Oil mill conveying · Bucket elevators · Screw conveyors · Feeders
Bucket elevators, screw conveyors and feeders, sized around the press
Almost everything written about bucket elevators is written for cement plants and mines — 40 metre lifts, hundreds of tonnes an hour, abrasive clinker. An oil mill almost never has that problem. What an oil mill has is a two or three metre lift of warm, oily, sometimes roasted seed that has to move without being crushed, and has to be cleanable before the next batch of a different seed goes through it.
That difference changes what you should be asking for. On the lines we build, the conveying equipment is rarely the capacity bottleneck. It is chosen on material behaviour, contact surface, and how easily it empties — and it is sized around the press it feeds, not around a catalogue number.
Start here: which one do you actually need
- Lifting cleaned seed into a press or roaster hopper — a bucket elevator. This is the common case in an oil mill, and the lift is usually short.
- Moving material along the floor between two machines — a screw conveyor. Enclosed, no lift, small footprint, and it can meter as it moves.
- Keeping a press chamber at a steady feed rate — a press feeder, not an elevator. A feeder controls rate; an elevator only controls height.
- Wet seed, or seed straight out of a washer — a screw conveyor in the cleaning module, with drainage. Buckets hold water and the boot never dries out.
- Roasted sesame or peanut — think hard before using buckets at all. Roasted oilseed is sticky. It clings inside buckets, and what stays behind goes rancid.
- Switching between seed types in the same workshop — whatever you choose, specify how it is opened and cleaned. This is the question buyers forget and regret.
The four things we install, and what each is for
We do not publish a fixed model list for conveying equipment, because it is built to the line. Length, lift, contact material and drive are set once we know the layout. What is fixed is the selection logic below.
| Equipment | What it does | Suits | Watch out for |
|---|---|---|---|
| Belt bucket elevator | Buckets bolted to a fabric-reinforced belt, running vertically between a head and a boot. | Clean, dry, cool, free-flowing seed. Lower cost, quieter, higher speeds. | Hot material and large particles can lodge between bucket and belt. Belting is normally kept well below about 150 °C. Needs belt tracking and tension checks, plus inspection of splices and bucket bolts. |
| Chain bucket elevator | Buckets fastened to one or two steel chains via link attachments. | Hot, abrasive or coarse material. Absorbs shock and surge loads better; resists stretching. | Higher initial cost, more wear, noisier. Chain and sprockets need routine wear monitoring. Usually more machine than an edible-oil workshop needs. |
| Screw conveyor | A screw turning inside an enclosed trough, moving material horizontally or on a slight incline. | Short transfers between machines, cleaning modules, wet or draining material, and anywhere you want the material enclosed. | Not for long distances or real height. Look for independent drives and food-grade contact surfaces where the seed is going to be pressed for edible oil. |
| Press feeder | Bolt-on hopper with an adjustable feed rate, sitting directly above the press inlet. | Holding chamber pressure steady on a screw or hydraulic press. | It is a rate device, not a transport device. It does not replace the lift into the hopper. |
Centrifugal or continuous discharge — the choice that affects your product
Two bucket elevators can look identical and behave completely differently, because of how the bucket empties at the top. This is worth understanding before you accept a quotation, because getting it wrong shows up in your oil, not in your paperwork.
Centrifugal discharge
The elevator runs fast. Buckets scoop their own load by plowing through the pile in the boot, and at the head pulley centrifugal force throws the material out into the discharge chute. It gives the higher capacity of the two and is more compact for the same throughput. It suits free-flowing, durable, granular material.
The cost is mechanical violence. Scooping at speed wears buckets, belt and head pulley, and it breaks things. On fragile or friable material a centrifugal elevator produces fines and dust — which for an oilseed buyer means broken kernels and a dustier press feed.
Continuous discharge
The elevator runs at roughly half the speed. Buckets are closely spaced and are fed from a chute rather than scooping. As each bucket inverts at the head, the material slides out gently down the back of the bucket in front of it, which acts as part of the chute. Capacity is correspondingly lower.
