the kiln the entire volume within which the kiln is located is defined in three directions to a resolution of 1mm. This we simply call the reference frame or reference grid. More easily said, we can locate any point near or around the kiln by an X,Y,Z address to within 1 mm in each direction.
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A note on accuracy ... The instruments used for these measurements are capable of an accuracy far greater than what will be reported. There are always prevailing site conditions which challenge the full capability of these instruments. Unless specifically noted otherwise in the alignment report, we almost always get well within acceptable tolerances for kiln alignment. Our standard for acceptability is to locate each of the centers of rotation within an envelope of 1/8” or about 3mm. This will meet, if not exceed, kiln manufacturer’s requirements for setting new kilns but we can do it on any kiln. Because this method is not affected by worn components there is no difference in the quality of the result from a new to a severely worn kiln.
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An Integrated Total Station (ITS) measures the prism positions and calculates their the coordinates. These are recorded on a PCMCIA card in the ITS. This card is then removed and placed in a computer PCMCIA reader. The information is then combined with the laser data and the coordinate position of all the centers of rotation are computed. Their deviation from the reference line is then calculated. Also shown is a radio control unit which is sometimes used to manipulate prism orientation. It should be emphasized that the condition of alignment has now been established without knowing any diameters, roller positions, and in spite of any shell pitching or eccentricity. The shell has simply been viewed as a tube rotating in space. In this way the physical problems associated with the conventional methods have been avoided.
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The discussion so far has focused on the most important part of multiple supported kiln alignment, that is pier to pier alignment when there are 3 or more piers. For good kiln operation another important part of alignment is certainly also roller skew and slope. Slope is the vertical position of each roller. Our alignment procedure also measures the actual slope of the kiln which some methods cannot do. Since we also measure the roller or roller base slope we can compare these to the kiln slope. Roller skew, its parallelness to the axis of the shell in the horizontal plane, is not measured but is determined by adjustment. Incorrect roller skewing can cause a great deal of damage to the kiln. Correctly skewing the rollers is a skill which our technicians can easily teach to your personnel. Only with proper slope and skew can face contact be maximized.
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The heart of the alignment report is the two diagrams shown above and the illustration for recommended roller adjustments on the following page. As stated at the outset, any alignment method must boil down to reporting the kiln position with respect to a reference line. We also stated that it takes two points to define a reference line. There are many options for selecting these points. First and most usual is to select the point representing the center of the gear. This ensures that gear position is not altered unless required. Using this point as a pivot, in the plan view, any second point that makes sense can be chosen; a seal, another pier etc. In elevation view the design slope of the kiln is the guide instead of a second point. Most often, using some constraints, the computer can give us a random second point determined by the “best fit” line. This yields the minimum amount of roller adjustments to bring the kiln into line. Again it is emphasized that the alignment measurement has been completed without knowing any dimensional information about the tires, rollers, roller spacing or tire to shell gap.
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In most instances the alignment report is not an end in itself. Actual roller adjustments to correct any misalignment are usually wanted. This illustration is another page out of the report which shows the actual roller moves that are required to correct the measured misalignment. Note that the moves are shown per roller rather than per bearing. The reason for this is that roller skew has not yet been measured. Skew will be determined during the adjustment process and left with the minimum amount required. Each bearing of a roller will therefore be moved by slightly different amounts. Their average move or adjustment however, must equal the recommended value per this illustration. Our crews can supervise these adjustments to assure that all goes well and that the work is completed to everyone’s satisfaction. Although the main alignment information can be presented with these last three illustrations, each report will be 30 to 50 pages in length depending mainly on the number of supports the kiln has. Although alignment is the main objective, it is always our intent to provide as much information about the mechanical condition of the kiln, that can be assessed during its operation, as possible. All these observations and associated recommendations are also contained in the final report Usually the alignment crew will present the final report within two days after completing the measurements. In this way an active discussion can take place on the findings - while the crew is still at site.
