Plastic and nonmetallic article shaping or treating: processes – With measuring – testing – or inspecting – Controlling heat transfer with molding material
Patent
1995-09-25
1997-11-04
Heitbrink, Jill L.
Plastic and nonmetallic article shaping or treating: processes
With measuring, testing, or inspecting
Controlling heat transfer with molding material
26432816, 36447507, 425144, 425552, B29C 4578, B29C 4573
Patent
active
056836333
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for tempering molding tools for the processing of plastics, in particular injection molding tools, and to a device for carrying out the process.
2. Prior Art
In injection molding, the tool temperature is one of the most important thermal quantities of function, in addition to the cylinder and melt temperatures. It has a large influence on the flowability of the plastic melt, the cycle time, and the quality of the molded parts, in particular on the surface quality, the shrinkage, and the distortion. Various processes for the tempering of injection molding tools are already known. Heretofore, only the operating method using tempering appliances found general acceptance.
A first variation consists in accommodating the tempering appliance in the injection molding machine ("Plaste und Kautschuk" 1982, No. 2, page 86). Hence the tempering appliance is located within the immediate proximity of the tool in order to avoid heat losses on account of the conduit system. Said solution leads to low space requirements for setting up the injection molding machine; however, the basic drawbacks of said tempering method continue to exist. These include primarily the energetically unfavorable operating method and the high acquisition cost for the tempering appliances.
A process is known from DD-PS 203 011, in which the cooling phase is interrupted following the injection process, whereupon a tempering phase takes place, followed by another cooling phase, which has to lastlong enough for the residual energy content of the molded part to suffice for heating the injection molding tool to a temperature that is favorable for the subsequent injection molding cycle.
The drawback of said process is mainly that technologically conditioned differences in the heat discharge of the individual cooling phases at the start of the manufacturing process have to be manually balanced by throttling the flow of cooling water on the set valves in different ways, or by controlling the duration of the cooling phases by varying the adjustment of adjustable time relays. This requires a considerable expenditure of work and makes greater demands on the operating personnel. Furthermore, with said process, as with conventional tempering devices, unavoidable interferences with the manufacturing process such as, for example, variations in the cooling water temperature and in the cooling water through-put, changes with respect to the temperature, in particular the temperature of the melt, and with respect to the cycle time cannot be controlled with respect to their energetic effect on the quality of the molded parts. Depending on the size of the energetic effect of such quantities of interference, the thermodynamic condition of the tool can change to a more or less greater extent, and differences in quality may occur in the manufactured molded parts, leading to reject loss.
U.S. Pat. No. 4,420,446 specifies a process for controlling the tool temperature in injection molding. In this connection, a selected control temperature is preset as the nominal temperature. The tool temperature is measured within the immediate proximity of the molding nest. The valves of the cooling circulation are opened or closed depending on whether the nominal temperature is exceeded or falls short of the nominal value. In addition, when preset upper and lower limit temperatures are exceeded or not reached, visual and sound warning signals are emitted.
A similar solution, in connection with which the heat supplied to the melt is to be exploited for tempering the tool wall, is described in trade publication "Plastverarbeiter" 1984, No. 5, pp 77 to 80. Tempering is controlled here by a microprocessor; the temperature increase caused by the introduction of the melt is measured on the tool contour via a thermosensor, and the microprocessor controls (in dependence on the measurement) the opening time of the magnetic valve system for the cooling water feed. A so-called impulse cooling takes place, an
REFERENCES:
patent: 4420446 (1983-12-01), Wieder et al.
patent: 5034168 (1991-07-01), Matsumoto et al.
patent: 5397515 (1995-03-01), Searle et al.
patent: 5411686 (1995-05-01), Hata
WO 92/08598 Evans May 29, 1992.
Plastverarbeiter, vol. 35, No. 5, May 1984, pp. 74/81 Kotzab "Exakte Temperierung . . . ".
Kunststoffberater, vol. 30, No. 6, Jun. 1985, pp. 22-25 "Fachbeitrag: Formtemperierung durch . . . ".
Heitbrink Jill L.
Kunststofftechnik F. u. H. Riesselmann GmbH
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