Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B5/00—Optical elements other than lenses
  • G02B5/08—Mirrors

Definitions

• the present invention refers to a mirror blank, a method as well as means for the production thereof .
• the mirror blanks according to the invention may be utilized for producing mirrors of optical quality, by which is meant that what is dealt with is a precision mirror the form correctness of which is better than about 0,001 mm.
• the mirror blanks according to the invention may be utilized also in other reflective systems, such as for example sun mirrors for winning sun energy, mirrors for radar purposes etc.
• the present invention represents a further development of ray earlier invention, as the shell forming step and large parts of the shell mould may be omitted without appreciably impairing the dimensional stability of the finished mirror.
• the present invention permits the production of a particularly light mirror blank with a porous support structure which adheres to the front glass of the mirror to be and which has a surface layer which has a higher density and less porosity than the rest of the support structure and which thereby also has a higher mechanical strength.
• the surface layer appears smooth but is to a certain degree porous.
• the finished mirror lends itself particularly for use in environments where it is not subjected, for example, to moisture or large mechanical strains but where the requirement of low weightis set high.
• the foamed surfaceof the support structure has lower strength than a homogeneous glass surface.
• Figure 1 shows a cross-sectional view of a mould which is used in the manufacture of a mirror blank according to the present invention with a flat front glass.
• Figure 2 shows a cross-sectional view of a mirror blank produced in the mould according to Figure 1
• Figure 3 shows a cross-sectional view of a mould for the production of a mirror blank according to the present invention with a concave front glass.
• Figure 1 there is shown in cross-section a mould which includes two mould parts 1, 2 of porous graphite or any other similar temperature resistant material, for example a ceramic material.
• a circular recess 3 is made in the upper mould part 1 .
• the circular recess is limited by a bottom surface 4 and a peripheral surface 5 inclined in relation to the bottom surface.
• a countersink 6 of circular ring-shape surrounds the peripheral surface 5.
• the countersink 6 is intended to receive a circular glass plate 7 which is to form the front glass of the finished mirror.
• the depth of the circular ring-shaped countersink 6 corresponds to the thickness of the plate 7.
• the lower mould part 2 has a forming surface 8 which when the mould parts 1 and 2 are placed against each other supports the plate 7 everywhere.
• a batch 12 of a composition of a powder of a normally solid material which is mouldable when heated and an expanding agent is placed in the recess 3 and lies on the top surface of the plate 7.
• the batch 12 is first laid on the bottom surface 4 of the mould part 1 which at that time occupies a reversed position in relation to that shown in Figure 1, whereupon the plate 7 is laid in the countersink 6.
• the mould part 2 is placed over the whole assembly and the fixing members 9 and 10 are tightened whereupon the entire mould is turned to occupy the orientation shown in Figure 1 with which it is introduced into an oven where the whole assembly is heated to a high temperature such that the composition swells up and completely fills the space 3 and fuses to the inner surface of the plate 7.
• the expanding agent produces an expansion pressure which causes the surface layer of the swollen structure, i.e. the layer next to the bottom surface 4 and the peripheral surface 5 , to be compressed.
• the heat treatment temperature and time are dependant on the material of the composition and of the plate and by experiments the time and temperature are determined which are required for the surface layer to form.
• the heat treatment is to be carried to the softening temperature of the powder composition and it is obvious that the plate must be of a material which stands this temperat ure.
• the powder of the composition is a powder of window glass or the like and when the expanding agent contains a lithium compound the last entioned compound lowers the softening temperature of the entire powder composition so that it becomes lower than that of window glass powder alone and of the window glass plate.
• the whole assembly is subjected to a controlled cooling. After the cooling being terminated the fixing members and the mirror blank are removed from the mould.
• Figure 2 shows the mirror blank in cross-section after its removal from the mould in Figure 1.
• the mirror blank may, if desired, be trimmed along the dot and dash line 13.
• the structure 14 fused on to the front glass is porous and imparts the desirable dimensional stability to the mirror.
• the surface layer 15 of the porous structure 14 is smooth and may be compared to a skin or a film.
• the material of the plate 7 and the material of the composition which is solid in normal condition but ouldable when heated are chosen so that the coefficients of expansion of the materi- ials are adapted to each other. Normally, the materials are chosen so that the coefficients of expansion are as like as possible.
• the material of the plate is preferably of glass but ceramics and plastics may also be conceivable. Equivalent conditions hold for the material of the composition. If the material of the plate is window glass the material of the composition also preferably is window glass and as expanding agent 0-2 percent by weight (counted on the glass powder) of viscosity reducing Li 2 CO 3 and 2-4 percents by weight (counted on the glass powder) of CaCO 3 are used. If borosilicate glass is used for the plate and the powder composition other expanding agents than those mentioned are used.
• Figure 3 shows a mould which is suitable for the production of concave mirrors.
• the top mould part 1 is built in the same way as the corresponding mould part in Figure 1 while the bottom mould part 2 has a convex forming surface 8 which is complementary to the shape of the desired concave mirror.
• the concave mirror blanks it is proceeded in the same way as has been described above in connection with Figure 1. If the curvature of the desired concave mirror blank is great the plate must be preformed which may take place by well-knovm glass modelling technique.
• the mould is made of the same material .as used in the mould according to Figure 1.
• the surface of the mirror may be of convex or other non-spherical form.
• the mirror blank may also be provided with through holes, for example for the suspension of the mirror or for other optical purposes.
• the hole or holes are formed by the forcing surface having an upright pillar in the form, for exar.ple, of a tube on to .which the preformed front glass is threaded.
• the trimmed mirror blank is then provided with a re lectant layer on its front surface.
• An alternative procedure is first to form the support structure only, for example in a graphite mould, and then, by means of a glass with a low melting ter.perature , for example sealing glass or lead glass, to fix the plate which is to be the reflecting surface of the mirror by fusing. If found desirable a back may be fixed by fusing at the same time to increase the mechanical strength of the blank.
• a glass with a low melting ter.perature for example sealing glass or lead glass

Landscapes

• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Optical Elements Other Than Lenses (AREA)
• Glass Compositions (AREA)
• Manufacture Of Porous Articles, And Recovery And Treatment Of Waste Products (AREA)

Applications Claiming Priority (2)

Publications (1)

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ID=20342058

Family Applications (1)

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Family Cites Families (5)

• 1980
  • 1980-10-22 SE SE8007421A patent/SE425440B/sv unknown
• 1981
  • 1981-10-21 WO PCT/SE1981/000313 patent/WO1982001422A1/en not_active Ceased
  • 1981-10-21 JP JP56503358A patent/JPS57502019A/ja active Pending
  • 1981-10-21 EP EP81902947A patent/EP0071606A1/de not_active Withdrawn

Non-Patent Citations (1)

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