A heat-insulating body such as a heat-insulating slab is made whose insulating and heat-absorbing material includes a fine powder, in particular a silica aerogel which is pressed to form the body. To carry out the pressing operation a sack-like sheath is required but between the sheath and the insulating material a separating agent is provided which results in the fact that the surface of the insulating material does not intimately engage with the sheath which is for example of glass fibre fabric, the sheath being movable with respect to the insulating material after the pressing operation. Apart from the fact that the sheath can be removed for any cases where it would be a cause of disturbance, additionally the insulating body provides improved bending properties and even when made with a high pressing rate has a homogeneous structure. To make the insulating body the separating agent may be applied to the inner surfaces of the sheath, the particulate insulating material then being introduced and the sheath sealed, whereafter pressure is applied.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to a heat-insulating body having a particulate 
insulating material and a sheath of a sheet material, which is made by 
filling the sheath with the insulating material and subsequently shaping 
the sheath filled with the insulating material and compacing the 
insulating material, by applying excess pressure to the outside of the 
filled sheath. 
2. Description of the Prior Art 
DE-PS No. 1,954,992 discloses heat-insulating slabs which include a core of 
a mixture of finely dispersed materials, for example expanded silica, 
opacifying agent and mineral fibres, and an outer sheath of glass fibre 
fabric or the like. To make such slabs, generally the mixture of the 
finely dispersed materials is introduced into a sheath of glass fibre 
fabric or the like. Thereafter, the sheath is sewn up and pressed in a 
pressing operating to form a slab whose size depends on the dimensions of 
the sheath. 
According to DE-PS No. 2,036,124 the pressing operation is carried out so 
that an intimate as possible interengaging of the finely dispersed 
materials together and with the surface or pores of the relatively rough 
sack material takes place so that upon completion of the pressing 
operation a sandwich is usually obtained. This sandwich includes the core 
of finely dispersed materials and the sheath. If the surface of the sheath 
is very rough or porous, without taking special steps, however, it is 
inevitable, or intended according to DE-PS No. 2,036,124, that the core 
material penetrates at least partially into the pores and thus anchors the 
core to the surface of the sheath. Such slabs have a relatively high 
bending stiffness and when subjected to bending stress break practically 
without appreciable deformation. Such insulating slabs are thus unable to 
adapt themselves to the irregularities of the object to be insulated, i.e. 
it is not readily possible to apply such slabs to surfaces curved in one 
or two dimensions. 
A further disadvantage resides in the fact that the pressing operation for 
making such insulating slabs must take place relatively slowly. When the 
pressing operation is carried out relatively rapidly the cores of 
insulating slabs made in this manner have a slate-like inhomogeneous 
structure so that due to the resulting irregularities, the coefficient of 
the thermal conductivity of these slabs is impaired compared with a 
homogeneously pressed slab. In addition, insulating slabs made by such a 
method tend after pressing, due to the slate-like structure, to spring 
back to a relatively pronounced degree so that the thickness differences 
from slab to slab are relatively great. 
SUMMARY OF THE INVENTION 
The present invention is based on the problem of providing a 
heat-insulating body which in spite of a relatively rapid pressing 
operation has an homogeneous structure, i.e. does not form a slate-like 
structure, is not bonded to the sheath, i.e. does not have a sandwich 
structure, and has a relatively high bending deformability. 
If a separating agent is provided between the sheath material and the 
insulating material and an adhering of the insulating material to the 
sheath during the pressing operation is thus reliably prevented, the 
surprising result is that the body thus made apart from the separation of 
sheath and core exhibits no slate-like core structure and has excellent 
bending properties. If the body made according to the invention, which is 
generally in the form of a slab, is subjected to a bending treatment it 
can be bent about 15 times better than the slab made according to DE-PS 
No. 2,036,124 before breakage occurs. 
Because of the structure of the heat-insulating body produced according to 
the invention it is possible to bend such a slab about a round body having 
a ratio R/D=15 and bend it back again without the core exhibiting after 
such a bending operation cracks or other disintegration phenomena wherein 
R is the radius of the circular body enclosed by the slab and D the slab 
thickness or thickness of the body. Corresponding to this flexibility or 
deformability the body made according to the invention may also be 
referred to as an enclosed plastically deformable body. 
This extremely desirable bendability and the homogeneity of the core 
portion may be attributed to the fact that the separating agent disposed 
between the sheath and the core material permits completely free 
movability of the core insulating material during the pressing operation. 
The separating agent prevents in particular penetration of the insulating 
material into the fibres or between the cavities of the sheath formed 
between the fibres and consequently also the bonding of the insulating 
material boundary layer to the sheath. During the pressing operation the 
friction produced between the insulating material boundary surface and the 
sheath is almost completely cancelled by the separating agent so that no 
shearing stresses of any kind can build up within the core material. The 
core material can thus be freely built up during the pressing operation 
within the sheath to form a homogeneous core which exhibits no slate-like 
structure at all and no inhomogeneities due to shearing stresses. 
The sheath may be made from various materials, for example glass fibres, 
quartz fibres, plastic fibres, natural fibres, such as cotton or silk, and 
from sheet materials such as paper or perforated plastic sheet, or fabrics 
or cloth, maintaining the permeability accordingly. Such materials are 
chosen in accordance with the pressure used, the operating temperature and 
the desired flexibility. 
