Molding method for PTFE by mould pressing

The crystallization melting point of PTFE is 327℃, but the resin cannot be in the melting state until it is above 380℃, and the melt viscosity is as high as 1 010 Pa*S. In addition, PTFE has strong solvent resistance. Therefore, it can neither melt processing method, can not be dissolved processing method, usually the production of its products can only be like metal and ceramic processing - sample, first powder compaction, then sintering and mechanical processing, or through extrusion molding, isotactic pressing molding, coating molding and calendering molding and other ways of processing.

1.  Molding

Molding is currently the most widely used molding method for PTFE. Molding technology is a certain molding materials (powder, granule, fibrous material, etc.) into the metal mold, in - - fixed temperature, pressure - - a method of forming. Molded polymers are not limited by their molecular weight, and almost all plastics can be molded. The main features of molding are; Low cost, simple equipment, low investment, not limited by the molecular weight of the processed plastics; The disadvantages are low production efficiency, high labor intensity and unstable product quality. PTFE is of high molecular weight and extremely poor fluidity. When other processing methods are not mature, PTFE products are mainly processed by molding all over the world.

In the molding can be subdivided into five methods according to the difference of specific process: (1) pressing - sintering a pressing method (also known as free sintering method);(2) sintering - pressing method;(3) rapid heating a pressing method;(5) simultaneous pressing and sintering method.

2.  Hydroform method

Hydraulic pressure method, also known as equalization method, isobaric pressure method or rubber molding method, is to add PTFE resin evenly between the bag and the mold wall, and then to the bag into the liquid (commonly used water), the pressure of the rubber bag to the mold wall expansion, compacting the resin and become a preformed product - a method. This method can be used to manufacture large-volume sleeve, bottom storage tank, hemispheric shell, tower column, large slab, etc., as well as complex products with PTFE composite structure, such as tee, elbow and profile. The main advantages of hydraulic molding are the simple structure of the equipment and mould - a common water pump replaces the high-tonnage press, and the products are compressed evenly and densely - resulting in the manufacture of large components, complex shapes and simple lining structure.

3.       Push molding

Push pressure is also known as paste extrusion molding, 20-30 mesh sieve of disperse resin and organic additives (toluene, petroleum ether, solvent oil, ratio of resin weight of 1/5) mixed into a paste, prepress into thick wall cylindrical blank, then put into the push press machine barrel, under heating with the plunker push molding. After drying and sintering at temperature of 360~380°C, strong and tough push and pressure tube and bar products are obtained after cooling. The pushing and pressing products are limited to the rod with diameter of 16mm or less and the pipe with wall thickness of 3mm or less.

4.       Spiral extrusion molding

The screw extruder of PTFE powder is different from the extruder used by other thermoplastic plastics. The extrusion molding of ordinary thermoplastic plastics is to push the material forward with the help of screw rotation, and meanwhile to compress, shear and mix the material. The material is also melted by the heat generated by shear force and the external heating of the material cylinder. However, the screw of PTFE extruder only plays the role of conveying and pushing, so that the material passes through the head of a single-screw extruder with double-head thread and the same pitch and depth, and then enters into the mouth mold for sintering and cooling, and forms with the pressure provided by the counter-pressure device to achieve the continuous purpose. It is often difficult to process PTFE by single screw extruder. The low friction coefficient of PTFE powder causes skidding during the feeding process, which greatly reduces the conveying capacity of the screw. And because of friction heat, may also make powder adhesion to the screw or barrel, making the feeding more difficult and unstable.

In recent years, twin-screw has also been applied in processing materials of this special nature. Its feeding principle is different from that of single-screw extruder, and it has a positive transport function, which can overcome the sliding problem of UHMWPE powder in the screw and greatly improve the feeding capacity of the screw. The counter-rotating twin-screw extruder has better mixing and homogenization effect than the same-direction twin-screw extruder, but due to its larger separation force, the shearing action at the gap of the screw is larger, which causes the material to overheat, and the molecular weight of the extruder can drop by about 40%.If the gap is large and the screw is not engaged, the material will stick to the hot metal. However, the use of the same rotation of the twin screw extruder, there is no such problem. Material in the extruder by the shearing action of smaller, plasticizing the required quantity of heat, all from plus heat source, and thus can be precise control, which can make the material in the extrusion process to minimize heat degradation, at the same time in order to maintain the material flow of normal and stable in the nose, the nose section size of design should be compatible with the volume of a screw conveying material. Screw speed is not fast, generally about 10 revolutions per minute. In order to avoid material suddenly sticking to the metal surface, the extrusion temperature must be strictly controlled.

