US2264146A - Method of making perforated molds - Google Patents

Description

Nov. 25, 19413. N. CRANE METHOD OF MAKING PERFORATED MOLDS 2 sheets-sheet 1 i x E w "ear: "av- A Filed July 27, 1937 ZW// 640%/ 51M Nov.25, 1.941.

N. CRANE METHOD OF MAKING PERFORATED MOLDS Filed July 27, 1937 2 Sheets-Sheet 2 Patented Nov. 25, 1941 perreo ordres r ermee Claims.

rhe present invention relates to molds adapted to form ,articles from paper pulp and siiniiar tures of fibers and liquids; in other words, molds adapted to give form under pressure, to vmasses of material containing liquid which must be Vreleased or extracted from the mass in the course of molding, in order that the resulting article may be sufficiently compact and dry to serve its intended purposes. Molds of this character are extensively used `for producing pl tes and other articles from wood pulp containing a very large proportion of water, as well as from other mixtures of bers and liquids. An essential characteristic of such molds is a multiplicity oi perforations or passages running from the molding surface to the discharge sigle of the mold, suiciently numerous, eapacious and well distributed to permit a rapid vdischarge of the `liquid when the pulp mass is subjected Vt0 Pl sure, and of vapor when the article is heated or otherwise dried to expel the residue of liquid which is n ot extractable by pressure alone. Such molds must also be rigid enough to retain their form and surface lcontours under the pressure of molding, whether such pressure is that o f the atmosphere effected by partiel vs odumei 'los discharge side of the mold, or is fluid pressure otherwise created and applied, or the mechanical pressure of a complemental molding die or f orin. The molds and dies of this nature heretofore made are expensive. and those lWhloll .are mede wholly or in part o f wire fabrie are more .or less weak and flimsy and liable -to injury land deformation.

My Yobject is to produce molds and dies of the type indicated, having adequate strength and rigidity to sustain `the greatest pressures used -in molding pulp articles and the like, which may have any configuration and Contours o f molding surface, are provided with adequate .escape passages for the liquid, and are producible Vat `a `fraction of the cost of the molds and dies heref tofore known. The invention Kcomprises a new method for making such perforated molds; -including the illustrative embodiment described in the following specification and all substantial equivalents of such embodiment within the scope of the appended claims.

In the drawings, a form of apparatus used in carrying out this method, the steps of the method, and two complemental or cooperative molds resulting therefrom are shown.

Fig. 1 of the drawings represents in perspective one of the elements of the apparatus which I may call the core extrusion block;

Yil is s sooioeel View of s sordos o# the Core extrusion block taken on line 2%2 of 1 and represented on an enlargedscali S is s, oersroooveiriev'oi s oldie or dieollrsem -Wllioh is. optionally 'dsebleto limit'fho somber .end looeiioos .of the ooliessxruded from the @difusion bloos.;

Fie l s seoilooel View .of the essentiel Peris of e Compete apparatus for olfyioe'out'lhe method; auxiliary' Peris sosh soooosog meanspump, etc., which are y'practical'ly\neces- `solo' out involve domine, .new with ills sessel lei/soiled beleg omitted:

Fis 51s .e View of 'ille apparatus shown in Fie- 4 oder bordel oser-ados iii odd-viedo die method:

Fleo .illustrates s further step of .lille oseredos:

Fdel shows the step of .sleeping the molding suraoe of a mold or "matrix produced byY this lsveoiioo; i

Fl 81s e oerspeoslre View o f the mold lioisiled lov #he operation ,shown lo .FieA 7, beide tlv .breton jewev .to show die lidild exile@- do.v` passages:

, les 9 .sed 10 are vlows similar to Fles- 'l sod 6 respectively showing the dpelloetion of lthe same xneiiiiod to4 produce a ,compleme'ntal`-mold wie de le of die non dominee.

