US2012259A - Friction lining - Google Patents

Description

UNITED STATES I PATENT OFFICE 2,012,259 mIorroN LINING Harry B. Denman, Pontiac, Mich.

No Drawing. Application December 16, 1932,

Serial No. 647,701

Claims.

. The present invention relates to a friction composition and in its more specific aspect the invention is directed to a friction lining adapted to be utilized as a braking medium.

5 The friction composition forming the subject matter of the present invention contains talc as one of its essential constituents, and particularly that type of talc occurring in the foot hills of the Adirondack Mountains and belonging to the Grenville series of crystalline limestones of the pre-Cambrian age. What is known as Gouvemeur talc occurs in this formation.

As to the nature of talc and its varieties, it is desired to refer to Bulletin 259, May 1925, of the New York Museum, wherein it is 'stated:'

Talc is a mineral of variable habits and qualities; and its uses vary with its characteristics, chemically, it is all one and the same materialhydrated magnesium silicate. It occurs in two 2 general forms: as a primary deposit from solution, and as a secondary product that results very commonly from local alteration of anhydrous magnesium silicate, such as tremolite (CaMga(Si03)4 and enstatite (MgFe(SiOa)2).

a mica in appearance, has certain definite'physical properties, and in chemical composition comes close to the proportions demanded by the formula, that is, silica 63.5%, magnesia 31.7% and water 4.8% (Mg3(SlOz)4.HzO). Secondary talc has no well defined physical structure but adopts the structure of the mineral from which it has originated, granular, fibrous or massive, as the case may be. It is likely to be somewhat impure, varyunaltered remnants of the parent substances.

Talc and its formation is also described in Bulletins 223 and 224, July and August, 1919, of the New York State Museum, as follows:

"Nature of talc.-The mineral is both a primary deposit from solution and a secondary product resulting from the alteration of an anhydrous magnesium silicate of the 'amphibole or pyroxene groups (tremolite, from which the 45 Gouverneur fibrous talc originates is an amphibole) The tale in the Edwards (now referred to as Gouvemeur) district is principally secondary and psendomorphic talc, derived by alteration ,of 50 tremolite whose physical structure is still re- Primary talc has a scaly or foliated habit, likeing with conditions, and particularly to contain tained. The talc occurs in small elongated to squarish particles, made up of many parallel fibres; and these fibrous aggregates are intergrown so as'to constitute a solid mass of schistose appearance. To the unaided eye the rock ap- 5 pears homogeneous, but when examined 'more carefully with the aid of the microscope it is usually observed to contain more or less residual tremo lite that has not succumbed to the alteration process. "Foliated or crystal talc 10 is present to a minor extent in most of the occurrences in the Edwards (Gouverneur) district.

It occurs in seams and other openings, where it has been deposited doubtless by waters circulating thru the deposits, to which the conversion of 15 tremolite into fibrous tale is ascribed; that some of the tale should be taken into solution and reprecipitated apart seems only natural.

From the above, it is clear that talc mayocour in three varieties-massive or granular, o fibrous and foliated, and in the Gouverneur district the three varieties are found.

The form of talc which has been found eminently desirable as a constituent of the friction composition forming the subject matter of the present invention is the short fiber talc, and pref erably that originating from the Arnold Mine located adjacent to Gouverneur, New York, and operated by the W. H. Loomis Talc Corporation.

The short fiber talc above referred to analyzes a as follows:

Silica 56.54%

i Fe2Oa+A12Oa 1.04% MnO -Occasional trace MgO -l 30.74% 35 CaO u e" 6.25% C02 .83% Loss on ignition 4.60%-

A recast analysis of the above is: v 40 Per cent Calcium silicate (CaSiOa) 11.00 Talc (HzMgzKSiOaM) n. 85.00 Calcium carbonate (CaCOa) 1.88 Water at 212 F .50

The talc has the following physical properties: Specific gravity '2.80-3.1 Hardness 4-5 Fusion point 2615 F. Dielectric strength 30 volts per mil.

Mineralogically speaking, the tale typified by the Gouverneur short fiber tale is an alteration product of tremolite (amphibole) having the formula CaMga(Si0s)4. The alteration consists in the removal of calcium and the substitution of water so that the alteration product is a fibrous talc containing more or less tremolite. The amount of calcium silicate in the talc depends on the state of alteration from tremolite, and usually varies not more than a point either way from 11%. The tale coming from the Arnold Mine is very constant in that respect. The analysis above set forth shows that the rock carries about 6.25% calcium which after deducting the amount necessary to combine as a carbonate with CO2 yields between 10 and 12% in different analysis to be combined as a silicate. Of course, the percentage composition of the rock is a recast one based on the chemical analysis. It is, therefore, obvious that while the percentage of tremolite present in the Gouverneur short fiber talc may vary, it is usually around the above figure and the tale is, therefore, a fairly pure one.

