Method of blow-moulding and fluorinating plastics tanks.

The present invention relates to a method for inflating and Fluorisieren of plastic tank according to the preamble of claim 1.

Such a method has become known from DE-PS 24 01 948th The local teaching assumes that the blowing gas used in addition to the inert gas 0.1 - contains 10 vol% fluorine. While this ensures that the preform into contact aufgeweitetwird to the inner contour, and that simultaneously an impermeable inner layer. A disadvantage, however, has been felt that this doctrine into account in any way the toxicity and corrosive properties of fluorine. Especially when using the known hydraulic devices for opening and closing of the blow molds, the risk is particularly high that harmful amounts of fluorine inadvertently leave the blow mold, for example, the plastic tank is leaking or fails the hydraulic lock.

The further prior art, according to US Patent No. 2,811,468, DE-PS 19 05 094, DE-PS 24 01 948, DE-AS 26 44 508, DE-PS 29 24 797, which deals with similar procedures, leaves when working with fluorine miss safeguards.

The present invention therefore has the object to improve the method mentioned initially such that it avoids fluorine damage to personnel and equipment safely.

This object is achieved by the method characterized in claim 1.

The invention thus provides a mechanical interlock is first of all intended to form Fuse instead or in addition to a hydraulic guard. It is understood that this is designed such that it withstands the prevailing loads. At the same time, however, the inflation method is divided into three stages, namely, having no fluorine content in a first stage of inflation, which is only carried out with inert gas. This step is carried out to a pressure of between 2 and 4 bar, preferably 3 bar, what join Sicherheitsontrollen as the second stage, the check on the one hand the mechanical lock and on the other hand, the pressure was constant. Should this time be noted that pressure losses occur, the process can still be aborted without harmful fluorine leaves the mold. the fluorine-inert gas mixture is only after this security checks then in a third stage is introduced into the blow mold, whereby then the inner impermeable layer is generated. The three stages of the invention leads so reliably to the desired operational reliability.

Further advantages and features will be apparent from the foregoing sub-claims.

In the following, a preferred embodiment will be explained in more detail with reference to FIGS. It shows:<ul><li>Fig. 1 is a schematic representation of the process unit and</li><li>Fig. 2 is a graph showing the pressure profile during the inflation of the plastic tank.</li></ul>

In Fig. 1, the two pressure vessels for the F₂ / N₂- mixture and the pure nitrogen at 10 and 12, respectively. They are each connected via a separate line 11 or 13 with the mixing station 14th First, this mixing station is supplied in the first stage only with pure nitrogen from the pressure vessel 12 via the line thirteenth The pure N₂ then passes through lines 15 and 17 for blow molding plant or 18. The pressure gauge (not shown) in the blowing system is connected to its display device 19 in the valves switch box 16, where the dominant political pressure can be read. As soon as this has reached 3 bar, the valve (not shown) which controls the nitrogen supply is closed. At this time, then check whether the pressure remains constant and that the blow mold is properly locked mechanically. Only when this pressure remains constant, thus the plastic tank is obviously sealed, the second stage uses, namely the bubbles with the fluorine-nitrogen mixture, the fluorine content is about 1%. It should be noted, however, that the Blasgemisch may also include another composition known to the prior art. The amount of information in terms of fluorine are in no way critical, but can be in the broad framework vary. The second stage is controlled in turn by the valves dashboard 16. In the second stage of the tank is inflated to about 10 bar, in which case the interior of the tank forming a layer of fluorinated polyethylene, the desired impermeability regarding solvents and the like. owns. The pressure of about 10 bar is then maintained over a period of about 30 seconds. Subsequently, the gas mixture from the blow mold is sucked through the lines 20,21, leading to a Kalksteinnaßfilter where the fluorine components are absorbed.

The blow mold 18 is washed several times subsequently with pure nitrogen from the pressure vessel 12 incoming or with dried air. Possibly remaining radicals of fluorine, which may be released when opening the blow mold 18 are sucked from the hose 23rd

The inventive method thus ensures in any manner that fluorine is no longer freely and uncontrollably escapes into the atmosphere.

In FIG. 2, the pressure course over 120 seconds is shown again schematically, where the individual process steps are given. The invention thus provides the security controls are then carried out at about 3 bar. The introduction of fluorine-nitrogen mixture is only bar off. 4

In detail, the first stage 1 is divided into the following steps:<ul><li>a. nitrogen flushing of the hose</li><li>b. Nitrogen pre-blowing of the hose</li><li>c. Closing the mold,</li><li>d. First pre-blowing with nitrogen from below</li><li>e. Second pre-blowing with nitrogen from below</li></ul>

In the second stage 2 is then carried out the security check the system for leaks by checking the pressure was constant, and the control of the tool locking. Finally, in the third step 3 the pressure is increased up to approximately 10 bar, at the same time the fluorine-inert gas mixture is introduced. The third stage 3 'is subsequently holding pressure at about 10 bar for a period of about 30 seconds is. Then the conclusion is repeatedly flushed with nitrogen or dry air, as this is indicated by the curve 4 of the curve.