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Since this method establishes the relative positions of the centers of rotation without needing to acknowledge the existence of tires, rollers or bearing housings there is a very practical need to tie the measurements to bearing positions. This can be done in a variety of ways. Most often one sees scribe lines on the sides of the roller housings pointing to similar lines on the base. Such lines can become obliterated over time or often more than one set of lines exist. All of this can lead to confusion. An example of a more permanent arrangement is shown. This allows the position of the bearing on the base to be measured at the time of the alignment using a inside micrometer. Although this measurement is initially arbitrary, subsequent measurements compared to the first will reveal how much and in which direction the bearing was moved since the time alignment.
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Compared to conventional procedures ... The astute reader will recognize that even though the position of alignment was obtained without measurement of tire or roller diameters or roller spacing, those measurements are in fact required to translate misalignments into roller moves. The immediate reaction would then be to conclude that the advantage of getting alignment position directly (without those measurements) is lost. Not so. There is a big difference between using those measurements to establish alignment and using those measurements only for roller moves calculations. A simple example will illustrate this point. Consider fig 1. An error in tire diameter of 20mm and an error in one roller diameter of 10mm will affect the location of the center in elevation by 14mm and in plan by 5mm. The vector sum shows that the center identified for alignment would be mislocated by 15mm.
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Consider fig2. Alternatively, already knowing the alignment via The Direct Method, the erroneous diameters are then only used to calculate the roller adjustment(s). First of all the plan view adjustment is completely independent of any diameters. If a plan view correction of 10mm was indicated, moving both rollers 10mm, irrespective of their diameters corrects the alignment. The error in diameter measurements therefore do not affect the recommended adjustment(s) at all. In elevation view lets also assume a 10mm vertical correction is required. Calculating the adjustments first using the erroneous diameters indicates an inward adjustment of both rollers of 17.41mm. If we had made the calculations using the correct diameters the adjustment would have worked out to be 17.31mm. A difference of only 0.16mm. Too small to worry about. By example we can see therefore that the inherent accuracy of The Direct Method is 10 times or at least one order of magnitude better than conventional procedures.
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The Direct Method has proven itself over the years to be accurate, reliable and repeatable. It is a method by which many companies have gained confidence in using alignment as a preventive maintenance tool. In this way the service life of all the kiln parts as well as the refractory are extended to their maximum. This gives the operator maximum mechanical reliability of the kiln by avoiding unexpected stoppages.
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Using the same laser scanning instrument a shell profile can be generated. Even though the actual variations of the shell profile are small compared to the overall diameter of the shell, by exaggerating their amplitude we can get a good visual impression of what the shell looks like. Were the shell to be truly cylindrical then the displayed mesh would appear perfectly flat. It is easy to see where the problem areas are. A shell profile such as this becomes a valuable tool in assessing the condition of the shell. An important consideration when it comes time to replace a section.
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As stated earlier in the alignment discussion, there is a difference between the geometric center of the shell and the center of rotation. This is in fact always the case and sometimes it is very significant. The heavy irregular line is the axis of the shell. The straight line up the center is the axis of rotation established by the centers of rotation at each support and drawing a straight line through them. The Method by Centers of Rotation clearly and accurately shows us this difference. When the shell movement is measured most often it is all taken to be run out. In fact when the kiln shell is not round, oval for example, it can still rotate on its physical center. In such a case the profile is non zero but the run out would be zero. Conversely a true circular shell not turning on its physical center, that is when it has some planetary motion, it has a zero profile (the mesh would look flat) but the run out would be non zero. Please also note this graph is three dimensional. The angular occurrence or phase of the maximum runouts is shown on the column far right. The procedures used here can differentiate between profile variations and true axial run out. This information along with the profile are key analytical tools not only to select the section of kiln to replace but also to position the kiln for the easiest fit up of the new section.
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We strongly suggest that a full alignment and shell profile be carried out on a new kiln. Unfortunately no kiln manufacturer supplies a fully documented alignment and ovality analysis as part of their commissioning program. Why do kiln manufacturers not provide a document of completion that verifies ovalities and alignment as soon as the kiln is commissioned? Isn’t the first alignment the most important one? It is the one that verifies the installation and gives a benchmark for evaluating future problems should they develop. New equipment warrantees are very short, usually only one year, but its expected service life should be more than 25 years. New equipment installations often have subtle problems that are not noticed or are even neglected during the hectic months of commissioning. Formal certification of mechanical fitness should be insisted on by every new kiln owner. This is especially true for the new kilns running 3 RPM or more. The half measures that were acceptable on older slower kilns cannot be tolerated by these newer kilns. A preventive maintenance program that actively involves kiln alignment and ovality measurement allows the kiln conditions to be properly monitored which in turn allows maintenance work to be properly planned. This puts the operator in full control by avoiding surprises. Done properly, these analytical measures can be revenue generators.
