Pulsed steam iron

Details Pulsed steam iron Pulsed steam iron

2003-08-27

2004-10-26

Izaguirre, Ismael (Department: 3765)

Textiles: ironing or smoothing

Smoothing implements

Flatirons

C038S077820

Reexamination Certificate

active

06807756

ABSTRACT:

The present invention concerns steam irons where vaporization of water is quasi-instantaneous.
There are known steam irons generally comprising a water reservoir, a steam chamber heated to rapidly evaporate water that arrives therein in droplets from the reservoir, a heated soleplate having the ironing surface, steam outlet holes being arranged in the soleplate.
The simplest irons have a valve with a controllable flow rate through which the water drops from the reservoir into the steam chamber under the effect of gravity. The steam produced exits the iron toward the environment through channels and outlet holes constituting an escape circuit for the steam. But the steam occupies a large volume and travels through the escape circuit at an elevated velocity. As a result of load losses of this circuit, the pressure of the steam in the steam chamber rises. Moreover, when the steam iron is applied onto material being ironed, the outlet of the steam through the holes of the soleplate is opposed and the pressure in the steam chamber increases further.
This internal pressure in the steam chamber is opposed to the passage of water into the valve having an adjustable flow rate, which substantially decreases the following quantity of steam produced. The internal overpressure cannot exceed a value corresponding to the height of a column of water between the water outlet of the valve and the level of water in the reservoir, generally several centimeters. By this fact, the quantity of steam varies substantially during ironing, depending on the materials and the ironing support. The load losses being proportional to the square of the velocity of the steam in the circuit, the speed is limited, in particular the outlet speed through the holes of the soleplate, which can be a drawback to the penetration of the steam into the material. In addition, one cannot use the steam in a sprayer, which requires much too much pressure for its operation.
These drawbacks justify the use, in more elaborate irons, of a pump that forces the passage of water from the reservoir to the steam chamber, the pressure delivered by the pump being considerably greater than that which is generated by the load losses. But this solution increases the price of the iron because of the value of the pump, of its installation, and of its supply device if it is electric.
There are also known devices utilizing variations of the steam pressure in the steam chamber between periods when the iron is placed on the fabric and those where it is not, this in order to force the passage of water. Such a device is described, for example, in the patent FR2626901. But these devices are equally costly and delicate.
The patent JP01262899 describes an iron having an excess steam valve having a control shank that is driven by an electromagnet. The valve is actuated periodically in order to produce an excess of steam in a manner to clean the steam chamber. An overpressure is produced by the closing of the valve. But this device is not provided to continuously obtain powerful steam.
The steam can also be placed under elevated pressure, which resolves these problems. This is the case when the iron comprises—or is associated with—a steam generator having a closed boiler in which a mass of water boils slowly, but these systems have a high price.
The object of the invention herebelow is to reduce these drawbacks by proposing an economical iron in which the average pressure of the steam generated is sufficiently high to be free of the overpressure due to the ironing and/or to permit high output velocities of the steam and/or to permit the utilization of steam in a sprayer.
The object of the invention is achieved by a pressing iron having a water reservoir at atmospheric pressure, water from the reservoir flowing through an ajutage between this reservoir and a heated and regulated steam chamber, a soleplate having the ironing surface, steam outlet holes being arranged in the soleplate, noteworthy in that the iron comprises means placing the water and steam circuit in resonance or relaxation vibration, the cyclic variation of the steam pressure being automatically maintained at an average pressure above that corresponding to the column of water available in the iron.
FIG. 1
attached shows how one obtains in a surprising manner such a pressing iron. This figure is a graph of the mass of flow rate Q of steam in grams per minute as a function of the total cross-section S in square millimeters of the steam outlet orifices, for different passage diameters of the ajutage of a prototype. The diameters are indicated on each curve.
The prototype equipped at the beginning with an ajutage whose diameter was 0.95 mm had an initial steam outlet cross-section of 80 mm
2
. Steam outlet holes were progressively eliminated in order to diminish the outlet cross-section. In this operation, until a cross-section of around 25 mm
2
, the steam flow rate was seen to diminish slowly as expected. Then, when continuing the reduction, the iron produced in a surprising manner more and more steam up to 24 grams per minute with a steam outlet cross-section of only around 10 mm
2
and with an elevated outlet velocity. Simultaneously it was noted that the iron emitted a noise and that the average pressure in the steam chamber increased in a very substantial manner to greatly exceed the value corresponding to the height of the water column feeding the ajutage. It was noted with satisfaction that the steam then had a high velocity and a good effect of penetration into the material being ironed, without the application of the iron onto the material substantially diminishing the steam flow rate. It was noted that the pressure varied in a periodic manner. There were also noted reversals in the flow of the steam through the ajutage. The steam recondenses quickly in the water reservoir while provoking small implosions at a rapid cadence.
The phenomenon is not clearly explainable. In part, one can think that the steam chamber behaves with the outlet holes like a Helmholtz resonant cavity that would be excited by the vaporization of the water. In part, one can think that the steam implosions in the reservoir just above the valve propel the water with force into the chamber as is done in a pump. Since the steam chamber is a cavity which is not designed to have a low resonant frequency from the acoustic point of view, one can think that the phenomena combine and that when enough energy can be maintained in the resonator thus constituted, it oscillates while generating substantial overpressures that lead to an increased average pressure.
This is obtained when the steam outlet passage is correctly adjusted with the passage in the ajutage. With respect to known irons, it is necessary to substantially reduce the steam outlet and to increase the passage in the ajutage which, without the effect previously described, would have caused a fear that the steam overpressures due to the abundance of water would impede the operation.
The overpressure is obtained for a value of the steam outlet cross-section below a critical value. For greater outlet cross-sections close to this critical value, the onset of the mode of operation described is obtained by a shaking or abrupt opening of the ajutage. The operation can then present an instability which one can attempt to explain by an excessive loss of energy through the outlet holes, or by a great difficulty in transforming the pressure energy into sufficient kinetic energy. This energy is used normally to create a temporary pressure drop in the chamber and to aspirate water through the ajutage.
On
FIG. 1
there are traced different curves of a prototype relative to ajutages whose passage diameter is different. The zone where the desired mode of operation is stable and begins spontaneously is limited toward the right by a curve A in dashed lines. This curve represents solution of a function f(S,Q)=0 that can be interpolated by a polynomial in the useful zone. By way of example, in the particular case of the prototype of
FIG. 1
this function is written:
F

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