This is the gentle option, and it is the one to ask about for fragile, friable or abrasive material, and for light powders that would otherwise aerate and spill. It also reaches higher when built on twin chains.
| Centrifugal | Continuous | |
|---|---|---|
| Speed | Fast | About half |
| Loading | Scoops from the boot | Chute fed, minimal scooping |
| Discharge | Thrown by centrifugal force | Gravity, over the back of the next bucket |
| Capacity | Higher | Lower |
| Best for | Free-flowing, durable, granular | Fragile, friable, abrasive, light powders |
| Wear | Faster, especially on abrasives | Slower at equal duty |
Bucket profile follows the same split: reinforced-lip buckets for centrifugal duty, medium-front profiles for continuous. If a supplier cannot tell you which discharge principle they are quoting, they are quoting a price, not a machine.
What this looks like on lines we have actually built
These are figures from our own project scopes, not catalogue maximums. They are here to set expectations about scale, because the numbers are much smaller than the bulk-handling literature would lead you to expect.
| Project | Conveying equipment in scope | What it serves |
|---|---|---|
| Coconut oil production line | 2 stainless-steel elevators, 1.5 kW each. One S500 conveyor, 10 m, 3 kW. | The elevators lift prepared, dried material to two Model 128 screw presses running 160 kg/hour each. The conveyor moves whole coconuts between the raw-material workstations, alongside 20 manual peeling tables at 600 × 600 mm. |
| Binzhou-format peanut oil shop | One bucket elevator: 1.5 m lift, 0.5 × 0.5 m footprint, low-power feed-style hopper. | Feeds a single Model 325 hydraulic press shop alongside a 200 kg thermal-oil pan and a 300–350 kg/h crusher. The entire equipment set occupies about 18–22 m². |
| Sesame washing and drying module | Screw conveyor integrated in the cleaning tank, feeding a stone and heavy-material discharge, then a centrifugal drying drum. | Handles seed while it is wet, which is exactly the duty buckets are bad at. Specify dual-motor independent drives and food-grade contact surfaces. |
Note the pattern: a 1.5 m lift and a 1.5 kW motor. A one-tonne-per-day shop does not need a heavy chain elevator, and paying for one buys wear and noise rather than throughput. On our line scopes the elevator line item reads “confirm lift height, capacity, contact material, and whether power is quoted per unit” — those four questions are the whole specification at this scale.
Where bucket elevators go wrong in an edible-oil workshop
Bucket elevators are a mature, reliable design. The failure modes are well known, and most of them happen to be the ones that matter most in food processing. Read this list as the case for asking questions, not as a reason to avoid the equipment.
The boot does not empty itself
Material sits in a pile at the bottom inlet so the buckets can load themselves. When you stop the machine, that pile stays there. It is not swept out by running the elevator empty. In a mill that presses sesame on Monday and peanut on Tuesday, that residue is a cross-contamination and allergen problem, and in an oily material it is a rancidity problem. Where sanitation genuinely matters, this is the strongest argument for a screw conveyor instead.
Sticky material clings to the buckets
Bucket elevators are a poor fit for cohesive or sticky material, which stays in the bucket instead of discharging. Roasted, oil-bearing seed is exactly that kind of material. Capacity quietly drops as buckets carry a permanent lining, and the lining is the part that spoils.
Light powders can fluidize
Very fine, aeratable powder can spill from the buckets in transit rather than ride up in them. If you are moving meal, press cake fines or ground product rather than whole seed, say so before the elevator is sized — continuous discharge exists partly for this reason.
Dust is produced, and dust has consequences
Any bucket elevator generates dust. Housings can take exhaust ports for collection, and explosion protection is available where the dust warrants it. Oilseed dust in an enclosed workshop is worth a serious conversation, not a line item.
One inlet, one outlet
A standard elevator serves a single destination. If you need to route to two presses or to a press and a silo, that needs either a gravity diverter valve with spouting or a horizontal screw conveyor at the top. Plan it into the layout; retrofitting it is expensive.
Belts and chains stretch
Take-up adjustment is not optional maintenance. Slack needs checking regularly, or alignment and discharge timing drift. Belt alignment, speed, bearing temperature and material plugging can all be monitored cheaply, and on a line where downtime costs you a pressing day, that instrumentation pays for itself.
How capacity is actually calculated
Buyers often ask for “a two tonne per hour elevator” without the one figure that makes the number meaningful. Here is the arithmetic, so you can see what is missing.
- Volumetric throughput — bucket volume, multiplied by belt speed, divided by bucket spacing.
- Gravimetric throughput — volumetric throughput multiplied by the bulk density of your material.
- Bucket volume depends on geometry and on how full the bucket actually runs, which is never 100 percent.
