Tape casting

Last updated

Tape casting (also called doctor blading,knife coating, and shank shifting) [1] is a casting process used in the manufacture of thin ceramic tapes and sheets from ceramic slurry. [2] The ceramic slurry is cast in a thin layer onto a flat surface and then dried and sintered. [3] It's a part of powder metallurgy. [4] :167

Contents

History

Tape casting was first described as a method to mass-produce capacitors. [1] In this first published description from 1947 the process was described as: [5]

"A machine is described which extrudes a ceramic slip with a resin binder on a moving belt. The thin sheet is strong enough when dry to be stripped off and cut or punched to any desired flat shape and fired satisfactorily."

In 1960 a patent was filed for multilayered tape casting and in 1996 the first tapes under 5 μm were cast. [1]

Production process

Schematic representation of the tape casting process. In brown the slurry, in grey the doctor knife and the arrow headed line indicates the surface on which the slurry is applied and its moving direction. This is just one of many different designs. Tape casting.svg
Schematic representation of the tape casting process. In brown the slurry, in grey the doctor knife and the arrow headed line indicates the surface on which the slurry is applied and its moving direction. This is just one of many different designs.

The tape casting process converts ceramic powder to a thin film by making a liquid form of it, casting it on a flat plane and drying it.

Ingredients

The starting point for the tape casting process is the powder that the 'tape' is to be consisting of. This is the active component of the final product and the other contents, such as binder material and solvents have to be compatible with the powder. The powder is in general very fine, with maximum particle sizes of 5 micrometers. [6] The solvent serves the purpose of allowing the powder to be cast, as if it were a liquid, and also to spread secondary components through the tape. Surfactants are added as well, to control the behaviour of the tape surface. Furthermore, binder material is added. This determines the bulk structure and mechanical characteristics of the tape. [1]

Slurry manufacturing

The slurry ingredients as mentioned in the previous section are mixed and stored in tanks.

Slurry casting

Tape casting machine HED International - Procast Tape Caster.jpg
Tape casting machine

The slip material is transported in pipes from tanks to the casting machine. The slip may be filtered before being applied, to remove imperfect particles. The cast slurry is called a green layer or green sheet (this is not referring to the colour of the sheet), and needs further processing such as cutting and drying. [6]

During casting it is important to cast a perfectly flat surface without streaks, for this different casting mechanisms have been designed to minimise slip streams in the slurry. The blades that flatten and thin the cast surface are called doctor blades. These come in different shapes such as thick or thin flat cutting surfaces, rounded edges and knife blade-shaped edges. [1] For tapes that are cast thinner than 50 micrometer, the coating is not applied from the top, but from the side (slot-die coater) or bottom (lip coater and micro gravure coater).

The surface on which is cast can be made from steel, glass, coated paper and polymers. Steel is the most economical surface, but removal of thin sheets from a steel surface is difficult and the steel surface needs relatively frequent replacement due to damaging. [1]

Green sheet drying

The cast tape only dries from one side, the exposed surface, as the casting surface is impermeable. Drying is dependent on two processes, namely the evaporation of the solvent from the surface, and the diffusion of the solvent through the tape towards the single exposed surface. The evaporation may be sped up by applying air drying. However, usually evaporation should be limited to ensure steady diffusion of the solvent. If the solvent does not leave the sheet in a controlled fashion, the tape may crack or curl. [1]

Several processing steps may be executed depending on the product requirement, such as cutting, laminating, punching or thermal treatment. [7]

Usage

The process is used in the production of ceramic capacitors, polymer batteries, photovoltaics, electrodes for molten carbonate fuel cells. This films as thin as 5 micrometer can be produced using tape casting. [1] [6]

Related Research Articles

Ceramic Inorganic, nonmetallic solid prepared by the action of heat

A ceramic is any of the various hard, brittle, heat-resistant and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcelain, and brick.

Paint Pigment applied over a surface that dries as a solid film

Paint is any pigmented liquid, liquefiable, or solid mastic composition that, after application to a substrate in a thin layer, converts to a solid film. It is most commonly used to protect, color, or provide texture. Paint can be made or purchased in many colors—and in many different types. Paint is typically stored, sold, and applied as a liquid, but most types dry into a solid. Most paints are either oil-based or water-based and each has distinct characteristics. For one, it is illegal in most municipalities to discard oil-based paint down household drains or sewers. Clean-up solvents are also different for water-based paint than they are for oil-based paint. Water-based paints and oil-based paints will cure differently based on the outside ambient temperature of the object being painted Usually, the object being painted must be over 10 °C (50 °F), although some manufacturers of external paints/primers claim they can be applied when temperatures are as low as 2 °C (35 °F).

