The present invention relates to a double- or multi-walled and upwardly open thermos container of a ceramic material, consisting of two or more containers which are disposed within each other and are mutually separated, but conti¬ guous at least along the edge of the upper opening.

The invention also relates to a method of producing such a thermos container and a mould for use in the performance of the method.

Double-walled or multi-walled containers are widely used as thermos containers, which may have the shape of bowls, bottles, flasks, cups or jugs, e.g. for the storage of hot or cold beverages. If the space between the container walls is approximately evacuated, the container will have a great insulation capability so that the contents may maintain the temperature for a long period of time.

Thermos containers are frequently made of glass by blowing of a glass mass softened in the heat. Such thermos con¬ tainers must have rather thin walls in order to resist strong temperature effects, e.g. _. when a boiling liquid is poured into a container at room temperature. To reduce the risk of cracking, thermos containers are generally provided with a protective jacket, e.g. of metal, which is impact and shock resistant.

There is a need for thermos containers and similar double- or multi-walled containers of ceramic materials, such as clay, stoneware clay or china clay which are fired or sintered and optionally also- glazed. Fired ceramic

containers have also great resistance to temperature fluctuations and have a relatively great strength as well, so that, normally, they can be used without any protective jacket.

It is known from the US Patent Specification 2,839,209 to mould a double-walled ceramic container directly in a plaster mould and then fire and glaze the container in the usual manner. The mould used there consists of an outer mould part with a cavity corresponding to the outer wall of the container, as well as a core introduced into the cavity. During moulding, a liquid ceramic mass is introduced into the space between the inner side of the outer mould part and the core. The plaster mould is porous and therefore absorbs water from the liquid ceramic mass, so that a layer of ceramic mass deposits on the mould inner sides, i.e. both on the core surface and on the inner side of the outer mould part. When this layer has reached a desired thickness, the still liquid part of the ceramic substance is poured out of the mould to provide a double-walled container with a cavity between the two walls.

After separation of the mould, including removal of the core, the resulting double-walled ceramic container is dried, fired and glazed in the usual manner.

This known method has limited application because it must be possible, of course, to remove the core from the container opening. Therefore, this method does not allow manufacturing of containers in the form of bottles, flasks or jars whose opening has a smaller diameter than the interior of the container.

The object of the present invention is to provide a double- or multi-walled container of any desired shape,

e.g. in the form of a bottle, flask or jar with an arbitrarily narrow neck or opening.

Ά

The thermos container of the invention is characterized 5 by the sub ect-matter defined in the characterizing portion of claim 1.

In the method of the invention, which is characterized by the features defined in the characterizing portion

10 of claim 7, comprising the use of a liquid-absorbing mould, the core consists of a first and pre-formed ceramic container which is to define the inner wall of the double- walled container. The liquid moulding mass is introduced into the space between the inner side of a liquid-absorb-

15 ing mould and the outer side of the first container introduced into the mould. The mould, constructed as stated in claim 9, absorbs liquid from the liquid moulding mass, so that a layer will deposit on the inner side of the .mould to form the outer wall of the container.

20 When this layer has reached the desired thickness, excess of liquid ceramic mass is poured out of the mould. This provides a cavity between the two walls of the container. If several layers or walls are desired, this process may be repeated by introducing the double-walled container

25 as a core, into another mould. Another layer will be formed along the mould inner side by introducing liquid moulding mass into the cavity between the inner side of this mould and the outer side of the inserted double- walled container. This results in the provision of a

30 multi-walled container with the number of layers or walls which are desired and useful in practice.

The formed double-walled or multi-walled container is removed from the mould, dried, fired and glazed. Since 35 firing and glazing are effected at a high temperature, with development of i.a. water vapours because of ceramic

reactions during the sintering process, practically any trace of air will be expelled from the space between the two container walls. During cooling, the glaze will solidify and form a gas-tight layer, so that a vacuum having a thermally insulating effect will prevail between the two or more container walls.

The mould used is preferably a mould of plaster, but, if desired, any other porous and liquid-absorbing material may be used, e.g. unglazed porous ceramic foam plastics or a fibre material, such as glass fibres, plant fibres or plastics fibres.

