Dosing assembly

Details Dosing assembly Dosing assembly

2000-05-24

2002-04-30

Fox, John (Department: 3753)

Dispensing

Drip, leakage or waste catching or disposal

C222S571000

Reexamination Certificate

active

06378734

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to an improved dosing assembly (valve/feed line/liquid collecting vessel) which permits nearly immediate response time to an actuator signal. Such an assembly is used for the controlled introduction of any liquid through a valve into a collecting vessel. In particular, the inventive assembly exhibits substantially no leakage from the feed line into the liquid collecting vessel when the valve is closed and an instantaneous introduction of the feed line liquid into the liquid collecting vessel upon opening of the valve, both when a liquid possessing a surface tension of about 50 dynes/cm
2
is used as the measurement standard. This assembly is particularly and preferably suited for injecting colorants into reactants for the production of polyurethane slabstock foam and permits a substantial reduction in foam waste due to low colorations during an on/off cycle. Preferably, this inventive assembly comprises a ball valve, a manifold, and a connector pipe which may contain at most 30 mL of liquid at any single moment and which is measured in diameter of at most 0.42 inches (about 1.07 cm). Such a connecting pipe permits substantially instantaneous shut-off and -on without appreciable leakage or pressure drop and without the need to utilize a high throughput flow rate. Also, such a specific connecting pipe is wide enough to permit high through-put rates should the need arise. The valve/pipe/manifold configuration is contemplated within this invention.
BACKGROUND OF THE INVENTION
The demand for a wide variety of colors in polyurethane slabstock foam has resulted in a significant move to blend-on-fly color dosing units based on the use of polymeric colorants. In this case color metering equipment is used to accurately dose two or more colors that are injected into the polyol stream and subsequently mixed in the foam mixhead to provide the correct shade and depth of color. The biggest advantage of this type of approach is that now an unlimited number of colors can be made from 4 or 5 “primary” colors. In addition, changes from one dark color to the next can usually be accomplished in relatively short distances minimizing the amount of foam that must be scrapped as a result of the color change. Light shades have proven to be more of a challenge since the color throughput is substantially lower causing the response time to increase before changes actually made in the system can take effect. A means was needed to reduce this response time to an acceptable level thus minimizing the length of time required to change from one color to the next even at flow rates (approaching 2 grams per minute or less.) To do this it was necessary to design a unique 3-way valve/injector system that minimized the volume between the injection port and the recirculation line. This results in a rapid build up of pressure and hence almost instantaneous feed when switching from recirculation to dispense mode. In addition to rapid initiation of color flow it also required that flow be almost instantaneously interrupted even at high throughput when the color was switched from dispensing mode back to the recirculation mode. This is to prevent the “bleeding” of color back into the manifold when the need for color ends. The near immediate start and stop of color flow has been accomplished as a result of the current invention.
Polymeric colorants (i.e., polyoxyalkylenated colorants) such as those described in U.S. Pat. No. 4,284,279 to Cross et al., herein entirely incorporated by reference, have been used for a number of years to color polyurethane slabstock foam (i.e., in a continuous process). Prior to the utilization of such polymeric colorants, pigment dispersions were the main source of polyurethane coloring compounds. Such dispersions have traditionally proven very difficult to handle, too viscous for use within standard injectors, highly staining and thus difficult to clean from standard injector equipment (without the need for environmentally unfriendly solvents), and very abrasive and thus potentially damaging to the delicate machinery associated with coloring slabstock polyurethane foam. As a result, polymeric colorants are widely accepted as the best materials for coloring polyurethane foam.
In the past, custom blends of polymeric colorants were made ahead of time using two or more “primary” colors prior to incorporation within the target foam. The components would be mixed together using some typed of agitation such as mixer or drum tumbler. Once the blend was of an appropriate shade it was transferred to a storage tank for further introduction within the foam substrate. Upon completion of coloring with a specific batch of polymeric colorant, the previously run color would have to be emptied from the storage tank; the tank would need to be cleaned; and then the next color to be run in the same tank would have to be charged in the tank. Cleaning of the tanks, pipelines, etc., was facilitated due to the water-solubility of the polymeric colorants (particularly as compared to pigments); however, the procedures followed were still considered labor intensive and not cost efficient. The general practice was then modified to maintain a dedicated tank for each separate color (shade) that was to run. This led to a number of inefficiencies and limitations that were not desirable if a foam manufacturer was to adequately meet demands in the market place.
Polymeric colorants such as those cited above in Cross et al. were designed to be totally miscible with one another as well as with most polyols, one of the two main ingredients used to produce polyurethane materials (isocyanates being the other). Pigment dispersions, on the other hand, are particulates dispersed in some type of liquid carrier. They require a high degree of agitation before they satisfactorily blend together to provide a uniform color. As a result the short amount of time that the polyol and colorant are mixed in the typical slabstock foam machine's mixhead may not be sufficient to produce an adequate mixture of components to insure a single, homogeneous coloration throughout the target foam. Thus, another modification was made permitting separate addition of desired polymeric colorants within a polyol manifold for subsequent blending as the polyol/isocyanate mixture passes through the mixhead. As a result, well over half of all the colored slabstock foam is produced in the United States through such a method.
A configuration of this “new” (now typical) on-the-fly colorant production line for slabstock foam is depicted in FIG.
1
. This new coloring system itself generally consisted of 4 to 6 “primary” color storage tanks (one of which is depicted as
10
in
FIG. 1
) each feeding color to at least one positive displacement spur gear pump
12
coupled to a variable speed motor/drive
14
(such as available from Viking). The motor/pump combination
12
,
14
was typically run continuously in either recirculation or dispense mode (depending on the position of a 3-way valve
16
) to minimize the time required to spool up the motor
14
to the proper rpm and to ultimately achieve the pressure required to initiate color flow into a pre-mix manifold
18
through an injector
20
. The throughput pressure was typically measured through the utilization of a pressure gauge
25
attached to the feed line
13
from the pump
12
to the 3-way valve
16
. The typical 3-way valve
16
was air actuated and used to direct the flow of colorant from the recirculation feed line
22
to the dispense feed line
24
(to the injector
20
) when color flow to the manifold
18
was required. From the manifold
18
, the colorant(s) was moved to the mixing head
26
and then further on to color the target slabstock foam (not illustrated). Although this configuration has proven effective in the past, there remain a number of problems associated with this procedure which have heretofore been unresolved. Most importantly, it has been found that although the injector
20
was intended to prevent leakage of unwanted colorant into the

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