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Laser alignment tools come in user-friendly kits to help you correct multiple types of misalignment. Below we'll discuss how to use a shaft and belt laser alignment tool and more.
It's estimated that 50 to 70 percent of vibration issues in rotating machinery are caused by misalignment, according to Texas A&M's OAKTrust study on coupling misalignment forces. In fact, reliability equipment supplier VibrAlign reported that one of its customers found that just over half of their plant's machinery was misaligned to some degree. So, why is shaft alignment a big deal?
While misalignment has no quantifiable effect on motor efficiency, correct alignment does ensure you have a smooth and efficient transmission of power from the motor to the driven equipment, according to research on motor shaft misalignment by the University of Tennessee's Maintenance and Reliability Center (MRC). Misalignment creates excessive vibration and high loads on bearings, mechanical seals, packing and couplings, impacting the operating life of rotating equipment. Other effects of misalignment are:
Modern laser alignment tools check for three types of misalignment: parallel (offset), angular and a combination of the two. Both of the two main types (parallel and angular) can occur in vertical and horizontal planes.
Below we'll take a look at how modern laser alignment tools work, the basics of setting up a laser alignment tool and steps to take before aligning your equipment.
The goal of a laser alignment tool is to ensure the two coupled shafts are aligned; that is, their center lines have a common axis (coaxial). Modern laser alignment tools have a big advantage over traditional alignment tools like a straight edge, optics and dial indicators. They consist of two sensors (a laser emitter and a receiver), brackets, rods, chains and a display unit. Let's break down the different components of a laser alignment tool.
When it comes to mounting the sensors, six things matter to obtain an accurate reading: measurement methods, distance, angular relationship (inclinometers), bracket assemblies, mounting location and miscellaneous looseness. Let's discuss a few in more detail.
The Tripoint method calculates the alignment condition by taking measurements at three points while rotating the shaft at least 60 degrees. Unlike the Express method, measurements are taken manually rather than automatically.
The Clock method is more of a dated method and involves taking three measurements at the 9, 12 and 3 o'clock points. The clock method is useful when a machine base is not truly horizontal or vertical, such as when mounted at an angle. It's also useful when a horizontal machine is mounted on a vertical plane.
Newer technology, such as Pruftechnik's sensALIGN technology, now provides users with thousands of measurement points. This multi-point feature takes hundreds of points at any degree; a continous (SWEEP) mode automatically collects those points.
When you purchase a laser alignment tool, it generally comes in a case with all the components you'll need, such as the display, extension rods, chains, sensors, brackets and user guide. Tool setup varies depending on the brand, type and model you purchase, but most brands are very user friendly. Pre-installed software typically guides you through the steps or setup process for shaft alignment.
|Shaft Alignment Tolerances for Direct-couple Shafts|
|Parallel Offset (mils)
|Angular Misalignment (mils)
|900||3.0 (E), 6.0 (A)||1.2 (E), 2.0 (A)|
|1,200||2.5 (E), 4.0 (A)||0.9 (E), 1.5 (A)|
|1,800||2.0 (E), 3.0 (A)||0.6 (E), 1.0 (A)|
|3,600||1.0 (E), 1.5 (A)||0.3 (E), 0.5 (A)|
Once setup is complete, you cannot make adjustments to the sensors or you'll get inaccurate readings. Upon setup, many laser alignment tool displays show you a 3D view of your machine as it takes the three readings while you adjust to the proper positions (9, 12 and 3 o'clock). The user friendliness of most laser alignment software indicates that you've taken an accurate reading at each position. For example, once the sensors are properly in the 9 o'clock position, a button will go from red to green, allowing you to record that measurement.
Probably the most common type of laser alignment tool on the market, dual laser alignment tools require you to adjust both lasers so they hit the opposite detector. This usually takes more time, requiring a pre-alignment period. Single laser alignment tools, as the name suggests, requires aligning one laser and is sometimes preferred because the distance between the spacer shaft or the distance between the machines doesn't usually affect the measurment. There's also no need for pre-alignment with single laser alignment tools.
Even though it's quicker and more accurate to align the shaft while the machines are coupled together, sometimes the coupling might need be separated. This might present itself when misalignment causes shaft deflection or bending, when the flexible coupling becomes stiff or when the long shafts protruding from the inboard bearing isn't rigid. To help with uncoupled shaft alignment, some laser alignment tools have built-in inclinometers in the sensors. Others have their own patented technology specific to uncoupled shaft alignment.
Belt alignment tools, or technically sheave alignment tools, are used to properly align the centerlines of sheave grooves (what the belt runs on) to the proper radial and axial alignment. Because belts are relatively inexpensive, belt or sheave alignment isn't typically considered a major issue; however, misalignment in sheaves can cause other problems in addition to reduced belt life. These problems include:
Belt or sheave alignment tools help detect three types of misalignment: radial runout of the shaft, radial runout of the sheave and axial runout of the sheave. Radial shaft runout usually means the shaft is bent. If it is bent out of tolerance, the shaft should be replaced.
Once you've confirmed there is no radial runout of the shaft, check for radial sheave runout. If runout is noticed, it's usually due to an abnormally bored sheave or bushing. You should replace the sheave before aligning if this is the case.
Axial sheave runout typically means you should check the taper-lock bushing to ensure it is mounted correctly and tightened. It could also mean the shaft is undersized or that the sheave or bushing is bored abnormally.
Belt or sheave alignment tools vary depending on the brand and type, but generally work by attaching two magnetic V-sensors into the grooves of the sheave. Unlike shaft alignment tools, with these tools you only have two components: a laser-emitting sensor and a receiver unit. The receiving unit uses a 3D target area to detect horizontal, vertical and/or parallel misalignment.
Performing accurate alignment starts before you even set up your laser alignment tool. These pre-alignment steps and checks are suggested by VibrAlign to ensure your laser alignment tools work properly and accurate alignment is achieved.
Proper coupling alignment can save you from a variety of problems, such as excessive wear and energy consumption, accelerated shaft and coupling failure, and increased vibration. Maintaining alignment requires regular monitoring. Modern laser alignment tools and their accompanying software have made it quite simple to accomplish this.
So, how much do the tools cost? Price depends on the type of alignment tool (shaft or belt alignment), what's included in the alignment kit and how advanced the tool's features are. For example, a more versatile laser alignment tool with ultra-compact measuring units for very narrow spaces might cost a little more than a standard model. By checking a few major distributor's websites, you can find current pricing for shaft and belt laser alignment tools, such as the following guidelines:
Properly aligned machines offer improved uptime and a reduction in maintenance costs. Checking for and correcting misalignment is a fairly straightforward process with the help of modern laser alignment tools.