Plastic and nonmetallic article shaping or treating: processes – Vacuum treatment of work
Reexamination Certificate
1996-09-17
2001-10-23
Silbaugh, Jan H. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Vacuum treatment of work
C264S328140, C264S328170, C425S200000, C425S449000
Reexamination Certificate
active
06306322
ABSTRACT:
DESCRIPTION
The invention relates to a method for filling at least one casting mold with a castable liquid compound, in particular casting resin, and a device for carrying out the method.
A casting device of this kind, in particular a pressure gelation device, is disclosed by DE-C 34 20 222. In this case, the casting compound is filled into so-called closed molds and is gelled at elevated temperature. The time until the castings are given their final shape depends inter alia on the volume of compound present in the lines and components of the casting device or on the accumulation of the volume of compound and is significantly longer for large-volume casting molds than for thin-walled castings. The resultant cycle time for the production of a casting essentially determines its production costs. Although heating the casting compound leads to a higher reactivity and thus to a shorter pot life, a higher temperature of the casting compound inevitably has the result that the throughput through the lines and the components of the casting device has to be high, in order to be able to exchange reactive material continually and to prevent sticking on the lines of the components. This means that the casting resin temperature and thus also the operating rate of the known casting device is determined by the production conditions during the breaks in production.
On this basis, the object of the invention is to provide a method and a device for filling at least one casting mold with a castable liquid compound, which substantially reduces the cycle time for filling the at least one casting mold and thus the mold occupation time.
The method according to the invention makes it possible to control the reactivity of the casting compound before and during the filling operation. During the filling operation, the reactivity of the casting compound is increased by supplying energy, so that the casting compound can be brought out into the mold much more quickly and thus, above all, gels more quickly in the mold. At the end of the filling operation and/or during the breaks in production, the reactivity of the casting compound is reduced by removing energy to a value at which there can be no sticking in the lines and components. During the processing and during the filling operation, therefore, the casting compound has a short pot life, with a view to a short mold occupation time. Toward the end of the filling operation, the pot life is increased again, so that the lower reactivity of the casting compound means that there is no sticking in the lines and components of the casting device. A further advantage of the method according to the invention is that, as a result of the control of the reactivity, it is also possible to process those casting compounds which need to have a certain minimum viscosity during casting, such as for example casting compounds for impregnating fine wire windings, such as in line output transformers or ignition coils. The fact that the temperature of the casting compound also approaches that of the conventionally heated casting mold has a beneficial effect on the quality of the castings, since stresses in the casting can be avoided. In the case of pressure gelation, a particularly advantageous homogeneity results on pressure gelation of the casting compound in the casting mold. A further advantage of the invention results from the fact that, as a result of the temperature control of the casting compound at the instant of processing, there is no need to heat components, such as for example reservoirs and the like, to a higher level. This results in an overall improvement in the energy balance, impairment of the material owing to material stress due to temperature stressing being further reduced.
Advantageous refinements of the method according to the invention result from the subclaims.
In accordance with one concept of the invention, it is possible, for example, for the reactivity during the filling phase of the at least one casting mold to be subjected to a repeated change, in order for instance to bring about a specific temperature profile of the casting compound, which may be of particular importance in the case of pressure gelation.
The change in the reactivity of the casting compound is preferably carried out conventionally by supplying and removing heat.
The method according to the invention is advantageously also suitable for the serial casting into casting molds, the removal of energy or reduction in temperature of the casting compound then taking place during the breaks in casting between the series using casting molds. Thus, the energy of the casting compound is not reduced after every individual part, but only after the casting molds arranged on one palette have been cast as a series and the next palette with casting molds has been introduced into the casting chamber. This significantly improves the energy balance. A procedure of this kind is always recommended when there are only relatively short breaks in casting between the individual casting operations, i.e. the casting molds are filled successively.
As an alternative or in addition to varying the reactivity by supplying energy to and removing energy from the casting compound, it is also possible, in the case of casting compounds which are formed or mixed from at least two components, to heat the components during the filling phase for filling the at least one casting mold. This results in a significantly lower viscosity of the individual components, with the advantage that mixers of smaller dimensions can be used. As a consequence of the lower viscosity of the individual components, in particular there is a smaller pressure loss within the mixer. An advantage which again results from a smaller mixer is that the volume of compound is correspondingly small, which leads to a rapid temperature change with regard to the technique according to the invention. A smaller mixer also has the advantage that the residual heat present in the casting compound at the end of the filling operation can be rapidly given off to the environment, so that in many cases a separate reduction of temperature is not required.
However, it is of course also possible according to the invention for the components to be subjected to at least one temperature change during or after the filling phase, a specific reduction in temperature of the individual components being performed. The reduction in temperature of the individual components takes place toward the end of the filling operation, so that the subsequent flow of cooler individual components drive the hot casting compound into the molds and at the end of the filling operation the lines carrying the compound as far as the runner are at a lower temperature level which is not critical with regard to the reactivity.
In addition or alternatively to the changing temperature control of the individual components, it is also conceivable for the individual components merely to be heated, while the casting compound is subjected to a cooling operation in the region between the mixing device and the runner of a casting device, toward the end of the filling phase. This may in some cases lead to an improvement in the energy balance.
The characterizing features of the device make it possible, in a manner which is simple in terms of design, to carry out heating and also reduction in the temperature of the casting compound or of the individual components in order to achieve a short mold occupation time. Advantageous refinements of the device according to the invention can be found in the dependent subclaims.
In one embodiment of the invention, it is then provided for the heat transfer to take place directly or indirectly by means of a heat exchanger surface. Direct heating can be carried out, for example, electrically by means of an electric heating means. Radiant heat may also be used to heat the compound, in that, for example, quartz lamps are directed on to a section of the line or a component of the casting device, transfer of the heat onto the compound taking place via the wall of the line section or o
Hauser Erhard
Hedrich Wilhelm
Liniak Berenato Longacre & White
McDowell Suzanne E.
Silbaugh Jan H.
Wilhelm Hedrich Vakuumanlagen GmbH & Co. KG
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