US 2369266 A
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Patented Feb. 13, 1945 ELECTBICALLY CONDUCTIVE CERAMIC THREAD GUIDE Hans Thurnauer, Chattanooga, Tenn., asslgnor to American Lava Corporation, Chattanooga, Tenn., a corporation of Tennessee No Drawing. Application January 28, 1941,
,Serlal No. 376,383
6 Claims. (Cl. 242-157) This invention relates to ceramic bodies of sufllcient electrical conductivity to dissipate static charges and more particularly to the use of T102 in the manufacture of thread guides and like bodies which not only are capable of preventing the accumulation of charges of static electricity but have many other desirable characteristics.
In Patent No. 2,214,703 I described a ceramic thread guide which'is formed by vitrifying a mixture of materials comprising chiefly T: at a temperature of between 1350 C. and 1400 C. Such thread guides, while possessing many properties which particularly suit them for use in the textile industry, are electrical insulators, having a resistivity of around 1 10 megohms per cm Accordingly, the TiOz thread guides of my prior patent, 2,214,703, with guides of glass, porcelain and enameled metal, which likewise are electrical insulators, when used in a dry atmosphere, are likely to be charged with an electrical potential by the friction between the dry thread and the thread guide. This is due to the well known law of physics that whenever two non-conductors are rubbed together static electricity is developed, the charges on the non-conductors being equal but of opposite sign. If the accumulated charge on either the thread guide or the thread is discharged suddenly by coming into contact with or close to a conductor, such as a human being or a metallic object, it will cause shock to the operator of the machine or snapping of the thread due to sparking.
Various possible methods may be utilized to avoid the accumulation of static electricity. In some cases the surrounding atmosphere may be humidified to such an extent that the surfaces of the thread and the guide become suillciently conductive to prevent the formation of static charges. While of some utility, this method is impractical when a dry and warm atmosphere is either required or desired to satisfactorily pro-; duce a yarn.
An alternative method is to use thread guides made of metal, such as steel and stainless steel. Such metal thread guides are good conductors for a resistivity of only -80 10- ohms per cm. and therefore do not accumulate electrostatic charges but are objectionable because they wear rapidly and must be replaced at frequent intervals.
As a third possibility, the thread guides may be made from sintered carbides which are electrical conductors similar to metals, their resistivity being in the range of 20x 10- ohms per cm. However, as in the case of the other suggestions,
sintered carbides are not a complete solution of the problem since they are expensive and dimcult to form the intricate shapes usually required for thread guides.
An ideal thread guide for use in a dry atmosphere must not only dissipate static charges but must also withstand abrasion, be smooth and not tear threads, and be economically formed into intricate shapes. Contrary to general belief, it has been found that it is not necessary to use highly conductive materials, such as metals or carbides, in order to dissipate static charges of electricity but that a material having a resistivity of 1 megohm or less per cm. will serve the same purpose. It is thus possible to manufacture thread guides of resistor materials rather than electrical conductors, and such materials, having in addition the characteristics required of the ideal thread guide, are the subject of this invention.
It is, therefore, the primary object of the invention to provide a ceramic thread guide or the like made chiefly from TiOz which has a resistance not greater than 1 megohm per cm Another object of the invention is to provide a ceramic thread guide or the like made chiefly from TiOz which is capable of dissipating static charges of electricity, resistant to abrasion, is smooth and will not tear threads and can be economically formed into the varied and often intricate shapes necessary for this purpose.
A further object of the invention is to provide processes whereby T102, either alone or mixed with other ingredients, can be converted into a material suificiently conductive to dissipate static charges of electricity.
An additional object of the invention is to provide processes for the utilization of TiOz, a nonconductor in the manufacture of ceramic thread guides having sufficient conductivity to prevent the accumulation of static charges of electricity on a guide or thread under all operating conditions.
Other objects will appear in the detailed description of the invention and, together with those previously mentioned, will be particularly pointed out in the appended claims.
In the process described in Patent No. 2,214,703, a body was formed from titanium dioxide (T102) according to known ceramic methods and fired vitrification in a neutral oxidized atmosphere at a temperature of between 1350 C. and 1400 C. The resultant product, while eminently satisfactory in general use as a thread guide, was an insulatin material and thus caused electrostatic cha to accumulate when used in a dry atmosphere with consequent ill eflect upon either the operator or the thread. Were T: to be rendered conductive to such a degree as to dissipate static charges of electricity without loss of other desirable characteristics, its value as a component of thread guides and like bodies would be tremendously increased.
