Fume extraction device for small-scale baking ovens intended for dewaxing, emanating from an exhaust outside the room where it is placed.

Abstract

Smoke evacuation device for small-sized baking ovens intended for dewaxing, characterized by: - ​​an air inlet (a) from outside the oven into the oven enclosure;this air inlet being placed to be received in the furnace enclosure near its hearth (b), that is to say in a low position in the furnace enclosure, - a fume evacuation (b) placed high up near the vault of the enclosure, on the wall opposite to that which receives the air inlet, - this fume evacuation (b) receives, outside the furnace enclosure, a pipe (c) whose surface area is at least 50 cm2, - inside this pipe (c) is placed a 0.001 µ filter (d), - inside the pipe (c), an electric suction system (e) which allows the air to circulate at a flow rate of 10 dm3 / h, - the pipe (c) is directed towards the air inlet (a), by an elbow (f) which mixes the recycled air with the fresh air and returns everything to the inside of the dewaxing furnace.;

Description

Title of the invention: DEVICE FOR EVACUATING SMOKE FROM SMALL COOKING OVENS INTENDED FOR WAX REMOVAL, RUNNING FROM AN EXHAUST OUTSIDE THE ROOM IN WHICH IT IS PLACED.

[0001] The present invention relates to the treatment of fumes which occur during the dewaxing operation in baking ovens which are used in the technique known as "lost wax casting"; particularly for ovens without an external chimney and in which the opening of the baking chamber is done by pivoting around a horizontal axis of the entire vault.

[0002] These ovens, which tilt around a horizontal axis, are characterized by an opening principle which pivots the entire roof towards the rear of the oven, thus leaving the oven floor entirely accessible for placing or removing objects. These ovens are used indoors, with supply voltages of 230V and without exhausting fumes to the outside of the room in which they are placed.

[0003] These furnaces were initially designed for ceramic or glass applications, however they are particularly popular with dental technicians (who use the lost wax casting technique) due to their small size and the total clearance of the floor. Prosthetists working in small existing spaces and for which bulky arrangements are not possible.

[0004] A problem arises with regard to the fumes emanating from the melted wax in the enclosure of this type of oven because the wax fume outlets are not provided and they escape from the oven when it is opened, which leads to the distribution of harmful gases in the room where the oven is exposed.

[0005] Waxes are often complex mixtures based on beeswax, vegetable, mineral or synthetic wax. They contain esters, fatty acids, alcohols and impurities such as rosin and paraffin. When heated, waxes produce fumes and gaseous releases of aldehydes (and in particular formaldehyde) and ketones, substances that are irritating to the skin, eyes and respiratory mucous membranes and are also allergenic. The thermal degradation products of rosin can cause tracheobronchial irritation and asthma, as well as allergic eczema. Formaldehyde can also induce certain cancerous conditions...

[0006] Known devices for the evacuation of fumes are applied according to principles of enveloping the emission zone by placing the furnace in a fume cupboard (enclosures with fume evacuation) or according to a principle of capture at closer to the source of the fumes. These devices have disadvantages: due to the thermal exchanges disturbed by the orifices necessary for the wax casting technique, and due to the space required for the movement of the furnace openings which does not allow the use of known techniques in small spaces.

[0007] State of knowledge: we will distinguish between the state of existing techniques and the state of science.

[0008] State of the art: The state of current knowledge in the technical field can be distinguished according to three distinct technological families.

[0009] The first technological family concerns the capture devices (chimney, fume cupboard, nearby suction) which are the most commonly used; These devices are characterized by a suction of fumes and gases which are then conveyed outside the room (of the building) via a conduit (chimney). This technological family includes three sub-families: - Chimneys, which do not have a motor and the evacuation is then done by ascending convection, - The fume cupboards, which are semi-closed enclosures that surround the ovens like those recommended by the INRS [2], these fume cupboards are equipped with forced suction and a chimney flue for the evacuation of fumes and gases, - Aspiration by capture as close as possible to the area where fumes and gaseous emissions are formed.

