United States Patent: 3640664

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United States Patent	3,640,664
Giffard , et al.	February 8, 1972

SHAPING MOLDS FOR PRODUCING FILMLIKE ARTICLES

Abstract

A shaping mold for producing filmlike articles by the fluidization process, this mold consisting of a completely closed enclosure formed in a metallic material having good heat-conducting properties but a reduced thickness. The enclosure communicates with the surrounding free atmosphere, during the heating thereof, via at least one tube carried by an opening into a portion of the enclosure which does not partake in the shaping of any portion of the filmlike article.

Inventors:	Giffard; Louis (Saint Brieuc, Cote du Nord 5, FR), Fougeray; Jean (RUEIL Malmaison, Hauts de Seine 21, FR)
Appl. No.:	04/866,466
Filed:	October 15, 1969

Foreign Application Priority Data


Nov 04, 1968 [FR]			172389

Current U.S. Class: 425/275 ; 425/DIG.3

Current International Class: B29C 33/02 (20060101); B29C 41/08 (20060101); B29C 41/10 (20060101); B29c 013/00 ()

Field of Search: 18/2K,2S,5.5,14R,14G,24,34S,38,41,46,DIG.3,27,29

References Cited [Referenced By]

U.S. Patent Documents


2605505	August 1952	Ruhland
2867847	January 1959	Miller et al.
1791060	February 1931	Keen
3496610	February 1970	Shelby et al.

Foreign Patent Documents


1,007,034	Feb., 1952	FR

Primary Examiner: Spicer, Jr.; Robert L.

Claims

What is claimed as new is:

1. A shaping mold for producing filmlike articles, comprising a closed hollow body of a uniform wall thickness having surfaces adapted to be disposed in a fluidized bed of thermoplastic particles and to be heated to a temperature in excess of the flow temperature of the thermoplastic, and at least one bottom element other than said surfaces; a plurality of appendages projecting from said surfaces and of a wall thickness approximately equal to that of said body, said appendages being hollow and communicating with the interior of said body, said body and said appendages having a wall thickness of the order of 0.5 to 0.6 millimeter; and at least one duct connected to said body and open to the atmosphere, said duct being joined to said body at said bottom element.

2. The mold defined in claim 1 wherein two ducts communicate with said body at said bottom element, said mold further comprising respective control valves in said ducts for regulating the flow of hot air from said body and the flow of cold air to said body respectively, said body and said appendages being composed of metal and said appendages being secured to said surfaces by weld fillets facilitating the stripping of the film from said surfaces.

Description

BACKGROUND OF THE INVENTION

This invention relates to shaping molds for producing filmlike articles by the so-called fluidization process.

Although a relatively old discovery, fluidization processing (i.e., processing a solid in such a form that it can be handled as a fluid) was not carried out on a commercial scale until about a score of years ago in the field of surface coating by using thermoplastic films.

Still more recently, a method of obtaining filmlike articles by the same process was proposed, but in contrast to the early practice aiming at producing a coating or lining, wherein the primary requirement is reliable adhesion between the support or carrier element and the film, nonadhesion is essential in the manufacture of very thin articles such as garments, high boots, hats, book dust jackets, banknote cases, etc.

Thus in the manufacture of articles of this character the use of massive molds consisting of the outline of the article out in a relatively thick metal plate was advocated. To facilitate the stripping of pieces comprising projections or the like, molds have also been proposed which had a U-section obtained for example by folding this outline in order to orient all the projections in the same direction.

The processing consists firstly in heating the mold in an oven or stove to a temperature ranging from about 250.degree. C. to about 300.degree. C., then suddenly dipping the mold, as it emerges from the oven, into a container in which the powdered plastic material is subjected to a turbulence in order to cause the powder to adhere to the hot mold walls and thus melt, and eventually cooling the mold for smoothing and stripping the article.

In the case of articles such as garments, the mold constitutes a closed vessel consisting of relatively thick metal-plate elements hingedly interconnected to facilitate the stripping of the filmlike articles by separating said elements.

Another proposition consisted of molds closed according to this method (as exemplified in the French Pat No. 919,852) the heating step is obtained by producing an internal circulation of a heating fluid such as oil, the enclosure being connected by adequate conduits to a circulation pump.

The applicants observed that these shaping molds did not give really satisfactory results and accounted for defects involving considerable failures and rejects. In fact, considering the manner in which these molds are designed and constructed any homogeneous heating and cooling thereof is definitely precluded, though this constitutes a sine que non requirement for producing commercially sound articles.

In the case of a shaping device consisting of a simple outline plate, a relatively thick metal plate is necessary (for example a 4-mm. thick steel plate) so that it can have a sufficient mechanical strength and a heat capacity adequate for melting the plastic powder deposited thereon. These requirements lead to a temperature rise taking about 10 minutes in the case of P.V.C.), a time obviously too long for an economical alternate operation of molds of this type.

This inconvenience is further aggravated by the fact that the least air current occurring during the transfer of the shaping tool from the oven to the bath (which air current may affect both faces of the outline will cause a wavelike propagation of a cooling effect detrimental to the temperature homogeneity and therefore to the regularity of the film thickness, in that it is attended by "clear" zones and by a poor smoothing.

