Most steel plants are unique in that hardly ever are two or more operating areas and/or plants exactly alike. They have a lot of similarities and, at times, do actually have uniquely designed components that are interchangeable from one plant to another. That, at times, may lead to an agreement, between the two plants to share an expensive spare which seldom fails, but if required, comes with a very long delivery time.Thus, if that kind of an agreement exists, it is only for very unusual situations and components.
When an operational area is being designed to meet the client’s objectives, the design may end up including 60,000 or more “blue prints” (or their electronic equivalents in today’s environment). Those drawings not only specify the physical dimensional aspects, but provide a whole lot more like for example, materials specifications, tolerances, weld specifications, assembly relationship, etc., etc.. However, not all parts are shown in detail. There will be parts that are referenced by a part number only and which may apply for a sub-supplier, a manufacture only and thus lack a lot of detail except perhaps that which is required for mating with other components of an assembly. Most of the detail and/or supplied information to the steel plantisusually adequate for obtaining replacement units if desiring exactly what was originally installed.
Due to the uniqueness of the plants there can be a lot of equipment which, in the designated application, is of first generation, i.e. it has not been tested in similar or identical situations and thus is yet to be proven for its suitability. Such can lead to what one may consider as premature and/or non-anticipated, failures at that stage of the unit’s life.
Once such a failure has occurred, the plant may be in luck by having a spare which can then be quickly installed; but that is not always the case as most plants start with low spares budgets.
When it comes to replacing/installing the replacement/spare for the prematurely failed part, it may be by a man who has a personal tool box worth more than $5,000 and contains more tools than the department tool crib, and he knows how to use them. It could be one of the better tradesmen whom the “$5,000 man” may have the confidence of allowing him to borrow in time of need, knowing it actually comes back in the condition it went out. It could also be a person who feels a tool bag with a pair of adjustable wrenches, a pipe wrench, a sledge hammer, pair of burning goggles and a pair of burning gloves is very sufficient; with such a set of tools he may believe he can tackle any or at least most problems. In case where the sledge hammer does not adequately correct the alignment concern, he can always get a 3T come along from the tool crib for the final adjustment (that would also leave the sledge hammer available in case the bolt still needs a bit of motivational assistance).
Where there usually is sufficient and available skill within an operating area, especially for the repetitive type jobs, the concentration of it may end up being primarily on days, Monday to Friday. Very few plants have policies that require not just the certification/demonstrated level of skill within a trade/profession but also a specified, extended experience within the operating area, for each and every operating shift. Even if it existed at some point of time, the need or desire to control man hours per ton has progressively diluted this particular consideration in many, if not most, plants or been affected by some other well known factors that often dictate who works what shift.
Regardless of which person ends up doing the replacement, the job usually will get done, in one form or another; and the operations people will be back at doing what they do the best. There usually is a follow up report that leads to someone who has to obtain another spare, and hopefully will also analyze or seek to find out why the failure occurred in the first place. As with the installation of the replacement, this person’s qualifications, or those of the team, may contribute to actual outcome of the next stage.
The person analyzing the failure/selecting the replacement unit may have one outstanding qualification. He may be one with very high qualification as an ex-tradesman, and thus, within his own trade have as good an insight that anyone can expect within that trade. The person may possess a science degree in some engineering field and thus be well on his/her way to bigger and more demanding things.