5.        Plunger extrusion molding

Plunger extrusion processing plastic, plastic processing is a relatively ancient method, since the emergence of this material, people began to use this method to process plastic. PTFE is processed with a plunger extruder by pressing the quantitative resin into the inlet mold, making the plunger reciprocate and pressing it into a preformed product. So back and forth, in the mouth mold to form a multi - stage pre - molding products. Due to the friction between PTFE resin and the friction between PTFE resin and the mold wall, and the volume expansion of the preformed product during sintering in the mold, the preformed product is sintered and cooled into a continuous whole under pressure. The advantages of this method are as follows: no shearing occurs in the molding process, the relative molecular weight decreases less, the product quality is good, and is not limited by the relative molecular weight. However, due to the small contact area between raw materials and heating parts in the extrusion process, the heating efficiency is low, which limits the extrusion speed.

6.        Other processing methods;

PTFE can also be processed by injection molding, calendering molding, coating molding or secondary molding.

Polymer PTFE production process Ram-punch extrusion

With the development of technology and economy, ptfe has been applied in more and more fields, and has become an indispensable material to solve many key technologies in scientific research, military and civil fields and improve the production technology level. In order to continuously improve the production efficiency of polymer ptfe, we began to adopt the advanced production process, which is suitable for high viscoelastic material —— Ram-punch extrusion.

According to the principle of "forging", plunger stamping extruder mainly adopts plunger with small cross section area and high frequency stamping to push material into the barrel of extruder. Compared with traditional hydraulic column extruder, it has the characteristics of high stamping frequency, good melt plasticizing effect, good product quality, simple equipment and process.

According to the forming characteristics of Ram-punch extruder, the extrusion process is analyzed and studied. The physical model of the whole extrusion process of plunger ram extruder is established, which is divided into five sections: solid feeding section, melting section, shunt section, forming section and cooling section. The influence of die length and pressure vibration frequency on extrusion process was analyzed. Analysis results indicate that: although there are large fluctuation of pressure at the entrance of the melt, but on the whole pressure from inlet to outlet were reduced gradually, thus ensure the enough pressure to push the material extrusion, and the closer it gets to the finish mold outlet pressure and speed fluctuation is smaller, so it can ensure the continuity of extrusion, finally get good quality products. The length and stamping frequency of the die have certain influences on the extrusion pressure and speed. Due to the high viscosity of PTFE, a longer die should be selected, and the stamping frequency between 5-6hz is appropriate.

Ram plunger extrusion machining polymer PTFE are very new machining method , but in the process of material forming process, also cannot leave the material flow and deformation, rheological behavior and the law, understanding the process of molding process of reasonable selection, operation and optimization control and improve molding equipment has very important practical significance. Plunger stamping is not a steady-state machining method, and there is vibration in the stamping process. It is of great significance to study the behavior response of polymer under the action of vibration field, and to discuss how much impact the vibration field will have on the flow stability, so as to study the dynamic forming of polymer materials and optimize production.

Performance introduction of PTFE Plastic Corrugated Pipe Machine

PTFE Corrugated Pipe Machine

Corrugated Pipe Machine Features:

ü  Power  Consumption: 380V, 1.5KW.

ü  Frequency Control, for the adjustment of  OD: 10mm to 50mm.

ü  Wall thickness: 1-2 mm PTFE convoluted hose.

ü  Imported heating system is used.

ü  heating temperature precision: + -1 degree.

ü  Single  person can operate two machines.

ü  In case 16/18 PTFE convoluted hose hourly capacity of 15-35 meters.

Equipment Accessories Details:

ü  A main engine.

ü   host of supporting tail stock.

ü  10 special bracket of PTFE convoluted hose for the production.

ü  30 with the following specifications bellows mold set.

PTFE Convoluted Hose Features

ü  To absorb effectively vibration, noise, thermal expansion from pipeline system.

ü  To resolve minor deviation because of piping connecting and eliminate the pipeline residual stress.

