Mantenimiento de ascensores en la década de 1930

Un vistazo al primer estudio exhaustivo sobre las prácticas de la industria británica de vídeo.

Por el Dr. Lee Gray, corresponsal de EW en el Reino Unido

Reginald S. Phillips' Ascensores eléctricos: Manual sobre las prácticas actuales en la instalación, funcionamiento y mantenimiento de ascensores., publicado en 1939, constituyó el primer estudio exhaustivo de las prácticas de la industria británica de transporte vertical (VT).[1] Este trabajo fue, de hecho, el segundo libro publicado sobre este tema. Sin embargo, el primer libro, de Ronald Grierson, que se publicó simultáneamente en 1923 en los EE. UU. como Equipos de ascensores eléctricos para edificios modernos y en Gran Bretaña como Equipos de elevación eléctricos para edificios modernos, was a blend of American and British information and practices and thus lacked a clear (and, in fact, more useful) British focus. While maintenance practices are referenced throughout Phillips' book, its final chapter is devoted to this important topic. In addition to lift maintenance, the chapter, "Chapter 16 Maintenance and Testing," also addressed "acceptance tests." This topic will be the subject of a future article.

Phillips divided lift maintenance into 12 areas, which he proposed should be addressed in the following order: switches and fuses, motor, brake, gearing, sheaves and pulleys, controller, floor selector, ultimate limit switch, governor, motor generator set and compressor, ropes and general maintenance. These areas were characterized as "the main items requiring inspection" and their proper attention was the "means of curing troubles." The sentence containing these statements was accompanied by a footnote: "See Manual de mantenimiento del ascensor, issued by Messrs. Marryat & Scott." Phillips offered no explanation of why he included this reference. Published in 1932, this 48-page manual was one of the first of several publications by Marryat & Scott, and it may have provided the outline for the content of Phillips' text.[2]

Phillips noted that maintenance should always be done by a "qualified mechanic," however:

"If the services of a qualified lift mechanic are not available, it is recommended that the periodical maintenance be undertaken by a firm of lift engineers, preferably the makers of the lift. Almost all the reputable lift manufacturers have schemes whereby they carry out periodical inspections on lifts, for a comparatively small charge, and after each inspection submit to the owner a complete test report showing the condition of the lift. In fact, most firms would prefer this method of maintaining their own lift. Usually, these standard inspections are carried out each month."

It's unclear, where, outside of a lift company, Phillips thought owners would find a "qualified lift mechanic." Additionally, his statement that regular lift maintenance occurred monthly raises questions about standard industry practice during the 1930s. It's unclear whether this maintenance schedule was found in practice. Following the conversational tone found throughout his book, he also noted that, "to carry out a thorough inspection the mechanic must have the assistance of a mate."

According to Phillips, the motor room was "probably the best and most usual place in which to commence an inspection." The first step was to turn off the main switches for the motor and control circuits. He observed that: "although an electric shock from a low voltage may not normally be dangerous, it may cause one to jump suddenly and come in contact with a moving part of the equipment which might result in serious consequences." The first examination concerned the lift switches and fuses and was predicated on using manufacturer's information found on the motor nameplate to ensure the presence of the proper "motor fuses" and to determine "the setting of any circuit-breakers."

El motor era el siguiente en la lista. Phillips comenzó su descripción de este paso llamando la atención sobre una característica crítica que, si bien normalmente solo se empleaba en caso de emergencia, también podía ser útil al realizar tareas de mantenimiento:

"On examining the motor, it will be noted that the end of the shaft is squared, the object being to allow of the insertion of a winding handle so that the car may be moved, in cases of emergency, or after overrunning a terminal landing and operating the ultimate limit switch. Before the motor can be turned by hand, however, it is necessary to release the brake. This is done either by turning the brake hand release lever, which is fitted to some brakes, or by wedging the shoes apart with a piece of wood. If the need for using the winding handle arises, care must be taken afterwards to remove the handle and either reset the brake hand release or remove the wooden wedge."

