There is a common misconception in the industry that new equipment is more reliable than machinery in operation. In reality, the machines that have been in operation for a year or more and are a part of a condition monitoring program are actually more reliable than startup equipment. Statistics and industry studies confirm that the most critical time for any equipment is during the break-in period. In fact, the weeks or months immediately following the initial startup are when machinery is the most susceptible to failure.
Vibration Specialty Corporation (VSC) has been providing solutions to gear manufacturers and users since 1918. With 90 years of experience analyzing problems for OEMs, users from all industries, and repair houses, we see an extraordinary share of gear problems. We’ve recognized that most of the problems users experience with a gear can be traced back to a problem at the very beginning of the gear’s life. For that reason, we have developed our list of four tips to avoid gear infant mortality. They are:
1) Ensure your manufacturing partner has a high level of quality assurance;
2) Create standards and systems for gear storage and shipping;
3) Make sure both contractors and manufacturers are involved in the installation process;
4) Monitor, monitor, monitor.
Following these tips will help you reduce the amount of time and money you waste every year replacing new gears that have gone bad. (Figure 1)
1: Quality Assurance
Manufacturing is the first step in creating gears that have a long, productive life. Any mistake in the manufacturing phase can plague a gear assembly for its entire life. The precision of today’s machining equipment has eliminated many of the issues that arise from gear imperfections, but some still exist. That is why a comprehensive quality assurance program is key.
There are some common areas that are too often overlooked. The manufacturer you are buying from should be able to answer these simple questions for you. Asking them will help you get the return on the investment you make in their gears. They are:
How current are your drawings? Too often, drawings are not kept current, resulting in problems. It is paramount that drawings remain up to date and that a strong quality assurance program is in place to limit human related flaws.
How are you balancing new gears coming off the line? One condition that is normal for a new gear keyed to a shaft is that an imbalance will be caused by the key or key way. Rarely are the key and way well matched in weight. Thus, there is normally an imbalance that must be corrected.
Balancing is normally the last step in the manufacturing or repair process. But your manufacturing partner should go beyond informal balancing—it should be an important part of the formal QA process. Further, the balancer and those responsible for QA should spend a reasonable period of time with the component. If a rotating element is unreasonably out of balance, this may be indicative of another problem.
Make sure your manufacturer balances high quality gears to the appropriate API or ISO standard. The balance process should also utilize the actual key that will be used in operation or an exact weight of that key. If key size is not specified, then the manufacturer should be contacted and the exact size determined based on the key weight during balancing. When the balanced gear leaves the balance service center, it should be noted on the paperwork as to size of the keys in each way. There is no sense in having your manufacturer balance a gear only to have your contractor put in a different size key for operating. Of course, the coupling must also be balanced with the weight of the exact opposite of the half or crowned key in the gear.
If you are unsure of a manufacturer’s ability to deliver high-quality gears that meet a high standard of QA and have long lives, look for a consulting partner to help. Because of our background and exposure, some of VSC’s customers include us in the process of developing a product.
2: Creating Systems
All gears must be stored and maintained properly while in storage or shipment. Without proper attention gears can develop flat spots, rusting, pitting, and bent shafting. Each of these conditions results in problems during operation that will yield vibration. Over the years we have noted that the most successful manufacturers and operators have well documented storage and shipping procedures that describe and offer images for the specific storage and shipping configurations and adaptations for each rotor. During monthly inventory checks personnel should inspect and verify not only the number of items in storage, but also that the rotors are stored in accordance to the documented procedures. In this way, the equipment gets the appropriate attention throughout its storage and shipment phase.
Gear systems installed in the field should receive the same attention that they received in manufacturing. It is all too common that newly installed gear systems are not properly aligned to adjoining equipment. Of course, this can cause severe damage to the gears and negate the money and attention devoted during the manufacturing phase.
It is not the intent of this article to go into the process of aligning a gear drive. The variety of applications makes this impossible. It should be sufficient to note that the highest machinery installation standards must be followed. Contractors or millwrights must know the proper process of installing, checking, and aligning gears during installation or repair. Rather, our experience indicates that contractors should go a step further by engaging manufacturers in the installation process.
In many cases, gears are sold by the manufacturer and then installed by separate contractors. Most contractors feel very confident in their own abilities, but always remember that sometimes these were the lowest bidders on the project. In some cases, insufficient time and/or attention is given to a proper installation.
When the equipment runs poorly during testing or startup, the contractor often reactively calls the manufacturer. Unsure of the situation, the manufacturer must send personnel to investigate and resolve the problem. By the time the OEM arrives, the installing contractor is long gone. Unfortunately, the manufacturer is often not compensated for the contractor’s error. Even worse, if the problem is not resolved quickly, the costs can soar. A proactive installation partnership between the contractor and the manufacturer can save time and money for all in the long-term and prevent the infant mortality for the gear.
