In the power transmission world, there are varying schools of thought regarding the quality versus price equation. In instances where avoiding machine failure is critical to the success of a business, risk management has evolved to help decision makers reduce the chances of costly machine breakdowns. After establishing the context, identifying and assessing risks, the best equipment is normally specified. There are, however, some applications that aren’t as critical, which is when price is perceived as being more important than quality.
Premature wormwheel failure, with a broken tooth section
Last week, a customer brought in a wormbox that he had purchased from a Chinese/Italian manufacturer to our workshop for assessment after it had failed prematurely and under little load. The customer was perplexed as to why a straightforward application (packaging industry) would cause the gearbox to fail. The initial teardown revealed a piece of the wormwheel had snapped off, although delving further into the reasons for it breaking off showed the true cause of the failure; the bronze wormwheel was cast to only an unmachined and irregular-shaped cast iron surface, with no positive keying of the two materials.
The Bonfiglioli wormwheel (right) features cast lugs to assist with transmission, whereas the offering on the left relies solely on casting irregularities.
We immediately checked one of our Bonfiglioli wormbox wormwheels for a direct comparison, and found that these come with cast lugs to mate the two parts together. The bronze fills the cast iron keyed sections to avoid failures like the one experienced by the other unit.
As the attached picture shows, the Chinese/Italian output hub (lower of the two, with a broken piece of wormwheel) relies solely on the roughness of the casting for its mating surface, whereas the genuine Bonfiglioli output hub has the lugs that assist the gearbox in transmitting the design torque that is claimed by the manufacturer in the catalogue.
The Total Cost of Ownership (TCO) is obviously more than simply a quality versus price equation, especially in mechanical power transmission. Factors such as diminished performance, outage and failure expenses, added future risks and even the damage to customer loyalty make any initial capital expenditure benefits seem very small. Sometimes the oldest adages still ring the most true: ‘you get what you pay for and you pay for what you get’. In support of this, All Torque Transmissions markets only quality brands of known manufacture.
