Apparatus for mixing at least two reactive plastic materials

A cylindrical mixing chamber opens into a subsequent cylindrical quieting chamber at an acute angle alpha against its direction of outflow to avoid spattering during the output of a plastic mixture formed of a reactive plastic components from a mixing apparatus.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to an apparatus for mixing two or more components and 
more particularly to a method and device for high pressure impingement 
mixing of two or more reactive components. The components are injected 
into a mixing chamber containing a reciprocating piston. The mixing 
chamber opens into a quieting chamber also containing a reciprocating 
cleaning piston. 
2. Description of the Related Technology 
The prior art includes devices such as shown in DE P 23 27 269, 25 13 492 
and 29 07 938, corresponding to U.S. Pat. Nos. 3,975,128, 4,115,299 and 
4,302,910 respectively, the disclosures of which are expressly 
incorporated herein, where a plastic mixture produced in the mixing 
chamber is transferred at right angles into the quieting chamber (FIG. 1). 
In practice the mixed components exit the mixing chamber and spinning flow 
component may be established in the quieting chamber. Upon the exit of 
components from the quieting chamber, the spinning action may result in 
spattering (FIG. 1). The mixhead geometry is extremely significant to the 
flow characteristics of the mixed components. For many applications a 
laminar output from the mixing head is absolutely necessary. 
SUMMARY OF THE INVENTION 
An object of the invention is to insure a laminar outflow of mixed 
components from the mixhead quieting chamber. A laminar flow of plastic 
mixture will result if all of the flow components are aligned exclusively 
coaxially relative to the axis of the quieting chamber. 
Another object is to provide a mixing head with a compact configuration. 
The mixing devices according to the invention may be much slimmer and 
trimmer than the prior L-shaped mixing devices. A slim configuration is a 
significant advantage because it allows manipulation of the mixing device 
over a mold cavity when required for the particular application. 
These objects can be achieved according to the invention by arranging the 
mixing chamber at an acute angle (alpha) to the quieting chamber so that 
the components undergo a change in direction of over 90 degrees. 
Advantageously alpha is significantly less than 90 degrees. 
The apparatus is for mixing at least two reactive plastic components under 
high pressure in a cylindrical mixing chamber. The plastic components are 
injected into the mixing chamber containing a reversible piston. The 
piston serves to control the flow of the components, i.e., duration of a 
shot and recirculation, and to clean the chamber by ejection of reactive 
plastic residues at the end of a shot. A cylindrical quieting chamber 
follows the mixing chamber and extends at an angle to the longitudinal 
axis of said mixing chamber. The quieting chamber contains a reversible 
piston. The mixing chamber and potentially one or more additional mixing 
chambers are arranged at an acute angle which may be significantly smaller 
than 90 degrees to the quieting chamber in a direction against the output 
direction of said quieting chamber. The angle may be within a range of 
about 30 to 60 degrees and may approximate or be 45 degrees. A reversible 
or reciprocating mixing chamber piston may exhibit a longitudinal groove 
for each plastic component defining a recirculation path for the plastic 
or reactive component involved between two successive injections or shots. 
The openings of the mixing chambers may advantageously be all located in a 
common radial plane of the quieting chamber. 
It is advantageous to a control a mixing device so that in a first mode of 
operation (mixing position) the mixing chamber piston releases the 
injection of the reactive plastic components and the other piston 
partially closes the outlet opening of the mixing chamber (throttling 
position). According to an alternative mode of operation the mixing 
chamber piston may be retracted to release the injection of the reactive 
plastic components into the mixing chamber and the second piston is 
retracted to a position past the outlet opening of the mixing chamber so 
that a swirl or mixing space is formed between the frontal surface of the 
second piston and the outlet opening of the mixing chamber. 
The invention is based on the concept of letting one or several mixing 
chambers open at an acute angle into the quieting chamber in a direction 
against or to a degree opposite the output direction of the quieting 
chamber. Preferably all mixing chambers are arranged in a common radial 
plane. The component mixture or mixtures introduced into the quieting 
chamber thereby undergo additional intensive mixing by the reverse flow 
forced upon them. Simultaneously the generation of a spinning flow in the 
outlet tube is counteracted. 
