In the thermoforming process of plastic film and sheet, the product quality problems caused by polymer degradation are often encountered. Once the raw material degradation, it will generally cause mechanical properties change, such as the elasticity disappears, the strength decreases, the viscosity increases and so on. Product visual characterization such as yellowing of the product, there are black spots (coke), both ends of the product is prone to crack edge, broken edge, and some of the material will gradually accumulate in the mold cavity adhesion in the mold cavity surface, or even plug the mold cavity affect the normal production of products.
Shortening the dwell time of materials in the mold cavity reduces the risk of material degradation, and it is of innovative value for producing high quality products, prolonging production cycle and reducing cost.
Specific cases Typically, if the retention time is too long, the material is degraded to adhere to the mold cavity, especially in the hanger runner flow and two ends prone to accumulation. As shown in Figure 1: There is significant material retention and carbonization in the flow path. If the raw material at the end of the flow path is too long, the raw material characteristics change, the product edge prone to crack edge and so on. In view of the above problems in the production process, the designer must consider shortening the material retention time, in order to further improve the flow path of the flat die to optimize.
The maximum possible reduction of the material in the mold cavity dwell time, improve product quality and continuous production stability. At present, the most common extrusion flat die Runner design has two types of hanger type and branch pipe type. The following is a comparison of the simulation analysis data before and after the improvement and we share the discussion. The design of the hanger-type runner is undoubtedly the best choice when the pressure distribution of the feed flow is reduced, the dwell time is shortened and the uniform velocity data is obtained.
But not all die hanger style runner design is the best design, due to the hanger-type runner design intermediate runner and the two ends of the flow channel at a certain angle design (as shown in Figure 2). For the wide width of the die, the mold body width l need to be very wide to meet the layout of the runner design, and secondly, because the middle runner is closer to the feed mouth end face, from the rack shunt start to the die lip outlet this distance becomes very long, the middle position of the mold tightening screw arrangement compared to L0 very short, L1 very long, The mold body under the action of extrusion pressure will occur the mold deformation, the entire cavity due to deformation of its flow path parameters have undergone a great change, the final result is the uniformity of the flow, pressure and so on completely inconsistent with the design parameters.
So is there a more reasonable runner design that can meet the wide extrusion flat die body strength design problem can effectively shorten the material dwell time?
For this reason, we have done a lot of simulation analysis and data comparison analysis, and obtained some results, an improved optimization of the branch pipe runner design has a surprising performance.
Optimized Solutions
The following is the effective output width of 3500mm cast film Die as an example, the simulation of the production of raw materials CPE, extrusion volume 1500kg/h do simulation analysis, on the previous standard branch pipe runner design and improve the optimization of the branch pipe runner design analysis and comparison. The early branch pipe flow channel can be designed to achieve reasonable extrusion pressure and uniform flow rate, the disadvantage is that the raw material at the end of the flow channel longer stay, not conducive to long-term production, the end of the product of the probability of defects.
Optimization of the pipe runner design can be pleasantly surprised to find that all design parameters tend to be more reasonable. The improved dwell time of the tube-type runner material has been shortened from the original design to 193 seconds to the present 39 seconds, and the product defects caused by material retention have been further solved. The innovation priority put forward in the final analysis is to focus on the actual needs of customers, but also has been exploring plastic film, plate extrusion processing defects caused by the causes and related solutions.
For continuous long-term stable production to provide the best customized design solutions for the end user to reduce production costs to create value.