ü  Applied to repeated motion in high temperature areas, good anti-fatigue performance.

ü  Good flexibility, resistant to high temperature, resistant to corrosion.

ü  Applied in the fields of petroleum, chemical industry, aerospace, metallurgy, electricity, gas, building, mechanical, construction, iron and steel, paper making, fabric, medicine, food and vessels etc.

PTFE Convoluted Hose Characteristics

PTFE (Polytetrafluorethylene) has the lowest coefficient of friction of any material known to man. PTFE tubing features unmatched chemical resistance and a non-stick surface that facilitates flow and eliminates media buildup.

One key important advantage of PTFE convoluted hose is its operating temperature range, it can easily out perform other engineering plastics by being able to perform continuously at-250°C, right up to an amazing 250°C. Another important advantage of PTFE is its outstanding co-efficient of friction, PTFE convoluted hose is in the record books as having one of the lowest friction values known to man.

PTFE convoluted hose also has excellent acid and chemical resistance. Another feature of PTFE convoluted hose is its ability to set by or due to compression. PTFE convoluted hose has excellent electrical resistance. PTFE convoluted hose is also water repellent and is often used in the manufacture of modern high performing, water repellent and breath able clothing.

PTFE Convoluted Hose Applications

PTFE convoluted hose is excellent for low friction bearings, bushes, rollers and pulleys. PTFE convoluted hose is also almost exclusively used in cryogenic components due to its ultralow operating temperatures. PTFE convoluted hose is regularly used for seals. PTFE convoluted hose has become a very important engineering plastic used within the aerospace industry and aeronautics. PTFE convoluted hose is often used within the food industry companies. Another useful application over the years has been in the use of product or component handles due to its resistance to heat and heat transfer. When an application for electrical resistance becomes too high for other materials, PTFE convoluted hose can fill a very important gap.

ü  Virgin Polytetrafluoroethylene resin ƒ

ü  Chemically inert ƒ

ü  Lowest coefficient of friction ƒ

ü  Superior dielectric strength ƒ

ü  Exceptional heat resistance ƒ

ü  Self extinguishing ƒ

ü  Non-wetting ƒ

ü   Excellent flex life ƒ

ü  Laser mark able

Applications/Markets

ü  Cable Liner ƒ

ü  Electrical Insulation ƒ

ü  Oxygen Sensor ƒ

ü  Paint Transfer ƒ

ü  Gas Sampling ƒ

ü  Laboratory

More detailed technical data sheet

                                                                                           

Polymer micro-mechanical mold assembly molding

In-mold assembly molding of polymer micromachines is a new technology in which technological bottlenecks of micromachines micro-assembly manufacturing process can be effectively solved,  however, the thermal-fluid-solid coupling effect between polymer  high temperature viscoelastic melt flow and preformed micro solid part can be caused which induces preformed micro solid part producing frequently the thermal-fluid-solid coupling deformation and  necking fusing fracture phenomenon, how accurate control and predict thermal-fluid-solid coupling deformation and necking fusing fracture phenomenon is key scientific issues of in mold micro assembly molding technology industrialized application.

Therefore, based on the developed variable combination  mold and Auto model FB-110C polymer co-injection molding machine, the polymer micromachines In-mold assembly molding experimental research platform was established, by which the influencing rule and influencing mechanism of process parameters and properties of polymeric materials on preformed micro shaft thermal-fluid-solid coupling deformation and necking fusing fracture phenomenon were  systematically studied, key regulatory parameters of thermal-fluid-solid coupling deformation and necking fusing fracture phenomenon in in-mold micro assembly molding process was clarified; the scientific foundation of the research and development of thermal-fluid-solid coupling deformation precision-shaped control technology  and the  prevention technology of necking fusing fracture phenomenon was laid. The main innovations and achievements as follows.

The variable combination mold of  typical micro mobile motion pair in-mold micro assembly molding was developed, and Based on the developed variable combination  mold and Auto model FB-110C polymer co-injection molding machine, the polymer micromachines In-mold assembly molding experimental research platform was established.

