BE635166A - - Google Patents

Description

       

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  "Porous metallic bodies and their manufacturing methods".



   The present invention relates as a whole to powder metallurgy and in particular relates to powder metallurgy processes for manufacturing porous or non-porous bodies of various metals such as aluminum and aluminum alloys.



   The technique of powder metallurgy relates to the manufacture of objects by heat treatment of compressed metallic powders, powders which may also contain non-metallic substances or bodies.



  This technique can be applied to elementary metal particles or to complex mixtures of particles. In many cases it is possible by means of powder metallurgy techniques to produce products having properties which cannot be obtained by conventional melting and molding methods. Thus, it is possible to

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 manufacture filters, self-lubricating cones and bearings as well as many other porous or compacted objects.

   Although the present invention is described with reference to the manufacture of porous aluminum alloy bearings, it is obvious that the principles of this invention can be easily applied in the manufacture or making of other products and can be applied. applied to other kinds of alloys such as those which include magnesium or titantum as the base metal instead of aluminum.



   The classic practice of manufacturing self-lubricating bearings consists in compressing metal powders such as a mixture of tin and copper so as to obtain a green agglomerate which is then sintered to obtain a porous body with an adherent structure. Percentages of graphites and volatile organic compounds are generally included in the powder mixture in order to allow control of porosity during the sintering operation. The resulting porosity in the sintered bearing can be up to 90% by volume. After forging the sintered bearing so that it reaches its final shape, it is impregnated with oil. During operation, the oil exudes from the pores of the bearing, and lubricates the shaft it supports.

   As the bearing heats up the amount of oil flowing out increases so that a lower operating temperature is obtained which promotes an increase in the effective life of the bearing.



   While porous iron or steel bearings as well as bronze bearings are in common use, porous aluminum bearings have not heretofore been commercially available, due to the special problems involved. the manufacture of porous aluminum or

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 its porous alloys. These problems are due to certain characteristics of aluminum.



   . As is well known, particles. Aluminum exposed to air forms an adherent oxide film of a refractory nature, which hinders the flocculent sintering of the particles. To overcome the resistance due to the presence of this oxide film, attempts have already been made with a view to sintering aluminum powder mixture in em.

   employing relatively high compaction pressures, these pressures ranging from 3,150 kg / cm2 to 9,450 kg / cm2. However, since aluminum is a soft material which sinks easily under pressure, the application of the high compaction pressures has created difficulties in making pores continuously connected together capable of providing a reserve of. suitable oil and impart lubricating properties essential to the manufacture of bearings.



   Another serious problem encountered when using high compaction pressures is that the die walls catch particles and ultimately seize when there is no wall lubricant. While such sticking can be reduced, die wall lubricants are used; this materially increases the production costs because the dies then have to be wiped clean and on the other hand the tolerances are more difficult to control. On the other hand, when in previous tests lubricants such as stearates were mixed with the powdered metal, discoloration, oxidation and lower strength of the compacted powder resulted when sintered.



   Another attempt to obtain porous aluminum alloy bodies has been to employ elevated sintering temperatures above the liquid phase.

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  The disadvantage of this method is that it results in excessive shrinkage and deformation of the parts. Mainly, when solid state sintering has been tried on aluminum alloys, at temperatures below the temperature of formation of the liquid phase, this has complicated oxidation problems because the The use of prolonged sintering times made necessary by the lower diffusion at low temperatures causes more oxidation per unit volume of powder. Another factor which has worked against the success of the realization of porous aluminum bodies is the inclusion of relatively fine powders (passing through a 130 mesh / cm sieve) in the mixture.

   This has been found to be one of the main reasons for sticking by the die walls as well as oxidation during sintering, simply because of the large surfaces presented by fine powders. such finely divided powders are risky as they tend to explode and combustions may occur during normal production.



   Thus, while many attempts have been made heretofore to make porous bodies made from mixtures of aluminum, the measures taken to solve the particular problems have served only to create new problems and the results have been limited. origin of a commercial failure.



   Consequently, one of the essential objects of the present invention is a new and efficient process for manufacturing aluminum products, this method being inexpensive, easy to perform and efficient and requiring neither complicated apparatus nor highly specialized technicians. .



   The invention relates more particularly to a

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 process for manufacturing porous aluminum bodies the porosity of which varies between 10 and 50% by volume, said bodies having controlled dimensions and being remarkable for improved resistance to crushing and good elastic bending.



   An important feature of the invention resides in that it facilitates the mass production of self-lubricating aluminum alloy bearings of commercially acceptable quality and exhibiting advantages which are lacking in the bearings produced. of other metals. Aluminum alloys exhibit relatively high thermal conductivity. which facilitates the dispersion of heat. At the same time, they have both a very low modulus and are soft so that the bearings will not wear excessively and will wear out when subjected to localized pressure. As a result, localized pressure will be relieved and the detrimental effects of misalignment and shaft deflection will be reduced.

   In addition, a soft material such as aluminum absorbs impurities and thus helps to avoid the presence of hot spots which can lead to destruction of the bearings. In addition, aluminum bearings exhibit excellent corrosion resistance as well as high fatigue resistance.



   Another object of the invention is the production of lightweight aluminum bodies which are extremely useful as structural elements, in particular for refrigeration techniques, since aluminum does not become fragile at very low temperatures. .



   A significant feature of the invention is that the porous aluminum body can be formed into an embossed disc of small area dimensions employed as a nicotine filter in a cigarette.

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 or other smoker's item,
The invention also relates to an improved process for the manufacture of porous aluminum bodies, this process using relatively low compaction pressures, in unlubricated dies, the lubricants being added only to the powder mixture in such a way that the discoloration and oxidation of sintered parts does not occur.



