Variable-speed conveyor for freezing fish and seafood: setting belt speed from freezing time, and choosing a belt that survives the cold
Fish and seafood freezing lines · the inverter-driven belt whose speed is the residence time in the cold zone, the belt and rod materials that stay usable at −46 °C, and tiered belts run at separate speeds
On a fish freezing line the conveyor is the clock. The product has to stay in the cold air or cryogen for as long as it takes to freeze, and that time is fixed by the product, so the belt speed has to follow it: a product that takes longer to freeze needs a slower belt over the same length. That is why the conveyor that carries trays or loose product into and through the freezing zone is bought with an adjustable drive rather than a fixed-speed gearmotor. Two further choices come with it: whether the run is a single straight belt or two or three stacked belts at their own speeds, and which belt and hinge-rod material keeps its strength at freezer temperatures.
Adjustable-speed belt conveyors that carry fish, shellfish and seafood portions or trays into and through air-blast, cryogenic and chilling sections: speed set from freezing time, belt length and loading; single-pass and stacked multi-pass belts with separate speeds; plastic modular belt and rod materials for sub-zero service; and drive arrangements kept outside the cold space. Cryogenic tunnel freezers as complete machines are covered on the Cryogenic tunnel freezers for fish and seafood page and their spray headers on the Liquid-nitrogen spray header and nozzle system page; spiral-freezer housings on the Insulated enclosure for spiral freezers page; the speed control units and inverter cabinets themselves on the Conveyor motor speed controller page; tray conveyors in front of tray sealers on the Tray infeed conveyor for tray sealing lines page; underwater pasteurizing and chilling conveyors on the Submerged belt conveyor page; and stainless wire belts on the Stainless Steel Conveyor Belt page. Machines that cut fillets from whole fish are covered on the Industrial fish filleting machine page and the blade units of portion cutters on the Cutting assembly for fish and meat portion cutters page.
CNFX editorial research · Sources checked October 13, 2026 · 4 sources
Working out belt speed from freezing time, belt loading and belt length
FAO's manual on freezing fish sizes a continuous belt freezer from three numbers: the freezing time, the throughput in kg/h and the loading density on the belt. [1] The same three numbers fix the speed the conveyor drive has to hold.
Editorial calculation on FAO's example: at the same 8.4 m and loading, a product that froze in 9 minutes would let the belt run at about 0.93 m/min and carry about 400 kg/h, while one needing 30 minutes would hold the belt to 0.28 m/min and about 120 kg/h. FAO puts the practical ceiling there, saying a product with a freezing time of more than 30 min is unlikely to suit a belt or conveyor air-blast freezer because the freezer would become too long. [1] The speed range the drive needs is therefore set by the shortest and longest freezing times of the products the line will run.
FAO adds that double or triple belts or a spiral reduce the floor space, but considers double and triple belt freezers more suited to battered and breaded fish portions unless the design provides for moving partially frozen fish off an open metal mesh belt onto the next one. [1] DSI Dantech's multi-pass tunnel for small portioned fish, shrimp, cockles and mussels with long cycles runs three stacked belts, discharges product from the first tier to the second and third, and makes the speed of each belt independently controllable. [3] Praxair's JE-U4 straight cryogenic tunnel, which lists seafood among its products, is built with variable speed and external drive components and with turn-up/turn-down capability, and reaches internal temperatures as low as −150 °F depending on conditions and cryogen. [4]
Step in FAO's example
Value
Editorial calculation: what it means for the drive
Give the conveyor supplier the shortest and longest freezing times you will run, the throughput for each, the loading in kg/m² or trays per metre, and the belt length inside the cold space; ask for the speed range in m/min at the drive's minimum and maximum, and where the motor and gearbox sit relative to the insulated section.
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Polyethylene, acetal with polyethylene rods or polypropylene: belt ratings below freezing
A plastic modular belt's temperature rating depends on the belt and hinge-rod pair as much as on the module. Intralox's continuous-temperature ratings for its Series 1600 open-hinge flat-top belt show how much strength is given up to run below 0 °C.
Editorial calculation from Intralox's table: swapping the polypropylene rod in an acetal belt for a polyethylene rod to get down to −46 °C keeps about 72 % of the belt strength (14,600 / 20,400 N/m), whereas an all-polyethylene belt rated for the same temperature has about 25 % (5,110 / 20,400 N/m). [2] Polypropylene is rated only from 1 °C [2]; editorial note: on a freezing line that confines it to conveyors ahead of the cold zone. Intralox describes the Series 1600 surface as smooth and closed with flush edges and cam-link hinges that open as the belt goes round the sprockets for cleaning access. [2]
Metal belts carry their own problems in fish freezing. FAO lists stainless steel mesh and chain link belts as the belts used in continuous belt freezers and names their drawbacks: cost, a crinkled or indented look on fish loaded directly on them, and difficulty getting the frozen product off. [1] Praxair specifies a mono-planar belt in its straight tunnel and says it prevents frost build-up. [4]
State the lowest temperature the belt will see in service and in defrost, the load per metre at the slowest speed, and whether tray or product release at the discharge end has been tested on the belt surface offered.
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Data for a variable-speed conveyor on a fish freezing line
Paste it into your enquiry below or into an email to a maker, then replace every bracket.
Products: [species and form; thickness; freezing time, shortest and longest]
Throughput: [kg/h per product; loading kg/m² or trays per metre]
Layout: [belt width; length inside the cold space; single pass or stacked tiers]
Speed: [range in m/min; separate speed per tier; control signal]
Belt: [material and rod; lowest service temperature; surface; release at discharge]
Drive: [motor and gearbox position outside the insulated section; washdown rating]
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Compiled and source-reviewed by the CNFX editorial team.
Each manufacturer above links to the page on that company's own website where the product is listed, with the date we checked it. How we source and review
· Page last updated 13 October 2026
Buyer questions
How fast does the belt in a fish freezer run?
It follows the freezing time. In FAO's example, 200 kg/h of fish needing 18 minutes at 7.2 kg per metre of belt requires about 8.4 m of belt; by editorial calculation that is a belt speed of about 0.47 m/min. [1]
Is there a limit to freezing time on a belt freezer?
FAO says a product with a freezing time of more than 30 minutes is unlikely to suit a continuous belt air-blast freezer, because the freezer would become too long. [1]
Which plastic belt materials work in a freezer?
Intralox rates polyethylene belts, and acetal belts with polyethylene rods, at −46 to 66 °C; polypropylene and acetal with polypropylene rods are rated from 1 °C upward. [2]
Can stacked belts in a tunnel run at different speeds?
Yes. DSI Dantech's three-tier multi-pass tunnel for shrimp, mussels and portioned fish makes the speed of each belt independently controllable. [3]
Sources and what still needs a direct check
Sources checked 2026-10-13. FAO's fisheries manual chapter on freezers supplies the sizing method; Intralox publishes the belt material ratings; DSI Dantech and Praxair describe how belt speed is handled in their tunnel freezers.
