GB2066428A

GB2066428A - Supply Control Apparatus

Info

Publication number: GB2066428A
Application number: GB8040292A
Authority: GB
Original assignee: Chemie-Anlagenbau Bischofsheim GmbH
Current assignee: Chemie-Anlagenbau Bischofsheim GmbH
Priority date: 1978-07-27
Filing date: 1980-12-16
Publication date: 1981-07-08
Also published as: GB2066428B

Abstract

Apparatus suitable for controlling the supply of a reactant to a mixing chamber comprises a housing 21 having an inlet 23 for the reactant, an outlet 24 to the mixing chamber, an inlet 25 for a flushing medium, an outlet 26 for recirculation of the reactant and, within the housing, an axially rotatable cylindrical member 20. The cylindrical member comprises an arcuate duct 27 allowing connection of the reactant inlet 23 with either outlet independently and a circumferential groove 28 allowing connection of the flushing medium inlet 25 with the mixing chamber outlet 24 when the reactant inlet 23 and the recirculation outlet 26 are connected. The flushing medium inlet is blocked when the reactant inlet and the mixing chamber outlet are connected. <IMAGE>

Description

SPECIFICATION Supply Control Apparatus The invention relates to supply control apparatus for use with mixing apparatus for producing multi-constituent plastics, in particular - those which are formed from isocyanates and solids. It is known to have supply apparatus disposed immediately in advance of a mixing chamber, the supply being controlled so that the reactants either enter the mixing chamber through a discharge duct or are recirculated without passing into the mixing chamber. This control can be made to depend on the setting of the supply apparatus.

In a system of this kind, the supply control consequently has the function of allowing the discharge, into a discharge duct, of a preselected amount, varying with time, of the reactant to be delivered to the mixing chamber. In addition, when desired, the supply control ensures that the reactant can be redirected to recirculate in the system in order to prevent separation of the constituent. This function is essential if the reactant contains solids which may easily settle, or liquids which have a tendency to separate out.

If a reactive multi-constituent system is employed, such as is present with isocyanates and other active reactants containing hydrogen atoms, flushing is also necessary.

It has recently been proposed to use supply control apparatus comprising a housing having an inlet for the reactant, two outlets for the reactant, one leading to a mixing chamber and the other for recirculation of the reactant, and a rotatable valve member in the form of a hollow shaft with a lead off duct to the periphery thereof. The reactant is introduced through the end of the shaft and, depending on the orientation of the valve, is conveyed through the duct to either of the outlets which may be, for example, spaced at 90 degrees.

The valve is turned from time to time to allow discharge into the mixing chamber or to the recirculation duct, as desired.

Recirculation follows discharge into the mixing chamber and, at the same time, flushing is started, usually by introducing a suitable flushing medium directly into the mixing chamber through a separate inlet. Air is subsequently blown into the chamber. During both flushing and blowing, the mixing stirrer in the chamber is actuated.

The disadvantage of known apparatus for the systems generally and specifically described above is that, after mixing, the outlet into the mixing chamber is filled with the reactant and that flushing does not clean the outlet, which may be regarded as a blind hole in the wall of the mixing chamber during flushing, thoroughly. After each mixing operation, a residue of the reactant may be left to harden in the outlet. Particularly detrimental consequences arise when using reactants containing high density solids. During flushing, the solid particles are flung against the inner wall of the mixing chamber by the tangential forces produced by the rapidly rotating stirring means in the chamber and deposits are formed in the cavities of the outlet, the deposits eventually hardening.This disadvantage is also found when a valve in the form of a hollow shaft is replaced by a three-way valve.

Known control supply apparatus comprises a valve which allows the passage of either flushing medium or air and an on/off valve on the mixing head which can be used to determine the duration of each of the flushing and blowing stages. The use of air subsequent to the flushing medium is necessary in order to remove the medium.

An improvement in the type of apparatus comprising a rotatable valve member is described and claimed in British Patent Application No.

7925925 (Serial No. 2,029,550). The improvement comprises providing a second, radial, inlet together with a circumferential groove in the valve member, the groove connecting the second inlet and the outlet to the mixing chamber when the valve member is rotated so that the axial inlet is in connection with the recirculation outlet.

U.S. Patent Specification No. 3,499,467 relates to multiple flow-pattern valves and particularly discloses a rotatable valve member in a housing having five ports. Various combinations of ports can be connected depending on the rotation of the valve member which has two segments cut away to allow connection of, in one case, two adjacent ports and, in the other case, three adjacent ports.

