Патент USA US2411254код для вставки
Nov. 19,‘ 1946. 2,411,254 G. H. FRANK MOLDING DEVICE Filed Sept. ‘29', 1942 F/a/ Z 9‘ 72 717 / I mv'zmroz 62 H Hen/w: BY ?lm? I; M HrTOKNE-Y 2,411,254 Patented Nov. 19, 1946 UNITED STATES PATENT OFFICE MOLDING DEVICE George 11. Frank, Oak Park, Ill., asslgnor to WesternElectric Company, Incorporated, New York, N. Y., a corporation of New York Application September 29, 1942, Serial No. 460,066 6 Claims. (Cl. 18-30) 2 This invention relates to molding and more par ticularly toan apparatus for injection molding of thermo-setting materials. . In the manufacture of molded articles from thermo-setting molding vcompounds, such as cer . from the preheating chamber to the molding die. _ Other objects and advantages of this inven-l ' tion will be apparent from the following detailed description taken in conjunction with the fol lowing drawing, wherein: ' ' tain phenol aldehydes, the molding, compound Fig. 1 is a front elevation, partly in section, of a molding apparatus constructed in accordance ' may be preheated prior to injection into the mold. Heat is applied to plastify the compound and with one embodiment of this invention, and Fig. 2 is a. fragmentary sectional view along render it soft enough to be injectable. Pressure is then applied to inject the compound into the 10 the line 2-2 of Fig. 1. -- mold. With some phenol aldehyde compounds, This invention will be described in connection with the molding of phenol aldehydes. However, the period of heat treatment prior to injection it will be understood that the invention is appli of the compound may be relatively short. For cable to any plastiflable materials exhibiting an example, with certain phenol formaldehyde com pounds, it may be a matter of only a few seconds 15 appreciable dielectric loss angle when subjected to a high frequency, high voltage field, such, for of heat treatment before the compound will set or cure and become impossible to inject. Thus, example, as rubber and the like. the heat treating should preferably be done by While most phenol aldehydes are excellent in a means that permits rapid and uniform preheat sulating materials for direct current or for "low ing and quick transfer of the compound to the 20 frequency alternating current, they‘ are gener ally poor insulators for high frequency use, be molding die when the optimum condition for plastic ?ow has been attained. ' Since the heat is usually transferred to the I . .cause the power factor of such materials increases ‘with increases in applied frequency. Thus, if compound from the walls of the steam or elec-' ' 'a high frequency current of from .1 to 100 mega trlcally heated container, and since most phenol 25 cycles, and of su?lcient energy, be applied. to . aldehydes are poor conductors of heat, that por tion of the molding compound which contacts the walls of the container is heated more quickly than that portion of the compound in the middle and such an insulating material, considerable heat will be generated. The percentage of electrical current transformed into heat will be, in general, proportional to the power factor of the insulating not contacting the walls of the container. Thus, 30 material and will increase with increases in fre quency. This heat is developed internally within the insulating material and may be regulated tainer may set before the remainder has been precisely by controlling either the strength or the plasti?ed. If, however, the compound is trans frequency, or both, of the imposed current. ferred to the mold as soon as this outer portion has been properly preheated, the inner portion 35 For a given power factor, that material which is likely to be so inadequately plasti?ed that an has the highest dielectric. constant will produce incompletely cured part may result. the greatest heating effect. In other words, the generation of heat is proportional to the product It is an object of the present invention to pro . the portion which contacts the walls of the. con 'vide an efficient and effective apparatus for in of the dielectric constant and the power factor. jection molding thermo-setting materials. 40 Certain types of Pyrex glass are obtainable which have a power factor of approximately .2 and a In accordance with one embodiment of this in vention, .a molding apparatus may be provided " dielectric constant of approximately 5 at 18 mega comprising a, molding die having an inlet to ad cycles, giving a product of 1. Phenol formal mit molding compound. A Pyrex preheater is dehyde, which is a commonly used phenol alde positioned adjacent this aperture and is pro 45 hyde compound,‘ has a power factor of approxi mately 6 and a dielectric constant of approxi vided with a pair of electrodes which are con- . mately 5 at 18 megacycles, the product of these nected to a source of high-frequency current. The transformation of high frequency energy into being approximately‘ 30. Comparing these prod heat in the dielectric molding material causes ucts, an energy loss ratio of about -1 to 30 may be the material to plastify uniformly and permit 50 seen to obtain between Pyrex and phenol form quick injection. The dielectric losses in the mold aldehyde. This indicates that per unit'volume of ing compound produced by the high frequency glass and phenol formaldehyde, the transmission electrostatic field cause the compound to heat suil‘lciently for injection. A ram is provided for. of high‘ frequency current through each at the proper energy level would cause the heating of transferring the plasti?ed molding compound 55 the ‘phenol formaldehyde through a range of 150° 3 2,411,254 4 . 