An abrasive is a material, often a mineral, that is used to shape or finish a workpiece through rubbing which leads to part of the workpiece being worn away by friction. While finishing a material often means polishing it to gain a smooth, reflective surface, the process can also involve roughening as in satin, matte or beaded finishes. In short, the ceramics which are used to cut, grind and polish other softer materials are known as abrasives.

Slip casting Technique for forming pottery

Slip casting, or slipcasting, is a ceramic forming technique for pottery and other ceramics, especially for shapes not easily made on a wheel. In this method, a liquid clay body slip is poured into plaster moulds and allowed to form a layer, the cast, on the inside walls of the mould. The process usually takes at least 24 hours per piece. It gives very precise and consistent shapes, and is now the most common technique used for commercial mass-produced pottery, although it began as a technique for fine pottery such as European porcelain in the 1750s, and Chinese Jingdezhen porcelain considerably earlier.

Ceramic forming techniques are ways of forming ceramics, which are used to make everything from tableware such as teapots to engineering ceramics such as computer parts. Pottery techniques include the potter's wheel, slip casting and many others.

Sharpening stone Abrasive slab used to sharpen tools

Sharpening stones, or whetstones, are used to sharpen the edges of steel tools and implements, such as knives, scissors, scythes, razors, chisels, hand scrapers, and plane blades, through grinding and honing.

Metal injection molding Metalworking process in which finely-powdered metal is mixed with binder material

Metal injection molding (MIM) is a metalworking process in which finely-powdered metal is mixed with binder material to create a "feedstock" that is then shaped and solidified using injection molding. The molding process allows high volume, complex parts to be shaped in a single step. After molding, the part undergoes conditioning operations to remove the binder (debinding) and densify the powders. Finished products are small components used in many industries and applications.

Powder coating Type of coating applied as a free-flowing, dry powder

Powder coating is a type of coating that is applied as a free-flowing, dry powder. Unlike conventional liquid paint which is delivered via an evaporating solvent, powder coating is typically applied electrostatically and then cured under heat or with ultraviolet light. The powder may be a thermoplastic or a thermoset polymer. It is usually used to create a hard finish that is tougher than conventional paint. Powder coating is mainly used for coating of metals, such as household appliances, aluminium extrusions, drum hardware, automobiles, and bicycle frames. Advancements in powder coating technology like UV curable powder coatings allow for other materials such as plastics, composites, carbon fiber, and MDF to be powder coated due to the minimum heat and oven dwell time required to process these components.

Buckypaper Thin sheet made of aggregated carbon nanotubes

Buckypaper is a thin sheet made from an aggregate of carbon nanotubes or carbon nanotube grid paper. The nanotubes are approximately 50,000 times thinner than a human hair. Originally, it was fabricated as a way to handle carbon nanotubes, but it is also being studied and developed into applications by several research groups, showing promise as vehicle armor, personal armor, and next-generation electronics and displays.

Ceramic engineering Science and technology of creating objects from inorganic, non-metallic materials

Ceramic engineering is the science and technology of creating objects from inorganic, non-metallic materials. This is done either by the action of heat, or at lower temperatures using precipitation reactions from high-purity chemical solutions. The term includes the purification of raw materials, the study and production of the chemical compounds concerned, their formation into components and the study of their structure, composition and properties.

Investment casting Industrial process based on lost-wax casting

Investment casting is an industrial process based on lost-wax casting, one of the oldest known metal-forming techniques. The term "lost-wax casting" can also refer to modern investment casting processes.

Rotary vacuum-drum filter

A Rotary Vacuum Filter Drum consists of a cylindrical filter membrane that is partly sub-merged in a slurry to be filtered. The inside of the drum is held lower than the ambient pressure. As the drum rotates through the slurry, the liquid is sucked through the membrane, leaving solids to cake on the membrane surface while the drum is submerged. A knife or blade is positioned to scrape the product from the surface.

Diamond blade Saw blade with diamond grit bonded to the cutting surface

A diamond blade is a saw blade which has diamonds fixed on its edge for cutting hard or abrasive materials. There are many types of diamond blade, and they have many uses, including cutting stone, concrete, asphalt, bricks, coal balls, glass, and ceramics in the construction industry; cutting semiconductor materials in the semiconductor industry; and cutting gemstones, including diamonds, in the gem industry.

