Paraffin molding machines typically operate in two modes: "gap-type" pelletizing and "contact-type" pelletizing. Understanding the advantages and disadvantages of these modes, as well as the causes of wear, can help optimize equipment lifespan and pellet quality.
1. Overview of Pelletizing Modes
Gap-Type Pelletizing: In this mode, the cutter maintains a fixed gap from the template. This method is simple to operate, causes minimal wear on the cutter and template, and has a longer service life. However, the pellets produced are irregular in shape, with more debris and noticeable tailing.
Contact-Type Pelletizing: In this mode, the cutter is always in contact with the template. The pellets produced have a neat appearance, with less debris and no tailing. However, this method causes faster wear on the cutter and template, leading to a shorter service life.
2. Causes of Wear on Templates and Cutters
Regardless of the pelletizing method used, both the template and cutter will experience wear. The pelletizer essentially functions as a pair of scissors: the discharge hole in the molding template forms a fixed blade, while the pelletizing knife acts as the moving blade. When the melt passes through the molding belt's discharge hole, it rapidly solidifies due to exposure to cooling water at 50°C to 60°C, and the material is sheared into pellets by the fixed blade. During the cutting process, the pelletizing knife encounters several sources of wear:
Friction Between Blade and Template: Friction occurs primarily during the run-in period of a new knife and template. Proper run-in ensures the blade edge and template are in ideal contact without causing damage.
Abnormal Wear: If the knife is not properly sharpened after being replaced, at least 85% of the blade edge will become conformed to the template shape before grinding out. This can lead to increased tailing and, if the knife is forced, the blade's front end will tilt up, widening the gap between the molding belt and the template, increasing tailing, and intensifying wear. In severe cases, the knife may become entangled, preventing normal operation.
3. Factors Contributing to Increased Wear on Cutting Tools
Over time, the die opening may expand and deform due to alternating heating and cooling, causing the die edges to become dull or damaged. Additionally, the cutter operates under complex conditions in the water chamber, experiencing various forces:
Forward Thrust: Includes feed pressure from hydraulic cylinder oil pressure (20-60 bar), which can be preset via the fully automatic paraffin molding machine control system or a potentiometer on the local operation panel; spiral thrust generated by rotation in hot water; and pressure from thermal expansion and contraction of the cutter shaft, which is temperature-dependent.
Reverse Forces: Includes the spring's elastic force (a constant set at the factory to retract the cutter when stopped); the pressure of hot water pushing back on the cutter; friction-induced backward force; and resin backward pressure, which is proportional to production load. Additionally, it includes molding machine force set by the operator, liquid power of cutting water on the blade when rotating in water, and the reaction force from the blade on the template surface. These forces increase shear rate and stress at the die opening, leading to suboptimal cutting. Material chips generated during cutting can accumulate as nodules at the die opening, repeatedly sticking and falling off. Furthermore, cutting water can cause cavitation at the cutting edge, exacerbating wear on the template pelletizing belt surface and the cutter.
Conclusion
The wear of templates and cutters in paraffin molding machines is complex, involving various factors related to cutting mode, operating conditions, and prolonged use. Understanding these wear causes and implementing appropriate optimization measures can effectively extend equipment lifespan and improve production efficiency.
For more information on how to optimize the use and maintenance of paraffin molding machines, contact us today. We provide professional solutions and technical support to enhance your production capacity, reduce equipment wear, and achieve optimal production results!