The invention will become more apparent from the following description with 
reference to the drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The partial view shown in FIG. 1 of a known mixing head contains a 
cylindrical mixing chamber 1. A component inlet line 2 for a plastic or 
reactive component A and a component inlet line 3 for a plastic or 
reactive component B open into the mixing chamber. The injection orifices 
4 and 5 of these component inlet lines 2 and 3 are opened and closed by 
the mixing chamber piston 6. The piston is guided reversibly or 
reciprocates in the mixing chamber. The mixing chamber piston 6 is in the 
mixing position, in which the injection orifices 4 and 5 are open, so that 
the plastic components A and B meet at high pressure and are mixed 
intensively. In a recirculating position (not shown) the mixing chamber 
piston is in an advanced position in which its frontal surface 7 closes 
the outlet opening 8 of the mixing chamber 1 in a flush manner. When the 
mixing piston is advanced, the component inlet lines 2 and 3 are connected 
to or in communication with component return lines 11 and 12 through the 
recirculating grooves 9 and 10 provided in the mixing chamber piston 6. 
The components A and B are returned into tanks or reservoirs in the 
nonmixing or recirculating position. In the mixing phase shown in FIG. 1 
the reactive plastic mixture enters the quieting chamber 13 through the 
outlet opening 8 after a right angle deflection from the mixing chamber 1. 
A second reciprocating piston 14 is located in the quieting chamber. The 
piston 14 is shown in a throttling position partially covering the outlet 
opening 8. The plastic mixture exits at right angles from the mixing 
chamber in both a throttling and a completely open position of the piston 
14 and impacts the wall opposite the outlet opening 8 of the quieting 
chamber 13. The mixture may tend to continue in a spinning flow D, whereby 
the flow of the plastic spreads out upon leaving the outlet opening 15 of 
the quieting chamber 13, thereby producing a spray (arrows 16). This 
spraying is particularly undesirable in the molding of plastic mixtures or 
polyurethane foam in open molds, as this may result in the formation of 
unacceptable air inclusions or bubbles in the finished product. 
The above described problems of the devices according to the previous state 
of the art (FIG. 1) are eliminated by locating a mixing chamber 101 at an 
acute angle alpha (FIG. 2), as the plastic mixture leaving the mixing 
chamber 101 flows initially at this acute angle alpha against the outflow 
direction of the subsequent quieting chamber 113 and is aligned by 
reversal and flowthrough into a laminar flow of the plastic mixture. A 
quieted flow with flow components coaxial relative to the axis of the 
quieting chamber 113 (arrows 116) appears at the outlet opening 115 of the 
quieting chamber 113. Air inclusions due to a spray flow, as indicated in 
FIG. 1 by the arrows 16, can be largely avoided. Further, a mixing device 
with such a "y" configuration allows ease of manipulation which may be 
important for many applications. This is particularly so in open mold 
applications where maneuverability of the mixing device before, during and 
after a pour may be required. Maneuvering ease of the mixing device 
between mold parts may be greatly enhanced by the slim "y" configuration. 
FIG. 3 shows the apparatus according to the invention in the mixing 
position with a piston 214 further retracted over the outlet opening 208 
of the mixing chamber 201. The space vacated by the retracted piston 
leaves a significantly larger swirlingspace between the frontal surface of 
the piston 214 and the outlet opening 208 relative to the configuration 
shown in FIG. 2 where the quieting chamber piston is aligned in a 
throttling position. The piston 206, located reversibly in the mixing 
chamber 201, is rotated 90 degrees compared to the embodiment according to 
FIG. 1, so that only one recirculating groove 209 is visible. A 
corresponding recirculating groove is located opposite to groove 209. 
Similarly, in the view according to FIG. 2 and 3 only one injection 
orifice 103 or 203 is visible. 
FIG. 4 shows a mixing apparatus in a nonmixing phase. Two mixing chambers 
301 and 301' open into a quieting chamber 313. Pistons 306 and 306' are 
reciprocal in the chambers 301 and 301' . The pistons are shown in the 
closed or recirculation position, in which the plastic components A and B 
(FIG. 1) are returned through the recirculating grooves 309 and 309' and 
the opposing recirculating grooves (not shown) into respective component 
tanks. The piston 314 located in the quieting chamber 313 is in the 
foremost or advanced position, in which the plastic mixture, initially put 
out from the mixing chambers 301 and 301' and ejected by the pistons 306 
and 306' in a cleaning stroke, is removed from the quieting chamber 313 at 
the end of a completed shot.