FR2515096A1 - METHOD FOR MAKING JOINTS BETWEEN THERMOPLASTIC BODIES - Google Patents

Abstract

THE PROCESS FOLLOWING THE INVENTION CONCERNS THE MAKING OF CRACKLESS JOINTS BETWEEN THERMOPLASTIC BODIES SUCH AS WAX BODIES. MORE PRECISELY, THE PROCESS CONCERNS THE MAKING OF SUCH JOINTS BETWEEN WAX BODIES, SUCH AS THOSE CONSTITUTED BY WAXES BASED ON PARAFFINS. THE PROCESS CONSISTS OF INSERTING BETWEEN THE COUPLING SURFACES OF AT LEAST TWO THERMOPLASTIC BODIES A PLATE SHAPED FROM A MATERIAL WHICH ABSORBES ELECTROMAGNETIC RADIATION, IN SUBJECTING THE ASSEMBLY TO ELECTROMAGNETIC RADIATION UNDER CONDITIONS SUCH AS THE STEP. PLATE CAUSES THE FUSION OF THE THERMOPLASTIC MATERIAL AT THE LEVEL OF THE COUPLING SURFACES WHICH ENSURES AFTER COOLING A STRONG BOND. THE PROCESS IS APPLIED IN PARTICULAR TO THE ASSEMBLY OF WAX MODELS AND OF THE SUPPLY MEANS OF THESE MODELS IN THE LOST WAX MOLDING PROCESS.

Description

PRCEDE OF REALISING OF JOINTS ERE THROMOPLASTIC BODIES

  The present invention relates to a process for producing joints without cracks between thermoplastic bodies. The invention applies, in particular, to the production of joints between wax models and also wax supply cores in the rolling process. lost wax.

  The lost wax process is one of the oldest techniques

  production of castings made of metal alloys.

  To obtain molded parts according to this method, a wax model, of identical shape to that of the metal molded part, is produced which it is desired to obtain. A ceramic mold is then formed around the model and

  the fired so as to obtain a negative of the desired metal molded part

  During cooking, the original wax pattern is removed by melting or burning. The molten metal is introduced into the ceramic mold and after cooling and solidification, the ceramic mold is destroyed.

  thus releasing the final metal molded part.

  To introduce the molten metal into the ceramic mold, a conduit must be arranged to form such conduits or channels in the molds.

  ceramics, the wax replica of these means of supply must be

  stained with nodel wax As the ceramic mold is only used once before being destroyed, many wax models are often linked to a series of wax bars all attached to the filling hole , thus constituting a single cluster of wax

many models.

  One of the most important operations in the taxiing process

  lost wax is the connection between them of the wax models and

  yens also feed in wax to form a cluster of wax

  The seal between the wax model and its means of

  be free of cracks, otherwise the ceramic grout will penetrate and become

  difies in these cracks, then, after removal of the wax, forms

  obstacles on the path that the liquid metal must follow.

  Ceramic particles detached by the liquid metal stream

2 515094

  can then contaminate and render unusable the final molded part.

  The wax itself must also be of a good degree of purity so that when it is removed by combustion, there is no residue left

  may contaminate the molded metal part Any method of

  joints to form clusters of wax models must, for

  therefore, to obtain watertight seals, vis-à-vis a li-

  quide, which are not likely to contaminate the final molded metal part, nor do they risk deforming the waxes and their feeding means; The usual method of producing these joints for clusters of

  wax models requires the use of highly qualified personnel.

  The workers carefully seal each individual joint

  by applying a heated tool, such as a hot knife blade

  This process is expensive and time consuming. There is a long-standing need to find a way to automate this process.

  step, but previous efforts have not been crowned with success.

  The object of the present invention is to provide a simple, safe, and relatively inexpensive method for forming a crack-free seal.

  between adjacent complementary solid bodies of thermoplastic

  tick. Other objects and advantages of the invention will be presented in the

  following description and will be partly made obvious by the

  description and may be learned through practice

of the invention.

  The objects and advantages of the invention can be realized and achieved with toyen instruments and combinations particularly specified in

  the claims of the present application.

  To achieve the objectives of the invention in accordance with the purpose it proposes, and as it is described in the widest manner and exemplified hereinafter, the method of the invention for forming a

  crack-free joint between complementary solid bodies

  takes: the insertion of a wafer absorbing the

  magnetic between thermoplastic bodies, the approximation of these bodies in the immediate vicinity, the plate being between them to form an assembly, the submission of the assembly to electromagnetic radiation whose frequency is such that it is substantially absorbed by the wafer , in order to melt thermoplastic surfaces

  adjacent and to form said crack-free seal between the pieces.

