Patent Publication Number: US-7721474-B2

Title: Method for controlling an ironing temperature during a steam ironing process and a corresponding steam iron

Description:
The present invention relates to a method for controlling an ironing temperature during a steam ironing process in which a steam iron having a soleplate for contacting items to be ironed and a steam generator for generating steam are applied. 
     Steam ironing processes are aimed at de-wrinkling fabric items such as garments or curtains. During a steam ironing process, the fabric item is flattened by means of a hot plate, while steam is supplied to the item to moisten the item, whereby the de-wrinkling effect of the ironing process is enhanced. 
     For the purpose of carrying out steam ironing processes, steam irons have been developed. A conventional steam iron comprises a soleplate having a contacting surface for contacting the items to be ironed, and a housing for accommodating various other components of the steam iron. The soleplate comprises a bottom portion of a steam chamber for generating steam during operation of the steam iron. A cover is provided for covering the soleplate and closing the steam chamber. The soleplate further includes a typically U-shaped tubular heating element, which serves for heating both the soleplate and the steam chamber during operation of the steam iron. When the steam chamber is heated, water that is inside the steam chamber is converted to steam. For the purpose of letting out steam, steam openings are arranged in the soleplate, which are in communication with the steam chamber. 
     During operation of the conventional steam iron as described in the preceding paragraph, the heating element is activated, and water is supplied to the steam chamber. Under the influence of the heat supplied by the heating element, the temperature of the contacting surface of the soleplate increases, while the temperature prevailing inside the steam chamber increases as well. As a result, water that is supplied to the steam chamber is converted into steam. During an ironing process in which the steam iron is applied, the items to be ironed are contacted by the hot contacting surface, while steam is supplied to these items through the steam openings. 
     It is a known fact that an ironing temperature, i.e. a temperature to which the item to be ironed is put during the ironing process, needs to be adjusted to the type of fabric of the item. For example, in case the item is made of cotton, the ironing temperature needs to be relatively high. Usually, in such case, the contacting surface of the soleplate of the steam iron is put to a temperature of about 200° C. However, for the purpose of ironing an item made of, for example, polyester, the ironing temperature should be much lower (about 150° C.) in order to avoid scorching of the item. 
     When the conventional steam iron, in which one heating element is used for heating both the contacting surface of the soleplate and the steam chamber, is applied for the purpose of items made of polyester or the like, there is a considerable chance that not all water is converted to steam in the steam chamber, due to the relatively low temperature. As a disadvantageous result, water droplets may be released by the steam iron, and it is even possible that scale particles are spit out by the steam iron along with the water droplets. 
     In US 2003/0094445, a solution to the problem mentioned in the above-mentioned paragraph is presented. According to this solution, a steam iron is provided, in which the temperatures of the steam generator and the contacting surface of the soleplate are controlled in an independent manner. Consequently, independently controllable heating elements are provided, wherein one of the elements serves for heating the steam chamber and wherein another of the elements serves for heating the soleplate. Moreover, both heating elements have their own thermostat. 
     During application of the steam iron as proposed in US 2003/0094445, it is possible to have a relatively low ironing temperature and still avoid the formation of water drops, due to the independence of the temperatures of the steam chamber and the contacting surface of the soleplate. During a steam ironing process in which delicate fabrics are ironed, the temperature of the contacting surface of the soleplate is set such as to be relatively low, so that the fabrics will not be scorched, while the temperature prevailing inside the steam generator is set to be so high that all water inside the steam generator is evaporated, whereby so-called dry steam is obtained. 
     Although the steam iron as proposed in US 2003/0094445 has important advantages, there are also some disadvantages associated with this steam iron. For example, when a user decides to iron a shirt made of polyester after having ironed a shirt made of cotton, the user needs to set the temperature of the contacting surface of the soleplate of the iron at a lower level, and then wait until the contacting surface has cooled down. In this situation, it is not inconceivable that the user does not have the patience to wait for the necessary temperature change. As soon as the user starts ironing the shirt made of polyester at a temperature, which is too high, scorching of the shirt may occur. This disadvantage is not only associated with the steam iron as proposed in US 2003/0094445, but also with other known steam irons. 
