Feeder Selection: The Grizzly Is a Stage, Not an Accessory
A feeder is bought as a conveyor and then judged as one, which is why so many are chosen on tonnage alone. It is actually the first stage of the plant: it absorbs the truck impact, it takes the fines out of the crusher's diet, and it sets the pace the jaw runs at. The bar gap on its deck is the first grading cut in the flowsheet — and removing those bars because they blocked is the most common way a plant quietly loses capacity.
This article covers what the feeder is really doing upstream of a primary crusher, where the vibrating and apron types actually divide, and why the wrong choice is paid for at the crusher rather than at the feeder.
I. Three Jobs, and Conveying Is Not One of Them
Material arrives at the primary in truckloads, in bursts, with a size spread that no crusher wants to see straight from the bucket. The feeder exists to turn that into something a jaw can accept.
• It buffers the impact. A truck tipping several tonnes into a hopper delivers a shock load. The feeder's deck and suspension take it, so the crusher frame does not.
• It removes fines before they are crushed. This is the job people forget. Material already smaller than the crusher's setting should never enter the chamber — it consumes capacity, adds nothing, and packs the chamber.
• It meters. The jaw wants a steady, full chamber, not surges followed by starvation. Feed rate control is what keeps the crusher's throughput curve flat through a shift.
• Conveying is what is left over. If a feeder is selected purely on "how many tonnes can it move", all three jobs above have been left out of the calculation.
II. The Bar Gap Is a Grading Decision
The grizzly section is not a cover over the deck. The gap between its bars decides which fraction bypasses the crusher entirely, and everything downstream is sized on the assumption that it does.
• Set the gap against the crusher's setting, not against the crusher's feed opening. The bypass should take out what the jaw would pass anyway. Set it too wide and usable rock skips the crusher; too narrow and the bars do nothing.
• Bypassed fines have to go somewhere useful. If there is no belt for them, they end up on the ground or back in the feed — and the grading cut exists only on paper.
• Bars block for a reason. Wet, clay-rich or needle-shaped material bridges the gap. The fix is bar spacing, deck angle, vibration amplitude or a different feeder type — never removing the bars.
• Removing them is a silent downgrade. Nothing breaks the day the bars come out. The crusher simply starts doing work it was never sized for, and the loss shows up as a plant that cannot reach its rated tonnage on wet days.
III. Vibrating or Apron: the Line Is the Material
Both types will move the same tonnage on paper. They do not accept the same material, and that is the only comparison worth making.
| Type | Handles well | Struggles with | Grading |
| Vibrating grizzly feeder | Dry, free-flowing, moderate lump size | Clay, wet sticky feed, very large blocks | Built-in bar section |
| Apron feeder | Large lumps, abrasive, sticky, high impact | Fine dry material that spills at the skirts | None, unless a screen section is added |
| Apron with grizzly section | Coarse and dirty feed needing a bypass | Height and cost | Bars over part of the length |
| Vibrating feeder without bars | Uniform feed to a secondary stage | Anything needing a fines bypass | None |
Read the second row against the first. The apron feeder is not the premium version of the vibrating one; it is the answer to a different material. Its chain flights carry the load instead of throwing it, so impact and stickiness stop being problems — at the cost of height, weight and a drive that needs more attention.
• Wet and sticky is the dividing line. Clay blinds a vibrating deck and bridges its bars. On an apron feeder the same material rides on the flights and leaves.
• Lump size decides the deck. A block that a vibrating feeder would bounce is simply carried by an apron. If your shot rock regularly arrives near the jaw's opening, that is an apron duty.
• Height is the hidden cost. An apron feeder needs a deeper hopper and more headroom under the crusher. In a retrofit, that geometry often decides the answer before the technical comparison does.
• Variable speed is worth it on either type. Being able to slow the feeder is how an operator recovers from a choked chamber without stopping the plant.
IV. Where the Wrong Choice Gets Paid For
A feeder is cheap relative to the crusher behind it, which is exactly why the compromise is made there. The bill arrives elsewhere.
• Jaw plates. A feeder that dribbles material into one side of the chamber wears that side first. Uneven plate wear is usually a feeding pattern, not a plate problem.
• Throughput. Every tonne of undersize that enters the chamber displaces a tonne of material the jaw could have reduced. The crusher looks under-sized while it is merely being fed the wrong diet.
• The chamber itself. Fines pack and compact, a condition that reads as a power problem, a blockage or a worn liner, and rarely as a feed problem.
• Loader cycle time. Feeder height sets how far a wheel loader has to lift and how tight it can turn. A tall hopper costs seconds on every bucket, all shift, for years.
• And the wet season. A plant that meets its rate in dry weather and falls short in the wet one is usually describing its feeder, not its crusher.
V. Misuse Worth Naming
• Running a feeder as a belt. Leaving it at one speed and letting the crusher take whatever arrives turns a metering device into a conveyor with extra wear.
• Welding up the bars instead of fixing the cause. A closed grizzly is a permanent loss of capacity disguised as a maintenance fix.
• No bypass belt. Bars without a destination for the undersize do nothing except drop material on the floor.
• Oversized hopper, undersized feeder. A hopper that holds three truckloads feeding a deck that cannot clear them gives you a plant that stops in bursts.
VI. What to Ask the Supplier For
• A capacity figure tied to a material description — bulk density, lump size and moisture — not a bare tonnage.
• The recommended bar gap and how it relates to your crusher's setting, plus the deck angle it assumes.
• Whether the drive is fixed or variable speed, and the turndown range, since that is the operator's only control.
• Hopper volume and the discharge height, because both set the loader cycle and the civil works.
• Deck and flight wear parts, with a cost per tonne for your material rather than a service interval in months.
• The maximum feed moisture the design allows, and what happens to capacity above it.
Frequently Asked Questions About Feeders
Q: Can I replace an apron feeder with a vibrating one to save money?
A: Only if the material is dry and the lumps are moderate. On sticky clay or blocky shot rock the saving is transferred to the crusher as impact damage and to the operator as constant clearing. The material decides, not the budget.
Q: My grizzly keeps blocking. Should I widen the gaps?
A: Widening is legitimate if the bypass is currently set narrower than the crusher's setting. If it is already correct, the blocking is a moisture and shape problem and the answer is deck angle, amplitude, or a feeder type that does not rely on gaps.
Q: Do I need variable speed?
A: If anything upstream is irregular — trucks, a loader, a stockpile that segregates — yes. It is the only way to slow the feed when the chamber starts to choke, and it is far cheaper than the downtime it prevents.
Q: Why does my jaw wear on one side?
A: Look at how material enters the chamber. A feeder discharging to one side, or a chute that throws the stream off centre, concentrates the work on one plate. Fix the delivery pattern before ordering new plates.
For apron, vibrating and grizzly feeders matched to the crusher behind them, see the feeding equipment range.