According to the present invention, apparatus suitable for controlling the supply of a reactant to a mixing chamber comprises a housing having first and second inlets and first and second outlets and, within the housing, an axially rotatable cylindrical member with respect to which the inlets and the outlets are radially disposed, the member comprising an arcuate duct and a circumferential groove which respectively allows connection of the first inlet with either outlet independently, but no other connection of the inlets and outlets, and connection of the second inlet with the second outlet when the first inlet and first outlet are connected, but no other connection of the inlets and outlets, the second inlet being blocked when the first inlet and the first outlet are connected.

The first inlet is for the reactant. The first outlet is for the passage of reactant to a mixing chamber. The second inlet is for flushing medium.

The second outlet is for recirculation of the reactant. The apparatus of the invention allows direct flushing of the reactant inlet when this is connected to the flushing medium inlet, while the reactant is recirculated.

A further advantage of the present invention is that a flushing medium/air control valve of the type used in the prior art is no longer necessary.

Instead, the direction of the reaction and flushing can be controlled by one control having three operating positions. In one position, the second inlet is blocked, so that no flushing can occur,-and the reactant passes to the mixing chamber. In the other positions, the first inlet and the second outlet are connected as are the second inlet and the first outlet, so that flushing can occur and the reactant is recirculated. In the second position, the flushing medium is passed through the system and, in the third position, air is blown in.

The two outlets and the two inlets are radially disposed with respect to the rotatable valve member. The outlets are disposed at equal angles, e.g. 900, to, and on opposite sides of, the reactant inlet. The duct which connects this inlet with either outlet is curved, and the end opposite the reactant inlet during mixing, when rotated to allow recirculation. is then opposite the recirculation outlet. In this way, a short flow path is achieved which can be designed for optimum flow, and the duct is flushed by the reactant in opposite directions during mixing and recirculation. The circumferential groove allows connection of the flushing inlet with the mixing outlet during recirculation of the reactant.

The invention will now be described by way of example with reference to the accompanying drawings, in which: Figures 1 and 4 are sectional views of apparatus embodying this invention in the mixing and recirculation modes, respectively; and Figures 2 and 3 are different cross-sections, the former only partially cut-away, of the apparatus shown in Figure 1.

Figure 1 shows an embodiment of the invention in the mixing mode. A rotatable valve member 20 is mounted in a housing 21 and separated therefrom by a seal 22. The housing comprises a reactant inlet 23, a mixing chamber outlet 24, a flushing inlet 25 and a recirculation outlet 26 (with respective corresponding seal apertures 23a, 24a, 25a and 26a). The valve member 20 includes an arcuate duct 27 and a circumferential groove 28. As shown in Figure 1, the flushing inlet is blocked.

Figure 2 is a plan view of the valve member 20, showing the groove 28, with the seal and the housing cut away along the line C-D of Figure 1.

Figure 3 is a cross-sectional view along the line C-D of Figure 1.

When, in the embodiment shown in Figure 1, the valve member is rotated anti-clockwise through 900, the configuration shown in Figure 4 is achieved. The duct 27 connects the reactant inlet 23 and the recirculation outlet 26, while the groove connects the flushing inlet 25 with the mixing chamber outlet 24. It will be readily appreciated that the reactant flows through the duct 27 in the opposite direction from that in which it flows in the configuration shown in Figure 1.

If desired, a number of supply control apparatus of the invention may be mounted sideby-side so that a number of reactant streams can be controlled from the same point. An arrangement of this type is particularly useful; when two mutually reactive reactants have to be metered into the same mixing chamber at exactly the same time. This is the case in the synthesis of polyurethanes, in which an exact amount of an isocyanate and an exact amount of a polyhydric alcohol must be metered in at the same time for the reaction to occur completely, which is the case within a few seconds.

The apparatus of the invention can be assembled, using prefabricated parts to form a composite supply control apparatus with as many inlets and outlets as may be desired. It is also possible to provide a plurality of adjacent ducts and/or grooves in one rotatable valve member.

Claims

1. Apparatus suitable for controlling the supply of a reactant to a mixing chamber, which comprises a housing having an inlet for the reactant, an outlet to the mixing chamber, an inlet for a flushing medium, an outlet for recirculation of the reactant and, within the housing, an axially rotatable cylindrical member with respect to which the inlets and the outlets are radially disposed, the two outlets being at equal angles to, and on opposite sides of the reactant inlet, in which the cylindrical member comprises an arcuate duct allowing connection of the reactant inlet with either outlet independently, but no other connection of the said inlet and outlets, and in which the member further comprises a circumferential groove allowing connection of the flushing medium inlet with the mixing chamber outlet when the reactant inlet and the recirculation outlet are connected, but no other connection of the said inlets and outlets, the flushing medium inlet being blocked when the reactant inlet and the mixing chamber outlet are connected.

2. Apparatus according to Claim 1 substantially as illustrated in the accompanying drawings.