Plastic and nonmetallic article shaping or treating: processes – With measuring – testing – or inspecting – Positioning of a mold part to form a cavity or controlling...
Patent
1982-10-05
1985-03-12
Anderson, Philip
Plastic and nonmetallic article shaping or treating: processes
With measuring, testing, or inspecting
Positioning of a mold part to form a cavity or controlling...
264 462, 264 51, 264145, 264DIG13, 264DIG84, 425 89, 425149, 425224, 425308, 425817C, B29D 2704
Patent
active
045044295
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
The invention relates to the production of foamed materials and in particular of polyurethane and other polymer foams, in terms of which it is largely described.
PRIOR ART METHODS
Expanded materials, particularly polyurethane foams, are made in both batch and continuous plant.
Batch production may be at any desired rate to suit subsequent conversion but is inherently labour intensive, can give variation from block to block, and is wasteful in giving blocks where all six sides are skinned and need trimming. The blocks, foamed in moulds, also show undesirable densification at the corners, which the rising and steadily more viscous material has to be forced to occupy by a weighted, floating cover or other means.
Continuous production as currently practised also has major disadvantages. The conventional, horizontal machines have inherent characteristics of large size and high minimum production rate, arising from the nature of the foaming reaction and the newly formed foam, and the curing time needed before material can be handled. This curing time, typically 5 to 15 minutes for polyurethane, sets the length of the plant once the rate of travel of the conveyor that carries the foamed material is determined. This rate of travel in turn depends on the height of the block required, only a certain steepness of profile being supportable by the material in the early stages of foaming and setting. An over-steep profile gives problems of underrun by dense, unfoamed material, or of slumping of unsupported newly foamed material, or both. The conveyor must travel fast enough to maintain the proper profile, giving a minimum production rate of for example 100-200 kg/min for 1 meter high polyurethane blocks, and thus a machine length of 40 to 50 meters. Any attempt to reduce the speed of the conveyor to give a lower production rate and hence in principle a shorter machine steepens the profile and causes underrunning or slumping, or both, making production of a uniform block impossible. Large machines thus have to be installed, at heavy capital cost, only to remain unused for much of their time.
The limiting factors are illustrated in the accompanying sketch drawings of the principle of two known kinds of machine for foaming polyurethane, the first (FIG. 1) having liquid reactants fed direct to a slightly sloped conveyor (about 6.degree. to the horizontal) and the second (FIG. 2) having the reactants fed to a trough, from which they spill over in the first stages of reaction onto a fall plate leading to a horizontal conveyor. Such machines are described in some detail in for example U.S. Pat. Nos. 3,325,823 to D. J. Boon and U.S. Pat. No. 3,786,122 to L. Berg.
The foam profile in the machine of FIG. 1 is approximately as shown at `B`, determined by the rate of feed of reactants at `A` and the rate of travel of the conveyor. The boundary between closed-cell foaming material and open-cell material after gelling and breathing is shown at `C`, the breathing zone being marked `D`. Cut-off is at `E`. The rate of travel has a certain minimum, since while to avoid slumping, on running more slowly, a more steeply inclined conveyor would in theory steepen the profile with respect to the conveyor but leave the effect of gravity unaltered, the liquid reactants fed at `A` would then underrun the foaming mass.
In the machine of FIG. 2 the risk of underrun problems has been reduced by conducting the first stages of reaction in the trough and feeding the resulting creamy and already somewhat viscous reacting mass to the fall plate `F`. There is still however a profile `C` between closed-cell fluid froth and open-cell newly gelled material, which cannot be steepened by reducing the conveyor speed and hence production rate without danger of slumping and thus loss of uniformity in the resulting block.
The difficulties with these machines are felt only when full size foam blocks at production rates below 100-200 kg/min. are required, but it is in fact only the very largest producers that can use capacity of that order. Ma
REFERENCES:
patent: 3325823 (1967-06-01), Boon
patent: 3584108 (1971-06-01), Nelson et al.
patent: 3660548 (1972-05-01), Komada et al.
patent: 3786122 (1974-01-01), Berg
patent: 3870441 (1975-03-01), Petzetakis
patent: 3971112 (1976-07-01), Amato et al.
patent: 4026979 (1977-05-01), Palomares
patent: 4032275 (1977-06-01), Schwab et al.
patent: 4069285 (1978-01-01), Morgan
patent: 4093109 (1978-06-01), Schrader
Hyman Development Bulletin: "Vertifoam Continuous Foam Process", Oldham, England, I & J Hyman P.L.C., 1984, 2 pp.
Anderson Philip
Hinds William R.
Hyman International Limited
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