The temperature setting of the injection molding machine cylinder has a significant impact on the entire plastics processing process. What is it and what are its advantages? How to choose the right temperature? What is a thermoanalytical test? In the following article you will find answers to these questions. We invite you to read more!

Influence of processing temperature on the injection process

Analyzing the processing of thermoplastics, it should be noted that one of the key elements in the production of plastic parts is the supply of energy to the polymer mass in order to plasticize it , and then the collection of this energy in the cooling step of the injection cycle. The influence of temperature on the injection process is therefore huge. Thanks to it, we are able to effectively produce details by changing the state of aggregation of the material, the viscosity of the melt and the processing parameters of the material.

The correct temperature setting of the injection molding machine and other processing devices involved in the injection process ensures stable, repeatable production. Selection of the appropriate temperature of the melt mass by setting the temperature of the plasticizer cylinder will ensure better surface quality of the manufactured detail , proper orientation of the fillers (isotropy of fibrous fillers) or a higher proportion of the crystalline phase during the processing of crystalline materials.

It is also worth paying attention to the influence of the processing temperature of the sockets and mold halves during stable, automatic processing work – to ensure the appropriate flow path of the material and reduce the internal stresses of the detail. Problems with heat accumulation inside mold cavities can lead to geometric deformations of the detail after molding – distortion of the molding.

 

Selection of the processing temperature

Plastics used in the industry for the production of details are usually called composite materials consisting of a polymer matrix – acting as a material base for a given material and many fillers that give the composite material special properties.

The basic tool when setting the processing temperature for a given material is the technical data sheet (Technical Data Sheet – TDS) provided by the manufacturer. It defines the range of process temperatures, recommended tool temperatures, processing method, material properties such as tensile strength, shear strength, processing shrinkage percentage, additional material properties such as resistance to UV radiation or non-flammable properties. The TDS card describes the given plastic based on laboratory tests.

Thermoanalytical research

The material’s technical data sheet usually specifies processing temperature ranges , but within these ranges the plastic may have completely different process properties during processing. Batches of the same raw material, depending on the method of preparation, production, production plant or technological parameters, may also have different processing properties.

In order to prevent production shortages due to differences in plastic viscosity resulting from problems with processing temperature or changes in process parameters related to a new batch of plastic, tests of material flow rate indicators should be carried out periodically. They are performed using a load plastometer. The methodology of testing the flow coefficient of the material is described in standards such as PN-EN ISO 1133 or ASTM D1236. MFR/MFI (mass flow rate) and MVR (volume flow rate) are the main factors that ensure the same process properties in terms of fluidity and viscosity of the material at a given temperature.

Lynx. 1. Diagram of the plastometer

m [kg] T [stC] sample no MFR [g/10min] MFR avg. [g/10min] MVR [g/10min] MVR avg. [g/10min]
10 270 1 5,39 5,80 4,60 4,96
2 5,47 4,69
3 5,50 4,71
4 5,71 4,89
5 6,93 5,90
10 280 1 8,67 10,07 7,45 8,66
2 9,82 8,49
3 10,45 9,01
4 10,49 9,03
5 10,94 9,33
10 290 1 12,48 14,67 10,84 12,59
2 13,67 11,83
3 14,62 12,57
4 14,87 12,75
5 17,71 14,96
10 300 1 19,01 21,67 16,55 18,82
2 19,96 17,40
3 21,76 18,89
4 22,63 19,56
5 24,99 21,68

Lynx. 2. Influence of temperature change on flow coefficients (own research)

A complete thermoanalytical study of a given plastic is an analysis using a differential calorimeter . The differential scanning calorimetry (DSC) test consists in thermal analysis of the heat flux supplied to the two chambers of the device – the measuring chamber, in which the material sample is located, and the reference (reference) chamber. In this way, it is possible to observe temperature changes (absorption or release of heat) by the measuring sample as a result of a phase change or a chemical reaction. Using this method, for the analysis of polymers, we can precisely determine the glass transition temperature , the phase transition points of the material, the moment of transition of the alloy from solid to liquid state and the temperature of material degradation. The results of the DSC test will allow you to determine the processing temperatures of a given material.

Advantages of choosing the right processing temperature for a given process

Appropriate temperature setting of the injection molding machine ensures low lack of the process due to its stabilization. The amount of mechanical energy needed to plasticize the mass is reduced , because the material is less frequently worn on the walls of the cylinder and the screw. It affects the physical properties of the part after production. The temperature of the melt is also directly related to the mass pressure and the coefficients of friction between the material and the steel walls of the tool during injection. An increase in cylinder temperature causes a decrease in melt viscosity , which translates into higher melt flow rates and lower process pressures. In this way, you can try to reduce the visibility of the joining line on the detail surface by changing, among other things, the fill speed parameters.

An increase in the temperature of the mold cavity will affect the path and nature of the material flow, significantly improving the isotropy (unidirectional arrangement) of the material’s fibrous fillers. By increasing the mold temperature, the visual quality of the surface of the details can be improved . In addition, by allowing crystalline details to cool for a longer time at higher temperatures, a greater proportion of the crystalline phase can be obtained – which will directly translate into the mechanical properties of the product.

An increase in the processing temperature significantly affects the electricity consumption of the cylinder heating system and peripheral devices (such as water thermostats). Too high a temperature may cause detail defects in the form of sprues or burns resulting from the degradation of the material. Increased mass and mold temperatures will result in a longer solidification time of the material in the inlet gates of the tool sockets, which will result in a longer clamping time and a higher weight of the detail. Increasing the temperature in order to increase the injection speed may lead to the appearance of air cavities invisible on the surface of details or the formation of a dangerous diesel effect. An increased proportion of the crystalline phase of crystalline materials may result in increased processing shrinkage.

Summary

Setting the optimal processing temperatures in the injection process is an essential element in every company focused on the production of plastic details. It is also worth taking care of the devices used during industrial works, the malfunction of which may affect the lack of production and contribute to undesirable costs. For this purpose, it is necessary to periodically service and repair injection molding machines and parts for injection molding machines . Ensuring appropriate water temperatures and properly selected peripheral devices will allow for effective and efficient operation of these machines. Thanks to this, we will have control over not only the processing temperature, but also the entire injection molding process.