Process and apparatus for the blow molding of containers using wall-thickness measurement of the molded article
The process and the apparatus serve for the blow moulding of containers ( 2 ). A parison ( 1 ) composed of a thermoplastic material is first subjected to heat conditioning along a transport path in the region of a heating section ( 30 ). The parison is then subjected to a forming process within a blow mould with exposure to blowing pressure to give heat container. The heat conditioning of the parisons is carried out by a plurality of mutually superposed radiant heaters ( 41 ). The blow moulding of the container is followed by wall-thickness measurement at at least one level within the height of the container. The heating power of a radiant heater associated with this height level is controlled. The control system receives a prescribed wall-thickness value as required value and the measured wall thickness as actual value.
1. A process for blow molding containers, in which a preform made of a thermoplastic material is subjected to thermal conditioning along a conveyance path in a heating line and then molded into a container in a blow mold by the action of blowing pressure, and in which the thermal conditioning is carried out by several radiant heaters arranged one above the other, wherein, after the container ( 2 ) has been blow-molded, a wall thickness is measured at at least one height level of the container ( 2 ), where the heating capacity of a radiant heater ( 41 ) only associated with this height level is automatically controlled, and where the automatic control system is supplied with a preassigned value for the wall thickness as the set point and the measured wall thickness as the actual value.
2. A process in accordance with claim 1 , wherein the wall thickness measurement of the container ( 2 ) is carried out at several different height levels.
3. A process in accordance with claim 1 , wherein at least two pairs of measuring devices ( 44 ) for the wall thickness of the container ( 2 ) and automatic wall thickness controllers ( 55 ), which are arranged at mutually corresponding height levels, are integrated in their own closed-loop control system for carrying out a level-specific automatic wall thickness control operation.
4. A process in accordance with claim 1 , wherein a temperature measurement of the preforms ( 1 ) is carried out.
5. A process in accordance with claim 1 , wherein automatic temperature control and automatic wall thickness control are carried out in a cascade control system.
6. A process in accordance with claim 1 , wherein the automatic temperature control is carried out in an inner closed-loop control system of the cascade control system, and the automatic wall thickness control is carried out in an outer closed-loop control system of the cascade control system.
7. A process in accordance with claim 1 , wherein a temperature measurement of the preforms ( 1 ) is carried out downstream of the heating line ( 24 ).
8. A process in accordance with claim 1 , wherein the temperature measurement of the preforms ( 1 ) is carried out between the heating line ( 24 ) and a blowing wheel ( 25 ) in the direction of conveyance of the preforms ( 1 ).
9. A process in accordance with claim 1 , wherein a wall thickness measurement is carried out downstream of the blowing wheel ( 25 ) in the direction of conveyance of the preforms ( 1 ).
10. A process in accordance with claim 1 , wherein only some of the heating elements ( 30 ) of the heating line ( 24 ) are controlled by the wall thickness controller ( 55 ).
11. A process in accordance with claim 10 , wherein at least the last heating element ( 30 ) in the direction of conveyance of the preforms ( 1 ) is controlled by the wall thickness controller ( 55 ).
12. A process in accordance with claim 1 , wherein at least two heating elements ( 30 ) are simultaneously controlled by the wall thickness controller ( 55 ).
13. A process in accordance with claim 1 , wherein at least the first heating element ( 30 ) in the direction of conveyance of the preforms ( 1 ) produces a base temperature of the preform ( 1 ) without any control.
14. An apparatus for blow molding containers made of a thermoplastic material, which comprises at least a heating line arranged along a conveyance path of a preform and a blowing station equipped with a blow mold, and in which the heating line has at least one heating element with at least two radiant heaters arranged one above the other, wherein the radiant heaters ( 41 ) are connected to an automatic control system, which is connected with at least one sensor ( 45 ) for detecting a wall thickness of the container ( 2 ), and that the sensor ( 42 ) is arranged at a height level that corresponds to a height level of the radiant heater ( 41 ), with the incorporation of a stretch factor, which is formed by the ratio of the length of the stretched region of the container ( 2 ) to the length of the corresponding region of the preform ( 1 ).
15. An apparatus in accordance with claim 14 , wherein several sensors ( 45 ) are arranged at different height levels relative to one another.
16. An apparatus in accordance with claim 14 , wherein pairs of sensors ( 45 ) and radiant heaters ( 41 ) assigned to different height levels are each arranged in a closed-loop control system assigned to the given height level.
17. An apparatus in accordance with claim 14 , wherein the automatic control system has at least one temperature sensor ( 53 ).
18. An apparatus in accordance with claim 14 , wherein at least one temperature sensor ( 53 ) and at least one sensor ( 45 ) for measuring the wall thickness are arranged together with an automatic wall thickness controller ( 55 ) and an automatic temperature controller ( 56 ) in a cascade control system.
19. An apparatus in accordance with claim 14 , wherein the temperature sensor ( 53 ) and the temperature controller ( 56 ) are arranged in an inner closed-loop control system of the cascade control system, and the sensor ( 45 ) for the automatic wall thickness control and the wall thickness controller ( 55 ) are parts of an outer closed-loop control system of the cascade control system.
20. An apparatus in accordance with claim 14 , wherein the temperature sensor ( 53 ) is arranged downstream of the heating line ( 24 ) in the direction of conveyance of the preforms ( 1 ).
21. An apparatus in accordance with claim 14 , wherein the temperature sensor ( 53 ) is arranged between the heating line ( 24 ) and a blowing wheel ( 25 ) in the direction of conveyance of the preforms ( 1 ).
22. An apparatus in accordance with claim 14 , wherein the sensor ( 45 ) for measuring the wall thickness is arranged downstream of the blowing wheel ( 25 ) in the direction of conveyance of the preforms ( 1 ).
23. An apparatus in accordance with claim 14 , wherein only some of the heating elements ( 30 ) of the heating line ( 24 ) are arranged in the closed-loop control system for controlling the wall thickness.
24. An apparatus in accordance with claim 14 , wherein at least the last heating element ( 30 ) in the direction of conveyance of the preforms ( 1 ) is designed as part of the closed-loop control system for controlling the wall thickness.
25. An apparatus in accordance with claim 14 , wherein at least two radiant heaters ( 41 ) arranged at the same height level in different heating elements ( 30 ) are simultaneously controlled by the closed-loop control system for controlling the wall thickness.
26. An apparatus in accordance with claim 14 , wherein at least the first heating element ( 30 ) in the direction of conveyance of the preforms ( 1 ) is arranged outside of the closed-loop control system for controlling the wall thickness.