Specifying Spiral Freezers
Non-Self-Stacking DesignA non-self-stacking spiral freezer most often is designed as an inline system to freeze myriad food products. The basic system consists of a stainless steel mesh conveyor belt that is arranged in a helical spiral onto which carefully controlled, high velocity refrigerated air is directed over the product to remove heat. The spiral is composed of a conveyor system, air-handling system, insulated enclosure and floor, and control system.
Conveying System. The conveyor belt is a continuous loop of stainless-steel mesh driven by a center-rotating cage. The width of the belt and the type of mesh depend on the application requirements. The conveyor drive uses an AC-frequency-controlled drive system to allow for smooth, continuous operation within a wide speed range. Some designs incorporate an enclosed, sealed, self-aligning center drive to eliminate chains and sprockets. The main drive and outfeed tension drive should be synchronized electronically.
Air Circulation. An efficient, directed airflow is utilized in a non-self-stacking spiral freezer. The air is pressurized by fans through a refrigerated coil and channeled over the product continuously. A slotted cage inside the helical-spiral conveyor and baffling around the outside of the bel t direct air onto the product, maximizing heat transfer efficiency. Available airflows include directed horizontal, vertical or double-vertical, using either axial-flow propeller or scroll-less centrifugal fans, depending on system requirements.
Sa fety. This is a critical issue. The spiral should be designed to be user-friendly with personnel safeties located inside and outside the freezer. The "human factor" should be addressed by a startup safety program. In addition to personnel safeties, pr otection devices should be included to safeguard the equipment in the event of a malfunction or operator error.
Evaporators and Fans. Evaporators and fans supply the cooling or freezing effect, and they should be engineered to minimize power co nsumption and extend running time. The evaporators should be generously sized with variable-fin spacing and can be manufactured from aluminum or hot-dipped galvanized steel. They can be combined with an integrated fan assembly to minimize noise level while ensuring high air-circulating capability, which will keep the freezer online longer.
Insulated Enclosure and Floor. The insulated enclosure should be made with a core of sturdy, expanded polystyrene- or polyurethane-laminated rigid panels to maintain good seam integrity. Surface treatments, both internal and external, are engineered for the application.
An insulated floor is the foundation of any freezer. Standard floor materials are aluminum treadplate, stainless steel or concrete. U nder-floor heating cables can be included where appropriate.
Electrical Equipment and Operator Control. The spiral freezer's control panel should be built to NEMA 4X standard. Controls can be PLC-based and may include an operator interface to d ispl ay all pertinent freezer variables and conditions. Automatic control simplifies freezer operation for many types of products. Temperatures, fault conditions and freezing times should be displayed on the status screen, and datalogging and trending capabilities provide convenient feedback to the operator. Accessories such as a belt washer or clean-in-place (CIP) system can be controlled from this panel.
Self-Stacking Spiral FreezerThis type of spiral freezer is a versatile unit suitable for processing a wide range of products. It is efficient and economical, combining maximum flexibility with minimum space requirements.
Conveying System. Each spiral is tailored to meet t he specific customer requirements for freezer capacity and product conditions. One self-stacking design employs a propriety conveyor belt with side links to allow the belt to stack upon itself as it spirals up and around the insulated enclosure. This design eliminates much of the internal support rail structure.
Air Circulation. In a self-stacking spiral freezer, the spiral belt forms a closed freezing zone through which cold air circulates. This energy-saving feature ensures efficient heat r emoval and minimizes product holding time and dehydration.
Product Range. An array of products can be frozen, chilled or proofed in a spiral freezer, including most cuts of meat and fish, chicken parts, prepared foods, bakery products, ice cream and juice concentrates. Essentially, the freezer can process any product that can be placed on its belt. The spiral stack should be designed so product cannot be blown off by air blasts.
Production Capacity. The self-stacking freezer should d es igned to maximize production capacity. As the spiral is formed, each new layer of the belt should be supported by the side links below it, eliminating the need for a traditional steel superstructure. The area within the freezer enclosure should maximize t he product-freezing zone -- the spiral. Variable belt speeds will allow precise setting of holding times for different products and ensure a quick, high quality freezing process.
Evaporator and Fans. The evaporator surface of the spiral is avai lable in many sizes. Fin spacing varies with the depth of the coil, which results in even frost buildup and minimal airflow restriction. Look for low-noise fans that are unaffected by pressure variations and ensure highly efficient heat transfer.
Control Panel. A self-stacking spiral freezer should employ a computer-based control system to monitor freezer operation to maximize performance. Many controls can be designed to run a specific program that meets the processor's production needs. During production and cleaning modes, the control panel's monitor can display freezer status, alarm faults in the system, and corrective actions to take for a system alarm. Some control systems can log data and keep a history of past performance and ope rator actions. Other features to look for include an emergency stop button and manual control switches for the evaporator fans, belt drive and belt speed in case of an emergency operation.
Safety Switches and Emergency Stops. To ensure operator safet y and minimize downtime, the freezer should be equipped with a number of safety switches, sensors and emergency stops. When activated, these functions stop the freezer.
The doors should be insulated, fitted with electrically heated gaskets and designed for easy access during cleanup and inspection. For the processing of fully cooked and raw meat, seafood and poultr y, a stainless-steel, continuous, seal-welded enclosure should be used. This enclosure design eliminates cracks and seams that can harbor bacteria.
The freezer floor can be constructed with galvanized steel, stainless steel, aluminum treadplate or concrete. Regardless of material, all freezer floors should incorporate a built-in slope and drainage. In addition, high-quality foamed polyurethane insulation will eliminate the need for subfloor heating in smaller size freezers. Larger units shoul d be installed with subfloor heating.
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