Traction Elevator Modernization
The Value of Traction Elevator Modernization
A gearless traction elevator can serve buildings of any height with speeds typically between 150 and 2000 feet per minute. On gearless machines the hoist ropes pass over a traction drive sheaves, which is integral with the armature.
The Direct Current (DC) version of the gearless machines have been in existence for over one hundred years and are very robust. When properly maintained they will last many, many years, and replacement is usually only warranted when parts obsolescence is a threat to continued use. When considering a modernization we commonly retain these machines and refurbish them in place. Refurbishment can include commutators being turned an undercut, brush holders replaced, coils tested and dressed, bearings replaced, brakes cleaned, re-pinned, relined and adjusted. Logistically large DC gearless machines are very costly and often difficult to replace.
The Alternating Current (AC) version of gearless machines is a newer technology and has only been installed in the USA in more recent years, beginning in the 1990’s. The use of small AC gearless machines has even more recently become very popular since around 2007 when the Machine Room Less (MRL) elevators have been approved for installation in many code jurisdictions. These are lighter duty AC machines than their large DC brothers and time will tell us if they will be as robust. It is likely these will require replacement when modernization of MRL elevators is considered. We have a few years before we encounter this.
Geared traction elevators typically serve mid-rise buildings with speeds normally found between 200 to 500 feet per minute. The geared machine is designed such that the drive sheave is connected to the motor through a gear train. Power from the motor is transmitted to the drive sheave through reduction gears. The geared elevator machine is more prone to wear and tear than the gearless elevators. The machines have a bronze spiral worm gear connected to the hoist motor which drives a bronze ring gear. These gears mesh at very tight tolerances.
Maintenance is critical to maintain these tolerances and if bearings fail or wear so do the gears. This wear causes heat, pitting, rumbling, friction and undesirable noise. Often times this gear wear results in the machine speed having to be reduced to avoid more damage. When considering a modernization replacement of geared machines is rather common. Newer and/or more reliable models can be refurbished to like new operation. Many of the older early designs however do not warrant retaining as their components are of out date designs and/or have become obsolete. When considering a modernization we will assess the condition of your machines and make recommendations for refurbishment or replacement as required.
Geared Winding Drum elevators are no longer installed for public passenger use elevators and typically serve mid rise buildings with speeds between 50 and 150 Feet Per Minute. The geared winding drum machine is designed such that the car and counterweight pulley drums are connected to the motor through a gear train. Power from the motor is transmitted to the winding drums through reduction gears.
The geared winding drum elevator machine is more prone to wear and tear then the gearless elevators. The machines have a bronze spiral worm gear connected to the hoist motor which drives a bronze ring gear. These gears mesh at very tight tolerances. Maintenance is critical to maintain these tolerances and if bearings fail or wear so do the gears.
This wear causes heat, pitting, rumbling, friction and undesirable noise. Often times this gear wear results in the machine speed having to be reduced to avoid more damage. When considering a modernization replacement of geared winding drum machines is very common. Often these machines are removed and new geared or gearless traction machines are installed. When this is done a great deal of other building structural work is required. The geared winding drum machine is an out-dated design and rarely warrants retention. When considering a modernization we will assess the condition of your machines and make recommendations for refurbishment or replacement as required.
The hoist motor is located on a geared or geared winding drum elevator. It couples with the brake drum and operates the spiral worm gear that meshes with the machines ring gear that turns the elevator drive sheave.
Prior to the late 1980’s these motors were DC for elevators traveling over 200 feet per minute, and were primarily AC on the slower elevators. DC power provided a smoother and more controllable elevator at the higher speeds. Since the late 1980’s advances in the use of AC Permanent Magnet Variable Voltage Variable Frequency (VVVF) drives has made AC more controllable at the higher speeds, so most geared elevators installed today now have AC hoist motors.
When considering a modernization the hoist motor both AC or DC is typically replaced with a modern AC motor and its related new AC VVVF drive.
Motor Generator Set
Elevators built according to today’s standards commonly no longer use elevator motor generators. Many, however, built before the late 1980s still use elevator motor generators. An elevator motor generator creates DC power by turning a DC generator with an AC motor. Before more modern elevators were developed starting in the late 1980s, DC power provided a smoother and more controllable elevator. These generators have carbon brushes which dust heavily in the machine room causing a considerable maintenance issue. Now with the introduction of AC PM and VVVF motor controls the generator is no longer needed and rarely is ever retained when modernizing. The existence of the M-G set is actually a primary reason to consider modernization. Parts for them are growing obsolete and harder to obtain.