  The wafer preferably exceeds the outer perimeter of at least one of the bodies. Moreover, the wafer is preferably capable of combustion without leaving ash. According to a preferred embodiment of the invention, the wafer comprises crystallized graphite bonded with polystyrene It is also preferable that electromagnetic radiation

  is in the field of microwaves so that an assembly occu-

  substantial volume can be attached simultaneously

che.

  Following a particularly favorable mode of implementation of the invention

  the thermoplastic bodies are wax models and also waxing means which are joined by joints in the

  lost wax casting process The wax model and the means of

  preferably have complementary m 2 and fem parts.

  and the plate preferably has an opening that adapts to the

  around the mile portion, so that it can be oriented

  The adjustment between the male part and the female part must be sufficiently precise to maintain the model and the feed means without exerting stress on the contact zone during the melting and solidification which takes place. produce during

  the process of making the joint.

  The attached drawings which are included in and form part of the description

  integral illustrate one embodiment of the invention and with the

  Description serve to explain the principles of the invention.

  FIG. 1 is a sectional view of thermoplastic bodies to be assembled and

  to join according to a preferred embodiment of the invention.

  Figure 2 is a plan view of a power bar used in

  the embodiment of the invention of FIG.

  FIG. 3 is a plan view of a wafer used for the mode of

  embodiment of the invention of Figure 1.

  Reference is hereinafter made in detail to the modes of implementation of the invention.

  are currently preferred and an example of which is given in

the attached figures.

  According to the invention, a cracks-free joint is formed between

  adjacent complementary thermoplastic lides; a wide variety of

  thermoplastic bodies can be joined by the process according to the invention.

  The preferred thermoplastic bodies are those which are not appreciably affected by the incident electromagnetic radiation used in accordance with the invention so that the thermoplastic bodies are not affected by the invention. not heated directly by radiation According to the embodiment described below, the thermoplanic solid bodies are

  wax models and feeding means, used in the pro-

  surrendered to lost wax.

  We see, for example Figure 1, wax models (1) and a bar of

  (2) Any wax and wax-based filler commonly used in the lost-wax process may be used in this process. The wax co-ordinates to which particular preference is given are those basedparaffins that allow the realization of good reproducible fago joints.

  According to the invention, a wafer absorbing electromagnetic radiation -

  The thermoplastic body is placed between the thermoplastic bodies as shown in FIG. 1 and the thermoplastic bodies are then brought close immudiate with the wafer between them. The average skilled artisan will be able to choose the electromagnetic radiation absorbing material from which the wafer can be made for a particular application. This absorbent material must be able to be rapidly heated by electromagnetic radiation, in order to

  cause fusion and the formation of joints between

  The wafer preferably comprises a carbonaceous material dispersed in a material that is substantially non-absorbent with respect to the electromagnetic radiation.

  which is given a special preference is graphite cris-

  polystyrene bonded tallin The composition used for the wafer preferably comprises between 20 and 30% by weight of crystalline graphite dispersed in 70 to 80% of polystyrene The size of the grain of the material

  carbonaceous is preferably between about 0.5 and 0.6 micrometers.

  The thickness of the wafer is preferably about 0.127 mm (0.005 inch). The wafer preferably exceeds about 1.6 mm (1/16 inch) the perimeter of at least one of the thermoplastic bodies it

  It's about joining to get the best results.

  If the wafer does not extend beyond the perimeter of at least one of the

  moplastics, we can observe a joint attack and results

irregular.

  In a preferred embodiment, in which the thermoplastic bodies

  There are also wax models and wax feeders used in the lost wax casting process, preferably a wafer that does not burn ash and is certainly non-metallic. subject of which

  plate is made to be floated at the moment of decision.

  during the preheating process, the material containing

  naked in the wafer that absorbs electromagnetic radiation does not

  should hardly leave any ash after burning.