Assuming there is follow up in finding the reason for the cause of the early failure, let’s consider, as an illustration, that the failure involved a breakdown of a worm gear reducer. Upon opening up the reducer box, they may discover, for example that the bronze gear on the worm gear drive has fractured and is now in pieces, inside the box. With that discovery, one may decide to replace the gear/or the whole gear box of the same make and model. Or, one may take it further by analyzing him/her self, or consult with another team member, who may just happen to be an engineer. As part of his training, he does some calculations and realizes that the whole gear box has an inherent weakness; the person originally selecting the gearbox had considered only the weight of the material to be moved and not the dynamics of the whole cycle. Under such initial assumption the gear box would perhaps have been perfect for the application. However and in this situation, when the transfer arms lift the billet, in the process of transferring from one line to another parallel line, the arms accelerate and the load, on the arms, during the lifting stage (and on the gear) is on one side. Once the arms reach the top dead center, the stresses shift quickly to the other side, the arms now are not lifting any more but are de-accelerating while also having to holding back for soft landing as part of the downward motion. When the mill operates on a 30 second cycle all that motion is very rapid and the transfer from one side to the other generates forces that exceed the specifications for the supplied gear box (as per the engineer’s calculations). So, the solution is easy, they need a gear box that is able to handle the newly determined forces which may mean a physically larger gear box. But, there may not be room for a larger unit. So, are there other options, one may wonder.
If another person had a chance to participate or was contacted for consultation, this person may realize the bronze gear wheel, in this case, relied on interference fit between the bronze gear and the steel hub. Such a fit, even at design stages, requires a very complex calculation to determine the exact pre-stress for mounting the gear onto the hub. Then there is the question of machining, was the specified interference obtained through correct machining; impossible to tell from the pieces. Thus “the new person” may request or do more calculations him/herself. For example, would the gear be sufficient under conditions where the gear wheel uses flange mount with bolted connections and maybe even a bit more bronze material under the teeth; remember, the gear teeth had not failed, there was only the fracturing through the area under the root diameter of the teeth. If the calculations showed that this method solved the problem, there would be no need to try to replace with larger gear box housing, just the same size of a gear, revised method of securing and bit more bronze under the teeth. (If the expertise is not in house, maybe there is someone else who does have it; only to seek it.)
Not all repairs end up being the final repair. Some may require an “aspirin” till more adequate repairs can be made. Some maybe shocked to see “an old time mechanic” take out the welding shield, few welding rods and the whip and start building up the excessively worn teeth of a bevel gear. While technically not correct, this tradesman may have salvaged many a shift in the past by finding a way to keep the mill going till the next repair day or till more proper repairs can be done. If the economies were such that the plant can do all that needs to be done when a potential problem is first detected, there would be no need to provide temporary built up teeth by welding; unfortunately most end up not being able to do all that should be done, when first anticipated, and thus the plant needs the “old timers with the tool bag” as well. In this case, the maintenance people may have known the gears were wearing. Once the wear extends from the harder into the “softer” core of the tooth the rolling contact is long gone and it may become necessary to apply some new metal while there is some resemblance of the old tooth and some metal to weld onto. The other option may have been to take a more extended down time/ operational delay; often the quick repair may end up being the choice of the time.
There usually are many members in a team, from varying backgrounds and experiences. None are born with 30 years of experience. Thus, those new to the process, tradesmen with or without experience, or engineers, etc., they usually end up, with a varying degree of experience and applicable knowledge as “part of the team”. To be fair to the management of the plant, generally speaking the teams are very qualified to handle most of the daily tasks. But, at the same time, the current economic realities do stress the time available so that the number of “permanent“ employees does keep on reducing; compared to few past decades the potential time to be able to a particular problem is conceivably less in today’s environment. To keep the plant operating, it is important for the management to assess the skill sets, have members perform tasks they can handle and/or learn from or and in addition to for the members of the team to recognize when they should seek help, either internally or from outside sources.
For example, for maintenance, it would be unusual to have metallurgical expertise within such a team even though, most likely, the plant itself has metallurgists who primarily specialize in the company’s own product lines. If the department had abrasive wear issues, they could end up benefiting by having access to that specialty, (or any other situation where sufficient expertise does not exist within the assigned team. This is even more so in first generation, situation where the supplied materials have not been tested.) They may have to try to decide whether heat treated abrasive plate is more or less suitable when compared with a cast plate with appropriately chosen metallurgy and where the hardness and other characteristics are uniform throughout the thickness v.s. just as a skin.
Companies such as Wabi Iron & Steel Corp. have the capabilities to re-engineer obsolete industrial plant replacement components, either as a casting, or a fabrication, or as a combination of both.