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  Ceramic Manufacturing

The word ceramic, derives its name from the Greek keramos, meaning "pottery", which in turn is derived from an older Sanskrit root, meaning "to burn". The Greeks used the term to mean "burnt stuff" or "burned earth". Thus the word was used to refer to a product obtained through the action of fire upon earthy materials.

Ceramics make up one of three large classes of solid materials. The other material classes include metals and polymers. The combination of two or more of these materials together to produce a new material whose properties would not be attainable by conventional means is called a composite. Examples of composites include steel reinforced concrete, steel belted tyres, glass or carbon fibre - reinforced plastics (so called fibre-glass resins) used for boats, tennis rackets, skis, and racing bikes.

Ceramics can be defined as inorganic, non-metallic materials that are typically produced using clays and other minerals from the earth or chemically processed powders. Ceramics are typically crystalline in nature and are compounds formed between metallic and non-metallic elements such as aluminium and oxygen (alumina- Al2O3 ), silicon and nitrogen (silicon nitride- Si3N4) and silicon and carbon (silicon carbide-SiC). Glass is often considered a subset of ceramics. Glass is somewhat different than ceramics in that it is amorphous, or has no long range crystalline order.

Most people, when they hear the word ceramics, think of art, dinnerware, pottery, tiles, brick and toilets. The above mentioned products are commonly referred to as traditional or silicate-based ceramics. While these traditional products have been, and continue to be, important to society, a new class of ceramics has emerged that most people are unaware of. These advanced or technical ceramics are being used for applications such as space shuttle tile, engine components, artificial bones and teeth, computers and other electronic components, and cutting tools, just to name a few.

Manufacturing Methods

Because ceramics employ many different types of manufacturing processes, the following is a basic outline. It will give you a good idea of what it takes to manufacture a ceramic component. It is important to note that all ceramics start as granular powder made up of a base material such as Alumina or Zirconia, mixed with other stabilizers and binders that give each "ceramic body" its own unique characteristics.

There are several basic forming methods

Isostatic pressing

Isostatic pressing is the use of force pressures of equal proportion from all directions. This can be achieved with fluid or by dry pressing. Isopressing is commonly used to form complex ID configurations by compressing powder around a pin.

Extrusion

Extrusion is done in the same manner that most materials are extruded, by forcing material through a die. This is a standard process for tubes, rods and bar stock material.

Injection Molding

Cceramics is also similar to the processes used for other materials. Injection molding is used mainly for very intricate or high volume components. The cost for injection mold tooling is expensive but when amortized across high volumes it can mean a lower per part cost.

Mechanical Pressing

Utilizes steel or carbide tooling that creates a "net or near net" shape. By filling the tool with powder and applying uniaxial pressures to compress the powder.

Green Machining

The machining of a ceramic in the unfired state is called green machining. Green machining of ceramics is done whenever possible since the machining of ceramics after firing is very costly. The machining centers found in our plant are very similar to those found in standard machine shops; CNC mills, and CNC lathes drilling equipment, cut-off saws, surface grinders, rotary grinders, as well as many machines that have been custom made in-house. However, the extremely abrasive nature of ceramics requires the use of carbide and PCD tools and abrasive wheels. In order for ceramic to be hard and dense, they must be "sintered", or fired to high temperatures for prolonged periods of time in gas or electric kilns. Typical firing temperatures for alumina, mullite, and zirconia reach 2850 F - 3100 F. Typical firing cycles can range from 12 - 120 hours depending upon the kiln type and product. Ceramics shrink approximately 20% during the sintering process. Non-uniform shrinkage as a result of standard forming and machining processes can cause deformation of the ceramic. Our experience and knowledge of ceramic processing allows us to utilize specific machining and firing methods to help limit these effects.

Diamond Grinding

Post firing machining may be required to achieve tight tolerances, and surface finishes. At this stage ceramic can only be machined with diamonds, so tooling can be costly. Standard machine shop equipment can be modified with diamond plated or impregnated wheels, drills and assorted tools, as well as necessary recirculating and filtered coolant systems.

Glazing

One of the reasons that parts are glazed is to make it easy to remove unwanted residue. For instance, spark plugs are glazed to reduce areas of potential arcing in high voltage environments. This process involves dipping, brushing or spraying a glass coating onto the surface of the fired ceramic. The glazed ceramic must then be fired to 1500 F - 2700 F to sinter the glazed coating.

Cleaning

Most fired alumina ceramics can become dirty through handling, machining or inspecting. These oils, dirts and metal marks can be removed using a variety of techniques. Ultrasonic cleaning in mildly acidic or basic solutions at elevated temperatures is commonly done. STC also offers special cleaning and packaging options which may be desirable for applications sensitive to contamination.

