High-temperature Chamber Furnaces & Tube Furnace

For production sintering operations, certain furnace design considerations are common regardless of whether you are working in metals, ceramics, or glass and regardless of what industry you work in. In order to achieve compression without liquefication, accurate temperature control and careful atmosphere monitoring are essential to uniformity and throughput.
Typically, the higher-temperature continuous furnaces used for sintering operations are known as “pusher furnaces” or “walking-beam furnaces.” A pusher furnace moves the work through on a series of boats or plates. One boat is pushed against another in a continuous train. A pusher furnace only pauses long enough to remove a boat at the exit end and add one at the entrance end. This is considered a constant push.
A walking-beam furnace utilizes a pusher mechanism to bring the boat into the furnace and place it on the beams. These beams are analogous to a series of rails. The rails are on cams, which lift up, forward and down, essentially walking the boat or carrier through the furnace. At the exit end, the boats are then commonly transferred onto a belt for the cooling section.
tube furnace is an electric heating device used to conduct syntheses and purifications of inorganic compounds and occasionally in organic synthesis. One possible design consists of a cylindrical cavity surrounded by heating coils that are embedded in a thermally insulating matrix. Temperature can be controlled via feedback from a thermocouple. More elaborate tube furnaces have two (or more) heating zones useful for transport experiments. Some digital temperature controllers provide an RS232 interface, and permit the operator to program segments for uses like ramping, soaking, sintering, and more. Advanced materials in the heating elements, such as molybdenum disilicide offered in certain models can now produce working temperatures up to 1800 °C. This facilitates more sophisticated applications. Common material for the reaction tubes include alumina, Pyrex, and fused quartz.
The tube furnace was invented in the first decade of the 20th century and was originally used to manufacture ceramic filaments for Nernst lamps and glowers.
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Plastic Extrusion Process

The extrusion process is a key component of many of our daily activities. It provides the tubing that distributes our drinking water, heats or cools our homes and could deliver life saving medication to a person in need. The process involves the use of polymers (plastics) that when heated change from a solid to a vicious liquid. Once the polymer is in its liquid state it is extruded (pushed) out a die that provides a specific shape. The process is contained in an extruder that consists of a round barrel with a screw inside. The polymer is placed into a hopper throat. As the screw rotates the polymer moves from the feed section up and through the die and takes shape of the orifice in the die.
Once the part is extruded out of the die in the molten state it passes through a sizer to control the shape of the part as it cools. This can be done in many methods depending upon the material and line rate (feet per minute) in the process. Typically with tubing products a vacuum tank is used. The tank creates a vacuum chamber in which the part is passed thru. This forces the tube to push out against a sizer that is shaped and controls the size of the polymer until it is cooled below its melting point (Tg – glass transition temperature). Similar methods to sizing are vacuum calibration, air racks and open water tanks.
The polymer is cooled and then pulled thru a take off puller. The take off puller is a key component to maintaining and controlling the size of the extrusion. The puller must take the material being exited from the die thru the sizer at the same continuous rate. The puller is typically set to a constant speed that is relational to the extruder output. The puller speed is typically given feet per minute (fpm). The fpm is key to determining the amount of sizer required to control the polymer and provide the right size product required by the customer.
Once the polymer is cooled and thru the take off puller then it can be cut to length, punched or formed to provide the finished product. Flexible products can be wound on spools or coils.

 

Differences between sintered & unsintered ptfe tape

More popularly known by the brand name Teflon, PTFE, or polytetrafluoroethylene, is an electrical insulator used in making high-grade cable and wire. PTFE tape is revered as a superior insulator for many qualities, including low dissipation, wide temperature tolerance, high-frequency stability, low smoke generation, resistance, dielectric constants and its resistance to flame, chemicals, solvents, moisture and volume. Sintered and unsintered PTFE tape are two of the three main types design engineers use in making high-performance cable and wire.
Design and Manufacture
Engineers produce sintered, or “full density,” PTFE tape by compression moulding a cylinder-shaped billet, heat sintering it in an oven and skiving the film off of it. Engineers produce unsintered PTFE tape by cold extruding a fine PTFE powder through a special die.
Properties
Sintered PTFE tape has a specific gravity, or density, of 2.15g/cm3, crystallinity of 50 to 70 per cent, porosity of less that 1.0, matrix tensile strength of 20-30 Mpa and thermal conductivity of 0.2 Kcal/m-hr in degrees Celsius. Unsintered PTFE tape has a specific gravity, or density, of 1.5g/cm3, crystallinity of 92 to 98 per cent, porosity of less that 10, matrix tensile strength of 10-20 Mpa and thermal conductivity of under 0.2 Kcal/m-hr in degrees Celsius.
Characteristics
Both unsintered and sintered PTFE tape have poor resistance to cold flow and excellent chemical resistance, but unsintered tape has poor abrasion resistance compared with the moderate abrasion resistance of sintered tape.
Applications
Design engineers most commonly use PTFE tape for insulation of aircraft electronic equipment hookup wire for military and commercial uses. Engineers wrap unsintered PTFE tape around a conductor and then heat sinter it to produce potent electric wires with integrity, rigidity and uniform insulation. Engineers use unsintered PTFE tape to create high-speed data cables of superlative quality and with minimal signal loss.

 

How does injection moulding work?

