FR2494171A1 - METHOD FOR MOLDING ARTICLES OF PLASTIC MATERIAL HAVING A LARGE SURFACE - Google Patents

Abstract

THE INVENTION RELATES TO A METHOD OF MANUFACTURING THE MOLDING OF LARGE SURFACE ARTICLES LIKELY TO BE USED IN OPTICS. THE DEVICE USED INCLUDES A MALE SHAPE WHOSE SURFACE CONDITION IS RELATIVELY COARSE BUT WHICH RECEIVES A SHIRT WHICH ADHESTS TO IT AND WHOSE EXTERNAL SURFACE IS OF HIGH FINISH. THIS SHIRT IS SHAPED BY HEATING BELOW 110C BETWEEN 90 AND 105C WITH A VIEW TO AVOIDING THE DISADVANTAGES OF THE SURFACE CONDITIONS OBTAINED BY THE PREVIOUS METHODS. THE SHIRT MAY THEN BE REMOVED WITH THE MOLDED ARTICLE THEN REMOVED FROM THE ARTICLE BECAUSE OF ITS FLEXIBILITY AND DEFORMABILITY LEAVING AN ITEM HAVING A POLISHED SURFACE FINISH. IT IS ALSO POSSIBLE TO OBTAIN A FEMALE MOLDING DIE BY THE SAME METHOD FOR PRODUCING MOLDED ARTICLES FROM THIS DIE.

Description

Inventi on relates to a method of molding shaped articles

  using the basic tecrinique known as

  the various names of manufacture or reproduction by molding.

  A well-known method of molding shaped articles is to use a mule form as a base, to cover this shape of the material to be made, such as partially treated resin and glass fiber, to treat the resin. the example given to transmit to the female article the male form and to remove the article from the

male form.

  It is also known to prepare a female matrix in the manner described in the preceding paragraph, and then prepare the final article in the reproduced form of the mile form using a

female matrix as a mold.

  In the case of either method, a common practice is to coat the mold with an ager.t to facilitate

  removal of the molded article from its mold.

  The present invention can be applied to one or the other

  the method described above and its purpose is to provide a

improved molding method.

  Small molded items can very easily be

  stripped of their male forms, if this form is covered

  beforehand with a separating agent. However,

  Large size keys, for example articles of continuous shapes with dimensions of the order of 2 meters by 3 and more, present great difficulty when they are removed from the form without damage. It has been found that the total holding force of the molded article can reach 74,000 Kg in such an example. In general, the finer the surface of the male form is united, and therefore the finish of the molded article, and the more the absolute finish of the

  Male form and the article is large, the greater the strength of adhesion-

  per unit area is large. This force can be reduced only at the cost of a degradation of the finish of the

surface obtained.

  The very important reason why the techniques of

  the prior art are unable to produce moving articles.

  large surfaces before a finish suitable for use

  optical techniques is that such techniques are fnondées on the heating of the article to be molded until it takes

- W'S4171

  a state plias: iue during the opra - rn of m oulaae. The standard used is in the field of about

  i4.0 to 160'_. We will, for example, refer to the United States patent.

  United States 3.317. 640 (Jones) who favors the use of tempera-

  between 143 and Z05'C. In addition, the use of

  such time is recommended in the manufacturer's manual.

  cants of Rohm e-t iass, main manufacturer of the material known in the United States by the trademark "Plexieglas" and in Europe by "Oroglas". The disadvantages of this approach in the manufacture of large mirrors are that a laws that

  the material becomes plastic it will adhere to all deficiencies

  In addition, the cooling of the material is impossible to control, as a result of which the film cools it at an unequal speed, thus giving rise to physical distortions in the thickness and curvature of the mold. the surface of the leaves These

  distortions of material provoke unacceptable imperfections

  The advantages of the finished mirror and these disadvantages are that the molding methods of the prior art are useless for us.

  achieve the objects of the present invention.

  According to the present invention, the shirt, used in the

  The molding of the molded article is itself formed at a temperature of

  relatively low erection so that the shirt does not cvie'nit

  not very difficult, avoiding the problems exnoses

  The temperature used is below 10 ° C. and preferably in the range of 9 ° C. to 105 ° C. These disadvantages of the prior art are overcome and

  training of artioles such as the very large mirrors

  satisfactory optical units becomes possible,

  According to another aspect of the invention, the preferred method of

  This is a molding apparatus comprising a male-shaped base and a flexible or deformable or demountable sleeve shaped to fit exactly the male shape.

  The molded article is formed above the shirt and, when

  that he is acnevé, is removed from the elm male with the shirt.

  The shirt being flexible, deformable or removable, is then

  easily removed from within the molded article (that this article

  molded either the definitive article or the female mold intended for the reproduction of the inal article), Thus, the present invention is distanced from the previous art by providing three bodies or three layers: the shape

  the shirt and the ground article, each being separate

  the other or both bodies previously provided.

