Tunnel oven process

There are two primary pultrusion processes. In one method, the pultrusion passes through a long heated die or oven for cure. This is called the tunnel oven process. In the second method the composite is cured with radio frequency energy. This causes cure in a much shorter period of time. 

Extrusion is the first really new technology to arrive in the food industry for many years. Tunnel ovens are a development of an oven while the sort of mixer used for the CBP process is a development of a mixer, albeit one that can apply a great deal of energy in a short time. 

The one stage of the baking process that can easily be worked continuously is baking. The bread is fed into a tunnel oven and emerges baked at the other end. 

In case of single firing the sherd and glaze are fired in a simultaneous process. This is applied for floor tiles and traditionally takes place in a tunnel oven or in a quick firing process at a temperature of about 1170 °C. In case of a quick firing process the tiles are not transported through the oven in a compact way as in the tunnel oven,... 

A suggested step-by-step sequence in the microbial validation of a dry-heat process for sterilizing and depyrogenating large-volume glass containers by a convection batch oven is presented. Procedures for the validation of a tunnel sterilization process have been reported by Wegel [25] and Akers et al. [26],... 

The two types of processes currently used in dry-heat sterilization include 1) dry-heat batch sterilization/ oven sterilization and 2) dry-heat tunnel sterilization. Process 1 is the type of dry heat unit widely used in the pharmaceutical industry it uses the principle of convective heat transfer to heat the load. Process 2 is only found in large-scale processes, and the main application of this process is in the sterilization and depyrogenation of glass.f ... 

An oven in the form of a tunnel mounted over or containing a continuous conveyor belt is used to shrink oriented films in the shrink packaging process. Also use a hot air blower on the film to provide the heat required in specific areas. 

Heating can be achieved by discontinuous processes, such as heated moulds, ovens, or by continuous processes such as hot tubes for wire curing or hot tunnels. 

Esveld et a/.81,82 developed a continuous dry media reactor (CDMR) for pilot-scale applications. It consisted of a multi-modal tunnel microwave cavity operating at a frequency of 2.45 GHz with a power range from 0 to 6 kW irradiated on a surface of 0.6 m2. Temperatures of up to 250°C were achieved. A web conveyor travelling at 17 cm min-1 transported the solid-phase reaction mixture to the oven in low, open Pyrex supports closely packed on a polytetrafluoroethylene (PTFE)-coated glass fibre. An open flat bed process was employed to facilitate easy evaporation. 

As with any sterilization process, the first step in dry-heat sterilizer validation involves qualification of all the equipment and instrumentation used. This step includes examination and documentation of all utilities, ductwork, filters, and control valves or switches for the oven or tunnel unit, and the calibration of the instrumentation used in validating and monitoring the process. The instruments used are as follows ... 

Principles as described above for the physical process validation of batch ovens apply also in the validation of tunnel sterilizers however, in addition to the variables affecting batch oven validation, tunnel sterilizers have an extra variable-belt speed. This variable can be held constant by maintaining the same belt speed throughout the validation process and not changing it after validation has been completed. 

Dry-heat tunnel sterilization is a continuous conduction process in contrast to the batch processes in ovens. A continuous conduction process is one in which a predetermined quantity of items is subject to a continuous conduction cycle at a predetermined rate to effect sterilization and/or depyrogenation. ... 

Compendia] cycles are only applicable to ovens because there are too many variables in tunnels (bell speeds, stoppages, preceding materials, etc.) lo be encompassed in simple generalized process specifications. Compendial cycles in the British Pharmacopoeia require 160 C for 2 hs, 170 C for I h, or I80 C for 30 min. The USP refers rather obliquely to temperatures in excess of 2S0 C. 

Tunnel. The tunnel is a thermally insulated passage through the length of the oven where the board is heated and cooled for a continuous reflow process. It serves to insulate the... 

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