6061 is a precipitation-hardened aluminium alloy, containing magnesium and silicon as its major alloying elements. Originally called "Alloy 61S", it was developed in 1935. It has good mechanical properties, exhibits good weldability, and is very commonly extruded. It is one of the most common alloys of aluminum for general-purpose use.

This is a list of pottery and ceramic terms.

Mass finishing is a group of manufacturing processes that allow large quantities of parts to be simultaneously finished. The goal of this type of finishing is to burnish, deburr, clean, radius, de-flash, descale, remove rust, polish, brighten, surface harden, prepare parts for further finishing, or break off die cast runners. The two main types of mass finishing are tumble finishing, also known as barrel finishing, and vibratory finishing. Both involve the use of a cyclical action to create grinding contact between surfaces. Sometimes the workpieces are finished against each other; however, usually a finishing medium is used. Mass finishing can be performed dry or wet; wet processes have liquid lubricants, cleaners, or abrasives, while dry processes do not. Cycle times can be as short as 10 minutes for nonferrous workpieces or as long as 2 hours for hardened steel.

Granulation

Granulation is the process of forming grains or granules from a powdery or solid substance, producing a granular material. It is applied in several technological processes in the chemical and pharmaceutical industries. Typically, granulation involves agglomeration of fine particles into larger granules, typically of size range between 0.2 and 4.0 mm depending on their subsequent use. Less commonly, it involves shredding or grinding solid material into finer granules or pellets.

Conveyor belt furnace

A conveyor belt furnace is a furnace that uses a conveyor or a belt to carry process parts or material through the primary heating chamber for rapid thermal processing. It is designed for fast drying and curing of products and is nowadays widely used in the firing process of thick film and metallization process of solar cell manufacturing. Other names for conveyor belt furnace include metallization furnace, belt furnace, atmosphere furnace, infrared furnace and fast fire furnace, to just list a few.

Industrial porcelain enamel is the use of porcelain enamel for industrial, rather than artistic, applications. Porcelain enamel, a thin layer of ceramic or glass applied to a substrate of metal, is used to protect surfaces from chemical attack and physical damage, modify the structural characteristics of the substrate, and improve the appearance of the product.

Freeze-casting

Freeze-casting, also frequently referred to as ice-templating, or freeze alignment, is a technique that exploits the highly anisotropic solidification behavior of a solvent in a well-dispersed slurry to controllably template a directionally porous ceramic. By subjecting an aqueous slurry to a directional temperature gradient, ice crystals will nucleate on one side of the slurry and grow along the temperature gradient. The ice crystals will redistribute the suspended ceramic particles as they grow within the slurry, effectively templating the ceramic.

References

  1. 1 2 3 4 5 6 7 8 Richard E. Mistler; Eric R. Twiname (1 December 2000). Tape Casting: Theory and Practice. Wiley. ISBN   978-1-57498-029-5.
  2. Dennis, James W. "Tape Casting Advanced Materials". Ceramic Industry. Retrieved 24 February 2010.
  3. Hotza, D.; Greil, P. (1995). "Review: aqueous tape casting of ceramic powders". Materials Science and Engineering: A. 202 (1–2): 206–217. doi:10.1016/0921-5093(95)09785-6. ISSN   0921-5093.
  4. Asthana, R. (2006). Materials processing and manufacturing science. A. Kumar, Narendra B. Dahotre. Amsterdam: Boston. ISBN   978-0-08-046488-6. OCLC   85814321.
  5. Howatt, G. N.; Breckenridge, R. G.; Brownlow, J. M. (1947). "Fabrication of Thin Ceramic Sheets for Capacitors". Journal of the American Ceramic Society. 30 (8): 237–242. doi:10.1111/j.1151-2916.1947.tb18889.x. ISSN   0002-7820.
  6. 1 2 3 Brian S. Mitchell (30 January 2004). An Introduction to Materials Engineering and Science for Chemical and Materials Engineers. John Wiley & Sons. p. 721. ISBN   978-0-471-47336-7.
  7. Beate Capraro; Stefan Barth; Michael Hofmann. "TAPE CASTING – MORE THAN 70 YEARS OF PRACTICAL EXPERIENCE IN HERMSDORF" (PDF). Fraunhofer.