4296 4300.output

* GB784703 (A)

Description: GB784703 (A) ? 1957-10-16

Improvements in or relating to the manufacture of gloves from rubber orflexible thermoplastic materials

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**WARNING** start of DESC field may overlap end of CLMS **. COMPLETE SPECIFICATION Improvements in or relating to the Manufacture of Glovesl from Rubber or Flexible Thermoplastic Materials We, LONDON RUBBER COMPANY LIMITED a British Company, of Hall Lane, Chingford, London, E.4, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to the manufacture of gloves from rubber or flexible thermoplastic material by dipping into a dispersion of the rubber or other material a former of the desired shape and size so that a film of the material is deposited on the former, and sub sequently heating the former with the film thereon. Gloves manufactured in this manner have a better surface internally than externally, and it is therefore customary to turn the finished gloves inside out before sale and use, so as to provide an improved appearance. Moreover, it may be advantageous to have a roughened external surface on at least some parts of a glove, and this can be obtained, if the glove is turned inside out after being manufactured,

by suitably roughening the former. It has been found, however, that a glove, when turned inside out, is considerably distorted so that it does not lie closely on the hand, and has an unnatural appearance. The object of the present invention is to avoid this disadvantage. The present invention comprises a method of manufacturing a glove of rubber or other flexible thermoplastic material which consists in preparing a former having the shape of a glove which has been produced on another former simulating the true shape of a hand and has been turned inside out, forming a glove thereon by dipping in the known manner, and turning the glove so formed inside out The former may be prepared by any one of those methods described in our Patent Application No. 34219/54 (Serial No. 784,702) in which the former is produced in a mould having the shape of an inside-out glove or by any other method such as, for example, by turning inside out a glove made on a former simulating the true shape of a hand, filling the said glove with any suitable material to give it a degree of rigidity, and copying its shape by means of a copying machine. The former is dipped in the usual manner into a dispersion of the material from which the gloves are to be formed so as to receive a film of that material, and the film is subjected to heat treatment in the known manner. After being stripped from the former the glove is turned inside out, and then has substantially the shape of a glove made on a former simulating the true shape of a hand, its external surface being that which was in contact with the former, What we claim is: - 1. The method of manufacturing a glove of rubber or other thermoplastic material which consists in preparing a former having the shape of a glove which has been produced on another former simulating the true shape of a hand and has been turned inside out forming a glove thereon by dipping in the known manner, and turning the glove so formed inside out. 2. The method of manufacturing a rubber glove substantially as herein described. PROVISIONAL SPECIFICATION Improvements in or relating to the Manufacture of Gloves from Rubber or Flexible Thermoplastic Materials We, LONDON RUBBER COMPANY LIMITED, a British Company, of Hall Lane, Chingford, London, E.4, do hereby declare this invention to be described in the following statement: This invention relates to the manufacture of gloves from rubber or flexible thermoplastic material by dipping into a dispersion of the

rubber o; other material a former of the desired shape and size so that a film of the material is deposited on the former, and sub sequently heating the former with the film thereon. Gloves manufactured in this manner have a better surface internally than externally, and it is therefore customary to turn the finished gloves inside out before sale and use, so as to provide an improved appearance. Moreover, it may be advantageous to have a roughened external surface on at least some parts of a glove, and this can be obtained, if the glove is turned inside out after being manufactured, by suitably roughening the former. It has been found, however, that a glove, when turned inside out, is considerably distorted so that it does not lie closely on the hand, and has an unnatural appearance. The object of the present invention is to avoid this disadvantage. The present invention comprises a method of manufacturing a rubber glove which consists in preparing a former having the shape of a glove produced on another former simulating the true shape of a hand and turned inside out, and turning the glove inside out after manufacture. The former may be prepared by any of the methods described in our Patent Application No. 34219/54 (Serial No. 784,702) or by any other method such as, for example by turning inside out a glove made on a former simulating the true shape of a hand, filling the said glove with any suitable material to give it a degree of rigidity, and copying its shape by any suitable method. The former is then dipped in the usual manner into a dispersion of the material from which the gloves are to be formed so as to receive a film of that material, and the film is subjected to heat treatment in the known manner After being stripped from the former the glove is turned inside out, and then has substantially the shape of a glove made on a former simulating the true shape of a hand, its external surface being that which was in contact with the former.

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* GB784704 (A)

Description: GB784704 (A) ? 1957-10-16

Articles comprising boron nitride and refractory oxide and the manufacturethereof




PATENT SPECIFICATION 784704 r Date of Application and filing Complete Specification:June 21, 1955. No 17885/55. Application made in United States of America on Oct 25, 1954. Complete Specification Published: Oct 16, 1957. Index at acceptance:-Class 22, J( 1: 6: 7: 9: 12: 19: 20: 22). International Classification:-C 04 b. COMPLETE SPECIFICATION Articles Comprising Boron Nitride and Refractory Oxide and the manufacture thereof We, THE CARBORUNDUM COMPANY, of Niagara Falls, in the County of Niagara and State of New York, United States of America, a Corporation organized and existing under the laws of the State of Delaware, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to shaped bodies or articles of manufacture consisting essentially of refractory oxide and boron nitride, and to compositions and methods for making the same. There is a constant search for new compositions or bodies that possess unexpected combinations of properties essential to or desirable in specific fields of use The bodies of the present invention possess certain combinations of properties and characteristics that render them of considerable value, and they offer outstanding possibilities in a number of fields of use It is, therefore, to be understood that

the refractory oxide-boron nitride bodies hereinafter more fully described are not to be considered as restricted to any particular field of use However, their outstanding characteristics as refractory mater Ials are particularly worthy of note and make them especially suitable for many refractory purposes The present invention therefore will be described primarily in resnect of the use of the herein described products for refractory purposes, although not intended to be limited thereto. Above all a refractory body must possess refractoriness, that is an ability to stand up under exposure to high temperatures without undue chemical or physical change Other desirable characteristics sought in a refractory body or shape include an ability toi resist sudden changes in temperature without cracking or otherwise breaking down, a satisfactorily high mechanical strength at elevated temperatures as well as at room temperature, l'p chemical inertness and resistance to various corrosive and erosive substances and conditions, a resistance to oxidation, and a density and hardness dependent upon the use to which the refractory body or shape is to be put. In order to obtain a high degree of perfection in one or more of the above properties, it has usually been necessary to forego the benefits of maximum performance in respect to certain other desirable properties Consequently, various refractory compositions exceptionally suitable for one use frequently are entirely unsatisfactory for other purposes. There is, therefore, a continual demand for refractory bodies of new compositions that will meet those demands of a special nature which require novel combinations of properties not to be found in compositions already available. It is an object of the present invention to provide bonded refractory bodies or shapes of unusual and distinctive compositions and properties. It is another object to provide refractory bodies or shapes having a particular combination of properties heretofore unavailable in refractory compositions. It is a further object to provide practical methods and compositions for making such articles. The shapes or bodies of the present invention comprise boron nitride and refractory oxidic material The amount of boron nitride present in the bodies may range from almost zero per cent, such as 1 or 2 per cent, to almost 100 per cent by weight of the bodies. The preferred compositions of the present invention, however, contain only un to 30 per cent by weight boron nitride The bodies of the present invention are hard and dense. having a density of 85 per cent or more of the theoretical density.