  For example, commercially available crystalline graphite whose ash content is only 0.2% by weight. The binder used for

  the material, preferably carbonaceous, absorbing the electromagnetic radiation

  The gnetic material is preferably a material which does not significantly absorb electromagnetic radiation. Additional factors in the selection of the binder are the low melting point and the low ash content, but with adequate mechanical strength to allow easy handling. binder should also be easy to mix with the carbonaceous material absorbing electromagnetic radiation and

  when mixed with this carbonaceous material, it should be

  cile to form, in thin wafer The preferred binders are

  polymers such as polystyrene and polyethylene The man of n

  Medium skill will be able to select other binders with such properties, but the binder currently preferred by the applicant is polystyrene. The thickness of the wafer is not important as long as there is sufficient material absorbing the wafer. rayon-

  electromagnetic energy to cause the melting of thermoplastic

  as long as the wafer is thick enough to handle

  As already indicated, the thickness of about 0.127 mm (0.005 inch) is preferred in the preferred embodiment which relates to the lost wax molding process. The wax models and the feeding toys should be be held together without creating stresses in the contact areas during the melting and solidification phases to form a smooth and crack-free bead A loose assembly may bend one of the

  parts to each other or to separate them and then the

  It is an advantageous method of the invention to obtain a correct physical fit between the thermoplastic bodies during the formation of the joint by making complementary male or female parts in the body.

thermocplastiques.

  As shown in FIG. 1, the tenon (4) is a non-circular male piece.

  the conical cavity, and the cavity (5) is a corresponding female part.

  The plate (3) of FIG. 3 may comprise a hole (6) whose

  turn adjusts around the tenon (4) The plate (3) should extend

  slightly beyond the perimeter of at least one of the thermoplastic bodies

  to be attached, such as model 1 shown in Figure 1.

  Other means to maintain the position of the thermo-bodies

  Plastics and wafer during joint formation without creating tension will come to the mind of the average skilled tradesman. After bringing the thermoplastic bodies and the wafer according to the present invention closer together, the wafer and the bodies are subjected to electromagnetic radiation of a frequency such that only the wafer absorbs it in a significant manner. The radiation causes an alignment of the wavelength. molecular structure of the absorbing material with the alternating electric field, which causes a rapid heating of this absorbent material due to the heat produced by the friction of the molecules As for the thermoplastic bodies, they are not affected by the radiation and consequently keep their interest

  The complementary contact surfaces of these thermoplastic bodies

  However, ticks are heated by conduction from the wafer above their melting point.

  the melted parts of the thermoplastic bodies mix and

  difient by forming a crack-free joint.

  Electromagnetic radiation can be used in a wide frequency range and in particular a radiation frequency of between 103 and 1014 Hz It is preferred to use electromagnetic radiation in the microwave field. The use of microwaves is advantageous because of their selective effect on many materials Non-polar materials such as wax, alumina and most ceramics are not affected by microwaves.

  that water and graphite are rapidly heated by microwaves.

  Standard microwave equipment operating at a frequency between 915 and 2450 M Hz can be used to provide the energy The time required to achieve the seal can vary widely; joints have

  have been successfully completed within the limits of time between

  condes and 2 minutes The greater is the power level of the microwave source and the shorter is the duration of the seal. In the case of particular test models, all the other variables being kept constant, the time of realization of the seal ranged from approximately 45 seconds for 100W power to 4 seconds for a power of approximately 700W For most practical applications, a microwave source capable of delivering power up to 2.5kW should be suitable Other variables that affect the time of realization of the joint are the proportion of graphite in the material

  which constitutes the wafer, the type and the nature of the particles of

  phite, the binder used, the thickness of this wafer, the importance of the relief formed by the wafer beyond the periphery of the model, the dimensions of the supply means that it is a question of joining, the number

  of models to join, and the shape of the resonant microwave cavity.

  According to a preferred embodiment of the lost wax molding process, the realization of the joint between the wax models and the kernels

  wax supply can be carried out quickly by connecting them with

  mechanically by means of a conical joint so that a thin polar plate is inserted between the bearing surfaces

  as shown in Figure 1.

  When such an assembly is placed in a microwave field, the seal is preferably made in less than 15 seconds. The wax of the mating surfaces of the models and feed means melts and flows around and coats the raised edges. of the wafer which remains solid

  and intact-forming a plain rim and without cracks.

  After about 30 seconds, the wax liquefied by the hot wafer solidifies again forming a seal between the model and the means

  which reaches its full strength in a few minutes following

  before configuring the assembly.

  We successfully made joints between models and both sides

  of a power bar as shown in Figures 1 to 3

  Thus, according to the present invention, it is advantageous to simultaneously join a set of thermoplastic bodies. It can thus be used to join a set of feed means.

  as well as a single feed means.