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For the record, using The Method by Centers of Rotation for alignment, Phillips is aligning more than 50 kilns per year. •
Cement
•
Lime Recovery - pulp and paper industry
•
Chemical - calcining bauxite, aluminum oxide
•
Mining - nickel, iron ore reduction
•
Refinery - Titanium dioxide reduction
Phillips has a complete capability of mechanical services for all rotary trunnion supported equipment including dryers, reactors, granulators, coolers and so on. We are experienced in setting gears, changing shell sections, installing seals, tires, rollers etc. Our founding business and still a major part of all activities is tire and roller resurfacing while the kiln or dryer etc. is in normal operation. This service is also based on patented equipment and highly skilled operators.
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Kiln Alignment Analysis – The Direct Method
Page 1
Why is alignment important? It is the starting point for any mechanical maintenance program for a rotary kiln. Without understanding alignment and the associated mechanical conditions of the kiln it is impossible to plan maintenance work effectively. The life of refractory is directly related to alignment of the kiln. Alignment measurement, which includes all the mechanical operating characteristics of the kiln, should be a preventive maintenance tool. Unfortunately it has mostly been used as a rectification procedure. Once the damage has been done to a kiln, alignment has lost most of its value as a preventative measure. Not using it as a preventive maintenance tool means the kiln will be running with less than optimum conditions. It often means that abnormal or high wear rates of kiln parts and premature refractory failure are accepted as normal. This means high operating costs and low kiln availability. Not using alignment as a preventive maintenance tool invites unpredicted kiln stoppages. It means the operator cannot fully rely on the mechanical operation of the kiln and that the costs of production will be higher than need be.
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This presentation is meant to highlight the single basic concept which makes this procedure completely different from the others. This key point is the basis on which all the patents have been awarded. We will not attempt to detail the procedure for alignment measurement. Many methods commonly in use are either not reliable or require the kiln to be shut down to get reliable measurements. The discussion here focuses on how alignment measurements can both be reliable and done with the kiln in full operation. This is The Direct Method. In order to understand the difference between The Direct Method and all other techniques let us look at the basic concept of alignment. No matter what alignment measurement techniques are used, the final step when all the calculations have been done, is to compare the position of the kiln to a straight line. We call this the reference line. Such a line is defined by the simplest of definitions in trigonometry as the shortest distance between two points.
Kiln Alignment Analysis – The Direct Method
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When we introduce a third point, its position can then be measured as a deviation from this line in two directions; Horizontal deviation and Vertical deviation.
Kiln Alignment Analysis – The Direct Method
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We can then extend that idea to consider a multiple of points. Once the reference line is defined by two points, then the position of the remaining points can be determined in horizontal and vertical deviation, from that line. This is a very simple idea. What must be considered and what is not straight forward is what are these points and how are their positions measured? The most important thing to realize is, that it is the accuracy with which these points are established that determines the accuracy of the alignment. The alignment therefore is only as good as the measurements used to establish the position of these points. Put even more emphatically, the accuracy of an alignment is only as accurate as its worst measurement.
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3 ways to do alignment: #1: Internal Alignment
Setting targets inside the kiln – NEW KILNS (Bore Sight Alignment)
All alignment measurement methods can be sorted into two groups; the internal alignment method and the external alignment method. The internal alignment method is an accurate way of measuring the shell position. This is the way a new kiln is installed. Most times a new kiln shell is too long to be transported to site in one piece. It is shipped in sections and these have to be assembled and welded into a straight tube. The method involves establishing physical centers at each of the supports using measurements made from the inside surface of the shell. Once having established these centers it is only a matter of viewing them, either by naked eye, or with a theodolite, or most recently using a laser, to see if they line up. With this very simple technique it is easy to established if all these points are in a straight line or not. This method is often referred to as the “bore sight alignment”.