rediris ses dore eslrusiooblools;

ll is d. perspeodve View of the mold fresdltioe from the les.t .mentioned performdnoe .of the method.-

lThe Ybasis Prlooiple on which ,this :invention :rests is that of oost/loe the molds irom e solidl- -fisble lluid mixture or Composition, dnd the .formation Within them of passages lov voo eells of extruded .Cores Wlllsh are Passed through sdoh composition while the latter is in the vSlui detente The preferred material .which I use yfor' the -iriold .eomDOSltfon is hydraulic cement in finelyA divided ooodltioo, mixed. wiih d lesse Xsess of Welser edd .smell Proportion@ solltest of kilo- Wn .materiels Wllioh roter-d. sel-doe to .elsif-else hsrdoessl-lle `sores ere mede from o sdsiilel Whlollls oepeble of extrusion lhfouslfoes 'ses sod .orldoes orefereblv s vos sovfdsleotly s- ;tio to be `thus extruded at ordinary room temperatures., oodllsrd enough lJo rotolo the form .given by the extrusion ,olfloe Whoo subioi'edlto externalforces of moderate intensi-ty. "Ihe ,riecosseo' ,qualities of such materiel Isle explained ,le elle following dssollolloo.- i t' en important factor of the @pharaons ,is en Velement which -I have called the core extrusion come completely enclosed passages. of the plates may also be of any desired value,k

purpose.

' used in crowding the platesltogether.

locations and dimensions.

The extrusion block here shown is made of flat metal plates c, c, in one face of each of which shallow grooves b are cut. The plates are thinly coated with solder d on oneface (which may be either the front face in which the grooves are cut or the back face), are placed'faceto back against one another and clamped in a compact bundle, and heated sufficiently to melt the solder so that,l after cooling, the plates are bonded together in a solid block. It is to be understood that in place of solder other means suitable for correspondingly bonding the plates together may be used and are within the scope of the invention; also that where solder is used the plates are suitably prepared in known manner to insure adhesion of the solder to them.

The plates may be made of any desired thickness and of any metal suitable to be secured together in the manner described. They may also be curved cylindrically instead of nat, although the flat form is preferable on account of the ease i of cutting grooves in them and of assembling them in a block without need of careful fitting. The grooves also may be of any desired depth, Width and spacing, provided only that their dimensions are large enough-to permit flow of the plastic or semi-liquid core material and to give sufficient strength and stiffness to the cores so extruded. For example, in the work -which I have done, I have found that grooves approximately .030 wide and .010" deep are satisfac-H tory; but these are not in any sense limiting* `values and the grooves may be wider or narvrower, deeper or shallower Without departure from the invention. The spacing of the grooves is limited on the one hand by the width of lands ,Y necessary to hold the bonding medium, and on the other hand by the required number of passagesin one row. When the plates are assembled as described, the originally open grooves be- The width and is established practically as that which makes the block as a Whole sufliciently rigid to withstand the pressure applied informing cores by extrusion.

It may be observed that while soldering or an' equivalent bond is desirable because it makes of the block a self-contained unit in which single plates cannot be displaced by the forces encountered iny service, yet it is not essential, as thel plates may be held and clamped in a form or frame tightly Vand firmly enough to serve the When solder or the like is used as described, even in the thinnest possible films, it maybe squeezed more or less into the'passageways b, when melted and under the pressure When this occurs the passageways may be cleared by passing a rod or drift through them. VWhen once completed, such extrusion block, though initially` expensive, may be used so many times without`V deterioration and in the production of so many molds, that the fraction of its cost chargeable to any single mold becomes inappreciable.

The extrusion block, whether of the construction above described, or of any other construction suitable for the purpose, is placed and secured within a casing or holder e, which is connected with another casing part or head f so as to form a chamber below the extrusion block. These parts e and f are here shown as detachably connected by bolts g passing through external anges h on their sides. But they may be joined integrally or by other suitable means.

The space in the chamber next to the head is coA available on the market.

occupied by a distensible bag 7, preferably made of a vulcanized rubber composition so that it is ,stretchable and elastic and capable of confining fluids without leakage. It is connected to a pipe 7c passing through the head f, through which Water or other fluid may be admitted and discharged. The wall y" of this bag is in elect a diaphragm which may be deiiected and displaced 'plasticity or fluidity required is that which will permit the material to flow through narrow passages ofthe order of the passages b when impelled by pressures of suflicient intensity, say in `the orderof 500 pounds per square inch. The

necessary firmness or hardness of the material is that which will enable rods or ribbons extruded -vertically from such Ypassages to pass through superposed liquid containing Iinely -divided solid rnatter in suspension, and to remain substantially parallel to one another. W axes and wax compositions having these qualities are known and It is within my contemplation, however, to use other plastics, or fusible solids, rwhichrvvill melt or become plastic at temperatures below the boiling point of water, and are substantially hard at room temperatures. Means for application of heat to the material belowrthe extrusion block, and absorption of heat from the region above the block may be applied within the purview of this invention to aid the carrying out of the operation when alloys and plastics of the type last indicated are used.

But it would not be a departure from the invention` to use' lead, and Vapply a pressure great enough to extrude it through the passageways.

