WO2001085877A1

WO2001085877A1 - Method for manufacturing an artificial log

Info

Publication number: WO2001085877A1
Application number: PCT/EP2001/005148
Authority: WO
Inventors: Roland Pierre Bouillart; Franck Olivier Bouillart
Original assignee: Roland Pierre Bouillart; Franck Olivier Bouillart
Priority date: 2000-05-05
Filing date: 2001-05-07
Publication date: 2001-11-15
Also published as: AU6391101A; LU90577B1

Abstract

A method for manufacturing artificial logs comprising the steps of: (a) providing a mixture of cellulosic material and combustible binder; (b) compressing said mixture in a mold so as to form an artificial log; and (c) removing said artificial log from said mold. The cellulosic material comprises hemicellulose. The hemicellulose includes more than 50 % in weight of C-5 compounds and less than 50 % in weight of C-6 compounds.

Description

Method for manufacturing an artificial log

Field of the invention

The present invention generally relates to a method for manufacturing an artificial log.

Background of the invention

Artificial logs, also referred to as artificial fire logs, suitable for burning in fireplaces are well known. Typically, artificial logs are made by mixing flamma- ble particles with a combustible binder to form a mixture and then molding or extruding the mixture into an elongated form that resembles a piece of natural wood. Wood particles, such as e.g. sawdust, and other cellulosic materials are readily available and are therefore used as flammable particles. Various types of inexpensive waxes, resins, plant extracts and related petroleum derived products are often used as combustible binders for the flammable particles.

A typical method for making such artificial logs includes the steps of mixing together sawdust and wax, and then passing the mixture through a screw extruder to form the mixture in an elongate shape generally resembling a natural log. The extruded product is then cut at desired lengths to provide individual logs. To ensure cohesion of such logs, binding additives are generally added to the mixture before extrusion. Such additives, which are only intended to reinforce the cohesion of the log, i.e. which do not take part in the reaction of combustion, are responsible for the emanation of unpleasant odors and smokes when the log is burnt. Compression molding is a more interesting method for making artificial logs, as the use of binding additives may be avoided. Indeed, such logs are produced by compressing together a mixture of cellulosic material and combustible binder, e.g. sawdust and paraffin wax, under relatively high pressure, to compact the mixture. A practical difficulty of compression molding is due to the friction of the mixture on the mold walls. Indeed, friction of the mixture on the mold walls causes a decrease in the intensity of the compressive forces towards the inside of the log. Thus, the density of such a log is inhomogeneous. Moreover, the coherence of conventional logs manufactured by compression is rather poor.

Object of the invention

The object of the present invention is to provide an efficient method for manufacturing artificial logs by compression. This object is achieved by a method according to claim 1.

Summary of the invention

A method for manufacturing artificial logs in accordance with the invention comprises the steps of: (a) providing a mixture of cellulosic material and combustible binder;

(b) compressing said mixture in a mold so as to form an artificial log; and

(c) removing said artificial log from said mold.

According to an important aspect of the invention, cellulosic material comprising hemicellulose is used. The hemicellulose should include more than 50% in weight of C-5 compounds and less than 50% in weight of C-6 compounds. This precise selection of the cellulosic material enables the manufacture very coherent logs by compression molding, only from cellulosic material and combustible binder, such as e.g. sawdust and paraffin wax. As a matter of fact, it has been observed that a phenomenon of percolation of the combustible binder, e.g. paraffin wax, may occur during manufacturing of the log. Furthermore, it has been observed that when, in the hemicellulose, the proportion of C- 6 compounds is greater than 50 wt.% and the proportion of C-5 compounds is less than 50 wt.% percolation cannot properly occur. By precisely selecting the cellulosic material as recommended in the method of the invention, there is obtained a mixture, which lends itself very well to compression molding, and which ensures, due to improved percolation of the combustible binder, a high cohesion of the compressed log. An artificial log manufactured in accordance with the present process may comprise 40 to 60% of cellulosic material and 40 to 60% of combustible binder.

