Chute liner repair and hopper wear repair: rebuilding chutes, hoppers and cyclones during a shutdown

Repair the chute you have, in the window you have

Chute liner repair and hopper wear repair start with the wear mechanism, not the product: sliding abrasion, impact, erosion and build-up each call for a different fix. During a shutdown, the usual toolkit is hardfacing, AR steel wear plates, bonded or bolted ceramic, trowel-applied ceramic-filled epoxy and elastomer linings, often combined zone by zone.

Choosing a liner material for a new chute is a design question, covered in our comparison of alumina ceramic vs AR steel. Crusher liners are cast parts with their own grade logic, covered in crusher wear parts alloy selection. This article deals with the common situation in mines and cement plants across Quebec and Ontario: an existing chute, hopper or cyclone is worn, sometimes holed, and must go back into service inside a fixed shutdown window, with whatever fits through a manway.

The four wear mechanisms in chutes, hoppers and cyclones

The same piece of equipment usually shows several mechanisms, each concentrated in its own zone. Reading them correctly on the worn surface is what makes the repair last.

• Sliding abrasion. Bulk material slides under its own weight along the chute floor or hopper walls. The surface comes out polished, with scoring in the direction of flow and a gradual, even loss of thickness. Hardness relative to the particles is the main defence.
• Impact and gouging. Lumps fall onto the drop point, the head of the chute or the hopper wall opposite the feed. The surface is dented, gouged or peened, and hard but brittle liners crack or lose tiles here. Toughness matters more than hardness.
• Erosion. Particles carried by air or slurry strike the surface: cyclone inlets and cones, the apex of a hydrocyclone, ducts after a mill or separator. In wet circuits, corrosion joins in, and the combined erosion-corrosion removes steel faster than either mechanism alone. The angle at which particles hit decides which material holds best.
• Build-up and hang-up. Wet, sticky or fine material packs in corners, valleys and behind ledges, then arches or ratholes in hoppers. It is not wear in itself, but it causes wear: barring and hammering damage liners, flow diverted around the deposit cuts a new channel, and steel corrodes under it.

Inspecting before the shutdown: thickness, impact zones, perforations

The repair scope is decided before the stop. Three things need to be known.

Remaining thickness. Ultrasonic thickness measurement on steel shells and wear plates, taken on a marked grid, gives the wear map. Where access is safe, much of it can be done from the outside while the plant is running. Measure the same points every time; a single reading tells you the state, a series tells you the rate and whether the chute will reach the next window. On ceramic or epoxy linings, reference marks and depth gauges replace the ultrasonic gauge.

Where the impact actually lands. Material trajectory changes with throughput, lump size and belt speed. The real impact zone shows as a gouged or peened patch, often offset from where the original designer placed the impact plate. Photograph it with a scale in the frame.

Perforations and hidden damage. Dust or slurry leaks, rust streaks on the outside of the shell, daylight visible from inside: all point to wear-through. Check behind lost tiles and missing plates, where the shell has run unprotected, and check liner bolts and weld attachments.

From these three readings comes a simple decision per zone: re-protect, rebuild then protect, or replace the section of shell.

Repair options for worn chutes and hoppers

Hardfacing adds heat to a shell that may already be thin, and softens heat-treated AR steel nearby. Bolted AR plates are the default for impact zones and can be changed piece by piece. Trowel-applied ceramic epoxy rebuilds irregular worn shapes cold, which makes it the natural choice for cyclone parts, transitions and areas too awkward to plate. Our comparison of cold bonding vs welding sets out when each route fits. A chute is rarely repaired with a single option: bolted AR or a rock box at the drop point, ceramic or ceramic epoxy on the sliding floor, epoxy to rebuild the transitions.

Applying ceramic-filled epoxy on site: the procedure

The material is rarely what fails. Bond failures come from preparation, moisture and cure. The steps below are the general sequence; quantities, thicknesses, temperatures and cure times come from the product's technical data sheet, not from habit.