Features requiring examination varied according to the type of motor. These included the commutator, sliprings and brushes, plain bearings with ring lubricator and ball or roller bearings. Philips also noted that: "excessive wear of the bearings can often be detected by a distinct knock."

The "brake and the coupling upon which the brake usually operates" was examined next. The coupling should be examined to detect any looseness, which if found, could be corrected by tightening bolts and shaft keys. Phillips suggested that: "If the motor winding handle is inserted, and turned in each direction, looseness of the key on the motor shaft can be detected." If possible, the brake linings should be assessed and adjusted independently, and "the clearance between the brake linings should be as small as possible and will be found in practice to be between 1/100 in. and 1/64 in." Additional inspection items included the solenoid plunger and the brake spring pressure. According to Phillips: "After the brake has set, the car travel should not exceed about four inches for each 100 ft/min. of running speed." Lastly, he recommended that "the operation of any emergency brake gear should also be examined."

The gearing "adjacent to the brake" was next on the list. The gear box should first be examined for leaks. If leakage was found, "the gland nuts should be tightened up in rotation." It was also important to ensure that the gear box contained the proper amount of oil. Phillips suggested that the "gear oil recommended by the makers should be used, but if this is not available, pure castor oil may be substituted" (he also cautioned against mixing different types of oil). The gear teeth should also be examined for excessive wear. Phillips noted that:

"A double thrust race is usually fitted at the outer end of the worm shaft to accommodate the worm thrust in both directions of travel, and an inspection of this thrust race is necessary to ensure that excessive wear has not taken place. If undue wear is present, the thrust is likely to be transferred to the motor bearings, which may overheat and cause a break-down. Wear may be compensated for by removing the thrust and making adjustment."

As was the case with many of his instructions, Phillips appears to have assumed that a "qualified lift mechanic" possessed the skills required to do basic tasks, such as how to adjust a thrust race.

El siguiente examen se centró en poleas y roldanas, y abarcó tanto máquinas de tambor como de tracción. En cuanto a las primeras:

"Play may be detected by observing the line of contact of the sheave and its shaft when the lift starts or stops, and the 'bubbling' of a little oil placed around the line of contact will clearly show any relative movement between the sheave or drum and the shaft. If looseness is present, the key should be driven in tightly, but it may be necessary to fit a new key."

Se deben examinar las poleas de elevación por tracción para detectar desgaste excesivo y deslizamiento de la cuerda:

"Rope slip may be detected by chalking the rope and sheave, and after the lift has made a few journeys, again examining the marks, which should still coincide. In addition to worn grooves, excessive use of lubricant on the ropes may be responsible for rope slip. In the former case the remedy is removing the sheave and having the grooves re-cut, whilst in the latter, removal of the excessive oil with a paraffined rag will cure the trouble. If the ropes 'bottom' in the grooves, slip may again result and it is then necessary to fit larger ropes. It should also be noted whether the ropes lead on and off the sheave without binding on the sides of the grooves."

Lastly, he noted that "the presence of a crack in the sheave, drum, or diverting pulleys may be detected by hammer testing." Again, he assumed that a "qualified lift mechanic" would have been familiar with how to conduct a "hammer test." This literally involved striking a sheave (or drum or diverting pulley) with a hammer – apparently a sound sheave would emit a bell-like tone while a cracked sheave would emit a flat tone. Lift science at its best.

The controller was examined next. Phillips claimed that "in carrying this out, more good will probably result from a very careful visual inspection than anything else that may be done." This involved looking for loose, disconnected or short-circuited wires, examining stranded wire for broken strands, noting "badly burned contacts" that required cleaning and (if necessary) adjustment, and "careful inspection of any controller dashpots."