   In order to obtain the results, the present invention provides a process for forming a deep-fried structure comprising mixing at least two powders (different metals, heating the mixture until a low melting point component is formed. form, providing a fluxing action and continuing to heat the mixture until the liquid phase turns back to a solid phase, and finally to heat the mixture in the solid state until sintering occurs,
The present invention also relates to an apparatus for sintering a raw agglomerate consisting of pure copper and aluminum powders so as to produce an aluminum alloy body, said apparatus comprising a furnace,

   a retort which can be inserted into said oven and in which there are provided means for circulating a reducing gas and a receptacle disposed in said retort and intended to contain said raw agglomerate, said receptacle comprising a removable cover intended to reduce gas turbulence in relation to said agglomerate.



   Other characteristics of the invention will become apparent from the description which follows.



   In the accompanying drawings, given unique. ment as an example - Figure 1 is a sectional view of a

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 furnace for carrying out the sintering according to the invention.



     -. Figure 2 shows in longitudinal section the retort used in the lathe.



   - Figure 3 shows the retort closure cover, seen from the side.



   Figure 4 shows the same cover seen from the end.



   - Figure 5 is a perspective view of the receptacle or covered tray, arranged inside the retort and intended to receive the bearings, - Figure 6 is an explanatory graph showing a diagram of a copper-aluminum phase FIG. 7 is a graph showing the effect of sintering temperature on the bearings.



   Figure 8 is a graph showing the effect of copper content and particle size on the bearings.



   - Figure 9 is a photograph of a porous structure obtained using a type of copper powder.



   - Figure 10 is a photograph of a porous structure obtained by using another type of copper powder, MELANGE DE POUDRES, -
In general, the process of making porous aluminum alloy products involves the stages of compacting the powder mixture into the desired shape, the green agglomerate being subjected to temperature conditions such as to cause the sintering of the powders. powders in a coherent, but porous mass.



   We will first consider the nature of the powders used in the process of the invention. The mixture

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 is composed of aluminum and copper powders, to which an organic lubricant is added. The aluminum component of the powder mixture should preferably have a very low oxide content. Relatively coarse aluminum powders exhibit lower oxide contents since their surface areas are relatively small per unit weight (less than 0.3 cc). Preferably, such powders are prepared by atomizing or spraying molten aluminum with an inert gas such as helium, neon, argon, krypton or nitrogen.

   For example, it has been found that helium-sprayed aluminum powder has a very low percentage of oxide when compared to air-sprayed powder and therefore sintered very well.



   According to the invention, it is also preferable to use aluminum powders in which the very small particles are practically eliminated so that the fraction of the powders passing through the 130 mesh screen per cm is between 0.0 and almost about 0.4%. weight. Three suitable examples of helium sprayed aluminum powders are given below in Table 1 as percentages of mesh size.



   TABLE I.-
 EMI8.1
 
<tb> Type <SEP> A <SEP> B <SEP> C
<tb>
<tb>
<tb>
<tb> Graulometric <SEP> analysis <SEP> (%)
<tb>
<tb>
<tb>
<tb>
<tb> Mesh <SEP> to <SEP> cm
<tb>
<tb>
<tb>
<tb>
<tb>> 40 <SEP> 0.501 <SEP> 2.0 <SEP> 1.73
<tb>
<tb>
<tb>
<tb>
<tb> 40 <SEP> - <SEP> 56 <SEP> 41.5 <SEP> 35.4 <SEP> 22.98
<tb>
<tb>
<tb>
<tb>
<tb> 56 <SEP> - <SEP> 80 <SEP> 49.8 <SEP> 44.0 <SEP> 48.5
<tb>
<tb>
<tb>
<tb>
<tb> 80 <SEP> - <SEP> 110 <SEP> 8.03 <SEP> 16.9 <SEP> 18.6
<tb>
<tb>
<tb>
<tb>
<tb> 110 <SEP> - <SEP> 130 <SEP> 0.250 <SEP> 1.31 <SEP> 1.16
<tb>
<tb>
<tb>
<tb> <130 <SEP> 0 <SEP> 0.402 <SEP> 0.302
<tb>
 

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These powders do not contain very small particles and the phenomenon of attachment by the matrix during compaction is thus eliminated,

   Another significant point is that the flow rate of air sprayed powders, as has been found by experiments, is about twice as slow. This means that in a given temple only a lower number of agglomerates can be produced in an automatic press. In addition, the aluminum sprayed with helium has a somewhat higher density.



   To make the helium-sprayed aluminum powder, molten aluminum is atomized or pulverized under a helium atmosphere and cooled in the same atmosphere, which prevents oxidation.



   As to the copper powder, a relatively coarse powder of suitable purity is preferably used, also having a high density and an adequate flow rate. An electrolytic copper powder (type "0") is suitable for this purpose, this powder exhibiting, on particle size analysis, a characteristic of 60 to 75% of particles passing to the mat of 32 to 40 mesh / cm. 20 & 35% passing through a 40 to 60 mesh / cc sieve and 0.25% maximum passing through a 60 to 80 mesh / cm sieve.



   The lubricant which is added to the powder mixture is preferably a "sterottx" which is added in small amounts only for the purpose of suppressing die friction problems and preventing the powder from sticking by the die. . It has been found that the addition of at least 1% by weight of "sterotex" powder works to limit the sticking problem, while optimum compaction or packing is obtained at 2%.