[0010] We can cite as an example the brand ® ENITHERM which presents different types of ovens with capture and suction principle, however these devices cannot be suitable for our object in that they are constrained: - They all require evacuation to the outside, - semi-closed enclosures do not allow the opening of ovens such as those described in our subject, moreover these devices also require external evacuations, - the closest captures do not allow the entire oven to be covered, which is completely open.

[0011] The second technological family concerns a filtration device. In order to filter effectively and adequately, there are four ranges of filters: - Coarse filters: also called pre-filters, they are mainly used in the first stage of air treatment and allow the largest particles to be removed from the air. They are also used in the first stage of filtration to protect the more sensitive filters of the following stages. They are designated by the letter G (Filtration up to 10 pm - example: pollens), - Fine filters: formerly called Opacimetric filters, they can di- directly placed in the first filtration stage. Their main application is the in-depth treatment of air in tertiary buildings. They are also used to effectively protect absolute filters. They are designated by the letter F (Filtration up to 0.1 pm - example: spores, bacteria), - Absolute filters: they are designated by the letter E, H or U. (Filtration up to 0.001 pm - example: fumes, soot), - Activated carbon filters: these are used to stop contaminants at the molecular level. They can stop odors (cooking for example), protect processes, or ensure the safety of nuclear facilities. (Filtration down to 0.1 nm or 0.0001 pm - example: gaseous molecules).

[0012] These devices are used to reduce the harmful effects of gases or to clean living spaces. We can cite the manufacturers ®SB Filters and technique, ® TORROS, ® SOFISE

[0013] The disadvantage of these devices is that: - They are designed for high flow rate extractors and for large cooking space environments, which is not the case for small ovens. Since the smoke volumes are also small, - Their temperature sensitivity is not defined for small filter dimensions with low flow rates.

[0014] The third technological family concerns pyrolysis or catalysis devices. These devices are constrained with respect to our object in that: - Pyrolysis devices implement technologies that require an additional energy source, which limits the power due to a domestic connection for which our oven is intended. We can cite as an example the patent CA621730 which presents a method for protecting the walls of pyrolysis chambers in hydrocarbon heat treatment furnaces, these devices are limited to the elements in contact with the walls, moreover, - Catalytic devices require maintenance that is beyond the reach of a user. We can cite as an example the patent CN206188547 which describes a catalytic phase furnace device.

[0015] State of the science: With regard to our subject, which concerns a smoke treatment device intended for a wax removal furnace (melting wax) which does not require evacuations via chimneys outside the building, the elements which are relevant on the scientific level are: - The different types of fumes from melted waxes do not allow the characterization of a universal fume treatment device suitable for horizontal tilting furnaces, - The orifice required for the recovery of melted waxes modifies the recirculation spatial control of fumes and gases in the furnace enclosure, - The treatment time adapted to all types of smoke to allow the furnace to be opened. The orifice required to recover the melted waxes modifies the spatial recirculation of smoke and gases in the furnace enclosure.

[0016] It is important to differentiate between a gas, which is a state of matter (in the same way as the liquid state and the solid state), and smoke, which refers to particles in a solid state suspended in the air and mixed with combustion gases and hot vapors.

[0017] Smoke can also be considered as a mixture of solid particles of different natures which are mixed. Due to their heavy state, the particles which constitute the smoke fall back to the ground due to their density which is greater than that of air. Our invention relates to the treatment of smoke without taking into account the indirect aspect of the gases.

[0018] We have searched in the state of science for the elements of response which allow us to determine the physical phenomena characterizing a device and a process adapted to our object.

