Sintered polymer moldings and composites having altered cross section(s): fluid compacting and sintering process and apparatus for making same

This invention is concerned with high density compacted and sintered polymer articles which previously could not be made entirely non-porous to liquid. It was inevitable, in an article with different parts, that frictional considerations in pressing one part would materially differ from those of another with the practical result that uniformity of density, throughout the article, could never be achieved. Fortuitously, for purposes of making various different parts of an article void free, the density values for each part need not be substantially all the same, but instead need only be raised above a predetermined threshold value. An object of this invention is the preparation of physically dense objects of sintered polymer with multiple parts, such as with abruptly varying cross section, which are uniformly void-free throughout, and of everywhere "theoretical" (reguline) density. Present application discloses simultaneous fluid pressing and sintering of sinterable polymer into high density shapes with multiple parts, recessed sections, and/or varied cross section(s), or attaching and/or adhering the polymer to various rigid materials and/or surfaces. By constraining heated fluid to deform thin sheet in contact with sintering polymer pieces, masses, or assembly, it has been found that the sintered polymer can be formed in multiple parts, of difficult and distributed shapes, recessed and varied cross section, etc., or adhered and/or interlocked to rigid material or surface(s) in faultless and void-free quality, everywhere of highest density. Composites with glossy and distributed surface, and undulating in polymer shape, are consolidated with rigid material the void-free combination benefitting from their respective and distinct individual properties and contours. Formed thin sheet or recessed section moldings per above may be combined integrally with the composites while still retaining void-free quality etc. throughout. Apparatus for producing the moldings and composites consists of one or several sheets of thin material sealed inside a split container composed of corresponding container sections and possible additional ones. Various combinations of single and multiple-diaphragm sets can be assembled for simultaneous fabrication of moldings or composites.

FIELD OF INVENTION 
This invention deals with fabricating special multi-part shapes, 
composites, and combinations from sinterable polymer particles, pieces, or 
assembly where difficulties arise in consolidating and sintering the 
polymer uniformly and completely throughout the final product in highest 
density. Any nominally rigid solid polymer material, of stable and high 
molecular weight, by itself or mixed with other substances, capable of 
being subdivided into particles, pieces, or small masses which physically 
develop mutual cohesion from pressure, and which upon appropriate heating, 
lose identity to become merged irreversibly into a self-sustaining, 
non-frangible solid mass, with physical reduction of polymer free surface, 
is considered to be sinterable polymer as used herein. Such type synthetic 
or other plastic can be consolidated and sintered into strong, properly 
densified, and void-free sintered products, as illustrated in the drawings 
for example, by the method and apparatus of the invention. Some aspects of 
it are the development of hot pressing apparatus and technique by which 
sheet material usually becomes permanently deformed and shaped in contact 
with polymer particles or pieces in what may be tacky condition to 
distribute the plastic in special shapes, or adhere or attach it to rigid 
material. By the suggested procedures, and using described devices, 
sintered polymer composites and other shapes, or combinations, can be 
produced with entirely uniform and void-free quality, having normally 
glossy and distributed surface and undulating shape, never previously 
made. 
DESCRIPTION OF THE PRIOR ART 
Early experiments were made by Cresap to form round shallow vessels from 
poly tetra fluoro ethylene flat sheet by blow forming at high temperature 
with the sheet in the gelled state. Draws up to about one radial depth 
could be obtained without frequent rupture of the fragile gell. With 
release of pressure, however, or reheating to gell temperatures, the 
shallow vessel would spontaneously revert once more to its initial flat 
configuration. This phenomenon, inherent with high molecular weight linear 
polymers, is called plastic memory. From initial solid formation during 
polymerization on through making an article by compaction, sintering and 
cooling, the physical effects of ultra long molecular reorientation and 
readjustment are readily observed, sometimes partial or delayed and on 
other occasions substantially completed. 
Shonka et al (U.S. Pat. No. 2,972,784) encapsulate small bar magnets with 
PolyTetraFluoroEthylene, (TFE) polymer (PTFE), by cold pressing and free 
sintering using a sliding rigid mold and oven, see FIGS. 6 and 9. This 
method is limited to small objects, for as further discussion of Bauer 
(U.S. Pat. No. 2,851,725) indicates below, the single stroke core pin 36 
FIG. 6 of the Shonka patent cannot accurately compress the thinly covered 
middle along with the more thickly covered ends FIG. 10 in this mold 
unless these thicknesses are essentially not much different. This is 
particularly true under Shonka's express condition, which is applicable to 
all solid preforming operations, to prevent slippage flaws, "without 
substantial flow" of or between powder particles. Furthermore, experience 
has shown that in free-sintering PTFE over a rigid inside core, its 
overall length need hardly exceed more than several inches before 
fractures, porosity, and usually complete breakage occurs as sintering and 
cooling effects become increasingly more pronounced relative to a 
differently or non-shrinking core. 
Reiling (U.S. Pat. No. 2,976,093) describes a sintered PTFE coating 
attached to rigid reenforcing member FIGS. 6, 8 and 18 of the patent. 
Unfortunately, he offers no insight, observation, or leastwise any 
suggestion how to improve on or eliminate the quality problem arising from 
making more than one thickness in the same compacted and sintered polymer 
molding. This is to say, the thicker portions, in Reiling's composites, 
being subject to the same unit pressure as other portions during 
performing "are compacted to a lesser degree and are therefore less dense 
and have a higher void content than other portions," Reiling col 1 lines 
56-61, also FIGS. 5 and 7. 
The thickness-porosity problems of Shonka and Reiling are of profound 
proportions. Technical papers on PTFE and ultra high molecular weight 
polyethylene compare the processing methods of these type polymers to 
those used for powdered metals and ceramics. And on account of particle to 
particle friction, and particle friction against rigid wall, it has long 
been apparent, in the dense type compacted and sintered metal and ceramic 
products, that highest (reguline) density, as well as uniformity of 
density throughout a fabricated article, can only be achieved under very 
special and rare conditions, significant variation throughout taking place 
most generally. 
For example, Kingery, Bowen and Uhlman, Introduction to Ceramics, 1976, 
page 10 2nd para state as follows "one limitation is that for a shape with 
high length to diameter ratio, the frictional forces of the powder, 
particularly against the die wall, lead to pressure gradients, and a 
resulting variation of density within the piece." And Sheinhart, 
McCullough and Zambrew, Journal of Metals May 1954 page 515, in article 
Method for Evaluation of Lubricants in Powder Metallurgy, say the 
following "As one progresses through the wall section of any pressed part, 
during the pressing operation, the pressure applied to the die falls off 
dramatically throughout the part. This is, in large measure, caused by 
part geometery--whenever section thickness changes, or when a vertical 
wall changes direction (example to a horizontal from vertical), the 
friction between wall and powder particles changes dramatically." 