0., while the temperature of the glass would be raised only 5° C. Thus. if a heating chamber be made of this type of Pyrex glass, it becomes pos sible to heat treat the phenol formaldehyde with out substantially increasing the temperature of the heating chamber. Because the heat is gen erated internally within the phenol formaldehyde is attached to the bottom of the plate 42 by a number of bolts 22 and associated clamps 23, which engage a projecting portion 24 at the base of the section 2I. A funnel shaped aperture 44 is formed through the middle of the supporting plate 4.2 to admit heated molding compound from the heating chamber 5 to the molding die. An resin, the preheating is uniform throughout the aperture 25 extends through the mid-portion of charge in the heating chamber. the upper section 2I of the molding die to permit The present invention contemplates heating the 10 passage of the molding compound to the molding molding compound through the heat generated in die. A replaceable sleeve 26 of hardened metal the compound by the presence of a high fre is inserted in this aperture and extends into the quency, high voltage electrostatic ?eld. Fig. 1 funnel-shaped aperture 44 of the cross plate 42. illustrates an article molding apparatus con By employing a replaceable sleeve of hardened structed in accordance with this invention. Es 15 metal, the maintenance cost, due to scoring of the sentially, this apparatus comprises a preheater die by the ram, is kept at a minimum. 5 for heating the molding compound prior to A relatively thin, removable wedge-shaped plate transfer of the compound by a ram ll to a mold 45 is positioned on the upper surface of the plate ing die 20. The preheater 5 is formed by a thick 42 so as to contact the lower end of the preheater walled shell 5 of Pyrex type glass having as low 20 5 and thereby to prevent the molding compound a dielectric constant, loss angle and power factor from moving downward out of the heating cham as feasible in order to keep heating of the pre ber before the period of heat treatment is com heater during the operation of the apparatus at plete. A number of guides 46 are attached to a minimum. As may be seen in Fig. 2, a pair of the upper surface of the plate 42 in which the electrodes 1 are embedded in the wall of the pre 25 plate 45 is slidable, and serve to position the plate heater and oppose each other. It is desirable 45 properly with respect to the aperture 44.. that these electrodes be made of a conducting A lower section 30 of the die 20 is mounted on material having a temperature coeillcient of ex a vertically movable cross plate 36 which is similar pansiomas near that of the glass used for the in size and appearance to the supporting plates heating chamber as possible in order to prevent 30 42 and I4. This section of the die is attached to strain and possible breakage of the glass due to the plate 36 by a number of clamps 31 and asso uneven expansion of the two materials during ciated T-bolts 38 which engage the plate 38, the base of the lower section 30 having a projecting heating. A properly terminated coaxial cable 9 is con- I portion 40 which is engaged by the clamps 31. nected to each electrode and may, in turn, be 35 The supporting plate 36 has an aperture in each connected to a suitable high frequencq, high volt corner and each aperture is provided with a sleeve age current. With a material such as phenol bearing 39. The posts II extend through these formaldehyde, it has been found that by employ sleeve bearings and, thus, serve as guide posts for ing a current of approximately 2000 volts at a the plate and lower section of the die as they are frequency of approximately 18 megacycles, the 40 raised and lowered by the ram 48. material will reach molding temperature in a A pair of feeders 3I are formed in the lower very few seconds. In order to obtain maximum surface of the upper section of the die to permit eiiiciehcy of the heating apparatus, a current fre the molding compound to be injected into mold quency is employed to which the heatingv appa cavities 21, also formed therein. The lower sec ratus is resonant, the apparatus in e?ect being a tion is provided with cavities 32 and the mold cav condenser: the electrodes ‘I serve as the conduct ities are shaped in accordance with the shape of ing plates while the molding compound, inter the articles to be molded. In operating position, posed therebetween, serves as the dielectric body. the lower section is held tightly against the up Once the resonant frequency is determined, ade per section by the ram 48 which presses against quate control of the heating is had by varying the the base of the plate 36 and raises or lowers it as voltage. may be required. When these two sections are in As shown in Fig. 1, the base of the preheater is closed or operating position, the cavities of the in a recessed portion of the under-side of a heavy, two sections of the die form a pair of enclosed supporting, cross plate I4 which is supported by mold cavities into which the molding compound four vertical posts II, two being shown in Fig. 1. 