CS254762B1 - Method of injection into semi-solid molds - Google Patents

Abstract

The present invention relates to a process for injecting epoxy, unsaturated polyester, phenolic or acrylate resins into semi-solid molds. The essence of the solution lies in the measurement of the continuous deformation of the mold caused by pressure changes inside its cavity. This will make it possible to determine very precisely the point at which the production cycle needs to be terminated or, on the contrary, to adjust the individual parameters of the injection device. In addition to controlling the manufacturing process, the method can be used to detect defects and structural defects in the injection molds during their recovery.

Description

SUMMARY OF THE INVENTION The present invention provides a process for injecting epoxy or unsaturated polyester, phenolic or acrylate resins into semi-rigid molds, particularly for the production of glass-reinforced composites.

The technology of injection molding of thermosetting plastics into semi-solid forms is a highly productive production process, which has been introduced into use in recent years mainly for increased product quality, substantial improvement of hygiene and safety at work and significantly higher efficiency of the production process.

The essence of this technology is pressure or vacuum impregnation in the form of pre-established fiber reinforcement, whereby pressure and vacuum can be combined with each other. The basic problem of this technology, however, is the relatively high reject rate and lengthy and costly revival of production forms, respectively. optimization of the operating mode of each individual mold. These are usually forms of considerable size and uneven stiffness, where individual technological elements and regimes can be verified almost exclusively empirically.

Because the parameters of the injection devices vary depending on the viscosity of the binder injected and a number of other variable factors, these technologies have so far operated with approximately 5 to 10% reject rates. This not only causes considerable damage to material and overall production, but also slows the implementation of this technology into practice.

The main cause of this difficulty is that it is not yet possible to follow the progress of impregnation of the bonding reinforcement during injection. Although the resin ideally spreads to all sides from the injection port evenly - concentrically, its spread is influenced by the way of placing reinforcement, joints or lintels, as well as changes in profile and shape of the mold. This results in slowing the impregnation at places of greater resistance and thus closing off often large air bubbles. Likewise, there are a number of defects at the end of the impregnation process, because the moment of impregnation termination is difficult to determine.

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Even at the optimum injection process, the mold may become overfilled due to insufficient venting, which is manifested by the amount of air bubbles and exceeded permissible tolerances in the wall thickness of the product, more often by molding part of the injected resin by prolonged venting. .

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These disadvantages are largely eliminated by the injection method of the invention. Since the measurement of pressure and vacuum within the mold cavity is usually quite difficult and impractical in practice, the solution lies in the fact that, during the injection molding process, the shape deformation of the mold is measured at one or more points critical to the injection molding process. The deformation is caused by changes in pressure ratios as a function of time, and by measuring the shape changes of the mold, it is possible to infer the changes in the injection ratios inside. The measurements can be performed either continuously or at predetermined intervals.

The injection process stops when the pressure and vacuum in the mold equalize to the initial state, which is also reflected in the offset of the measured deformations of the mold to the zero point. However, with respect to changes in the temperature conditions during injection, a certain tolerance must be established empirically for each mold, but this must not exceed 10% of the maximum shape deviation achieved.

The solution according to the invention can reduce rejects in production far below 1%, whereby excellent manufacturing accuracy can be achieved, in particular in the continuous measurement of shape deformations and in the evaluation of pressure changes in the form of, for example, graphical recording according to the reference standard.

Another advantage is the relatively low cost of adjustments for this evaluation and the rapid return on costs incurred, especially if this technology is already taken into account in the construction of production molds.

The process according to the invention can be evaluated in the following example: Example 1

Semi-rigid large-dimensional form of sandwich construction

-3,254,782 discs with a diameter of 2,100 mm were provided with a needle gauge with an accuracy of 0.01 mm at a preselected location in the upper, less reinforced portion. During the injection, deformations indicating changes in pressure within the mold were read after about 1 minute. The curve, constructed according to the measured values, showed the critical points of the injection mode as a function of time. During repeated production, only the values that were decisive for the correct impregnation process were monitored and the injection parameters were continuously adjusted to suit the optimum curve of the diagram. The course of impregnation in this form is evident from the diagram in Figure 1.

The procedure outlined in Example 1 can also be used to identify defects in manufacturing molds, since the deformations also show unreinforced or leaking mold spots and other defects.

Claims (1)

Method for injecting epoxy or unsaturated polyester, phenolic or acrylate resins into semi-solid molds, characterized in that during the injection process, at one or more points of the mold, the deformation is measured continuously and / or at preselected time intervals caused by changes in pressure conditions during injection wherein the injection process is stopped when the pressure and vacuum are equalized in in the mold cavity to the level of the initial state, that is to compensate the elastic deformation of the mold to the level before the injection starts with a tolerance of not more than 10% of the maximum deviation achieved.