   "Sterotex" is a refined vegetable oil produced by Capital City Products C. de

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 Columbus Ohio, USA and present * the properties! and following characteristics
Color (Lovibond) yellow 20 red 1.2
 EMI10.1
 
<tb> Free <SEP> fatty <SEP> <SEP> acids (tele <SEP> than oleic <SEP> acid <SEP> <<SEP> 0.03
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> Melting point <SEP> <SEP> (capillary) <SEP> 61.6 <SEP> 62,

  2 <SEP> 0
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> Point <SEP> of <SEP> socket <SEP> 69 <SEP>% <SEP> C <SEP> plus
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> Number <SEP> of iodes <SEP> 2-10
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> Pass <SEP> to <SEP> sieve <SEP> of <SEP> 40 <SEP> link / or
<tb>
<tb>
<tb>
<tb> (wet <SEP> method) <SEP> 99.4 <SEP>%
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> Pass <SEP> to <SEP> sieve <SEP> of <SEP> 80 <SEP> meshes / or
<tb>
<tb>
<tb>
<tb>
<tb> (wet <SEP> method) <SEP> 92.8 <SEP>%
<tb>
 
The helium atomized aluminum powders are thoroughly and thoroughly mixed with the other powders in such a percentage that the copper content does not exceed 5% by weight and is preferably between 1.1 / 4% to 2,

  1/4 The sterotex lubricant is added to this mixture of Aluminum-copper in a proportion of between 1 to 3% by weight.



    COMPACTION.-
As an example, it will be assumed that a bearing is to be manufactured having an outside diameter of 19.05 mm and an inside diameter of 12.66 mm. The powder mixture is first pressed into a die capable of providing the required outside diameter and a core rod is introduced inside said die to determine the required inside diameter. To maintain a uniform increase in density throughout the chipboard, equal displacements are used on the upper and lower members of the punch.

   The raw densities of 69 to 89% theoretical (2.74 9 / cc) are obtained with compaction pressures varying between approximately 470 and 1100 kg / cm2. No further lubrication is required other than that provided by the sterotex of the powder mixture.



   On leaving the matrix, we obtain an ag-

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 Raw glomerated having the shape of a bearing composed of a mixture of copper and aluminum.



   Despite the low compaction pressure, the nature of the mixture of powders is such that the raw agglomerate is sufficiently consolidated to be able to be subsequently treated without risk of crumbling or disintegration.



  FRITTING.-
The compacted body is now ready to be sintered. The furnace used for this purpose is shown in FIG. 1. It included a thermally insulated chamber 10 into which a retort 11 can be inserted, the chamber comprising suitable heating elements 12 and a fan 13 ensuring the circulation. As shown separately in FIG. 2, the retort 11 has the shape of an elongated rectangular box, the rear end of which protrudes outside the oven, this end being hermetically sealed by means of a removable cover 14 comprising. a seal 15.

   The retort is filled with an atmosphere of hydrogen by means of an inlet tube 16, the hydrogen leaving the retort through an outlet port 17 where it is burnt. The temperature in the retort is measured by means of a thermocouple 18 in a sheath as seen more clearly. ment in Figures 3 and 4. The closure cover has three holes 16a, 17a and 18a intended for race. see the tubes passing through it.



   A receptacle 18 comprising a removable cover 19 is disposed inside the retort 11 in the vicinity of the front end thereof, the cover 19 comprising projecting pins 20 which can penetrate into openings arranged correspondingly in the side walls of the receptacle so as to hold the cover in place.

   The receptacle is divided by a wall of

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 separation 21 into a main compartment for receiving the bearings 22 of compacted raw powder to be sintered and an auxiliary compartment filled with aluminum powder which acts as a getter and absorbs oxygen and humidity.



   The arrows in Figure 2 show the direction of flow of hydrogen in the retort. The d. this covered receptacle 18 is not sealed against hydrogen, but free circulation of the gas as well as turbulence within the receptacle are prevented. It has been observed that the use of iron receptacles and lids having thick walls is essential in obtaining neat sintered bearings showing no signs of contamination. It has also been found that thin-walled receptacles and lids are not as effective as those made from thicker materials because temperature differences cannot be absorbed so as to prevent dumbbell-shaped distortions in the cells. bearings.



   After the sintering operation the retort is cooled with water. Although the sintering has been described as being carried out under a dry hydrogen atmosphere, nitrogen or any inert gas can be used for the rubbing which can also be carried out under vacuum. The furnace described above has been described only by way of example and other furnace devices such as pot furnaces can be used provided that the principles described above are observed. For example, a continuous conveyor belt furnace can be used comprising receptacles or trays for the bearings.



   The results in Table II correspond to the "0" type of copper powder (4%) as defined above mixed with helium atomized aluminum powder, in which the fine particles are removed.

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 which has been described above so as to form a porous bearing, These test pieces in three densities of flood compacta
 EMI13.1
 <[69.7 and 77 theoretical) were sintered in iron receptors as described above at temperatures varying between 5890 0 and 595 * 0.

   The obtained crush strength and dimensional characteristics were excellent as indicated for the optimum sintering temperatures and properties given below for different densities of compact growth.



      BOARD -
 EMI13.2
 
<tb> Density <SEP> of <SEP> Temperature <SEP> Resistance <SEP> to <SEP> Variations <SEP> of <SEP> '
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> body <SEP> "raw" <SEP> of <SEP> sintering <SEP> crushing <SEP> dimensions
<tb>
 
 EMI13.3
 - - --¯-¯. ##### 1 ext. 0 Int.



  69 588 861-959 +0.0254 0.000 73 590 949-1113 * 0.050 +080254 77 592-595 u3-.3? $, 5 +0.1016 +0.0762
 EMI13.4
 It should be noted that from the results shown in Table II the final dimensions were increased by several hundredths of a millimeter. This allows good forming qualities and characteristics to be obtained as will be seen later.