Advantageously, the mixture provided at step (a) results from the following steps. Firstly, the combustible binder is heated to at least its melting temperature. Then, the melted combustible binder is mixed with the cellulosic binder, and the obtained mixture is rapidly cooled. These mixing conditions promote the cohesion of the mixture by capillarity, i.e. the penetration of liquid binder in the cellulosic material. Moreover, it is believed that by rapidly cooling the obtained mixture, the liquid binder fixes in the cellulosic material, and does not run out of it. Preferred combustible materials, and namely waxes, have a melting point of 69 to 78°C. Hence, the combustible binder may be heated up to a temperature between 69 and 85°C. The hot mixture shall then be rapidly cooled down to a temperature below 25°C, preferably about 20°C. The cellulosic material preferably consists of finely divided wood particles, such as e.g. wood chips, wood shaves or sawdust. The size of those finely divided wood particles may range from about 0.3 mm to about 3 mm in length. The combustible binder may be chosen from the group consisting of paraffin wax, slack wax, and vegetable oils. In fact, the preferred materials for manufac- turing artificial logs are finely divided wood particles and paraffin wax, as they permit to achieve a good imitation of natural wood logs.

In a first embodiment, the artificial log may be formed at step (b) by uniax- ial bidirectional compression. For example, a tube may be filled with the mixture provided at step (a), and axial compressive forces applied at both ends of the tube to compress the mixture in the mold. It shall be noticed that the compressive forces should preferably be applied simultaneously and substantially equally at the two opposite ends of the mold so as to obtain a cohesive log, with a homogeneous and symmetric density profile.

In a second embodiment, the artificial log is obtained by radially compress- ing the mixture in a mold having a substantially circular cross-section. For example, the mold may comprise a lower element and an upper element having inner sides of half cylindrical form. The mixture may be placed between the upper and the lower element, i.e. in contact with the inner sides, and opposite compressive forces applied to the elements to compress the mixture into a cylindrical log. It shall be appreciated that friction of the mixture on the mold walls is less problematic with radial compression than with uniaxial bidirectional compression in a tubular mold, as the log is compressed in its small dimension. Furthermore, the compressive forces are applied simultaneously and substantially equally at the two mold elements, so as to provide an essentially homogeneous density profile within the log. It will be understood that the density at the center of the log may be slightly lower than the density at the outer periphery of the log. This causes air to be drawn through the log, thereby assisting the combustion of the log. Hence, the fire behavior of such a log is improved.

When wood is used as cellulosic material, the latter may comprise cellulose, hemicellulose and lignin. The total proportion of cellulose, hemicellulose and lignin should preferably be greater than 85% in weight. Besides, the proportion of hemicellulose in the cellulosic material may range from 15 to 35% in weight. Such a precise selection of the cellulosic material permits a constant quality of the artificial logs.

Brief description of the drawings

The present invention will now be described, by way of example, with ref- erence to the accompanying drawing, in which:

Fig.1 : is a cross-sectional view of a molding apparatus for manufacturing an artificial log.

Detailed description of a preferred embodiment

The method in accordance with the invention permits the manufacture of artificial logs by compression molding, from cellulosic material and combustible binder. It shall be appreciated that, through the precise selection of the cellulosic material, artificial logs exhibiting a high cohesion can be obtained. As a matter of fact, according to the present method, the cellulosic material should comprise hemicellulose consisting of more than 50% in weight of C-5 compounds and of less than 50 % in weight of C-6 compounds. Indeed, it has been observed that by using cellulosic material having such precise proportions of C- 5 and C-6 compounds in the hemicellulose, percolation of the combustible binder can be improved. It follows that artificial logs manufactured from such cellulosic material exhibit a high cohesion.

In a preferred embodiment of the method of the invention, artificial logs are made from wood particles and paraffin wax. It is clear that wood, which contains generally from about 40 to 52% in weight of cellulose, is particularly suited for the manufacture of artificial logs that are intended to look like natural logs. Moreover, it will be understood that hemicellulose is necessarily present, as it is one of the constituents of wood. Indeed, a general composition of wood is the following (in percent of the weight of wood): cellulose 45%, lignin 20%, hemicellulose 20%, water 10% and other constituents 5%. More generally, a cellulosic material with a hemicellulose content of 15 to 35% in weight may be used in the method of the invention.

The cellulosic material to be used in this preferred embodiment of the method should be finely divided. Hence, sawdust, wood chips and shaves, or other finely divided wood particles may be used. Wood particles having sizes within the range of 0.3 mm to 3 mm in length are preferred. This means that, when observing a wood particle under an optical microscope, its largest dimension should be within the range of 0.3 mm to 3 mm.

The present method may be implemented on a production line comprising conventional devices and e.g. the molding apparatus of Fig.1. The first step (a) of the method is to prepare a mixture of finely divided wood particles and paraffin wax. In the production line, paraffin wax is heated above its melting temperature e.g. in heated, cast-metal containers. The melted wax is transferred by means of an electric pump from the containers to a large, heat-insulated tank, wherein it is maintained at a temperature ranging from 69 to 85°C by a heating cable.

