US2044359A - Apparatus for casting - Google Patents

Description

June 16; 1936; QM. KUETTEL 2,944,359 i APPARATUS FOR CASHNG 1 Filed July 24, 193 2 Sheets-Sheet 1 INVENTOR. Glen M.Kue He] ATTO June 16, 1936. s. M. KUETTEL APPARATUS FOR CASTING Filed July 24, 1934 2 Sheets-Sheet 2 INVENTOR. Glen MKveHel ATTORN Patented June 16, 1936 APPARATUS FOR CASTING Application July 24, 1934, Serial No. 736,679

1 Claim.

This invention relates to an apparatus for easting and, more particularly, to an improved apparatus for casting polymerizable organic liquids.

There is a substantial class of organic liquids capable of being polymerized by suitable agencies to form solid resins of more or less rigid character which, in the form of blocks, rods, tubes, and other primary shapes, are capable of being fabricated by machining processes, and the like, into useful articles of commerce. For the preparation of these so-called turnery resins it is desirable to effect the polymerization of the initial materials in formsv or molds so as to secure by means of a single operation either the primary shapes which in turn constitute the raw material for the fabrication of the ultimate article, or, in some cases, the shape of the ultimate article itself, or a close approximation thereto, which can be finished by a minimum of machining operations, polishing, and the like.

Unfortunately, however, serious obstacles to the successful formation of resin shapes in this manner are offered by the considerable contraction in volume which takes place in these substances during, and as a result of, their polymerization, and by the exothermic nature of the polymerization reaction.

One result of the'exothermic nature of the polymerization reaction is the formation of bubbles and internal flaws in the cast shape. Ostromislensky U. S. Patent 1,683,403 recognizes to some extent the problem and suggests that, in casting rods and shapes more or less in the nature of rods, the molds in which the resin is polymerized be disposed horizontally rather than vertically. Although this suggestion by no means completely solves the problem, it is advantageous in casting articles which are elongated in shape so that when the mold is disposed horizontally the height of the mold cavity is not very great.

However, even where the Ostromislensky procedure may be employed to obtain shapes free of internal flaws, the contraction of the resin during the polymerization results in a rod or other article of incomplete cross section. Thus, in a mold of circular cross section, the polymerized rod would be flat along the top. Accordingly, in the production of rods by the Ostromislensky procedure it is necessary to employ a mold of larger diameter than that desired in the finished product, and then from the incompletely shaped resulting rod a perfect rod of the desired diameter may be machined. Obviously, this entails an appreciable loss of polymerized resin and is uneconomical.

An object of the present invention is to provide a molding apparatus wherein polymerizable organic liquids may be polymerized and cast free from bubbles and shrinkage flaws. A further object is to provide such a mold in which the pro- 5 portion of polymerized resin which must be removed in order to obtain a product of perfect cross section is reduced to a minimum. Other objects of the invention will be apparent from the description given hereinafter.

The above objects are accomplished according to the present invention by constructing an apparatus which comprises, in operative casting position, a mold chamber proper substantially horizontally disposed with respect to its major axis and having a cavity whose vertical section at right angles to its major axis is of the shape to be molded, a reservoir chamber disposed vertically above said mold chamber and communicating with the cavity thereof through a relatively narrow opening extending horizontally along the top of the mold chamber throughout substantially the complete length of saidcavity, and. means for introducing a substantially liquid polymerizable composition into the mold chamber.

Specific embodiments of the invention are illustrated in the accompanying drawings wherein:

Fig. 1 is a more or less diagrammatic perspec-' tive view of one end of an apparatus for casting;

Figs. 1A and 1B are vertical sections along the lines |A|A and IBIB of Fig. 1;

Figs. 2A to 2D are vertical sections of the apparatus shown in Fig. 1 indicating the level of the organic liquid being polymerized at various stages of the polymerization cycle;

Figs. 3A and 3B are vertical sections through the polymerized solid body after removal from the casting apparatus; I

Fig. 4 is a perspective view of an apparatus for manufacturing the mold shown in Fig. 5;

Fig. 5 is a perspective view of the mold, with cork inserted in the open end, made from the apparatus illustrated in Fig. 4;