  It is known, according to the prior art, to cover the shape

  basic, for example with a paint or glass for

  to obtain a highly polished surface or to glue or fix by means of a. cement a coating on the base form this coating being processed to obtain; an ifini having a high quality polish. Such a covering or covering then becomes part of the base and can not be removed in

  the molding process of the above articles.

  Preferably, according to the present invention, a finish relating to

  The basic form of the shirt is easily removed so that the shirt can easily be removed and is given a releasably finished finish to communicate such a finish to the final article or to the female die molded on it. shirt. Other features and advantages of the invention

  will be exposed or will appear in the detailed description

  following of the preferred embodiments of the invention.

  In order to facilitate the understanding of the invention and to facilitate its implementation, an embodiment of the invention

  method of the invention will be described in detail and by way of example

  With reference to the accompanying drawing, the single figure of which is an isometric view of a portion of the base shape, the jacket and the molded article, shows these three layers.

  The present invention is applied in the example

  dere, to the manufacture of a set of partial forms

  which when joined by abutting their edges form a continuous large-sized body of a shape made of spherical parts or spheroidal parts having

  a surface texture with a high finish or sufficient

  it, so that when it is silvered or otherwise coated, it provides a reflective surface suitable for optical applications, or for wave reflection

  radio waves near the infra-red region.

  Such a surface is referred to in this plain text as

  mirror. The following description refers to only one

  sections to assemble and it will be understood that other

  sections can be made in a similar fashion.

  Referring now to the annexed drawing, it can be seen that the form 1 of the male base comprising in this example a weldable metal base, is constructed according to the required shape, a terminal section being in this example of a shape spherical, and being provided with a surface 2 having a finish

  whose accuracy is of the order of 3 microns.

  The material selected for the construction of the form

  must be rigid and not deformable for a temperature

  varying surface area during a cycle between the temperature

  ambient temperature and 150 C. Surface temperature sensors

  this and telemetry, represented by a single sensor 3 in the figure, are provided to control the instantaneous temperature

  of the surface during such a cycle.

  An intermediate liner 4 is shown in the figure

  after removal from base 1 and partially detached from the

under the molded article 5.

  The jacket 4 is previously molded under vacuum from a sheet of methyl methacrylate and intentionally molded with a radius of curvature smaller than that of the surface 2 of the basic form 1. During the initial assembly, the jacket 4 is attached in strips or otherwise laterally secured to the base form 1. The surface temperature of the shirt base combination is increased so that the acrylic jacket 4 deforms sufficiently to

  Fit yourself exactly on the basic form. The temperature regime

  ture / time required for such deformation of the liner 4 in order to fit exactly on the basic shape 1 can be

  calculated or determined empirically, the temperature

  both in an area of 90 to 105 C as mentioned above

and described below.

  To retain the liner 4 on the base 1 so that the upper surface 6 of the liner 4 is both rigid and laterally static, a depression may be applied between the base 1 and the liner 4, at the edge of the liner 4, by

  means not shown but according to a known practice.

  It has been found that when the jacket 4 is applied

  by adjusting exactly on base 1, the phase of de-

  described training of the shirt can be avoided and that the

2 4 9 4 94171

  empty can be used to get a static application

  perfect of the shirt 4 on the base 1.

  But all the cases, the emptiness is maintained during the whole

  molding molding phase of Article 5.

  A substrate is then made on the base covered with the jacket using a technique known to form a

  substrate 5 honeycombed epoxy resin / fiberglass. The epoxy resin

  xy is applied to the nonr or partially processed state and is

  then finally processed to provide a rigid molded article 5.

  The finish of the surface 2 of the base allows the molded article 5 to which the liner 4 is attached to be easily removed from the base 1, since there is no longer only between them

  a low adhesion force per unit area.

  When the shirt and article have been removed from

  1, the sleeve 4 can be easily removed from section 5 for two reasons. First, the folder 4 is flexible for

  withdrawal, then there is no connection between the material

  acrylic material of the liner and the epoxy resin material of the substrate. The jacket 4 is thus removed to leave the surface 6 '

  with a high finish of the molded article 5 without risk of damage

  is lying. It will be understood that the liner 4 is progressively removed from the article 5 starting from an edge or a corner. The liner 4 is thus separated along a separation line of a very small area. As the adhesion force per unit area is itself small, the total detachment force

required is low.

