GB1584989A - Thermal expansion properties of structural components - Google Patents

Description

(54) MODIFYING THE THERMAL EXPANSION PROPERTIES OF STRUCTURAL COMPONENTS (71) We, MORTOREN-UND TURBINEN-UNION MUNCHEN GmbH, a joint stock company organised under the laws of Germany, of Postfach 50 06 40, 8000 Munchen 50, Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a method of adapting a structural component such as an engine casing to avoid or reduce thermal stresses therein caused by differential expansion of the component and a body associated therewith.

It is generally possible to produce a structural component which has the desired properties by choosing a suitable material for the component, but in practice the choice is often restricted by other factors such as the permissible stress or temperature.

For example, structural components of precision gearing of engines are subjected to high temperature differences. The gear case is preferably a light metal casting for reasons of weight but other components such as the bearing, for example, must be made of steel.

A system of this kind undergoes differential thermal expansion which causes changes in important dimensions. Another disadvantage is that the metal casing, though suitably light in weight and cheap to manufacture, has poor dimensional stability due to its low modulus of elasticity.

Composite fibre materials are known which have a high modulus of elasticity achieved by a suitable orientation of the fibres in the material and also a low coefficient of thermal expansion.

Structural components can also be moulded from such composite fibre material.

It is known that composite fibre materials which contain long fibres have a high modulus of elasticity in the direction of the fibres as well as low coefficients of thermal expansion. However, components with highly complex contours can only be manufactured from moulding materials which are mixed with short fibres, and these materials, as in the previous case, have a low modulus of elasticity and high coefficient of expansion due to the matrix material.

It is an object of the present invention to provide an economical process for the manufacture of structural components which have the desired modulus of elasticity and the optimum coefficient of thermal expansion for their particular structure and which are capable of withstanding all-round, and in particular very high stresses.

According to the invention, we propose affixing to at least a portion of the surface of the component, a plurality of superimposed layers of a fibre material, which may take the form of composite fibre sheets or strips or loose fibres, the number of layers and the relative orientation of the fibres being selected to produce in the said portion or portions of the component a desired coefficient of expansion matched to the coefficient of thermal expansion of the body.

The desired properties may be achieved by suitable selection and orientation of the fibres applied to the body. Suitable high tensile fibre materials are carbon and glass but carbon fibres are preferred because of their low coefficient of expansion.

The choice of material for the manufacture of severely stressed structural components thus acquires degrees of freedom which make it possible to produce very lightweight and economical structures whose properties can be adapted to the given requirements.

The sheets of composite material used in this process need not have any particular contours but are simply applied in a suitable size to the structural components which require to be reinforced. It has thereby become possible to use high strength composite materials containing long fibres, which, when used in combination with the basic material of the component which may be considerably less rigid, result in a structure which has a high and, if desired, directional rigidity, whereby it becomes possible to produce apparatus whose high precision must be maintained during operation in spite of mechanical and thermal stresses.

If the component is produced by moulding, the long fibres, suitably orientated, may be embedded in the moulding material while it is still soft as it is introduced into the mould.

Loose fibres may also be laminated to the surface of the main body by means of a suitable synthetic resin.

Sheets or strips of composite fibre material may also be glued or cemented to the component, and the fibres may be orientated in the direction of the stress to which the body will be subjected or in the direction in which expansion is to be adjusted.

If the structural component is to be subjected to multi-dimensional stresses, several layers of composite sheets or strips containing suitably orientated fibres or loose fibres are applied to the component.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings of which: Figures 1 and 2 are a cross-section and a plan view, respectively, of a portion of a casing 13 of precision gearing, which casing supports two bearings at 11 and 12. The casing 13 consists of a main body 15 made of a thin light metal, e.g. a magnesium casting, or of GFK (glass fibre reinforced plastics) which has the necessary contours for connecting it and fixing it in position. These materials, used on their own, have only a low modulus of elasticity and, compared with the materials conventionally used for gear wheels, a relatively high coefficient of thermal expansion, so that when such a casing is used, severe warping of the casing is liable to occur, and hence one-sided stress on the gear wheels, and secondly, the distance A would undergo more change on heating than is suitable for gear wheels made of steel.

To prevent this, sheets of composite fibre material 20, 21 are laminated to the main body 15 in the areas which are subject to stress. The fibres in the individual sheets are arranged to intersect and lie in the direction in which a certain rigidity and/or optimum thermal expansion is required to be obtained.

The desired properties can be obtained by the choice of fibres and the direction in which the fibres are applied to the main body.

By constructing casings in this way, their thermal expansion can be adapted to that of the other parts of the gearing. which are generally made of steel. This results in a reduced backlash and consequently also a reduction in the vibration and noise and in the stress on the bearings and gear teeth.

