Abstract: The invention relates to the formation of a protective skin on blocks of microporous thermal insulation material. Such material is difficult to protect because the securement of a protective layer by some form of adhesive securement provides only a relatively loose bond. According to the invention, a laser beam is used to fuse a surface layer of particles in the material to form a protective skin. The beam may be passed over an otherwise "raw" edge of a block of material, or used also to cut the block from a workpiece while simultaneously forming the skin. This enables the cutting of accurate shapes either by manual or automatic control of the passage of the beam through the workpiece, the latter much facilitating mass production of relatively complicated shapes.

Abstract: The invention relates to electric heater units for "smooth top" cookers which employ two or more heater elements in the same unit. It is directed particularly at the problem of monitoring the temperature of the unit and/or the "smooth top" thereover to protect against overheating. It is known to use a thermal cut-out device extending over the heater unit where a single element is used, but design problems develop when two or more elements are employed in the same unit, of which at least one element is independently energizable. According to the invention an elongate thermal cut-out device (10) extends across said one element (10) but is thermally isolated from the other element or elements. Thus, the device operates only in response to the one element.

Abstract: A radiant heater for use in "smooth top" cookers of the type in which a smooth top normally of glass ceramic overlays one or more generally circular electric heater elements supported on a layer of thermal and electrical insulating material such that the element is spaced from the top.The radiant heater comprises at least two heater elements (10 and 12) supported on a base of electrical and thermal insulating material (4) at least one of which elements is energizable independently; and a peripheral wall (8) of thermal insulating material surrounding the elements.The radiant heater of the invention is used in "smooth top" cookers and is covered by a top which is transparent and substantially non-absorptive to radiant cooking heat so that only the areas of the top which are exposed to the element will be heated. Preferably, the utensil being heated should have a base equal to the heated or exposed area of the top for maximum efficiency.

Abstract: The invention relates to the shaping of coils in the form of helically wound bare wires, particularly for use in "smooth top" cookers. In so-called "smooth top" cookers an unprotected helically coiled wire is secured in an electrically and thermally insulative base to transmit heat primarily by radiation through a smooth top, normally of glass ceramic. The coils used in such cookers are normally very springy and require careful securement if they are not to free themselves during the life of the cooker. According to the present invention, the stresses which cause this springy resilience can be relieved by holding a coil in a groove of the desired configuration and heating it, normally to the annealing temperature of the material of the coil. The subsequently cooled coil will then hold its shape and not tend to straighten and can be more easily held in place in the cooker.

Abstract: Described herein is an electrical heating unit for smooth top cookers. The unit comprises a heating element in the form of a spiral coil of bare wire which has then been helically rolled together with a strip of flexible thermal and electrical insulation such as a ceramic paper around a central core. The resulting rolled structure is some-what analogous to a "Swiss roll". This structure rests on and is supported on a base layer of thermal and electrical insulation which is desirably dish-shaped and contained an outer metal pan for earthing and mechanical protection. The rolled structure is retained in its configuration and held against the base layer by a number of spoke-like members of heat resistant and electrically insulating material across the top of the element.

Abstract: A material having good thermal insulation properties can be made from an intimate mixture of a microporous silica aerogel, a ceramic fibre material and optionally an opacifier. According to the invention alumina is added to those mixtures, e.g. in the form of alumina particles or alumina fibres constituting all or part of the ceramic fibre material. The resulting materials have a reduced tendency to sinter and consequently shrink at high temperatures.

Abstract: Shaped insulation material is formed by passing a porous envelope containing insulation material such as that comprising silica aerogel and an opacifier through a series of rolls followed by making the shape so formed rigid.

Abstract: A method of making a thermal insulating panel in which particles of microporous insulating material are put into a bag consisting of porous sheet material which is then subject to pressure to cause the particles to bond together and consolidate the insulating material and to create a tension strain in the material of the bag.