Laser Borescope Faster Than Older Technologies
By Mark A. Keyser, Hamar Laser
Lasers can generate the straight lines needed to make extruders operate efficiently. The principles behind laser alignment date back more than 25 years when it was found that a laser could duplicate both the properties of tight-wires or optical borescopes. In simplest terms, the setup of the laser is very similar to that of both the borescope and the tight-wire in that a near point and far point are used to determine a straight line which will be used as a reference line on which the alignment of the barrel and gearbox will be based. The laser projecting a beam of light down the length of the barrel is set in the hollow quill of the gearbox and a target, placed in the downstream end of the barrel, is used to “buck-in” or to “indicate” the laser in to the axis of rotation of the gearbox. Small micrometers on the rear of the laser allow the light source to be “qualified” to the axis of rotation of the gearbox through a simple operation known as the Normin (for normal & inverted readings) procedure. A reading is taken with the laser in what can be termed the “12:00” position of the quill. The entire quill (laser and all) is then rotated 180 degrees and the laser is read again and 1/2 of the error is removed using the micrometers on the rear of the laser. During the operation the self-centering target, which is connected to an X-Y readout reading in thousandths of an inch, looks back at the laser. The Normin procedure assures the operator that the laser spot is rotating on itself as opposed to projecting a cone shaped light. From here, it is simply a matter of pushing the target up the bore towards the laser and recording the X-Y readings as stops are made along the length of the barrel. (In the case of twin screw extruders where a hollow quill is not available in which to place a laser, a rear mount/front adjust laser is placed on the splined shaft that drives the screw.) Corrections to the alignment are then made with the laser/target/readout combination acting as a realtime display showing not only the direction of the misalignment but also the magnitude.
The time needed to set up and take readings on a single screw extruder should be no more than 15 to 20 minutes. (The time needed on a twin would be a bit longer.) The laser system will generally cut the total time required for the job by nearly 1/2 to 2/3 of older technology.
The cost of a system is generally comparable to the cost of optical borescopes. Given the accuracy of the laser, and the greatly reduced machinery downtime requirements of the procedure, when coupled with the fact that the laser is extremely simple to use (especially for in-house maintenance crews with reduced manpower and budgets) the laser is now a cost-effective alternative to older, less precise technology.