Injection moulding along with extrusion ranks as one of the prime processes for producing plastic articles. It is a fast process and is used to produce large numbers of identical items from high precision engineering components to disposable consumer goods.
Most thermoplastics can be processed by injection moulding; the most common materials used include:
  • Acrylonitrile-Butadiene-Styrene ABS
  • Nylon PA
  • Polycarbonate PC
  • Polypropylene PP
Injection mouldings count for a significant proportion of all plastics products from micro parts to large components such as car bumpers and wheelie bins. Virtually all sectors of manufacturing use injection moulded parts. The flexibility in size and shape possible through use of this process has consistently extended the boundaries of design in plastics and enabled significant replacement of traditional materials thanks to light weight and design freedom.
Material granules for the part is fed via a hopper into a heated barrel, melted using heater bands and the frictional action of a reciprocating screw barrel. The plastic is then injection through a nozzle into a mould cavity where it cools and hardens to the configuration of the cavity. The mould tool is mounted on a moveable platen – when the part has solidified, the platen opens and the part is ejected out using ejector pins.
After a product is designed, usually by an industrial designer or an engineer, moulds are made by a mouldmaker (or toolmaker) from metal, usually either steel or aluminum, and precision-machined to form the features of the desired part..
Parts to be injection moulded must be very carefully designed to facilitate the moulding process; the material used for the part, the desired shape and features of the part, the material of the mould, and the properties of the moulding machine must all be taken into account. The versatility of injection moulding is facilitated by this breadth of design considerations and possibilities.

 

Extrusion is a process used for creating a product (an extrudate) by forcing a material through a die or an orifice to form a shape, or alternatively an extruder is used to produce semi-finished or finished products.
In a thermoplastic extrusion, the material is first softened by heating so that it can be shaped. This process is performed by the extruder, or extrusion machine. This heat softening is referred to by different names, such as ‘thermal softening’, ‘plasticization’, or ‘plastication’.
Most extruders are single screw machines. The screw is what forces the material towards, and then through, the die. Shape is imparted by the die, and/or by post-extrusion forming, and the product is then set to shape by cooling while maintaining its shape. The equipment used to perform this process is known as the post extrusion equipment, while the entire system is known as an extrusion line.
The extrusion products include:
  • Plastic Film: This is generally used for packaging or sealed into bags.
  • Plastic Tubing: Used for tubing and hose for laboratories, automobiles, etc.
  • Plastic Pipe: Used for water, drains, gas, etc.
  • Plastic Insulated Wire and Cable: Used in the industry and home for appliances, for communications, electric power distribution, etc.
  • Feedstock for Other Plastics Processes: Extruders are widely used as compounders, or mixers. The output from an extruder compounder is chopped or granulated to form the feed for another process, such as extrusion or injection molding.
  • Plastic Coated Paper and Metal: Used for packaging.
  • Sheet: Used for lighting, glazing, signs, etc.
  • Filaments: Used for ropes, twine, brushes, etc.
  • Nets: Used for soil stabilization, packaging, etc.
  • Profile: Used for home siding, gaskets, windows, doors, tracks, etc.

How does twin screw extruder work?

Extrusion processing aims to physico-chemically transform continuously viscous polymeric media and produce high quality structured products thanks to the accurate control of processing conditions.
Twin screw extruders consist of two intermeshing, co-rotating screws mounted on splined shafts in a closed barrel. Due to a wide range of screw and barrel designs, various screw profiles and process functions can be set up according to process requirements. Hence, a twin screw extruder is able to ensure transporting, compressing, mixing, cooking, shearing, heating, cooling, pumping, shaping, etc. with high level of flexibility. The major advantage of intermeshing co-rotating twin screw extruders is their remarkable mixing capability which confers exceptional characteristics to extruded products and adds significant value to processing units.
In twin screw extrusion processing, the raw materials may be solids (powders, granulates, flours), liquids, slurries, and possibly gases. Extruded products are plastics compounds, chemically modified polymers, textured food and feed products, cellulose pulps, etc.
The Advantages of Twin Screw Extrusion:
  • More consistency in production and control of product quality
  • Increased productivity due to continuous processing, faster start up and shut down between product changes, quick changeover and advanced automation
  • Greater flexibility, with the capability to process a wide range of raw materials
  • Optimized footprint thanks to energy and water savings
  • Simple and easy to maintain and clean
Twin screw extrusion is used extensively for mixing, compounding, or reacting polymeric materials. The flexibility of twin screw extrusion equipment allows this operation to be designed specifically for the formulation being processed. For example, the two screws may be corotating or counterrotating, intermeshing or nonintermeshing. In addition, the configurations of the screws themselves may be varied using forward conveying elements, reverse conveying elements, kneading blocks, and other designs in order to achieve particular mixing characteristics.

 

UHMW Ram Extrusion Process

UHMW powder is gravity fed into a chamber and a hydraulic ram pushes the powder from this chamber into the die. The die is the shape of the desired plastic, a certain diameter rod, a certain OD and ID tube, or a profile shape.
Heaters are employed on the outside of the die to heat the plastic and make it form into the shape of the die. The hydraulic ram moves back and forth continuously feeding the powder into the die.
As the material comes out of the die, it travels the length of the conveyor after which it is cut to length. Ram extrusion does not shear the material that is being manufactured as does single screw extrusion which employs a rotating screw to move the material.
It moves the material by hydraulically pushing it through the die which is the desired shape of the end product. UHMW-PE, which becomes gelatinous when it melts instead of molten, can only be extruded with this type or similar type process.