1. Isolation and entry. Lock out feeders, conveyors, gates and any upstream equipment that can deliver material, according to the site's lockout program (CSA Z460 is the Canadian reference). A chute or hopper is usually a confined space: atmosphere testing, an attendant and a rescue plan apply under provincial rules and the site's confined space program. The bin must be emptied and hang-ups cleared from outside before anyone enters; nobody works below hung-up material.
2. Clean-out. Remove build-up, scale, loose tiles and failed liners, then confirm the wear map against the grid measurements.
3. Structure first. Perforations and thin areas are repaired before the wear protection: a welded plate where hot work is allowed, or a bonded steel patch where it is not. Epoxy is a wear surface, not a structural repair of a holed shell.
4. Surface preparation. Abrasive blast to a clean, dry metal with an angular surface profile as specified on the data sheet. Where blasting is not possible, power tools to bare metal with a profile. In slurry service, check for soluble salts. The steel must be dry and above the dew point during application and cure.
5. Application. Mix full units, press a first layer into the profile to wet it out, then trowel the compound to the thickness shown on the data sheet. Use templates or straightedges to restore the original geometry of cones, inlets and transitions. Terminate edges in a keyed groove or against a retaining edge so that flow cannot lift them.
6. Cure. Hold the surface within the temperature range specified until the product reaches the cure stated for service. Restarting early is the most common cause of premature loss.
7. Record. Photograph, measure the applied thickness at the grid points and add it to the wear map. The next inspection starts from these values.

The same preparation and application logic applies to slurry pump casings; our guide to centrifugal pump epoxy repair details it for rotating equipment.

Designing out part of the wear: angle, rock box, deflectors

A repair that restores the original geometry also restores the original wear pattern. Where a zone keeps failing, the geometry deserves a second look.

Angle. Chute and hopper walls must be steep enough for the material to slide on the liner itself, which depends on the material's wall friction against that liner, measurable with a shear tester (ASTM D6128 covers the Jenike method). Hopper valleys, where two walls meet, are shallower than the walls and are where hang-ups start; rounded corners or valley liners help. Changing the liner changes the wall friction, so a new lining can change flow behaviour.

Rock box. A ledge that traps material so that incoming material lands on itself rather than on steel. It takes impact out of the liner entirely. It does not suit wet, sticky material, which can pack the box and turn it into a dam, and the weight of trapped material must be checked against the structure.

Deflectors and curved chutes. Replaceable impact plates at the actual trajectory, and curved hood-and-spoon designs that keep the stream in contact with the chute, reduce impact at the transfer and on the belt below.

Cyclones. Wear concentrates at the inlet, cone and apex. Steps at joints between liner sections create local turbulence and a new wear point, so rebuilds should be flush. Cement preheater cyclones run at temperatures far beyond an epoxy's range and belong to refractory work, not cold repair.

Planning around spring and winter shutdown windows

Many cement plants in Quebec and Ontario take their annual kiln stop in winter or early spring, before construction demand returns, and mines schedule concentrator and crushing plant shutdowns through the year. Both seasons shape a wear repair.

Winter. Steel inside an unheated chute can sit well below the application range of an epoxy. The work is then tented and heated, the substrate brought into range before application and kept there through cure, or a low-temperature formulation is selected. Our article on cold-weather epoxy application during winter shutdowns covers the four readings that decide whether a product will cure.

Spring. Thaw brings water: frozen material releases moisture and cold steel condenses. Dew point checks become the governing control, with dehumidification or heating when needed.

In both cases, the wear map and material quantities should be ready before the window opens: long cure times and late deliveries are what push a chute repair past restart.

FAQ

Can a worn chute be repaired without welding? Yes. Ceramic-filled epoxy, bonded ceramic tiles and bolted wear plates can all be installed without hot work, which matters in dusty areas or where a hot work permit is hard to obtain. Heavy impact zones still need plates, composites or a rock box rather than epoxy alone.

Can ceramic epoxy be applied over a perforated shell? Not as the only repair. The perforation is restored first, with a welded or bonded patch, and the wear protection is applied over sound metal.

What is the best wear resistant coating for chutes? There is no single one. Ceramic-filled epoxy suits sliding abrasion, erosion and irregular shapes on moderate duty; it does not replace plate or composite liners at a drop point. Choose zone by zone, by mechanism.

How long before the chute can be put back in service? It depends on the product's cure schedule and the temperature held during cure. The data sheet gives the values; plan the cure inside the shutdown window, not after it.

Why does the new liner wear out in the same place every time? Because the geometry sends material to the same spot. Look at the trajectory, the chute angle and the possibility of a rock box or deflector before relining again.

In practice

A chute or hopper repaired by mechanism, with the geometry checked and the cure planned inside the window, stops being a recurring emergency at every shutdown. Induscoat carries out on-site wear repairs on chutes, hoppers, cyclones and slurry equipment in mines and cement plants in Quebec and Ontario through its maintenance and rehabilitation service, using the cold bonding repair method where hot work is not wanted. Send photos of the worn zones, the material handled and your next shutdown dates to request a quote. Technical data sheets for the Induscoat range are published on the brand site, induscoat.com.