Bauer (U.S. Pat. No. 2,851,725) has noted there are serious difficulties in 
trying to mold parts made up of sections with different dimensions. His 
floating piston mold (see FIGS. 4 and 5 of this patent) is capable of 
pressing cylindric and prismatic objects with a common axis of 
compression. The device allows each compressing piston a variable stroke 
whose length is determined by the amount of material placed above it along 
the axis of compression. The statement immediately above of Kingery etc., 
is applicable to Bauer's prismatic molding portions; however, on account 
of die wall friction each part of the molding will exhibit corresponding 
pressure decay, and consequent density impairment, the figures becoming 
lower with increasing distance away from each compressing piston surface. 
Although variability of stroke is rather important, it is only one of the 
factors that must be overcome in filling out and achieving sintered 
uniformity and highest density in more difficultly sectioned multi-part 
shapes. Beakers for example, fluid pressed cold from PTFE, fail to achieve 
as high sintered density between sidewall and bottom (intersection) as 
that found respectively in the portions themselves, see Sheinhart, 
McCullough and Zambrew immediately above. What is evident from the art, 
and unmistakeable by the failures set forth in examples 1, 2, 3 and 5 (see 
Summary) is that, even under circumstances as favorable as Bauer, with 
cold pressing using conformal surface and variable stroke, there are many 
difficult sections as discussed herein (see drawings) that cannot be 
successfully made on account of friction arising between polymer pieces 
etc., and against rigid surface of mold or matrix. 
SUMMARY OF THE INVENTION 
Part of this invention relates to making an object from sinterable polymer 
comprised of more than one part, such as plain and shoulder portions, a 
shape where the cross section changes abruptly in thickness, or at a 
discrete angle etc. Some such changes are characterized as independent 
projections or depressions of polymer cross section incorporated into its 
overall mass and bulk. Sinterable polymer herein is one or a blend of 
several type compatible polymeric substances, of high and stable molecular 
weight, alone, with inert fillers, or mixed with other ingredients, that 
when subdivided into a plurality of particles, pieces, small or partially 
compressed masses, having large free surface (unglazed area to ensure 
cohesion) are able to cohere and agglomerate physically as a result of 
pressure, and which when heated below the major constituent melting point, 
or near or above its transition temperature, maintain shape with the 
subdivided forms losing identity, by reduction of free surface and 
physically diffusing together to become irreversibly sintered into a 
strong, nominally rigid, and no longer frangible solid homogenous sintered 
mass. By previous methods, it has not been possible to mold an article 
with more than one part, and at the same time achieve in all attached 
portions a uniform, faultless and void-free high quality comparable with 
that of the simplest portion. When heated fluid under pressure is applied 
to polymer pieces at or above their sintering temperatures, the steps of 
compaction and sintering, always separately and individually performed in 
molded and sintered polymer products of the prior art, are simultaneously 
merged becoming one and the same. Pore generation by polymer chain 
readjustment, disorientation from close molecular juxta position at 
contact surfaces, and other linear high polymer dimensional effects of 
plastic memory are eliminated or greatly reduced. By containing fluid 
under pressure, and heated near or above the polymer transition 
temperature, or near but below its fusion point (as may be applicable), on 
thin sheet, a conformal surface is produced by the deforming sheet that 
faultlessly, and without creating voids or fractures, distributes and 
shapes the coalescing particles or pieces into recessed section etc. above 
described. 
Another part of the invention is to cause sintering polymer to become 
adhered to surfaces, projections, or depressions of rigid material by 
application of hot fluid under pressure, sometimes against a deforming 
thin sheet which distributes and properly densifies the polymer throughout 
its entire void-free molded mass. In addition, the permanently deformed 
thin sheet strongly adheres to, and faithfully reproduces the undulating 
shape and distributed polymer surface to which the minutely conforming and 
congruently shaped sheet becomes attached. To take advantage of the 
reenforcement, the deformed sheet offers a soft hot molding, the former 
should not forcibly be peeled away from the latter until cooling has well 
progressed. 
A further object of this invention is to make composites based on these 
shapes of void-free sintered polymer, which interlock and/or adhere it to 
rigid matrix material, in undulated shape and normally glossy, reflective 
surface. Where the thin sheet material may be desired adhered to the 
composite, the resulting unified aggregation consists of more than two 
elementary constitutents in void-free union, no reason existing for 
forcible removal of the adhered sheet. 
Apparatus to carry out the invention consists of a split container and one 
or several diaphragms. In a certain embodyment one part of the container 
retains the polymer (and matrix if used) and the other part seals the 
margins of the sheet in order to hold the fluid on the diaphragm. In 
another type only diaphragms may be used in contact with the polymer (and 
matrix if present), the fluid being contained on each diaphragm 
simultaneously with the others. Different combinations of each may be put 
together for the multiple production of several objects, two diaphragms 
being placed back to back over a single container part, or as may 
otherwise be suitable. 
By such apparatus and method it has been possible to mold sintered polymer 
attached to rigid material to make a faultless and void-free composite 
with undulating shape, distributed and normally glossy surface. Such a 
composite, or molding, is of uniformly perfect quality throughout, in all 
its parts, being entirely free of voids, liquid permeating porosity, 
incipient and actual flaws, fractures, crazes etc. Its fluid pressed 
parts, immediately obvious to the skilled observer, are relatively 
undulated and gently rounded, seldom truly planar-exactly flat, nor 
uniformly curved at a constant radius. Their normal surface texture is 
reflective and glossy, and never retains the granular surface analagous to 
fine sandpaper (like moldings which are cold pressed). Surface conditions 
of thin sheet and rigid mold are reproduced in the molding surface (in 
mirror image). Contamination by dust, dirt, corrosion, heat decomposed 
deposits, or sizes are unavoidably impressed and baked into the sintered 
polymer to discolor its surface and mar its usual texture. The composites 
provide a combination of physical properties that neither constituent 
could have alone. Significant adhesion results between matrix (rigid 
surface) and polymer by close molecular juxta-position and from surface 
roughness. Several polymer layers may be consolidated. Adhesion may be 
supplemented by mechanically interlocking the polymer and rigid material 
with independent projecting part systems involving properly sintered and 
densified polymer. Thus the polymer may be attached to one matrix (or 
several) by part extensions of polymer, into the matrix, by extensions 
around an extremity, by abruptly thicker polymer extensions, or by 
interlocking sections with discrete angular changes or curvature. 
Generally speaking, the interlocking of sintered polymer parts to rigid 
matrix material involves shaping projections outwardly from the mass or 
bulk polymer which extend into congruently contoured and independent 
depressions within the matrix material. Of course, the rigid material may 
have the projected sections, instead of depressions, in which case 
corresponding and congruent depressions are formed within the bulk of the 
sintered polymer. Variation of projecting part cross section may be 
effective to increase and make more effective the interlocking, curvature, 
complete or partial reversal having corresponding benefits.

