1. Liquid - Working Time
The working time, also known as the pot life or active time, is a critical phase in the curing process of epoxy resins. Once the resin and hardener are mixed, the compound remains in a liquid state, allowing for proper application, positioning, and adjustment. It's essential to complete all assembly and alignment tasks during this period to ensure strong and reliable bonding. If you wait too long, the mixture will start to thicken and become less workable.
2. Gel - Curing Begins
As the curing process progresses, the mixture enters the gel stage, where it starts to solidify and lose its fluidity. At this point, the epoxy no longer flows and begins to "set" into a soft, rubber-like consistency. You can press it slightly with your thumb, but it’s not yet fully hardened. This is a crucial moment because while the material is still partially cured, it can still chemically react with new epoxy, making it possible to bond to the surface. However, the ability to integrate with fresh epoxy decreases over time.
3. Solid - Final Curing
Once the epoxy reaches the solid stage, it becomes firm and can be sanded, shaped, or machined. At this point, the material has achieved about 90% of its final strength, so it's safe to remove any clamps or fixtures. However, the surface is now too cured to allow for chemical bonding without proper preparation. To achieve good adhesion, the surface should be sanded or otherwise treated to improve mechanical interlocking.
Second, Polyisocyanate Curing Agents
Polyisocyanate-based curing agents are widely used in various applications such as paints, foams, and coatings. Hybrid polyisocyanate curing agents are especially popular in two-component polyurethane systems, which have become the standard in many industries, including automotive refinishing, industrial coatings, wood finishes, and plastic coatings. These materials offer excellent performance and durability, making them ideal for high-demand environments.
Blocked water-dispersible polyisocyanates are also gaining popularity because they can be combined with melamine-based curing agents to reduce costs while maintaining quality. These types of curing agents help improve overall performance, especially in terms of flexibility, adhesion, and environmental friendliness.
Looking ahead, the development of curing agents is moving toward more advanced, multi-functional, and eco-friendly options. Future trends include flame-retardant, toughened, latent, energy-saving, and low-VOC (volatile organic compound) formulations. With increasing environmental awareness, there is a growing demand for sustainable solutions that minimize harmful emissions. Hybrid polyisocyanate curing agents are well-positioned to meet these needs due to their versatility and broad range of applications.
Venous cannula is also a deep venous puncture catheter. The method is to select the appropriate puncture site and insert the needle under the skin, and insert the needle with negative pressure until the dark red blood is absorbed, indicating that the needle has entered the vein, and the guide wire is inserted. Withdraw the puncture needle to leave the guide wire in the blood vessel, and then insert the venous catheter that needs to be indwelled along the guide wire, then exit the guide wire, inject diluted heparin saline and fix the catheter, the deep venous catheterization is completed. The veins for puncture and catheterization are usually selected clinically, including the subclavian vein, internal jugular vein, and femoral vein. After the puncture catheter is indwelled, attention must be paid to the care of the puncture site to avoid infection with thrombus or catheter falling off.
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