Solid State Drive Units Brake Assembly
The brake is a spring loaded clamping device that prevents the elevator from moving when the car is at rest and no power is applied to the hoistway motor. When considering a modernization and the hoist machine warrants retention, then the brake type and condition should be assessed for refurbishment. Refurbishment normally includes new coil, pins, core, sleeve, pads, and springs, and a thorough cleaning, painting and testing. If it is does not warrant retention a new replacement brake can be added to the existing machine. Resurfacing or replacement of the drum can be required also. If a new machine is being installed, it is most cost effective to purchase a new brake as part of the new machine assembly which is installed and test at the factory prior to delivery.
In recent years, safety codes have introduced a need for protection against injuries caused by elevator cars leaving the floor with the doors open and over-speeding in the up direction. The rope Brake is a device used to grab elevator suspension ropes to stop the elevator in the event of a mechanical or electrical failure. It activates if an ascending elevator over-speeds in the up direction and also if the elevator leaves the floor with the doors opened. Though not required in all locations, it is common to consider adding a rope brake device when modernizing your elevators. Special fit considerations are required before a brake can be added to an existing machine. We will assess conditions and advise on the feasibility of adding a rope brake as part of our modernization survey for you.
Over Speed Governor/Governor Rope Tension Sheave Assembly
The over speed governor is a speed monitoring device on cable equipped elevators that triggers the safety when the elevator over-speeds. When planning a modernization these devices can be retained provided they are properly equipped to meet current code requirements. Should they not comply with current code requirements replacement will be necessary.
The governor rope tension sheave is required to keep proper tension on the governor cable during operation of the elevator. When planning a modernization this device can normally be retained unless conditions exist that require its replacement. We will include inspection of your governor tension sheave assembly when we assess your equipment for a modernization.
The Sling is the basic frame which consists of two stiles, a crosshead and a bolster or safety plank which supports the platform and cab of an elevator. The platform or floor of the elevator is placed in the sling and supported by brace rods in each corner, on which passenger stand or the load is carried.
- The Crosshead is the upper member of the car frame.
- The Stiles are the vertical member of the car sling, one on each side, that fasten the crosshead to the safety plank.
- The Brace Rod is a rod extending from the elevator platform framing to another part of the elevator car frame or sling for the purpose of supporting the platform or holding it securely in position. Brace robs are supports for the outer corners of the platform, each of which tie to upper portions of the stile.
- The Platform Isolation is Rubber or other vibration absorbing material which reduces the transmission of vibration and noise to the platform. These pads are often replaced when modernizing as new isolation is more resilient and helps to reduce vibration and improve the comfort of the ride for passengers.
- The Bolster is the bottom horizontal member of a hydraulic car sling, to which the platen plate attaches.
- The Safety Plank bottom member of a sling for a traction elevator which contains the safety.
The safety is a device on the car or counterweight that will stop the car or counterweight and keep the elevator from falling in case of overspeed, free-fall, or rope stretch. When considering a modernization in most cases the safeties can be reused. We normally recommend cleaning and adjusting them. In cases of very old elevators there are cases where the existing safeties can not be reused as they are out dated and parts are obsolete.
Counterweight, Frame and Fillers
A counterweight is added weight on traction elevators which counterbalances the weight of an elevator car plus approximately 40% of the capacity load. These assure a more balanced load and help maintain proper traction for the elevator while under varying loads.
Counterweight fillers are metal pieces stacked and bolted together within the counterweight frame to form the counterweight. When modernizing the possibility exist that modification to the cab and car weight could be enough that there will be new filler required to maintain the proper balance and maintain the 40% of the capacity load. If there is not enough space left to add filler weights to accomplish the added weight needed, replacement of the counterweight frame may be required. Final determination of this requirement is often not made until engineering and final approval drawing are complete
Guide shoes are devices mounted on the top and bottom of the elevator sling which slide or roll on the rails to guide the elevator through the hoistway. They are equipped with rollers, liners and tension springs which are subject to wear and tear. Some older style guide shoes require a poured lead babbitt shoe, rather then a replacement nylon or neoprene liner.
If guides are not maintained or adjusted properly your elevator will tend to rock, sway, squeak or even rumble its way through the hoistway. We will assess you guides type and condition and recommend repair or replacement as required.
A Buffer is a device designed to stop a descending car or counterweight beyond its normal limit and to soften the force with which the elevator runs into the pit during an emergency.
A Spring Buffer is one type of buffer most commonly found on hydraulic elevators or used for elevators with speeds less than 200 feet per minute. These devices are used to cushion the elevator and are most always located in the elevator pit.
An Oil Buffer is another type of buffer more commonly found on traction elevators with speeds higher than 200 feet per minute. This type of buffer uses a combination of oil and springs to cushion a descending car or counterweight and are most commonly located in the elevator pit, because of their location in the pit buffers have a tendency to be exposed to water and flooding.
They require routine cleaning and painting to assure they maintain their proper performance specifications. Oil buffers also need there oil checked and changed if exposed to flooding.
When planning a modernization we will assess the type and condition of your buffers and recommend repair or replacement if required.