DE3111223A1 - Vacuum-drying process - Google Patents

Abstract

The invention relates to a process for the drying of parts and articles consisting of materials which are sensitive to excessive temperatures and to impurities, by the supply of an inert gas under reduced pressure.

Description

ARTHUR PFEIFFER VAKUUMTECHNIK WETZLAR GMBH 6334 ASSLAR vacuum drying process

The invention relates to a method for drying parts and goods _f which consist of materials which are sensitive to excessive temperatures and to contamination, at reduced pressure with the supply of inert gas.

Parts and goods that are exposed to moisture during manufacture and processing must often also be subjected to a drying process. There are a number of ways to dry these parts Processes that belong to the state of the art. However, these procedures are especially critical when it comes to Parts are made of materials that are sensitive to excessive temperature and contamination are.

For example, one takes advantage of centrifugal force by hurling the parts in centrifuges. The disadvantage of this Process consists in the high mechanical stress on the parts, the unclean operation of centrifuges and in the unwieldiness of automatic loading and unloading.

Drying processes under reduced pressure are much more gentle on the parts to be dried. Here is in the simplest case, the heat of evaporation required to evaporate the liquid from the parts to be dried withdrawn. However, this is only possible to a limited extent without additional heat supply, especially when it comes to substances acts with low heat capacity. To remedy this disadvantage and to reduce the vapor pressure of the liquid substance to be discharged to increase and thus to accelerate the entire drying process, the dry goods are heated by adding heat is supplied from the outside.

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However, this cannot be done without hesitation when it comes to temperature-sensitive materials or parts. In addition it is not important to add heat to the parts to be dried, but rather to the liquid to be evaporated, which in a large number of applications are predominantly or exclusively on the surface of the Parts is located.

In the absence of heat conduction in a vacuum, the parts are heated, for example by radiation. However, this is where the disadvantage occurs on that as a result of the radiation shadow, 'in which the sides of the parts facing away from the radiation are located, a uneven and incomplete heating and thus incomplete drying takes place. There is also the Danger of overheating of the dry goods, especially if they are temperature sensitive and have a low thermal conductivity having.

The object of the invention is to provide a device and method with which the drying of parts and goods, which are sensitive to excessive temperature and contamination, in a reasonably short time under gentle Conditions and while avoiding an inappropriately high expenditure on equipment is possible.

The object is achieved in that a heated gas stream is introduced from the outside into a vacuum drying chamber is that the parts to be dried have been washed around by the gas stream. Thus, the vapor pressure is the one to be discharged Increased liquid and the heat of evaporation supplied from the outside, without the parts to be dried being excessive Temperature. This rinsing around the parts is always carried out continuously. that the amount of gas supplied is correctly dosed. If the amount is too small, it will not be noticeable Transferring the amount of heat. If there is too much of the fed

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Inert gas, this acts as a diffusion barrier and hinders it thus the drying process at the same time. The amount of gas supplied is optimal when its partial pressure is within of the drying chamber in the order of magnitude of the vapor pressure of the liquid medium to be discharged at the final temperature of the dry material is held.

Another criterion for the size of the supplied gas flow is the vapor tolerance of the used Vacuum pump. With the methods known since then, the A vacuum pump is connected upstream of this with a steam condenser. In order to avoid such an outlay on equipment, the Here presented method according to the invention the size of the supplied gas flow to the vapor tolerance of the used vacuum pump adapted. This is done by optimizing the flow strength in relation to the time average the amount of steam and the mean self-cleaning time of the vacuum pump, relative to the entire drying cycle. This means that a steam condenser can be used can be dispensed with in front of the vacuum pump, which results in a significant simplification of the system.

Another disturbing factor when drying under reduced pressure are impurities that either come through Back diffusion from the vacuum line can get into the drying chamber or by desorption from the walls of the The drying chamber itself or its components come from. According to the invention, this disadvantage is eliminated by the use of the in Eliminated suitable direction guided inert gas flow. With this .Gasströmung impurities are removed from the The drying chamber is flushed in the direction of the vacuum pump and can thus be pumped out more quickly. Likewise, a Prevents back diffusion of any pump medium that may be present.

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With an additional device, the optimal gas flow can be achieved using the maximum acceptable gas flow Flow velocity can be directed from the outside specifically to the parts to be dried. That way you can Liquid droplets on the parts are blown away. This becomes an additional option given the moisture removal. This process can also be used to prevent contamination of the parts adhere, to be eliminated in part.

The device and the procedure are to be explained in more detail using the illustration.

The parts to be dried are located in the drying chamber 1, which is evacuated by the vacuum pump 3 The pressure in the chamber can be monitored by a vacuum measuring device 4. Via the gas line 5 and the control valve 6, the gas to be supplied is sent to the heater 7. The heated gas passes through the lines 8, 9, the valves 10, 11 and the inlet nozzles 12, 13 in the Drying chamber. Instead of using the heater 7, the gas can also be fed through heating devices 14 within the drying chamber be heated. Through the valve 6, the dosage of the gas to be admitted can be regulated, and through the Adjustment of the valves 10 and 11 determines the direction of the gas flow in the drying chamber.

Claims (9)

Claims Process for drying parts and goods, especially those that are sensitive to them elevated temperature and against contamination are, under reduced pressure, characterized in that the evaporation heat from the liquid medium to be discharged by flowing into the drying chamber from the outside Inert gas is supplied. 2. The method according to claim 1, characterized in that the partial pressure of the heat of evaporation transferring Inert gas in the drying chamber of the order of magnitude of the vapor pressure to be discharged liquid medium at the final temperature of the material to be dried. 3. The method according to claims 1 and 2, characterized in that the current strength of the inert gas to the vapor compatibility and the suction capacity of the vacuum pump used through optimization in relation to the time mean of the amount of steam and the mean Self-cleaning time of the vacuum pump, is adjusted relative to the entire drying cycle. 4. Device and method according to claims 1 to 3, characterized in that the evaporation wiirme is supplied by heated gas. 5. Device and method according to claims 1 to 4, characterized in that the heat of evaporation is supplied by heated gas with fluctuating partial pressure. -6- 6. Process according to claims 1 to 5, characterized in that the inert gas is outside the drying chamber is heated. 7. The method according to claims 1 to 5, characterized in that the inert gas within the Drying chamber is heated. 8. The method according to claims 1 to 3 or 4 to 7, characterized in that the supplied from the outside Gas flow is given a certain direction and thus the influence of impurities in the drying chamber and back diffusion of any pump medium that may be present is prevented. 9. The method according to claims 1 to 3 or 4 to 7, characterized in that by the outside directed optimized gas streams the liquid media or impurities to be discharged blown away from the parts to be dried.