Figs. 5A, 5B, and 5C are vertical sections along the lines 5A-5A; 5B5B; and 5C5C, respec- 45 V tively, of Fig. 5;

Figs. 6A, 6B, and 6C are vertical sections at right angles to the major axis of molds adapted to give different specific shapes with respect to their vertical section;

Fig. '7 is a vertical section at right angles to the major axis of a mold similar to that illustrated in Fig. 5 but with'a differently shaped reservoir. I

In the drawings like reference numerals refer to like parts throughout.- Reierring particularly to Figs. 1, 1A, and 1B, a mold is illustrated in operative position, being disposed substantially horizontally to its major axis. The mold comprises an elongated mold chamber proper I having a cavity whose vertical section at right angles to its major axis is of the shape to be molded, and a reservoir chamber 2 disposed vertically above the mold chamber I and communicating with the cavity of mold chamber I through a relatively narrow opening 3 (shown in Figs. 1A and 1B) which extends horizontally along the top of mold chamber l throughout substantially the complete length of the mold chamber. As shown in Fig. 1, one end of the mold is closed, and the other end, not illustrated, being left open for removal of the solid cast product and, if desired, for introduction of the liquid to be polymerized. Preferably the liquid is introduced through a small opening in the top of the apparatus with the mold proper in horizontalposition. As explained later, means are provided for closing the open end of the mold so that, during polymerization, the mold may be entirely closed. To facilitate removal of the cast product, the mold, including both mold chamber I and reservoir chamber 2, is tapered slightly outwardly from the closed end toward the open end. This is illustrated in somewhat exaggerated form by Fig. 1A and 1B, Fig. 1A showing a section of the mold on the line iA'|A of Fig. 1 adjacent the closed end thereof while Fig. 1B shows the larger section on the line IB|B of Fig. 1 adjacent the open end of the mold. The taper may be very slight and may be eliminated entirely in molds that are to be broken apart for removal of the cast product.

The procedure with respect to use of the apparatus of the present invention will be described with reference to Fig. 1 to Fig 3B, inclusive. The mold is filled with a substantially liquid polymerizable composition 4, e. g. methyl alpha methacrylate, to substantially the top of the reservoir 2 as indicated in Fig. 2A, the open end of the mold closed and the mold disposed horizontally with respect toits major axis in an oven maintained at 70-7 5 C. to polymerize the composition.- The process of polymerization of .these polymerizable organic liquids results in a gradual increase in viscosity of the liquid and a gradual increase in specific gravity thereof or, in other words, a gradual shrinkage.

As the shrinkage of the composition develops in the mold chamber proper it is compensated by a corresponding fiow'of the composition from the reservoir chamber, with the result that during polymerization the mold chamber I remains filled, at all times while the level in the reservoir chamber 2 gradually falls as a result of the shrinkage. This isillustrated in Figs. 23, 2C, and 2D showing the lowering of the liquid level in successive stages of the polymerization as the shrinkage progresses. If the dimensions and relative cross sectional areas of the mold chamber i and reservoir chamber 2 of the mold have been properly calculated with reference to the known shrinkage behavior of the material in question, there will remain, upon the completion or substantial completion of polymerization, a small excess of material in the reservoir chamber 2, sufficient to provide the full cross sectional area of the desired circular rod. The polymerized product as removed from the mold will thus have the cross sectional configuration shown in- Fig. 3A. It is machined to the desired circular cross section as shown in Fig. 33 with a minimum loss of polymerized composition.

In the procedure described above, the reservoir chamber 2 had a volumetric capacity just slightly in excess of the volumetric contraction of an amount of the polymerizable composition in question equal to the volumetric capacity of the mold chamber 1. It will be understood that, in order to obtain a product of the full cross sectional area desired, it is necessary that the reservoir chamber 2 have this slightly excess capacity and that it be filled. Obviously, a reservoir chamber of greater capacity may be employed but, in

.that case, it is not completely filled asthe greatest economy is effected in providing just suflicient polymerizable composition so that upon substantially complete polymerization, the level of the resin will be just sufiiciently high to insure a full cross sectional area of the desired product.

In order to illustrate a practical embodiment of the invention, the procedure for the construction and operation of a mold designed to produce a circular rod of polymerized resin of diameter 0.75" from a material in which the shrinkage from monomeric to polymeric condition amounts to 20% of the volume of the liquid monomer, will be given.