DESCRIPTION OF EMBODIMENTS 
It is an object of the invention to mold sinterable polymer into an article 
with different parts such as having at least one section with abruptly 
altered thickness, one or more sudden change of direction, or a 
combination of thickness and directional change of cross sectional 
features, while maintaining uniform and void-free sintered quality 
throughout the entire article. The multipart geometrical sections or 
portions referred to herein, sometimes loosely referred to as shoulders or 
recessions, may be characterized in some instances as having at least one 
projection or depression made integral with the rest of the sintered 
polymer part body or mass. 
By sinterable polymer is meant any high molecular weight solid capable of 
self diffusion and becoming what may be described as tacky at suitable 
elevated temperature, while still retaining shape and chemical stability, 
which may be constituted as subdivided particles, pieces, small or 
partially compacted masses, such subdivisions developing cohesion with one 
another as a result of compacting pressure, and becoming irreversibly 
drawn together by heating, with large reduction of free surface, losing 
their individual identity, to form a single strong and dense solid mass, 
of no longer frangible nature. It is customary for sinterable polymer to 
be prepared in the form of one pure component, or a compatible blend of 
several high polymers. Sometimes inert fillers may be added, coloring, 
fire retardents, lubricant or other ingredients with specific properties, 
etc., reducing cost or achieving other purposes. 
Another object is to adhere sintered polymer to rigid material or thin 
sheet. 
Still another purpose is to prepare single or combined composites with 
distributed and essentially stress-free polymer attachments, and of 
relatively undulating shape with normally glossy, reflective surface, by 
adhering and/or interlocking the sintered plastic to rigid material, the 
attached polymer parts being entirely faultless and free of porosity or 
voids (liquid non-permeable). Physical attachment can be accomplished by 
several extensions of polymer into separate and corresponding matrix 
depressions. Variations in cross section of projection and depression part 
members can be done in many ways to lock sintered polymer to the matrix 
material more effectively-by reversing polymer direction partially or 
completely around a matrix extremity, discrete angular change of width or 
curavature etc. Where it is desired to adhere a thin sheet to an irregular 
or undulating sintered polymer countour or rigid surface, the invention 
accomplishes this effectively. 
A further part of the invention is to make useful combinations which are 
partly molding and composite together, and perhaps from different but 
compatible polymer constitutents. A unified aggregation consisting of 
adhered thin sheet, polymer and matrix constitutents can be the first 
product, the thin sheet being forcibly peeled away from the basic sintered 
polymer as a matter of choice. 
Another objective of the invention is to provide several type of metal foil 
or thin sheet hot fluid fabricating vessels in which the above and other 
articles can be effectively produced. One purpose of the invention 
concerns application of hot fluid to deform thin sheet to shape and 
distribute sintering polymer into the various shapes and multi-part 
products described here in uniform void-free quality, undulated and 
varying shape, and with normally glossy and reflective surface. Such type 
of device may use only a single diaphragm while other types require 
several, and may be operated, preferably, with simultaneous fluid 
application. The devices may be combined back to back in the same split 
container, etc. (see drawings FIGS. 8 and 9 for some examples), offering a 
number of different combinations for multiple shaping of various kinds of 
moldings by suitable application of the processes of this invention. 
The method of making the products, by simultaneous compacting and sintering 
etc., of course is part of the invention. 
Another purpose is to adhere metal foil or other thin sheet material to 
shaped polymer or rigid material by deforming the sheet material with hot 
fluid, in contact with sintering polymer or rigid material. Because of its 
complex contour and relatively undulated shape, some structural 
reenforcement and additional surface properties may be introduced in a 
recessed molding or polymer rigid matrix composite via the adhered thin 
sheet etc. 
To function properly in compacting and sintering, irreversible physical 
manipulations, a polymer type material must be chemically mature to 
maintain shape near its melting point (has to be fully polymerized), or 
around or above its transition temperature, (stable, high molecular 
weight) and be physically defined initially as solid particles, pieces or 
small masses with large and unglazed surface so as to cohere under 
pressure and densify in a desired shape, and sinter on heating at suitable 
temperature, the subdivided polymer losing identity to merge by diffusion 
and sticking together, with large reduction of free surface, irreversibly 
into a strong, no longer frangible mass. The basic characteristics of a 
sinterable polymer are: 
(1) Nominally rigid type polymer for performing into a shaped article, 
(2) Divideable into physical form of high surface area, 
(3) Exhibits irreversible coherence and densification under physical 
process of applied pressure, 
(4) Chemical stability to maintain rigid shape hot-high molecular weight, 
(5) Apparent hot tackiness-tostick to itself, with self diffusion under 
stable high viscosity conditions, via irreversible process of temperature 
induced free surface reduction, with compacted densification and 
generation of non-frangible strength. 
I have discovered that simultaneous fluid pressing and sintering such as 
via a hot thin deforming sheet, is capable of compacting, shaping, and 
distributing sintering polymer particles, pieces or assembly into properly 
pressed shapes without producing voids, cracks, porous areas, or other 
defects at any place within the polymer or at any place of contact with 
the sheet. The amount of consolidation, shaping and distribution of 
sintering polymer depends on filling and pressure, the extensibility and 
inward collapse of a thin sheet also, in addition to thickness and 
conformation of polymer particles, pieces, masses etc. or aggregate in all 
its parts, on the bulk physical properties of constituents, and 
configuration of rigid matrix or retaining mold surface(s). The interplay 
of these manifold factors results in an irregular and undulated shape 
being achieved which, although proceeding continuously, reflects these 
factors somewhat differently yet characteristically, along with specific 
geometry as well, at each and every infinitesimal area of the sintered 
product. Generally speaking, the amount of permanent deformation, and/or 
inward stretching of the sheet material at each location of the sintered 
molding gives measure of the consolidation, working, distribution etc. 
achieved in each part of a molding. Sometimes in areas of heavy 
deformation, super high densities may be found. The sintered polymer 
always retains a characteristic undulted shape, not flat but at the same 
time randomly irregular, being gently rounded when curved, and always 
continuously glossy and reflective, its internal quality uniform, stress 
relieved, and void-free (to liquid). When used, it is usually quite hard 
to peel the metal foil or other thin sheet (from sintered polymer surface) 
which adheres strongly to the polymer, and conforms completely and 
minutely to its distributed contours. (Quenching sometimes will serve to 
strip away partially.) If a normally reflective and unmarred surface is to 
be achieved on the sintered polymer, any thin sheet and mold surfaces must 
be smooth, clean, and free of contaminants. When shaped and distributed in 
this way, the polymer appears to exist in an essentially stress relieved 
condition relative to constraints imposed by rigid mold, matrix, or 
adhered surfaces, simultaneously pressed and sintered, and later cooled. 
Composites combine the best features of sintered polymer and rigid matrix 
material in a uniform single piece, having the strength of stainless steel 
combined with the chemical inertness of PTFE for example. 
