1. Technical Field
The invention relates to wax imitation candles and more particularly to an imitation candle resistant to cracking at low temperatures.
2. Description of the Problem
Many people find candle light pleasant. The flickering of light and movement of shadows across a floor or on a nearby wall can be almost hypnotically soothing. As a result, candles have remained popular for generations since the invention of more practical electrical lighting, especially for decorative and mood setting purposes.
Consequently, numerous manufacturers have attempted to meet a demand for a candle like luminary using electrical illumination. A now popular imitation candle is taught in International Publication Number WO 03/016783 A1. This imitation candle uses an internal LED as a light source within a solid appearing body. While a classical image of a candle is of a long, thin, tapering rod, which stands upright in a candle stick and which leaves its flame exposed as it burns down, this imitation candle comes as a relatively short to circumference block or cylinder which is self supporting. Such candles commonly leave the outer wall of the candle intact as the candlewick burns down. When this happens, the candle flame is no longer directly visible when viewed from the side. This results in a diffuse, flickering glow visible through the paraffin wall of the candle, which is imitated by the external shape of the imitation candle.
While the imitation candle of WO 03/016783 appears to be a solid body to users it is in fact hollow. This provides space for the installation of batteries, the LED, LED excitation circuitry and possibly light directing internal components. In addition, the contour of the void's internal surface may be chosen for light transmission issues. While the imitation candle can readily be made in plastic, fabricating it in more realistic wax has presented particular problems.
Wax is highly susceptible to compressive and tensile stress. Waxes also tend to have high coefficients of thermal expansion. Differential heating and cooling of sections of a cast wax body introduces stress. Stress tends to be focused along sharp corners and edges of a wax body. Stress can occur during manufacturing and shipping of the wax shell imitation candles when the imitation candles are subjected to rapid cooling or great temperature extremes, respectively. The cavity adds the problem of internal edges, as well as reducing the strength of the body compared to a solid wax body. In addition, the insert on which battery, excitation circuitry and the LED are mounted will typically be constructed by plastic with the wax body being formed in part on the insert body. Wax will typically have a higher coefficient of expansion than the plastic does, which results in additional stress as temperature of the body decreases and contributes further to the problems of the inherent weakness of wax.
Wax bodies, such as candles, are formed by a process of casting. Where it is desired to incorporate a plastic module in the wax body the plastic module may be fixed in position in a mold and hot wax poured around the module, adding wax as earlier poured wax cools and shrinks, until all voids around the module are filled. Alternatively, a wax shell can be formed that produces the outer visible surfaces of the candle while leaving a space for the module. After the shell is produced a second pour is done to secure the module in position. The amount of wax in the second pour is less than in the first, with the attendant advantages of quicker cooling and faster production speeds. While true, solid wax candles have reasonable durability to withstand cold temperature induced stress, wax bodies made by either of the foregoing casting techniques have proven highly susceptible to cracking. Thin sections of the casting adjacent the module cool more rapidly than thicker sections. Leading edges of the imitation candle also cool rapidly. These sections of rapid cooling result in differential rates of contraction, which can easily result in formation of a crack to relieve stress. Once such a crack propagates into a thicker section of the body it can become a focal point for other stresses and can extend to encircle the imitation candle body.
According to the invention there is provided an imitation candle. The imitation candle has a wax shell having a central cavity defined by an interior surface. A artificial lighting module, which tends to exhibit a different thermal coefficient of expansion than the wax, is positioned in the central cavity. A bonding layer between a portion of the module and the interior surface of the wax shell retains the module in the shell. The bonding layer leaves a gap between the insert and the interior surface near any exterior edges of the wax shell. The gap is preferably filled with air.
Additional effects, features and advantages will be apparent in the written description that follows.
The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself however, as well as a preferred mode of use, further objects and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein:
Referring now to
Referring to
Insert 12 is undersized compared to the cavity 14 in which it is to be retained. Bonding between a plastic insert casing 18 is provided by bonding layer 20 which lines the upper portion of cavity 14 between casing 18 and interior surface 15. As described below, bonding layer 20 is formed by a second pouring of a small quantity of molten wax into an inverted, but already cooled and hardened shell 10. Bonding layer 20 is shaped by fitting insert 12 into cavity 14 while the second poured wax is still molten. Bonding layer 20 does not line all of interior surface 15 in the preferred embodiment, but only enough to cover casing 18 around LED 16 and about the top half of the main body of insert 12. An air gap 30 surrounds the bottom half of insert 14 spacing the insert from interior surface 15. The top 32 of illumination module 14 abuts an upper horizontal face 34 of interior surface 15, displacing molten wax and positioning the illumination module vertically. Horizontal positioning of illumination module may be achieved by careful reference to the spacing between casing 18 and interior surface 15 and by the careful, mutually parallel orientation of the elements. The bottom surface of insert 12 is slightly recessed (2.5 mm) from the surrounding bottom surface of shell 10 allowing accurate determination disposition of the insert in cavity 14.