WHAT WE CLAIM IS: 1. A method of adapting a structural component to avoid or reduce thermal stresses therein caused by differential expansion or contraction of the component and a body associated therewith, comprising affixing to at least a portion of the surface of the component a plurality of superimposed layers of a fibre material, the number of layers and the relative orientation of the fibres being selected to produce in the said portion or portions of the component a desired coefficient of expansion matched to the coefficient of thermal expansion of the body.

2. A method according to claim 1, wherein the component is produced by moulding and in that suitably orientated long fibres are embedded in the moulding material while it is still soft and as it is introduced into the mould.

3. A method according to claim 1, wherein loose, long fibres are laminated to the component by means of a synthetic resin.

4. A method according to claim 1, wherein fibre material is glued or cemented to the component and arranged such that the fibres are orientated in the direction of stress to which the structural part is to be subjected or in the direction in which the expansion is required to be adjusted.

5. A method according to any one of claims 1 to 4, wherein several layers of fibre material containing suitably orientated fibres are laminated or glued to the component.

6. A method of manufacturing a structural component substantially as hereinbefore described with reference to the accompanying drawings.

7. A structural component when produced by the method according to any one of the preceding claims 1 to 6.

8. A structural component constructed and arranged substantially as herein before described with reference to and as illustrated in the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. combination with the basic material of the component which may be considerably less rigid, result in a structure which has a high and, if desired, directional rigidity, whereby it becomes possible to produce apparatus whose high precision must be maintained during operation in spite of mechanical and thermal stresses. If the component is produced by moulding, the long fibres, suitably orientated, may be embedded in the moulding material while it is still soft as it is introduced into the mould. Loose fibres may also be laminated to the surface of the main body by means of a suitable synthetic resin. Sheets or strips of composite fibre material may also be glued or cemented to the component, and the fibres may be orientated in the direction of the stress to which the body will be subjected or in the direction in which expansion is to be adjusted. If the structural component is to be subjected to multi-dimensional stresses, several layers of composite sheets or strips containing suitably orientated fibres or loose fibres are applied to the component. An embodiment of the invention will now be described by way of example with reference to the accompanying drawings of which: Figures 1 and 2 are a cross-section and a plan view, respectively, of a portion of a casing 13 of precision gearing, which casing supports two bearings at 11 and 12. The casing 13 consists of a main body 15 made of a thin light metal, e.g. a magnesium casting, or of GFK (glass fibre reinforced plastics) which has the necessary contours for connecting it and fixing it in position. These materials, used on their own, have only a low modulus of elasticity and, compared with the materials conventionally used for gear wheels, a relatively high coefficient of thermal expansion, so that when such a casing is used, severe warping of the casing is liable to occur, and hence one-sided stress on the gear wheels, and secondly, the distance A would undergo more change on heating than is suitable for gear wheels made of steel. To prevent this, sheets of composite fibre material 20, 21 are laminated to the main body 15 in the areas which are subject to stress. The fibres in the individual sheets are arranged to intersect and lie in the direction in which a certain rigidity and/or optimum thermal expansion is required to be obtained. The desired properties can be obtained by the choice of fibres and the direction in which the fibres are applied to the main body. By constructing casings in this way, their thermal expansion can be adapted to that of the other parts of the gearing. which are generally made of steel. This results in a reduced backlash and consequently also a reduction in the vibration and noise and in the stress on the bearings and gear teeth. WHAT WE CLAIM IS:

1. A method of adapting a structural component to avoid or reduce thermal stresses therein caused by differential expansion or contraction of the component and a body associated therewith, comprising affixing to at least a portion of the surface of the component a plurality of superimposed layers of a fibre material, the number of layers and the relative orientation of the fibres being selected to produce in the said portion or portions of the component a desired coefficient of expansion matched to the coefficient of thermal expansion of the body.

2. A method according to claim 1, wherein the component is produced by moulding and in that suitably orientated long fibres are embedded in the moulding material while it is still soft and as it is introduced into the mould.

3. A method according to claim 1, wherein loose, long fibres are laminated to the component by means of a synthetic resin.

4. A method according to claim 1, wherein fibre material is glued or cemented to the component and arranged such that the fibres are orientated in the direction of stress to which the structural part is to be subjected or in the direction in which the expansion is required to be adjusted.

5. A method according to any one of claims 1 to 4, wherein several layers of fibre material containing suitably orientated fibres are laminated or glued to the component.

6. A method of manufacturing a structural component substantially as hereinbefore described with reference to the accompanying drawings.

7. A structural component when produced by the method according to any one of the preceding claims 1 to 6.

8. A structural component constructed and arranged substantially as herein before described with reference to and as illustrated in the accompanying drawings.