Patent Publication Number: US-2011076631-A1

Title: Self-extinguishing candlewick

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Embodiments of the present invention relate generally to candles and, more particularly, to a self-extinguishing wick for such candles. 
     2. Description of the Related Art 
     Wax-based candles are commonly used for specialized illumination, such as emergency lighting or to contribute to ambience. In addition, candles are used to provide a desirable scent. For any of these applications, an individual candle is typically sized to provide illumination and/or scent for a large number of uses. For example, candles are often sized to have a burn time of dozens of hours or more, but may only be used for a few hours at one time. However, candles commonly known in the art typically are not designed to self-extinguish and, therefore, will continue to burn until completely exhausted unless extinguished by the user. This can make the use of candles inconvenient and, in some cases, a safety hazard. In fact, according to Candle Fires in Residential Structures, a report by U.S. Department of Homeland Security, candles are responsible for an estimated 23,600 residential structure fires each year and cause 1,525 civilian injuries, 165 fatalities, and $390 million in direct property loss. 
     Accordingly, there is a need in the art for a candle designed to burn for a specified period of time, self-extinguish, and be ready for relighting when next required by the user. 
     SUMMARY OF THE INVENTION 
     One or more embodiments of the invention provide a self-extinguishing candlewick. The embodiments employ a plurality of flame-extinguishing sleeves positioned on the candlewick. Each flame-extinguishing sleeve is configured to conduct enough heat from a flame disposed at the top of the flame-extinguishing sleeve to form a wax pool that contacts the bottom edge of the flame-extinguishing sleeve. 
     One advantage of the disclosed invention is that a candle can be used for a predetermined interval and will self-extinguish at the end of said time interval. Another advantage of the disclosed invention is that modification of a conventional wick to incorporate the disclosed invention is relatively simple to implement. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
         FIG. 1  is a schematic cross-sectional view of a typical candle  100  known in the art. 
         FIGS. 2A-2D  are schematic cross-sectional views of a self-extinguishing candle  200  during use, according to embodiments of the invention. 
     
    
    
     For clarity, identical reference numbers have been used, where applicable, to designate identical elements that are common between figures. It is contemplated that features of one embodiment may be incorporated in other embodiments without further recitation. 
     DETAILED DESCRIPTION 
       FIG. 1  is a schematic cross-sectional view of a typical candle  100  known in the art. Candle  100  includes a body  101  and a wick  102 . Body  101  is a solid candle base material, such as paraffin-containing wax, that serves as fuel for candle  100  when lit. Wick  102  is a liquid-wax-absorbing material known in the art, such as a braided fiber wick. When candle  100  is in use, wick  102  is lit, producing a flame  103  as shown. Heat produced by flame  103  melts the solid candle base material proximate wick  102 , creating a pool  104  of liquid fuel. In its liquid state, the liquid fuel in pool  104  is carried to flame  103  by capillary action within wick  102 . As candle  100  burns and body  101  is consumed, the position of flame  103  advances downward along wick  102  until no liquid fuel is available or wick  102  is consumed. Consequently, candle  100  will continue to burn until completely consumed unless candle  100  is actively extinguished by a user. 
     Embodiments of the invention contemplate a candlewick with a plurality of flame-extinguishing sleeves disposed thereon that are configured with a length and spacing that cause the candlewick to self-extinguish after a pre-determined time interval. Each flame-extinguishing sleeve is comprised of a non-combustible material that prevents consumption of the candlewick contained therein, and is configured to conduct heat into the body of the candle when a flame is disposed at the top of said sleeve. The wall thickness and the material making up the non-combustible sleeves are selected to provide sufficient heat transfer into the body of the candle to melt the candle base material, e.g., wax, that is in contact with the flame-extinguishing sleeve when a candle flame reaches the top edge of said sleeve. Because of the heat transfer capability of the flame-extinguishing sleeves, a pool of molten candle base material is formed around said sleeve and fuels the candle flame by being drawn up through the wick. As the candle flame continues to burn, the pool of molten candle base material surrounding the flame-extinguishing sleeve is drained and the candle flame burns out. The flame-extinguishing sleeve may then be removed and the candle relit. 
       FIGS. 2A-2D  are schematic cross-sectional views of a self-extinguishing candle  200  during use, according to an embodiment of the invention.  FIG. 2A  illustrates self-extinguishing candle  200  burning normally. Self-extinguishing candle  200  includes a candle body  201  and a self-extinguishing wick  202 . As shown, during use a flame  203  is disposed on the end of self-extinguishing wick  202 , and is fueled by molten candle body material that is drawn by capillary action through self-extinguishing wick  202  from a wax pool  204  of molten candle body material. Heat from flame  203  melts the candle body material located near flame  203  to form wax pool  204 . 