The boron nitride used in carrying out the present invention may be either a high or a low purity boron nitride material available on the market For example, it may be a low purity boron nitride material made in accordance with the process described in Specification No 13838/53 (Serial No 742,326) This boron nitride material is made by nitriding a porous pelleted mixture of boric acid or boric oxide and tricalcium phosphate by heating it in ammonia gas at a temperature of around 900 C After nitriding, the resultant nitrided pellets are treated with dilute hydrochloric acid to dissolve the tricalcium phosphate and other extraneous materials The undissolved boron nitride after washing with water is usually treated with hot 95 % alcohol solution to further lower the content of extraneous material The material is then dried by allowing to stand overnight at room temperature followed by heating for 2 hours at 300 F A typical analysis of the boron nitride is as follows: Boron 41 45 % Nitrogen 45 60 % Free Boric Acid (Calculated as HBO 0,) 75 % Silica 28 %o, Calcium trace Phosphate (P 04) trace Material volatile at 110 C 26 % Although this material contains no alcoholsoluble material, it is believed that it contains up to about 20 % of an oxidic boron compound tied up either chemically or physically so as to be alcohol-insoluble. An example of a high purity boron nitride material that may be used in the process of the present invention is the mtserlal made in accordance with the process described in specification No 6158/55 (Serial No. 777,000) Boron nitride material is made in accordance with this patent application by first preparing a low purity boron nitride material, such as the boron nitride material prepared in accordance with the process of specification No 13838/53 (Serial No. 742,326) and then heating the low purity boron nitride material in an atmosphere of ammonia at a temperature ranging from 1100 to 1500 C A typical analysis of the resultinc high purity boron nitride material is as follows: Boron 43 3 % Nitrogen 53 3 % Oxygen 2 23 % Silica 25 % Calcium Nil Iron and aluminium oxides 16 % The refractory oxidic material employed in the process of the present invention may be any of the well-known simple refractory oxides, preferably being selected from the groun consisting of zirconia, alumina, thoria, beryllia and combinations thereof Instead of employing one or more simple refractory| oxides, complex refractory oxidic material mayg be used, such as the various refractory silicates or aluminates, including mullite, sillimanite, olivine, and refractory porcelains When 65 zirconia is employed, it is preferably a stabilized zirconium oxide in which all or a major portion of the zirconia is of the cubic crystalline variety such as a

zirconium oxide that has been stabilized with around 5 % of calcium 70 oxide. In accordance with the present invention, shaped articles of manufacture comprising boron nitride and refractory oxidic material are made by the method which comprises pre 75 paring or selecting a raw mix comprising finely-divided refractory oxidic material and boron nitride, and consolidating the raw mix by the simultaneous application of pressure and heat, that is, by hot pressing 80 The hot pressing is carried on by heating the mold containing the raw mix in an inert atmosphere within the temperature range of 1400 C to 1900 C, preferably from 1600 C. to 1700 C The maximum temperature of 85 1900 C should not be exceeded in firing, because firing at higher temperatures frequently causes partial disintegration, part of the refractory oxide being converted to a boride. For example, when a body consisting of 80 % 90 stabilised zirconia and 20 % boron nitride was fired at 2000 C it Dartially disinterated the presence of zirconium boride having been established by X-ray diffract;_n analysis. The articles of the present invention are 95 hard and extremely dense and have a low sandblast penetrati-n factor The densities of the hot pressed bodies are greater than 85 % of the theoretical density, frequently being as high as 95 % or more of the theoretical density 100 It is therefore apparent that by practising the process of the present invention bodies of extremtnely low porosity can be produced. Furthermore if the raw mix employed consists essentially of high purity boron nitride material 105 and refractory oxidic material, hard dense bodies composed of, or consisting essentially of, boron nitride and refractory oxidic material can be made. In contrast to the high density, hard bodies 110 of the present invention made by hot oressing, bodies of similar composition consolidated by cold pressing and sintering are in most instances relatively weak and porous, even when low percentages of boron nitride are employed 115 Boron nitride-refractory oxide bodies consolidated by cold pressing and sintering and containing more than 2 ( O % by weight boron nitride, usuallyv are so weak that they are easilv crumbled by hand Therefore, boron nitride 120 refractory oxide bodies made by cold Dressing and sintering are hiurhlv unsatisfactory for uses where bodies of high strength, hardness, density and purity, and/or containing high percentages of boron nitride are required 125 To demonstrate the practice of the present invention, the following examples are given: 784,704 784,704 EXAMPLE 1. In accordance with the practice of the present invention, boron

