In the process of blow molding extrusion, sagging of parisons due to their own weight is a critical issue that affects the uniformity of wall thickness.
This article delves into the reasons behind parison sagging during the extrusion process and explores how controlling sagging can lead to the achievement of uniform wall thickness.
We will also focus on key factors such as parison weight, extrusion time, and melt viscosity, while introducing how advanced blow molding extrusion machines can be utilized to optimize the production process.
1. Causes of Parison Sagging
Parison sagging is caused by the gravitational force acting on the parison itself, and the severity of sagging directly impacts the uniformity of the final product's wall thickness. In the blow molding extrusion process, parisons are prone to sagging, especially for larger-sized parisons.
2. Analysis of Key Factors
Several factors influence parison sagging during extrusion, subsequently affecting wall thickness uniformity.
2.1 Parison Weight
Parison weight is a crucial factor in determining the degree of sagging. Heavier parisons are more susceptible to the effects of gravity, so designing parisons requires a careful balance between weight and structure to minimize the likelihood of sagging.
2.2 Extrusion Time
Extrusion time directly influences the time parisons spend at the extrusion orifice. Excessively long extrusion times increase the chances of sagging, necessitating precise control of extrusion time to ensure an appropriate dwell time for the parisons at the extrusion orifice.
2.3 Melt Viscosity
Melt viscosity also plays a significant role in parison sagging. Higher viscosity melts result in longer dwell times at the extrusion orifice, elevating the risk of sagging. By controlling melt temperature and incorporating suitable flow enhancers, it's possible to adjust melt viscosity and reduce the likelihood of sagging.
3. Solutions for Optimizing Parison Sagging
To optimize parison sagging and enhance wall thickness uniformity, the following measures can be implemented:
Choosing blow molding extrusion machines equipped with advanced control systems and precise extrusion technologies allows better control of extrusion time and melt viscosity, thereby minimizing the risk of parison sagging.
3.2 Optimize Parison Design
By optimizing the structure and reducing the weight of parisons through tools like CAD, stability during the extrusion process can be ensured, lowering the probability of sagging.
3.3 Control Melt Temperature and Add Flow Enhancers
Adjusting melt temperature and incorporating flow enhancers in a judicious manner can modulate melt viscosity, reducing the probability of sagging while ensuring process stability during extrusion.
Strictly controlling parison sagging is crucial for improving the wall thickness uniformity of products produced through blow molding extrusion. Leveraging advanced technology and thoughtful design in the production process is key to achieving high-quality products. By adopting a comprehensive approach, including optimizing parison design, selecting appropriate extrusion machines, and controlling melt properties, it is possible to effectively minimize the impact of sagging on wall thickness uniformity, thereby enhancing production efficiency and product quality.
As a professional blow molding machine manufacturer, Yankang has always been committed to the development and production of large hollow blow molding equipment.