     Candle body  201  includes any solid candle base material known in the art, such as paraffin-containing wax, that serves as fuel for candle  200  when lit. The term “candle base material” refers to any material that can be used to form a candle. A suitable candle base material may be solid or semi-solid at room temperature, which, upon melting due to exposure to flame  203 , provides a liquid fuel source to self-extinguishing wick  202 . One common form of candle base material is wax, which usually refers to a substance that is plastic to brittle solid at room temperature and becomes a low viscosity liquid when heated by flame  203 . Suitable waxes for forming candle body  201  include any known waxes, including, paraffin wax, microcrystalline wax, beeswax, animal wax, vegetable wax, mineral wax, synthetic wax, and mixtures thereof. In addition to wax, semi-solids (such as petrolatum), synthetic polymers and mixtures of synthetic polymers with one or more organic compounds may be included in the solid candle base material contained in candle body  201 . Other candle fuel source components, such as hydrocarbon oil, stearic acid, etc., may be also included in the candle base material. 
     Self-extinguishing wick  202  includes a wicking element  205 , which is made up of an elongated, liquid-wax-absorbing material, such as a conventional braided fiber wick known in the art. The performance-related characteristics of wicking element  205 , such as wick size, wick density, and fiber material, depend on a number of factors, including the type of solid candle base material contained in candle body  201 , the diameter or width of candle body  201 , the desired burn rate and flame height of the candle, etc., and may be selected using methods commonly known in the art. In addition to wicking element  205 , self-extinguishing wick  202  includes a plurality of non-combustible sleeves  206  positioned on wicking element  205 , as shown. Non-combustible sleeves  206  are separated by a gap  213 . In one embodiment, gap  213  is no less than about ⅛ inches, to ensure the flow of molten candle base material to flame  203 . The composition of non-combustible sleeves  206  is described below in conjunction with  FIG. 2B . The length  207  and spacing  208  of non-combustible sleeves  206  are selected so that flame  203  is extinguished a pre-determined time interval after self-extinguishing candle  200  is lit. For example, length  207  and spacing  208  may be selected so that self-extinguishing candle  200  will burn for 3 hours after being lit and then self-extinguish. The self-extinguishing mechanism of self-extinguishing wick  202  is also described in greater detail below. 
       FIG. 2B  illustrates self-extinguishing candle  200  after a portion of candle body  201  has been consumed and an exposed non-combustible sleeve  206 A projects above top surface  210  of candle body  201 . Non-combustible sleeves  206  are comprised of a material that is non-flammable at the temperatures present in a candle flame, and prevent the portion of wicking element  205  contained therein from being consumed by flame  203 . Consequently, flame  203  remains at the top of exposed non-combustible sleeve  206 A, as shown, and molten candle body material is drawn to flame  203  through the length of wicking element  205  that is disposed inside exposed non-combustible sleeve  206 A. 
     In addition to protecting wicking element  205  from being consumed by flame  203 , non-combustible sleeves  206  are also configured to conduct heat from flame  203  to candle body  201 , so that wax pool  204  continues to provide fuel to flame  203  even as flame  203  is displaced further from surface  210 . Therefore, each of non-combustible sleeves  206  is configured to transfer sufficient heat from flame  203  to surrounding candle body  201  so that wax pool  204  wets wicking element  205  at the point that wicking element  205  enters bottom opening  220  of exposed non-combustible sleeve  206 A. In addition, each of non-combustible sleeves  206  is configured with an inner conduit  221  sized so that wicking element  205  can wick molten candle base material from wax pool  204  at bottom opening  220  to flame  203 , i.e., inner conduit  221  is large enough to allow the wicking action of wicking element  205  to keep flame  203  burning. Thus, because of the size of inner conduit  221  and the heat transfer of non-combustible sleeves  206  to surrounding candle body  201 , molten candle body material can continue to be drawn to flame  203  through wicking element  205  when flame  203  is disposed on exposed non-combustible sleeve  206 A. If such were not the case, liquid fuel will not be available for combustion and flame  203  will extinguish once it is in contact with exposed non-combustible sleeve  206 A, leaving exposed non-combustible sleeve  206 A almost completely enclosed by candle body  201  and very difficult to remove for subsequent lighting of self-extinguishing candle  200 . Consequently, the heat-conducting capability of non-combustible sleeves  206  is considered in embodiments of the invention. To that end, non-combustible sleeves  206  may be comprised of a heat-conducting material and configured with a wall thickness T that enables sufficient heat conducting capability to form wax pool  204  at bottom opening  220 , as shown. 