From the results described in Examples 1, 2, 3, 5, 6 misc., and 7 (see 
summary of conclusions) and other experimentation using conventional 
methods done by the inventor, but not reported here, it is demonstrated 
that sintered polymer articles of the prior art resembling these herein, 
and when not grossly defective to the eye, do not possess comparable 
undulated shape nor a glossy surface. And importantly these two qualities 
go more than skin deep, for these inferior imitations are always found to 
have defective density (porous parts) and lack consistent uniformity of 
parts from one cross sectional location to another in the article. 
Although live elastomer blocks or thin elastomeric diaphragms operating 
under cold fluid overcome locally variable stroke per Bauer (see 
Description of Prior Art), the added frictional factors between subdivided 
polymer, multi surfaced, rigid elements, with inter-sections in complex 
geometries of a multi-part article, generally defeat these expedients of 
the prior art in producing these objects. While it may be effective, in 
cold pressing some geometrical features to apply several times the usual 
pressing intensity, the use of brute force, so to speak, raises the level 
of frictional forces which have to be overcome, to oppose and defeat the 
uniformity and high densities sought in the first place, same remaining 
inevitably beyond reach. And as noted in the Prior Art discussion of 
Shonka, the criterion "without substantial flow" between particles must be 
retained at all times, if cleavage fractures are to be prevented in the 
sintered product. Of course, pressure equipment is costly, and even mere 
schedule 80 pipe with modest 500 to 1,000 psi ratings can be expensive to 
obtain and keep in operable condition. What is needed to make the new 
objects is a device and procedure which can overcome frictional defects 
between polymer pieces, rigid molding elements of specific geometry, 
effectively transfer heat, distributing polymer mass, and relieving stress 
as well. Simultaneous fluid compacting and sintering such as via a heated 
and deforming thin sheet, for example accomplishes this result. 
The quality of sintered polymer article may be determined in a number of 
ways, density, dielectric strength, torsional modulus, and by measuring 
other physical properties. Since density is a common criterion, and the 
one most used here, some of the factors that effect it should be 
discussed. The density of a sintered polymer article depends on the size 
and character of polymer pieces from which it is compacted, crystallinity 
of polymer, size of article, conditions of fabrication like molding 
pressure, sintering time and temperature, cooling rate etc., (in most 
experiments given here cooling took place naturally in air, usually in 
about an hour or slightly longer at an estimated rate of 
4.degree.-7.degree. F. per minute). In actual use, the all important 
feature is to attain a uniform, faultless, and void-free material, 
throughout the various parts, for otherwise the polymer in the shaped 
article will tend to leak liquid (being porous in places), or electricity 
and fail prematurely under physical stress. Far apart and tiny gas 
molecules often penetrate between gigantic macro-molecules of a high 
polymer mass, perhaps as hydrogen is known to pass through palladium 
metal. Liquids do not show such anomalous behavior; the term void-free as 
used herein refers to non-permeation of sintered polymer masses by liquids 
only. This is to say a minimum specific gravity must be achieved in all 
parts of a molding, at every location, at least 2.15 for PTFE particles 
averaging 35 micron size (assuming usual crystalinity for this form). A 
density below 2.15 would point to some degree of porosity and questionable 
quality; for the PTFE coagulated latex of tiny mass, (extrusion grade) a 
minimum of 2.19 has been used; and 2.12 is usual for the coarsest type 
PTFE usually encountered. With high (ultra) molecular weight polyethylene 
(high density) one kind would have a minimum figure of 0.93, FEP Teflon 
2.14, and polyphenylene sulfide 50% asbestos 1.67. 
The Commodity Standards Division of U.S. Dept. of Commerce has set up 
standards for various poly tetra fluoro ethylene products. The density 
range for non-porous premium grade sheet is 2.15 to 2.20, figures based on 
ASTM procedures and subject to normal experimental fluctuatuions etc. As 
noted in above paragraph, fine powder extrusion grade polymer would be 
expected to give normally higher densities than 35 micron and larger 
particle forms of commercial poly tetra fluoro ethylene; and common platen 
pressed sheet, too, shows place to place density variations, owing to 
inequalities in filling and pressure application via a rigid platen, 
usually equalized with fluid compaction procedures herein. 
Of course there is extreme variation in mass between different forms of 
sinterable polymer materials. Chopped slugs of roughly 1/8 inch long FEP 
Teflon are estimated to be at least one hundred million times heavier than 
0.6 micron coagulated latex particles of PTFE fine powders. Filled pieces 
of sinterable material can be similarly massive, while air classified 
dusts may be comparably minute. 
Large moldings seem to require somewhat less pressure for molding than the 
smaller ones, to achieve the same density, and in fluid pressings, there 
may be a tendency for specific gravity to improve, sometimes according to 
the distance from the mold center. In practicing this invention, the 
degree to which foil or plastic sheet or polymer undergo working and 
deformation, reduced by high frictional factors in particular shape, 
appears to determine the ceiling of density in any particular parts of the 
molding. A procedural, factor that often produces densities well over 2.15 
with 35 micron PTFE particles involves the stepwise application of fluid 
pressure at just the previously determined right intervals of the heating 
cycle via practical experience with a particular mold set up, see example 
3. Of course, in a large molding, conditions vary from one location to 
another, and in time, as do the effects of pressure, not to mention 
features involving special geometrics. And furthermore, experience has 
shown in determining specific gravities that the normal fluctuations from 
experimental and statistical factors can never be entirely eliminated, 
even in the same parts or a molding. Suffice it to say that while the 
density of a sintered piece may be expected to vary and change in various 
parts of the molding, it cannot, for purposes of adequate quality be 
allowed to fall below a minimum value (for each type and piece or particle 
size of polymer). Furthermore, no faults, cleavages, or flow weaknesses, 
discontinuities, etc. some visible under light or X-ray can be allowed. 
Specific gravities were determined experimentally with an analytical 
balance at room temperture (about 68.degree. F.), in each of the examples, 
using distilled water and working to four places. In the case of example 
6b, ethyl alcohol was substituted. 
The shaping of sinterable polymer by deforming heated thin sheet in contact 
with the sintering material requires basically a heat resistant split 
container and an appropriately selected metal or plastic in thin section. 
Naturally, a source of high pressure heat resistant fluid is needed as 
well as some kind of heat source to maintain high temperature. Good 
tensile elongation and extensibility are the properties appropriate for 
the thin sheet, the newly discovered super plastic metal alloys permitting 
fabrication of large and very deep shapes, and perhaps low strength 
reducing some what the level of fluid intensity needed for compaction. 
Generally speaking, an increase in available elongation is provided by 
raising the thickness of the foil or plastic sheet. For smoothest polymer 
surface, the finish of the sheet material must be of high quality and 
scrupulously clean-from all dirt, size, or physical imperfections, all of 
which becoming unavoidably impressed upon the polymer surfaces, faithfully 
and in mirror image. 
