Cooling and Freezing of food products is in most cases an integral and final part of the processing line just before the primary packaging.
The typical machine in these cases is a spiral conveyor that can work either in ambient temperature or in air conditioned or refrigerated cabinets, even if some straight freezing tunnels are still sold, they are not even closely as popular.
In this article we are going to concentrate on the main conveyor technologies used for these applications, spirals conveyors are not all the same and each technology has its ups and downs that should be taken into consideration for the overall machine selection. All the systems are based on a sideflexing chain and what we have been seeing is polymers constantly replacing steel, now not only for the body of the chain but also for the connection pins. Modular chain give huge advantages for maintenance and sanitation and new materials are increasing the versatility in terms of temperature range and properties for direct contact with food products.
The first technology on our is the side drive, in this case the chain is pulled by pinions placed on each spire on the outer edge of the spiral conveyor. These pinions are connected with the same shaft and joint; depending on the configuration and speed multiple shafts with pinions may be needed on different sizes of the spiral.
The downside of this system is immediately evident due to the complicated mechanics and extra safety enclosure needed, but on the up side the side drive gives almost unlimited flexibility in terms of layout and configuration allowing oval tracks and intertwined spires that give great benefits in terms of space occupation. This technology has been available for quite a long time now, so it’s mature but far from fading and the switch to plastic modular chain promise interesting developments.
The introduction of modular chain is what drove the development of the drum drive technology that allowed to use normal sideflexing modular chain for the longest conveyors section without any special reinforcement. The whole concept of the drum drive is to have a rotating drum (either continuous or a cylindrical cage) inside the spiral on which the chain is pulled. The drum will move at a little bit higher speed compared to the one required by the conveyor (called overdrive) and doing so will pull the chain applying low tension.
The advantage of being able to drive many meters of chain, filled with products, with just two motors (one of the drum and one to help the chain to get out from the drum) is significative even if balanced with the complication of the chain tensioning system as well as a control system that allow to finely adjust the speed of the drum to the correct overdrive speed.
Another downside is that the configuration of the spiral is pretty much fixed to a cylindrical shape with just the possibility to choose the position of in and out.
Kind of a middle way between the two solutions above there is the direct drive system, also thought for a modular chain, this uses a rotating drum too, but this one acts as a giant sprocket, actively engaging the inner side of the chain. It retains the same low tension capacity of the drum drive as well as simple mechanics and low number of motors, but its limit is still the circular configuration only, while resolving the issue of the control system for the overdrive speed.
Last but not least, M.H. Material Handling has another quite unique solution that can be used only after the primary packaging but is extremely compact and allow many meters of conveyor even with products in a single row. The Heliflex System is a special table top chain that uses double rotating drums with direct drive concept (so the drums act as pinions), that uses a single motor. It is suitable for a niche of applications, mainly the cooling of melted cheese after the wrapping and of ready-made dishes in open or sealed trays. While being limited to the packed product and to one or two lanes, the Heliflex still is a great deal after primary machines allowing to make the cooling in a compact footprint with competitive costs.