55 may be injected by the ram I1. A number of A number of bolts I3 and associated clamps I2 apertures 28 are formed in both sections of the “ serve to hold the heating chamber in place. Holes die to permit heating thereof, either by steam or are provided in each of the corners of the plate hot air, to complete the curing of the compound. I4 through which the posts extend and the plate The high injection pressures required for mold‘ is ?xed in position on the posts by a number of 60 ing thermosetting materials are such that even nuts I5 which are threaded to the posts. An aper the hardest metals may be scored or deformed. ture ‘I5 is provided in the middle of the plate I4 Thus, a removable insert 33 of hardened metal is to permit an operator to place molding compound positioned in the upper surface of the lower sec in the heating chamber. This aperture is made tion of the die to receive the brunt of the pres 65 somewhat larger in diameter than the inner diam sure exerted by the ram I ‘I in forcing the molding eter of the heating chamber in order to facilitate compound into the mold cavity. This insert may easy insertion of the molding compound. The be replaced by inserting a suitable tool in an aper four posts together with'a base plate 50 form a ture 34, which extends from the base of the lower frame for the whole apparatus. The apparatus ‘section of the base of the insert, and knocking it may be supported on a table 5i. out. The lower section of the die, of course, must The lower end of the ‘preheater‘ is tapered and be removed from the plate 36 in order to do this; is positioned slightly ‘above a second heavy cross its removal is facilitated- by the use of the T-bolts plate 42 which is ?xed to the posts I I by nuts 43. 38 and clamps 31. This plate serves as a ?xed support for summer In the operation of this apparatus, a quantity section 2| of the molding die 20. This section 2! of molding compound to which a small percentage . 75 2,411,254 of carbon black may be added to accelerate the heating, may be placed in the preheating cham ber. Among other materials that‘ accelerate the rate of heating, zinc sulphide and zinc oxide may also be cited. The presence of moisture in 5 amounts up to 6% also has a de?nite accelerative effect on the heating. The compound may be previously compacted to form a‘cylindrical block '6 said stationary mold section to form a mold cav ity, means for moving said movable mold section to open and close the mold, means for heating said mold sections, said stationary moldl section having an extrusion cylinder for ?lling said mold cavity, a preheating chamber in alignment with said extrusion cylinder, removable means for clos ing one end of said chamber means for electro-‘ of substantially the same size as the inside of the statically heating molding material in said cham heating chamber. Due to heating and the appli ber to a plastic ?ow condition, and a plunger in cation of pressure, the molding compound will or dinarily be reduced’to one-third of its original vol ume, and by compacting the compound in advance as much as possible, the required size or the heat ing chamber is kept at a minimum. The ram 11, 15 a which is supported by a cross plate It ?xed to the upper ends of the posts II by a number of nuts I9, is then caused to move downward to compact the compound in the heating chamber alignment with said preheating chamber. and said extrusion cylinder for compressing the molding material in said preheating chamber and for transferring the plasticized molding material from said preheating chamber to the extrusion cylinder and then to the mold cavity. 2. A molding apparatus for molding thermo setting material comprising a stationary mold section, a movable mold section cooperating with by actuating a suitable driving means (not 20 said stationary mold section to form a mold cav ity, means for moving said movable mold section shown). A pressure on the order of 150 pounds to open and close the mold, said stationary mold per square inch may be used in the preheating section having anextrusion cylinder for ?lling chamber. Compacting the compound is desir said mold cavity, means for heating said mold able to obtain maximum e?lciency ofthe electro static ?eld applied to the compound by the elec 25 and extrusion cylinder, a preheating chamber in alignment with said extrusion cylinder, means for electrostatically heating molding material in said The ram, being metal, is withdrawn so as not chamber to a plastic ?ow condition, and a plunger to be in the electrode ?eld and the high’frequency in alignment with said preheating chamber and current is then applied. when the compound has become sumciently heated and plasti?ed, the 30 said extrusion cylinder for transferring the plas ticized molding material from said preheating retaining plate 45 is withdrawn and the driving chamber to the extrusion cylinder and then to means for the mm H is again actuated toforce the mold cavity. the compound out of the heating chamber, 3. In a molding apparatus for molding thermo through the funnel-shaped aperture 44 in the plate 42, through the aperture“ in the upper sec 35 setting material. a