     It is an objective of the present invention to find a solution to the problem of the relatively long time involved in a change of the ironing temperature, while also avoiding the problem of the steam iron dripping water at low temperatures. According to the present invention, the objective is achieved by applying a method for controlling an ironing temperature during a steam ironing process in which a steam iron having a soleplate for contacting items to be ironed and a steam generator for generating steam are applied, wherein required changes of the ironing temperature are obtained on the basis of changes of a temperature of the generated steam, while a temperature of the soleplate is kept within a predetermined limited range of temperatures throughout the steam ironing process. 
     Contrary to conventional steam ironing processes, in which the temperature of the contacting surface of the soleplate of the applied steam iron is changed when the ironing temperature needs to be changed, the present invention proposes a steam ironing process in which a change of the ironing temperature is obtained by only varying the temperature of the steam that is supplied to the item to be ironed. According to the present invention, the temperature of the soleplate is kept at a substantially constant level throughout the entire ironing process, without regard to of the type of fabric that needs to be ironed. 
     In situations in which the steam ironing process according to the present invention is applied, a change of the ironing temperature is obtained on the basis of a change of the temperature of the steam that is supplied to the item to be ironed. The realization of a change of the temperature of the steam takes significantly less time than a change of the temperature of the soleplate. The difference is explained by taking into account the fact that the soleplate is a relatively bulky component of the steam iron, as the soleplate plays a role in flattening the items to be ironed. 
     As far as heat transfer to the items to be ironed is concerned, it is noted that studies which have been performed in the context of the present invention have shown that steam is more effective in heating up the items to be ironed than a hot contacting surface, due to an involvement of a mass transfer and latent heat. This is another reason why it is very advantageous to vary the temperature of the steam in order to obtain a variation of the ironing temperature, contrary to varying the temperature of the soleplate. 
     According to the present invention, the temperature of the soleplate of the steam iron is set such as to be within a predetermined limited range of temperatures. Preferably, the temperatures of this range are above the condensation temperature of steam, whereby it is ensured that the items to be ironed will not be stained by water droplets leaking from the steam openings of the steam iron. 
     In an embodiment of a steam iron suitable for carrying out the method according to the present invention, a thermostat for setting the temperature of the soleplate is adapted to keeping the temperature of the soleplate within a predetermined limited range. For example, this thermostat can be adapted such as to keep the temperature at a level of 110° C. 
     In case the soleplate is kept at a relatively low temperature, for example a temperature of 110° C., the chance of scorching fabrics is considerably reduced. Furthermore, at the start of the steam ironing process, it takes a relatively short time for the steam iron to heat up and get ready for use. 
     In the steam iron according to the present invention, the soleplate does not need to have a function in varying the ironing temperature. Two remaining functions of the soleplate are providing the contacting surface for flattening the items to be ironed, and serving as a conduit for the steam. For the purpose of carrying out these functions, it is not necessary that the soleplate comprises aluminium or another conventional material (metal). Instead, the soleplate may comprise a wide variety of materials, such as thermally conductive plastic and composite materials. According to an advantageous possibility, the soleplate comprises thermally conductive plastic which is not electrically conductive, wherein electrically conductive plastic is moulded in the thermally conductive plastic in order to create a resistive element for heating the soleplate. 
     It is noted that EP 1270796 discloses a so-called all steam iron with which ironing is conducted with supplied steam. The all steam iron does not comprise heating means for heating a contacting surface of the soleplate. During operation of the all steam iron, the soleplate is heated by the steam. The items to be ironed are flattened and stretched by the hot soleplate, moisturized by the steam and heated by the soleplate and the steam. The all steam iron is an industrial iron, the soleplate of which is heated under the influence of re-circulation of steam, in order to avoid condensation of steam to water droplets, causing spitting of water droplets during ironing. In the process, the temperature of the soleplate is kept above the condensation temperature of steam. 