Hinge-type shaping molds seemed to constitute a definite improvement in the art since the accidental cooling could affect only the outer face thereof, i.e., the only face likely to receive the air current; however, the applicants found that when the mold was dipped into the fluidized bed its temperature was not sufficiently homogeneous, so that the same defects as those mentioned hereinabove in connection with outline molds were again observed. In fact, the hot air trapped within the mold tended to escape through all the joints, notably at the hinges, so that these portions were kept at a higher temperature than the others, thus frequently impairing the already poor heat distribution in the mold.

Heating by oil circulation leads to a poor economical efficiency of the production process, for the heating and cooling phases are excessively long.

SUMMARY OF THE INVENTION

The present invention relates to a novel type of shaping molds for the purpose set forth hereinabove, but free of the inconveniences of prior art devices of this character.

The mold according to the present invention is basically characterized in that it consists of a completely closed enclosure made of a relatively thin material having a good heat-conductivity, said enclosure communicating with the external free atmosphere, during the heating thereof, through at least one tube carried by and opening into a portion of the enclosure which does not partake in the shaping of any portion of the filmlike object.

According to a specific feature characterizing this invention, said tube is provided with a valve.

According to another embodiment of invention, said enclosure comprises at least two tubes, each tube having a valve inserted therein, one valve controlling the outward flow of hot air and the other the inward flow of cold air.

DESCRIPTION OF THE DRAWING

The attached drawings illustrate diagrammatically by way of example the manner in which the present invention may be carried out in practice. In the drawings:

FIG. 1 is a perspective view of a mold according to the invention;

FIGS. 2 and 3 are detail views showing in a section projections to be formed on filmlike articles; and

FIG. 4 is a sectional view showing another embodiment of a shaping mold according to this invention.

SPECIFIC DESCRIPTION

As shown in the drawing, the shaping mold according to this invention consists of a completely closed vessel or enclosure C reproducing the shape of the object or article to be made, the projections of this object being obtained by means of internal or external appendages such as A and P, secured to the mold C. The walls of this enclosure and of these appendages A and P are obtained by using very thin sheet metal (for example having a thickness of 0.5 to 0.6 millimeter). The rigidity of the shaping mold is obtained by using bottom elements such as F. Slots D interconnect the inner space of the main shaping body with the inner space of each appendage, so that air can circulate freely throughout these inner spaces. In fact, the applicants found that if the appendages such as P (in this example for forming a pocket in a garment) or B (in this case a button) were formed simply by means of a solid, massive element (such as a cutout plate or a turned element), these elements had necessarily a heating capacity other than that of the enclosure-forming material, due to the difference in the thicknesses and or nature of the metal, so that the inconveniences listed hereinabove were observed again, with the additional drawbacks of the resulting projections in comparison with the main body of the article.

In contrast thereto, as can be seen in FIGS. 2 and 3, all the appendages, including appendages B, are made of sheet metal of same nature and thickness as the main body of the enclosure, and formed with a double wall connected to the main body on either side of the slot D by a weld seam S constituting a fillet facilitating the stripping operation.

To afford convenient handling, the bottoms F are provided with legs or handles such as G1 and G2.

As already explained hereinabove, the air contained in the shaping molds spreads into the inner space of the main body and also into inner spaces of the ancillary enclosures of the appendages. It will be readily understood that if these enclosures were closed completely the expansion of the air contained therein, as a consequence of the temperature increment (up to and above 300.degree. C.) would lead to a distorsion of these enclosures and make the shaping mold useless.

To avoid this distorsion the tube T is secured to one of the bottoms, so that the hot air can remain at the atmospheric pressure without causing the escape of this air to overheat certain parts as in the case of "leaks" observed in so called "hinged" molds. Thus, without displaying any of the above listed inconveniences, the shaping mold according to this invention has all the advantageous features of the same molds, that is, the possibility of utilizing the accumulation of internal hot air as an additional heat reserve maintaining the wall of the enclosures at a uniform temperature by simple conductivity.

In certain cases it may be advantageous to provide the tube T with a valve or any other means adapted to cut off when necessary the fluid communication between the inner space and the surrounding medium. This cutoff device may consist for example of a gaged valve becoming operative when, as a consequence of temperature, the pressure within the enclosures attains a predetermined maximum permissible value. If desired a plurality of tubes T each controlled by adequate valve means may be contemplated, some of the valves permitting the ingress of air into the enclosures and other valves permitting the exhaust of air therefrom. The air-inlet tube T may be used for introducing a cold fluid (for instance air) into the enclosure during the step following the smoothening step, in order to accelerate the cooling of the shaping device to the temperature permitting the stripping therefrom of the film constituting the manufactured object or article.

Considering FIG. 4, it will be seen that in the inner space of enclosure C there are disposed a pair of blind appendages A1, A2 retained therein for example by means of distance-pieces H, the inner space of these appendages communicating freely with the exterior via orifices 01, 02 also adapted to be used for introducing the plastic powder into this space and discharging any excess powder therefrom. The hot valve Vh and cold valve Vc are also shown in this figure.

Of course, various modifications and variations may be brought to the specific forms of embodiment shown and described herein without departing from the spirit and scope of the invention set forth in the appended claims.

* * * * *

Current U.S. Class:	425/275 ; 425/DIG.3
Current International Class:	B29C 33/02 (20060101); B29C 41/08 (20060101); B29C 41/10 (20060101); B29c 013/00 ()
Field of Search:	18/2K,2S,5.5,14R,14G,24,34S,38,41,46,DIG.3,27,29