An Overview on the Properties and Testing of Metal Powders
The main purpose of powder testing is to ensure that the powder is suitable for subsequent processing. The basic properties or characteristics of powder are chemical composition and purity, particle size and its distribution, particle shape, particle porosity and particle microstructure. The secondary properties or characteristics are specific surface, apparent density, tap density, flow rate, compacting characteristic and sintering characteristic. The important secondary properties such as apparent density and flow rate are most widely used in specification and control routine. Below is an overview on the properties and testing of metal powders.
Basic Characteristics of Metal Powders
Chemical composition
The chemical composition of powders is the outstanding characteristic. It usually reveals the type and percentage of impurity and determines the particle hardness and compressibility. The term impurity refers to some elements or compounds which has an undesirable effect. Impurities influence not only the mechanical properties of the powder compacts, but also their chemical – electrical and magnetic properties. It may also exert a decisive effect on pressing, sintering and other post – sintering operation which are essential for the production of finished product from powders.
The chemical composition of a powder is determined by the well established standard techniques of chemical analysis. Oxygen content is determined either by wet analysis or by loss of weight in hydrogen. Some oxides may not be reduced at all or there may be error due to incomplete reduction of oxides, therefore it is desirable for both processing and optimum properties of the final product to have a low oxygen content.
Particle size
The particle size has a great important in properties and testing because it affects most of the properties such as mould strength, density of compact, porosity, expulsion of trapped (occluded) gases, dimensional stability, agglomeration and flow and mixing characteristics. Particle size is expressed by the diameter for spherical shaped particles and by the average diameter for non – spherical particles. Average employed is defined in different ways according to the method employed for size distribution. When the method involves sizing, the particle size is measured as the opening of a slandered screen which just retains or passes the particle. When determined by micro count method, the diameter is measured by averaging several dimensions.
According to the sedimentation method the particle size is defined as the diameter of the spherical particle having the same specific gravity and setting velocity as the non – spherical particle under test. The average diameter in the case of large particle sizes can be determined by counting and weighing at the cube root of the volume.
Practical properties and testing metal powders are divided into three distinct classes – the sieve, sub sieve and sub – micron or ultrafine. The screen with the opening of finest standard mesh – sieve for production purposes is the 325 mesh screen having the aperture of 44 micron.
Metal powders has a lot of advantages that make it suitable for a lot of metal forming applications. If you want to learn more about its properties and testing, contact us now at PM Distributors so that we can readily provide you with more information about this process.
Powder metallurgy is a process where fine powdered materials are pressed into a desired shape or form and then heated or sintered in a controlled atmosphere to form the final product. To date, numerous alternative processes have been deployed under powder metallurgy. One of them is the powder injection moulding process.
What is the origin of powder injection moulding?
The powder injection moulding process is usually recommended for the high-volume production of shaped components out of powder metal. This specific process shares some similarities with polymer injection moulding since they use the same technology. Powder injection moulding is also a by-product of batch sintering processes that are frequently applied in powder metallurgy and ceramic processing.
How does powder injection moulding work?
Powder injection moulding starts with the fusion of polymeric binders with metal or ceramic powders. This specific mixture is heated in a screw-fed barrel and then forced under pressure in a die cavity. The placement of this mixture in a die cavity allows it to cool before ejecting it. Afterward, the polymer will be removed. The sintering of the component to the required density then follows.
The outcome of the debinding stage can directly influence the mechanical properties of the sintered component. Polymer binders, which comprises around 35 to 50 volume percent of the sintered component, must be removed during this stage. If the removal is inconsistent and unsuccessful, then your sintered component may contain swelling, surface blistering, or formation of large pores.
One way to effectively remove polymer is through the multi-component binder system. This system can reduce the percentage of polymers by either removing them with solvents or degrading them at different points of a thermal debinding cycle.
Components shrink during the polymer removal process, but they can still retain the shape of the mould. Nonetheless, your final sintered component can still be made to near-net shape. With powder injection moulding, you can achieve tolerances of 0.2 to 0.3 percent of nominal dimensions and average surface roughness of 15 to 30 micrometres.
What are the benefits of powder injection moulding?
Powder injection moulding is utilised by different industries because of numerous reasons. One, this process can effectively manufacture high-volume complex parts. Another reason is that the production time is significantly reduced compared to casting. Material waste is also minimised with this kind of powder metallurgy process. Powder injection moulding can also readily accommodate a wide range of pre-alloys and master alloys.
Where can powder injection moulding be applied to?
As mentioned, powder injection moulding is suitable for high-volume production of powder metal components. This moulding process can be utilised in making small components. Some applications of powder injection moulding include medical, dental, electronic, firearms, aerospace, jewellery, watchmaking, and automotive sectors. Some examples of products out of this process include silicon carbine turbochargers and radial rotors for heat engines, alumina thread guides, and stainless steel gear wheels for electric toothbrushes.
The popularity of powder injection moulding is increasing because of its effectiveness in producing a huge number of small intricate metal parts. If you want to know more about it, you are free to contact us at PM Distributors Pty Ltd.