nitride-refractory oxide bodies in the form of cylinders 1 " diameter x about 1 " long were made as follows:Intimately conmmingled granular raw mixes having a particle size of 20 microns and finer and consisting of refractory oxide and high purity boron nitride material made in accordance with the aforementioned Patent Application No 6158/55 (Serial No 777,000) were prepared by passing the mixed ingredients through a fine meshed screen several times. The desired amount of each, raw mix was then put in a mold and the mold and contents were heated under a pressure of about 2000 pounds per sq in at the temperature indicated in Table I below, the mold and contents being held under pressure a maximum temperature until the required density has been obtained Table I below presents fabricating data and physical properties of the various bodies consisting essentially of boron nitride and refractory oxide made in accordance with the process of the present invention. TABLE I Bodies Consisting of Boron Nitride and Refractory Oxide Fired in an Atmosphere of Helium Raw Mix Firing Sand Apparent Theoretical Percent Bar Composition, Type BN blast Density Density Theoretical No % by weight Used Max Temp Penetration gms /cc gms /cc Density 1 80 % Zr O 2; % BN Pure 1650 C 006 " 4 19 4 38 96 % 2 80 % A 1203; % BN Pure 1600 C 023 " 3 15 3 41 92 % 3 80 % Mullite; % BN Pure 1600 C 015 " 2 75 2 82 98 % 4 80 % Th O 2; % BN Pure 1800 C 032 " 5 35 5 86 91 % 50 % Zr O 2; % BN Pure 1700 C 010 2 85 3 22 88 % 6 10 % Zr O 2; % BN Impure 1800 C 004 " 2 14 2 40 89 % 7 12 % Th O 2; 88 % BN Impure 1800 C 006 " 2 25 2 49 90 % Standard penetration on plate glass when subjected to the same penetration test is 010 ". As can be seen by the data in Table I, superior, hard, high density bodies having a wide range of compositions can be made by the preferred hot pressing process of the present invention. EXAMPLE 2. To demonstrate the inferiority of the physical properties of cold pressed and sintered boron nitride-refractory oxide bodies in contrast to the outstanding physical properties given in Table I above for similar compositions hot pressed in accordance with the present invention, a series of pieces in the form of small test bars 1 2 " x , x 4 r" were made as follows: Intimately commingled mixtures of refractory oxidic material and boron nitride of the aforementioned high purity variety, were prepared The mixes had a particle size of 20 microns and finer To about 10 parts by weight of each mixture was added 5 by weight of "Carbowax" No 4000 dissolved in 1 part by weight of benzene, and the thusly formed raw mixes were ground in a mortar until the benzene had evaporated "Carbowax" No.

4000 is a trade mark denoting a polyethylene glycol composition The mixtures were then molded to the desired shape at pressures up to '30,000 psi The temporary binder of "Carbowax" was removed by slowly heating the molded shapes at 400 C The pressed shapes were then heated in an atmosphere of helium Table II below presents fabricating data and physical properties of the various bodies comprising boron nitride and refractory oxide in various proportions made by cold pressing and sintering. 784,704 TABLE II Bodies Consisting of Boron Nitride and Refractory Oxide Fired in an Atmosphere of Helium Firing Raw Mix Type Sand Apparent Theoretical Percent Bar Composition BN Max H Iolding blast Density Density Theoretical No % by weight Used Temp Time Penetration gms/cc gms/cc Density 8 80 % Zr O 2; Pure 1650 C 60 Not co% BN Min herent 9 80 % A 1 03; Pure 1650 C 60 Not co% BN Min herent 80 % Mullite; Pure 1650 C 60 435 " % BN Min. 11 80 % Th O 2; Pure 1650 C 60 Not co% BN Min herent 12 80 % Zr O 2; Pure 1800 C 60 310 " 2 80 4 38 64 % % BN Min. 13 80 % A 1203; Pure 1800 C 60 Soft 1 73 3 41 51 % % BN Min. 14 80 % Mullite; Pure 1800 C 60 375 " 1 88 2 82 67 % % BN Min. 80 % Th O 2; Pure 1800 C 60 Soft 3 15 5 86 54 % % BN Min. Standard penetration on plate glass when subjected to the same penetration test is 010 ". Too soft to test. It is to be noted that the compositions of bars 8 through 15 are identical with the compositions of bars 1 through 4 in Table I Cold pressing and sintering these compositions, even at temperatures as high as 1800 C with holding times of 60 minutes, resulted in bodies having densities ranging only from 51 to 67 per cent of the theoretical densities for non-porous bodies of the same compositions. In contrast densities approaching 100 per cent of the theoretical densities for completely non-porous bodies are obtained by hot pressing raw mixes containing any desired percentage of boron nitride. While in the above examples the practice of the present invention is demonstrated primarily by raw mixes containing only a single simple oxide, as was pointed out above more than one refractory oxidic material can be included in the raw mixes of the present invention Furthermore, if desired, minor amounts of an inert refractory filler, such as a refractory boride or silicide, can be included in the raw mixes in place of some of the refractory oxidic material to produce bodies that are satfsfactcly for cer-tin uses. While the above examples have described the making of molded bodies in which the body is consolidated to the exact shape or form in which it is intended for use, the present invention is not intended to be so

restricted Another way of making and using the refractory oxide-boron nitride bodies of the present invention is to consolidate the raw batch into briquettes or other shapes, after which the resulting briquettes or shapes are crushed to granular form of the desired grit size The resulting granular material can then be used in loose granular form as high temperature refractory material, as layers of insulation in industrial furnace chambers, as insulation around jet engines and rocket combustion chambers, and the like It may also be used as loose filtering media or as catalyst or catalyst carrier materials The granular material can also be bonded by means of sintered metals, vitreous or ceramic bonds, or other bonding material, or it may be cold pressed and sintered or hot pressed per se to form articles suitable for many of the industrial uses set forth elsewhere herein. It is to be understood that the products of the present invention in their various modifications are not limited to any specific field or fields of use such as might be defined by the specific examples previously set forth. The products can be made in any desired shape as well as provided in granular aggregate form They are, therefore, not only suited for many of the uses for which industrial refracteries are required, including bricks, blecks, setter tile, muffles, kiln furniture, and special shapes for application in and around furnaces and other high temperature equip% boron nitride and at least 70 % refractory oxidic material. 3 As a new article of manufacture, a body as claimed in claim 1 or 2, in which the refractory oxidic material consists of zirconia, alumina, thoria, beryllia, or mixtures thereof. 4 As a new article of manufacture, a body as claimed in claim 1, 2 or 3 and containing an inert refractory filler. A method of making shaped articles of manufacture comprising selecting a raw mix comprising boron nitride and refractory oxidic material and consolidating said raw mix to the desired shape by simultaneously pressing and heating in an inert atmosphere at 14001900 C. 6 A method of makling shaped articles of manufacture as claimed in claim 5, in which the refractory oxidic material consists of zirconia, alumina, thoria, beryllia or mixtures thereof. 7 A method of making shaped articles of manufacture as claimed in claim 5, or 6, in which the raw mix contains up, to 30 % boron nitride. 8 A method of making shaped articles of manufacture as claimed in claim 5, 6 or 7 in which the hot pressing is effected at 16001700 C. 9 A method of making shaped articles of manufacture, as claimed in any of claims 5-8, in which the raw mix is placed in a mold and the mold