The next area of inspection was the lift floor levelling equipment. For "automatically controlled" lifts, the inspection focused on the floor selector: "the operation of each striker arm and its associated switch should be examined to see whether the best possible levelling is obtained at each floor." This inspection began by examining the "up direction switch contacts" by recording the car's movement through the shaft. Two sets of measurements were taken, one with the car empty and one with the car carrying its "full load." The assumption was that an empty car would "level slightly high, say 3/4 in.," and that a loaded car would level low. The goal was to set the floor selector such that "the stopping distances above the floors, when light, and the stopping distances below the floors, when carrying full load, are all equal." According to Phillips: "This adjustment will provide the best average levelling in the up direction for all loads if the counterweight is equal to the weight of the car plus 50 percent full load." This process was then repeated with the lift traveling in the down direction. The same methodology was applied to lifts levelled by direction switches in the well with a cam fitted on the car. This description of levelling maintenance and operational practices provides interesting, and perhaps surprising, insights into the limitations of VT systems during the 1930s.

The next items on the inspection list included the ultimate limit switch, governor, motor generator set and (where appropriate) the compressor. Testing the ultimate limit switch involved "holding in the appropriate controller contactors and allowing the car to operate the switch after over-travelling each terminal landing in turn." Phillips recommended that "two paint marks on the operating rope or pieces of adhesive tape" could be used to indicate an overrun. After running the lift, "when the marks are opposite each other, the rope stops are in their correct positions in the well." The governor should be "lubricated where necessary and kept clean," and "the weights should be operated by hand to see that, firstly, the control cut-off switch operates, and secondly, the governor gripping jaws are released and grip the governor rope." For lifts equipped with a motor generator set, Phillips' guidance was simply that it should be inspected. The reference to a compressor referred to systems that employed "pneumatic door operating gear."

A "careful visual examination" of the lift ropes was next. This inspection focused on the "portions of the lifting ropes which pass over the sheave or drum during a complete journey of the lift." The lift mechanic was advised to watch for "any needling of the ropes, i.e., broken wires," and they were advised that the detection of needles was "greatly facilitated by the aid of a small mirror used for the underside of the ropes or by a wad of cotton waste held lightly against the ropes." Philips noted that it was "very difficult to quote any rule for determining when ropes should be renewed," and that "the decision to renew a rope rests largely upon the engineer's experience." If rope renewal was required, key factors included determining the correct rope size, the fastening method (sockets, splicing, or bull-dog grips) and care of the rope during re-roping: "care must be taken to bind the ends of the ropes before cutting (unless preformed ropes are used) to prevent unravelling." The suggested re-roping process was as follows:

"It is usually possible to position the car at the top landing so that the car top is accessible from that landing, and the bottom accessible from the landing below. When in this position, the counterweight is supported by a wooden prop in the well bottom. The car is next raised a few inches by means of lifting tackle and all is in readiness for removal of the old ropes and fixing of the new ones. The worn ropes may conveniently be used for towing the new ropes into position by temporarily fixing the former to the latter. "

Phillips concluded by noting that "oil should not be used on the lifting ropes unless the lift is in a damp location, when a little may be applied to prevent rusting of the ropes."

The discussion on ropes was followed by a section on general maintenance, which addressed a broad range of subjects. The first concerned car-related systems. These included hall-call buttons, car floor-buttons, landing car-position indicators and door interlocks. Additional related inspections occurred from the car top and bottom. The former included inspections of the "rope fastenings and equalizing gear, governor rope release, guides and guide shoes, any electrical door operating gear, retiring cam mechanism and counterweight rope fastenings." The latter, which occurred from the lift pit, included the buffers, ultimate limit switch pulley, safety gear, bottom guide shoes and the rope compensation gear.

Phillips' book had a long life within the British VT industry. Five new editions followed the initial 1939 publication, with the subsequent editions appearing in 1947, 1951, 1958, 1966 and 1973. A future article will examine the changes to maintenance practices that occurred from 1939 to 1973. 

Referencias

[1] Reginald S. Phillips, Ascensores eléctricos: Manual sobre las prácticas actuales en la instalación, funcionamiento y mantenimiento de ascensores.Primera edición, Londres: Sir Isaac Pitman & Sons, Ltd. (1939). Nota: Todas las citas, salvo que se indique lo contrario, proceden de esta fuente.

[2] Marryat & Scott Ltd., Manual de mantenimiento del ascensor Marryat-ScottLondres (1932).