   Table III shows the differences in results obtained when using "O" type coarse copper or a finer type of copper referred to below as.
 EMI13.5
 type "90" (0.1% passing through a 32 to 40 mesh / cm sieve, 0.1% passing through a 40 to 60 mesh / cm sieve, 4.0% at most
 EMI13.6
 60 to 80 mesh / cm sieve, 1.5 "fi maximum to 80 to 100 mesh3 / cm sieve, 2 to 7 to 100 to 130 mesh / cm sieve and 90% to 130 mesh / cm sieve. in both cases the percentage of copper in the mixture was 2% by weight based on the aluminum.



   It will be noted that an excellent control of
 EMI13.7
 dimensions is made with powder of the type nOu 3ndépen.

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 Regardless of the crush strength, it will further be noted that comparable results were obtained when bearings having a raw density of 77% were sintered in two different turns. The only apparent difference between the ovens is a temperature difference of 3 ".

   But under the same sintering conditions the "90" type powder exhibited excessive shrinkage, which is a definite disadvantage for the forming or stamping operations.
 EMI14.1
 

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 EMI15.1
 t A BLASAT SX Summary of densities after sintering and resistances 3.tcrsaemeni for various temperatures and densities of green bodies (bearings containing z copper)
 EMI15.2
 Temp.

   Density Density after sintering Crushing resistance X / cm2 Variations in diaaed dimensions of Copper Copper Coarse copper Fine copper (2) 'outside in # raw JE coarse (2) fine (2) rosaier (2) Fine copper (2) 590 69 67.5 80.50 - + 0.0762 / + 0.1270 - 595 69 67-69 136, 3 * 02 540: 1524 - 600 77 73.6-7.8 (3) - 483.00-578 , 90 (3) + 0.0508 / + 0.1016 (3) - 601 73.1-73.7 73.4-73.6 197.40-251.30 156.80-237.30 +0, 0254AO, 0762 + 0.0508 / + 0.0'62 601 77? 5s-? 6.4? 4 -77.1 229.60-281.80 1305.50-1463.00 + 0.0254 / + 0 , 05O8 -O, 4O64 / -o'o762 605 69 68-69 66 -67 236.60-271.60 158.20-186.40 + O, ü508 / + 0.152 + 0.152 / + 0.250 605 72.5- 73.5 73 -73.5 154.50-185.50 91.00-110.60 + 0.0254 / + 0.0762 + 0.0762 / + 0.1016 603 77 S'î-35 f 72, 1-75, X 141.40-276.50 707.00-1386.00 -0.08 / + O, 1o16 -0.1778 / + 0.1778 606 73 73.9-? 4.2 73.9 -74.9 170.80-242.20-376.60 156.80-256.20 -0.0508 / + 0.025 + 0.0508 / t0.0762 606 77? 5.5-? 6.8 75,

  5-78.6 220.50-292.60 146 ', 00-1617.00 0: 000/0: 0254.-0.4'18 / -0.0254 610 73 72.5-73.4 73, 0 204.40-205.80 93.80-110.60 +0: 0254AO: 10l6 + 0.0762 / + 0.1016 fi10 77 75.4-76.0? 2.1 - ?, 6 134.40 -147.00,, 742.70-782.60 +0.025,% + t3.0508 -0.0508, / + 02T9 612 77 75.0-75.9 (3) - 724.50-887.60 ( 3) +0: 02540: 1016 (3) ##.



  615 69? 1.0 - 1128.40 -0.0? 62f-0.25.0 615 5 72.3-? 2.7 71.5-? 2.3 306.60-361.90 214.20-249 , 90 '' ## '' * t0.1270 / + Osl? 78 615 77 72.4-75.7 78 721.00-869.40 1596.00 + 0.0254 / + 0.0762 -0: 482 : 2286 620 73? Ls8-? 3s6 70.8-74.0 553.00-647.60 501.20-602.00 -0.1016 / + 0.1016 + 0.0254 / + 0.2794 620 77 74.0-76.2 72.9-74.513: 00: 00 470: 40-609.00 + 0.0254 / + 0.1.270 -0.4826:

  1-0.6'50 625 .. "72.7-76.0 72.9-74.5 104 ', 00-1064.00 470.40-609.00 -0.1778 / + 0.0762 - 0.1016 / + 0.1'78 625 77 73.5-76.1 81 4-41.0 <> - 462.00 1890.00 + 0.0254 / + 0.0762 -0, '048 / - 0.9'98 630 76.5-78.1 U69.00-1.86, OO -0.1016 / -0.2794 630 81 80.1-82.1 - 1575, 00-1596.00 - - 0.025.f + 0.1? 78 il
 EMI15.3
 (1) Sintering time 1 hour in all C (2) Coarse copper - Type "0 * Fine copper - Type '* 90'0 (3) Kiln-oven type Revi-Duty

 <Desc / Clms Page number 16>

 
 EMI16.1
 In Table III the results have been given for a copper proportion of 2%.

   To mount the effects of sintering when using smaller ..! or greater proportions of copper, the results obtained with type "0" type copper are shown in Table IV below in a range from 0 to 4% by weight relative to the aluminum powder, TABLE IV.

   -
 EMI16.2
 copper% Resistance to Density Density Ttmp'ratur8 by weight crushing Moruo body after sintering ¯¯¯¯¯¯¯ ¯¯¯¯¯¯ ci-tt 019 0 650.7 * 77 80 6 $ 0 1 2iq0e 73 7215 640 4/4 462.0 77 615
 EMI16.3
 
<tb> 11/2 <SEP> 616.0 <SEP> 77 <SEP> 615
<tb>
 
 EMI16.4
 33/4 721.0 77 615
 EMI16.5
 
<tb> 2 <SEP> 669.4 <SEP> 77 <SEP> 75.7 <SEP> 615
<tb>
 
 EMI16.6
 2JL / 4,966.0 77 - 615
 EMI16.7
 
<tb> 3 <SEP> 1694.0 <SEP> 77 <SEP> 85.4 <SEP> 620
<tb>
 
 EMI16.8
 4 1378e5 77 - 592-595 x The specimens showed excessive shrinkage.



