日本語 
English 
Español 
हिन्दी 
العربية 
Português do Brasil 
Русский 
Deutsch 
한국어 
Français 
Türkçe 
Polski 
Tiếng Việt 
Italiano 
简体中文 Cemented carbide rod bars often face challenges such as deformation, cracking, and uneven carbon content during binder removal (debinding). Current debinding methods mainly include thermal debinding, solvent debinding, siphon debinding, and catalytic debinding, among which thermal debinding and solvent debinding are the most widely used in industrial production. Simple thermal debinding has inherent drawbacks: slow debinding rate, easy deformation of cemented carbide rod bars due to uneven thermal stress, difficulty in controlling carbon content, and high energy consumption.
In contrast, solvent pre-debinding before thermal debinding can quickly remove soluble components in the binder, significantly improving debinding efficiency and reducing deformation risks. However, solvent debinding itself has a critical problem: cemented carbide bars are prone to cracking during the process, which sharply reduces product yield.
Previous studies have indicated that residual internal stress in extruded cemented carbide bars is the main cause of cracking, and introducing an annealing step before solvent debinding can effectively relieve this stress. Based on this, this research focuses on the binder system design for extrusion-molded cemented carbide rod bars and the optimization of solvent debinding technology, aiming to develop a high-performance binder and a crack-free debinding process, thereby providing technical support for the high-quality production of cemented carbide bars.
Preparation of Extruded Cemented Carbide Bars
Binder Selection
The binder for cemented carbide bars consists of a plasticizing component, a binding component, and an activating component, with mass fractions designed as follows: plasticizing component (solid paraffin wax (SPW) + liquid paraffin wax (LPW)): 60%–80%; binding component (high-density polyethylene (HD-PE) + ethylene-vinyl acetate copolymer (EVA)): 10%–30%; activating component (stearic acid (SA)): 5%–10%.
This three-component system is tailored to the extrusion forming requirements of cemented carbide rod bars, balancing formability and debinding efficiency—ensuring the green bar has sufficient plasticity during extrusion to avoid extrusion defects, while enabling rapid removal of soluble components in subsequent solvent debinding.
Preparation of Extrusion Feed and Cemented Carbide Bars
WC powder with an average particle size of 0.6–0.8 μm (with a certain proportion of VC and Cr₃C₂ added as grain growth inhibitors) and Co powder with an average particle size of 0.9 μm were used as raw materials. After wet milling to achieve uniform mixing, a WC-10% Co cemented carbide mixture was obtained.
The mixture was then dried, and the pre-prepared extrusion plasticizer was added; after thorough mixing and kneading, an extrusion feed with a powder loading (volume fraction) of approximately 50% was prepared. The feed was extruded in a plunger extruder to form Φ10 mm cemented carbide bars, which were cut into 100 mm-long samples for subsequent experiments. Strict control of mixing time (optimized to 10 h) and extrusion parameters ensures uniform distribution of the binder in the cemented carbide rod bar, minimizing initial defects such as binder segregation.
Selection of Solvent Debinding Process for Cemented Carbide Bars
Debinding Experiments
Cemented carbide rod bar samples were weighed using an electronic balance, placed on a V-groove graphite plate, and immersed in n-heptane (the selected solvent for debinding). The solvent temperature was controlled at 30 ℃ using a constant-temperature water bath to ensure stable debinding conditions. After debinding for a specific duration, the samples were dried naturally and weighed again to calculate the debinding rate (Debinding rate = Absolute weight loss of bars after debinding / Weight of binder in bars before debinding). The variation of debinding rate with debinding time and the morphology of cemented carbide bars after debinding are shown in Table 1. The morphology of cracked and collapsed cemented carbide bars after excessive debinding is presented in Figure 1.
Selection of Debinding Process
For the three-component binder system of cemented carbide bars, paraffin wax (SPW + LPW) as the plasticizing component accounts for the majority of the binder and is highly soluble in n-heptane, while the binding component (HD-PE + EVA) and activating component (SA) have poor solubility. Experimental results show that immersing cemented carbide rod bars in n-heptane for 6–12 h can remove 60%–80% of the plasticizing component, achieving the goal of pre-debinding and laying a foundation for subsequent thermal debinding.
With debinding time exceeding 12 h, although the debinding rate can be further increased (reaching 63.7% at 24 h), the probability of cracking in cemented carbide bars rises sharply from 35% to 60%, and some samples even collapse. Analysis indicates that retaining a small amount of plasticizing component can maintain the structural strength of cemented carbide bars, preventing crack initiation and propagation during debinding. Therefore, the optimal solvent debinding time for cemented carbide rod bars is determined to be 6–12 h.
Analysis and Countermeasures for Cracking of Cemented Carbide Bars
Analysis of Cracking Causes
Cracking of cemented carbide rod bars during solvent debinding is a result of multiple factors, including binder segregation, inappropriate debinding temperature, unreasonable liquid-solid mass ratio between solvent and bars, and residual internal stress. Among these, binder segregation and residual internal stress are the most critical factors.