As for the particulate insulating material, powder or fibre particles 
and/or mixtures thereof may be used, and it is pointed out that the basic 
material itself used need not be a good thermal insulator. Advantageously, 
aluminium silicate fibres, quartz or glass fibres or further ceramic 
fibres, pulverulent aluminium or mixtures of flue ash with expanded 
silica, finely divided aluminium or chromium oxide and silica aerogel, 
possibly containing an opacifying agent such as titanium dioxide 
(ilmenite) may be used. The size of these particles may vary in a wide 
range; it generally lies however in a range from 10 A to 2 mm. 
As for the separating agent, materials may be used which reduce the 
adhesive forces and friction between the two adjoining surfaces so that 
adhesion is prevented. They should be chemically inert with respect to the 
materials to be processed, only slightly soluble therein and on the whole 
have a low volatility. Usually, such separating agents are used in the 
form of dispersions (emulsions or suspensions), pastes or powders. The 
separating agents may be applied by being powdered on, sprayed on, brushed 
or dipped. As separating agents organic or inorganic substances and/or 
mixtures thereof may be used. 
Specific examples for separating agents on an organic basis are silicones, 
which are used either in solid form (in the form of the powder) or in the 
form of mixtures with water, oil, fats and the like; paraffin hydrocarbons 
such as waxes, hard waxes, paraffin wax, bee wax, candelilla wax, whereby 
the paraffin hydrocarbons may be of a natural or synthetic nature and 
possibly substituted with functional groups; fatty acids, such as stearic 
acid or palmitic acid, or their metal salts for example the calcium, lead, 
magnesium, aluminium or zinc salts; fats of an animal or vegetable origin, 
such as tallow, wool fat, palm oil; polymers, for example polyvinyl 
alcohol, polyamide and polyethylene, polymers of the fluorohydrocarbons, 
such as polytetrafluoroethylene; mineral oils, such as fatty oils, 
synthetic oils or their mixtures with fatty acids and/or chemically active 
substances, such as soaps. 
Specific examples for inorganic lubricants are pulverulent talcum, mica, 
water-repellent pyrogenic silica, carbon black, graphite, prepared chalk, 
lime, clay, molybdenum sulphide and zinc sulphide. They may also be used 
in suspensions in water or mineral oil. 
When selecting the solvent it must however be ensured that the structure of 
the core made is not impaired. Preferably, water-repellent pyrogenic 
silica is used in powder form, particularly when the core constitutes a 
mixture of pyrogenic silica, opacifying agent and fibres. To obtain an 
adequate separating effect generally 0.1-10 g separating agent is applied 
to the inner surface of the sheath in powder form.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The body illustrated in FIG. 1 includes a sheath or envelope 1 which is 
defined at its side edges by seams 2. Prior to being sewn up a layer 3 of 
separating agent is applied to the inner surfaces of the sheath 1, for 
which a glass fibre fabric is generally used. If as core mixture pyrogenic 
silica, an opacifying agent and glass fibre components are used, the glass 
fibre fabric is powdered with 0.2 g water-repellent pyrogenic silica per 
m.sup.2 fabric area. Thereafter the sheath is sewn up along three edges. 
The material 4 to be compacted is introduced into the resulting sack. 
Thereafter the last edge of the sheath 1 is sewn up . The particulate 
material 4 in the sheath 1 is subjected to a mechanical pressure load; the 
pressure exerted can vary in wide limits. Generally, however, it is 
between 0.07 and 21 kg/cm.sup.2 or more, taking account of the strength of 
the fabric. 
A slab made by such a treatment with addition of separating agent includes 
a core which is completely separate from the sheath material because both 
parts can undergo deformation independently of each other under the 
pressure. Independently of the pressing rate, the core of the slab itself 
has a homogeneous structure which is free from slate-like irregularities. 
In a comparative test two slabs were subjected to a bending strength test, 
one slab having been made by the method of the prior art and the other 
slab by the method according to the invention. The samples each had 
dimensions of 680.times.440 mm and were placed on two supports with a 
support spacing of 600 mm. Thereafter, a ram was applied to the center to 
subject the sample to a continuous shock-free load. Per minute the bending 
was increased continuously by one tenth of the slab thickness. At the same 
time a graph was plotted which is shown in simplified form in FIG. 2, the 
bending being plotted against the pressure exerted. From such a diagram 
the bending behaviour and the maximum breakage load can be determined in 
dependence upon the cross-section. 
It is apparent from the diagram according to FIG. 2 that the sample made 
without separating agent (curve 5) broke after bending only 2 mm under a 
load of 40 N whilst the sample made with separating agent according to the 
invention (curve 6) did not break even after bending of 37 mm with a 
pressure of 35 N. Thus, whereas the slab made by the known method breaks 
almost immediately under load the slab according to the invention can be 
loaded in a wide range without breakage. 
Similar results can be obtained if instead of water-repellent pyrogenic 
silica 5-10 g talcum or 1-2 g magnesium stearate per square meter of 
fabric area is used. Equally satisfactory results can be obtained by 
spraying the fabric surface with a polytetrafluoro ethylene spray. 
FIG. 3 shows the boiler of a tank car in cross-section. This boiler is 
insulated with the heat-insulating body according to the invention. The 
boiler 7 is enclosed by several insulating slabs 8 which can easily adapt 
themselves to the curvature of the boiler. The insulating layer consisting 
of the slabs 8 is enclosed and held by the jacket and an annular member, 
denoted as a whole by 9. The heat-insulating slabs according to the 
invention are also disposed at the rounded head part of the boiler, to the 
curvature of which they also adapt themselves without breakage. The boiler 
itself rests on the underframe 10. 
Obviously, numerous modifications and variations of the present invention 
are possible in light of the above teachings. It is therefore to be 
understood that within the scope of the appended claims, the invention may 
be practiced otherwise than as specifically described herein.