Pipes and tubular conduits – Distinct layers – With intermediate insulation layer
Reexamination Certificate
2000-11-28
2003-03-04
Brinson, Patrick (Department: 3752)
Pipes and tubular conduits
Distinct layers
With intermediate insulation layer
C138SDIG002, C428S034500
Reexamination Certificate
active
06527014
ABSTRACT:
TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION
This invention relates generally to insulated flexible ducts for use in heating and air conditioning applications, and more particularly to an insulation product for a flexible duct having improved flame resistance.
BACKGROUND OF THE INVENTION
Various types of insulated flexible ducts are known for use in heating and air conditioning applications. Because the flexible ducts are employed in buildings, the ducts are subject to local building codes and regulations. To comply with building codes and receive a UL rating, flexible air ducts must pass a UL 181 Standard. This standard includes many requirements relating, e.g., to strength, corrosion, mold growth and burning characteristics. The requirement of interest in the present invention is a flame penetration requirement. Current flexible ducts do not always pass the flame penetration test of the UL 181 Standard. Passing the flame penetration test is particularly an issue for flexible ducts containing a relatively thin layer of insulation, e.g., an insulation layer having an R value of 0.74 m
2
° K/W.
Efforts have been made to improve the flame resistance of insulated flexible ducts. For example, U.S. Pat. No. 5,526,849 describes a flexible duct including a flame resistant yarn helix disposed between the inner and outer walls of the duct. This structure requires additional material and cost. U.S. Pat. No. 4,410,014 describes a flexible duct including a glass fiber scrim laminated to the insulation to improve the flame resistance of the duct. Drastically increasing the weight of the scrim greatly increases the probability of passing the flame penetration test, but at an unacceptable cost.
Thus, it would be desirable to provide an insulation product for a flexible duct having improved flame resistance.
SUMMARY OF THE INVENTION
The above object as well as others not specifically enumerated are achieved by a flame resistant insulation product according to the invention. The insulation product comprises a fibrous mineral material that has been rotary fiberized, preferably a fibrous glass. The composition of the mineral material has a softening point of at least about 699° C. An insulated duct according to the invention includes a tubular wall that defines a hollow interior for conducting a fluid, and a layer of the insulation product wrapped about the wall. The mineral material improves the flame penetration resistance of the insulated duct as measured by the flame penetration test of a UL 181 Standard compared to the same insulated duct with a mineral material having a softening point of less than 699° C.
Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment.
DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS OF THE INVENTION
The flame resistant insulation product of the invention comprises a network of intertwined fibers of mineral material. Mineral fiber insulation is well known and has been a commercial product for an extended period of time. Such insulation can be formed from fibers of mineral material such as glass, rock, slag or basalt. Preferably, the insulation product is formed from glass fibers such as fibrous glass wool.
The insulation product is made from mineral material fibers that have been fiberized by a rotary process. In the rotary process, molten mineral material is introduced into a spinner having a plurality of fiber-forming orifices in its peripheral wall. Rotation of the spinner causes the molten mineral material to flow by centrifugal force through the orifices and form fibers. The fibers flow down from the spinner and are collected. The fibers are usually coated with a binder as they flow down from the spinner. A conveyor typically collects the binder-coated fibers in the form of a blanket, and the blanket is heat cured to produce the final insulation product. Insulation materials of various densities can be produced by varying the conveyor speed and the thickness of the cured insulation. Preferably, the insulation product is fibrous glass wool having a density within a range of from about 8 kg/m
3
to about 48 kg/m
3
.
The present invention improves the flame resistance of the insulation product by increasing the softening point of the mineral material when compared with conventional mineral material, and thereby increasing the viscosity of the mineral material at the temperature of the flame in the flame penetration test of the UL 181 Standard. The composition of the mineral material has a softening point of at least about 699° C., preferably at least about 703° C., more preferably at least about 707° C., and most preferably at least about 710° C. The softening point is defined as the temperature at which the viscosity of the mineral material is 10
7.6
poise, as measured according to ASTM C338. Of course this parameter, like any other parameter mentioned in this application, can be measured by any other suitable test.
The mineral material having a softening point of at least about 699° C. increases the probability of the insulated duct passing the flame penetration test of the UL181 Standard compared to the same insulated duct with a mineral material having a softening point of less than 699° C. Preferably, the new mineral material reduces the number of insulated ducts failing the flame penetration test by at least about 15%, more preferably by more than about 30%, and most preferably by more than about 50%.
While not intending to be limited by theory, it is hypothesized that increasing the softening point and the viscosity of the mineral material improves the flame resistance of the insulation product by reducing the chances of a flame penetrating the product. In the flame penetration test of the UL 181 Standard, a sample of the insulated air duct is mounted in a frame, loaded with a weight and placed over a flame at 774° C. Failure occurs if either the weight falls through the sample or the flame penetrates the sample during the 30 minutes of the test. Research indicates that the mineral material of the sample softens and forms a film or crust on its surface in contact with the flame. The film stretches and deforms under the load of the weight, and eventually forms a hole that allows penetration of the flame. It is hypothesized that increasing the viscosity of the mineral material slows the deformation of the film so that the sample is less likely to form a hole and allow flame penetration during the test. Instead of measuring the viscosity of the mineral material at 774° C., it is more convenient to measure the softening point temperature which, for the glass compositions of interest, is fairly close to 774° C. The inventor does not know of previous work disclosing that increasing the viscosity of the mineral material at the test temperature increases the flame penetration resistance of the mineral fiber insulation in an insulated duct.
In view of the above, the goal was to increase the softening point of the mineral material while maintaining the other properties of the mineral material compatible with requirements for fiberizing by a typical rotary process (e.g., delta T and high temperature viscosity) and product requirements (e.g., thermal conductivity).
Increasing the softening point of the mineral material above that of conventional mineral material also increases the high temperature viscosity of the mineral material, as defined by its log 3 temperature. The “log 3 temperature” is the temperature at which the mineral material has a viscosity of 1,000 poise (roughly the fiberizing viscosity), where the viscosity is determined by measuring the torque needed to rotate a cylinder immersed in the molten material, according to ASTM Method C 965. The “liquidus temperature” of the mineral material is the temperature below which the first crystal appears in the molten mineral material when it is held at that temperature for 16 hours, according to ASTM Method C 829. The difference between the log 3 temperature and the liquidus temperatur
Barns Stephen W.
Brinson Patrick
Eckert Inger H.
Owens Corning Fiberglas Technology Inc.
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