As a critical component in an iron ore circuit, there’s no easy workaround when a damaged trunnion causes a ball mill to malfunction. With no viable alternatives, the customer kept the equipment in operation to maintain its production of 4.5 million tons of iron ore concentrate per year. It was imperative that the new trunnion arrive in the shortest possible amount of time. To facilitate a quick and accurate installation, the mine opted to leverage the expertise of FLSmidth technicians.

Speedy delivery


The customer approached FLSmidth in September 2019, requesting our assistance in replacing the damaged trunnion for their 18-ft-diamater ball mill. Our team acted swiftly to get the 20-tonne trunnion manufactured at one of our patronized supplier’s workshops. The discharge trunnion was ready in just seven weeks, and to further expedite the process we arranged an airlift to deliver it. The trunnion quickly arrived onsite, and installation work commenced on November 11, 2019. 

A team of four FLSmidth service engineers, with a combined experience of over 40 years in servicing mining equipment, began the installation work with the new trunnion. Their experience proved to be invaluable during this phase. 

There isn’t a lot of room for error with a trunnion installation – you have to make sure everything is carefully cleaned, tightened, sealed, protected and lubricated. Even one oversight in the process can cause a problem that shortens the lifespan of the ball mill

Gilberto SilvaService Engineer, FLSmidth Mexico

Proper trunnion installation requires careful attention and precise execution of a lengthy task checklist:

  • Check trunnion flange flatness and setting; remove protrusions with a grinding wheel
  • Clean pads and eliminate scratches to ensure uniformity and surface flatness
    - Thoroughly clean flanges and check for flatness
    - Record original length of each assembly screw
  • Administer general cleaning of the bearing
  • Position trunnion; using a 0.0015" (0.0381 mm) feeler gauge, check that each flange connection is completely in contact
  • Expose connection screws of the trunnion-head connection to a 3-stage elongation process: 50%, 75% and 100%
  • Position the mill on the pads, with the lubrication system running
  • Ensure proper sealing between the trunnion and trunnion liner to impede ingress of foreign materials
  • Protect seal half-rings and trunnion-head connections using a rubber liner to impede contact with slurry circulating inside the mill
  • Verify the twelve screws holding the ring are properly installed; place shims in the discharge head and ring
  • Install trommel
  • Elongate trommel screws in a 2-stage process: 50% and 100%
  • Check oil return pipelines
  • Optimise the lubrication system by checking the high-pressure pump for flow, pressure and amp
  • Test the emergency system performance in supplying oil to the pads during a general power outage
  • Run performance test; monitor and record results to ensure optimal function

Eight-day installation: no small feat

Establishing a new record for trunnion installation, ball mill operation at the mine resumed just eight days later, enjoying a smooth start-up. The plant monitored performance for six days, with no signs of disturbance to flow, pressure or temperature. Parameters proved to be stable within proper specifications.


Because temperature is the most significant indicator of a problem, the team monitored the mill for temperature variation during mill-loading tests as the balls were fed. The feed trunnion showed a 2° C (3.6° F) difference between resistance temperature detectors (RTDs) and a 1° C (1.8° F) difference in the discharge trunnion, which is considered to be an extremely stable temperature across the trunnion. 


Long-term outlook


The new discharge trunnion has been in place since November 2019, keeping the ball mill in operation to meet the plant’s production requirements.


In addition to providing a highly technical installation service within a short timeframe, our FLSmidth team provided the necessary supervisory services and support for onsite controls.

As we typically do for installations, FLSmidth provided customised solutions throughout the process to prevent instances of contamination and wear, including:

  • Sleeve installation in the interior trunnion liner to impede the ingress of foreign material
  • Silicone sealant applied to the “O” ring and halfmoon-shaped plates
  • Silicone sealant applied to the trunnion-discharge head connection
  • Rubber liner to protect the head and seal half rings
  • Trommel modification to provide access to indicators that report material circulation
  • Replacement of carbon steel pipes with stainless steel to reduce potential for rust contamination
  • Lubrication system adjustment to upgrade from ISO 220 oil to ISO 320 oil
  • Modification of the mill inlet’s inner diameter by 70 mm (2.76") to facilitate installation of rubber lining 
From identifying the problem to bringing the equipment back to optimal running condition in less than three months, this has been an extraordinary accomplishment from our very capable service personnel. 

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