A master mold of metal, such as steel, is made which, when dipped into molten lead. and then withdrawn therefrom, becomes coated with a solid lead jacket which, upon being stripped off the master mold, constitutes the mold in which polymerization is eifected. In Fig. 4 a perspective view of this master mold is given. It

consists of a tapered cylindrical metal rod 6 to which is riveted or welded a tapered triangular metal strip 1. These two parts may be made from one integral piece of metal. The junction of the metal strip 1 with the cylinder 6 is made along the total length of one of the apexes of the strip 1. A slightly tapered metal plug 8 of circular cross section and of diameter equal to the combined height of the diameter of the cylinder 6 and triangular strip 1 is secured thereto in order to create a space in the open end of the lead mold that may be readily stoppered with a cork, or the like. A handle 9 is provided for holding the master mold while dipping it into the lead. The length ofthe master mold up to the metal plug 8 was 14 and the master mold was provided with a taper of .016" in that length, the end of the mold adjacent the plug 8 being the larger.

The ratio of the volume of the triangular strip I which will form the reservoir chamber of the mold and the volume of the cylinder 6 which forms the mold chamber proper of the mold, is dependent upon the change of density of the resin, or its shrinkage, as polymerization progresses. It was found that the cross sectional dimensions of a master mold for manufacturing resin rods of diameter from the material under consideration required a reservoir chamber in which the section at right angles to' its major axis was an incomplete equilateral triangle whose internal dimensions were /3" on a side at the small end of the mo d with the diameter of the cylindrical rod 6%" and the width of the junction between the two All of the joints and corners of the master cylinder. This permits ease of stripping the lead ,there is formed upon the spective in Fig. 5 and the mold on the line 5A 5A of Fig. 5 is shown in Fig. 5A. In Fig. 5 a cork H is shown inserted in the open end In of the mold. This is shown also in Fig. 5B which is a section on the line 5B-5B of Fig. 5. The opposite end of the mold is a solid lead wall is a section on the line 5C5C of Fig. 5.

In the upper wall of the reservoir chamber 2 in Fig. 5 is drilled a hole l2 having a diameter of for the purpose of filling the stoppered and horizontally placed lead mold with the use of a funnel or some automatic loading device.

In operating the mold described, it is placed in horizontal position with respect to its major axis with the cork preferably covered with metal foil, inserted firmly in the open end. The mold is then filled with liquid monomer through the hole l2 which is then likewise stoppered. Alternatively, the hole l2 may be first stoppered and, holding the mold in vertical position, the liquid monomer may be poured in the open end which is then plugged with the cork H before the mold is placed in horizontal position. As shown in Fig. 5, the mold is substantially horizontal with the reservoir chamber 2 vertically above the mold chamber l. The liquid monomer is then polymerized by the application of heat to the material and, upon completion of polymerization, the polymerized product may be removed through the open end of the mold.

The combined volume of the reservoir chamber and mold chamber of i a lead mold created by a master mold of the dimensions given, excluding the end stoppered with the cork, is 150 cubic centimeters. When such a mold is completely filled with a monomeric methyl methacrylate with specific gravity approximately 0.94 yielding a polymer of specific gravity approximately 1.2, a rod will result which is completely cylindrical, save for a minor, narrow, slightly elevated fin,

which may be easily removed. The percent waste.

of polymerized resin is substantially negligible.

The apparatus of the present invention has been described with respect to a mold adapted to produce rods but it is to be understood that the mold cavity can be made in all variations of design to yield rods, tubes, or other shapes which may be cut into bracelets, napkin rings, or other shapes. Sections of various shaped molds at right angles to their major axis areillustrated in Figs. 6A, 6B and 6C. The mold shown in Fig. 6A is particularly adapted for the production of an annular rod to be used in the manufacture of bracelets, whereas Fig. 6B shows a mold of special shape for clock cases and Fig. 6C a mold for producing a polygonal rod. These figures merely illustrate some of the infinite variety of shapes which may be cast.

Those skilled in this art will understand that as indicated in Fig. 50 which operating position of the" tween the two chambers it is not necessary for the reservoir chamber 2 to have any plicity's sake a herein illustrated is usually employed.