   Table IV shows very clearly that a suitable resistance as well as controlled dimensions are obtained when the percentage of copper
 EMI16.9
 is in the range of 1.1 / 4 to 2.1 / 4Zen weight of copper, THE SINTERING PROCESS.-
It has been found that if the sintering is carried out above the eutectic temperature but below the solidus temperature, preferably using
 EMI16.10
 With very low dew point hydrogen (between -62 "0 and -73 ° C), the difficulties can be eliminated or reduced.

   Ties which have been encountered in previous attempts and which relate to contamination and distortion,
Figure 6 summarizes the results of deep frying

 <Desc / Clms Page number 17>

 tage in a * schematic representation of the relevant angle of the diagram of the aluminum-copper phame at temperatures varying from the eutectic temperature to the melting point of the main element of the alloy, aluminum. Area B of the diagram defines the optimum range of temperature and composition which is necessary to achieve Al-Ou primers or other porous structures having excellent strength and size control.

   It should be noted that for the lower percentages of copper in this area the range of acceptable sintering temperatures increases. This is significant in that at the higher temperatures approaching that of the solidus the sintering time can be reduced considerably for these compositions without resulting in a decrease in the crush strength. This results in a more economical manufacture of the parts.



   With regard to the frying process, additions of copper to aluminum powders up to an amount of nearly 5.7% by weight (the maximum solubility of copper in aluminum at the temperature of eu-tactic) achieves a low eutectic melting point of 548 "C for a short period of time.

   This liquid phase (Al-Ou) is apparently attracted by capillarity within the set of compact elementary powders and melts all the residual aluminum oxide present on the surface of the aluminum particles. During these early stages of the sintering cycle the agglomerate clearly expands, the magnitude of the expansion depending on the copper content which controls the amount of the liquid phase present above the eutectic temperature.



   As the temperature and duration of the operation increase and as the entire

 <Desc / Clms Page number 18>

 liquid phase is solidified on the surfaces of particles. The rapid diffusion of aluminum and copper continues to occur in the direction of equilibrium concentrations.



  The maximum temperature that can be used for sintering, after diffusion is almost complete, is given by the phase diagram, as the solidus temperature for the aluminum alpha phase. If this temperature is exceeded, excessive shrinkage and distortion occurs in the agglomerates.



   If excess copper has been added and the final sintering temperature is lower than that of the solidua; an exaggeratedly expanded agglomerate is obtained after sintering. When the sintering temperature approaches and / or exceeds the solidua temperature for such a copper content shrinkage occurs rapidly and little or even no control of the dimensions can be obtained (see figures 7 and 8). It will be noted in FIG. 7 that the curve for a body containing 3% copper presents a steep slope which limits the possibilities of control.



  Figures 7 and 8 also show the advantage of using coarse copper powder.



   In addition, Figure 7 shows that when the copper percentage and the particle sizes are properly chosen, a bearing on the curve results, allowing dimensional control over a temperature range below the temperature. solidus. It will be noted that for a percentage of 2, * 0 of copper the final dimensions of the body are slightly increased, which has proved to be an ideal advantage for subsequent stamping operations,
The following general characteristics for elemental powder sintering can be considered to apply in the early stages.

 <Desc / Clms Page number 19>

 



   1 / The diffusion coefficient depends on the concentration gradient,
2 / The diffusion coefficient is an expositor tial function of the absolute temperature, ie the diffusion rate increases rapidly with temperature.



   3 / In general, the rate of diffusion of an individual metal in a given network is higher the closer the temperature is to the melting point.



   In a binary system, therefore, the component with the lowest melting point exhibits the highest so-called melting rate at a given temperature.



   4 / The rate of equilibrium and homogenization by diffusion during sintering of mixed powders depends on the size of the particles, which determines the distances between the maximum and minimum concentrations. With a given mixture, the fastest homogenization occurs when the particles of the secondary component have the smallest dimension.



   5 / In general, the secondary component of a binary system will alloy more quickly than the main component, the diffusion layers forming envelopes around the particles of the secondary component.



   As the process continues and the body approaches the final sintering temperature (above or below the solidus) the over expansion and shrinkage processes begin to take effect.



   Once again, the characteristics of the powders have a significant effect here. It has been noticed that two different processes determine the process of shrinkage or contraction namely the volume contraction of the particles or the effect!

 <Desc / Clms Page number 20>

 settlements which change the shapes of the particles and the relative positions of the particles, the volume thereof remaining constant. These effects can occur neither and overlap, and it has been observed that finer grain powders increase their importance.

   In these coarse powders, the pores formed in the raw compacts do not allow a significant increase in density to be obtained by the compaction process.



   In summary, it is noted that the additions of copper to the aluminum make it possible to obtain a faster sintering and an increased resistance, for sintering temperatures lower than those necessary for pure aluminum powders, the copper also makes it possible to limit contamination by sulphides or oxides which may be present on the surfaces of the powders and such additions of copper make possible sintering of agglomerates at low pressures, thereby
It has been found that the use of coarse aluminum powders is important for a manufacturing process because it eliminates the explosion hazards which normally exist when processing finely divided powders which have large surface areas.

   This is in particular the case when using a hydrogen atmosphere, THE FRITTEZ STRUCTURE ,,.



   Figures 9 and 10 respectively show the porous structure obtained with coarse copper powders and that obtained with fine powders. It is evident that coarse pores are randomly distributed throughout the structure when using copper powders. coarse copper.