The influencing rule and influencing mechanism of secondary molding melt injection temperature, secondary molding melt injection pressure  and  screw stroke on necking fusing fracture phenomenon of preformed micro shaft, the research results show  key regulatory parameter of preformed micro shaft necking fusing fracture phenomenon is secondary molding melt injection volume,  when the secondary molding melt injection volume exceeds its critical melt injection volume, the critical melt injection volume of induced preformed micro shaft necking fusing fracture phenomenon depends on secondary molding melt injection temperature, which is positively proportional to secondary molding melt injection temperature. Improving of secondary molding melt injection temperature will help improve the critical melt injection volume of induced preformed micro shaft necking fusing fracture phenomenon, which increase the secondary molded part density and strength in In-mold assembly molding process, at the same time, but also to avoid preformed micro shaft necking fusing fracture phenomenon.

Experimental research results show that the micro shaft unidirectional necking fusing fracture phenomenon possible ways  have two main factors, firstly, the axial tensile force is too large; secondly, the preformed micro shaft near-surface temperature in a secondary molding process  is too large, which led to partial melting  and a sharp decline of elastic modulus. The heat transforms time contact between secondary molding high temperature and preformed micro shaft will prolong with increasing of secondary molding melt injection volume, which make the preformed micro shaft near-surface temperature improve with increasing of screw stroke.

 When the preform micro shaft near-surface temperature exceeds the glass transition temperature, local micro assembly interface of preformed micro shaft will experience continuous phase transition evolution from elastoplastic solid state to viscoelastic plasticity glassy state ,final to viscoelastic high-elastic state, which led to a sharp decline of elastic modulus and make polymer material in local phase transition evolution region lost the ability to resist deformation, preformed micro shaft in local phase transition evolution region of micro assembly interface must produce necking phenomenon under tensile force effect.

When the tension force reaches a certain level, preformed micro shaft will produce the necking fusing fracture phenomenon. In order to preform micro shaft near-surface temperature does not exceed the glass transition temperature, which requires its secondary molding melt injection volume does not exceed the critical injection volume. Based on above necking fusing fracture mechanism, the preparatory proposed necking fusing fracture mechanism theory and prevention technical method of preformed micro shaft necking fusing fracture provide technical support for the industrialized application of In-mold micro assembly molding technology.

Experimental research results show that the preformed micro shaft thermal-fluid-solid coupling deformation depends on secondary molding melt injection temperature，secondary molding melt injection pressure ，secondary molding melt injection volume and preformed micro shaft material properties，and the process parameters affect its thermal-fluid-solid coupling deformation  by adjusting pre-formed micro shaft micro assembly interface to withstand the impact of the thermal-fluid-solid coupling pressure, viscoelastic supporting normal stress, viscous friction drag shear stress and micro shaft stiffness against deformation，the preformed micro shaft thermal-fluid-solid coupling deformation increase with increasing of secondary molding melt injection temperature，secondary molding melt injection pressure, secondary molding melt injection volume, and based on key regulatory parameters of viscoelastic supporting normal stress, viscous friction drag shear stress and micro shaft stiffness against deformation, the formation mechanism of preformed micro shaft thermal-fluid-solid coupling deformation was revealed.

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Measurement for shear viscosity spectrum of polymer melts by using screw extruder capillary

Most polymer materials are processed in the melt state, which involves melt flow and deformation, which not only affects the processing process itself, but also affects the final performance of the product. Therefore, the study of rheological properties of polymer materials has been a hot topic. Accurate measurement of rheological parameters is the basis of in-depth study of rheological properties.

Shear viscosity is an important parameter to characterize the rheological behavior. The so-called shear viscosity of polymer melt is the ratio of shear stress and shear rate that melt is subjected to in the process of flow. Polymer melt causes pseudoplastic fluid, and its flow behavior has the characteristics of shear thinning. It is usually necessary to use the relationship curve between shear viscosity and shear rate, namely shear viscosity spectrum, to fully reflect the processing characteristics of polymer melt.

The basic method of measuring melt viscosity is to try to make the melt flow through a long and thin capillary tube, such as a round capillary tube. The shear stress can be calculated by measuring the pressure drop at both ends of the melt as it flows through the capillary tube. The shear rate can be calculated by measuring the flux of melt per unit time. Thus the melt viscosity can be obtained.