A frame or flask m is secured detachably, and liquid tight, to the upper end of the apparatus so constituted, as by the bolts and iianges shown inthe drawings. Into this ask is poured a mixtur'eofwater and finely divided hydraulic cement, of which the watervcontent is suilcient togive ita fluidity approximating'that of cream; or at least to make it thin enough so thatrods of wax extruded from the block a will pass Y through it.

Water or other fluid, being then forced or pumped into the bag 9' distends the bag fand its diaphragm 7" and forces the wax through the extrusion block, as shown in Fig. 51 'I-he streams of Wax issuing from the block form rods o r Iribbons n which rise through the body o of cement overcomes the tendency of gravity to bend and deiiect them. The has sufficient cohesion to prevent its buoyancy from. detaching the extruded rods from the masses in the passageways of the block or from attenuating them;

The flask is allowed to remain in connection" When the removed casting has become rm enough to be carved without distortion, but while it is still soft and friable, one of its surfaces is carved to the shape and contours of any desired hollow mold or protuberant die. To form a mold of circular shape, such as that for a plate or other dish, the flask may be secured in the' chuck of a turning lathe, as shown in Fig. '7, and rotated relatively to a cutting or scraping tool p,

which is fed in the directions required Vto cut the prescribed contours. .Or `other contours can be carved in any other suitable way. During the cutting operation, the cores n remaining in the casting support the cement in contact with them and are firm enough to prevent being distorted in the cutting operation and thus prevent distortion of the surfaces of the cement body in Contact with them.

Finally, after the casting has aged to a condition of sufficient hardness 4and cohesiverness, it is heated sufciently to melt the containedcores whereupon the latter run out, or may be blown out. There is thus produced a casting o inthe form of a s olid rigid block, having a molding cavity lq and passages r running from the surface of the molding cavity to the opposite side of the block. Such passages are like, fin dimensions, number and spacing, unto thepassages b of the extrusion block, and provide discharge or extraction outlets for liquid when the mold is used in molding objects from pulp, whether by suction, mechanical pressure, air pressure and permeation, or with the application of heat to discharge residual moisture.

In order to limit the formation of passages in the casting to the area only where such passages are desired, a mask or screen s may be placed between the extrusion block and the plastic composition, as shown in Figs. 4 and 5. The mask suitable for the specific mold here illustrated is a plate having a central circular opening s (see Fig. 3) with the same diameter as the mold cavity q. But obviously the outline, placement and number of equivalent openings may be of any character to correspond with the mold to be produced.

Any mold made as before described is capable of being used alternatively as a combined block and matrix for a counterpart mold or die. Such use is illustrated in Figs. 9 and 10, wherein the casting o is placed in the extrusion apparatus in substitution for the block a, and used in the same manner as described to cast a complemental die t. In this procedure, the formation of the ultimate product is simplified in that the molding portion is shaped directly by the molding cavity of the matrix, wherefore no final cutting or carving operation is needed. And the last described mold .or die may in its turn be used to make other molds of the rst form. Thus from an original extrusion block of neutral character, and by subsequent carving, a'n endless variety ofY mold forms may be made which are usable' not only for molding, but also for the reproduction of molds in geometrical progres'- sion.v The casting process, with the use of extruded cores, is a most inexpensive mode of making rigid and durable perforated ,molds with any required number cf exhaust passages.

The oblong or flattened shape of the passages in cross section is an important feature, in that such passages provide area enough for rapid dish-a'rg of water, while at the same time they may be so narrow that the 'pulpcannot be impressed into them to any appreciable extent. That is, molds having passages of this character mark the pulp much less, evenunder extremely heavy molding pressure, than molds of which the contact lfaces are made of wire mesh or which have circular perforations. The construction of the original or master extrusion block from grooved plates enables such passages of unequal transverse dimensions to be made.

While, as previously stated, other materials than wax may Vbe used for extrusion cores as described, wax is preferred because of its light specific gravity and' because its hardness is very nearly equal to that of the partially cured cement casting when the latter -is in condition for turning', or carving. 'Ihus the cutting tool cuts the cores as easily as the cement and the tendency, which exists with harder cores, to be displaced by the cutting tool and to break and crumble the cement, is avoided. I reserve the right to use, and to protect within the scope of this invention, other materials than waxes which may be discovered or developed and which may have qualities superior to wax in this regard. I also reserve the right to use and 'protect other substances than hydraulic cement which may be available for casting in molding flasks and in association with core extruding apparatus as described.

