Maintenance of large 4t-class foreign-made reducers - KBK Engineering


Maintenance of large 4t-class foreign-made reducers

Maintenance of a large reduction gearbox made overseas, in which spiral bevel gears are used. A pinion shaft with a broken gear section was manufactured, and a spiral bevel gear, which is the mating part of the pinion shaft, was manufactured, and the drive parts were newly manufactured. The mating parts where bearings and oil seals are inserted were repaired, and parts that did not conform to standards were modified to reduce costs. The overseas manufacturer also went out of business due to a merger, so without a company that could service the machine, it had to be scrapped.

Receiving and disassembly

After cleaning the oil stains from the casing, disassembly begins. It is 1.5 m high and 1.2 m in diameter, but it is heavy for its size and is a massive reduction gearbox
When the input shaft was removed and a look inside was taken, the gear part of the pinion gear was completely broken off and had fallen into the casing
The upper casing has been removed to reveal the gear section of the broken pinion shaft. There appears to be little evidence of grinding inside the casing.
Disassembly is now complete. The spiral bevel gear can be seen on the left. The case is also quite large

Inspecting the inside of the reduction gear

Having completed disassembly, each component was inspected. Various pieces of information, such as the intended use of the machine, the surrounding environment and the way the load is applied, are synthesised to determine which parts need repair.

The spiral bevel gear tooth surface is inspected. Numerous scratch marks were observed, which were thought to be caused by contact with the broken gear on the pinion side. The tooth surface is clean, but it cannot be used as it is, so it will have to be manufactured.
This is the broken gear section on the pinion side. The gear is broken from the r part near the bearing. It is presumed to be due to alternating loads caused by a defective bearing fit.
The case in which the bearing fits also needs to be repaired because the dimensions of the part where the outer ring fits have deteriorated. The structurally important elements are also measured at the same time and repaired to ensure that the gear is not damaged again.
The mating part of the output shaft was also dimensioned and surfaced, and it was decided that it would be better to carry out repairs. The blackened areas appear to be the result of corrosion.

Spiral bevel gear production, condition of parts after repair

Photograph of the completed gear. The gear is assembled after cleaning up the black skin from the heat treatment
Fabrication of the broken pinion gear has also been completed. Improvements have also been made to prevent similar broken damage
The case where the bearing outer ring enters has also been repaired. The dimensions and structurally important parts have also been finished with revised tolerances in light of the damage caused this time
The mating parts of the output shaft have also been repaired by changing the tolerances normally used. Repairs were carried out using plating, taking into account usage conditions and damage

Start of assembly

The spiral bevel gears we produced and the number of parts to be repaired increased to several. The case is cleaned and assembly is started
The spiral bevel gear is inserted into the output shaft and the upper case is fitted
After fitting the case, the pinion gear on the input side and the spiral bevel gear on the output shaft are checked for mesh
After assembly is complete, the unit has been neatly painted and is awaiting shipment

Don’t give up even when repairs are not possible

KBK Engineering has a track record of manufacturing components in Japan, procuring consumable parts from overseas and modifying them to domestic specifications so that machines can continue to be used without being scrapped, even if they are made overseas. If your machine is at a crossroads between scrapping and survival, for example because a gear tooth is missing or parts are not available from overseas, please contact us.