The conventional way to get the melt out of the capillary tube is to use piston propulsion. The advantage of this method is that it USES fewer test materials and can obtain higher shear stress. The high pressure capillary rheometer is based on this principle [4].However, the disadvantage of this test method is that the material cannot be tested under the actual processing conditions, and it is difficult to obtain the rheological properties of the polymer melt when it is processed. Especially in the study of blending modification of several polymer materials, the polymer melt needs the strong shearing action of screw to achieve the purpose of blending. High pressure capillary rheometer is not suitable for testing such materials.

The screw extrusion capillary rheological test device can solve the above problems. The device USES the propulsive force of the screw to make the polymer melt flow through the capillary tube. Therefore, the shear viscosity of polymer melt can be measured under conditions closer to real processing. This method is particularly suitable for the measurement of the rheological properties of thermoplastic materials and their mixtures. Because the measurement simulates the real experimental environment, the obtained test parameters can more accurately describe the behavior of materials in actual processing.

Shear viscosity spectra of polymer melts can be measured using specialized test instruments, such as high pressure capillary rheometers, or combined revolutions. However, these devices are expensive and limited in practical use, especially in the application of large-scale industrial production. In fact, it is not necessary to rely on the special test instrument, as long as the shear viscosity test principle, you can use a simple small single-screw extruder and capillary mold, constitute a low-cost shear viscosity spectrum test device. Combined with computer data processing, the shear viscosity spectrum of polymer melt can be easily and quickly obtained. This method is especially suitable for small and medium-sized enterprises to carry out product development and raw material inspection.

Polymer plasticized compounding extruder screw design

Screw is the most important part of extruder, can be said to be the heart of the extruder, it can directly affect the application of the extruder and production efficiency. The performance of screw determines the productivity, plasticizing quality, dispersion of filler, melt temperature and power consumption of an extruder. Through the screw rotation, the polymer plastic can be extruded, and the plastic can move, pressurize and obtain some heat from friction in the cylinder. During the movement of the cylinder, the plastic can be mixed and plasticized.

1.     The screw structure of polymer plasticizing and mixing extruder.

During processing, when the material moves forward along the screw, it experiences changes in temperature, pressure, viscosity, etc., which are different within the full length range of the screw. There are three physical states of   polymer plastic in extruder: glass state, high elastic state and viscous flow state. In order to adapt to the requirements of different states and according to the changing characteristics of the material, the screw can be divided into three sections: feed section, compress section and homogenize section.

The function of the feeding section is to feed the material supplied by the hopper to the compression section. During the movement of the plastic, it generally remains a solid state and partially melts due to heat. The length of the feeding section varies with the type of plastic. Compression section (transfer section) is the role of physical material pressure, so that the material from solid into molten, well out of the air in the material; In order to adapt to the characteristics of reducing the volume when pushing the gas in the material back to the feeding section, pressing the material and melting the material, the screw in this section should produce greater shearing effect and compression of the plastic. 

The function of the homogenizing section (metering section) is to feed the molten material to the machine head at constant volume (volume) and pressure so that it is formed in the mouth mold. The volume of the spiral groove in the homogenizing section is the same as that in the feeding section.

In order to avoid material retention in the end of the screw head dead corner, causing decomposition, screw head is often designed into a cone or semicircle; Some screw homogenization section is - the surface is completely smooth body called torpedo head, but there are also engraved grooves or milling patterns. The torpedo head has the function of stirring and controlling the material, eliminating pulsating (pulsating) phenomenon in the flow, reducing the thickness of the material layer with increasing the pressure of the material, improving the heating condition, and further improving the screw plasticizing efficiency. 

According to melt transport theory, melt flows in the screw homogenization section in four forms, and the flow of molten material in the screw groove is a combination of these four flows: positive flow -- plastic melt flows between the cylinder and the screw in the direction of the screw groove toward the machine head. Counter-current flow direction is opposite to the positive flow, which is caused by the pressure gradient caused by the resistance of the nose, porous plate and filter plate. The flow of the melt in a direction perpendicular to the thread wall affects the mixing and heat exchange of the melt during extrusion. Leakage flow - a backflow formed by the pressure gradient between the screw and the cylinder, along the axial direction of the screw. Different flow patterns have important effects on the mixing uniformity of polymers.

Screw diameter and the determination of structural form, mainly according to the production of product output, specifications, types of processed materials and various structural screw characteristics to determine. Generally, the feeding section of the screw has a deeper groove and the groove depth is unchanged, compression section (melt section) of the screw groove depth along the direction of discharge from the deep to shallow, metering section (homogenized section) of the screw has a shallow groove and the groove depth is unchanged.

