Injection nozzles are known, both in the form of partially squeezable hole-type nozzles and in the form of annular gap nozzles. In the known gap nozzles, a needle, which is axially adjustable, is arranged concentrically in the nozzle housing, and, together with the concentric nozzle opening of the nozzle housing, defines a variable gap with respect to the injection mixing chamber. This gap can be altered by means of adjustable stops. The reaction components to be mixed flow from the nozzle opening or the annular gap into an injection mixing chamber in which they are mixed together. The energy required for injection mixing is substantially dependent on the rate of flow, the viscosity, the solubility and the metering ratio of the reaction components. In addition to the distance and the position of the injection nozzles relative to each other, the shape and, in particular, the cross-sectional area of the nozzle openings (or the cross-section of flow) have a great influence on the degree of mixing. The nozzle openings (or their cross-sectional areas) are adjusted manually depending upon the rate of flow and viscosity of the reaction components passing therethrough. Adjustment is usually carried out after a largely subjective judgment of the degree of mixing. Such adjustments can be conducted, for example, by axial adjustment and fixing of the nozzle needle.
It has proved helpful to use the hydraulic pressure which has built-up between the metering pump and injection nozzle as a measure of the mixing energy available for injection mixing purposes. The minimum pressure needed for mixing is dependent on the above-mentioned parameters. Such pressure normally lies between 50 and 150 bar, but can reach 350 bar or even more in some cases. Since deviations from the optimum operating pressure in the metering system impair the degree of mixing, a constant, securely adjusted metering rate and viscosity of the reaction components and also a constant, securely adjusted opening cross-sectional area of the associated injection nozzles are preferably adopted during injection mixing.
A significant disadvantage of this mode of operation is that it is not possible to effect significant change in the metered quantity of reaction components per unit time. This change may be desirable in order to adapt the metered quantity of the resulting multi-component reaction mixture optimally to the geometric conditions within the mold cavities during the mold filling process.
The object of the invention is to allow a significant change in the metered quantity of reaction components per unit time, adapted to the geometric conditions within the mold cavity, of multi-component reaction materials, which may be highly reactive, during a mold-filling process even when using injection mixers, without impairing the mixed product of the reaction mixture produced in the injection mixers.