Drying tunnel

In paste drying the leather is spread on glass or porcelain plates and held in place with a low strength water-soluble paste. The plates are on a conveyor and the drying is done in a drying tunnel. The dryer usually has several temperature- and humidity-controUed zones to control the rate of drying and to prevent overdrying. 

After this the dough is rolled into sheets, dusted with rye flour and cut into pieces. The pieces are then baked for 10-12 min at 216 249°C. The product is finally dried to below 1% moisture by standing the baked piece on edge in a drying tunnel for 2 3 hours at 93 104°C. 

Fig. 2.13.1. Freeze drying tunnel plant. Upper part in front monorail of the transport system. In the tunnel transport rail for the carrier with trays. In the tunnel heated shelves in between which the carrier with trays is moved. When the carrier is position, the trays are lowereed on to the shelves by lowering the carrier (System CQC , ALD Vacuum Technologies GmbH, D-63526 Erlensee).

Drying tunnel in A 2, valve before the condenser 3, lift- and transport device 4, trays in transport position 5, trays on the shelves during drying 6, heated shelves in B 7, radiation plates 8, trays 9, guide rails for the tray transport 10, separation plate between tunnel and condenser 11, condenser 12, vacuum connection. 

In the final step, a viscoelastic tape is formed as the casting moves through a drying tunnel and the solvent vaporizes. The drying rate varies directly with the solvent concentration on the surface and the temperature and solvent content in the drying medium, which is typically air. Capillary forces transport the solvent to the drying surface. Initial vaporization is relatively slow because the counterflowing air contains... 

Trays of wet material loaded on trucks may be moved slowly through a drying tunnel When a truck is dry, it is removed at one end of the tunnel, and a fresh one is introduced at the other end. Figure 9.8(c) represents such equipment. Fresh air inlets and humid... 

Drying tunnel in A 2, valve before the condenser 3, lift and transport device 4, trays in transport position 5, trays on the shelves dur-... 

The acid process of gelatin preparation is as follows (21) (a) the hides, usually pig, are washed with water and soaked in dilute sulfuric acid (pH - 2 (b) they are washed free of acid and soluble proteins (c) they are placed in extraction kettles and hydrolyzed with successive portions of hot water at an acid pH (d) the dilute solution is filtered and evaporated (e) concentrated solutions are chilled to a gel and (f) the gel is dried with filtered and conditioned air in drying tunnels or in continuous driers. 

Fig. 9 Tray drying of Softgels in controlled drying tunnels.

Paper and pulp are usually dried on atmospheric drum dryers heated by steam, and also in drying tunnels which are divided into several compartments that are kept at various temperatures. 

Diagram of experimental drying tunnel (1) test section, (2) fan, (3) controller air flow, (4) heating element, (5) valve controller of gas, (6) thermometer of wet bulb, (7) thermoanemometer, (8) spheres, (9) video camera. 

Solvent casting for example, cellulose acetate dissolved in acetone. The liquid is metered onto a continuously moving belt which then passes through a drying tunnel where the solvent is driven off. 

Either a drying tunnel, or another means such as rotating (tumbling) basket, sufficient to prevent cleaned parts from carrying out solvent liquid or vapor. 

In the three-tunnel dryer arrangement, wet loads are moved at intervals into outer wet tunnels. At the end of the wet tunnels, the trolleys are alternately loaded to the central dry tunnel. This in effect reduces the residence time in the dry tunnel to half the time spent in wet tunnels. Dry tunnels are normally operated at a lower temperature than wet tunnels to prevent long exposure of the product to high... 

Metal parts can be pre-heated to 40 - 70 °C depending on the heat sink characteristics of the component. Several light passes with a spray gun produce a better film than one heavy application. If higher temperatures are used it is of the utmost importance that the component surface is wetted and not dry sprayed. The surface should remain wet for at least 5 seconds to allow complete wetting of the substrate. The primer will be dry after 30 - 45 seconds when the top coat can be applied. The topcoat may be applied to surfaces preheated to 40 - 60 °C. Air temperatures in a drying tunnel up to 120 °C may be used provided the component temperature does not exceed 80 °C. The top coat should dry within a minute. 

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