Plastic article or earthenware shaping or treating: apparatus – With mechanical means forming or expanding pores
Reexamination Certificate
2000-05-05
2002-09-24
Kuhns, Allan R. (Department: 1732)
Plastic article or earthenware shaping or treating: apparatus
With mechanical means forming or expanding pores
C425S086000, C425S81700C
Reexamination Certificate
active
06454553
ABSTRACT:
The invention relates to an apparatus and a process for producing moldings from expandable plastic particles, it being favorable for already pre-expanded plastic particles to be used.
Such plastic particles are introduced by means of a central filling device into a mold, the inner contour of which corresponds to the molding to be produced and, after introduction, both the mold and, through openings in the mold, the plastic particles contained in the mold are heated by means of steam, and said particles expand and fuse with one another, so that a relatively lightweight molding is formed. To remove the molding produced in this way, without damaging it, from the mold formed generally by at least two parts, a reduction in the foaming pressure of the expanded and fused material of the molding is required by means of cooling. Before this cooling, a pressure reduction is often also carried out in a steam chamber enclosing the mold, in order to extract residual steam both from the steam chamber and from the mold, and as a consequence also from the molding. At the same time, residual gases formed during expansion are of course also drawn off.
Normally used for the cooling during this stabilizing phase is a large volume of water, which is sprayed or jetted onto the outside wall of the mold.
If, as a result of this cooling, stabilizing of the molded part is achieved, the mold can be opened and the molded part can be demolded, whereupon a new production cycle can be carried out for a corresponding molding.
As a result of the energy-intensive production process, caused by the constant heating up and cooling of the steam chamber, intermediate frames and molds, the production costs due to energy and water consumption are correspondingly high. Furthermore, the heating for expanding and fusing as well as the cooling during the stabilizing phase require corresponding times, which cannot be reduced below certain limits owing to physical constraints.
In the past, therefore, various efforts have been made to achieve a cost reduction by reducing the energy and water consumption required, while at the same time retaining or even reducing as far as possible the cycle times required.
For instance, DE 38 36 875 A1 discloses a process and an apparatus for producing such moldings from expandable plastic particles. It is proposed there that condensate occurring during steam treatment be collected and returned to the process. In this case, the condensate is to be injected or sprayed into the steam chamber at relatively high temperatures, at least in the proximity of the pressure-dependent boiling temperature, so that the desired cooling effect is to be achieved virtually exclusively by extraction of the required heat of evaporation.
According to the teaching described there, hot steam is again to be used for the corresponding heating up of the returned condensate and for the spraying in or injection, but, since the residual steam occurring in the process may be contaminated by plastic particles, it is not readily suitable for this and it is essentially additional hot steam that is consumed, so that the energy balance is correspondingly influenced in an adverse way.
The conventional apparatuses for producing corresponding molded parts not only use molds made from metallic materials, such as aluminum or aluminum alloys for example; the steam chambers and intermediate frames in which the molds for producing the molded parts are accommodated likewise consist of metallic materials, so that high heat losses occur as a result of the relatively good thermal conductivity. Furthermore, during steam treatment a relatively large amount of condensate is also precipitated on the inside walling of the steam chamber.
In the subsequent cooling phase, steam chambers, intermediate frames and the mold are accordingly cooled down, so that this entire mass has to be heated again in the subsequent production cycle by being subjected to fresh saturated steam. Additional energy is of course required for this purpose.
Since the conventional steam chambers are designed with corresponding intermediate frames for a wide variety of mold configurations, i.e. a wide variety of molding dimensions, the design generally being based on the molds of the largest dimensions, when correspondingly smaller molds are used there is a correspondingly large dead volume in the space inside the steam chamber, which however has to be included in the heating and cooling processes and, accordingly, correspondingly more energy is required, since the correspondingly greater volume is taken into account in the pressure reduction and a greater volumetric flow of gas accordingly also has to be drawn off from the steam chamber. Since the corresponding pressure reduction is often carried out by means of vacuum pumps, these have to be dimensioned to a corresponding size with respect to their performance parameters.
On this basis, it is therefore the object of the invention to propose an apparatus and a process with which the energy and water consumption required for the production of moldings from expandable plastic particles can be reduced.
This object is preferably achieved by the characterizing features of an apparatus and a process according to the invention. Advantageous embodiments and further developments of the invention will be apparent from the description of the invention provided herein.
In this case, the solution according to the invention is based on conventional possibilities. For instance, conventional molds, which comprise at least two parts, are used, so that demolding of the molding is readily possible when the mold is opened.
The filling of a closed mold may take place via a central filling means, which is in connection with the cavity in the mold, if appropriate with pressure or negative-pressure assistance. Following filling of the mold, excess plastic particles can be removed again from the injectors by applying a negative pressure or by blowing back with positive pressure.
Following filling, steam is introduced into the steam chamber, it being possible for the steam also to enter the interior of the mold, and accordingly also reach the plastic particles directly, through suitable openings in the mold. As a result, both the mold and the plastic particles contained in the mold are heated, so that said particles expand and “fuse” with one another, so that a molding corresponding to the inner contour of the mold is formed.
After ending the steam cycle and the pressure reduction, a stabilization of the molding produced is carried out by cooling. In this case, it is favorable to work with a pressure below ambient pressure, the pressure reduction only being able to commence after the beginning of cooling. The cooling is carried out by spraying water into the steam chamber.
Used for this are ultrafine spraying heads, through which temperature-controlled water is sprayed in an atomized form onto the surface of the mold. For this purpose, the temperature of the water is controlled in a temperature range between 40 and 80° C., it actually being possible to work in the entire designated temperature range. However, it is required to control the temperature to a specific temperature within this temperature range in order to ensure reproducible production conditions. This temperature range is particularly favorable, since condensate occurring from the steam chamber can be collected, cleaned and returned into the steam chamber for renewed cooling. However, this condensate precipitates at corresponding temperatures, so that there is no need for additional heating, as was required according to the prior art referred to in the introductory part of the description, and the waste heat immanent in the process can be utilized to the greatest extent. For controlling the temperature of the condensate to be returned, it is possible if need be to use residual steam which has been sucked out of the steam chamber, passed through a heat exchanger and subjected to corresponding control, so that no additional energy is required for this either.
The chosen temperature of
Kuhns Allan R.
Schaumaplast Sachsen GmbH
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