Heat insulating moulded body and process for producing the same

Details Heat insulating moulded body and process for producing the same Heat insulating moulded body and process for producing the same

1999-04-20

2001-01-30

Paik, Sang (Department: 3742)

Electric heating

Heating devices

Combined with container, enclosure, or support for material...

C501S087000, C501S094000

Reexamination Certificate

active

06180927

ABSTRACT:

TECHNICAL FIELD
The invention relates to a thermally insulating molded body comprising inorganic material and inorganic reinforcing fibers and to a process for producing the molded bodies. In particular, the invention relates to a thermally insulating molded body which is suitable as a spacer in radiative heating elements for cooking appliances and ovens.
DESCRIPTION OF THE RELATED ART
Such a spacer has to meet particularly demanding requirements:
it has to have a high degree of mechanical stability while still being sufficiently elastic to survive automated installation in a radiative heating element without damage and to be able to be permanently pressed against the underside of a ceramic hob;
it must give off no substances which are hazardous to health, for example pieces of fibers which can enter the lungs;
it must not be a source of substances which impair the function or life of articles such as heating bands or heating spirals when these articles come into contact with these substances;
it must provide particularly efficient thermal insulation so that the heat produced by the heating element can be utilized for cooking or baking without substantial losses;
it has to be an electrical insulator;
it must retain its mechanical and physical properties over a wide temperature range.
EP-204 185 A1 describes a radiative heating element comprising a molded body referred to as a pot rim which is also used as spacer. The pot rim consists essentially of particles of expanded mica, e.g. vermiculite, which have been pressed together with a binder. This material meets the criterion of sufficient mechanical stability. Its thermal insulation properties no longer meet the minimum requirements which apply today.
SUMMARY OF THE INVENTION
EP-560 479 B1 describes an annular, thermally insulating spacer and its use as spacer. The molded body comprises an intimate mixture of microporous material and certain reinforcing glass fibers such as E-glass fibers. This molded body meets, in particular, the requirements in respect of thermal insulation. However, its mechanical stability is significantly less than that of a comparable molded body made of vermiculite pressed together with binder. In addition, experiments on the glass fiber-reinforced molded body have indicated that its use reduces the life of heating bands or heating spirals used in radiative heating elements. It has been found that the sometimes very thin heating bands or heating spirals corrode and burn through relatively quickly at places at which material abraded from the molded body has deposited. Such abraded material cannot be avoided, since it is formed, for example, when the molded body is installed in the radiative heating element, during transport of the radiative heating element and on drilling holes in the thermal insulation of the radiative heating element.
The invention relates to a molded body which is particularly suitable with regard to the requirements mentioned at the outset.
The invention provides a thermally insulating molded body comprising inorganic material and inorganic reinforcing fibers, which is characterized by the following, weight-based composition:
a) 30-70% of expanded vermiculite
b) 15-40% of inorganic binders
c) 0-20% of infrared opacifier
d) 15-50% of microporous material
e) 0.5-8% of reinforcing fibers containing not more than 2% of B
2
O
3
and not more than 2% of alkali metal oxides, based on the weight of the reinforcing fibers.


REFERENCES:
patent: 4713527 (1987-12-01), Kicherer et al.
patent: 5302444 (1994-04-01), Jackson et al.
patent: 5439624 (1995-08-01), Anderson et al.
patent: 5498854 (1996-03-01), McWilliams
patent: 5517002 (1996-05-01), Higgins
patent: 5532458 (1996-07-01), Kratel et al.
patent: 0 560 479 B1 (1993-02-01), None
patent: 0 204 185 (1996-05-01), None

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