1 Overview
The hollow blow molding machine is mainly used for producing various single-layer, double-layer, (double-layer) visible liquid level line blow molding hollow products such as bottles, pots, cans, barrels and small shaped parts, especially suitable for PVC, PE, Hollow blow molding of raw materials such as PC, PP, PS, and PA. The market outlook is promising.

The principle of the hollow blow molding machine is “squeeze-blowing” molding. The extruder adopts variable frequency motor speed regulation, which can obtain a large speed regulation range to meet the requirements of different products, and can make the extruded parison quite stable to ensure the uniformity of product weight. The molten plastic plasticized by the extruder forms a parison through the extruder head, and the parison enters the mold for blow molding, that is, a cycle is completed. At present, the hollow blow molding machines on the market have large models and small models. Small machines are divided into single and double stations. When the double-station work, the left and right work stations each complete a work process to calculate a cycle.

The blow molding machine consists of mechanical, electrical, hydraulic, pneumatic, water and servo oil sources (optional):
The mechanical part includes: extrusion device; machine head; mold shifting and opening and closing mechanism; frame; lifting mechanism; air blowing device; blank electric hot cutting blade;
Gas path part: used for cylinder work and blow molding of products.
Waterway part: Cooling water is used for cooling of molds, barrels, blowers, gearboxes, etc.

2. System Description
The hollow blow molding machine adopts the speed control system of the variable frequency motor; the heating and temperature control system of the machine head and the extruder; the action program control system (PLC) and the corresponding safety protection system. The human machine interface uses touch screen input.

The feeding extruder has higher starting torque. The inverter adopts Schneider ATV58 high torque series, ATV71 series, etc. The PLC adopts Twido 40 point body plus expansion module; because the temperature heating section generally has 6-8 sections, the Schneider special temperature module is adopted. 8 inputs. The touch screen uses Schneider’s XBTG touch screen as the master station, the PLC acts as the slave station, and the communication uses the Modbus protocol. The drive speed reference is given by an external potentiometer.

Process flow: barrel die heating and insulation – start extrusion – forming tube blank – [clamping – blowing needle – electric section cutting section tube blank – lifting die head – mold frame moving right – blowing needle down – blowing Cooling and setting – blowing needle micro-pumping – pulling bottom – opening mold – opening mold blowing needle – mold frame left shifting – pulling bottom – closing mold > automatic circulation. Among them, the finished product is opened.

3. Solve the temperature drift problem
Since the hollow blow molding machine adopts Twido PLC to realize fully automatic control, the hollow blow molding machine is a machine that is formed by heating plastic particles “squeezing-blowing”, in which the temperature plays an important role in realizing the quality of the finished product, so the temperature control The requirements are relatively high, and the general control temperature is about -4 to +4 degrees. For this reason, we use Twido PLC to achieve this requirement. The main control idea is: collect the signal every 0.1s (the time that can be manually changed by the Schneider PLC temperature module), sort it when the collection is ten times, take the middle value, and start the first time as the temperature output value. At the same time, it is sent to the intermediate variable and saved until 5 times. The two maximum values ​​are removed, the two minimum values ​​are removed, and the middle value is taken as the normal temperature output value. PLC programming ideas are as follows:

For temperature heating, the temperature range (ie, temperature control zone) is used to control when the heater is on and when it is off, rather than using a temperature control point to determine the heater’s switching. When the temperature is heated to the set temperature, it is heated in a stable range, and the heater contactor does not work very frequently, which not only ensures the service life of the contactor, but also ensures the stability of the temperature, and improves the product. Quality and production are of great help. The specific programming ideas are as follows:

In order to minimize the temperature drift, the temperature module does not collect the signal within 2 seconds of the heater being sucked, which can reduce the influence of current on the temperature due to the contactor.

4 Conclusion
The electric control system of the hollow blow molding machine is controlled by touch screen + Twido PLC. The time, pressure and temperature parameters can be adjusted at will, and there are alarm queries, which can be adapted to match various functions. High degree of automation: It can complete the fully automatic cycle work from feeding to qualified products. With Schneider’s complete solution, the system is very stable, the temperature drift is very small, the product quality and output are improved, and it is highly praised by customers.