CA1118562A - Method and apparatus for making composition friction materials - Google Patents

Abstract

JLS:Pm 6/8/77 case 5538 Rev. 7/13/77 METHOD AND APPARATUS FOR MAKING
COMPOSITION FRICTION MATERIALS

ABSTRACT OF THE DISCLOSURE
Composition friction materials particularly adapted for use in making railroad brake shoes include an elastomer such as synthetic rubber or natural rubber. The elastomer forms part of a bond for the remaining friction ingredients.
The elastomer, solvent and nonsolvent absorbing granular abrasive materials of the composition are mixed in a manner such that the elastomer is quickly reduced to a paste-like consistency to which the remaining ingredients are added and mixed to form pellets which can be conve-niently formed into brake shoes.

Description

JLS:p~ 6/9/77 Case 5538 BACKG~OUND OF THE INVENTION
Field of Inven~ion This in~ention relates to a method and apparatus for making composition friction materials and particularly to a method and apparatus for-making a composition fro~
which brake shoes for the railroad industry may be readily 0 5 produced. -Prior Art Composition friction materials such as those used to make brake shoes and brake li~ings are commonly made - ~y either a dry or wet-dry mix procedure.
In the dry mi~ method the various ingredients are combined and thoroughly mixed, as for example in a Lodige type mixer presently sold in the United States by Littleford Bros. Inc., Cincinnati, Ohio. The dry mixture so produced is then placed in a mold eo which heat and pressure are appLled to bind the lngredients into a physical friction unit.
The wet-dry mix method is the more commonly used to make composition friction materials for railroad brake shoes. Most such composition friction ~aterials include an elastomer, i.e. a synthetic rubber such as

2~ butadieQe-styrene, butadiere-ac yloni~rile or chlor-butyl rubber, or a natural rubber which is mixed in the ?resence of a solvent, a resin base and friction materials such " .
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~ JLS:pm 7/13/77 l~li85~Z Case 5538 as powdered ircn grit, lead sulfide and other fillers.
After sufficient agitation and exposure to the solvent, the elastomer becomes sufficiently so~vated or dissolved to allow dispersion therein o~ the bal~nce of the fillers, resin curing agents and reinforcing fibers and to permit blending with a resin solution. This wet mix is the~
opened as in a hammermil~ and dried i~ trays in a circulating O
oven to remove substantially all of the solvent. The dry product then may be briquetted and then cured under heat and pressure in a mold to the desired shaped friction body.
The wee-dry procedure offers a number of distinct advantages over the dry mix procedure in the forming of composition friction materials for making railroad brake shoes.
Firstly, high percentage, heavy granular fiIlers such as iron grit, desirable in railroad brake shoes, remain dispersed and suspended throughout the mixture and i8 not gravitationally separated as occurs when using V the dry-mix procedure. Secondly, the use of elastomeric materials has been found ad~antageous in producing a high performance railroad brake shoe and such material cannot be readily used in a dry mix procedure. Lasely, a - resin binder, also a desirable ingredient, can only be effectively handled and utilized in the presence of a - ~
801vent. As used herein, any bra~e shoe mixture in which ~ solven~ is used defines a wet-dry procedure.

-~' JLS pm 7/~3/77 li~85~2 United States Patent No. 3,227,249 discloses a wet-dry mixing method for preparing a friction composition for use in making railroad brake shoes including generally the followi~g steps: -1) a.mixture of. an elastome , partially cured cashew nut-shell oil resin, reinforcin&-'fillers and a curing agent is,blended in a rubber mill or a banburv type ~ixer;
, 2) the mixture of Step 1 is formed into a sheet;

3) the sheet stock is soaked in a solvent such as naptha or toluol in a closed container for a:sufficient time period (24 hours) to swell the sheet mixture;
. 4) granular filler, friction modifiers and fibers '' are added to the swelled mixture;
5) the composite of Step 4 is mixed with an intensive mixer such as a siO~a blade or dispersion blade mixer with a pressure lid to form a.wet lumpy mix;
6) the mix of Step 5 is granula~ed with a hammermill to reduce the size of lumps; and 7j the mixture. of Step 6 is dried in flat trays' for proximately 15 hours at 150~F .~ 'C,rin an,i,n,directly flred air oven to drive off the solvent. ~
The dried mix.of Step 7 then may be formed into a briquette, in any physical shape desired.