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Once a kiln has gone into operation some preparation is necessary before an internal alignment can be made. Naturally this internal method requires the kiln to be shut down. Not only does the kiln need to be shut down but because this method requires free internal line of sight and the ability to make several turns of the kiln, no other work can be done on or in the kiln at this time. Recreating the centers also means drilling the coating and the bricks at several locations for each target so that measurements can be made from the kiln shell plate directly. If the kiln has a chain section, usually a target must also be located in it as well. This means tying back the chains so that the work can be done. In order to get reasonable results the centers need to be established using at least three kiln positions. The changes that take place when the kiln is heated to its operating condition must be estimated and factored into the results. Usually these considerations are ignored. If the shell is distorted from heat damage more measurements are needed for good results. To work with accuracy under these conditions with the limited time available is difficult. But the most difficult problem is to make the time available for the kiln alignment in the first place. All of these restrictions usually means that alignment measurement is not done on a routine basis but only when damage is already visible. The value of alignment measurement as a preventive maintenance tool is therefore lost and is then only used as a rectification procedure.
Kiln Alignment Analysis – The Direct Method
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Bore Sight Alignment: Fig A. Two targets are established each using a single post (4’’ [100mm] diameter pipe) welded to the shell. A small area of refractory must be removed to do this. Their position along the length of the kiln will be at the center of a support tire. A sighting scope or laser is set outside the kiln on the burner floor, the fire-hood having been pulled back to facilitate this. The scope is positioned such that the line of sight strikes both targets. This is the rough setting. The position of the target post is significant and should start at either 3 or 9 o’clock position. The position of the line of sight is marked on both targets. Fig B: The kiln is rotated approximately 90 degrees such that the target post is at or near bottom dead center. The targets are re-sighted and positions on both targets are again marked. Fig C: Rotate another 90 degrees so that the post position is approximately opposite to its original position (either 9 or 3 o’clock) and mark the positions a third time. Find the center of rotation per the next illustration. Fig D. Reposition the scope so that its line of sight is coincident with the centers of rotation on both targets.
Kiln Alignment Analysis – The Direct Method
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The Center of Rotation is established on each target based on the three positions of the shell. 1) Join points one to two and two to three. 2) Bisect lines 1-2 and 2-3 3) The intersect of the bisects is the center of rotation based on the three positions. For increased accuracy the procedure can be repeated. It should be noted that due to ovality effects in the upper half of the shell, the selected target positions must avoid have the post located in the upper half of the kiln.
Kiln Alignment Analysis – The Direct Method
Page 9
Bore Sight Alignment: Fig A. Two targets are established each using a single post (4’’ [100mm] diameter pipe) welded to the shell. A small area of refractory must be removed to do this. Their position along the length of the kiln will be at the center of a support tire. A sighting scope or laser is set outside the kiln on the burner floor, the fire-hood having been pulled back to facilitate this. The scope is positioned such that the line of sight strikes both targets. This is the rough setting. The position of the target post is significant and should start at either 3 or 9 o’clock position. The position of the line of sight is marked on both targets. Fig B: The kiln is rotated approximately 90 degrees such that the target post is at or near bottom dead center. The targets are re-sighted and positions on both targets are again marked. Fig C: Rotate another 90 degrees so that the post position is approximately opposite to its original position (either 9 or 3 o’clock) and mark the positions a third time. Find the center of rotation per the next illustration. Fig D. Reposition the scope so that its line of sight is coincident with the centers of rotation on both targets.
Kiln Alignment Analysis – The Direct Method
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With the external alignment method the kiln still needs to be shut down so scheduling problems still exist. But, with this method the harsh environment inside the kiln is avoided. Instead, the centers are established by a series of external measurements. These are usually the roller and tire diameters, the roller spacing and the tire to shell gap since the shell is not concentric with the tire. Although we do not have to work inside the kiln, these measurements are an additional handicap since they are not easy measurements to make accurately. The most difficult problem is the roller spacing since no easy reference surface is available to measure from. On some kilns, where the rollers and tires are badly worn, diameter measurements can also be a problem. It must be remembered that the accuracy of the final alignment is only as good as the worst measurement made. With kilns in poor mechanical condition, this type of alignment usually gives poor results. Since down-time is still required and since results are often poor, this method is not a popular preventive maintenance tool and is just a rectification tool.