preheating chamber, a pair of electrodes associated with said chamber, means tion of the die 20 and toinject it into the mold for supplying current to said electrodes, said elec cavities. The ram continues its downward move trodes comprising substantially ?at plates of con ment until the die cavities 21 and 32 have been ducting material, said plates being spaced from ?lled. An injection‘pressure as great as 30,000 pounds per squareinch may be employed in order 40 and parallel to each other so as to create a sub trodes. ‘ , . ‘ ‘ to force the compound into the mold cavities. The molded articles are permitted to cure in the mold cavities and then the driving means for the ram 48 is actuated to lower the ram and cross plate 30 so as to separate the two sections of the molding die, thus permitting removal of the molded articles by means such as ejector pins ‘ ‘ stantially uniform electrostatic ?eld therebe tween. a mold chamber having an extrusion cyl inder in alignment with said preheating chamber, means for heating said molding chamber and extrusion cylinder. means including'a ram in alignment with said preheating chamber and said extrusion cylinder for transferring the plasti cized molding compound from said preheating commonly employed in the art. ‘The sections are chamber to said extrusion cylinder and then to then brought together again by the ram 48 and 50 said , mold chamber, and means for retaining the cycle or operation is ready for repetition. molding compound in said preheating chamber Since for most phenol aldehyde compounds, both the power factor and dielectric constant in crease at a much faster rate with increases in temperature than is the case for glass, while the during preheating. 4. A molding apparatus for molding thermo setting material comprising a stationary mold heating of the molding compound may be rela 55 section, a movable mold section cooperating with said stationary mold section to ‘form a mold cav tively slow at ?rst application thereto of the high ity, means for heating said mold sections, means frequency ?eld, the percentage of energy in the for moving said movable mold section to open and circuit transformed into heat will continuously close the mold, said stationary mold section hav increase at a rapidly accelerated rate as the tem- , ing an extrusion cylinder for ?lling said mold perature of the molding compound increases. In , cavity, a preheatingr chamber in alignment with short, the higher the temperature of the com said extrusion cylinder, means for electrostati~ “ pound, the greater is the speed of heating. Since cally heating molding material to a plastic ?ow this heating characteristic is many times greater condition in said chamber, a removable member for the phenol formaldehyde than for glass, the for retaining the molding material in said cham glass remains relatively cool throughout the op ber, a feeder groove extending laterally from the eration of the apparatus. ‘ ‘base of said extrusion cylinder to the mold cav While but one embodiment of the present in ity, said groove being formed in the surface of one vention has beenshown and described, it will be ' understood that many changes and modi?cations vof said mold sections, and a means including a may be made therein without departing from the 70 plunger in alignment with said preheating cham ber for compressing the molding material in said spirit or scope of the present invention. preheating chamber and for transferring molding What is claimed is: material from said preheating chamber to the 1. A molding apparatus for molding thermo extrusion cylinder and then to the mold. cavity. . setting material comprising a stationary mold 5. A molding apparatus for molding thermo ‘ section, a movable mold section cooperating with 75 7 2,411,254 setting compound comprising a preheating cham ber, means for electrostatically heating molding ing chamber being made of a Pyrex type glass, means for electrostatically heating said molding compound in said preheating chamber to a plas material in said chamber including a pair of » tic ?ow condition, means for retaining said mold spaced electrodes imbedded in the walls of said ing compound in said preheating chamber until chamber, a removable member for closing one end heated, a mold having an extrusion chamber in or said chamber, a mold having an extrusion cyl alignment with said preheating chamber, and a inder in alignment with said preheating chamber, plunger in alignment with said preheating and means for heating said mold and extrusion cylin extrusion chambers for compression the mold der to a temperature to maintain said plastic flow ing compound in the preheating chamber and for 10 condition, and a plunger in alignment with said transferring the plasticized molding compound preheating chamber and extrusion cylinder for from the preheating chamber to the extrusion compressing said molding material in. said pre chamber and then to the mold. heating chamber and for transferring the plasti 6. A molding apparatus for molding thermo ‘cized molding material from the preheating setting material comprising a cylindrical pre chamber to the extrusion cylinder and then heating chamber for heating a charge of molding extruding it into the mold. material to a plastic ?ow condition, said preheat GEORGE H. FRANK.