2.     The screw material.

Screw is the key part of extruder, as the material of screw must have high temperature resistance, wear resistance, corrosion resistance, high strength and other characteristics, at the same time should have good cutting performance, heat treatment residual stress, small thermal deformation and other characteristics. For extruder screw material, there are specific requirements as follows:

(1)   High mechanical properties. To have enough strength, to adapt to high temperature, high pressure working conditions, improve the service life of the screw.

(2)   Good machining performance. Good machining performance and heat treatment performance.

(3)   Good corrosion and wear resistance.

(4)   Easy to draw.

Teflon coating is introduced

1.     Antifouling finishing properties of (PTFE)teflon coatings

（1）The clothes

Keeping their clothes clean is no longer a problem for many children returning to school after the holidays. Their tracksuits, skirts and trousers are treated with teflon-coated anti-fouling, which keeps the children's clothes looking sleek and tidy. The clothes also stand the toughest tests of comfort, even when they are close to sensitive parts of the body. For office workers, leaving coffee stains or ink stains on their clothes can be embarrassing. Make consumers' life more comfortable.

（2）Leather aspect

(PTFE)Teflon coated antifouling finish gives leather perfect waterproof and antifouling protection. But when it comes to vision, taste and touch, consumers are unaware of the TeflonB coating.

（3）other aspects

Teflon coating finishing is not only used in the field of clothing and leather, but also widely used in luggage, umbrella and other textile products, hunting and fishing and other recreational textiles, bedding, all kinds of decorative textiles and so on.

Surface properties：

The molecules slide easily between each other, and the friction coefficient is the lowest in all polymers. It has good lubricity, is difficult to be wetted by ordinary liquid, and has little adhesion to other substances.

Chemical resistance：

Teflon is even more resistant to chemical corrosion than rare metals. Except      perfluoroalkane and perchloroalkane can make it slightly swelling, ketones,        ethers and other organic solvents can not act on it. Because (PTFE)teflon        has little wettability, its absorption rate to acid and alkali solvent is very low.      Even at high temperature, concentrated acid, concentrated alkali and strong      oxidant cannot react with teflon uplift.

Heat and climate resistance:

Teflon has good thermal stability, and is not affected by oxygen, ozone and        ultraviolet radiation, and is not easy to age. The combustion oxygen index          of teflon is greater than 95, which is incombustible.

Innovation of industrial furnace combustion technology

Industrial furnaces are mainly divided into smelting casting and heat treatment furnace two types. The former is used for refining and smelting casting, while the latter is used for heating and heat treatment of billets before processing. Most of the fuel used for metal heating is natural gas or city gas, which must be fed into the air by air blower to support combustion. 

As we all know, the air is composed of nitrogen, which accounts for 78%, and oxygen, which accounts for 21% (and about 1% of the noble gases). Nitrogen, which has no combustion effect, becomes a drag, which not only delays the heating speed, but also takes away the heat in the flue gas, adding to the environmental problems. After years of research and development, The Linde Group of Germany has invented The low-temperature pure oxygen combustion technology (LTOF), which is suitable for smelting, melting casting and heat treatment of non-ferrous metals such as steel, copper and aluminum.

1. Introduction of low temperature pure oxygen combustion technology (LTOF) in industrial furnace

The main effects of pure oxygen combustion technology are:

(1) No nitrogen enters the furnace;

(2) No nitrogen removes heat in the flue gas;

(3) Iincrease the efficiency of radiation heat transfer;

(4) The flue gas stays longer in the furnace, so as to improve the heat transfer effect;

(5) Since there is no nitrogen in combustion supporting gas, it has little impact on environmental protection when discharged;

(6) The combustion supporting effect of pure oxygen reaches 77%, while the atmospheric combustion supporting rate is only 23%.

2. Advantages of low temperature pure oxygen burner (LTOF) flame in industrial furnace

The objective of low temperature pure oxygen combustion (LTOF) technology development is to improve the melting capacity and efficiency of reflector. The unique LTOF burner allows the flue gas from the entrainment furnace to enter the burner mixing zone, diluting the oxygen concentration at the front of the burner and slowing down the rate of combustion reaction, resulting in a lower flame temperature that is close to the flame of air-fuel combustion. 

