After mixing, the still-hot black rubber mass is extruded and, after a period of cooling, calendered. A special roller works a textile or wire mesh into the rubber and brings it to the desired strength. After tailoring, the individual layers of fabric of the tyre are brought together in a tyre production machine. Finally, the individual layers are joined together in a heat press. The blank tyre is then vulcanised in heating moulds at over 150 degrees celsius for several minutes depending on its size. This gives the tyre its final shape, its profile and the markings on the sides.
Monitored systematically – failure and downtime prevented
During trend analyses from over 60 mixers and presses which Pirelli carried out in April 2014, the lab report gave a red light twice! Red exclamation marks in the lab report concerning the gear oil from a stamp kneader as well as the hydraulic oil from a press prompted Pirelli Yanzhou to act.
The gear system, which is filled with 750 litres of CLP 320 industrial gear oil, powers the Banbury mixer‘s kneading rollers at the start of the production process. If the mixer fails, no raw materials are available to produce tyres. But almost everything was wrong with the gear oil. Even with the naked eye, large wear particles were visible. With a value of over 300, the PQ index was extremely high and warned against gear damage, because a high PQ index generally indicates severe wear processes progressing rapidly, regardless of the iron value in mg/kg. The AN (acid number) was also raised significantly, and the gear oil showed signs of being burdened and oxidised by the acids in keeping with this.
In his report, the experienced OELCHECK tribologist recommended an inspection of the gearing and that the oil be changed immediately. The gear oil was promptly replaced by the maintenance team at the Pirelli plant in Yanzhou, but due to the favourable situation in terms of incoming orders, the Banbury mixer could not be switched off straight away. It was not until three months later during the next scheduled downtime that the gears were inspected and the damage which OELCHECK predicted was verified.
The constant overloading of the gears had taken its toll. But thanks to the early warning from the OELCHECK laboratory, the repairs could take place during regular maintenance. Sudden failure and unplanned downtime was avoided.