     When the all steam iron is applied, the ironing temperature is determined by the temperature of the supplied steam. However, an important difference between the all steam iron and the steam iron according to the present invention is that in the all steam iron, the temperature of the soleplate varies along with the temperature of the supplied steam, whereas in the steam iron according to the present invention, the temperature of the soleplate is kept within a predetermined limited range. 
    
    
     
       The present invention will now be explained in greater detail with reference to the figures, in which: 
         FIG. 1  diagrammatically shows components of a steam iron assembly according to a first preferred embodiment of the present invention and a course which is followed by water and steam through this steam iron assembly; and 
         FIG. 2  diagrammatically shows components of a steam iron assembly according to a second preferred embodiment of the present invention and a course, which is followed by water and steam through this steam iron assembly. 
     
    
    
       FIG. 1  diagrammatically shows components of a steam iron assembly  1  according to a first preferred embodiment of the present invention. In the following, this steam iron assembly  1  will be referred to as first steam iron assembly  1 . The first steam iron assembly  1  comprises a steam iron  10  having a soleplate  11 . A planar contacting surface  12  of the soleplate  11  serves for contacting items to be ironed. In the soleplate  11 , steam openings (not shown) for letting through steam are arranged. Furthermore, the first steam iron assembly  1  comprises a steam generator  20  for generating and supplying steam, a water reservoir  30  for containing water and a pump  40  for forcing water to flow from the water reservoir  30  to the steam generator  20 . 
     Besides the soleplate  11 , the steam iron  10  comprises a housing  50 , which is positioned on top of the soleplate  11 , and which has a handle  51  to enable a user to pick up the steam iron  10  and move the contacting surface  12  over an item to be ironed. In  FIG. 1 , the housing  50  is diagrammatically depicted by means of dashed lines. In the shown example, the steam generator  20 , the water reservoir  30  and the pump  40  are arranged outside of the housing  50 . That does not alter the fact that alternative embodiments in which these components are accommodated by the housing  50  are also possible within the scope of the present invention. In such embodiments, the pump  40  may be omitted or relocated. 
     For the purpose of heating the soleplate  11 , first heating means  13  are provided. Preferably, these heating means  13  comprise at least one flat resistive heating element arranged on a surface of the soleplate  11 , but another embodiment of the heating means  13  is also possible. 
     For completeness&#39; sake, it is noted that flat resistive heating elements are heating elements, which are deposited as a thin layer on a surface by means of printing or other suitable techniques. Under the influence of an electric current, the flat resistive heating elements are capable of generating heat. For example, the flat resistive heating elements are formed by a layer of synthetic resin in which electrically conducting particles are embedded. When the flat resistive heating elements are arranged on a surface comprising an electrically conducting material such as metal, an electrically insulating layer needs to be arranged between the surface and the heating elements in order to avoid short-circuiting. Flat resistive heating elements can be arranged on planar surfaces, but it is also possible to arrange this type of heating elements on curved surfaces. 
     For the purpose of heating the content of the steam generator  20 , second heating means  21  are provided. Like the first heating means  13 , the second heating means  21  preferably comprise at least one flat resistive heating element, but it is also possible that the second heating means  21  are designed in another way. 
     During a steam ironing process in which the first steam iron assembly  1  is applied, an ironing temperature, i.e. a temperature at which the item to be ironed is actually ironed, is mainly determined by the temperature of the supplied steam. According to the present invention, both temperatures are controlled by means of thermostats or other suitable temperature controlling means. In  FIG. 1 , a first thermostat associated with the first heating means  13  for heating the soleplate  11  is indicated by reference numeral  14 , and a second thermostat associated with the second heating means  21  for heating the content of the steam generator  20  is indicated by reference numeral  22 . 