   It was explained, when examining the sintering process, that additions of power *

 <Desc / Clms Page number 21>

 Fine copper dres led to increased density and smaller pore sizes. Randomly distributed coarse pores are advantageous for the operation of the bearings since these coarse pores provide oil storage cavities which can feed the small capillaries formed by the smaller particles.

   In addition, this type of structure has the advantage that large holes in the surface can be blocked more difficult by polishing or wear. this ensures more continuous lubricating qualities and a greater safety factor for the operation and replacement of the bearings.



     In addition, the lower the temperature, the better the surface finish and the more uniform the dimensions. This is obtained by polishing which eliminates dimensional malformations and ensures that bearings with perfectly polished inside diameter are obtained.



  IMPREGNATION AND STAMPING. -
By way of example, to show the effects of stamping and oil impregnation, bearings comprising 4% copper and having a density after sintering of 69.7 theoretical and slightly expanded dimensions were impregnated. of oil then stamped. The oil impregnation was carried out under vacuum for three quarters of an hour and the stamping was carried out with a pressure of 2200 kg / cm2.



  The density increased to 75.7 and the strength & crushing increased from 960 kg / cm2 to 1750 kg / cm2, while the elastic strain decreased from 7.9 to 1.6%.



   It is interesting to note that the impregnation can be carried out before or after the stamping operation. Impregnation carried out before stamping results in

 <Desc / Clms Page number 22>

 very uniform dimensions after stamping. The oil acts as a hydrodynamic pressure equalizer resulting in a more uniform application of the burst pressure. It has also been observed that the immersion impregnation in a bath is not satisfactory because considerable variations in length result after stamping. In addition, the pores of the ends tend to be blocked when stamping impregnated test pieces by immersion.

   As a result, vacuum impregnation has become a standard operation. It is also possible to impregnate the stoves with lead so as to prevent the bearing from burning out if the oil is used up.



   From the data obtained for the sintering it is evident that by using suitable compositions as well as suitable sintering conditions, suitable crush strengths as well as good elastic deformation and dimensional control can be achieved without stamping. Thus, it is possible to omit the stamping operation so as to lower the production cost.

   With such bearings, it is only necessary to carry out a polishing operation to obtain uniform dimensions and a smooth surface,
OTHER TYPES OF ALLOYS AND PRODUCTS OBTAINED. -
It has been observed that other metals in the form of elemental powders can be mixed with the aluminum to form good quality plots after sintering provided there is a low melting point component and that the solidus temperature line in the phase equilibrium diagram is established so as to
Band the maximum sintering temperature.

   The following elementary additions have been tried

 <Desc / Clms Page number 23>

 
 EMI23.1
 
<tb> Element <SEP> or <SEP> alloy <SEP> added <SEP> Percentage <SEP> in <SEP> weight <SEP> added
<tb>
<tb>
<tb>
<tb> Tin <SEP> 1.5
<tb>
<tb>
<tb>
<tb>
<tb> Titanium <SEP> 1.5
<tb>
<tb>
<tb>
<tb>
<tb> Molybdenum <SEP> 1.5
<tb>
<tb>
<tb>
<tb>
<tb> Magnesium <SEP> 1
<tb>
<tb>
<tb>
<tb>
<tb> Magnesium <SEP> (ZK-10) <SEP> 2.4
<tb>
<tb>
<tb>
<tb>
<tb> Iron <SEP> 1.5
<tb>
<tb>
<tb>
<tb>
<tb> Nickel <SEP> 1
<tb>
<tb>
<tb>
<tb>
<tb> Lead <SEP> 1.5
<tb>
<tb>
<tb>
<tb>
<tb> Chrome <SEP> 15
<tb>
<tb>
<tb>
<tb>
<tb> Cobalt <SEP> 1.5
<tb>
<tb>
<tb>
<tb>
<tb> Copper <SEP> plus <SEP> Nickel <SEP> 4 <SEP> (each)

  
<tb>
<tb>
<tb>
<tb>
<tb> Brass <SEP> 1
<tb>
 
The results obtained show that a raw agglomerate containing 1% tin, sintered at 625 ° C. for one hour, has a crushing strength of 791.70 kg / cm2 and an elastic deformation of 9.89%. Aluminum-tin specimens were sintered under vacuum or in an atmosphere of hydrogen and gave satisfactory parts ...



  An agglomerate containing 4% magnesium (ZK-10) and sintered at 600 C for one hour exhibited sowing resistances varying from 980 kg / cm2 to 1070 kg / om2 with elastic deformations varying from 7 , 43 to 9.50%. A body containing in addition 4% copper and 4% nickel, sintered at 600 0 for one hour exhibited crushing strengths varying from 840 kg / cm2 to 972 kg / cm2, exhibiting elastic deformations of 5 .08 to 5.50%.



   It has been found that the magnesium obviously volatilizes to a certain extent during the sintering process, leaving suitable pores the size of which depends on those of the original metal particle. This was also observed in the case of

 <Desc / Clms Page number 24>

   sterotex so that it can be concluded that metallic or non-metallic products can be used to achieve the required porosities.



   Parts with a porous structure can be made using an aging treatment following the sintering operation. For example, an aluminum specimen containing 4% copper has been sintered. Bile then had a density of 86.3%, a crushing strength of 2121 kg / cm2 and an elastic deformation of 12.1%.



  Hot treatment at 500 ° C. for one and three-quarters hours, followed by cooling in water, followed by heat treatment under vacuum at 150 ° C. for a period of 2 to 89 hours allowed the obtaining test pieces with crushing strengths of up to 2500 kg / cm2 with elastic deformations of 4.1%.