The product produced from the short fiber tale of the Gouverneur district, the properties and composition of which have been set forth, may be considered as a talc carrying a proportion of tremolite. The Governeur fibrous talc is of course to be distinguished from foliated or bestos fiber is in use, it very frequently is heatedslippery talc. Fibrous and massive tales lack slip, and this is also true of the granular variety. The short fiber Gouverneur talc has a hardness of about 4 to 6, depending on how far the alteration of the parent material has proceeded. The foliated talc, due to its slipperiness, has a much lower coefficient of friction than the fibrous talc, and since the foliated talc is softer than the fibrous talc the latter gives a better wear factor. The difference between short fiber talc. and foliated tale is quitedistinct and easily seen. In addition to the physical properties above set forth which distinguish the two varieties of talc, they may be distinguished by merely rubbing a finely powdered sample of each variety between the fingers. The foliated talc and the massive steatite have a greasy feel and are shiny, while the finely divided short fiber Gouvemeur tale is smooth and lacks the greasy feel and shiny appearance.

' The tale typified by Gouverneur talc has given particularly satisfactory results, and therefore it is the preferred talc component of the friction composition herein disclosed. However, other tales originally occurring in the fibrous state and having high coefiicients of friction when finely divided may also be used, although-the results are not quite so satisfactory.

The fibrous tale in 'its original condition resembles some forms of asbestos and is therefore known as asbestine.

The above described talc and/or asbestine when finely ground, for example so that 98%Ithereof passes through a 325 mesh sieve, forms a powderlike mass and to all intents and pu p ses is, as compared to ground-up asbestos, a non-fibrous material. In other words, if asbestos is ground up'to a fibrous state, due to the inherent character-of the material, that is the strength, toughness and pliability of .its fibres, the fibrous'state is maintained. Talc on the contrary forms a powder-like mass. To the naked eye, when asbestos fibers are finely ground .up the fibers still appear fibrous. On the contrary, when the short fiber talc and asbestine is finely ground up, to the naked eye the tale. appears non-fibrous,- although underfthe microscope it is somewhat fibrous, showing very short and minute fibers with a large proportion of the fibers broken down to form a granular mass. The term non-fibrous as applied to short fiber talc and asbestine is used in thesense above set forth. However, the difference between the two materials may be perhaps better brought out by describing their action in a friction composition while in actual use. When asbestos is mixed with a binder such as rubber, the asbestos fibers do not blend thoroughly but remain visible, giving the composition a fuzzy appearance. The composition is not homogeneous and the asbestos fibers tend to form small agglomerates or lumps which may be picked out of the friction composition quite readily. The presence of the small agglomerates or lumps makes the composition non-homogeneous and materially decreases the effective contact surface of the composition, resulting in a corresponding decrease in braking power.

When finely divided talc or asbestine is mixed to a temperature varying between 700 F. and 800 F. At that temperature the asbestos fiber undergoes a chemical or physical change, and it becomes hard enough to score the braking drum producing in some instances inefficient braking conditions, and the tendency of the drum to score is magnified after the brake lining has been in use for sometime. Finely ground talc typified by Gouverneur .talc does not undergo that change, except at much higher temperatures not usually attained under ordinary conditions, and there.- fore scoring of the brake drum is substantially eliminated.

As stated, the tale is reduced to a finely divided state. While it is not desired to be lim- .ited to any particular mesh size, in general it may vulcanizable fatty residue, reclaimed rubber, or

artificial rubber known as Duprene, the latter being chloroprene or polymerization products thereof, as hereinafter set forth. The chloroprene polymerization products may be mixed with rub-. ber and have a friction constituent of any type dispersed therethrough. When using a. mixture of rubber and chloroprene, the mixture together with the friction constituents dispersed therethrough may be vulcanized. The preferred friction constituent is the herein disclosed tale.

The friction composition may have mixed therewith a waterproofing agent usually resins and/or waxes. By-varying the amount of the resin, and particularly rosin and/or wax, the coefiicient of friction of the composition may be varied over quite a wide range. The wax used in making the composition also facilitates the -mixing thereof and serves as a'waterproofing agent in the'finished product. Various waxes such as mineral, hydrocarbon and vegetable waxes may be used, it not being desired to be limited to any particular wax. For example, there may be usedozokerite, beeswax, Mont-an wax, paraflin'wax or ceresin wax, paraffin wax being preferred.

The friction composition mix prior to vulcanization has present a vulcanizing agent. This may include the ordinary inorganic vulcanizing the 'diphenylguanidine.

compounds which usually contain sulfur, or an organic accelerator may be used to decreasethe time of vulcanization. Usually, there is also present compounds functioning as'an activator for the particular vulcanizing agent or accelerator used. For example, zinc oxide may be used as an activator. Lime, magnesium oxide, or mixtures of the same, also may be present in the mix to assist in the vulcanization, although neither is essential, as both may be omitted without greatly affecting the desirable characteristics of the finished product. Zinc oxide also, while desirable, is not absolutely necessary.