     According to an important aspect of the present invention, the first thermostat  14  has a fixed setting, while a setting of the second thermostat  22  is adjustable. In other words, the first thermostat  14  is adapted to keeping the temperature of the soleplate  11  within a predetermined limited range, while the second thermostat  22  is adapted to putting the steam exiting the steam generator  20  to a temperature which is related to a required ironing temperature. For the purpose of receiving input from a user regarding the required ironing temperature, the first steam iron assembly  1  comprises input means (not shown) such as a rotatably arranged disc or the like. 
     Prior to the start of a steam ironing process, the user checks the setting of the input means of the first steam iron assembly  1 . In case the setting reflects the desires of the user, which are related to the type of fabric that needs to be ironed, there is no need for an adjustment of the setting of the input means. In case the setting of the input means is not representative of the required ironing temperature, the user adjusts the setting of the input means. 
     At the start of the steam ironing process, the soleplate  11  of the steam iron  10  is heated to a predetermined temperature, wherein the heating process is controlled by means of the first thermostat  14 . The predetermined temperature may for example be 110° C. The first thermostat  14  is adapted to keeping the temperature of the soleplate  11  around this predetermined temperature throughout the steam ironing process. 
     Furthermore, the pump  40  is activated to pump water from the water reservoir  30  to the steam generator  20 . In  FIG. 1 , a path, which is followed by the water, is indicated by means of arrows. Inside the steam generator  20 , the water is evaporated to steam under the influence of heat supplied by the second heating means  21 . The setting of the second thermostat  22  is determined by the setting of the input means, wherein a relation between these two settings is determined by the requirement that the second thermostat  22  has to control the second heating means  21  in such a way that the set ironing temperature is reached on the basis of the temperature of steam exiting the steam generator  20 . 
     The generated steam is supplied to the steam iron  10 , and is supplied to the item to be ironed through the steam openings in the soleplate  11  of the steam iron  10 . In  FIG. 1 , a path which is followed by the steam from the steam generator  20  to the soleplate  11  of the steam iron  10  is indicated by means of an arrow, and a path which is followed by the steam through the soleplate  11  and the steam openings is indicated by three relatively small arrows. A cloud of steam, which is released by the steam iron  10  through the steam openings, is diagrammatically depicted in  FIG. 1  and indicated by reference numeral  15 . 
     As soon as the user changes the setting of the input means during the steam ironing process, the setting of the second thermostat  22  and the operation of the second heating means  21  are changed as well, while the setting of the first thermostat  14  remains the same. In case the input means indicate that a higher ironing temperature is required, the second thermostat  22  is set at a higher temperature and the second heating means  21  are controlled such as to supply more heat to the content of the steam generator  20 , so that the temperature of the steam exiting the steam generator  20  is increased. In case the input means indicate that a lower ironing temperature is required, the second thermostat  22  is set at a lower temperature and the second heating means  21  are controlled such as to supply less heat to the content of the steam generator  20 , so that the temperature of the steam exiting the steam generator  20  is decreased. According to this procedure, a variation of the requested ironing temperature is obtained on the basis of a variation of the temperature of the steam only. 
     Contrary to the conventional situation in which the ironing temperature is mainly determined by the temperature of the soleplate, in this case, the ironing temperature is mainly determined by the temperature of the supplied steam when the first steam iron assembly  1  is applied. For example, for the purpose of ironing polyester, the steam temperature is set around 150° C., and for the purpose of ironing cotton, the temperature is set at a higher level, approximately 180-200° C. The temperature of the steam can easily be varied by adjusting the setting of the second thermostat  22  and/or varying a power supply to the steam generator  20 . 
     Throughout the steam ironing process, the temperature of the soleplate  11  of the steam iron  10  is kept around a constant level under the influence of the first thermostat  14 . The temperature of the soleplate  11  is kept at a relatively low level. Preferably, the temperature of the soleplate  11  is just high enough to ensure that the formation of water droplets in the supplied steam does not occur. A suitable value of the temperature of the soleplate  11  is 110° C., which is a temperature just above the condensation temperature of steam. 
     An important advantage of the first steam iron assembly  1  is that required changes of the ironing temperature are very quickly realized, as such changes only require a change of the temperature of the supplied steam. Therefore, a situation in which a temperature of the soleplate is too high and the item to be ironed gets scorched is virtually excluded. 