Plasticisers and setting accelerators are known which, when added to cement mixtures, produce desired effe-cts in retarding or hastening the setting of the cement suspension into a rigid body. I may use any suitable plasticiser or accelerator with cementmixtures in this process to obtain whatever time may be needed to bring acasti'ng to the carving step, or to minimize the delay necessarily intervening before the lcasting is firm enough to be carved. Such plasticiser's and others may be used also for the purpose of 'giving the partially cured casting a quality of plasticity and cohesiveness enabling it to be carved smoothly, particularly on protuberant portions, without crumbling or tearing away below the path of the cutting tool.

The amount of wax used is calculated in accordance withthe areas of the extrusion passages and the depth of the cement mixture or the like placed in the molding flask, so that the individual cores will not rise above the surface of the liquid casting mixture; and the pressure bag 7' has sufcient flexibility and extensibility to carry its diaphragm wall up to the under face trusion block to admit the said prescribed quantity of wax. It results from these factors that, even though the streams and ribbons of wax might flow more easily and rapidly through the passageways in the middle area of the block than in the peripheral parts, yet ultimately the cores extruded from all the passageways will rise to approximately the same height. Where the flow is most rapid, the diaphragm is locally deflected, in principle as illustrated in Fig. 5, until the most advanced portions come into contact with the block; after which the further distention of the bag displaces the wax from surrounding, or other adjacent, areas, until all of the wax in the chamber or space Z has been expelled from such space. When the diaphragm comes into Contact with any part of the under side of the extrusion block, it shuts off the passages in such part, wherefore the remaining portions of the unextruded wax body can enter only the passages which still remain uncovered.

Thus the extruded core rods are made all of nearly the same length and height, which is sufficient to bring their upper ends above the solid body of the casting when the suspended particles of cement have settled, but all are below the level of the water layer which then overlies the sedimentary block. The value of this feature is that the buoyancy of the extruded rods holds them from deflection, and that the passages resulting from their core effect extend throughout the thickness of the final casting, straight and `duce undesirable effects in the case of hollow articles made by transfer of pulp from ay body or mass of pulp by suction. The less resistance to escape of water through the shorter passages would cause deposit of pulp to greater thickness in the deep parts of the mold than in the higher or shallower parts. To prevent this, and make the passages of the same or approximately the same length in all parts of the mold, the back` may be carved with contours the reverse of those in the face. Thus for instance, ifv a mold like that shown in Fig. 8 is sotreated, the back would have the same contours as the mold shown in Fig. ll. Obviously a mold of any shape or formA may thus be 4made by any desired manner or means of carving.

What I claim and desire to secure by Letters Patent is:

1. The method of producing perforated molds which consists in providing a block having a plurality of passageways opening through its upper surface, placing a frame on the upper surface of such block, pouring a fluid cement; mixture into such frame, forcing a plastic substance through the passages of said block and upwardly therefrom through the fluid cement in the superposed space, said substance having stiffness and cohesion sufficient for penetration through said fluid cement and to maintain its extruded shape, and, after solidification of the cement, discharging the masses of plastic material therein so as to leave open passageways.

2. The method of making perforated molds which consists in providing an extrusion block with passageways opening in one face thereof, mounting the block with such face substantially horizontal, providing a body of extrudable plastic material having stiffness and cohesion sufficient for penetration through the aftermentioned cement and to form the after-mentioned cores, adjacent to the opposite ends of such passageways, conning a body of fluid cement mixture in contact with the substantially horizontal face of said block, and applying pressure to the extrudable material suicient to cause flow thereof through the passageways of the block and extrusion from the block as cores which are advanced through the fluid cement.

3. The method as set forth in claim 2 combined with the further step of carving the cement mass and the contained cores after solidification of the mass, and then removing the cores.

4. The method of making perforated molds which consists in providing a mass of fluid cement, placing cores in such mass extending through from one face to an opposite face thereof while fluid, allowing the mass to solidify, carving a face of the mass and the portions of the cores which lie in and near such face, and removing the cores.

5. The method of producing perforated molds and the like, which consists in placing a quantity of solidifiable fluid material in a confined space, extruding through such material, from one boundary of the space containing it, a plurality of cores formed of cohesive material which is liquefiable by heat and, at temperatures below the liquefaction temperature, is plastic with sufcient hardness to maintain the shape of such extruded cores while being forced through said fluid solidifiable material, and, after solidifying of said fluid material, melting and discharging said cores.

NEWTON CRANE.

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