   In addition to the above, it has been discovered that mixed elemental powders can be loaded into receptacles, leveled and sintered, allowing high strengths to be obtained without prior tamping. For example, a mixture containing 4% copper and the remainder of aluminum (these powders all being coarse powders) was thoroughly mixed for half an hour, loaded into receptacles, leveled and sintered as described above. high at 620 C for one hour.

   A very strong, porous, sintered sintered cake product was obtained. Air atomized or helium atomized aluminum can be used. If it is necessary to have a greater density or a greater resistance, the cake thus obtained can be stamped or rolled, cold or hot. These sintered cakes can also be impregnated with lead. The agglomerated cake can be reinforced, to obtain parts with a dense structure, by cold or hot rolling or extrusion. Like-

 <Desc / Clms Page number 25>

 parts can also be heat treated and aged to give them required structural properties.



   A tobacco smoke filter can be made by forming an extremely porous aluminum alloy plug made as described above. The green compact can be packed very lightly so as to present a high porosity, the sintered product having pores joined together which allow the passage of smoke.



  The stopper can be inserted in a cigarette holder or in a pipe pipe. The filter can also be produced in the form of a small wafer inserted at the end of the cigarette, this end being of the type now used in a conventional manner with filters made of fibrous material. The advantages of aluminum filters are due to their high conductivity so that they cool. smoke, cause harmful vapors containing nicotine to condense and filter smoke and tobacco particles. A filter of this type on the other hand does not affect the taste or smell of the smoke. Such a filter has only negligible weight and can easily be inserted into a cigarette end.



  CONCLUSIONS.-
The process just described makes it possible to manufacture porous metal parts having porosities varying from 10 to 50% by volume as well as improved crush strength, good elastic deformation and high strength. dimensions controlled in an excellent way. This new process offers a large number of technical and economic advantages over the prior processes. The solutions to the problems that existed before and the advantages of the new process are as follows
Point 1.- The problem of the sintering atmosphere leading to contamination of the treated part.

   This is resolved

 <Desc / Clms Page number 26>

 using a protective sinter pan to receive the parts in the furnace and employing an alloying element such as copper which is a low melting point component (in the early stages of sintering) and acts as a melting agent on the surface of the powder. It should also be noted that the corrosion resistance of the solid, Al-Cu or other solution formed on the surface of the powders is greater than that of pure aluminum.

   Such sintering has been successfully achieved in different atmospheres such as dry hydrogen, nitrogen, and vacuum;
Point 2.- The problem of refractory oxide or other contaminating films on the surface of elementary powders which cannot be reduced at the sintering temperatures employed The solution was obtained by employing a low melting point flux as indicated in paragraph 1 above Also the degree of flux required can be controlled by the alloy content. For example, if a very pure powder (for example aluminum atomized with helium) is used, a loss of the component to constitute the flux, for example copper, must be compensated for.

   The purity of the powder in turn is controlled by the removal of very fine particles (passing through a 130 mesh / cm sieve). This can be done for both the most important component and the secondary component of the alloy.



   Point 3.- The problem of the adhesion of the particles by the wall of the matrix and their setting, during the pressing of the agglomerates bears. This problem is solved by using low compaction pressures of the order of 470 to 1100 kg / cm2 and by controlling the particle sizes of the powders so as to have optimum compaction qualities. The happy use of a powdered lubricant is also very helpful.



  The use of motor lubricants that would be necessary

 <Desc / Clms Page number 27>

 if high compaction pressures were used and / or if the powder could not be lubricated, would lead to higher production costs since it would be necessary to wipe the die, the wear would be greater and that the tolerances would be more difficult to control, etc. ,.



    The use of low compaction pressures also makes it possible to manufacture plastic dies.



  In any case, the use of steel tools is no longer necessary and cheaper alloys such as cold rolled steel can be used,
Point 4.- The problem of using lubricants mixed with powders. About 1 to 3% of sterotex mixed with elemental powders combined with the use of a special sintering plate device in the sintering operation suppressed discoloration and oxidation of the sintered parts.



   Point $ .- The problem of long and expensive sintering times encountered when performing sintering in the as-state. completely solid below any temperature corresponding to the liquid state. Sintering times are reduced to times which are economically achievable, by performing the sintering above euteotic temperature and just
 EMI27.1
 below the temperature of the soil.



   Point 6.- The problem of excessive deformation due to shrinkage resulting from sintering of the liquid phase. This problem has been eliminated by keeping the sintering temperature below the temperature of the solidus. When it is absolutely necessary to employ sintering of the liquid phase (for example for 4% Cu) it is possible to obtain suitable results by carefully controlling the cycle in time, the size of the particles and the cooling cycle ** ment /
Point 7.- The problem of controlling the dimensions during

 <Desc / Clms Page number 28>

 sintering to obtain proper dimensional control.

   By producing a slightly expanded sintered part, # the die forging of the parts was facilitated by this study. This is achieved by properly selecting the copper content, particle sizes, and sintering conditions such as temperature and time.



   Point 8.- The problem of obtaining a suitable resistance to crushing while maintaining a sure control of the dimensions. This is achieved by the use of coarse copper powders and by maintaining the sintering temperature below the temperature of the solidus for a suitable period of time.



   Point 9.- The problem of controlling the size of the pores and the production of coarse pores distributed at random presents a phasing towards more finite pores.



  This problem has been solved by employing coarse aluminum powder and adding the proper percentage of coarse copper powder which maintains the pore size during sintering.



   Point 10.- The problem of manufacturing parts does not show contamination after compacting at low pressure (470 to 1100 kg / om2). Contamination can now be removed despite the low compaction pressures by using the sinter pan and the flux component as described above.



   Point 11.- The problem of storing mixed powders. This is facilitated by using coarse copper and aluminum powders, which limits the exposed surfaces of the particles.