     Another important advantage of the first steam iron assembly  1  is that the temperature of the soleplate  11  of the steam iron  10  may be at a relatively low level of for example 110° C., whatever the circumstances. Measures may be taken to stop the production of steam as soon as the hand of the user is off the steam iron  10 . In this way, it is assured that the temperature of the item to be ironed is only influenced by the temperature of the contacting surface  12  of the soleplate  11  when the steam iron  10  is left unattended. As the temperature of the contacting surface  12  is relatively low, there is little risk of the item to be ironed getting scorched. The application of the first steam iron assembly  1  is safe with respect to the application of a conventional steam iron or a conventional steam iron assembly. In the latter case, the temperature of the contacting surface of the soleplate of the steam iron may be much higher than 110° C., for example 150° C. or even 230° C. 
     As a result of the relatively low temperature of the soleplate  11 , a heat up time of the steam iron  10  is relatively short, especially in case the soleplate  11  is chosen such as to be a low mass type soleplate. For example, the time it takes to heat up to a temperature of 110° C. is only 18 seconds for a soleplate  11  of 200 grams, starting from an initial temperature of 25° C. 
     As the temperature of the soleplate  11  of the steam iron  10  is kept at a more or less constant level, which is relatively low, many materials are suitable to be incorporated in the soleplate  11 . For example, thermally conductive plastics or composite materials may be applied. It is also possible that the soleplate  11  comprises a conventional material such as aluminium. 
     In case the soleplate  11  comprises a thermally conductive plastic, the first heating means  13  may comprise at least one portion of electrically conductive plastic that is moulded in the thermally conductive plastic such as to create a flat resistive heating element. 
     It will be clear to a person skilled in the art that the scope of the present invention is not limited to the examples discussed in the foregoing, but that several amendments and modifications thereof are possible without deviating from the scope of the present invention as defined in the attached claims. 
     With respect to the first heating means  13  for heating the soleplate  11 , it is noted in the foregoing that these means  11  preferably comprise at least one flat resistive heating element. It is also very well possible that the first heating means  13  comprise at least one PTC heating element (PTC stands for Positive Temperature Coefficient). An important feature of such a heating element is that its electrical resistance rises as the temperature rises. As a consequence, a PTC heating element is very well applicable for the purpose of keeping a temperature within a predetermined range. In case the first heating means  13  comprise a PTC heating element, there is no need for a thermostat for controlling the operation of these heating means  13 , and the first thermostat  14  can be omitted. 
     In the foregoing, a steam iron assembly  1  is disclosed, which comprises a steam iron  10 , a steam generator  20  and a water reservoir  30 . Furthermore, a pump  40  is provided for pumping water from the water reservoir  30  to the steam generator  20 . Inside the steam generator  20 , the water is heated to steam. The generated steam is conducted through the steam iron  10  to an item to be ironed. 
     The steam iron  10  comprises a soleplate  11  having a contacting surface  12  for contacting items to be ironed. A temperature of the soleplate  11  is kept at a relatively low level of for example 110° C. throughout an entire steam ironing process, whereas variations of an ironing temperature are obtained on the basis of variations of a temperature of the supplied steam. 
     Due to the relatively low and constant level of the temperature of the soleplate  11 , and the fact that variations of the ironing temperature can be realized very quickly, the risk of scorching of the items to be ironed is reduced. 
       FIG. 2  diagrammatically shows components of a steam iron assembly  2  according to a second preferred embodiment of the present invention. In the following, this steam iron assembly  2  will be referred to as second steam iron assembly  2 . Like the first steam iron assembly  1 , the second steam iron assembly  2  comprises a steam iron  10  having a soleplate  11  and a housing  50 , and first heating means  13  for heating the soleplate  11 . Furthermore, the second steam iron assembly  2  comprises a boiler  60  for converting water to steam, which is located outside of the steam iron  10 . 