SinceTlOz is an insulating material, the desired conductivity must be dependent upon other contents ofthe ultimate product. I have found that the presence of a relatively small percentage of a conductor material, such as titanium sesquioxide (T1201) or a titanate of copper, vanadium or chromium, in the fired body is sufiicient to reduce its resistivity below the optimum of 1 megohm per cm. To produce a conductive body as opposed to the insulating body of my prior patent, it is necessary either to add the conducting material to TiO: or to so treat a T10: mixture that the. conducting material content will be obtained by chemical reaction during the firing.
In each of the several processes by which the requisite conductivity can be given to a TiOz body, T10: is the chief raw material. The T102 may be in precipitated form, calcined at a temperature of between 1000 and 1400" C., or powdered rutile material, preferably air floated, or a mixture of these forms, in which event the materials are carefully mixed either wet or dry according to known ceramic methods. While T102 has suificient inherent plasticity for simple shapes, it is desirable to add plasticizers, such as dextrin, goulac or wax, to the original mixture, when more intricate or complex forms or shapes are required. Fluxes, such as clay, kaolin, feldspar or aluminum oxide, may also be added to the mixture to both decrease the firing temperature and increase the hardness of the fired body, the maximum amount of fluxes which can be added without injury to the properties of the body being percent.-
The TiOz, after being mixed with such plasticizers and fluxes as may be required, is then made into a vitrified body having the desired characteristics by any one of the following processes:
1. A body is formed in the desired shape from T102 and fired to vitrification in a kiln in a re.- ducing atmosphere. The reducing atmosphere may be either C0 or H: or a mixture of these gases. Above 1000 C. T10: is reduced to T1203 and the vitrified body is thus given the requisite conductivity. v
2. A body is formed in the desired shape from T10: and fired to vitrification in a neutral or oxidizing atmosphere. The vitrified body is then refired above 1000" C. in a reducing atmosphere of C0 or H: or a mixture of these gases to partially or completely reduce the TiO: to T1203. This process has the advantage over the first that it is possible to control the extent of the reduction and, therefore, the resistivity of the ultimate product more closely.
3. Th0; as such is mixed with T10: and the mixture formed into a body or article of the desired shape. Th article is then fired to vitrification in a reducing atmosphere to prevent oxidation of the T1203, sufilcient of the Th0: being to reduce the resistivity of aseaaes introducedto lower the resistivityof the ultimate product to at least 1' megohm per cm..
4. An oxide of copper, vanadium or chromium or a compound of one of these oxides is added to and mixed with T102. The mixture, after being formed into the desired shapes, is fired to vitrification in a neutral or oxidizing atmosphere, the metallic oxide reacting with the T10: during the firing to form the titanate of the metal. 01 these titanates, that of vanadium is most efiective in reducing the resistivity of the T101, 10
percent of vanadium titanate in the fired body being sufiicient to reduce its resistivity to less than 1 10 megohms per cm. In each case a sufilcient amount of the metallic oxide or compound of the metallic oxide is mixed with the T10: to reduce the resistivity of the ultimate product to at least 1 megohm per cm 5. A titanate of copper, vanadium or chromium as uch is added to and mixed with T102, the resultant mixture, after being formed into the desired shapes, being fired to vitrification in a neutral or oxidizing atmosphere. This process is preferable to the fourth because closer control can be exercised on the final resistivity of the fired article.
Whether one or another of the above processes is utilized the ultimate product is a vitrified crystalline body in which are combined the physical characteristics of the vitrified T10: bodies described in Patent 2,214,703 and sufficient conductivity to dissipate electrostatic charges. It is thus apparent that there has been provided a product of wide utility and several processes by which this product can be produced exp ditiously and inexpensively.
Having now described the invention, I claim:
1. A ceramic thread guide body comprising a vitrified mixture of titanium oxide and a metallic oxide, said vitrified body having a resistivity not greater than 1 megohm per cm.
2. A ceramic thread guide body comprising a vitrified compound containing both titanium dioxide and titanium sesqui-oxide, said vitrified body having a resistivity not greater than 1 megohm per cmfi.
3. A ceramic thread guide body comprising a mixture of titanium dioxide and an oxide of a metal of the class consisting of copper, vanadium and chromium, said thread guide after vitrification having a resistivity not greater than 1 megohm per cm.
4. A thread guide body comprising a vitrified ceramic material composed of titanium dioxide and a titanate of a metal of the class consisting of copper, vanadium and chromium, said thread guide having a resistivity not greater than 1 megohm per cm.-".
5. A ceramic thread guide body comprising a vitrified mixture of titanium dioxide and a titanium sesqui-oxide, said titanium sesqui-oxide forming a sufilcient percentage of said mixture said thread guide to at least 1 megohm per cm..
6. A thread guide body of vitrified ceramic material containing titanium sesqui-oxide as a reaction product of titanium dioxide and having a resistivity not greater than 1 megohm per cm).