In the polymerization of the organic liquids adapted for use in the apparatus of the present invention, it is preferable that no loss shall take place through volatilization and, as a result, it is preferred that The width of this passage will, as a matter of economy, always be relatively narrow in order that the slightly elevated fin which must always result shall use as little polymerizable composition as possible.

In order that the flow of the material from the reservoir chamber into the mold chamber shall not be obstructed, it is, of course, necessary that the width of the passage between the two chambers be appreciable, with due considera tion being given to the her is approached. For terial through a relatively narrow passage beis possible until almost the end of the polymerization of the material in the mold chamber and, as a result, all shrinkage in the mold chamber is compensated for.

While reference has been made specifically to the polymerization of liquid methyl alpha methacrylate monomer, it is to be understood that the mold of the present invention is broadly applicable to polymerizable compounds which shrink during polymerization. Other compounds of this class which may be mentioned include: ethyl methacrylate, butyl methacrylate, phenyl methacrylate, glycol di-methacrylate, vinyl acetate, vinyl chloroacetate, acrolein, vinyl chloride, styrene, alpha-methyl styrene, methyl vinyl ketone, divinyl acetylene, ethylene oxide, benzyl chloride, and dlmethyl itaconate.

' Many methods of polymerizing such compounds are well known in the use of heat, light, or polymerization catalysts, or some combination of the three. Obviously the present method can be used regardless of the method of polymerization. In applicant's copending application Serial No. 736,678, entitled Preparation of cast resins, is described a particular method of polmerizing these compounds, layer by layer, to build up a final product of any desired thickness. In this method each layer polymerized is thin enough so that polymerization may be carried on at a relatively rapid rate without danger of formation of bubbles or other art and usually involve the v it is possible to for the shrinkage in volume of the final layer of compound.

In the production of cast articles in the mold of the present invention, it is by no means necessary that the polymerizable compound be intro duced in the monomeric state, as partially polymerized material may be employed-so long as it is fluid enough to accurately take the impression of the mold. Where a partially polymerized material is being employed, it will be appreciated that the percentage of shrinkage will be less than where the monomeric compound is employed and, consequently, the capacity of the reservoir chamber may be diminished.

The mold of the present invention may be used in the polymerization of these various compounds, either with, or without auxiliary agents such as would occur to those skilled in the art, among which may be mentioned plasticizers, coloring matter both soluble and insoluble, various modifying resins both natural and synthetic, "effect materials, and similar ingredients in compositionsof this type.

The mold of the present invention can be used for the production of rods and tubes from which finished articles are subsequently machined and for the production of a limitless number of finished or semi-finished articles in individual molds.

By employing a mold such as herein described, obtain articles of complete cross section regardless of the shrinkage coefficient of the material being polymerized, whereas this has not heretofore been possible in the molds held in centage of cases, make the products totally unfit horizontal position during p lymerization for the manufacture of rods. and the like. Although this objection was not met in the manufacture of rods in molds held in vertical position, as previously 3 pointed out, it is'diificult to polymerize these 5 compounds in appreciable depths without the formation of internal bubbles and other visible flaws which greatly detract from the value of the products obtained and, in fact, in a large perfor commercial purposes.

As many apparently widely diiferent embodiments ofthis invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claim.

I claim:

Apparatus for casting substantially liquid polymerizable compositions comprising, in operative 20 'position, an indivisible, integral mold chamber proper substantially horizontally disposed with respect to its major axis and having a cavity whose vertical section at right angles to its major axis is of the shape to be cast, a lead reservoir chamber made integrally with the mold chamber and disposed vertically above said mold chamber and communicating with the cavity 01 the mold chamber through a relatively narrow opening extending horizontally along the top of the mold chamber throughout substantially the complete length of said cavity, the reservoir chamber in vertical section at right angles to its major axis being substantially the shape of an equilateral triangle with one apex truncated by the opening 3 communicating with the mold chamber and said mold chamber and reservoir chamber being closed at one end and open at the other and tapered slightly outwardly from the closed end toward the open end, and removable means for closing said open end whereby the polymerized product may be removed mm said mold chamber.

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