   Point 12.- The problem of the risks of explosion, encountered with aluminum powders exposed to various stmospheres. Through the removal of small particles

 <Desc / Clms Page number 29>

 dimensions (passing through a 130 mesh / sieve) in the $ powder mixes. The surfaces of the particles are stabilized so that ignition tendencies and / or explosion tendencies are suppressed.



   Point 13.- The problem of manufacturing non-contaminated sintered agglomerates, directly from the powders without having tamped them beforehand. This can be achieved by coating the particles of the main element of the alloy with the elemental powder of the secondary element of the alloy (e.g. copper coating the aluminum) and sintering the powders at temperatures and during a suitable time. The dimensions of the particles are controlled to allow the attainment of a suitable strength and porosity if desired,
Point 14.- The use of aluminum and its alloys has a number of advantages.

   a) Aluminum and its alloys are softer and less elastic than bronze, for example, and therefore offer less spring effect when mounted in boxes. went up; etc ... In the case of aluminum-copper bearings, the tightening is only 40% while the bronze bearings have a tightening of 77% or approximately twice as much; b) Aluminum bearings operate at lower temperatures in PV tests than bronze bearings of the same dimensions.

   The temperature difference depends on the PV value of the test; c) the density of aluminum being about a third of that of bronze, the energy required to sinter the aluminum is markedly lower; d) the good thermal conductivity qualities of aluminum allowing a more uniform heating during the

 <Desc / Clms Page number 30>

 sintering cycle which is very beneficial for: #s short cycles, e) in addition to the other advantageous characteristics * mentioned above, aluminum has the advantageous qualities for the bearings which are as follows:

   excellent corrosion resistance, high fatigue resistance, high compressive strength, good impurity absorption quality, easy shaping, wear resistance, good seizing characteristics, high thermal conductivity and price not high;
Point 15.- The following summarizes the advantages of the porous bearings according to the invention which have not already been listed in paragraph 14 above: a) coarse pores are advantageous for the accumulation of oil which can supply fine capillaries. Furthermore, this type of structure can be easily calibrated by various methods (for example by polishing) without running the risk of clogging the oil supply channels;

   b) it is possible to manufacture usable bearings, stamped or not. The only measure necessary when using non-stamped bearings is polishing or the like before use. The elimination of the calibration operation increases the economic advantages of the process.



   Point 16.- Other various advantages afforded by the process are as follows: a) the compaction method eliminates high pressure ejection and oxidation problems encountered in other processes; b) by using the protection means described for sintering it is not necessary to make high initial investments for the furnace intended to produce.

 <Desc / Clms Page number 31>

 such bearings in series; c) metallic (for example magnesium) or non-metallic (aterotex) elements can be added, in a controlled quantity, these elements being intended to volatilize or to melt during the sintering operation and thus to contribute to the production of pores of suitably scaled dimensions.



   Of course, the invention is in no way limited to the embodiments described and shown which have been given only by way of example.



    -CLAIMS, -
 EMI31.1
 ... ¯M¯¯ - ¯¯ -------------- ..



     1.- A method of forming a sintered structure, characterized in that it comprises the phases which consist in mixing at least two said metal powders. heat the mixture until a low melting point component is formed which provides a melting action and continue heating the mixture until the liquid phase returns to a solid phase, and finally heat. mixing in a solid state until sintering occurs.


    

Claims (1)

2. A method according to claim 1, characterized in that one of these powders is aluminum, magnesium or titanium. 3.- Method according to claim 1, characterized in that these metal powders comprise aluminum powder and copper powder and in that the mixture of these metal powders is compressed to form an agglomerate, after which the agglomerate is sintered at a temperature higher than the eutectic temperature of these powders, but lower than their solidus temperature. 4.- The method of claim 3, <Desc / Clms Page number 32> characterized in that these powders are relatively coarse and are free from particles passing through a sieve of 118 mesh per cm, 5. A method according to claim 4, characterized in that these aluminum powders have particles passing through the sieve of about 40 to 118 mesh, as well as an oxide content of less than 0.3% by weight, 6, - Process according to claim 3, characterized in that the copper content is of the order of 1 to 5% by weight, 7 ,. Process according to Claim 6, characterized in that this copper content is of the order of 1 1/4 to 2 1/4 by weight. 8. A process according to claim 3, characterized in that the compaction pressure is of the order of 470 to 1100 kg / cm2. 9, - Process according to claim 3, characterized in that the sintering temperature is of the order of 550 to 625 C. 10. A method according to claim 3, characterized in that an organic lubricant is added to the mixture of the aluminum powder and the copper powder, to form a raw agglomerate, the aluminum powder having a low content. in oxide. 11. - Process according to claim 3, characterized in that this sintering is carried out in hydrogen. 12.- Apparatus for sintering a raw agglomerate consisting of copper and aluminum powders, to form a body of aluminum alloy, characterized in that it comprises a heating furnace, a retort which can be insert into said oven and in which are provided means for <Desc / Clms Page number 33> circulating a reducing gas and a receptacle disposed in said retort and intended to contain said agglomerate, said receptacle comprising a removable cover intended to reduce gas turbulence with respect to said agglomerate. 13. Apparatus according to claim 12, characterized in that said receptacle and the cover for the latter are made of relatively thick iron, 14, - Apparatus according to claim 13, characterized in that said receptacle is partitioned, to form a compartment for a getter powder, 15.- Porous body formed from a sintered mixture of aluminum powders and relative copper. Coarse, the powders passing through a sieve of more than 130 mesh per cm and being sintered at a temperature above the eutectic temperature, but below the solidus temperature. 16. A body according to claim 15, shaped in the form of a bearing and containing pores filled with oil. 17. A body according to claim 15, shaped in the form of a stopper having dimensions permitting its introduction into a cigarette end.