Tungsten cemented carbide is the preferred material for parts that must withstand all forms of wear (including sliding abrasion, erosion, corrosion/wear and metal-to-metal galling) and exhibit a high degree of toughness. It exhibits high compressive strength, resists deflection, and retains its hardness values at high temperatures, a physical property especially useful in metal-cutting applications. It provides long life in applications where other materials would not 0ast or would fail prematurely.

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Binder is linked with skim , skim binder determines the way . Degreasing methods include conventional thermal degreasing, solvent degreasing, siphon degreasing , BASF Catalysis skim . Wiech invention also includes degreasing solvent vapor degreasing solvents and high pressure degreasing . Degreasing process caused by changes in C content alloys have a great impact . The success of defatted skim from deformation, cracking , size change , degreasing time , environmental factors, such as the level of cost considerations.

Several methods have their own shortcomings skim . Binder with skim selection should be based economy, no environmental pollution , alloy composition and thickness of the parts . Although there are many ways bonding agent and degreasing , but the wax-based bonding agent has many advantages , in practice, still wax based adhesives and hot degreasing .

PIM thermal debinding is the most difficult and most important step . Degreasing process the incorrect way and skim skim process parameters lead to distortion , cracking, stress and gas inclusions , the product contraction inconsistent. After degreasing its sintering is also important in the cracks generated during degreasing and sintering deformation can not be compensated for densification of the alloy and detrimental to the performance . Thermal debinding temperature is too high , easy to produce carbonation, the alloy performance is greatly affected. Therefore, the selection process is correct or not defatted sample would produce internal defects and alloys have a great impact . PIM contains large amounts of feed in the binder , the strength of the blank after degreasing is very low, almost loose powder aggregates. Therefore , a large shrinkage during the sintering process , easy to collapse , and bending deformation . Especially for liquid-phase sintering of tungsten alloy, high density , required to achieve full densification sintering temperature , the liquid volume, the sintering time is long , W phase and liquid phase density difference is large, the liquid phase sintering process , under the action of gravity , because the liquid flow W rearrangement generation of particles , the collapse and deformation more severe , seriously affecting the homogeneous nature , alloys and control of dimensional accuracy , limiting the complex near-net- shape forming part of . Hence, throughout the injection molding technique, how to control the deformation of the liquid phase sintering process but PIM key issues need to be addressed . Lower the sintering temperature and promote densification during liquid phase sintering can be controlled deformation .



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However, since the PIM using a large number of organic binder , an organic binder in a volume percentage content of 40% -60 % . In these organic binder before sintering must be removed clean. Otherwise they will have many flaws , the sintered product performance has a great influence . Especially for injection molding process especially in the case , this is mainly because :

First, because the fine particle size , irregular shape , was reunited shape, powder large surface area , the required wetting powder binder content more powder volume content ( ie powder loading ) lower , only 45 % to 55 % or so. Adhesive surface of the powder and the powder formed in the inner hole of the adsorption layer is very thick , adhesive removal of more complex and difficult. Incorrect difficult to skim through the cracks caused by the subsequent densification remedy , which performance is very sensitive to pore and crack high-density alloy very unfavorable ; powder loading is low, degreasing process prone to warping , easy deformation ; in the liquid phase sintering shrinkage is too large , the deformation is more serious , making control of dimensional accuracy and stability of physical and mechanical properties is very difficult.

Second, the high density of the alloys are very sensitive to impurities and microstructure , porosity and porosity are important. - Areas produced during removal of large pores and other defects is difficult to compensate by sintering , large pores and high residual porosity ( porosity of> 1.0% ) of the performance is very harmful . On the other hand , the high -density alloy elements are very sensitive to carbon . Degreasing binder removal process is not complete, even if only a small amount of residual carbon will lead to copper and tungsten, nickel, iron , to form brittle intermetallic compounds , thereby reducing the tensile strength , ductility and toughness .
These factors severely restrict the PIM technology in high -density alloy application and development. At home and abroad by powder injection molding technique can only be prepared relatively complex shape , the thickness ( or diameter ) smaller (10mm) parts. For the cross-section changes, large diameter , thickness and width of the ring is very small changes in the large size of a large shotgun and larger diameter tungsten ring tungsten alloy penetrators bomb core ( greater than 20mm), powder injection molding using current technology to prepare very difficulties at home and abroad were no patents and literature reports .