;, ' , SUMMARY OF THE INVENTION ., , The method o~ this Lnvention comprising mixing the same ingredients as heretofore were utilized thereby to - :~11856Z

produce a friction material having similar physical characteristics and frictional qualities.
The present invention provides a method of preparing a composition fric-tion material particularly adapted for forming railroad brake shoe liners, the method comprising the steps of:
1) loading into a mixer a first portion of ingredients including an elastomer, a solvent and nonsolvent absorbing materials, 2) mixing the first ingredient portion with mixing means carried by the mixer to produce a solvated paste-like substance, 3) adding into the mixer a second portion of ingredients including curing agents, friction modifiers, solvent absorbing materials and resin,

4) energizing a vacuum source connected to the mixer to draw off the solvent in the mixture,

5) mixing the first and second portions with the mixing means to produce a mixture of the ingredients,

6) adding heat to the ingredients in the mixture carried by the mixer at least during Steps 2 and 5, and

7) withdrawing the mixture of ingredients from the mixer upon a sufficient amount of the solvent being removed from the mixture by the vacuum source, wherein the mixture of ingredients may be conveniently formed into rallroad brake shoes.
In a preferred embodiment a granular elastomer such as a crumbed rubber, a solvent, the granular nonporous fillers having superior abrasive and cutting qualities and a curing agent for the elastomer are placed in an intensive mixer which is sealed from the atmosphere and to which heat is applied to heat the ingredients held therein.
The mixer is operated several minutes at an elevated temperature until '' ., . "' '':
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the elastomer is solvated, i.e. becomes paste-like. The rapid solvation of the elastomer results from the cutting action of the granular fillers which reduces the size of the elastomer crumb thereby permitting the warmed solvent to more effectively soften and break up the elastomer. Moreover, the amount of solvent required to render the elastomer as a paste is maintained at a minimum because the granular fillers added are nonsolvent absorbing.
In this manner, only such quantity of solvent required to solvate the elastomer need be added.
After solvation, further ingredients such as porous filler friction modifiers, resin curing agent and fibers are added and mixed for a relatively short time. Then a liquid resin is selectively added. Also, a vacuum is slowlydra~m on the mixer to evaporate the solvent. To prevent the mixture - 4a -, Y
'1 ~ ~ 11185~Z Case 5538 from cooling because of the evaporation of the solvent under the vacuum, heat is added. The solvent vapor so removed is condensed and stored for reuse if desired.
During and after ~he addition of the resin, intense ~ixing is continued as the vacuum increases significantly. When a significant amount of solvent has O evaporated, mixlng is continued at a lesser intensity until the mixture is dry~ The mixer is the~ stopped and the mixture now in pellet size with a maximum diameter of one inch is removed from the mixer and ready for further processing.
The process of the present invention for producing friction materials from which railroad brake shoes may be formed ha& a number of significant advantages over prior , I 15 processes utilized.
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~- F~rstly, the time period for processing a batch of friction material has been reduced signif~cantly O allowing a higher utilization of equipment and plant space.
Secondly, the number of manhours required to pro-duce a batch has been reduced to less than one-quarter of the number heretofore required. ~~~
A further advantage of this new and useful process is that the process uses only l/lOth of the energy used heretofore. This low energy requirement is of particular signi~icance because of the present nat~onal commitment to energy conser~tion.

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A still further advantage of the process of this invention is the controlled use of solvent. Firstly, only sufficient solvent is added to effectively solvate the elastomer. Secondly, the solvent is held in a closed system to prevent environmental damage. Lastly, such solvent that is recovered may be reused so that the quantity of additional solvent required to be added to the reused solvent is reduced to minimize the cost of the solvent significantly.
The present invention further provides apparatus for preparing friction materials which can be conveniently formed into railroad braking devices, comprising, a mixer having an elongated cylindrical-shaped, sealable chamber, a first mixing means within the chamber including a drive shaft rotatively carried by ends of the chamber and spaced plow means carried by the shaft to circle about an inner circumferent surface of the chamber, and a second mixing means within the chamber, the second means including chopper means , positioned between the spaced plow means and adjacent to the inner chamber surface and carried on a drive shaft positioned transversely to the plow shaft, heating means for adding heat to ingredients in the mixing chamber, the means carried about an outer circumferent surface of the chamber, filtering means to remove particulate matter from a solvent in a vapor state, the filtering means having an intake connected to the chamber, condensing means to change the solvent vspor into a liquid state, the condensing means having an intake connected to an outlet of the filtering means, reservoir means for collecting the solvent changed from the vapor state to the liquid state by the condensing means, the reservoir means having an inlet connected to a discharge of the condensing means, and ., . . . ~ : .... :
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vacuum source means to reduce pressure in the chamber to less than ambient atmosphere pressure, the vacuum means having an intake connected to the reservoir means, wherein the friction material may be made in an energy efficient and environmental protective manner by charging the chamber of the mixer with a first portion of ingredients to fill approximately 11 percent of a holding capacity of the mixer and mixing the ingredients with the mixing means to produce a solvated paste-like substance, then adding into the mixing chamb~r a second portion of the ingredients and mixing the ingredients to produce a mixture thereof which upon being subjected to heat from the heating means and vacuum from the vacuum source dries by withdrawal of the solvent.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic block flow diagram showing the steps of the process of this invention and related material inputs.
FIG. 2 is a schematic of the Lodige mixer and related equipment used in the process of FIG. 1.
FIG. 3 is a cross-sectional view of the mixer of FIG. 2 along the line 3-3 in FIG. 2.
DESCRIPTION OF THE PREFERRED PROCESS