There are three areas of the installation process that require the collaboration of the contractor and the manufacturer.
Build a Strong Foundation
The most critical part of any installation is the foundation.(Figure 2) A gearbox with a poor foundation is immediately handicapped and may never operate well. Our observations show that the manufacturers with the least installation headaches provide their client with base designs or requirements that specify the way the foundation should be constructed for a successful installation. Some even send a representative to witness the base installation to verify adequate construction. In any case, the manufacturer should have a standard by which they can evaluate the contractor’s work and absolve themselves from a warranty controversy. Normally you want the base to be at least five to 10 times the weight of the assembly.
An inadequate structural base can also damage an OEM’s reputation, as they will normally get blamed for the poor performance of the equipment. Meanwhile, the installer walks away clean. Deficient bases can often create resonant conditions that wreak havoc on machinery and surrounding structures.
In some cases, you may even want to bring in a consultant such as VSC to serve as your advocate working with the contractor and the manufacturer. This onsite installation consultation has provided significant savings to OEMs and customers through the years. Using all pertinent technologies, we document and resolve installation and manufacturing issues immediately. This way, problems do not fester and create poor customer relations, costly warranty complications, or a damaged reputation for any of the parties involved.
Make Sure Gears are Properly Aligned
Poor coupling alignment can also have an extremely detrimental effect on a machine’s operation. Most contractors today use the precision and speed of laser alignment equipment, believing that it will automatically result in a precise alignment. Many fail to recognize that a laser alignment system is only a tool and can be as inaccurate as a straight edge if the operators are not properly trained. This is a situation where the manufacturer’s experience in aligning the gears can be invaluable. Strict surface preparation is vital to a precise alignment.
Installing the laser and reflector improperly on the shafting can result in inaccuracies depending on their placement. All too often VSC has witnessed installations where the laser and reflector holddowns run across the key, causing the laser to shift each time the shaft is rotated. We have also noted burrs on the shaft that cock the laser and reflector, creating chaos with the readings. There are countless ways to improperly affix an alignment system to the shaft. These issues are often tolerated by the contractor in order to complete the job, resulting in poor craftsmanship.
Look Out for a Soft Foot or Thermal Growth
Even if the contractor does mount the system correctly, some do not understand the importance of detecting and resolving a soft foot condition (caused by unlevel, bumpy bases). Soft foot often results in a distortion of the casing which can also distort internal rotors, potentially misaligning the gears inside the housing. This can result in improper gear mesh, which shows up in operation and vibration testing. Most alignment systems come with a soft foot check, and it is recommended that the check takes place prior to the alignment. If not performed the contractor would likely be unable to resolve the soft foot condition. This will result in inconsistencies of the alignment readings, making the readings less repeatable and unreliable.
Thermal growth is another critical item that is not taken into account by contractors. Manufacturers often provide thermal growth information for their product. Some contractors do not realize the importance of such growth information or they do not know how to make their system integrate those numbers into the alignment. In any case, if the offset is not performed, the machine will be misaligned and have undue forces acting on it, which will start as vibration and end with premature wear and failure. Obviously, a machine’s temperature will increase as it operates and different components heat up at dissimilar rates. If this is not accounted for in the alignment, the components will grow and contract unevenly, causing misalignment, distortion, and undue forces. As a result, the machinery may exhibit vibration or distinct noises that were not present upon initial startup. These can build the longer the machine operates. Consequently, it is always important to ensure the contractor conducted a “hot” alignment, which accounts for the growth characteristics of the machine’s operation.
Machinery operating under normal conditions is subject to stress. If the stress of any component becomes excessive, failure quickly follows. Monitoring machinery with vibration and other predictive technologies during the startup phase is critical to stopping any infant mortality problem in its tracks before it can reach failure.
Typically, once a machine gets past 10 million cycles without encountering problems, it demonstrates acceptable design, manufacturing, installation, and operational processes. But monitoring should continue beyond the infant mortality phase.
Vibration analysis is the ideal technology for scrutinizing a machine’s condition throughout its life, especially beyond its infant mortality stage. VSC has been remotely monitoring clients’ equipment from across the globe for over 30 years, helping them to maximize performance and the greatest return on their investment. (Figure 3)
In this day and age, gears should easily make it beyond the infant mortality stage. By asking the right questions of your manufacturing partner, creating standards for storing and shipping gears, insisting your manufacturer and contractor work together for installation, and following the “monitor, monitor, monitor” golden rule, you can be sure your gears will live long, productive lives. This will result in a more efficient process that ultimately improves the return on investment in your machines.
No matter what stage your equipment is in, VSC can assist you in getting the most out of it. Gear assemblies are rather complex pieces that can last a lifetime if properly maintained and observed. Our predictive maintenance products and services—including precision balancing, laser alignment, training/instruction, and consultation—offer everything you need throughout the life of your machinery to help it last well beyond its rated years.