Studies have confirmed that it is difficult to achieve absolute uniformity in the mixing of extrusion feed for cemented carbide bars. Local variations in binder content (binder segregation) are inevitable. During solvent debinding, the rapid removal of soluble paraffin wax in segregated regions leads to the formation of large pores, which become potential crack sources. The morphology of binder segregation on the fracture surface of cemented carbide bars, observed by scanning electron microscopy, is shown in Figure 2.
Residual internal stress in cemented carbide rod bars is the fundamental driver of crack propagation. During extrusion, the feed undergoes significant shear and tensile deformation: a longitudinal velocity gradient is formed along the extrusion direction, and polymer molecules in the binder are stretched longitudinally and compressed transversely, resulting in elastic deformation and orientation of molecular chains. Paraffin wax, as the main plasticizing component, has a high condensation shrinkage rate.
After extrusion, cemented carbide bars cool rapidly, and the rapid shrinkage of paraffin wax “freezes” the oriented polymer chains in a constrained state, storing a large amount of elastic energy inside the rod bar as residual internal stress. During solvent debinding, the removal of paraffin wax increases the free volume of polymer chains, triggering the release of residual internal stress. This stress acts on the pre-existing pore defects (crack sources) formed by binder segregation, leading to crack propagation and even complete collapse of cemented carbide bars.
Countermeasures to Eliminate Cracking
To solve the cracking problem of cemented carbide rod bars during solvent debinding, two approaches were tested: improving binder uniformity through optimized mixing and relieving residual internal stress through post-extrusion treatment.
Optimizing the mixing process: Experiments show that the optimal mixing time for the extrusion feed is 10 h. Prolonging mixing beyond 10 h reduces the flowability of the feed, making extrusion difficult, while insufficient mixing exacerbates binder segregation. However, even with optimized mixing, complete elimination of binder segregation in cemented carbide bars is impossible. Therefore, relieving residual internal stress is a more effective and reliable countermeasure.
Two post-extrusion stress relief methods were compared:
- Natural aging: Extruded cemented carbide rod bars were placed indoors at room temperature for 30–45 days to allow gradual relaxation of polymer molecular chains and release of residual stress.
- Annealing treatment: Extruded cemented carbide bars were placed in an oven, heated to 70 ℃, held for 10 h, and then furnace-cooled to room temperature. This process accelerates the relaxation of molecular chains and efficiently relieves residual stress.
The morphology of cemented carbide bars after solvent debinding (6–12 h) under different stress relief methods is shown in Table 2. The results indicate that both methods can effectively prevent cracking, but annealing treatment is far more efficient than natural aging (10 h vs. 30–45 days), making it more suitable for industrial production. Thus, annealing at 70 ℃ for 10 h is determined as the optimal stress relief process for cemented carbide bars.
Effect of Pre-Debinding and Product Quality of Cemented Carbide Rods
Effect of Binder Pre-Debinding for Cemented Carbide Bars
The fracture morphology of cemented carbide rod bars before and after the combined pre-debinding process (annealing + 6–12 h solvent debinding) was observed by scanning electron microscopy. The results (Figure 3) show that after pre-debinding, most of the soluble paraffin wax in the binder is removed, and a network of interconnected debinding channels is formed in the bar. These channels not only facilitate the rapid escape of residual binder during subsequent thermal debinding but also reduce internal stress accumulation, laying a foundation for the preparation of high-quality sintered products.
Quality of Cemented Carbide Rod Products
Cemented carbide bars after pre-debinding were subjected to thermal debinding, vacuum sintering, and low-pressure sintering to obtain finished WC-10% Co cemented carbide rods. Standard Type A flexural specimens (numbered 1–4) were prepared by wire cutting and grinding, and their physical and mechanical properties were tested. The test results are shown in Table 3, and the metallographic structure of the finished rods is shown in Figure 4.
The results indicate that the finished cemented 炭化物 rods, derived from high-quality cemented carbide bars, have a uniform and fine microstructure with no obvious defects such as cracks, pores, or large grain growth. The hardness and transverse rupture strength of the samples reach high levels, meeting the performance requirements for ultrafine cemented carbide rods. This confirms that the optimized binder system and pre-debinding process (annealing + solvent debinding) can effectively ensure the quality of cemented carbide bars and the final product.
Conclusions
- Cemented 超硬ロッド bars are the key intermediate in extrusion molding of cemented carbide products, and binder removal is a critical link determining the quality of bars. Solvent pre-debinding combined with thermal debinding is an efficient and reliable binder removal method for cemented carbide bars.
- The optimal solvent debinding time for the three-component binder system (SPW + LPW + HD-PE + EVA + SA) is 6–12 h, which balances debinding efficiency and structural integrity of cemented carbide bars.
- Annealing treatment at 70 ℃ for 10 h before solvent debinding can effectively relieve residual internal stress in extruded cemented carbide bars, reducing the cracking probability during solvent debinding to nearly zero.
- The combined pre-debinding process of annealing and solvent debinding achieves efficient removal of soluble binder components in cemented carbide rod bars, forms interconnected debinding channels, and ensures the final cemented carbide rods have excellent microstructure and mechanical properties.
