As you know, getting a quality product at a plastic injection largely depends on the temperature of the forming mold. However, There is a misconception that the colder walls of the forming tool, the shorter molding cycle and as a result – higher performance injection molding machine …

In this and subsequent articles, I will try to bring some clarity to the issue of temperature modes of injection molding equipment. “

Alexander Kozlov,
a leading specialist company “FORMOTRONIK” refrigeration equipment

1Alexander Kozlov KozlovAleksandr in 2011 he graduated from Kazan Chemical-Technological Institute. Kirov in the department of “Refrigeration and technology.” He defended his “excellent” diploma project on “Low-temperature freezing”, which was successfully implemented at the production of refrigeration equipment company.

Then, Alexander worked in the company “RosHolod” as an engineer for refrigeration. Conducted projects to develop water-cooling equipment, condensing units and freezers installations. He participated in the pre-commissioning and commissioning of systems customers.

In 2014 he was invited to LLC “FORMOTRONIK” for the post leading specialist in refrigeration and temperature control processes.

To lead the development and production of refrigeration Cold Point ©.

Let’s start with the properties of polymers. As is known, all the polymeric materials in a certain temperature range capable of melt – the transition from solid state to liquid and vice versa. Each polymer its melting temperature and solidification – crystallization. This range is between the melting temperature and the decomposition temperature (thermal degradation) is called working range. (Table 1)

Таблица 1. Температурные режимы переработки полимеров.
Материал Теплоемкость Диапазон температур
расплава материала
Температура
кристаллизации
С (кДж/кг∙K) T (C) Ts(С)
ABS 1,6 220-260 105
CA 1,8 170-200 40
PA6 2,0 250-270 50
PC 1,5 290-320 80
PE HD 2,5 190-280 30
PET genenc 1,4 300 120
PET preform 1,4 310 15
PMMA 1,8 220-260 70
POM 1,8 180-225 85
PP 2,4 200-270 30
PS 1,8 180-280 45
PUR 2,0 225 20
PVC 1?5 180-215 20
SAN 1,8 220-270 50
SB 1,7 250 45

And here appears the other properties of the polymer material – its shrinkage. As you know, this is an unpleasant feature of not only plastics. A trouble is that it greatly affects the quality of the future product.The working range we polymer melt. When the melt cools below the crystallization point we obtain a polymer in the solid state.

Why then is uncontrolled polymer shrinkage during cooling?

It is in the process of crystallization of the polymer, the speed and temperature of the cooling core defects associated products produced by casting!

The first group of defects:

Silver schlieren;
“Cold plug”;
Not completely molded castings;
Bowls and troughs;
The second group of defects:

Violation of geometry (warpage, sink marks);
burr;
Roughness / matte surface with glass-molding materials;
Stuck in the form of products.

If the first group is associated defects are likely to incorrect preparation melt temperature and they can be eliminated on the molding machine by changing temperature conditions, the melt flow rate, pressure delay, the second group of defects directly associated with impaired temperature forming surfaces of molds!

Therefore, in order to neutralize the effect of shrinkage on the quality of the product, the surface of the forming molds should be at a temperature close to the temperature of crystallization of the material. That is – you need to keep the shaping in a certain temperature range – thermostated them. This technique will help you not only to minimize the defect rate, but possible – to reduce the casting cycle.

The crystallization temperature of polymer materials also varies in a certain range, which for most polymers does not exceed 10.8 degrees. Going beyond this range, just involves the formation of a number of product defects or undue increase in cycle time. Both agree – frustrating!

To control the temperature of molds, there are special thermostatic devices – thermostats that can accurately control the temperature. Their device, features and principle of action I’ll discuss in the next article.