Is to obtain high-quality injection preform having a high dimensional accuracy and high performance components a very critical factor. Unstable injection process , injection preform serious impact generated defect control of dimensional accuracy and performance. The injection process stability depends directly on the binder , and thus in research and development of high-density alloy near net shape technology , adhesive , injection , skim a few important research aspects .




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( 1 ) The tungsten powder , nickel powder , iron powder according to the proportion required weighed , the V-shaped blender mix 12h, speed 36r/min.

( 2 ) Preparation of Binder . Three types of experiments were prepared and ten kinds of binder ingredients , they are: wax Quito component adhesives, oil-based plastic binder system , ( Oil + Wax ) -based system to improve the plastic binder . Preparation of binder , the first binder were weighed according to the proportion of each component of the weight , the blender ohmic heating . Mixer until the temperature rose to a certain temperature, the first polymer by adding a certain amount of HDPE, PP, PS, PP, EVA , etc. Subject to soften the polymer melt , adding low molecular binder component PW, oil. Then add the coupling agent SA and DOP. Hybrid 0.5-2h , stop heating , pour the liquid binder , after cooling bag sealed to be done experiment.

( 3 ) Mixed Feeding . The W - Ni - Fe mixed powder and binder prepared in accordance with a certain proportion weighed , powder loading of 51%. First binder was added to XSS-300 torque rheometer , until melted , then add the metal powder mixture . Mixture temperature of 100 ~ 700 ℃, the PW series adhesives, compounding temperature is 115-125 ℃. For BO binder , mixing temperature of 180 ℃. For the OP series adhesives, mixing temperature is 140-165 ℃. Mixing time was 2h.

( 4 ) Granulation. Single- screw extruder using LSJ20 device will feed extruded strip , strip . Extruder, the feed and shear stress at a given temperature, the powder binder no separation phenomenon , while extruding the powder binder that a more uniform distribution . The screw speed in this experiment is 50r/min, extrusion material temperature is 110 ~ 160C.



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Affect the quality of the injection process and process parameters green lot, quite complex, due to improper control will produce injection, holes, deformation, wire, broken edges, sandwich, density gradient, surface defects and other defects of varying green singlet. Through the rational choice matching material mild mold temperature control plus quantity, adjust packing pressure, dwell time, injection speed, injection pressure, improved mold design, mold with improved accuracy and other measures, can effectively control the generation of defects injected green . The following are some common causes of defects and solutions.

(1) Owes Note (or can not be injected). Note refers to the feed in less filling process can not fill the mold cavity. Specific causes and solutions are:

1) Material temperature or mold temperature is too low, you need to increase the material temperature or mold temperature;
2) Feeding Quantity Insufficient;
3) Feed the viscosity is too large, the general approach taken by elevated feed temperature;
4) Runner improper size, gate should be wider, shorter runner should thus filling behavior of simple and easier to fill the cavity.

(2) Holes. Holes is the cross section of the green can be found in the pores. Some of the holes of a nearly circular, almost throughout the development of some of the central through hole green body, which is a common defect, be carefully controlled. Produce this defect causes and solutions are:

1) Clip person when injected gas, kneading feeding clip person filling gases and bad, will lead to, at this time needs to be adjusted or trimmed feed mold;

2) Powder with the binder separation; mold temperature and melt temperature does not match; holding pressure is too small, dwell time is insufficient. When these problems, the need to improve the mold design, mold filling process so that feeding can be evenly filled cavity; reduce mold temperature or injection temperature; reduce injection speed.

(3) Deformation. Causes and solutions are:

1) Ejection green strength is low, you can reduce the mold temperature or melt temperature, injection unit time decreases the number of blank birth, improve loading capacity, the use of higher-strength adhesive system, etc. to solve;
2) Feed mixing powder and binder uneven or separation;
3) Residual stress is too large, can be appropriate to reduce the injection temperature and also slightly elevated mold temperature, lower injection pressure and holding pressure to resolve.




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Injection molded preform by a large amount of organic binder and the powder is composed of a polymer, an organic binder of the powder body from the bonding role in ensuring the injection molded preform having a sufficient strength, however, these bonding agents must be completely removed before sintering (i.e. skim process), otherwise it will affect the alloy properties.

