Idler Roller Case Study: Clinker Dust at a Cement Plant

A cement plant was replacing idler rollers on its clinker line every twelve months, and the failures were not worn shells. They were seized bearings on rollers running in fine dust at elevated temperature. We supplied a double sealed roller with a heavier shell and the correct bearing series for the load. Replacement moved from a recurring nuisance to a planned item in the annual outage.

Project Snapshot

The Problem: Fine Dust Finds Every Gap

Clinker dust is not like coal dust or grain dust. It is fine, abrasive and slightly hot when it leaves the cooler, and it settles on the roller housing where the bearing sits. A shell that looks perfect outside is a seized roller inside.

The plant's history showed the pattern. Rollers failed in the same places: under the transfer point and along the first 200 m of the line where the dust had not yet settled out of the air. The failures were not gradual. A seized roller flat-spots the cover and starts a bearing noise, and maintenance found out at the same time as production.

Two constraints shaped the answer. The line runs at high availability, so a roller change has to fit a planned stop. The plant had already paid for cheap rollers once: the price was low and the labour to change 320 of them was not.

Why We Chose Double Sealed Steel Rollers Over Three Other Options

Standard steel rollers with a single felt seal. Excluded. Felt holds dust against the bearing instead of keeping it out, which is why rollers from one batch failed together.

Greased for life rollers with a light contact seal. Excluded. Fine for clean bulk handling, and no protection in a clinker line where the dust is abrasive.

Non-metallic or polymer shell rollers. Excluded. They suit corrosive duty, and clinker brings heat and impact that a polymer shell does not like.

Steel rollers with a double labyrinth and lip seal, the correct bearing series and a heavier shell. Selected. Sealing is the specification that matters here, and the shell thickness matters at the transfer point.

The Rollers We Manufactured

Two sizes carry the line: 133 mm for the main run and 159 mm at the transfer point, where the drop height was also raised. The shell is 4.0 to 4.5 mm steel, which resists flat-spotting when a roller does stop turning.

The seal arrangement solved the problem. A labyrinth path and a lip seal together keep dust out of the bearing, and the housing is bored so the seal seats correctly rather than being pressed in by feel. Bearings are the 6305 and 6306 series, matched to the 1,200 N load per roller rather than to the cheapest part that fits.

Every roller is tested on the plant's own equipment before dispatch: radial runout to a limit below 0.35 mm, drag coefficient below 0.010 and a 72 hour water tightness test that catches a seal that is not seated. The steel idler roller is the model supplied here, and our metal idler roller range covers the same spec in the diameters used along the line.

Installation: How the Work Ran

The rollers went in during a scheduled six day stop, section by section.

The team replaced the transfer point first, with impact rollers and return idlers behind the skirt, because that section produced most of the failures. Alignment was checked with the belt running and again after 24 hours, since a line that has been disrupted always settles.

Troughing angle was set at 35 degrees on the replacement frames, matching the existing installation, and each roller was checked for free rotation by hand before the belt was released. The crew also marked the replacement date on the transfer point frame, which gave the plant a simple way to see the new interval.

Testing and Quality Control

Rollers are inspected through the process rather than only at the end: shell straightness, weld quality, seal seating and bearing fit are all checked, and the finished roller is measured for runout and turning resistance.

At the cement plant, the maintenance team checked runout on a sample of the delivery with a dial gauge and confirmed free rotation on the rest. Seal seating is what the plant now writes into its own receiving inspection, because a badly seated seal cannot be detected by hand rotation.

Results: What the Numbers Show

Bearing seizure on the clinker line has stopped, and roller replacement is now an item in the annual outage rather than a job that arrives without warning. The six day stop replaced the affected section, and nothing there has been changed since.

The plant's maintenance planner keeps a small rather than large buffer of rollers, which the stated service life target makes possible. Energy consumption on the line also fell slightly, which the plant attributes to the drag coefficient of the replacement rollers turning more freely than the mixed set they replaced. The planner now uses the common causes of idler roller failure as a training note for its own fitters.

What This Case Means for Your Project

Idler rollers are bought on price and paid for on labour. On a dusty line, the seal decides whether a roller lasts a year or five, and the shell thickness decides what happens on the day one fails.

If your conveyor runs in dust, heat or corrosive material, send us the belt width, the duty, the troughing angle and the load per roller. We will propose the diameter, bearing series and seal arrangement, confirm the runout and drag limits we test to, and quote with the impact and return rollers included. Send your conveyor data to our team and we will come back with a roller schedule for the whole line.