Kiln Alignment Analysis – The Direct Method
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DIMENSION “H” MUST BE CONSTANT FOR EVERY OFFSET MEASUREMENT There are 8 triangles to calculate in order to establish the correct position of each bearing. The three sides of the triangles are: Side 1, the base line - these are our 8 off-set dimensions, a, b, c, d, e, f, g, & h Side 2, the vertical line -H - which is common for all of the offset dimensions above Side 3, the hypotenuse - which is sum of the roller radius and the tire radius associated with each of the offset dimensions. Since “H” must be the same for all, and the roller and tire diameters can be measured, then each of the offset dimensions can be calculated: Any base line where I and j are the correct combination of radii associated with each of the offsets:
(a to h ) = ( Ri + rj ) 2 − H 2
Kiln Alignment Analysis – The Direct Method
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In the mid ‘80’s the “hot kiln alignment” method was introduced to the industry. These hot kiln alignment methods are based on the conventional external principals but done while the kiln is hot and running. It was already difficult to get accurate results based on external geometric measurement and now it must be done with the kiln in full operation! It was only because of the introduction of the portable computer and the development of the laser equipped theodolite that this even became possible. It should be understood however, that although such measurements (on moving machinery) became possible through the development of new measurement tools nothing in principle had changed in the alignment method and the quality of the results certainly did not improve. At the same time a great deal of interest and enthusiasm in “hot kiln” measurement arose since for the first time alignment could emerge from a corrective technique to a preventive technique since it appeared that checking alignment would not compete with down-time and the kiln could be aligned to its operating conditions.
Kiln Alignment Analysis – The Direct Method
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Here then is a summary of the conditions that have prevented the hot kiln alignment method from becoming an accurate, convenient and powerful preventive maintenance tool. In order to accurately establish the position of the centers, both the internal and external methods including the hot kiln alignment methods, have several physical problems to deal with. These are: shell eccentricity - the shell is not on the same center as the kiln tire. shell ovality - the shell undergoes continuous deflection during rotation. pitching - the shell may be moving from side to side because of a bent shell axis. permanent shell deformations - from refractory failure and heat damage. worn rollers’ and tires’ surfaces. no reliable surfaces on the kiln components to measure to.
Kiln Alignment Analysis – The Direct Method
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The key question must now be asked. How can The Direct Method overcome all these difficulties? It is simply this: To determine alignment, we do not measure the support components (tires or rollers) at all. Alignment measurement only involves monitoring shell position. The Direct Method does not consider the rotation of the kiln as an obstacle. It is the first method to recognize that rotation is a key to new information. The heretofore hot alignment methods simply considered rotation an obstacle to overcome. A body in rotation (the shell) has a center of rotation which is usually not the physical center of the body. It can be found without knowing the shape of the object. The object does not have to be round, and we need not know how it is supported. To find its center of rotation requires only that the rotary movement of the object, the kiln shell in our case, be monitored in three places around its periphery. If the points to be aligned are the centers of rotation rather than physical geometric centers of the shell then we are actually aligning the kiln to its true operating condition. To determine alignment, we do this without actually measuring any diameters or roller positions.
Kiln Alignment Analysis – The Direct Method
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Schematically represented by the heavy outline is a kiln shell in cross section. It is not round and it has some planetary motion because we assume it has a bent axis. Although the shell turns continuously only eight positions representing one rotation are shown by the dotted outlines. Three position monitors, displacement measurement lasers in this case, placed anywhere around the periphery of the shell continuously measure the shell position during rotation. Each laser simply sees the shell move back and forth in front of it. A computer frequently samples the readings. Since the relative position of the lasers with respect to each other is either fixed or otherwise known, the average shell position determined by their respective measurements yields three points P1, P2, and P3. Three points define a unique circle since only one circle can pass through them. The center of this circle is the center of rotation of the body being scanned. Since the shell is generally expected to be round it is tempting to think of this circle as being the shell. In principal it is not, because the “body” being scanned can be rectangular, triangular or any shape for that matter, and a “working circle” will still evolve with this method. A fixed frame of reference has also been selected within which the shell rotates. The position or location of this frame of reference only requires that the kiln shell be completely contained in it. Carefully placing an instrument at known locations within the reference grid allows the center of rotation as determined in the foregoing, to be located in real distances, x millimeters longitudinally, y millimeters laterally, and z millimeters in elevation. It is worth noting that there is a distinct difference between the center of rotation and the physical center of the shell. This difference may not be great but what is significant is that the center of rotation has been determined totally independently of the kiln supports. Additionally, the ease of getting these measurements and their accuracy and reliability are far superior than trying to measure the support components’ geometry in order to derive physical centers.