Melted paraffin wax from the tank is delivered by a volumetric pump to a mixer. Finely divided wood particles, which are contained in a hopper, are also delivered to the mixer through a worm screw. The flow of material through the volumetric pump and the worm are preferably adjusted so as to obtain a mixture comprising about 60% of wood particles and about 40 % of paraffin wax. This hot mixture is collected and spread on a conveyor belt to allow a rapid cooling to about 20°C. Rapid cooling occurs by means of a refrigerating system comprising blowers arranged along the conveyor belt for blowing cool, dry air on the mixture.

The mixture is then sent to the molding apparatus 10 illustrated in Fig.1 for next step (b), in which it is compressed into a log. The molding apparatus 10 comprises an upper element 12 and a lower element 14, which are slideably mounted between two lateral walls 16 of the structure (not shown) of the apparatus 10. Each element has an inner surface 18 of half-cylindrical form for shaping the mixture into a cylindrical log, and an outer surface 20, on which compressive forces may be applied. The upper element 14 may be removed in order to fill the molding apparatus 10 with the mixture, indicated by reference sign 22 on Fig.1. When the apparatus has been filled with the mixture 20, the two elements 12 and 14 are spaced apart. Opposite compressive forces, indicated on Fig.1 by arrows, are then applied at the outer surfaces 20 of the upper 12 and lower 14 elements to compress the mixture 22. These compressive forces cause the upper 12 and lower 14 elements to move towards each other until they meet (configuration of Fig.1). Thus, the mixture 22 is compressed radially into a cylindrical log. It remains to be noticed that the molding apparatus 10 has a front and a rear wall (rear wall is indicated by reference sign 24) on the inner sides of which the ends of the log are formed. This means that logs produced by the apparatus of Fig.1 have a constant volume. It shall be appreciated that friction of the mixture 22 on the mold walls is easily overcome with radial compression, as the log is compressed in its small dimension. Hence, a very compact log may be produced. Furthermore, it shall be noted that the compressive forces are advantageously applied simultaneously and equally at both elements 12 and 14 so as to allow a homogeneous density profile within the log. At the last step (c), the log is removed from the molding apparatus 10. Obtained logs have a high cohesion as well as good mechanical and in fire behaviors.

Claims

1. A method for manufacturing artificial logs comprising the steps of:

(a) providing a mixture of cellulosic material and combustible binder;

(b) compressing said mixture in a mold so as to form an artificial log; and

(c) removing said artificial log from said mold; characterized in that said cellulosic material comprises hemicellulose, said hemicellulose including more than 50% in weight of C-5 compounds and less than 50 % in weight of C-6 compounds.

2. The method according to claim 1 , characterized in that said mixture comprises 40 to 60% of cellulosic material and 40 to 60% of combustible binder.

3. The method according to claim 1 or 2, characterized in that step (a) comprises the steps of: heating said combustible binder to at least its melting temperature; mixing said cellulosic material with melted combustible binder; and then rapidly cooling the obtained mixture.

4. The method according to claim 3, characterized in that said combustible binder is heated up to a temperature between 69 and 85°C.

5. The method according to claim 3 or 4, characterized in that said mixture is rapidly cooled below 25°C, preferably to about 20°C .

6. The method according to anyone of the preceding claims, characterized in that said cellulosic material consists of finely divided wood particles.

7. The method according to claim 6, characterized in that the size of said finely divided wood particles ranges from about 0.3 mm to about 3 mm.

8. The method according to anyone of the preceding claims, characterized in that said combustible binder is chosen from the group consisting of paraffin wax, slack wax, and vegetable oils.

9. The method according to claim 8, characterized in that said combustible binder is paraffin wax.

10. The method according to anyone of the preceding claims, characterized in that said artificial log is formed at step (b) by uniaxial bidirectional compres- sion.

11. The method according to anyone of the preceding claims, wherein said mold has a substantially circular cross section, characterized in that, at step (b), said mixture is radially compressed into said artificial log.

12. The method according to claim 10 or 11 , characterized in that compressive forces are applied simultaneously and substantially equally, so as to provide a homogeneous density profile within the log.

13. The method according to anyone of the preceding claims, characterized in that said cellulosic material comprises cellulose, hemicellulose and lignin; and in that the total proportion of cellulose, hemicellulose and lignin is greater than 85% in weight of the cellulosic material.

14. The method according to anyone of the preceding claims, characterized in that said cellulosic material is composed of about 15 to 35% of hemicellulose.