Click to enlargeLaser Alignment
Click to enlarge
1. Coupling Alignment
Why bother with laser alignments when
modern flexible couplings are claimed to be able to tolerate a generous
alignment error? In transmitting drive from one shaft to another if the
relative axis are not aligned the force becomes dived into two vectors, one of
these vectors applies a force at 90° to the drive direction. The
flexibility of the coupling is said to absorb this force, but the force cannot
disappear so where does it go? Some of the alignment error force is
converted to heat by repeated elastic deformation of the coupling and some
of the force is applied to the machine bearings.
Flexible couplings are deceptive; they seem nice and free and compliant when stationary or hand rotated. However, imagine the tension/distortion in the coupling when transmitting 100 hp across it.
Misalignment of machine couplings cause: -
bending forces on the machine shafts.
premature bearing failures.
premature Seal failures.
premature coupling failure.
vibration.
Misalignment of coupling can therefore lead to:-
unnecessary downtime.
increased maintenance costs.
lost production.
The reason for using Laser Alignment to align couplings is not just because it is more accurate. Skilled practitioners using quality dial indicators and the reverse rim method can under some conditions achieve the same accuracy as a laser alignment. However modern laser alignment equipment realises the following advantages: -
Accurate alignments are quick to achieve.
Long spans are easy (no bracket sag to account for).
Not susceptible to axial movement errors.
The instrumentation is easy to use.
Accessories enable carden shaft alignments.
Provides good record keeping data.
The real cost of laser aligning tools are falling and they can often be hired for a reasonable amount.
2. Thermal Growth
When aligning machines often a tolerance for thermal growth and gear climb is factored in. The thermal growth cold offset is really often just an estimate of the machine re-positioning due to temperature changes. Machine supports and temperature distribution are very rarely simple. Laser systems allow the machine thermal growth and re-positioning to be actually measured and factored into the final alignment.
3. Torque Reactions
Machines are aligned statically applying offset to account for gear and bearing climb and thermal effects. However, practical experience has shown on several occasions that the alignment of drives changes as torque is applied. Lasers offer the opportunity to measure these torque distortions and optimise the final alignment to take account of production loads.
4. Machine Base Levelling
For new machine installation it is far more convenient to place the machine on a bed which has been levelled to ±0.01mm over any distance up to 50 meters (100 meters total). The typical procedure is to level the machinery bed plates using stand off studs to adjust (at least four studs per plate). Once all the plates are level and flat the are grouted in place. Before the machine is put in place 2mm thin stainless steel shim is often put on each plate to allow for future adjustment/machine changes.
An important prerequisite for accurate and speedy alignments - is "Cleanliness" and a minimum number of shims (3 or 4 max). Getting dirt under the contacts or using a `pack' of shims is a very good was getting frustrated when trying to correctly align a machine drive. Such a condition is almost guaranteed to bolt down at a different `height' each time. Save time in the long run - clean the area thoroughly and replace a stack of thin shims with a thick one.
5. Heavy Gearing Alignment
Lasers can be used as light weight straight edges. The sensors can accurately measure distances from this beam to within 12µm. This can be useful in establishing the initial alignment of heavy gearing. The thermography measurement method, while it will correctly show misaligned meshing does not very accurately indicate the amount of correction required.