As an example of a suitable accelerator, diphenyl-guanidine may be used. However, it is obvious that other organic accelerators well known and on the market may be substituted for The following is a specific example of a suitable rmxr A master batch is made from rubber, rosin and an accelerator. For example, the specific composition of the master'batch may be:

Parts by weight Rubber -i Rosin 25 Accelerator 1 The amount of accelerator used may be varied,

depending on the type of accelerator used and the length of cure-desired.

The rosin in the above example may be replaced in whole or part by a synthetic resin. Satisfactory results are obtained using a phenol formaldehyde condensation product produced by the Bakelite Corporation of New York and known as CEO-220. The resin is added preferably in the powdered form, asin this form the incorporation into the batch is facilitated.

Instead of using 25 parts of rosin in the master batch, the same may be replaced by a phenola synthetic resin of which a phenolic formaldehyde condensation product is illustrativemay. be used in the master batch when the brake lining is used on trucks or other vehicles having a relatively low"speed;"In"'high"speed vehicles where excessive heat is generated, when the brakes are applied, it is desirable to use in the master batch only the synthetic resin insteadof mixtures of the same with. rosin. A portion of the master batch prepared a above, is mixed with the talc or asbestine and a suitable example is as follows:

i or metal shoe.

present invention.

In making the complete mix, the following represents the preferred mode of procedure, and

gives the most satisfactory results. However,

the invention is not limited to the particular manner of mixing herein setforth.

The master batch is mixed separately, either in an internal type of mixer or in a standard mixing mill. The rubber is first broken down to run smoothly, after which the waterproofing agent, for example rosin, and the accelerator are added as rapidly as possible. The entire mass is thereafter mixed thoroughly until the rosin is entirely blended into the rubber. The batch is then sheeted out and allowed to cool.

The required amount ,of the master batch is placed on a mixing mill or in an internal mixer and warmed until it begins to run smoothly.

Thereafter, the finely divided talc or asbestine, together with a wax and suitable activators are added as rapidly as possible. In the specific example given, the activating material comprises lime and zinc oxide. The wax is preferably added during the early stages of the mixing to facilitate the blending of the mixed constituents. The sulphur is added towards the end of the mixing period and allowed to mix just long enough to become thoroughly blended in the batch. The batch is thereafter sheeted out and allowed to cool.

The complete batch is warmed in the customary manner and passed through a sheeting calender to sheet it. out to the requiredthickness and width. The sheeted material is then ready for vulcanization, and in carrying-out the vulcanization the sheet of material may be placed between heated plates under pressure for a sufiicient time to allow vulcanization to occur. In the example given above, the material is'vulcanized for twenty minutes'at 315 F. under a hydraulic line pressure of 2250 pounds per square inch. It is obvious that the time and temperature of vulcanization. as well as the hydraulic pressure, may be varied as desired. The degree of vulcanization may of course be varied to meet predetermined service conditions. In general, however, the vulcanization is carried to a point where .the vulcanized material will give a test reading of 98 to 100v on a Shore durometer.

The sheeted mix may be vulcanized alone or it may be vulcanized to a base'material to form a friction facing. The base material may consist of another rubber compound or a rubber and fabric combination, or fabric with and without reinforcements, or it may consist of a metal strip The braking element is made up of two distinct materials, a facing material to function as a braking surface, and a base material such as a metal strip or the like function- It is desired to point out that the particular method of mixing the ingredients may be considerably varied. For example, instead of making a master batch and then compounding this with other ingredients, all the materials may be mixed in one operation. Any method of mixing consistent with good manufacturing practice may be used, and this will depend in a measure upon the type of equipment which a particular. rubber manufacturer has available. However, the twostep method of mixing has given very satisfactory results.

In the above examples illustrative of the preferred form of the invention, the major constituents of the mix are finely divided Gouverneur talc and rubber, the Gouverneur talc or asbestine being present in a predominating quantity. In the examples given, the asbestine may be replaced by a mixture of asbestine and foliated or slippery talc, the percentage of, the foliated talc running from about to 25% based on the weight of the asbestine. The important point is. that the foliated talc should not be added in a quantity sufilcient to impair the braking efiiciency of the friction material. ,Stated differently, the coefiicient of friction should not be materially reduced. There may be mixed with the asbestine or talc other diluents instead of the foliated talc, as for example finely divided serpentine. ever, the predominating proportion of the friction ingredient or component should always be a fibrous talc in a predominating proportion, and

45 preferably Gouverneur talc or asbestine.