I have found that soft aluminum, with its 650.degree. F. recommended 
annealing temperature, is ideal for working PTFE with crystaline 
transition point of 621.degree. F. In example (1), six consecutive foil 
ruptures were reported for cold fluid pressing whereas a single trial was 
immediately successful when fluid and foil were both heated in the 
650.degree. F. range. Industrial aluminum foil is available in 5-12 mil 
thickness. Copper is another foil that is suitable, and new alloys of 
aluminum and titanium are under development with elongations of tenfold 
and over which promise unbelievable versitality. 
Teflon sheet is available in 1/32 inch thickness and serves well as a heavy 
duty diaphragm with a temperature limit of perhaps 600.degree. F. or 
somewhat higher. Repeated tightening of the sealing surfaces may be needed 
to offset creep. By retaining the margins and "brushing" with a low 
temperature and bushy flame, a Teflon sheet may be vacuum formed just like 
cold metal foil. A draw limitation of one to one, depth to radius can 
usually be accomplished without fear of rupturing this plastic sheet. Most 
any other distensible sheet material can be used if it can resist the 
temperatures and remain impervious to the hot fluid used. 
The container for holding hot fluid against the diaphragm, and retaining 
the polymer as required etc. must be a pressure vessel of split 
construction to allow for insertion of polymer or assembly, and 
subsequently to permit removal of the article. In addition, on account of 
its usual permanent deformation, the used diaphragm, when and if detached, 
cannot under most circumstances be employed again. The margins of the 
diaphragm may be effectively sealed between hard flat surfaces. If 
desired, a raised face of appropriate area is useful for bringing the 
gasket loading to proper levels, and consistent with the magnitude of 
fluid intensity to be used. The actual pressure selected for properly 
deforming the diaphragm and working the sintering polymer depends on the 
nature and form of the particular plastic used, the foil or sheet 
material, its tickness, and the temperature at which the operation is 
conducted. A much lower intensity is needed for hot deforming a metal foil 
or thin plastic sheet in shaping sintering polymer than what is usual for 
cold pressing work. A split container made to the specifications and 
temperatures usually encountered for extra heavy pipe and fittings is 
often adequate for construction design of the apparatus herein. 
Devices for fabrication of several objects at a time are shown in FIGS. 8 
and 9. Two formed thin sheets 18 FIG. 3 are placed back to back on ring 64 
FIG. 8 to permit fabrication of two single sided composites 10 FIG. 3 with 
the same application of hot fluid acting on each 62 and 63, 
simultaneously. In FIG. 9, two sieve plate composites 41 FIG. 7 are made, 
each with its own diaphragm pair, 78 and 79 FIG. 9 and 76 and 77. Foils 76 
and 79, comprising parts of adjacent pairs, are positioned back to back on 
ring 74. Such construction reduces the number of parts needed to complete 
the split container. In using devices with more than one diaphragm, it is 
well to make certain that equal and simultaneous application of fluid 
takes place on adjacent diaphragms of the same molded piece. If an 
imbalance does arise, the molding or composite may be injured in addition 
to damaging the diaphram(s). Such a condition can always be prevented by 
connecting together the corresponding passages of split container 
portions, 75, 80 and 81 FIG. 9 for example. 
Summary of Conclusions Taken from Examples 
(Example 1). The multi-shouldered PTFE object FIG. 1 made by apparatus and 
procedures here recommended, after being forcibly pried out, was found 
free of faults and showed void-free density of 2.15 or higher throughout. 
It had undulated shape reflected by the tenaciously adhering deformed 
foil, which when forcibly peeled, revealed a glossy and reflective 
surface. The same object pressed cold was found to be cracked; its free 
sintered pieces were broken and non-uniform, and of dubious quality with 
specific gravity 2.13 and 2.14 with granular dull surface. 
(Example 2). A single-sided TFE adhered coating, made by the procedure and 
devices given here, included various parts like sectional features of 
polymer thickness extension, recessed 60.degree. interlock, and recessed 
shoulder interlocking edge with reserse section. The coating tested 2.20 
in density, identical with the interlocking edge sample, with 2.16 for the 
thickness extension, and 2.17 for the 60.degree. interlock; all values 
were above the 2.15 minimum density for PTFE of this type and were 
therefore void-free, non-permeable to liquids. Faults or cracks were not 
present, and the shape and surface were comparable to that reported under 
Example (1). An effort to make the same object by cold pressing under 
fluid pressure followed by free sintering was unsuccessful. 
(Example 3). A covered flat disk with edge reversed bend was prepared, edge 
and flat giving annomolously high specific gravities, (lowest) of 2.22. 
The identical object became cracked and broken in attempts to cold press 
and free sinter this shape. 
(Example 4). An annular ring 31 FIG. 6a was totally encapsulated in 
sintered PTFE and found to be non-permeable to hot acid plating bath, 
after six weeks continuous exposure. 
(Example 4b). A single sided ring composite like 10 FIG. 3, in the form of 
a ring 33 FIG. 6, can be simultaneously fluid pressed and sintered from 
PTFE with recessed shouldered preform FIG. 1 inside its center to produce 
a void-free molding-composite combination 105 FIG. 11. 
(Example 5). A sieve plate composite was prepared and hole samples cut; 
they tested 2.16 density, flat strips 2.15, and edge 2.17, all uniformly 
void-free and faultless in quality. On the same matrix, a cold fluid 
pressed and free sintered composite had been made; hole buttons of 2.14 
density indicating porosity and likelihood of penetration by corrosive 
liquid environments of chemical process equipment. 
(Miscellaneous Examples 6a)., (6b), (6c) and (6d) show that polymers like 
FEP Teflon, HMW Polyethylene, Polyphenylene Sulfide with filler etc may be 
effectively pressed and sintered into recessed sectioned moldings and 
composites, and their combinations, using the methods and apparatus of the 
invention. Compatible types such as PTFE and FEP Copolymer may both be 
sintered together in combination like molding-composite pairs etc., 105 
FIG. 11a. 
(Example 7). Shows that thin sheet material such as Teflon is suitable for 
diaphragms used for hot pressing and sintering with the apparatus used 
herein. Also projecting metal and other independent punched sections etc 
can be used effectively interlocking sintered polymer to rigid material, 
or forming depressions therein. 
(Example 1). It was desired to make the shouldered object 1 in FIG. 1 with 
two adrupt recessions and progressively larger thickness changes 3 and 4 
from PTFE. A metal foil 5 and rigid mold surface 6 were provided and 
housed for operation in split container 19 and 20 FIG. 2. PTFE powder was 
placed in mold 6 and leveled, the flat circle of metal foil 5 being sealed 
there over by placing foil, polymer and mold within the two portions of 
the split container 19 and 20 FIG. 2 and secruing the latter together. 