  It is preferred that the planes of the walls of the surfaces to be joined are

  mentally parallel, and oriented to prevent the flow of

  However, this problem can be minimized by a suitable choice of the thermoplastic material because some of these materials are more resistant to flow than others In any case, after having mechanically connected all the assembly of the thermoplastic bodies , all joints can be made in one

  operation with a single exposure to electromagnetic radiation.

  As the thermoplastic bodies are not affected by the electromagnetic radiation, it does not need to be focused on a joint

  to be carried out, but can safely be directed to the assembly.

whole.

  As a result of the present invention, as generally described and practiced herein, a higher degree of regularity in obtaining satisfactory seals or higher speed with significant cost savings is achieved by the present invention. workforce. As it turned out, the process can be easily automated. For example, because of the speed with which seals can be made using electromagnetic radiation, a single source of electromagnetic radiation can process the entire

production of a factory.

  A conveyor can bring assemblies from a plurality of

  workstations A cutting press using suitable dies

  can be used to cut wafers to the desired size from a coiled thin strip (at the same rate as

  assemblages penetrate into the electromagnetic field).

  An automatic system can be used to control the operational cycle.

  the intensity of the field and the shape of the pulses, so that

  ensure optimal performance for each assemrblage.

  Workers placed along the conveyor can assemble the bodies

  thermoplastics and arrange them in the desired position for

  joints on a tray that is not significantly affected

  by electromagnetic radiation.

  Information coded on the tray, or otherwise provided, may be automatically introduced into the automatic control system, so as to adjust the operating conditions of the electromagnetic radiation source for each assembly as it passes.

in the electromagnetic field.

  It is clear to those skilled in the art that various modifications and variations

  can be made to the process according to the invention without

  firing of the domain or the spirit of it.

Claims (16)

  1 / Process for producing joints without cracks between thet   Adjacent solid complementary soplastics, characterized in that an electromagnetic radiation-absorbing wafer is placed between the thermosplastic bodies, these bodies are brought into close proximity, the wafer lying between them, to form an assembly, and it is known as Mt. electromagnetic radiation assembly whose frequency is such that the wafer absorbs it significantly to melt the adjacent thermoplastic surfaces and form a seal between the bodies. 2 / A method according to claim 1, characterized in that the thermoplastic bodies are not significantly affected by the radiation electromagnetic incident.   3 / A method according to claim 1 or 2, characterized in that   outside the outer perimeter of at least one of the thermo-   plastics when they are near and close, z: -. the wafer lying between them.   4 / A method according to one of claims 1 to 3, characterized in that that the wafer is combustible.    Process according to claim 4, characterized in that the combustion   the wafer does not leave ashes.   6 / A method according to claim 4 or 5, characterized in that   quette comprises a carbonaceous material dispersed in a material which is   sorbant not significantly the electromagnetic radiation.   7 / A method according to one of claims 1 to 6, characterized in that   that the electromagnetic radiation is in the field of microwaves.   8 / A method according to one of claims 1 to 7, characterized in that   that in one of the thernmoplastic bodies comprises a wax.   9 / Method according to claim 8, characterized in that toinsins one   thermoplastic bodies is a model in wax.    / Method according to claim 8 or 9, characterized in that toins one of the thermoplastic bodies is a wax supply means.   11 / Method according to one of claims 1 to 10, characterized in oe   that the wafer has a thickness of about 0.127 minutes.   12 / A method according to one of claims 10 and 11, characterized in   the wafer comprises about 20 to 30% by weight of crystalline graphite.   13 / A method according to one of claims 1 to 12, characterized in that   that the wafer comprises about 70 to 80% by weight of polystyrene.   14 / Joint without cracks joining at least two thernmoplastic bodies made by melting at the mating surfaces of these bodies,   characterized in that a wafer absorbing electro-magnetic radiation   tick is inserted between the mating surfaces.    Crack-free joint according to claim 14, characterized in that   the edges of the plate are raised in relation to the outer perimeter   thermoplastic bodies between which it is inserted.   16 / seal without cracks according to claim 15, characterized in that   the raised edges of the wafer are coated with thermal material   solidified noplastic which forms a plain rim and without cracks.   17 / seal without cracks according to one of claims 14 to 16,   characterized in that at least one of the thermoplastic bodies which it assembles ble is a wax model.   18 / seal without cracks according to claim 17, characterized in that it combines at least one wax model with a feed means also in wax.   19 / Application of the seamless joint according to one of the claims   14 to 18 to the realization of a ceramic mold for the manufacture of a metal alloy part by the lost wax molding process.