Kiln Alignment Analysis – The Direct Method
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Kiln Alignment Analysis – The Direct Method
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The Apparatus A variety of laser scanning arrangements can be used to scan for the three positions at each cross section of the shell. Shown here is one configuration of the side shot set up. Shown is a single laser arrangement at an angle with a locating prism. This arrangement is most convenient for the largest kilns. It allows the exact location of the laser to be determined accurately. The prism mounted on the apparatus is used to optically locate the position of the entire apparatus within the reference frame or reference grid. Each laser scans the entire surface of the shell and reports its mean position. These three “means” combined with the ITS locations of the prism positions allows the computation of the center of rotation of the shell to the nearest millimeter in the axial, transverse and azimuth directions.
Kiln Alignment Analysis – The Direct Method
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Another arrangement is the bottom shot. The laser continuously scans the shell to track movement which is made up of both run-out and shell shape variations. This method requires that the shell be moving, preferably with the kiln in steady state, normal, operating conditions. Prior “hot alignment” methods could actually be performed with the kiln shut down since those measurements were not not sensitive to movement and only considered rotation as an additional obstacle to overcome. The direct method uses rotation as a new source of information to find the centers of rotation! Note too that the shell, not the kiln tires are being targeted. Consequently the size of the gap between the shell and the tire does not influence the determination of alignment. There is a good deal of flexibility in avoiding or working around obstructions with this method. Theoretically positions anywhere around the circumference can be selected.
Kiln Alignment Analysis – The Direct Method
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With the use of reference prisms located around the kiln the entire volume within which the kiln is located is defined in three directions to a resolution of 1mm. This we simply call the reference frame or reference grid. More easily said, we can locate any point near or around the kiln by an X,Y,Z address to within 1 mm in each direction.
Kiln Alignment Analysis – The Direct Method
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A note on accuracy ... The instruments used for these measurements are capable of an accuracy far greater than what will be reported. There are always prevailing site conditions which challenge the full capability of these instruments. Unless specifically noted otherwise in the alignment report, we almost always get well within acceptable tolerances for kiln alignment. Our standard for acceptability is to locate each of the centers of rotation within an envelope of 1/8” or about 3mm. This will meet, if not exceed, kiln manufacturer’s requirements for setting new kilns but we can do it on any kiln. Because this method is not affected by worn components there is no difference in the quality of the result from a new to a severely worn kiln.
Kiln Alignment Analysis – The Direct Method
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An Integrated Total Station (ITS) measures the prism positions and calculates their the coordinates. These are recorded on a PCMCIA card in the ITS. This card is then removed and placed in a computer PCMCIA reader. The information is then combined with the laser data and the coordinate position of all the centers of rotation are computed. Their deviation from the reference line is then calculated. Also shown is a radio control unit which is sometimes used to manipulate prism orientation. It should be emphasized that the condition of alignment has now been established without knowing any diameters, roller positions, and in spite of any shell pitching or eccentricity. The shell has simply been viewed as a tube rotating in space. In this way the physical problems associated with the conventional methods have been avoided.
Kiln Alignment Analysis – The Direct Method
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The discussion so far has focused on the most important part of multiple supported kiln alignment, that is pier to pier alignment when there are 3 or more piers. For good kiln operation another important part of alignment is certainly also roller skew and slope. Slope is the vertical position of each roller. Our alignment procedure also measures the actual slope of the kiln which some methods cannot do. Since we also measure the roller or roller base slope we can compare these to the kiln slope. Roller skew, its parallelness to the axis of the shell in the horizontal plane, is not measured but is determined by adjustment. Incorrect roller skewing can cause a great deal of damage to the kiln. Correctly skewing the rollers is a skill which our technicians can easily teach to your personnel. Only with proper slope and skew can face contact be maximized.