As the assembly was heated to 621.degree. F. in a salt bath, compressed air 
was applied to the metal foil on the side opposite from the polymer in 
slowly increasing intensity from atmospheric to 1,000 psi (Expt 27). After 
about one half hour, the temperature having risen to 660.degree. F., the 
device was removed from the heating bath and cooled, the air finally being 
released. The piece FIG. 1, which reflected an undulated shape wrapped 
congruently in deformed foil on one side, had to be pried out of mold 6 on 
account of its adhesion to the surfaces of the mold. After peeling away 
the foil by folding backwards and pulling strongly (the thin metal ripping 
frequently), the molding FIG. 1 was found to be free of faults or cracks 
by examination under strong light. The edge density was 2.15, the middle 
2.15, and the center 2.20. A glossy and reflective finish was evident on 
the upper face, and the polymer was observed to be distributed uniformly 
with gently curved intersections above the shoulders, 2, 3, and 4 FIG. 1. 
The experiment was repeated six times at room temperature using the same 
metal foil (5 mil aluminum) and others (10 to 15 mil) annealed etc. and 
under various conditions of prepackaging. In all cases the metal failed at 
low pressure and the piece was not adequately shaped. Finally (Expt. 16) 
the 10 mil foil was made to hold 2,350 psi for proper cold pressing. The 
piece that had been formed, however, was cracked underneath each shoulder. 
Notwithstanding, the faults, the three fragments were free sintered; they 
showed a specific gravity of 2.13 edge, 2.14 middle and 2.16 center. A 
1/16 inch thick rubber sheet was substituted for the foil and 2,500 psi 
applied for four minutes (Expt. 23). The resulting piece was cracked just 
as the previous one, but nevertheless the three pieces were free sintered 
with the following densities determined; edge 2.15, middle 2.14, and 
center 2.15 indicating porosity in the fragments. The surfaces, though 
somewhat curved and distorted, were relatively planar in one direction, 
non-reflective, and had a granulated texture like fine sandpaper. 
For preparing a lightly and cold compressed TFE shouldered preform for 
making molding-composite combinations such as 105 FIG. 11a, a thin rubber 
sheet works well, using a few hundred psi, enough to provide coherence and 
strength of the pre-pressed PTFE for handling. Actual hot fluid pressing 
and sintering the final molding-composite is described in Example 4b. If 
it is desired to incorporate a molding of FEP copolymer as part of the 
composite, a partial sintering is suitable, and the FEP slugs, or a 
mixture of that and TFE powder is charged mold 6, and sintered as above 
using appropriate lower temperatures. 
(Example 2). A circular single sided composite 10 FIG. 3 (approximately 5 
inch O.D.) was consolidated together consisting of polymer cover 11 
adhered and attached to steel disk 12 (Expt. 32). The polymer was anchored 
to the edge by a recessed metal shoulder, having been specially formed and 
distributed in a section of complementary shape 13. Further sectional 
attachments were made by forming the polymer in straight cylindrical 
extension 14 and conical 60.degree. interlocking extension 15. 
A circle of metal foil was cut from sheet and vacuum formed to concave 
shape 18 FIG. 3 by placing it on split container 20 FIG. 2 and pumping 
down the inside. The matrix 12 FIG. 3 was attached to the upper half of 
the split container for convenience (screw 21) and a ring 22, somewhat 
larger and higher than the disk was placed around the matrix temporarily 
for retaining the polymer during packing. The polymer powder was spooned 
inside the ring, tamped down with more added to the hollows over the holes 
and recessed edge, and tamped again several times until a level preform 
had been packed. The packing ring was then removed and the concave foil 18 
placed over the preform 23. Its margin was sealed to the split container 
by placing the lower half 20 over the foil and securing the container 
pieces together (with bolts). 
The assembly was heated over a period of about half an hour to 
approximately 550.degree. F. Then at intervals of several minutes, 
compressed air was admitted to raise the pressure on the foil inside the 
container from atmospheric to 500 psi, the temperature rising meanwhile to 
620.degree. F. After about an hour, the split container had attained a 
temperature of 660.degree. F. and it was then cooled to room temperature 
while maintaining pressure to 500 psi. 
After release of compressed air, the container was opened and the deformed 
foil peeled forcibly off the composite. The polymer cover 10 FIG. 3 had 
been rather evenly distributed in about 1/16 inch thickness, but with an 
undulated configuration. Small indentations 16 were formed over extensions 
14 and 15, and a rounded shoulder was apparent at the recessed extremity 
(circumference) 13 of the composite. These features were reflected in the 
metal foil, of course, which had been deformed in a mirror image of the 
shaped polymer surface. 
Samples from the recessed edge 13, the plain extension 14, and the 
60.degree. recessed interlock 15 were cut from the covering. In order to 
obtain comparative samples of the relatively flat polymer cover, two cuts 
were made about one inch apart and extending across the disk. This strip 
adhered so strongly to the surface of the disk that it could be detached 
and separated only by forcing a thin steel blade into the interphase to be 
forcibly and repeatdly bent upward to get the strip free. Specific 
gravities were determined as follows: plain extension 14, 2.16, recessed 
edge 13, 2.20, flat cover strip 11, 2.20 and 60.degree. recessed extension 
15, 2.17. The polymer cover was rather evenly distributed, being slightly 
undulated and variable rather than exactly flat and planar, and possessed 
a glossy and reflective surface; it was free of cracks and faults as 
became evident from careful examination under strong light, nor were any 
flow patterns or weaknesses detected. 
In order to illustrate the ineffectiveness of other methods, the recessed 
matrix 12 was screwed to a plain flat disk of somewhat larger diameter and 
a preform prepared (Expt. 33) in the manner described above (same example 
2 FIG. 2). The assembly was then placed in a 6 mil vinyl chloride bag and 
heat sealed for pressing. Bag and preform were inserted in a pressure 
vessel and subjected to 2,450 psi air for about four minutes at room 
temperature. The unheated but pressed compact was well densified but could 
be seen to be of different dimensions and configuration than the composite 
10 FIG. 3 above. A sharp ridge had formed above the recessed edge, and the 
piece was straight sectioned from top to side at about 90.degree.. After 
free sintering on a tray for forty minutes above 620.degree. F., peak 
temperature 660.degree. F., the molding was examined (after cooling). The 
bottom face of the polymer edge had been bent upward at 30.degree. or 
thereabouts, from the horizontal, with the recessed edge broken off around 
the circumference. The softness of the edge portion, still underneath the 
steel shoulder, to fingernail pressure indicated gross porosity and lack 
of proper compression of any description. The tearing probably arose from 
excessive shrinkage across the face of the matrix. The polymer was found 
to be detached from the surface of the matrix, and there was no adhesion 
at all, or in any locality between polymer and flat metal disk. 
(Example 3). Fabrication of a completely covered plane disk composite 25 
FIG. 5a required a multiple foil and split container device. The apparatus 
FIG. 4a consisted of two flat circular metal foils 51 and 52, a split 
container ring 53, and two identical split container ends 50. Plane disk 
composite 25 FIG. 5a consisted of PTFE exterior adhered to steel disk 27 
with continuous reverse bend 28-29 where metal projected into sintered 
polymer around the circumference of the disk. 
