Thinking Outside the Gearbox
A major pet food manufacturer operates four product extrusion lines, each incorporating a gearbox sourced from an American manufacturer. Initially designed to run with a nominal input speed of 1,400rpm, for operational reasons, the customer has increased this to 2,000rpm. Unfortunately, the result has been repeated gearbox failures.
ERIKS’ Norwich Service Centre was called in to make running repairs as often as every three to six months. These repairs were made even more challenging due to the difficulty of obtaining spare parts for a gearbox made in America.
The customer felt it was time to upgrade to gearboxes with a faster running speed. But that wasn’t as simple as it sounds.
The customer’s co-axial extrusion line gearboxes have the input and output shafts directly in line. With gearboxes of identical design, size and footprint being impossible to source, a gearbox upgrade would mean reordering all four extrusion lines to accommodate them – with all the additional design and engineering costs involved.
In addition, between failures, the existing gearboxes are doing the job they are designed for. So if the root cause of failure can be addressed and rectified, then there’s no reason to go to the expense of replacing them.
ERIKS’ engineers assessed the situation and discovered that the higher running speed is causing the oil in the gearboxes to overheat. The overheated oil then breaks down, so it no longer effectively lubricates and protects the gears and bearings.
For example, the gear case outer temperature was measured to be 100°C; therefore, the oil temperature would be assumed to be up to 110°C – unsustainable without breaking down and failing as a lubricant.
However, the oil being used was the correct specification and viscosity for the application. So it’s not an option to change to a different oil to cope with the higher running speed and temperatures.
PLAYING IT COOL
If the gearbox is the right gearbox for the application, the oil is the oil right for the gearbox, and the high operating temperature can’t be avoided at the required running speed, the problem isn’t the gearbox. It is how the oil behaves when the high operating temperature of the gearbox heats the oil.
This means the solution is not to change the gearbox but to resolve the overheating of the oil.
ERIKS’ answer has been to design and engineer a cooling system to remove the oil from the gearbox, cool it to a suitable temperature, and return the newly cooled oil to the gearbox.
The design involves the lubricant being drawn out of the box through a pipe, carrying the oil through a vessel full of chilled water. This chilled water is already part of the production process on the extruder side, so providing it requires no more engineering or energy than simply piping it into the vessel.
Passing the oil through the vessel rapidly reduces the lubricant temperature to just 60°C; in just a fourminute cycle, the 40 litres of lubricant is cooled, at which point it can be returned to the gearbox once more.
Not only has ERIKS designed and manufactured the solution. They have also made all the necessary food-contact parts out of food-grade stainless steel, so there are no food safety complications arising from the new system.
Now installed on one of the extrusion lines, the oil cooling system has proved so effective at preventing gearbox failures that the customer has commissioned the same system for their remaining three identical gearboxes.