Hardening tunnel

Personnel access to operating areas through hardened tunnels with close control of entry/exit... 

Ice cream is hardened in a hardening tunnel, an enclosed chamber into which the ice cream passes on a conveyor belt from the factory freezer. Inside, cold air (typically —30 °C to —45 °C) is blown over the ice cream. The lower the air temperature, and the faster the air flow, the faster heat is removed from the ice cream. Air turbulence also increases the rate of heat transfer. The chamber is enclosed to minimize exchange of cold air inside the system with warm ambient air, and so to reduce the build up of frost that would reduce the efficiency. Cold stores, which are typically about — 25°C, are not suitable for hardening because they are not cold enough and have still air, so they cannot cool the ice cream rapidly enough to minimize recrystallization. 

Tube products use their own package as the mould. The tube is dispensed from a stack into a holder where it is held vertically by its rim. The liquid mix is dispensed into the tube, and the lid is picked up from a stack, placed on top by a vacuum sucker and heat-sealed onto the rim. The filled and sealed tubes are then frozen on a conveyor belt in the hardening tunnel. 

Containerized ice cream is hardened on a stationary or continuous refrigerated plate-contact hardener or by convection air blast as the product is carried on a conveyor or through a tunnel. Air temperatures for hardening are —40 to —50° C. The temperature at the center of the container as well as the storage temperature should be <—26°C. Approximately one-half of the heat is removed at the freezer and the remainder in the hardening process. 

Multiplexed diode laser sensors have also been applied for measurements of gas temperature, velocity, and H2O partial pressures in hypervelocity air flows at the Calspan University of Buffalo Research Center s (CUBRC) Large Energy National Shock Tunnel (LENS Tunnel) in Buffalo, New York [12]. The sensors were developed to provide quantitative characterization of the facility operation and, in particular, the freestream flow properties as a function of time. The measurements were recorded using a hardened probe, which contained critical optical components and photodetectors, that was installed directly into the hypersonic shock-tunnel near the nozzle exit to minimize complications due to boundary layers and facility vibration. 

Adhesion Adhesion of the plastic dry-mix silica fume shotcrete, particularly in wet areas, is substantially improved. For example, adhesion in areas such as locks, dry docks, tunnels, and even leaking structures, can only be achieved through the use of high concentrations of shotcrete accelerators, to create a flash-setting condition, a process that is detrimental to the long-term durability of the hardened shotcrete. Silica fume has been found to promote excellent adhesion in such conditions with minimal or no accelerator addition. 

Bonded insulating materials, e.g. sheets or rolls, are manufactured by spraying a binder resin, generally phenol/formaldehyde, onto the fibers and hardening under compaction in a tunnel kiln... 

In the manufacture of bonded insulating materials, the fibers in the fleece shaft or on the conveyor belt are sprayed with an aqueous binder, generally a phenol-formaldehyde resin. The binder content in the bonded insulating material is 3 to 4%. Compaction to the desired density and hardening of the resin binder occurs in a tunnel kiln, through which the fibers are continuously transported on a conveyor belt. The compaction is achieved with a second belt which exerts the required pressure on the upper surface of the continuous sheet. This is often followed by laminating the sheet with e.g. paper, aluminum or plastic foil. Finally the product is rolled up or cut into sheets. 

Portland cement, invented in 1892 by Joseph Aspdin of Leeds, was so called because it resembled expensive Portland stone (at least to the eye of the inventor). It is made from about 80 % limestone and about 20 % clay. It was widely adopted because it possessed superior qualities to the older quicklime-based material, including the especially important property of being able to harden in damp conditions. This latter property was especially valuable at a time when tunnel constmction was widespread, including amongst other projects, the London underground system. 

Specially hardened bunkers and tunnels have been constructed to protect Scud-Cs deployment, indicating their strategic value. 

The final stage of the production process involves curing, which can be based on room temperature treatment in a tunnel in which moist conditions are maintained, or higher temperature steam curing to accelerate the hardening process. Autoclave curing is also common in the asbestos-cement industry, and in such instances part of the cement is replaced with finely ground silica. Replacement of part of the cement with low-cost inert fillers or fly ash is also sometimes used, for economic reasons. 

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