As its major mixing component, the process of this invention incorporates a "Lodige" mixer of generally well-known German design and made in this country by Littleford Bros. Inc., and designated 10. Heretofore, this mixer had been exclusively utilized in dry mix processes while the well-known Banbury* type mixer had been exclusively used in wet-dry mix applications.

* trade mark - 6a -. . . .
, ~Ll~ 8 5~2 JLS pm 7 /13 / 7 7 The Lodige mixer 10 includes a heatable jac~et 12 about a sealable, cylindrical-shaped mixing chamber 14.
Th~ chamber 14 is designed to prevent lea~age of solvent - vapors to the surrounding atmosphere as well as allowing a substanti-l vacuum to be drawn thereon.
To provide mixing, the Lodige mixer has a plurality of spaced plows or blades 16 which are rotated about an inner circular surface 18 of- thP chamber 14 by a drive shaft 20 extending through the chamber 14 and proximately aligned with a longitudinal axis o$ the chamber 14. On - the inner surface 18 of the chamber 14 and between ~ adj~cent plows 16 are circular choppers 22 which have a : pLane of rotation pasitioned proximately perpendicular to a plane of rotation of the plows 16 so as to provide further agitation as the material within. the chamber 14 is directed by the p-lows 16 in the spaces in which the choppers 22 are positioned.
To the mixing chamber is connected an intake 24 O of a vacuum source 26. Between the i~take 24 of the vacuum source 26 and the mixing chamber 14 is a filter 28 and.a conventional condensing means 30 which in turn is connected to a solvent reservoir 32.
. As shown in.the flow diagram of FIG. 1, ~
a first portion of ingredients comprising a crumbed rubber, for example butadiene-styrene, having a particle size proximating 1/4 inch (.6 cm), an elastomer curing agent such as sulfur, solvent such as toluol and non-absorben~, abrasive fillers such as iron grit, galena - ~1856Z case 5538 (lead sulfide) and mullite (silicate of aluminum) are placed in the mixer 10 with the jacket 12 having a temperature approximating 200F (93C). The terms "nonabsorbent" or "nonporous" define a physical characteristic of the fillers in that they are not affected by the solvent. This first portion of the ingredients fills approximately 11% of the holding capacity of the mixer 10. The mixer 10 is sealed and its plows 16 and choppers 22 activated. After approximately five minutes, the rubber crumbs are completely solvated or in pa~te form with the fillers suspended therein.
The mixer is then stopped, unsealed and a next portion of the ingredients comprising absorbent fillers, friction modifiers, a resin curing agent such as hexa and fibers such as asbestos needed to complete the brake shoe composition are added. The mixer 10 is again activated with its plows 16 and choppers 22 operative for a period approximating one minute.
~ During the next four minutes of mixing, a metered quantity of liquid resin such as a cashew nut shell liquid resin is added to the mix~ure in the chamber 14 while at the same time the vacuum source 26 is àctivated.
The heat, vacuum and constant agitation of the plow~ 16 and choppers 22 gradually drive off a substantial amount of the solve~t after about twenty minutes.
; At this time, the friction materia~ is in pellet form in which the pellet size ranges from 1/16 to 1/4 inch (.lS to .6 c~). This allows the choppers 22 to be de-energized with the plows 16 continuing to rotate or ap-proximately an additional ten minutes when effectively ~ 56Z JLS pm 7/13/77 all remaining solvent has evaporated, been recondensed by the condenser 30 and stored in liquid form in the reservoir 32.
While various modifications may be suggested by those versed in the art, it should be understood that I wish to embody within the.scope of my contribueion Q to the ar~ al~ such mo~ifications as reasonably and ,. properly come within th~ scope of my contribution to the art.