     To ensure that wax pool  204  is formed around exposed non-combustible sleeve  206 A as shown in  FIG. 2B , both the wall thickness T and the thermal conductivity of the material making up non-combustible sleeves  206  may be considered. In one embodiment, non-combustible sleeves  206  are comprised of a non-combustible metal, such as copper or aluminum, having a higher thermal conductivity than many other non-combustible materials, such as glass or ceramics. Other metals may also be used, such as steel. In one embodiment, wall thickness T is configured to further increase heat transfer by non-combustible sleeves  206  from flame  203 . Namely, wall thickness T may be selected to be thicker than required to simply act as a non-combustible appliance that encloses wicking element  205 . For example, for a paraffin-wax candle with a standard pre-waxed wicking element  205  having a diameter of approximately 0.08 inches to 0.09 inches, non-combustible sleeves  206  may be comprised of copper and have a wall thickness of at least 0.01 inches to conduct enough heat from flame  203  to form wax pool  204 . One of skill in the art, upon reading the disclosure herein, may readily devise a non-combustible sleeve  206  for a candle having a different candle base material and/or a different size wicking element  205  than that described herein. 
       FIG. 2C  illustrates self-extinguishing candle  200  after enough of candle body  201  has been consumed that flame  203  is too far from candle body  201  to melt more of the candle base material making up candle body  201 . Consequently, wax pool  204  is no longer replenished with molten candle base material from candle body  201  and is depleted as shown. Because wicking element  205  is still wetted by wax pool  204  at bottom opening  220 , flame  203  continues to burn.  FIG. 2D  illustrates self-extinguishing candle  200  after wax pool  204  has been consumed and molten candle base material can no longer be provided to flame  203 . As shown, exposed non-combustible sleeve  206 A projects above candle body  201  and can easily be removed by the user to reveal an exposed length of wicking element  205  that can be lit for subsequent use of self-extinguishing candle  200 . When enough of candle body  201  is consumed so that a non-combustible sleeve  206  is again exposed above candle body  201  and wax pool  204  is again consumed, self-extinguishing candle  200  will again self-extinguish. The user may repeat this process until candle body  201  is substantially consumed. 
     As noted above, the predetermined burn time of self-extinguishing candle  200  depends on a number of factors, including length  207  and spacing  208  of non-combustible sleeves  206 , as well as on the diameter of self-extinguishing candle  200 , the burn rate of wicking element  205 , and the candle base material. In one embodiment, self-extinguishing candle  200  is a paraffin-wax candle having a diameter of approximately 3 inches and a pre-waxed wicking element  205  with a diameter of 0.085 inches, and is configured to burn in approximately 2-hour intervals before self-extinguishing. In such an embodiment, non-combustible sleeves  206  are comprised of copper, gap  213  is approximately 3/16 inches, wall thickness T is approximately 0.01 to 0.02 inches, length  207  is approximately ⅜ inches and spacing  208  is approximately 9/16 inches. One of skill in the art, upon reading the disclosure herein, can readily determine the spacing  208  and length  207  of non-combustible sleeves  206  for other configurations of self-extinguishing candle  200  than that described herein. 
     In order for even burn internals for self-extinguishing candle  200 , the positioning of non-combustible sleeves  206  on wicking element  205  should be robust and relatively precise, for example within ± 1/32 inches. In one embodiment, non-combustible sleeves  206  are precisely held in place on wicking element  205  by crimping one end of the sleeve onto wicking element  205 . In this way non-combustible sleeves  206  are firmly attached to wicking element  205  and will not slide downward as the wax of wicking element  205  is melted by flame  203 . In one embodiment, non-combustible sleeves  206  are crimped at the top edge to facilitate removal from wicking element  205  after self-extinguishing candle  200  has self-extinguished. In another embodiment, other means are used to precisely position and hold in place non-combustible sleeves  206 . For example, wicking element  205  may be knotted or include other means for holding non-combustible sleeves  206  in place as desired. 
     In one embodiment, non-combustible sleeves  206  are substantially cylindrical in shape. However, other configurations of non-combustible sleeves  206  are also contemplated by embodiment of the invention. 
     While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.