Powder metallurgy of common sense(2)

11.the shape of the powder particles used in powder metallurgy is determined by what? There are roughly what kinds?

Due to the different method of preparing the powder, the particle shape is different. Generally have an irregular shape, sheet, polyhedral, dendritic, granular, spherical droplets, fibrous ……

12.What is the powder particle size? Usually determined by what method?
Particle size refers to the size of the powder particles. Usually determined by sieving.

13.What is the size of powder composition?
Composition of the powder particle size, particle size distribution is also known. Refers to all levels of powder pink powder as a percentage of the total weight.

14.What is a powder particle size range?
Powder particle size range of the powder particles is the change between two predetermined particle size.If the particle size in a range of -80 +150 mesh powder, the powder particle size that is equal to or smaller than 80 mesh and larger than 150 mesh. In other words, the powder passed 80 mesh sieve, and they pass a 150 mesh sieve.

15.What is the powder screening level?
Powder screening level refers to the powder particle size classification by sieving

16.What is the powder sieve analysis?
Sieve analysis of the powder by means of a standard sieve sieved powder sample.finds the weight percentage of powder at all levels, to indicate that the powder particle size distribution.

17,what is the mesh of sieve?
Mesh (such as Taylor’s standard screen) refers to all the number of mesh in 1-inch lengths.

18.What is the surface area of powder?
Which is the sum of all of the particle surface area means 1 gram of powder (Ｃ㎡ or square m㎡), aalso known as gram of surface area.

19.What is the bulk density of the powder?
The bulk density of the powder is under the conditions defined for the powder to flow freely into a standard container (cup),and then scrape,measure mass per unit volume of powder, expressed in g/cm 3.

20.What is the tap density of the powder?
When the power flow freely into a standard container,there was reason of friction between the particles formed arch bridge.If the qualifying conditions.the powder subjected to vibration,arch collapses,the measured mass of powder per unit volume, called the powder tap density.

21.What is the green density?
Green density per unit volume is the average of the actual quality of the compacts, represented by g/cm3.

22.What is the relative density of compacts and relative density of the sintered parts?
Green density compared with the dense matter density of the same composition, called compact relative density.sintered density and density of the dense matter with the same composition is called the relative density of the sintered parts.

23.What is the fluidity of powder?
The terminology describes the flowability of a powder passing through the hole defining.Usually 50 grams all through the exit aperture of 2.54mm, cone angle is 60 degrees the flow funnel time (s).

24.What is the compressibility of the powder?
Compressibility of the powder is the powder at a predetermined pressure units (e.g., 392Mpa, i.e. 4tf/cm2) can lower the degree of compression.Represented by green density.

25.What is the powder moldability?
Powder moldability is the ability to keep the powder in the molding of a predetermined shape.Available with a drum test measured compressive or flexural strength and compacts to represent.

26.What is the powder injection molding?
Be powder injection molding process is instructed has a powder characteristics, size, density and strength of compacts.

27.What types of special methods of powder injection molding?
Special powder injection molding method has the following five categories:
(1) isostatic pressing;
(2) continuously shaped;
(3) non-pressure molding;
(4) energy forming;
(5) injection molding.

28.What is the purpose of mixing powder?
By mixing powder of different properties can form a uniform powder mixture component, in order to facilitate pressing and sintering, the material to ensure a uniform product, and stable performance.

29.The time of mixing powder have any effect on the powder?
Mixed powder for powder time based on the specific requirements and equipment availability.Time is too short, uneven mix; rather long time it will produce many negative factors, such as iron, copper and other metal powder will produce work hardening but also make the particle shape and size distribution changes.

30.Pressed die-what is the purpose of each part?
The main purpose of the mold parts: the female mold which is outer surface of the molded green compacts measured ;the upper end surface of the compact is the punch forming; the lower end surface of the forming mandrel compacts which is lower punches, the green compacts formed in the measuring surface; pressure sets, measuring surface forming compacts and face.

31.What is the principle of material selection for the manufacturing of powder metallurgy mold?
Make main parts of powder metallurgy mold based on their specific usage on wear resistance of materials, process, cost and other factors, considered a reasonable choice of,Its hardness must reach HRC55 or more.Selection of carbon tool steel, alloy tool steel and tungsten carbide, hardness and strength can meet the requirements.

