Sometimes a customer comes not for a replacement, but for memory. We were called to one of the machine-building plants in Tashkent in order to bring back to life the AIR-100L4 asynchronous electric motor, which had been working on the assembly line since 1990. This case is about the repair of a Soviet-made AIR engine, about how original components are searched for in 2017, and why restoration is sometimes more profitable than buying a new engine.
Customer and problem statement
A machine-building plant in the industrial zone of Tashkent. On the assembly line there is a roller table gearbox that pulls metal structures through the welding section. Drive - AIR-100L4 engine: power 4 kW, 1430 rpm, 380 V, IP54, cast iron body, paws. The production date according to the plate is 03.1990, the manufacturing plant is the Vladimir Electric Motor Plant.
The chief power engineer of the plant described the situation directly: “This motor survived the entire assembly line. Gearboxes, chains, frames were changed - it worked. Now it's up, humming and warming up. I don’t want to install a new Chinese one - I want to restore this one.” The statement of the task sounded like this:
- to preserve the original AIR-100L4 engine;
- to restore the parameters to a level no worse than the factory ones;
- to provide a service life of at least 10 years of further operation;
- to meet an adequate budget compared to the new engine.
Diagnostics: what the Soviet AIR showed
The engine was delivered to workshop An external inspection immediately gave a picture of 30 years of operation: the cast iron body is intact, but the cooling fins are clogged with a layer of welding dust and oil up to 4 mm thick. The fan is broken on one side (two blades out of six). The terminal box is cracked, the sealed lead-in has been replaced with a twisted one. The pulley sits dead on the shaft - traces of three pullers over decades.
Electrical measurements:
| Parameter | Measurement 2017 | Passport 1990 |
|---|---|---|
| Phase resistance U–V | 3.8 Ohm | 5.2 Ohm |
| Phase resistance V–W | 5.1 Ohm | 5.2 Ohm |
| U-W phase resistance | 3.9 Ohm | 5.2 Ohm |
| Isolation (megaohmmeter 1000 V) | 0.18 MOhm | ≥ 10 MΩ |
| Radial clearance of bearings | 0.42 mm | ≤ 0.08 mm |
The diagnosis is typical for its age: interturn short circuit in two phases, destroyed insulation (BT-987 varnish has become completely embrittled in 30 years), dead bearings, shaft runout. At the same time, the stator core and rotor itself are in excellent condition. Soviet AIR steel - cold-rolled electrical steel, sheet thickness 0.5 mm; You won’t find such metal in modern budget engines anymore.
The main technical question: to repair or replace?
We always give the customer an honest estimate. Replacing with a new AIR-100L4 of Uzbek or Russian production is about 60–70% of the cost of a major overhaul. That is, formally the new one is cheaper. But in this particular case, we recommended restoration for three reasons:
- The quality of the laminated iron of the 1990 stator is higher than that of most modern analogues in the average price category.
- The cast iron housing and bearing shields are cast, with a reserve of rigidity, which is implemented thinner in new motors.
- Installation dimensions (shaft length, seat diameter) after 30 The years of operation of this motor have become unique - the new one will have to be adjusted to the drive.
The chief power engineer agreed. We put the motor in line for a complete restoration: rewinding of the electric motor winding, repair of bearing units, balancing, painting. More information about such work can be found in the section repair of asynchronous electric motors.
Search for components: quest 2017
The most difficult part of the case is not winding, but purchasing. For authentic restoration we needed:
- enamel wire PET-155 with a diameter of 0.8 mm - found in a warehouse in Tashkent, remnants of a Soviet supply;
- Imidoflex groove insulation of class H - ordered through an intermediary from Yekaterinburg;
- bearings 180306 (closed, ball) - replaced with a modern analogue 6306-2Z SKF with the same mounting dimensions;
- original AIR-100 fan - found used while dismantling an old motor in Chirchik, perfect condition;
- terminal box - re-cast according to the old model, processed on a milling machine.
The search took 11 days. During this time, we managed to prepare the stator: we burned out the old winding in an oven at 380 °C (controlled pyrolysis so as not to destroy the iron), cleaned the grooves, and checked the geometry of the core. No discrepancies with the passport were identified.
Rewinding and assembly
Winding was carried out according to the original AIR-100L4 scheme: 4 poles, 36 slots, pitch 1–9, concentric winding, star-delta connection with switchability. This allowed the plant, if necessary, to start the motor through an autotransformer during network sags - a function that modern cheap motors lack.
After installation, impregnation with ML-92 varnish in two passes with intermediate drying. This is a more durable system than the original BT-987, and it increases the TBO by approximately 30–40%. Measurements after impregnation:
| Parameter | After repair | Passport |
|---|---|---|
| Phase resistance | 5.15–5.18 Ohm | 5.2 Ohm |
| Insulation winding-housing | 1200 MOhm | ≥ 10 MOhm |
| Loss tangent | 0.028 | ≤ 0.05 |
The rotor is balanced according to class G2.5 (vibration ≤ 1.8 mm/s). For more information about our standards for working with rotors, see the section rewinding an electric motor rotor. The bearing shields were machined for new bearings with H7 approval, the cuffs were updated, 1/3 of the chamber volume was filled with Mobil Polyrex EM grease.
Bench tests and delivery
At the stand, the restored AIR-100L4 showed parameters even better than the passport ones: no-load current 3.1 A (passport 3.4 A), Efficiency at rated load 82.6% (certificate 82%), power factor 0.84. The engine worked on the stand for 8 hours without any comments on heating and vibration.
The customer accepted the engine on the conveyor with a certificate and an extended warranty of 18 months. At the time of writing this article (August 2017), the AIR-100L4, produced in 1990, is again pulling the roller conveyor of the assembly shop in Tashkent - now, we expect, another 15 years to come.
Conclusions for chief power engineers
This case shows several important points about working with Soviet asynchronous motors of the AIR, A series, 4A:
- iron and body are the main value of a Soviet engine, and they are almost always subject to restoration;
- modern insulating materials make it possible to raise the insulation class from B to F or H without reworking the core;
- replacing bearings with SKF/FAG/NSK analogues with the same fits is a standard and proven practice;
- properly done repair of an industrial electric motor of Soviet production provides a resource comparable to a new middle-class motor.
Do you have Soviet AIR, A2, 4A, AO working in your production? Don’t rush to change - first invite engineers to diagnose it. Contact the Elektromotors team via contact page, and we will visit your enterprise in Tashkent or the region, assess the condition of the motor and give an honest recommendation: repair or replace.