     During operation of the second steam iron assembly  2 , steam exits the boiler  60  and is transported to the steam iron  10 . In many cases, the steam supplied by the boiler  60  is saturated, and steam condenses on the way to the steam iron  10 . In order to convert the water that is obtained as a result of the condensing process to steam again, the steam and the water are re-heated in the steam iron  10 . For this purpose, the steam iron  10  comprises a re-heating device  65 . This re-heating device  65  comprises conducting means for conducting the water and the steam, for example multi-steam channels or chambers, and second heating means  66  for heating the water and the steam. 
     Like the first steam iron assembly  1 , the second iron assembly  2  comprises input means (not shown), by means of which a user is capable of setting a required ironing temperature. According to an important aspect of the present invention, the temperature of the soleplate  11  is maintained within a predetermined limited range of temperatures, without regard to the setting of the input means, while the temperature of the steam exiting the re-heating device  65  is accurately controlled in order to realize the required ironing temperature. 
     The temperature of the soleplate  11  is controlled by means of a first thermostat  14 , which is associated with the first heating means  13 . In a suitable embodiment, this thermostat  14  has a fixed setting. For example, the first thermostat  14  is set to keep the temperature of the soleplate  11  at 110° C. 
     The operation of the second heating means  66  is controlled by a second thermostat  67 . The setting of the second thermostat  67  is related to the setting of the input means, which is representative of the required ironing temperature. The second thermostat  67  may for example be coupled to power control means (not shown), by means of which the operating power that is supplied to the second heating means  66  is controlled. 
     During operation of the second steam iron assembly  2 , the following steps take place: 
     Step 1: Water is converted to steam in the boiler  60 . 
     Step 2: The steam is transported to the steam iron  10 . This is diagrammatically depicted in  FIG. 2  by means of an arrow starting from the boiler  60 . 
     Step 3: The steam, which is partly condensed, is heated in the re-heating device  65 . 
     Step 4: The steam is transported from the re-heating device  65  to the soleplate  11 . This is diagrammatically depicted in  FIG. 2  by means of an arrow starting from the re-heating device  65 . 
     Step 5: The steam exits the soleplate  11  through steam openings. These steam openings are not shown in  FIG. 2 , but a path which is followed by the steam through the soleplate  11  and the steam openings is indicated by three curved arrows. Furthermore, a cloud of steam, which is released by the steam iron  10  through the steam openings, is diagrammatically depicted in  FIG. 2  and indicated by reference numeral  15 . 
     During the above-sketched process, the temperature of the soleplate  11  is kept around a fixed temperature, whereas the temperature of the steam supplied by the re-heating device  65  is accurately controlled such as to realize the required ironing temperature. In the re-heating device  65 , the steam is heated under the influence of the second heating means  66 . Important factors which play a role in determining the temperature of the steam are the heating power supplied by the second heating means  66  and the flow of the steam through the re-heating device  65 . Preferably, it is not only possible to vary the supplied heating power, but also the flow. For the purpose of controlling the flow, flow control means of any suitable type may be arranged. 
     On the basis of the foregoing, it will be clear that there are many similarities between the second steam iron assembly  2  and the first steam iron assembly  1 . In fact, the only significant difference is that the second steam iron assembly  2  comprises a combination of a boiler  60  and a re-heating device  65  for supplying the steam, whereas the first steam iron assembly  1  comprises a single steam generator  20  for the same purpose. Therefore, it will be clear that both steam iron assemblies  1 ,  2  function according to the same principles, and offer the same advantages. Consequently, many remarks which are made in respect of the first steam iron assembly  1  are also applicable to the second iron assembly  2 . For example, it is also true for the second steam iron assembly  2  that the soleplate  11  may comprise a thermally conductive plastic or a composite material, and that the heating means  13 ,  66  preferably comprise at least one flat resistive heating element. Also, in the second steam iron assembly  2 , the first heating means  13  may comprise at least one PTC heating element in stead of at least one flat resistive heating element, wherein the first thermostat  14  may be omitted.