While use of a bonding layer 20 is preferred due to the assurance of a good fit between the bonding layer and insert 12, it is possible to substitute a molded or shaped shoulder 60 which is formed as part of interior surface 15 defining cavity 14. As seen in
After pouring of the wax for shell 10 the wax is allowed to cool. Where no form is used the wax is allowed to cool until the wall thickness is at least 10 mm. Where a form 42 is used the wax is allowed to cool until the entire shell 10 has hardened. A water bath may be used to expedite the cooling process. If no form was used a hole is formed into the cooling body from what will be become the bottom surface of the shell to the interior, still molten wax. The mold is partially inverted to allow the molten wax to be poured out and reclaimed. Removal of the central, molten wax speeds the cooling process and relieves stress on the walls of shell 10. The shell continues cooling, again potentially placed in a water bath to quicken the process. Mold 40 is advantageously shaped to impress an upper surface central depression into shell 10. Where, however, the mold did not incorporate such a shape, a bit contoured with the cross section of the upper surface may be used to shape the upper surface after withdrawal of the shell 10 from mold 40.
The position of insert 12 is controlled by the depth of cavity 14. An inner bit may be used trim the bottom of shell 10 and to machine cavity 14 where no interior form 42 is used, or where adjustment of the shape of a cavity left by a form is required. Shell 10 should be properly fixtured during shaping with a bit to insure a uniform core depth and candle height.
With the shell 10 fully hardened and the shape of cavity 14 finalized, shell 10 is reinverted and a second pour 46 of a small quantity of molten wax is made into the top of cavity 14. By the term “small” it is meant that the amount of wax in the second pour is a small percentage of the quantity of wax in the first pour. Where the depth of cavity 14 is 86 mm, the pour will leave the upper 58 mm empty before insertion of the insert 12. The formulation of the wax may be the same for both pours. With the second pour 46 still molten, insert 12 is lowered into cavity 14 of the inverted shell 10, displacing molten wax of the second pour 46 upwardly around the insert along the interior surface 15 of the cavity to form a bonding layer 20. Insert 12 is pressed as far as possible into shell 10, until the casing around upper surface 16 hits the top surface of the interior surface 15. An air gap of about 30 mm extends upwardly from the bottom of shell 10 into cavity 14 around insert 12. This helps prevent cracking.
The invention impedes the genesis and spread of cracks in the wax shell of a two component imitation candle. The assembly method for embedding insert 12 moves the point of maximum stress to a position where the stress is more readily tolerated. This is achieved by forming a gap between the insert and thin walled sections of the wax starting from a leading edge of the wax (e.g. the bottom edges of the shell). The gap can be air, or it can be filled with substances which offer insubstantial resistance to contraction of the wax as it cools. Leaving a gap between the bottom edge of the shell moves the point of maximum stress to an area of the shell where the gap ends and the bonding layer begins. This places the point of maximum stress away from any corners or edges. Cooling of the shell is also retarded here due to the greater local thermal mass, allowing more time for internal stress relief. The invention also achieves reduced concentration of stress by maintaining a maximum degree of uniformity in wax wall thickness and eliminating sharp corners.
While the invention is shown in only two of its forms, it is not thus limited but is susceptible to various changes and modifications without departing from the spirit and scope of the invention.
Number | Name | Date | Kind |
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3761702 | Andeweg | Sep 1973 | A |
3890085 | Andeweg | Jun 1975 | A |
5597300 | Wohl et al. | Jan 1997 | A |
6375455 | Frandsen et al. | Apr 2002 | B1 |
6491517 | Freeman et al. | Dec 2002 | B1 |
6544303 | Calzada | Apr 2003 | B1 |
6616308 | Jensen et al. | Sep 2003 | B1 |
6966665 | Limburg et al. | Nov 2005 | B1 |
Number | Date | Country |
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WO 03016783 | Feb 2003 | WO |
Number | Date | Country | |
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20050207171 A1 | Sep 2005 | US |