[0019] Three reference works are appropriate for the problem we are discussing. - "Engineer techniques / Ref.: M3580 VI Investment casting - Application to superalloys This article is from: Materials I Metal forming and foundry" by Jean-Claude DORIATH, Serge PRIGENT. This article deals with the characteristics of investment casting for one of its most modern applications, that of turbojet blades. This type of casting is well suited to metallic materials with high hot mechanical properties such as nickel-based or cobalt-based alloys, used in turbomachinery. In addition, investment casting makes it possible to obtain reduced dimensional tolerances and high-quality surface finishes at considerably lower manufacturing costs than any other machining technique, conventional or not." - "Engineering techniques; Ref.: G1820 VI Reduction of dioxins, furans and polychlorinated biphenyls This article is from: Environment - Safety I Environment by Pierre LE CLOIREC, Alain LAPLANCHE". It states that "Dioxins, furans and PCBs are complex compounds belonging to the family of persistent organic products. They are present in particular in emissions from household waste incinerators, steel industry, cement works and represent a significant pollution risk. After a presentation of the structures and characteristics of these molecules, this article focuses on the impact on human health. The analysis methods, which are relatively difficult to carry out on these compounds, are then presented, followed by the available processes for decontaminating fumes." - finally, the third work "The techniques of the engineer; Ref.: BE8856 V2 Smoke treatment - article is from: Energies I Energy resources and storage, by Pierre LE CLOIREC. It is noted "The need to reduce the pollutant loads emitted by smoke is part of a global approach to environmental protection. After an introduction on the nature of pollutants and their impacts on human health, the article presents the regulatory aspect of controlling emissions into the atmosphere and methods of analysis of some pollutants. The smoke treatment processes are then described. Due to complex mixtures of compounds at low concentrations, their reduction requires a wide variety of technologies."

[0020] Consequently, there are no scientific elements capable of characterizing a smoke treatment device intended for a wax removal furnace (melting of wax) which does not require evacuations via chimneys outside the building.

[0021] Synthesis of the state of knowledge

[0022] Relative to the state of the art, there is no device that is capable of meeting the object of our study. Existing devices are constrained in that: - The first technological family of capture devices (chimney, fume cupboard, nearby suction) has the disadvantage of requiring a transformation of buildings for the integration of a chimney. This is to allow an evacuation of fumes which are then either simply diffused into the environment or reprocessed or filtered. The advantage of this technological principle is that the hot fumes are cooled before encountering a filter element which they could deteriorate by the heat. These devices use the convection phenomenon created by the temperature difference allowing the fumes to rise. Suction becomes necessary when the height of the chimney is significant or when the volume of smoke is significant.

[0023] - The second technological family of filtration devices presents several disadvantages to our object: They require capture and suction which are not determined for the different types of fumes which are produced by waxing, The time required for the treatment of the fumes in order to allow the opening of the furnace is not known because we do not know how the recirculation takes place inside the enclosure, - The third technological family of pyrolysis or catalysis devices presents disadvantages to our object. These disadvantages are related to: . As for pyrolysis, these devices are geared towards residues that are in contact with the oven walls and that need to be cleaned. The principle consists of overheating the wall to dry out and separate the residues. These are found then on the bottom of the oven and they must be removed. For wax melting, the particles do not constitute solid residues that will be placed on the walls of the oven. As for catalysis, the additional elements to transform the compounds cannot and recognized and universal for the different fumes that occur when melting wax. The devices are also bulky.

[0024] Relative to the state of science, it is not possible to directly determine a method and a device as desired for the object of study. Indeed, scientific knowledge is constrained in that: - The different types of fumes from melted waxes do not allow for the characterization of a universal fume treatment device suitable for horizontal tilting furnaces. This is due to the fact that each wax is different in its composition and the nature and quantities of the components can vary. The densities are different and the particle sizes are also different. The fume temperatures are not the same depending on the various types of fumes. - The orifice required for the recovery of melted waxes modifies the spatial recirculation of fumes and gases in the furnace enclosure. The state of science does not allow us to know the evolution of fumes in the enclosure according to the volumes of the objects to be heated and the recirculation of air flows linked to the openings required for melting wax. The movements of fumes cannot therefore be determined for and a treatment of fumes. - The treatment time suitable for any type of smoke to allow the furnace to be opened is not known and depends on multiple parameters. In the case of our study, complete treatment of the smoke is required before opening the furnace because the smoke is dispersed by the movement of opening the furnace, the tilting of which towards the rear produces a vertical and forward displacement of the smoke.