Skim is the use of physical and chemical methods of injection molded preform dissolved organic binder and forming blanks from cracking thus removing process. Degreasing before sintering is a very important process. By injection of the feed pressure of the large number of preform binder (i.e., organic polymer), the volume ratio of 40070 to 60%, and sintering the binder must be removed prior to, or, in the sintering, these organic polymers degradation and thermal decomposition can occur, producing many gases generated in large compacts internal pressure, so that cracking and porosity compacts. Binder removal requires several steps, PIM process manufacturing costs to a large extent controlled by this stage. Binder in the form of a liquid or gas to escape from the inside surface of the sample in turn, form a connected open pores, adhesive removal speed, while no dirty degreasing blanks, and has no distortion.

Non-fat will be successful bubbling, cracking, peeling, holes, cracks, dirty technology and deformation and other defects. Main causes of skim rate is too fast, improper bonding mode selection, removal of the temperature control is inappropriate, improper control of the heating rate. Degreasing the defects affect the subsequent sintering, skim defects generated by a stop to make the sintering step, degreasing defects generated significantly affect the properties of the alloy.

Degreasing Methods: divided into thermal degreasing degreasing, solvent degreasing, catalytic skimmed, skimmed siphon of four.

Thermal Degreasing: Thermal degreasing injection molded preform is embedded in the alumina powder filler material in a vacuum, oxidizing or reducing atmosphere under heating according to a certain process.

Solvent Degreasing: degreasing solvent injection molded preform is immersed in a low molecular weight organic solvent or inorganic solvent (or solvent vapor), the use of organic molecules similar to the principle of compatibility.

Catalytic Skim: catalytic catalytic skim skim also known as BASF, which skimmed way linked with BASF binder.

Siphon Degreasing: degreasing siphon injection molded preform is buried in the micron, sub-micron powder, alumina powder, or other fillers, the use of fine powder of the molded preform by capillary action of the organic binder in the process of the gradual discharge.




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Cemented Carbide is one of the most successful composite engineering materials ever produced. Its unique combination of strength, hardness and toughness satisfies the most demanding applications.

Tungsten carbide is an equal mixture of tungsten and carbon. When the alloy is created, it is typically made as a fine gray powder. This powder is compressed into the desired shape using a modified die-casting process. After hardening into its new shape, this material is extremely hard and can withstand heat that would melt other metals.

The most valuable property of Cemented Carbide is that it offers a safer and more dependable solution than any other known material to one of the toughest problems engineers contend with - reliability. Learn all about Cemented Carbide!

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The actual definition of a tool bit is a matter of some debate. In some circles, a bit is a non-rotary cutting tool like the blade on a lathe or the head on a shaping machine. In other places, it is any removable or exchangeable tool piece, such as the drill part of a handheld drill. Both definitions have one thing in common—the bit is the part that directly interacts with the worked material, and any changes to the material are done by the bit alone.

Manufacturers use a carbide bit when the material or manufacturing process requires high tolerances or precision. These bits are often used when a material is hard enough that a typical bit won’t work it properly, such as with hardened or carbon steel. Since that’s what a common bit is made of, it isn’t hard enough to work the material. Interaction between two pieces of the same material typically results in both parts being ruined.

Another common reason for a carbide bit is when the material being worked needs exposure to very high temperatures either before or during the process. Since a carbide bit can withstand greater temperatures than steel, it is often used in high-heat situations. This is also true when the friction created by the working process would create enough heat to melt a steel bit, such as in high-speed grinding.

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The manufacturing process begins with the composition of a specific tungsten carbide powder mixture - tailored for the application.

The tungsten carbide powder is compacted into a form.

In a high-temperature sintering furnace, the tungsten carbide structure of the blank is shaped at precise temperatures for strictly defined periods. During this heat treatment, the tungsten carbide blank undergoes shrinkage of some 50% in volume.

The sintered Cemented Carbide component gains its final finish by additional grinding, lapping and/or polishing processes.

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The manufacturing process begins with the composition of a specific tungsten carbide powder mixture - tailored for the application.

The tungsten carbide powder is compacted into a form.

In a high-temperature sintering furnace, the tungsten carbide structure of the blank is shaped at precise temperatures for strictly defined periods. During this heat treatment, the tungsten carbide blank undergoes shrinkage of some 50% in volume.

The sintered Cemented Carbide component gains its final finish by additional grinding, lapping and/or polishing processes.

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