To make this composite (Expt. 28), a preform 30 was prepared by placing a 
temporary packing ring somewhat larger and higher than Disk 27, on the 
flat surface to permit the tiny PTFE pieces to be leveled off inside, and 
well below the top of the ring. The disk 27 was then placed on the PTFE 
and the ring completely filled, see FIG. 5, the assembly being pressed 
down manually to make a handleable agglomerate 30. This was removed from 
the ring. The second foil 52 FIG. 4a was placed on second split ring 
container end 50, polymer assembly 30 and split container ring 53 rested 
on foil 52 concentrically, and then first foil 51 and first split 
container 50 were placed thereover, the split container sections being 
secured together. 
The container was heated to 500.degree. F. and compressed air was admitted 
to bear upon each foil concurrently in increments of several hundred psi 
at intervals of several minutes. By the time the container had reached 
635.degree. F., the pressure had been raised to about 1,000 psi which was 
maintained at this level for forty five minutes, the peak temperature 
rising to 675.degree. F. After cooling to roughly 250.degree. F., the 
gasses were released and the deformed foils peeled off the composite. 
The total enclosure 25 FIG. 5a had a glossy and evenly distributed polymer 
exterior 26, with undulated, non-planar shape with a peaked edge between 
28 and 29 around its circumference where the rigid metal projected into 
the reverse bent polymer. With difficulty, the tightly adhering polymer 
was pried off and cut in strips for running specific gravity with the 
following results: flat and edge at one location 2.217 and 2.218 
respectively, and at another 2.226 and 2.227. These values are anomalously 
high for 35 micron size PTFE, and with the material, experimenter Cresap 
had never before seen densities this high (comparable crystallinity). 
Examination of the strips and edge in strong light failed to reveal any 
flaws or other defects. 
Another 31/2 inch O.D..times.1/4 thick metal disk was fluid compressed in 
Saran bag at 2,500 psi and room temperature. On free sintering the 
compact, the polymer part was found to have cracked around the entire 
circumferential edge with additional cracking evident on one plane face. 
There was no evidence of adhesion of polymer to the metal surface. 
(Example 4a). The annular ring 33 FIG. 6 with plain holes 35 drilled 
through, was assembled for total encapsulation with TFE polymer 32 to make 
the covered torous 31 by the procedure used for disk 26 FIG. 5 in Example 
3). immediately preceeding. 
The aggregate 40 was lightly compressed at room temperature in a Saran bag 
with 500 psi air. Then it was placed in the split container of FIG. 4a). 
comprised of two ends 50 and ring 53, and between foils 51 and 52. After 
securing the container, 100 psi air was applied simultaneously to the 
exterior of each foil and the assembly was immersed in a salt bath heated 
to 700.degree. F. After 20 minutes the pressure was raised to 300 psi, the 
container having heated to 600.degree. F. and the pressure was raised to 
450 psi. Fifteen minutes later the vessel had reached 620.degree. F. and 
the pressure was raised to 600 psi and held for twenty five minutes, peak 
temperature 660.degree. F. The compressed air was vented and the piece 
removed. 
Composite 31 FIG. 6a had a smooth glossy finish with rounded and peaked 
edges 36-37 both on the interior edge as well as the outside circumference 
where matrix extremities extended into the reversed sectioned polymer. 
Where holes had been, the polymer apparently flowed in leaving slightly 
and gently curved depressions 34 on each surface. The foil had been 
deformed and stretched tightly over the undulating faces and rounded 
extremities inside and out 31 FIG. 6a. Where the two foils came together, 
a blunt edge was formed 36-37. The foil adhered strongly in exact and 
conforming undulating contour to the polymer composite. Since the 
composite was desired without thin sheet adhering thereto, this was peeled 
back and delaminated by pulling heavily backward. Sometimes the foil 
strength was exceeded, portions tearing off and remaining adhered, 
indicating bond strengths exceeding the foil tensile strength. The torous 
was immersed in 135.degree. F. acid chrome plating bath (H.sub.2 
SO.sub.4), where it remained for six weeks. Upon removal of the ring 
composite it was cut apart to inspect for evidence of attack from the 
corrosive environment. There was no evidence of metal attack nor of any 
kind of fluid penetration or any corrosion etc. 
(Example 4b). It is an easy matter to make a combination molding composite 
having special features, say of a recessed molding, and the combined 
structural-polymer characteristics of a particular composite. In order to 
make shoulder molding-single sided disk composite combination 105 FIG. 
11a, unfinished molding 1 is first prepared as indicated in the last 
paragraph of Example 1), page 17. Plane flat disk of Example 2). is bored 
slightly larger in diameter than the second shoulder 3 FIG. 11, and 
centrally located, to form ring 33 into which the molding 1 is introduced 
to produce article 105. A centering ring 111 is made to fit into the bore 
of the ring on its outside while having an opening on the inside to fit 
shoulder 4 of the molding. The ring 108 (33) is attached to mold 19 FIG. 2 
by screws (tapped holes 109) and spacer ring 111 is dropped into ring 108 
around its center. The procedure of Example 2)., the third and fourth 
paragraphs page 24 and first and second paragraphs page 25, using mold 19 
FIG. 2 are applicable with the following exception. Instead of charging 
PTFE powder above the spacer ring 111, the lightly pressed unsintered PFE 
pre preform of the shouldered molding FIG. 1 (from Example 1 above) is 
first placed over the spacer ring 111 to complete this part of the piece. 
The PTFE powder is spooned only to the area outside the extremity of the 
molding 1 at the shoulder 2 FIG. 11, since what might be otherwise needed 
inside has now been provided by the molding preform itself, 1 FIG. 1. 
Molding-composite 105 FIG. 11a has the recessed shouldered molding 107 
within the ring 108 (33) with interlocked and adhered polymer 106 
continuing inward across the ring surface to become integral with, and a 
part of, the central recessed molding 107, all with usual contour and 
glossy surface features, void-free quality, lack of faults etc. 
(Example 5). A one eighth inch steel circular plate 31/2 inch O.D. 43 FIG. 
7 was drilled with twenty seven 11/32 inch holes arranged on equilateral 
triangular centers 9/16 inch apart, to make a sieve plate matrix for a 
distillation column. Two somewhat larger circles were cut from 5 mil soft 
aluminum and vacuum formed to concave shape 54 and 55 FIG. 4b. Instead of 
using one split container ring 55, two identical half thickness rings 56 
were substituted, in order to seal the margins of the foil as will be 
described. 
Second foil 55 was placed over one ring 56 which was rested on second split 
container end 50 using a foil gasket. Powdered PTFE was sifted and leveled 
in the concavity of the foil 55 and matrix 43 was laid on the powder 
surface after which a second portion of PTFE was sifted on to cover the 
matrix and its edges. After wiping the excess from the foils flat edge, 
the first foil 54 was placed over the second foil 55 with the powder and 
burried matrix within the concavity of the foils. First ring 56 was placed 
over the margin of the first foil 54 and first split container end 50 put 
thereon (with foil gasket), the container assembly being secured together. 