and contents are heated under pressure at 1600-1900 'C. A method of making shaped articles of manufacture as claimed in any of claims 5-9, in which the raw mix comprises refractory oxidic material, inert filler and up to 30 % boron nitride. MARKS & CLERK. ment, but they are also well suited for many specialty high-temperature applications, such as jet engine combustion chambers, linings for exhaust nozzles, rocket combustion chambers and exhaust nozzles, turbine blades, stator blades, lens fusion blocks, spark plug bodies, and the like They are also suitable for the fabrication of laboratory ware, including combustion boats, crucibles, burner holders and other shapes The resistance of such bodies to chemical attack make them highly suitable for the making of articles used in the containing, conveying and handling of many acids, molten metals and other corrosive chemicals, including such articles as chambers and chamber linings, crucibles, pipes and pipe fittings, and other sundry shapes The bodies of the present invention are also highly useful as diffusion and filtering media, such as diffusion tubes and plates, filtering tubes, plates and shapes, or as catalysts or catalyst carriers and supports The materials and articles of the present invention can also be used for making abrasive articles such as grinding wheels, sharpening stones, razor hones, and other grinding and polishing shapes and materials. The present bodies offer possible applications in the electrical and radio industry including supports in electric light bulbs, radio tubes, X-ray tubes and radar equipment, resistors and grid leaks.


* GB784705 (A)

Description: GB784705 (A) ? 1957-10-16

Refractory bodies containing boron nitride and a boride, and the manufacture

thereof




PATENT SPECIFICATION 7 fi Date of Application and filing Complete Specification: July 22, 1955. No 21245/55. Application made in United States of America on Oct 25, 1954. (Patent of Addition to No 742,327, dated May 18, 1953). Complete Specification Published: Oct 16, 1957. Index at acceptance:-Classes 22, J( 1: 2: 6: 7: 11: 12: 19: 21: 33); and 70, F 2 A( 2: 3). International Classification:-CO 4 bo COMPLETE SPECIFICATION Refractory Bodies Containing Boron Nitride and a Boride, and the Manufacture thereof We, THE CARBORUNDUM COMPANY, of Niagara Falls, in the County of Niagara and State of New York, United States of America, a Corporation organized and existing under the laws of the State of Delaware, United, States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to improvements in or modifications of the shaped bodies or articles of manufacture and the compositions and methods for making the same, according to specification No 13839/53, (Serial No. 742,327). According to specification No 13839/53, (Serial No 742,327) bodies stuch as refractory bodies comprise boron nitride and either zirconium boride or carbon boride Such bodies are made by forming a mixture of boron nitride and the selected boride, placing the mixture in a mold and hot pressing said mixture at a temperature of at least 1800 C and a minimum pressure of 500-750 pounds per square inch. It is an, object of the present invention to provide alternative materials for use in the manufacture of such bodies.

The shapes or bodies of the present invention consist of boron nitride and either refractory boride material other than zirconium boride and carbon boride, or zirconium or carbon boride together with the other refractory boride The amount of boron nitride present in the bodies may range from almost 0 %, such as 1 or 2 %, to almost 100 % by weight of the bodies The preferred compositions of the present invention, however, contain only up to 50 % by weight boron nitride, with the best bodies containing not over 20 % by weight boron nitride. The bodies or articles of the present invention are made by hot-pressing the raw mixes in a graphite mold at a temperature somewhat lPrice lower than the temperature at which the particular raw mix becomes so plastic as to be extruded from the mold around the plunger. With compositions high in boride content, the maximum hot-pressing temperature is usually slightly below the melting temperature of the boride However where compositions high in boron are employed, temperatures above the melting temperature in the neighborhood of 2500 C may be used The hot-pressing is preferably carried on at pressures of from 500 to 750 pounds per square inch or more. The boron nitride used in carrying out the present invention may be either a high or low purity boron nitride material available on the market For example, it may be an impure boron nitride made in accordance with the process described in specification No. 13838/53, (Serial No 742,326) This boron nitride material is made by nitriding a porous pelleted mixture of boric acid or boric oxide and tricalcium phosphate by heating it in ammonia gas at a temperature of around 900 C After nitriding, the resulting nitrided pellets are treated with dilute hydrochloric acid to dissolve the tricalcium phosphate and other extraneous tuaterials The undissolved boron nitride, after washing with water, is usually treated with hot 95 % alcohol solution to further lower the content of extraneous materials The material is then dried by allowing it to stand overnight at room temperature followed by heating for two hours at 300 F. A typical analysis of the boron nitride is as follows: Boron 41 451 % Nitrogen 45 60 % Free Boric Acid (calculated as H 3 BO 3) 75 % Silica 28 % Calcium trace Phosphate (P 04) trace Material volatile at 110 a C 26 % Although this material contains no alcohol ijc 4,705 soluble material, it is believed that it contai up to about 20 % of an oxidic boron cot pound combined either chemically physically so as to be insoluble in alcohol ai water. An example of a high purity boron nitric material that may be used in the process the present invention is the material made accordance with the process described specification No 6158/55, (Serial N 777,000) Boron nitride material is made accordance with this patent

application by fir preparing a low purity boron nitride materi such as the boron nitride material prepare in accordance with the process of specificathi No 13838/53, (Serial No 742,326), and the heating the low purity boron nitride materi in an atmosphere of ammonia at a temper ture ranging from 1100 to 1500 C We prefi a minimum temperature of 14000 C A typic analysis of the resulting high-purity borc nitride material is as follows: Boron Nitrogen Oxygen Silica Calcium Iron and aluminium oxides 43.3 % 53.3 % 2.23 % 0.25 %? nil 0.16 % We have further found that if boron nitrid prepared in accordance with specification N, 13838/53, (Serial No 742,326), is sue sequently, before use, subjected to a heatin pre-treatment in which the material is heate in an inert atmosphere at a temperature in th neighborhood of 1900 to 2200 TC, molde shapes containing the thusly treated materik are superior for certain uses. The refractory boride material employed i the process of the present invention may b any of the well-known refractory borides othe than zirconium boride and carbon boride, suca as titanium boride, molybdenum boride chromiunm boride and mixtures thereof ins including mixtures with zirconium or carbon a boride. or The refractory borides used in carrying out ad the present invention may be any 1 igh purity grade of refractory boride available on the ide market It is preferred to use a product made of by reacting a mixture of metal oxide, boron in carbide and carbon and/or metal to produce in metal boride. To In order that the invention may be more in clearly understood, the following example is rst submitted as illustrative of compositions for al, and the manner of carrying our the present ed invention. on Raw mixes consisting essentially of boron en nitride (made as described in specification No. al 6158/55, (Serial No 777,000)) and finely a divided molybdenum, chromium and titanium er borides were mixed by grinding together for al 24 hours in alcohol in a ball mill lined with an sintered tungsten carbide The resulting mixtures were placed in a cylindrical graphite mold having two movable graphite plungers. The assembled mold was placed in a graphite chamber of a high frequency furnace and heated as follows: The temperature of the mold was raised to preferably, a minimum temperature of 1600 C, e g 1600 TC for the bodies incorporating molybdenum and chromium borides, and approximately 1800 C le for bodies containing titanium boride, over o a period of 1 hours and held at the stated temperature for 10 minutes under a minirnum g pressure of 2000 p s i The furnace was then d allowed to cool to room temperature The e furnace chamber was cylindrical, 12 " long and d 4 " inside diameter and was closed during