  The surface 6 of the liner 4 is similarly unlikely to be damaged in the removal operation, so that the liner 4 can be relocated to the base 1 for repeated use. As discussed above, an important aspect

  of the invention relates to the use of relative temperatures

  low in the forming of the shirt 4 in the form of acrylic sheet so as to prevent the shirt becomes plastic. As mentioned, it was discovered that if the

  shirt in the form of sheet became plastic, she devier, -

  would be without optical application because the article would then take the defects of the mold, and because the control s6 2494171

  ue reri, i sieer th e raetoirau from th e reimperatures

  iveenit h-auuts used It is impossioble to have a classic iacon. The method of the present invention avoids these problems by conforming to the key folder.

  the temperature is below 10 ° and is preferentially

  does not include 90i and.105oC.

  that the material is the corresponding phase - temperatures above the known critical temperature

  cotlme "hot rupture region" is characterized by a rup-

  ture in the material exposing the edges of a plain mirror

  while the phase below the critical temperature is

  that is, the phase employed according to the invention, known as the "cold break region", is characterized by a disruption of the irregular and jagged edges.

  this fact provides an empirical method for determining rapidly

  Mernt the exact critical temperature for any batch of plastic materials. Although the invention has been described with reference to pre-alisation modes chosen as examples, those skilled in the art will understand that variations and modifications can be made to these various examples without departing from the present invention.

  scope and spirit of the invention.

  IEVENI: CA'I lONS), 1allode of molding of an article whose structure is constituted of Libres and synthetic resin, must the area

  of its surface is of the order of one square meter, having a surfa-

  this mirror polished with an accuracy and a high texture

  finish and sufficient to provide, after an appropriate coating

  required, a reflective surface suitable for

  optical cations, said method being characterized in that it comprises the following phases:

  the use of a mold whose surface has the exact

  study and the finite defined above, -

  forming a removable molding surface having

  and said finish to provide a polished mirror surface, said forming step comprising heating said removable molding surface to a temperature below the critical temperature at which said removable molding surface becomes plastic and forming a fiber and resin structure article

  as a substrate on said amorphous molding surface

vible.

  2) Metnode as claimed in 1 in which

  the temperature is below 110 C.

  ) Method as claimed in 2 in which

  the temperature is in a range between 90 and 1050C.

  4) A method as claimed in 1 wherein said article has a polished concave mirror surface, and wherein a rigid convex base shape is employed, said method comprising the following steps: a) using said basic form having a relatively coarse convex surface finish, b) the preforming of a reusable sheet made of a thermoplastic sheet to approximate the shape of the convex surface of the base shape, c) the attachment of the jacket to the shape of the based,

  (d) the fastening of the shirt to fit exactly

  to the convex surface of the base form, e) the manufacture of said fiber and synthetic resin structure article as a substrate on the convex surface of the jacket, and the simultaneous release and withdrawal of the jacket

8 2494171

  and the substrate made from the base elm and, g) removing the liner from the substrate made for

obtaining said article.

   A method as claimed in 4, wherein the liner is preformed to a smaller radius of curvature than

  that of the convex surface of the basic form.

  6) Method as claimed in 4 in which the pre-finished shirt is subject to adjust exactly to the

  convex surface of the base form by raising the temperature

  erase the surface of the base form for a time sufficient to deform the preformed sleeve on the base shape. 7) the method as claimed in 4, wherein the

  preformed shirt is attached to the basic shape by the application

  cation of a depression between the contact surfaces of the

shirt and base.

  8) A method as claimed in 1 in which the

  said article has a convex mirror polished surface and according to which a convex base shape is used, said method being characterized in that it comprises the following phases:

  (a) the use of a basic form having a finishing finish

  relatively rough convex side, b) the preforming of a reusable shirt formed of a

  thermoplastic sheet to take an approximate form

  similar to the convex shape of the basic shape, c) the fastening of the shirt to the basic shape,

  (d) the fastening of the shirt to fit exactly

  to the convex surface of the basic shape, e) -the manufacture of a concave article by means of a fiber and synthetic resin structure as a substrate on the convex surface of the jacket, f) the release and withdrawal simultaneously with the liner and substrate made from the base shape, g) removing the liner from the fabricated substrate to provide a mold shape having a concave surface, and h) molding said article having a convex polished mirror surface employing said concave substrate manufactured as

mold. -

  A method as claimed in 1 in which 1) a set of component articles are molded using

9 2 4 9 2494171

  the following steps: (a) the use of a basic forimi having a relatively convex surface filin, b) b) the preforming of a reusable thermoplastic sheet foil for communicating approximation of the convex surface of the basic shape, c) fastening of the jacket to the basic shape, d) securing of the jacket to accurately slice on the convex surface of the basic shape, O10 e ) the manufacture of the article by means of a structure

  of synthetic resin and fibers as a substrate on the surface

  this convex of the liner, f) the simultaneous release and withdrawal of the liner and the substrate produces the basic form and g) the removal of the liner from the substrate manufactured for obtaining said article, II) the component articles thus molded are assembled by juxtaposing them to each other so as to obtain a composite article. 10) Method as claimed in 1, wherein a set of component articles are molded separately and the component articles thus molded are assembled by juxtaposing them to one another so as to form a complete article. 110) A method as claimed in 4, wherein the convex surface of the shirt is polished to modify the

surface characteristics.

  12) A method as claimed in 8 wherein the convex surface of the shirt is polished to, modify the

surface characteristics.

  13) A method as claimed in 9 wherein the convex surface of the shirt is polished to modify the

surface characteristics.