It is to be understood that the particular examples given are merely illustrative of suitable mixes and are not by way of limitation. The percentage of .finely divided asbestine may be considerably below 65% and still come within the spirit of the invention. In the preferred form of the invention the asbestine which forms the major friction constituent should be present ina predominating proportion. .It may be as low at 50% and in some cases, depending on service conditions to be met, even lower. However, it'is desired to point out that the final product should be a homogeneous one, and in s cc should not form lumps or agglomerates, or in other words it should have non-pitting characteristics.

In the-place of natural rubber there may be used synthetic rubber, commercially known as Duprene, manufactured by E. I. du Pont de Nemours and Co. The preparation of this product is described in the Journal of the American Chemical Society for November, 1931'. Nieuwland, Calcott, Downing and Carter describe on pages 4197 to 4203 the polymerization of acetylene in their article entitled Acetylene polymers and their derivatives. 1. The controlled polymerization of acetylene; and Crothers, Williams Collins and Kirby discuss chloroprene and its polymers in I. A new synthetic rubber: chloro elusive. The u-polymer of chloroprene can be vulcanized like ordinary rubber. The vulcanized product however has greater oil resisting and heat resisting properties than natural rubber. Natural rubber swells considerably under the 'action of oils, and this disadvantage is eliminated when using the a-polymer of chloroprene.

Any of'the artificial rubber products described in the above articles by Nieuwland, Calcott, Downing and Carter or Carothers, Williams, Collins and Kirby may be mixed with a friction constituent to produce a brake lining or other friction compositions. This phase of the invention is not limited to the utilization of talc as a friction constituent and, as stated, other friction con stituents may be used in place of the tale. While it is preferred to use the a-polymer of chloroprene, other polymers, the production of which is described in the articles referred to, may be combined with a friction consituent such as talc and particularly the short fiber talc 'or asbestine, the properties of which have been enumerated. The chloroprene products above described and particularly the a-polymer may be mixed with rubber, and this mixture may have dispersed therethrough a finely divided friction constituent, and particularly finely divided talc, it being preferred to use the short fiber talc of the Gouverneur type, although other forms of talc such as foliated talc may be wholly or partly substituted therefor.

In place of the specific phenolic condensation product set forth there may be added to the master batch any phenolic condensation product or any synthetic resin now on the market or disclosed in the prior art which will function to waterproof thefinal friction composition and/or modify its coefilcient of friction.

The present application is a continuation-inpart of application Serial No. 475,640, filed August 15, 1930.

What I claim is:

1. A homogeneous friction element free of fibrous material and containing as its essential ingredients, an organic binder, and a predominating proportion of fine divided asbestine.

2. A homogeneous friction element freeof fibrous material and substantially non-pitting in character containing as its essential ingredients vulcanized rubber and finely divided asbestine dispersed therethrough, the latter being present in a predominating proportion.

3. A homogeneous friction element free of fibrous material and substantially non-pitting in character containing as an essential element an organic binder and at least 50% of finely divided asbestine.

4. A homogeneous friction element free of fibrous material and substantially non-pitting in character containing as its essential ingredients vulcanized'rubber and at least 50% of finely divided asbestine dispersed therethrough.

5. A homogeneous friction element free of fibrous material and substantially non-pitting in character containing as its essential ingredients an organic binder-and a predominating proportion of finely divided asbestine together with rosin and wax acting to modify the coemcient of fric-' tion of the friction element.

6. A homogeneous friction element free of fibrous material and substantially non-pitting in character containing as its essential ingredients vulcanized rubber and finely divided asbestine in apredominating proportion dispersed therethrough together with rosin and wax acting to A $012,259 modify the coemcient of friction of the friction element. 7. A substantially non-pitting homogeneous friction element characterized by the absence of agglomerates under service conditions, containing as its essential ingredients an organic binder and a predominating proportion of finely divided non-fibrous asbestos.

8. A homogeneous friction element containing as its essential ingredients an organic binder and a predominating proportion of finely divided asbestine, said friction element being free of fibrous and filamentous bodies adapted to cause pitting of the friction element under service conditions.

.9. A homogeneous friction composition com prising the vulcanized product of a mixture of rubber, a predominating proportion of finely di-- vided asb eetine and a synthetic resinhaving similar characteristics under heat as the phenolic formaldehyde condensation resins, said synthetic resin acting to modify the coefiicientof friction of the composition, the latter being non-pitting in character.

10. A friction composition comprising the vulcanized product of a mixture or rubber, a predominating proportiog of finely divided asbestine, a teristics synthetic resin aving similar charac under heat as the phenolic formaldehyde condensation resins, and rosin, said synthetic resin and rosin acting to modify the coefilcient of friction of the composition, the latter under service.

conditions being non-pitting.

v -EARRY B. DENMAH-v