Heating of the split container was started and after twenty minutes the 
temperature had risen to 515.degree. F., 100 psi compressed air was 
applied concurrently to each foil. After one hour and a number of 
successive pressure increases, the temperature of the split container 
reached 622.degree. F. and the pressure inside was 1,000 psi. Eighty 
minutes later the container had reached 650.degree. F. and the heating was 
discontinued. After release of the gas, the container was opened and the 
molding withdrawn with the deformed foils tightly adhering to it. After 
removal, a high gloss and well distributed molding 41 FIG. 7 was apparent 
with undulated surfaces and rounded and blunt edge circumference. The 
polymer material in the holes 44 were cut out with a cork borer to make 
test buttons. Also the outside faces with cut holes from the cork borer 
were laboriously pried free of the matrix and made into strips, keeping 
portions from the same location together for test purposes. Edge sections 
were taken similarly. Specific gravity measurements were as follows: 
buttons 2.16 and 2.16 (two locations), hole strips 2.15 and 2.15 
respectively, and the edge strips 2.17 and 2.17. No faults or cleavages 
were found. 
The same matrix had been covered with PTFE and pressed previously in vinyl 
bags at room temperature under 3,000 psi air, being sintered thereafter 
under typical conditions (Expt B-7 261). The average specific gravity was 
2.14 for bottons taken from the holes while the flat hole strips averaged 
2.16, porosity being indicated in the hole polymer. The hole strips and 
other exterior portions did not stick or adhere in any way to the 
stainless steel matrix. 
Miscellaneous Example 6a). A sieve plate composite 41 was prepared from FEP 
Copolymer pieces, the standard form of this material. The 1/8 inch long, 
or so, roughly cylindrical slugs were placed in the concave foil 55 FIG. 
4b in comparably the same manner described for Example 5 (second paragraph 
page 29). A 31/2 O.D..times.1/8 inch thick matrix 43 FIG. 7 was used with 
double foils 54 and 55 FIG. 4b. 
The bolted apparatus FIG. 2 was heated in a 620.degree. F. molten salt bath 
for fifteen minutes, compressed air at 200 psi applied, with the 
temperature rising to 495.degree. F. In twenty minutes following, the 
pressure was raised in steps to 800 psi and the temperature of the 
pressing rose to 575.degree. F. after which it was removed and allowed to 
cool in air. 
The translucent and faintly milky composite, perfectly formed, was examined 
for flaws under strong light to see there were no bubbles, faults, cracks 
or voids etc., and that all matrix holes contained only sintered polymer. 
A segment of polymer was sawed to metal, cut off and pried away to check 
results further. Besides having an undulated shape, a somewhat varigated 
surface outlining and reproducing somewhat the form of the original 
polymer slugs had still been retained. The surface was glossy and 
reflective, none the less, and undoubtedly could have been made smooth by 
adapting the temperature, time, pressure sequence. 
Miscellaneous Example 6b). Another sieve plate composite 41 FIG. 6 was made 
almost identically to Example 5) and 6a) using ultra molecular weight 
polyethylene (range 2-4 million, High Density). This was pressed about 
half an hour at 550.degree. F. and 800 psi with cooling at 1,500 psi (Expt 
38). The white, translucent milky, smooth and undulated surfaced composite 
on an aluminum matrix was very light in weight and found to be perfectly 
formed. Buttons, hole strips, and edge sections showed specific gravities 
of 0.930, 0.932, and 0.930 respectively, (immersion in purified ethanol) 
with previously pressed samples indicating 0.932 (manufacturer). 
Miscellaneous Example 6c). A still further composite sieve plate was 
prepared as above by sintering poly-phenylene-sulfide resin 50% asbestos 
filled. The pieces of this resin were brown lumps about the size of the 
FEP Copolymer slugs, though not identically shaped, of course. A matrix of 
hot rolled steel 1/10 inch thick.times.31/2 O.D. was selected, and the 
same procedure used as in the other of these Miscellaneous Examples 6). 
The mold assembly underwent the sintering operation for about a half hour 
at approximately 625.degree. F. and 1,000 psi with atmospheric cooling at 
1,500 psi. The composite was found to be perfectly formed, and a segment 
of the hard brown sintered plastic had a density of 1.65. 
Miscellaneous Example 6d). To make a molding-composite type product from a 
combination of several sinterable polymers, of compatible nature, the 
following procedure is used. A mixed TFE and FEP, or straight FEP 
Copolymer recessed shoulder molding 1 FIG. 11 is either partially or 
completely sintered according to procedure of Example 1) last para page 
23, et seq. This portion is then sintered as a mass with other pieces of 
PTFE as in Examples 4b to obtain the composite-molding combination 105 
FIG. 11. 
Molding-composite combination 105 FIG. 11a in this example consists of 
matrix ring 108 covered by attached and adhered PTFE sintered polymer 106 
over exterior edge and faces extending inwardly to join and unite 
integrally with FEP copolymer recessed section molding 107, molded 
centrally within ring 108. In instances where polymer sheet material is 
used for the final fluid pressing and hot sintering, and may be retained 
and not stripped away, the resulting void-free aggregation can consist of 
more than two different polymer types etc. 
(Example 7). HMW Polyethylene Composite 95 FIG. 10a was made from 
1/8.times.31/2 inch O.D. aluminum matrix 90 and coarsely ground pieces of 
polyethylene. Feature 91 comprised several partial through punchings, 92 
and 93 projecting steel screws, and 94 several 11/32 holes. The thin sheet 
diaphragms were cut from 1/32 inch thick Teflon sheet which had been flame 
formed under vacuum by "brushing" with a propane torch to shape to form 54 
and 55 FIG. 4b. These were practically identical to cold formed metal 
foils of the previous Examples. 
The ground pieces and matrix were placed properly in the Teflon diaphragms 
as described previously and the apparatus heated for half an hour or 
thereabouts at 530.degree. F. and under about 1,000 psi air. After cooling 
under increased pressure, a segment of properly formed composite was 
selected which revealed the material under the rigid screw heads 98 and 99 
and extended punched metal 97. By sawing, prying, twisting, and cutting, 
the immediate cross section of polymer was parted and inspected to 
determine if it had been properly formed, the particular pieces being too 
small for gravimeteric density determination. The sintered polymer was 
found to be strongly attached and had to be stressed heavily beyond 
failure before removal. A yellow surface discoloration was present over 
the polymer surface, probably from a size or organic film left on the 
Teflon sheet, but his was readily scraped off with a knife. The plastic 
sheet had extended inwardly at hole locations 96 and stretched over screw 
projections 96a reflecting and undulated shape but still comparable with 
the composite inside, and in corresponding detail. 
While there are described herein certain embodyments of this invention, it 
is understood to be capable of many variations and modifications. Change, 
therefore, may be made in its various manifestations without departing 
from the spirit and scope of the invention and the claims which follows 
herewith.