This LTOF pure oxygen combustion flame characteristics make the temperature in the furnace more uniform, eliminate local hot spots, reduce fuel consumption, reduce flue gas emissions and improve metal recovery rate. Comparison between air combustion and low-temperature pure oxygen combustion, among which, air combustion, burner power is 311kW, water cooling is 231kW, the average constantly measured in molten aluminum is 1131℃, and heat flux is 79kW/m2.Low-temperature pure oxygen combustion, burner power 257kW, water cooling 66kW, continuous measurement of aluminum in the average value of 1152℃, heat flux 79kW/m2.

3. Flame form of LTOF low-temperature pure oxygen burner in industrial furnace, flame free combustion is the most effective

(1) Can reduce NOx emission by 90%;

(2) Compared with regenerative or ordinary pure oxygen combustion, flameless combustion is the least sensitive to air leakage, and there is no significant change in NOx production. The average energy consumption and thermal balance of LTOF pure oxygen combustion technology in 28t aluminum alloy melting reflector.

Design of microwave sintering furnace

1. Principle of microwave sintering of ceramic materials

The reaction of materials to microwave can be divided into four situations: microwave reflection microwave transmission; microwave absorption; partial absorption of microwave. Most metals fall into the first category, while all glass and ceramic materials fall into the latter three categories. When a ceramic body is placed in a microwave field, the absorbed power can be expressed by the following equation：

P = (2π fε ) ( E2/ 2) tan δ，When the microwave penetrates the material, its intensity decreases with the penetration depth. The distance from the material surface to the attenuation to 1/ e of microwave energy is defined as the penetration depth Dp of microwave:

3λ 0

  DP =       π tan δ (ε r/ε 0) 1/ 2    

8. 686

Where, P is the microwave power absorbed by the ceramic body; F is the frequency; ε is the composite dielectric constant; λ 0  is the wavelength of microwave in vacuum; E is the intensity of electric field; tan δ is the loss tangent of dielectric ceramics; The loss tangent (the ratio of the loss factor to the dielectric constant) is usually used to express the coupling capability of the material to the microwave.The higher the loss tangent value is, the stronger the coupling ability between the material and microwave is.

2. Design of microwave high temperature heating furnace

Microwave heating furnace is mainly composed of monitoring system, control system, insulation box, microwave generator, heating box and gas storage tank. The heating box is made of stainless steel mirror plate. Cooling water can flow in the sandwich between two layers of stainless steel plate to achieve the cooling of heating box. The temperature sensor we use is RAYR3I1MSCL2U infrared thermometer of American leitai company. The control system can realize manual control and automatic control. In order to prevent in the microwave oven door closed after microwave heating furnace from the oven door and leak out of the gaps between the cavity, in addition to heating furnace door in processing and manufacturing to ensure the high dimensional precision and assembly precision, we in the microwave oven door installed around the choke groove structure, this structure can effectively reduce the leakage of microwave. The selection, field design and insulation of the microwave generator are the key factors in the sintering furnace design.

3. Microwave generator selection

Mag netron, Klystron and Gyrotron are generally selected in microwave heating devices. As the "heart" of microwave sintering equipment, its choice will directly affect the performance and cost of the whole equipment. The commonly used frequency in microwave sintering device is:

915 MHz, 2.45 GHz, 6 GHz, 28 GHz and 60 GHz, etc. Generally, magnetron can be selected as microwave generator for lower frequencies such as 915 MHz and 2.45 GHz,6 GHz can be selected as speed regulating tube, and higher frequencies such as 28 GHz and 60 GHz can be selected as magnetic coil.

As the frequency and power of various microwave generators increase, their price ratio ($/ Watt) will increase significantly. If high power microwave generator is needed in the design, it is recommended to use the same frequency and low power generator to obtain by power superposition.

4.Design of insulation structure

The most commonly used insulation structure in microwave sintering furnace is buried powder type and box type. Buried powder insulation structure has the advantages of good insulation effect. However, when samples are sintered at a higher temperature, adhesion between samples and buried powder is easy to occur. After the samples are sintered, direct contact will occur. But this structure is not as good as buried powder insulation structure. Combining the characteristics of two insulation structures, we designed a box-type insulation structure.