Kiln Alignment Analysis – The Direct Method
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The heart of the alignment report is the two diagrams shown above and the illustration for recommended roller adjustments on the following page. As stated at the outset, any alignment method must boil down to reporting the kiln position with respect to a reference line. We also stated that it takes two points to define a reference line. There are many options for selecting these points. First and most usual is to select the point representing the center of the gear. This ensures that gear position is not altered unless required. Using this point as a pivot, in the plan view, any second point that makes sense can be chosen; a seal, another pier etc. In elevation view the design slope of the kiln is the guide instead of a second point. Most often, using some constraints, the computer can give us a random second point determined by the “best fit” line. This yields the minimum amount of roller adjustments to bring the kiln into line. Again it is emphasized that the alignment measurement has been completed without knowing any dimensional information about the tires, rollers, roller spacing or tire to shell gap.
Kiln Alignment Analysis – The Direct Method
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In most instances the alignment report is not an end in itself. Actual roller adjustments to correct any misalignment are usually wanted. This illustration is another page out of the report which shows the actual roller moves that are required to correct the measured misalignment. Note that the moves are shown per roller rather than per bearing. The reason for this is that roller skew has not yet been measured. Skew will be determined during the adjustment process and left with the minimum amount required. Each bearing of a roller will therefore be moved by slightly different amounts. Their average move or adjustment however, must equal the recommended value per this illustration. Our crews can supervise these adjustments to assure that all goes well and that the work is completed to everyone’s satisfaction. Although the main alignment information can be presented with these last three illustrations, each report will be 30 to 50 pages in length depending mainly on the number of supports the kiln has. Although alignment is the main objective, it is always our intent to provide as much information about the mechanical condition of the kiln, that can be assessed during its operation, as possible. All these observations and associated recommendations are also contained in the final report Usually the alignment crew will present the final report within two days after completing the measurements. In this way an active discussion can take place on the findings - while the crew is still at site.
Kiln Alignment Analysis – The Direct Method
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Since this method establishes the relative positions of the centers of rotation without needing to acknowledge the existence of tires, rollers or bearing housings there is a very practical need to tie the measurements to bearing positions. This can be done in a variety of ways. Most often one sees scribe lines on the sides of the roller housings pointing to similar lines on the base. Such lines can become obliterated over time or often more than one set of lines exist. All of this can lead to confusion. An example of a more permanent arrangement is shown. This allows the position of the bearing on the base to be measured at the time of the alignment using a inside micrometer. Although this measurement is initially arbitrary, subsequent measurements compared to the first will reveal how much and in which direction the bearing was moved since the time alignment.
Kiln Alignment Analysis – The Direct Method
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Compared to conventional procedures ... The astute reader will recognize that even though the position of alignment was obtained without measurement of tire or roller diameters or roller spacing, those measurements are in fact required to translate misalignments into roller moves. The immediate reaction would then be to conclude that the advantage of getting alignment position directly (without those measurements) is lost. Not so. There is a big difference between using those measurements to establish alignment and using those measurements only for roller moves calculations. A simple example will illustrate this point. Consider fig 1. An error in tire diameter of 20mm and an error in one roller diameter of 10mm will affect the location of the center in elevation by 14mm and in plan by 5mm. The vector sum shows that the center identified for alignment would be mislocated by 15mm.
Kiln Alignment Analysis – The Direct Method
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Consider fig2. Alternatively, already knowing the alignment via The Direct Method, the erroneous diameters are then only used to calculate the roller adjustment(s). First of all the plan view adjustment is completely independent of any diameters. If a plan view correction of 10mm was indicated, moving both rollers 10mm, irrespective of their diameters corrects the alignment. The error in diameter measurements therefore do not affect the recommended adjustment(s) at all. In elevation view lets also assume a 10mm vertical correction is required. Calculating the adjustments first using the erroneous diameters indicates an inward adjustment of both rollers of 17.41mm. If we had made the calculations using the correct diameters the adjustment would have worked out to be 17.31mm. A difference of only 0.16mm. Too small to worry about. By example we can see therefore that the inherent accuracy of The Direct Method is 10 times or at least one order of magnitude better than conventional procedures.