The first container, which is to form the inner wall of the double-walled container, may be manufactured in a known manner, such as by throwing, pressing or moulding.

Thus, the first container may be moulded separately in a liquid-absorbing ^" "mould, e.g. of plaster, without a core, by introduction of liquid ceramic mass into the mould cavity so that a layer of the desired thickness will deposit on the inner side of said cavity.

After moulding of the first container, it may be expedient to impregnate or lacquer its outer side, so that it does not absorb liquid. To this end, e.g. shellac or another lacquer may be used, or a metallic layer may be deposited. This prevents deposit of ceramic mass on the first container during moulding of the other, outer container. Instead, the first container might be moulded with thin walls. When the outer container is moulded, the wall thickness of the inner container would be increased at the same time. Deposit of moulding mass on the outer side of the inner container may be controlled by adjusting the moisture content of the

inner container wall when moulding in the second step is performed. Thus, if the first container has a high moisture content when introduced into the second mould, no or only little moulding mass will deposit on the outer side of the first container.

If the first or inner container is given a lacquer finish on its exterior, a zone should be kept free at the opening of the container, so that the outer container can be moulded together with the inner container at that zone. If an organic resin is used for the lacquer finish, it will burn away during the firing and/or glazing of the container. In the event that the outer side of the inner container and optionally also the inner side of the outer container are provided with a heat-reflecting metallic coating, improved thermal insulation capability is obtained.

The ceramic moulding mass may be clay or stoneware clay to which sufficient water has been added to impart a liquid consistency to the mixture. Instead, an aqueous china clay solution may be used. In that case, finished containers of porcelain are obtained.

An expedient embodiment of the invention will be explained more fully below with reference to the drawing, in which

fig. 1 is a section through a mould for the making of a first ceramic container, and

fig. 2 is a cross-section of a mould for the making of another ceramic container around the first container.

The mould shown in fig. 1 consists of two mould parts 1 and 2 of a liquid-absorbing material, such as plaster, and has upwardly an opening in which a plug 4 is inserted

The plug has a through bore 5 and a guide face 9 mating with a guide face 8 in the opening of the mould. The underside 14 of the plug 4 and the inner side 13 of the through bore 5 are given a shellak finish to avoid deposits of ceramic mass on these faces. The mould is filled with a liquid ceramic moulding mass, such as an aqueous suspension of clay or porcelain. The porous mould absorbs liquid from the liquid ceramic moulding mass, so that a layer 7 of the ceramic mass deposits along the inner side 6, 11, 12 of the mould. When this layer has reached a desired thickness, excess of liquid moulding mass is poured out.

The mould 1, 2 is separated, and the formed first con- tainer 7 with the plug 4 in the container opening is removed. The outer side 16 of the container 7 is given a shellak finish, apart from a .zone 30 along the upper edge of the container. The treated container 7 with the plug 4 in the opening is intTpduced into another mould 21, 22 likewise of a liquid-absorbing material. The mould 21, 22 is inverted, and the mould is filled with liquid ceramic moulding mass through an opening 23 in the bottom of the mould. Owing to absorption of liquid in the mould, a layer 27 of ceramic mass deposits on the inner side 26 of the mould, whereas no layer deposits on the lacquered surface 16 of the first con¬ tainer 7, apart from the unlacquered zone 30.

When a suitable layer thickness 27 has deposited on the inner side of the mould 21, 22, most of the still liquid moulding mass is poured out. A porous plug is now inserted into the opening 23, and the mould is turned. The liquid moulding mass residue will settle on the bottom of the space 20, so that a layer of moulding mass deposits opposite the plug-closed opening 23 to close the bottom completely. The mould 21, 22 is separated,

and the formed double-walled container is dried. The container is fired in a furnace at normal sintering temperature.

After cooling, the container is glazed on the inside and the outside and fired again in a furnace. During the last firing, the glaze closes all pores. Prior to this, most of the volatile substances and gases have been expelled from the space 20 between the two container walls, and accordingly, a vacuum prevails in this space after cooling.