Loss Exposure

The materials used in the ceramic manufacturing process are not generally hazardous except for materials that are used for packing or other fittings that may be attached to specific ceramic products. The fire load in ceramic manufacturing is not significant. However due to high temperature operation using furnaces and kilns chances of fire and explosion cannot be ruled out.

  • Ceramic Manufacturing Kilns: Fire and Explosion
  • Hydraulic Equipment used for presses : leakage and ignition of hydraulic fluid
  • Electrical Equipments : Short Circuit leading to Fire and/or breakdown
  • Storage : Fire in combustible packing materials and consumables

As regards furnaces and kilns, workers have been killed and property badly damaged in explosions through the ignition of unburnt fuel in gas-fired kilns. Gassing by carbon monoxide produced by incompletely burnt fuel also presents a serious risk, as do spillages of liquefied petroleum gas used as a fuel. With electric kilns, there is danger of electrocution, electric shock and burn injuries from heating elements and other conductors.

Risk Management

Installation and location of the kiln

Kilns should be sited with due regard to ventilation and heating, mechanical hazards, means of access, lighting and noise. Many of the fires involving ceramic kilns occur at night, due to overheating of wood forming part of the construction of roofs, ceilings or floors above the kiln. Kilns should be located away from general work areas and preferably be sited in a separate room or area. They should be situated on a load bearing floor and there should be adequate clearance between the kiln and the ceiling. Where there is limited headroom above an electric kiln other fire precautionary measures should be taken such as the use of a heat shield or the installation of a metal canopy hood and flue to extract the heat to atmosphere. The canopy may require insulation and should extend well over the kiln door. If the flue has to pass through or near combustible materials proper measures should be taken to avoid the risk of fire. The installation of flues should only be carried out by a properly trained competent person with a specialist knowledge of flue installations. The floor, ceiling and walls adjacent to the kiln should all be made of, or covered with, a non-combustible material.

Safe use of electric kilns in craft

Sufficient clearance should be left around the kiln to allow access for maintenance, servicing and free movement of air. All kilns that are not permanently wired should be positioned so that they can be plugged directly into an adequately rated and protected socket without the use of an extension cable . Good housekeeping around kilns is essential and combustible materials should never be stored near the kiln or allowed to accumulate around it.

Electrical safety

The following measures are recommended

  • Conveninent means of isolation from the electrical supply are required.
  • Protection against overload and short circuits is required by suitably rated circuit breakers or fuses
  • Wiring to kiln and control panel should be suitably insulated (with heat-resisting insulation) and protected against damage
  • External metalwork should be effectively earthed
  • No access to live heating elements should be possible: this will require the kiln door to be interlocked with the power supply (usually by means of a trapped key or key exchange system)
  • Any work on the electrical system should be undertaken only by a competent electrician

The kiln's electrical installation should be regularly inspected, particularly where plugs, sockets and flexible cables are used. It should be periodically tested to ensure that the earthing, insulation and

Safe Operation

Electric kilns should only be used by trained operators who are familiar with safe working procedures (including proper use of controls and safety devices) and are capable of recognising faults and coping with emergencies. Where practicable, two or more people should be capable of operating the kiln and be familiar with the emergency procedures, in order to ensure that there is sufficient cover in the absence of the normal operator. Written instructions outlining the safe operation and emergency procedures for the kiln should be clearly displayed in a prominent position next to it, together with a list of those people responsible for the kiln. Safe systems of work should be adopted at all times when the kiln is in use. Gloves providing suitable thermal protection and protective eye wear should be worn when removing ware while the kiln is still warm. In addition, protective eye wear fitted with filters conforming to should be used when removing spy hole plugs to inspect cones when the kiln is hot.

Kiln Maintenance

The electrical installation and the kiln should be regularly maintained. This includes regular inspection, particularly where sockets and flexible cables are used. Both the electrical installation and the kiln should be periodically tested to ensure that the bonding, earthing, insulation, connections, and electrical protection will operate for faults on the installation and the kiln. If faults are found, the kiln and installation should be taken out of service until the faults can be corrected. It is advisable to keep an up-to-date record of the nature and extent of all maintenance and repair work carried out on the kiln, including any servicing documentation. As regards electrical and hydraulic equipment losses and storage loss exposures, discussions have been done in detail in respect of earlier papers and are not being repeated.

Important

The information set out in this document constitutes a set of general guidelines and should not be construed or relied upon as specialist advice. Independent legal advice should always be sought. Therefore Risktechnik accepts no responsibility towards any person relying upon these Risk Management Guides nor any liability whatsoever for the accuracy of data supplied by another party or the consequences of reliance upon it.

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