[0025] The state of scientific knowledge highlights several obstacles that needed to be overcome in order to find an appropriate technology: - A first technological barrier existed, in that the state of knowledge does not allow the characterization of a smoke treatment device because the nature and behavior of the smoke in a low-volume furnace enclosure cannot be modeled for all types of wax smoke. - A second technological barrier existed relating to the movements of fluids in the enclosure because the state of knowledge does not provide a solution for knowing the flow of recirculation of fumes in the presence of one (or more) opening(s) necessary for the recovery of the wax. - A third technological barrier existed in that the state of knowledge does not allow us to know the processing times of the different fumes to determine how long the oven should be kept closed.

[0026] It is for the purpose of providing a satisfactory solution that the present invention is intended.

[0027] [Fig-1] [Fig.l] is a schematic representation of the oven according to the invention.

[0028] Presentation of the invention: the invention relates to a device for evacuating fumes from small baking ovens intended for wax removal, without requiring evacuation outside the room where it is placed. This device is intended to be placed in a domestic electric oven. It is characterized by: - an air inlet (a) from outside the furnace into the furnace enclosure; this air inlet being placed to be received in the furnace enclosure near its floor (b), that is to say in a low position in the furnace enclosure, - a smoke outlet (b) placed high up near the enclosure vault, on the wall opposite the one receiving the air inlet, this opposite position being intended to promote the circulation of air in the furnace, - this smoke evacuation (b) receives, outside the furnace enclosure (outside the perimeter of the furnace enclosure) a pipe (c) whose surface area is at least 50 cm2, - inside this pipe (c) is placed a filter of 0.001 p (d), - inside the pipe (c), an electric suction system (e) which allows the air to circulate at a flow rate of 10 dm3 / h, - the pipe (c) is directed towards the air inlet (a), by an elbow (f) which mixes the recycled air with the fresh air and returns everything to the inside of the wax removal oven.

[0029] Thus, by this device, the fumes which are naturally (by the laws of physics) returned to the top of the enclosure, exit through the fume evacuation (b) and are treated in the pipe (c) by the filtration (d), the suction system (e) ensuring the circulation inside the pipe (c), the hot air released from the fumes is then reintroduced into the furnace enclosure.

[0030] Furthermore, note that the reintroduction of the hot air released from the fumes, through an elbow (f) which connects the hot air to the ambient outside air, makes it possible to ensure continuity of temperature inside the furnace enclosure.

[0031] Ovens having the invention have numerous advantages: - firstly, opening the oven no longer requires the user to receive the fumes, which in a conventional device remain at the top of the oven enclosure and are released when the door is opened. This arrangement contributes to improving working conditions. - secondly, the combustion air supply (via the fresh air supply from outside the furnace) is heated by the mixture permitted by the elbow (f), which improves the efficiency of the said furnace.

[0032] Glossary: (a) air inlet (b) smoke evacuation (c) pipeline (d) 0.001 p filter (e) suction system (f) elbow

Claims

Claims

1. Device for evacuating fumes from small baking ovens intended for wax removal, characterized by: - an air inlet (a) from outside the oven into the oven enclosure; this air inlet being placed to be received in the oven enclosure near its floor (b), that is to say in a low position in the oven enclosure, - a smoke outlet (b) placed high up near the enclosure vault, on the wall opposite the one receiving the air inlet, - this smoke outlet (b) receives, outside the furnace enclosure, a pipe (c) with a surface area of at least 50 cm2, - inside this pipe (c) is placed a 0.001 p filter (d), - inside the pipe (c), an electric suction system (e) which allows the air to circulate at a flow rate of 10 dm3 / h, - the pipe (c) is directed towards the air inlet (a), by an elbow (f) which mixes the recycled air with the fresh air and returns everything to the inside of the dewaxing furnace.

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