- Bucket spacing is commonly around twice the bucket projection, measured from the outer lip back to the belt.
The consequence: an elevator rated in cubic metres per hour tells you nothing in tonnes until you supply bulk density, and oilseeds vary widely. Rapeseed, whole peanut kernel, shelled sunflower and press cake all fill a bucket differently. Send the material and the moisture, and the tonnage figure becomes real.
One rule of thumb worth knowing: bucket elevators start to make sense as the vertical distance exceeds roughly three to six metres. Below that, a screw conveyor on an incline, or simply a better machine arrangement, is often cheaper and easier to clean.
Where conveying sits in the line
Receiving and cleaning
Seed arrives, stones and metal come out. If washing is involved, transfer here is a screw conveyor with drainage, not buckets. Cleaning quality decides more of your yield than the choice of press does.
Lift to the roaster or press hopper
The classic bucket elevator duty. Short lift, enclosed, sized to the press it feeds rather than to a round number.
Feed the chamber
A press feeder holds the rate steady so the chamber keeps pressure. Elevator and feeder do different jobs and you generally need both.
Move the cake away
Press cake leaving the machine is warm, sometimes broken, and often sold as feed. Enclosed screw transfer keeps it clean and keeps the workshop walkable.
Oil side and packaging
Past the press, transport becomes pumps and pipe for oil, and bottle conveyors on the filling and packaging line. Different equipment, different questions.
What to send us so the quotation means something
Conveying equipment cannot be quoted from a model number alone. Six answers are enough to configure it properly.
- The material — which seed, whole or cracked, raw or roasted, and its moisture. Roasted and oily changes the answer completely.
- Rate and the machine it serves — kilograms per hour, and what is downstream. We size to the press, not to a catalogue figure.
- Lift height and horizontal run — floor to hopper inlet, and the distance between the machines being linked.
- Contact material — whether you need stainless product-contact surfaces, and whether a grade has to be stated for your market.
- Cleaning regime — how often you change seed type, and whether the machine has to be opened and cleaned between runs.
- Power supply — local voltage, phase and frequency, plus whether quoted power figures should be per unit or for the set.
If you are still deciding the shape of the whole plant rather than one machine, start from turnkey oil mill solutions and let the conveying fall out of the layout, which is the order that avoids rework.
Common questions
Do I need a bucket elevator for a small shop?
Often not. Bucket elevators earn their place once the vertical distance is more than about three metres. A single-press shop is frequently better served by a feeder plus a sensible machine arrangement. The Binzhou-format shop we supply does use one, but at a 1.5 m lift and a footprint of half a metre square — that is a small device, not a plant item.
Belt or chain for oilseed?
Belt, in most edible-oil workshops. Chain exists for hot, abrasive and coarse duty — clinker, ore, coal. Clean dry seed is neither, and chain brings higher cost, more wear and more noise for capacity you do not need. Chain becomes the right answer when material arrives hot or in large lumps, or where surge loads would stretch a belt.
Can one elevator feed two presses?
Not directly. An elevator has one inlet and one outlet. Feeding two presses means a gravity diverter valve with spouting, or a horizontal screw conveyor across the top. Our coconut line solves it the other way, with two elevators for two presses.
How do I clean a bucket elevator between seed types?
By opening it, not by running it empty. The boot holds a pile of material that does not clear itself. Ask specifically about access panels at the head and boot, the contact surface finish, and how long a changeover cleaning takes. If the answer is vague and you change seed often, use a screw conveyor for that transfer instead.
Why does nobody publish a capacity table?
Because capacity in tonnes depends on your material’s bulk density, and a rating in cubic metres per hour is what the machine actually has. Two mills with identical elevators moving rapeseed and press cake get different tonnages. We quote the figure against your material rather than printing a number that would need a footnote.
Is stainless steel necessary?
It depends on the market you sell into and on where in the line the machine sits. Our coconut line uses stainless elevators because the material is a wet food product before pressing. Confirm the product-contact grade explicitly in the quotation rather than accepting “stainless” as a single word — that is standard practice on all of our process specifications.
Related equipment and reading
Send us the layout and we will specify the conveying
Tell us the seed, the rate in kilograms per hour, the lift from floor to hopper, the machines being linked, your local voltage, and how often you change seed type. We will come back with the elevator or conveyor that fits the line, the contact material, and what it costs delivered.