the al heating and cooling periods except for an, opening in the topn about one half inch in n diameter through which temperature observae tions were made The table below presents r fabricating data and physical properties of the h various bodies made in accordance with this e, example of the process of the present invenf, tion. BODIES CONSISTING ESSENTIALLY OF BORON NITRIDE AND METAL BORIDE Bar No. Raw Mix Composition Percentage by Weight Pretreatment of BN SandMolding Molding blast Temp Pressure Penetration Apparent Density gms/cc. 1 15 % BN; Prefired in 1600 C 2000 psi 006 " 5 75 % Mo 2 B No at 1900 C. 2 15 % BN; Prefired in 1600 C 2000 psi 009 " 4 15 % Cr 2 B N 2 at 1900 C. 3 80 % BN; None 1800 C 2000 psi 008 " 2 24 % Ti B 2 Standard penetration on plate glass when subjected to the same penetration test is 010 ". 784,705 784,705 While we have described in the above example the making of various molded bodies in which the body is molded and fired to the exact shape and form in which it is intended for use, the present invention is not intended to be so restricted Another way of making and using the nitride-boride bodies of the present invention is to mold the raw batch of material into briquettes or other shapes or otherwise compress a mass of the material having a composition in the desired proportions, after which the resulting briquettes or compressed bodies are hot pressed in a manner already described After removal from the furnace, they are crushed to granular form of the desired grit size The resulting granular material can then be used in loose granular form as a high temperature refractory material or as a layer of high temperature insulation material, as, for example, insulation or protection around jet engines and rdcket combustion chambers, or as a layer of insulation around industrial furnace chambers It may, also be used as a loose filtering media or as a catalyst or catalyst carrier material The granular material can also be bonded by means of sintered metals, vitreous or Iceramic bonds' or other bonding material to form articles suitable for many of the industrial uses set forth elsewhere herein. Likewise, articles or bodies can be made in accordance with the present invention in which pore-forming materials are incorporated in the raw batch from which the body is made for the purpose of providing a greater degree of porosity in the final body A pore-forming material such as carbon, which requires oxidation for removal from a body would require a preliminary burning out of the pore-forming material at lower temperatures Therefore, the pore-forming material preferably

should be a material which is removed by volatilisation during the drying and/or firing operation such as powdered or granular naphthalene, various organic resinous materials such as phenolic resins or one which provides pores by reason of the generation of a gas The resulting bodies, which have greater porosity than those made with no pore formers, are particularly useful in the fabrication of porous filtering media, catalysts and catalyst carriers, insulation bodies and the like, whether in crushed granular form or in the form of molded shapes of pre-determinedl contour. The products can be made in any desired shape as well as provided in granular or aggregate 'form They are, therefore, not only suited for many of the uses for which industrial refractories are required, including bricks, bldcks, setter tile, muffles, kiln furniture, and special shapes for application in and around furnaces and other high temperature equipment, but they are also well suited for many specialty high temperature applications, such as jet engine combustion chambers, linings for exhaust nozzles, rocket combustion chambers and exhaust nozzles, turbine blades, stator blades and lens fusion blocks They are also suitable for the fabrication of laboratory ware, including combustion boats, crucibles, burner 70 holders, and other shapes The bodies of the present inventions particularly when modified by the use of pore formers in the raw batch from which the bodies are made, are also highly useful as diffusion and filtering media, 75 such as diffusion tubes and plates, filteringl tubes, plates and shapes, or as catalysts or catalyst carriers and supports Materials and articles of the present invention can, also be used for making abrasive articles such as 80 grinding wheels, sharpening stones, razor hones, and other grinding and polishing shapes and materials The present bodies offer possible applications in the electrical and radio industry including supports in electric light 85 bulbs, radio tubes, X-ray tubes and radar equipment, resistors and grid leaks.


* GB784706 (A)

Description: GB784706 (A) ? 1957-10-16

An improved fungicidal composition




PATENT SPECIFICATION Date of Application and filing Complete Specification: Sept 21, 1953. 784,706 No 25975153. Complete Specification Published: Oct 16, 1957. Index at acceptance:-Class 81 ( 1), E 1 C( 5 D:6:7 B:13). International Classification:-A 611. COMPLETE SPECIFICATION An Improved Fungicidal Composition I, AMERICO MOSCA, an Italian Citizen, of 27, Via Carlo Boggio, Cuneo, Italy, do hereby declare the invention for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to products used for fighting the diseases caused in plants by fungi or vegetable parasites where it is usually necessary to use Bordeaux mixture or other copper derivatives, or barium, sodium, calcium polysulphides or zinc dithiocarbonates, and the object of the invention is to provide a very efficient fungicidal product to overcome said diseases which combines a very reduced cost with a remarkably easy production. Preparations employed for this purpose are already known, and depend on the use of copper derivatives, as for instance, copper sulphate for the basic component However, these preparations have the main disadvantage of high manufacturing cost. According to the present invention, it has now been found that extraordinarily satisfactory results can be achieved by using a Fungicide on the basis of Aluminium and its salts having as basic component, aluminium powder or sulphate or other simple organic and

