Custom Tungsten Spheres/Tungsten Ball Manufacturers

Industry Knowledge

How to control porosity and density during sintering of tungsten balls

In the production process of high-performance tungsten balls, the sintering process is the key link to determine its final physical properties and application adaptability. Porosity and density are two core parameters for evaluating the sintering quality of tungsten balls, which directly affect its density, mechanical strength, wear resistance and thermal conductivity.
The concept and importance of porosity and density
Porosity refers to the proportion of residual voids in the material after sintering in the total volume; density refers to the percentage of the solid part of the material in the total volume. For tungsten balls, which have extremely high requirements for density and strength, the control of porosity often represents the overall quality of the product. Excessive porosity will lead to:
Reducing the actual density of tungsten balls, which is not conducive to their use in inertial components;
Weakening mechanical properties, which can easily cause material breakage or wear;
Reducing thermal and electrical conductivity, affecting its performance in electrical contact situations.
Therefore, achieving high-densification sintering technology close to the theoretical density (the theoretical density of W is 19.3 g/cm³) is one of the core problems in the manufacture of tungsten balls.
Key factors affecting porosity and density
1. Control of raw material powder
The first step in sintering tungsten balls is to select tungsten powder with high purity and reasonable particle size distribution. Nantong Rongxin Electrical Control Technology Co., Ltd. uses advanced spectrometers and particle distribution instruments to strictly control the quality of tungsten powder during the raw material screening stage to ensure that the powder has good fluidity and sintering activity.
The narrower the particle size distribution, the higher the filling density between the powders, which is conducive to improving the density of the initial compact;
The higher the powder purity, the less interference the impurity elements have on the sintering reaction, and the better the sintering densification effect.
2. Molding pressure and compact density
The compact density before sintering determines the initial distribution of pores. Nantong Rongxin uses automatic static pressing or isostatic pressing molding technology to improve the consistency and density of the compact by reasonably setting the pressure (generally between 150 and 300 MPa).
The higher the molding pressure, the smaller the initial pores and the more uniform the shrinkage during sintering;
Improper molding may cause cracks or internal cavities, which ultimately affect the density.
3. Sintering temperature and atmosphere control
The sintering temperature of tungsten balls is usually set at around 2700℃. In this process, the design of the temperature curve and the atmosphere control are crucial to the sintering effect. Relying on years of technical accumulation, Nantong Rongxin uses vacuum sintering or hydrogen protection sintering furnaces to ensure:
The pores are closed and diffused out at high temperatures;
Reducing the probability of tungsten reacting with impurity gases such as oxygen and nitrogen;
Controlling the sintering shrinkage rate to prevent warping or deformation.
In addition, the company introduced an advanced temperature control system to achieve automatic and fine control of temperature changes, effectively improving the degree of densification and product consistency.
4. Use of sintering additives
In some applications, trace sintering aids such as nickel, copper, iron, etc. can be added to promote sintering activity. Nantong Rongxin controls the proportion of additives in special tungsten alloy balls (such as W-Ni-Fe) to achieve higher densification without reducing the strength of the material.
Testing methods and quality verification
In order to ensure the density and low porosity of each batch of tungsten balls, Nantong Rongxin is equipped with a complete set of advanced testing equipment including ultrasonic flaw detectors, metallographic analyzers, density measurement systems and tensile testing machines.
The Archimedes method is used to measure the density of the sintered body and compare it with the theoretical density;
The pore structure and distribution state are observed through metallographic sections;
Use ultrasonic waves to detect internal defects and voids;
Tensile and compression tests verify its stability under stress.

What defects are prone to occur in the processing of tungsten balls? How to detect and avoid them?

The main defects that are prone to occur in the processing of tungsten balls
Porosity and inclusions
During the sintering and molding process of tungsten balls, if the powder purity is not high or the molding pressure is insufficient, it is easy to form unclosed pores or internal inclusions. These pores not only reduce the density of the material, but also become stress concentration points, reducing the mechanical strength of the sphere.
Cracks and fractures
Due to the hardness and brittleness of tungsten materials, the concentration of mechanical stress or thermal stress during processing often leads to micro cracks. Especially during cold processing or grinding, if the operation is improper, the cracks will expand rapidly and eventually lead to fracture.
Surface defects
The surface of the tungsten ball may have scratches, pits, sintering scars and other defects, which not only affect the appearance, but also cause local stress concentration, reduce wear resistance and fatigue life.
Deformation and dimensional deviation
Temperature fluctuations and uneven stress release during processing may cause deformation of the tungsten ball. Especially in high-precision applications, dimensional deviation will directly affect assembly and functional performance.
Impurity penetration and surface oxidation
Tungsten balls are prone to oxidation during high-temperature sintering or heat treatment, if the atmosphere is not strictly controlled, forming an oxide layer or oxide inclusions, reducing electrical conductivity and corrosion resistance.
Defect detection technology
Nantong Rongxin knows that the key to high-quality tungsten balls lies in the early detection and accurate evaluation of defects, so it is equipped with a variety of advanced detection equipment:
Ultrasonic flaw detector: Use ultrasonic waves to perform non-destructive testing on the inside of tungsten balls, which can effectively detect internal pores, cracks and inclusions to ensure the internal quality of the product.
Metallographic microscope analysis: Through metallographic analysis of sliced ​​samples, the organizational structure and pore distribution of the material are observed in detail to evaluate the density and defects.
Spectrum analyzer: Used to detect the chemical composition of raw materials and finished products to prevent impurity content from exceeding the standard.
Surface roughness meter and three-coordinate measuring machine: Detect surface defects and dimensional accuracy to ensure that the surface quality and processing tolerance of tungsten balls meet the design requirements.
Tensile and hardness tester: Evaluate the mechanical properties of materials and indirectly reflect the impact of defects in the processing process on performance.
Defect avoidance strategy and process optimization
As a leading tungsten and molybdenum material company with a 40-year history and more than 120 professional employees, Nantong Rongxin Electrical Control Technology Co., Ltd. has formed a mature system for defect control:
Strict material selection and powder processing
The company uses high-purity tungsten powder and uses advanced powder pretreatment technology to remove impurities and optimize particle size distribution, laying the foundation for subsequent densification sintering.
Precise molding process control
The uniformity and density of the pressed green sheet are improved through automatic isostatic pressing technology to avoid pores and cracks caused by uneven density of the pressed green sheet. At the same time, the molding pressure and speed are precisely controlled to reduce the accumulation of mechanical stress.
High-temperature sintering atmosphere and temperature control
Nantong Rongxin uses vacuum or hydrogen to protect the sintering furnace and strictly controls the sintering atmosphere to prevent oxidation and impurity infiltration. Through precise temperature curve design, cracks or deformation caused by thermal stress are avoided.
Multiple processing procedures and surface treatment
Subsequent processes such as grinding and polishing use high-precision equipment and optimized parameters to minimize surface scratches and thermal damage. At the same time, the company implements strict quality inspections between processes to eliminate abnormal products in a timely manner.
Full-process quality management system
Nantong Rongxin has established a closed-loop quality management system from raw material procurement to finished product delivery, combining advanced testing equipment and information management to achieve early detection and early rectification of defects and ensure stable product quality.