Feeding Mechanisms: Screws, Vane Pumps, and Roller Feeding Compared
Feeding Is the "Heart" of an Encrusting Machine
Encrusting machines look similar from the outside. What really determines whether a machine works well is often the feeding mechanism you cannot see. It has three jobs: draw the material down from the hopper, push it toward the nozzle, and deliver exactly the same amount every second. If feeding is unsteady, the weight fluctuates; if it pushes too hard, the dough gets overworked.
Twin Screws: "Drawing and Pushing"
The most common first stage is the screw. RHEON's U.S. patent US6408899B2 describes this approach: each material has its own pair of horizontal screws with flights running in opposite directions, rotating in sync in opposite directions to push material forward from the bottom of the hopper.
Twin screws do two things:
- Continuously draw the material down: Soft, sticky dough or bean paste will not flow down on its own; screws are needed to pull it from the bottom of the hopper.
- Push without kneading: The patent specifically emphasizes that counter-rotating twin screws "push without kneading," preventing the dough and filling from being worked together during feeding.
In its descriptions of the KASEIJIN (火星人) CN050 and CN601, RHEON's Japanese website also mentions that the screws' drive shafts do not come into direct contact with the food, as part of the hygienic design.
Vane Pumps: "Metering"
Screws can push, but they are not precise enough. So screws are often followed by a vane pump: a rotor fitted with vanes that slide radially, forming separate chambers between the vanes. Material fills a chamber, rotates around, and is discharged at the outlet. Each revolution delivers a fixed volume.
The patent points out a problem with conventional designs: on small machines, the spaces between the vanes often do not fill completely, so feeding becomes uneven. The improvement is to align the end of the screw directly with the pump inlet, make the inlet a wide guide surface, and control the speed ratio of the screw and pump separately, so every chamber fills completely without excessive pressure at the inlet.
Roller Feeding and Cycloid Flow Regulators
Besides screws plus vane pumps, there are other approaches to feeding:
- Roller feeding: One or more pairs of rollers grip the material and move it forward, which works well with firmer materials. RHEON's AN210 adds "stabilizing rollers" inside the hopper cylinder; according to the manufacturer, this lets firmer materials feed smoothly.
- Cycloid flow regulator: The KASEIJIN CN700, released by RHEON in 2020, uses a cycloid feeding mechanism. According to the manufacturer, it can steadily extrude dough containing chocolate chips or whole beans, handles highly viscoelastic materials such as caramel and nougat smoothly, and noticeably improves weight accuracy once the flow is stable. The large multi-row Mega Former also uses cycloid feeding.
- Single screw plus a positive-displacement pump (such as a mohno pump): Commonly used for near-liquid fillings such as sauces and sesame paste. The pump-type feeder in RHEON's triple-encrusting options is a screw plus a mohno pump.
Which Feeding Method Suits Which Material
| Material characteristics | Common feeding approach |
|---|---|
| Regular dough, bean paste, meat filling | Twin screws + vane pump |
| Contains particles (beans, chocolate chips, nuts) | Cycloid or large-chamber metering mechanism to avoid crushing particles |
| Fermented dough, highly elastic Chinese-style steamed bun dough | Dough-specific feeding with gentle pushing |
| Fresh cream, custard | Vertical screw + small flow regulator |
| Sauces, liquid fillings | Screw + positive-displacement pump |
This is a guideline, not a rule. Even with the same "bean paste," different water and oil content call for different feeding conditions; see Rheology and Encrusting.
Can the Feeding Method Damage Gluten?
Yes, which is why manufacturers put so much effort into this part. When dough is repeatedly sheared and squeezed, the gluten network breaks down, and the product slumps, the surface turns rough, and the texture suffers. RHEON's CN511 for bread dough and the two-row KASEIJIN WN156 both use a "bread-dough-specific feeding mechanism" designed not to damage the dough, while the CN601 for Chinese-style steamed buns can adjust the feed ratio between the hopper cylinder and the flow regulator according to the material.
Dong-Yih Machinery's DY-201 Automatic Steamed Bun and Mantou Machine is likewise designed around "a traditional technique that does not break down the dough structure."
In practice, besides the mechanism itself, you can reduce damage by not leaving dough in the hopper too long, keeping its temperature from rising, matching the feed speed to the forming speed, and not letting material get stuck in the passages where it is squeezed over and over.
Feeding Methods on Dong-Yih Models
The feeding details on each Dong-Yih model vary by model and custom requirements. Feel free to call us at 06-257-4644 or ask through our Contact page. It is best to bring your own ingredients so we can discuss them together.
FAQ
Q: How are the dough and filling pushed into the machine?
A: Usually screws at the bottom of the hopper draw the material down and push it forward, and a metering mechanism such as a vane pump delivers it into the nozzle at a fixed volume.
Q: What do twin screws do?
A: Two screws with opposite flights rotate in sync in opposite directions to continuously draw and push the material, pushing rather than kneading as much as possible so the material is not overworked and the two materials do not mix.
Q: Will particles in the filling get crushed?
A: Ordinary feeding may crush particles, which is why there are specialized designs such as cycloid feeding and solid-ingredient feeders; see Triple Encrusting.
Q: Does feeding warm up the dough?
A: Materials heat up when sheared and squeezed. In its description of the CN511, RHEON notes reduced machine heat generation to support long production runs. Keep an eye on material temperature during production.