32.Suppression of mold parts are made of what material?
Die and mandrel carbon tool steels can be used (T10A, T12A, etc), alloy tool steel (GCr15, Cr12, 9CrSi, Cr12Mo, and Cr12W, and Cr12MoV, and CrWMn, CrW5), high-speed steel (W18Cr4V, and W9Cr4V, and W12Cr4V4Mo), hard metal (steel-bonded cemented carbide YG15 YG8); carbon tool steel punch can be used (T8A and the T10A), Alloy tool steel (GCr15, Cr12, 9CrSi, Cr12Mo, and CrWMn CrW5); pressure sleeve made of alloy tool steel (GCr15, 9CrSi, Cr12, Cr12Mo, and CrWMn CrW5).

33.How targeted selection of mold material?
Suppression of large quantities of pressure parts shall be made good wear resistance materials such as high-speed steel, carbide, etc.; suppress small quantities of pressure parts, can be inexpensive materials such as carbon tool steel.Suppression of pressure parts of complex shape,to use alloy tool steel and heat deformation processing of materials; suppress copper, lead and soft metal powder, to use carbon tool steel or alloy tool steel; suppression of tungsten, molybdenum and other hard metal powder materials, as well as carbide, friction materials, carbide materials shall be used.

34. How much the heat treatment hardness of the major powder metallurgy pressing mold?
The heat treatment hardness of the major powder metallurgy pressing mold is: a female mold, requiring steel is HRC60-63, steel bonded carbide is HRC64-72, carbide parts of HRA88-90; mandrel requirements HRC60-63 , may be appropriate to reduce the hardness of the elongated mandrel, the mandrel connection motorized local hardness HRC35-40; punch requirements HRC56-60; pressure sets requirements for the HRC53-57. Protective cover, no heat treatment; or quenching, hardness HRC28-32.

35.What is a single compact, double compacts?
Single compact refers to the same component made of powder compacts; double compacts are of two different kinds of powder compacts; is made up of two or more layers of multilayer compacts made of different components of powder compacts.

36.What are the common causes of defects when producing the powder compacts ？
1)Uneven density
The reasons are:
① all parts of the compression ratio is inconsistent;
② low finish mold, increasing the frictional resistance;
③ lack of lubrication;
④ Part unreasonable size (aspect ratio is too large, much longer than the thickness …… );
⑤ pressed the wrong way.

2)Crack
The causes are: uneven 1) density; 2) Powder poor formability, springback compacts large; 3) stripping the wrong way; 4) die poor rigidity; 5) mold has inverted taper.
3)Off the edge off angle
Reasons are: 1) powder forming poor; Low 2) green density.
4)Scratch the surface
Reasons are: 1) mold surface scratches; 2) model tumor.

37.What is Powder Metallurgy Sintering?
Sintering is one of the main processes of powder metallurgy.
The powder is usually heated to a temperature or compacts the main component of a melting point of 2/3 to 4/5, so that the occurrence of adhesion between the particles and other physical and chemical processes has become required for the process material or article.

38.What is sintering atmosphere? What is its role?
Refers to the protective atmosphere sintering powder products sintering, used to prevent oxidizing atmosphere.Sintered protective atmosphere to prevent oxidation, can also restore the surface of the oxide powder particles, the powder particles and moisture removal gas adsorbed on the surface, but also for the iron-based powder products, while ensuring that it does not decarburization nor carburization.

39.What are the commonly used protective atmosphere sintering?
Reducibility of sinter protective atmosphere for neutral gases, such as hydrogen, synthetic ammonia, carbon monoxide, nitrogen and vacuum.

40.Powder metallurgy materials which use porous characteristics?
Hole is one of the important characteristics of powder metallurgy materials. you can ues this feature as f0llows:
1).Manufacturing sweating materials.Manufacturing sweating materials. That material is impregnated with a low melting point material in the pores of ordinary powder metallurgy, work at high temperatures, melting oozing impregnated material, and the material “sweating” cooling. Such conventional materials can be used to replace the expensive heat-resistant alloys, heat-resistant parts of the further temperature increase.
2).Manufacture of filter material. Such as air filter, filtrate and filter
3).Impregnated with antifriction agents, manufacture of oil and oil-free lubrication of bearings; impregnated with spices, making sweet crafts.
4).In some cases, to replace the copper with iron, non-ferrous metals such as lead
5).Manufacturing vibration, noise reduction, insulating materials
6).Increasing the surface area of material, which acts as a carrier material (such as carrying a catalyst)