inorganic aluminium salts such as aluminium chloride, aluminium nitrate or double aluminium salts which with the exception of aluminium powder when dissociating in water will free aluminium ions, some aids to adherence and dyeing substances being added in an appropriate amount to said basic component. An aid to adherence according to the present invention is a substance used in the said mixture which has as its object to achieve a better adhesion of the preparation to the leaves, and must present the essential feature that it does not form insoluble compounds with the aluminium sulphate if present, nor must it attack the aluminium powder. As substances aiding adherence of the type described, kaolin, talc, bentonite or calcium sulphate may be used. Furthermore, since the fungicide of the 50 invention is a limpid solution having a light pink shade, it is necessary to add to the composition a dyeing substance, such as methylene blue or malachite green, which performs the function of showing where the composi 55 tion has been sprinkled during spraying operations. When aluminium powder is used as the active ingredient of the fungicide according to the invention, the fungicide is normally 60 used as a solid and water is not an essential ingredient, but can be added when a medium to facilitate spraying is necessary. When however the fungicide is prepared with aluminium sulphate and like salts which 65 will free aluminium ions when dissociating water, water becomes an essential ingredient which may be added before application of the fungicide or if conditions are suitable the fungicide can be used as a solid for the dis 70 infestation of the soil against all kinds of fusarium in which case the water, necessary for the dissociation of the aluminium ions, is the water as a rule contained in the soil. From the above it will be appreciated that 75 the fungicide according to the invention will nonnally be sold as a solid and water will be added when necessary by the user. Since aluminium ores are widely spread all the world over in the percentage of about 8 % 80 of the whole mass, the economic importance of the discovery becomes apparent, when taking into account that the soluble aluminium derivatives, when substituted for the copper salts as a remedy against the common 85 plant diseases up to now fought by said salts, present the advantage of being able successfully to fight all the other plant diseases hitherto resisting the action of all the other known fungicidal compounds, as the tomato 90 784,706 and pepper-plant " Fusarium vasinfectum", the " Fusarium dianthi " affecting the carnations and all the other " Fusarium" species which cause heavy damages to the vegetables, flowers, bulbs or bulbous

plants, and to acid fruits, vines, cereals, mulberry-trees, potatoes, cucumbers, pumpkins and melons. Starting from 1921, both in France and in Italy the application of aluminium derivatives in the form of aluminium sulphate added with quick or slaked-Lime in the colloidal state was attempted, but the results were useless. Essentially, the invention resides in the fact that the aluminium powder or stable aluminium derivatives which when dissociating in water provided free aluminium ions, represent very efficient fungicidal products, while the aluminium hydrate and oxide, under any physical (colloidal or powder) form or structure, are not able to avoid the sporule germination, due to their very poor water solubility. The use, as a fungicide, of aluminium sulphate, chloride or nitrate, treated with slaked or quick-lime or with any other base, is completely deprived of useful results, since these compounds produce immediately aluminium hydrate which is substantially insoluble and free from aluminium ions. The action exerted by the sodium or potassium aluminates is very limited in extent, since these compounds being unstable derivatives, the atmospheric agents will form aluminium carbonate and, successively, hydrate, thus strongly reducing the fungicidal power of aluminates. Excellent fungicidal results are also achieved by the use of double aluminium and potassium salts (for instance: double aluminium and potassium sulphate), that is by the use of double salts which, when dissociating in water produce free aluminium ions. Unsatisfactory results are produced by the use of organic compounds of oxygen, which, although soluble, do not present free aluminium ions, while aluminium organic derivatives (as for instance aluminium acetate) which, dissociating, will free aluminium ions, have excellent fungicidal features. The results of Laboratory and field tests effected during two consecutive years confirmed completely the power of the aluminium powder or of aluminium derivatives having free ions to overcome plant diseases. Field tests were effected with a mixture, which in the following descriptions is referred to as the standard mixture, having the following composition: 6 o Aluminium sulphate 550 grams. Bentonite 430 grams. Methylene blue 2 grams. Calcium carbonate 20 grams. the mixture being diluted in 50-100 litres of water, when necessary to

free aluminium ions. Addition of calcium carbonate is necessary in order to neutralise the free acidity which, usually, accompanies commercial aluminium sulphate since such acidity is harmful to some plants, even if present in very reduced amount 70 (as for instance 1 part per 10 000). The experiments were effected on a very great number of plants for a duration of two agricultural years giving excellent results. As an example: the test was effected on 75 30,000 pear and apple trees of every type: on 10,000 peach trees of every type: on 50,000 vine plants (of the -barbera". " dolcetto", " freisa", -nebbiolo", " barbaresco", "muscat", " ripening in July " 80 types and of assorted types); on 200,000 pepper-plants of every type, on 20,000 tomato plants of every type, on 250,000 potato plants of every type; on 400,000 carnation plants of all the best praised varieties including 85 " valentine " and " minerva"; on 100,000 rose-bushes, bulbs and bulbous plants, chrysantema, ornamental plants and so on, and also on cereals, spinach, asparagus, onion, celery, pumpkin, apple, cucumber, water 90 melon plants and on nursery beech trees. In none of the experiments did the fungicide exhibit any toxicity, and a flourishing vegetation with excellent crops was observed. In effect, since the aluminium sulphate 95 mixtures are provided at a p H value equal to that of the plant lymph, the result is the absorption of aluminium with subsequent formation of proteinate which acts as a catalyst, thus favouring the attainment of an 100 excellent crop. The accurate examination of the produce obtained with the aid of the novel fungicide allowed a premature or earlier ripening and a better crop than that obtained by plants 1 oa treated with other fungicidal mixtures. It will be noticed that the preparation according to the invention is positively harmless and non-toxic to the plants, while it appears to be also harmless and non-corrosive 110 for the farm-tools.