Kiln Alignment Analysis – The Direct Method
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The Direct Method has proven itself over the years to be accurate, reliable and repeatable. It is a method by which many companies have gained confidence in using alignment as a preventive maintenance tool. In this way the service life of all the kiln parts as well as the refractory are extended to their maximum. This gives the operator maximum mechanical reliability of the kiln by avoiding unexpected stoppages.
Kiln Alignment Analysis – The Direct Method
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Using the same laser scanning instrument a shell profile can be generated. Even though the actual variations of the shell profile are small compared to the overall diameter of the shell, by exaggerating their amplitude we can get a good visual impression of what the shell looks like. Were the shell to be truly cylindrical then the displayed mesh would appear perfectly flat. It is easy to see where the problem areas are. A shell profile such as this becomes a valuable tool in assessing the condition of the shell. An important consideration when it comes time to replace a section.
Kiln Alignment Analysis – The Direct Method
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As stated earlier in the alignment discussion, there is a difference between the geometric center of the shell and the center of rotation. This is in fact always the case and sometimes it is very significant. The heavy irregular line is the axis of the shell. The straight line up the center is the axis of rotation established by the centers of rotation at each support and drawing a straight line through them. The Method by Centers of Rotation clearly and accurately shows us this difference. When the shell movement is measured most often it is all taken to be run out. In fact when the kiln shell is not round, oval for example, it can still rotate on its physical center. In such a case the profile is non zero but the run out would be zero. Conversely a true circular shell not turning on its physical center, that is when it has some planetary motion, it has a zero profile (the mesh would look flat) but the run out would be non zero. Please also note this graph is three dimensional. The angular occurrence or phase of the maximum runouts is shown on the column far right. The procedures used here can differentiate between profile variations and true axial run out. This information along with the profile are key analytical tools not only to select the section of kiln to replace but also to position the kiln for the easiest fit up of the new section.
Kiln Alignment Analysis – The Direct Method
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Kiln Alignment Analysis – The Direct Method
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Kiln Alignment Analysis – The Direct Method
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We strongly suggest that a full alignment and shell profile be carried out on a new kiln. Unfortunately no kiln manufacturer supplies a fully documented alignment and ovality analysis as part of their commissioning program. Why do kiln manufacturers not provide a document of completion that verifies ovalities and alignment as soon as the kiln is commissioned? Isn’t the first alignment the most important one? It is the one that verifies the installation and gives a benchmark for evaluating future problems should they develop. New equipment warrantees are very short, usually only one year, but its expected service life should be more than 25 years. New equipment installations often have subtle problems that are not noticed or are even neglected during the hectic months of commissioning. Formal certification of mechanical fitness should be insisted on by every new kiln owner. This is especially true for the new kilns running 3 RPM or more. The half measures that were acceptable on older slower kilns cannot be tolerated by these newer kilns. A preventive maintenance program that actively involves kiln alignment and ovality measurement allows the kiln conditions to be properly monitored which in turn allows maintenance work to be properly planned. This puts the operator in full control by avoiding surprises. Done properly, these analytical measures can be revenue generators.
Kiln Alignment Analysis – The Direct Method
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For the record, using The Method by Centers of Rotation for alignment, Phillips is aligning more than 50 kilns per year. •
Cement
•
Lime Recovery - pulp and paper industry
•
Chemical - calcining bauxite, aluminum oxide
•
Mining - nickel, iron ore reduction
•
Refinery - Titanium dioxide reduction
Phillips has a complete capability of mechanical services for all rotary trunnion supported equipment including dryers, reactors, granulators, coolers and so on. We are experienced in setting gears, changing shell sections, installing seals, tires, rollers etc. Our founding business and still a major part of all activities is tire and roller resurfacing while the kiln or dryer etc. is in normal operation. This service is also based on patented equipment and highly skilled operators.
Kiln Alignment Analysis – The Direct Method
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Kiln Alignment Analysis – The Direct Method
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