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Claims (4)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A batch process for preparing composition friction materials particularly adapted for forming railroad brake shoes therefrom, said process utilizing a mixer having a sealable mixing chamber with a first plow means and a second chopper mixing means rotatively carried within said chamber, a source of vacuum having an intake port connected to said mixing chamber, a condensing and reservoir means connected between said chamber and said vacuum source and means for heating said mixing chamber, said process comprising the steps of:
1) preheating said mixing chamber to a temperature approximating 200°F. (93°C.), and continuously adding heat to said mixing chamber thereafter, 2) placing a selective amount of ingredients including a crumb elastomer, an elastomer curing agent, a solvent and nonsolvent absorbing abrasive grit in said mixing chamber and sealing said chamber, 3) operating said mixer with said first plow and second chopper mixing means energized for a period of time proximating five minutes to solvate said elastomer, 4) de-energizing said mixer and placing said mixer in an unsealed condition, 5) adding a selective amount of additional ingredients of the group of solvent absorbing fillers, pigments, a resin curing agent and fibers to said mixture of Step 3 and then resealing said mixing chamber, 6) operating said mixer with said first plow and second chopper mixing means energized to a time period approximating one minute, 7) activating said vacuum source to draw off said solvent in a vapor state, 8) adding a selective amount of a resin solution to said mixing chamber through a sealable inlet port connected to said chamber over a time period approximating four minutes, 9) de-energizing said second chopper mixing means after a lapse of time from a completion of said Step 8 proximating twenty minutes, 10) de-energizing said mixer after a lapse of time approximating ten minutes from completion of Step 9, and 11) condensing said solvent vapors and collecting said condensed solvent in said reservoir between Steps 7, 8, 9 and 10, wherein said ingredients are formed by said process into pellets of friction material which may be conveniently formed into railroad brake shoes.

2. A process defined by Claim 1 and further char-acterized by, said source of vacuum drawing a vacuum on said mixing chamber approximating 28 inches (71 cm) of mercury, wherein said friction pellets are substantially free of said solvent upon completion of said process.

3. A method of preparing a composition friction material particularly adapted for forming railroad brake shoe liners, said method comprising the steps of:

, . _ 1) loading into a mixer a first portion of ingredients including an elastomer, a solvent and nonsolvent absorbing materials, 2) mixing said first ingredient portion with mixing means carried by said mixer to produce a solvated paste-like substance, 3). adding into said mixer a second portion of ingredients including curing agents, friction modifiers, solvent absorbing materials and resin 4) energizing a vacuum source connected to said mixer to draw off said solvent in said mixture, 5) mixing said first and second portions with said mixing means to produce a mixture of said ingredients, 6) adding heat to said ingredients in said mixture carried by said mixer at least during Steps 2 and 5, and, 7) withdrawing said mixture of ingredients from said mixer upon a sufficient said solvent being removed from said mixture by said vacuum source, wherein said mixture of ingredients may be conve-niently formed into railroad brake shoes.

4. Apparatus for preparing friction materials which can be conveniently formed into railroad braking devices, said means comprising, a mixer having an elongated cylindrical-shaped, sealable chamber, a first mixing means within said chamber including a drive shaft rotatively carried by ends of said chamber and spaced plow means carried by said shaft to circle about an inner circumferent surface of said chamber, and a second mixing means within said chamber, said second means including chopper means positioned between said spaced plow means and adjacent to said inner chamber surface and carried on a drive shaft positioned transversely to said plow shaft, heating means for adding heat to ingredients in said mixing chamber, said means carried about an outer circumferent surface of said chamber, filtering means to remove particulate matter from a solvent in a vapor state, said filtering means having an intake connected to said chamber, condensing means to change said solvent vapor into a liquid state, said condensing means having an intake connected to an outlet of said filtering means, reservoir means for collecting said solvent changed from said vapor state to said liquid state by said condensing means, said reservoir means having an inlet connected to a discharge of said condensing means, and vacuum source means to reduce pressure in said chamber to less than ambient atmosphere pressure, said vacuum means having an intake connected to said reservoir means, wherein said friction material may be made in an energy efficient and environmental protective manner by charging said chamber of said mixer with a first portion of ingredients to fill approximately 11 percent of a holding capacity of said mixer and mixing said ingredients with said mixing means to produce a solvated paste-like substance, then adding into said mixing chamber a second portion of said ingredients and mixing said ingredients to produce a mixture thereof which upon being subjected to heat from said heating means and vacuum from said vacuum source dries by withdrawal of said solvent.