* GB784707 (A)

Description: GB784707 (A) ? 1957-10-16

Improvements in integrators for computing the mean value and othercharacteristics of voltages derived from electrical testers

Description of GB784707 (A)

PATENT SPECIFICATION Inventor: JOHN LIGHTFOOT SPENCER-SMITH Date of filing Complete Specification: Oct 8, 1954. Application Date: Oct 9, 1953. No 27763/53. \ 1 Complete Specification Published: Oct 16, 1957. Index at acceptance:-Class 37,,G 2 B( 1: 2: 4: 6), G 3 A( 3: 6). International Classification:-G 06 g. COMPLETE SPECIFICATION Improvements in Integrators for Computing the mean Value and other Characteristics of Voltages Derived from Electrical Testers We, LINEN INDUSTRY RESEARCH ASSOCIATION, of The Research Institute, Lambeg, Lisburn, County Antrim, Northern Ireland, a body corporate organised under the Laws of Great Britain, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particul 3 arly described in and by the following statement: - This invention relates to inmprovements in integrators for computing the mean value or other characteristics of voltages derived from electrical testers. The integrator circuit may be employed to give statistical information about any quantity the variations of which form a mean value can be expressed as a varying voltage. An integrator is described in the specification,of Patent No 681,447 which claims a method of determining the mean deviation of the variable quantity of substance in the cross-section of slivers, rovings or yarns from its average value, characterised in that an equivalent electrical current is first obtained from said variable quantity of substance in the cross-section, the average value of this electrical current being separated from its deviations from the average value with the aid of an electrical frequency-dependent

filter, including 'a pair of input and two pairs of output terminals, the first pair of output terminals supplying an electrical direct current equivalent to the average value of the quantity of substance in said cross section, the second pair of output terminals supplying fan electrical alternating current equivalent to the deviation value from the average value of said quantity of substance in the cross-section, said alternating current being rectified by means of an electrical rectifier, and the output direct current of said rectifier which is equivalent to the deviation value of the variable quantity of lPrice 3 s 6 d l said substance from its average value, being averaged by means of at least one electrical capacitor connected in series with at least one electrical impedance and then the averaged direct current equivalent to the mean deviatifon of said variable quantity of substance in the cross section being made visible in an electrical measuring instrument. The integrator described in specification No 681,477 is substantially as shown in Fig. 1 of the accompanying drawings 'and consists of a full wave rectifier, 2, providing a voltage which is proportional, either to the rectified value of the voltage output of the yam or sliver tester 1 or to the square thereof, connected in series with a resistance, 3, and a condenser 4, which is connected in parallel' with a high resistance voltmeter or similar device S for measuring voltage, so that the voltage registered by the voltmeter represents an average value of the rectified values of the applied voltages or to the squares thereof. This integrator performs two distinct functions: (a) it converts the;alternating voltage from the tester into a direct voltage, (b) it provides a relatively low impedance circuit for charging the condenser compared with the relatively high impedance of the discharging circuit and so provides a greater time constant for discharging the condenser than for charging it. The response of the integrator to a deviation in the size of the yarn or sliver, therefore, depends upon whether it is greater or less than the average deviation as indicated by the voltmeter; when a deviation in the size of the yarn or sliver is greater than the value indicated by the voltmeter, the response of the integrator is disproportionately greater than when a deviation is less than the value indicated by the voltmeter, which consequently indicates 'a biassed average which is greater 784,707 2 784,707 than the actual value of the meai or of the mean squared deviation mean size of the yarn or sliver. The values of the time constants, for charging and discharging the respectively, can be expressed mat in terms of the values of the corn follows: RV(R, R + R,-) T, = C x sec. R, + R + R, + Rx and T 2 = C x R, sec.

where C is the capacitance of the cond Rv is the resistance of the vltm R, is the resistance of the resist R 'is the forward resistance of the rectifier 2, and R, is the output impedance of th or electronic yarn and sliver i tester 1. From this it follows that T, must less than T. When a varying voltage v, whi( portional to the deviations in size sample, is fed from the tester into tor which contains a linear rectifier meter fluctuates about a mean voltag given by: R.Rv R+Rs+Rs where l is the solution to the eqt J(t-u) F(,) Am cc CV and F (v) is the frequency distribut varying voltage, supplied by the tes When T = T, the value of v obt equation ( 3) is equal to the Mean of the variations in the output of but when T 1 is less than T, the will be greater than the mean devia amount which depends both on th T./T 1 and the form of the frequ tribution. When T is equal to or greate times T,, the bias becomes so gre n deviation effectively becomes an average of the larger from the deviations only-i e deviations which exceed a value determined by the bias and thus by T 1 and T the ratio T,/T,-and approximates to half condenser of the mean range as defined, there bring hematically only a certain small probability that any deponents as viation will lie outside this range. Values of T 2/T, equal to 80 or 1,370 are preferred because, with deviations which follow a normal frequency distribution, the in( 1) tegrator indicates a mean range which can be defined as the value which is exceeded by approximately 5 per cent or 0 1 per cent of ( 2) the deviations, respectively Similar considerations apply when the rectifier provides a current which is proportional to the square of tenser 4, the deviations in voltage supplie d by the aeter 5, tester. ance 3, Therefore measurements of the mean devia e full wave tion and the mean squared deviation by the said integrator are subject to errors, whose e electrical magnitude depends both upon the ratio of irregularity the time constants, T /T,, and the form of the frequency distribution of the sizes of always be short lengths of the sliver or yarn, the correct values of the mean and mean squared dech is pro viations being only obtained when the time along the constants T, and T are equal. an integra The invention comprises an integrator for the volt measuring the mean value or the mean squared ge which is value of the output of electrical testers in which the tester feeds a capacitor-charging circuit and a measuring instrumnent through a control unit, which comprises a rectifier and a pair of electronic valves whereby the said control unit isolates the capacitor-charging circuit from the tester and delivers tce the uation: capacitor-charging circuit a voltage which is proportional to the

rectified output of the tester or to the square thereof, and whereby the time constants for charging and discharging capacitor-charging circuit are made equal. The invention further comprises an integrator for measuring the mean of the values of the range or the mean of the maximum or minimum values of the variations which occur in equal consecutive prescribed intervals of ,3 time in the output of electrical testers in which the tester feeds a capacitor-charging circuit through a control unit which comprises a pair of electronic valves and a rectifier in ion of the series with a variable resistance, whereby the ter time constant of the capacitor-charging circuit ained from may be adjusted ito give a prescribed ratio of Deviation the time constants; for discharging and chargthe tester, ing the capacitor circuit. value of v In an application of the invention where tion by an the integrator measures the mean squared e ratio of value it contains a linear rectifier and a rectiency dis fying and controlling unit which serves the dual purpose, firstly of squaring the tester outrthan 30 put, and secondly of permitting the time coneat that, stants, T, and T, for charging and discharg8 C 784,707 784,707 3 ing the circuit to be equal. When the integrator is intended for measuring the mean of the values of the range of the deviations there is introduced into the Integrator circuit, a rectifying and controiling circuit, which allows the time constant T,, for charging the condenser, to be varied independently of the time constant T 2, for discharging the condenser, so that the ratio T 2/T 1, is made at least 30 to 1 and the integrator indicator sensibly responds only to comparatively large signals and indicates 'an average value of their larger deviations The preferred ratios of the time constants To/T 1 are 80 or 1,370 so that when the output signals follow the normal frequency distribution, only approximately 5 per cent or 0 1 per cent, respectively, of the signals exceed the value indicated by the integrator. For measuring the average or mean values of the maximum and minimum values of the variations which occur in equal consecutive prescribed intervals of time a similar arrangement is employed to that for measuring the mean of the values of the range with the exception that the full wave rectifier is replaced by a half wave rectifier, which is arranged to pass only currents which correspond either to positive deviations in the signals for measuring the average of the maximum values of the sgnals or to negative deviations in the signals for measuring Ithe average of the minimum values of the signals. For measuring these average of the maximum and minimum values of the variations of the signals respectively the time constant T 2 for discharging the condenser is at least 30 times greater than the time

