Inspection and repair on MAAG LGD-50 gearbox

This client from VIETNAM came to us with this MAAG LGD-50. We inspected the gearbox and performed a repair. After a succesful testrun we shipped the gearbox back to the client.

The condition of the ball mill gearbox can be considered as good, no acute damage has been observed on the gears or in the bearings. On the electromotor indications for bearing damage have been observed. All additional checks were carried out successfully. Vibration measurement

No immediate signs of bearing damage have been observed. However without gear teeth numbers it is not possible to identify the origins of individual signals, making measurements less efficient. To make optimal use of vibration measurement technologies it is advised to obtain gear teeth numbers from the manufacturer.

The vibration measurement shows indications for bearing damage in the electromotor. High overall values and random shocks in the TWF have been observed. When the operation temperatures of the bearings were requested a temperature of 114 degrees Celsius was given. This is very high for a grease lubricated bearing and indicates severe damage.

Developing bearing damage will first give off high frequency signals, as observed by FLSmidth in 2017. These signals will gradually become worse (becoming visible in the acceleration and later the velocity spectrum). Since the last measurement in by FLSmidth in 2017 the bearing defect frequencies have disappeared. They have been replaced by general high vibration values (noise) and raised temperature, therefore substantial bearing damage is the most logical conclusion.

Alignment

The current alignment error is too large, however it does not require immediate corrective action. Part of the alignment error could be caused by bearing damage in the electromotor. Allingment errors will damage couplings and limit the lifespan of roller bearings in the gearbox too. Unfortunately the correct allignment specifications for this installation are not known, technical documentation can be obtained via the service department of Maag. In case this data is not available, the calculation of allignment specifications and thermal expansion problems is a service which GBS provides.

Girth gear

The manual provides no acceptance values for the girth gear runout or backlash. The assessment therefore has to be made based on the previous FLSmidth report and the results of the visual inspection. The damage that was observed (scoring in the root of the teeth) can be an indication for an incorrect gearmesh or too little backlash possibly caused by too much runout. Frequent visual inspections will have to be carried out to monitor progress of the scoring. When the scoring in the root of the teeth takes more serious forms corrective action needs to be taken.