constant T, for charging the condenser, land the preferred values of the ratio are 80 and 1,370. In order that the invention may be fully understood it will be more particularly described with reference to Figs 2 to 5 of the accompanying drawings, Fig 1 of these drawings being the integrator previously described as being the kind described in specification 681,477 In these drawings: Fig 2 is a diagram of a preferred circuit of an integrator for computing the mean value in which the time constants T, land T, for charging and discharging the condenser are made equal by means of a rectifying and controlling circuit. Fig 3 is a diagram of a circuit of an integrator for computing the mean squared value in which the time constants T, and T, for charging and discharging the condenser are made equal by means of a rectifying and controlling circuit. Fig 4 is a diagram of a circuit of an integrator for measuring the mean of the values of the range of the variations in such a way that the time constant T 1 for charging the condenser is at most 1/30th of the time constant T, for discharging the condenser, and Fig 5 is a diagram of an integrator for measuring average values of the maximum or minimum values of the variations of the signals. In the diagram shown in Fig 2 of the circuit of an integrator for computing the mean value in which the time constants of the circuit T 1 and T 2 for charging and discharging the condenser are made equal by means of a capacity changing circuit ior rectifier and control unit consisting of a rectifier 2 followed by a cathode follower stage, which effectively isolates the rectifier 2 from the condenser 4, an electrical or electronic yarn and sliver regularity tester, 1, provides an output voltage which is proportional to the deviations about the mean of the weight per unit length of the material being tested, the output voltage being fed through the linear full wave rectifier, 2, to the grids of two electronic valves, 6 land 7, which are operated as cathode followers having equal cathode resistances 8 and 9 The cathodes of the valves, 6 and 7 are connected through a resistance 3 to a condenser 4, which is connected in parallel with a high resistance voltmeter 5. The operation of the circuit is as follows:the rectified signal from the rectifier 2 induces a voltage between the cathodes of the valves 6 and 7 which is fed to the damping circuit consisting of the resistance 3 the condenser 4 and the high resistance voltmeter 5, which registers the mean deviation of the variations. The time constants of the circuit T, and T. for charging,and discharging the condenser are both equal and given by R 1 x R, Tl=T=C x Rz + R where R, and Rv are the resistances of the resistance 3, and the voltmeter 5 respectively 105 and C is the

capacity of the condenser. An integrator circuit for computing the mean squared value may be the same as that shown in Fig 2, but using a square law instead of a linear rectifier 2 Fig 3 shows an 110 alternative form of integrator circuit for computing the mean squared value In this arrangement the output voltage from the tester 1 is fed through a rectifying and controlling unit 10 comprising a full wave linear 115 rectifier 2 and a known type of voltage squaring circuit, the output of which is fed through a resistance 3 to a condenser 4, which is connected in parallel with a high resistance voltmeter 5 The rectifying 'and controlling 120 circuit serves two purposes, firstly, it provides a current which is proportional to the square of the rectified values so that the integrator averages the squared values, and secondly it effectively isolates the tester 1 from the con 125 denser 4, and equalises the time constants T 1 784,707 and T, for charging and discharging the condenser, and the reading on the voltmeter 5 is therefore proportional to the mean squared value Fig 4 shows an integrator circuit for measuring the mean of the ratios of the range of the variations in which the circuit shown in Fig 1 is modified in such a way that the time constant T, for charging the condenser is tat most 1/30th of the time constant, T 2 for discharging the condenser, the preferred values of the ratio, T 21/T 1 being 80 and 1:370 as already stated In Fig 4 the output voltage from the tester 1 is fed through a rectifying and controlling circuit 11, consisting of two electronic valves 12 and 13, operated as cathode fllowers a variable resistance 14 and a full wave linear rectifier 2 The cathode followers 12, 13 are operated in such a way that the output impedance of the unit 11 is kept small The output from the cathodes of the valves 12 and 13 is fed through the variable resistance 14 'also included in the control unit, to the full wave rectifier 2, which should preferably consist of diode valves, having a low resistance to current passing in the forward direction and a very high resistance tc current passing in the reverse direction The output from the rectifier is fed to the condenser 4, which is connected in plarallel with a very high resistance voltmeter 5 With such arrangement the time constant T 1 of the circuit for charging the condenser depends sensibly upon the capacity of the condenser 4, output impedance of the cathode follower stage 12 and 13, the forward resistance of the rectifier 2, and the resistance 14 and may therefore be varied over a wide range by means of the variable resistance 14 The time constant T of the circuit for discharging the condenser depends upon the capacity of the condenser 4, and the resistance of the voltmeter and is very much greater than T, The integrator is adjusted by varying the resistance 14 in the control unit until the ratio of the time constants T,/T 1 has the

desired value. Fig 5 shows an integrator circuit, for measuring averages of the maximum or minimum values corresponding respectively to the positive and negative larger deviations in the SO signals from the tester The circuit is identical with that shown in Fig 4 with the single exception that the full wave rectifier 2 is replaced by a half wave rectifier 15, which is arranged to pass only currents which correspond either to positive deviations in the sig 55 nal for computing the average of the maximum values of the variations of the signal, or to negative deviations in the signal for computing the average of the minimum values of the signals The other components CO are the same as those described ill Fig 4 and as previously described the resistance 14 is used to adjust the value of the time constant T for charging the condenser until the ratio of the time constants TI/T, has the de 65 sired value, which should be at least 30 and preferably 80 or 1370.
