Method and device for tempering preforms
A method for tempering preforms in a blowing machine, wherein at least one heating box is arranged along a transport path for the preforms. The heating box has reflective walls and forms a heating channel through which the preforms are guided. The heating box also has a heater for heating the preforms in the heating channel, and a cooling device, having a blower, for cooling the reflective walls. The walls are cooled by a quantity of air flowing along the walls outside the heating channel. The heating output of the heater is adjustable. A control device provides open-loop and closed-loop control of the cooling output produced by the cooling device, in particular the supplied quantity of air, depending on the respective heating output of the heater, depending on a measurement of the heating output.
1. A method for tempering preforms is a blow-molding machine, comprising the steps of: arranging at least one heating box equipped with reflective walls along a transport path for the preforms, said heating box forming a heating channel; guiding the preforms through the heating channel in a transport direction, the heating box comprising heating elements for heating the preforms in the heating channel and at least one cooling device comprising a blower for cooling the reflective walls of the heating channel, wherein the cooling of the walls is achieved by a quantity of air flowing along the walls outside the heating channel, wherein heating output of the heating elements of the heating channel is adjustable; controlling the cooling of the reflective walls by adjusting cooling output of the cooling device with a control device that provides open-loop or closed-loop control of the cooling output of the cooling device as a function of an associated heating output of the heating elements of the heating channel; and monitoring a temperature of the reflective walls and/or of neck areas of the preforms with temperature sensors that are connected to the control device.
2. The method according to claim 1 , wherein the control device controls the quantity of air flowing along the walls as a function of a measurement of the heating output.
3. The method according to claim 1 , including arranging several heating boxes along the transport path in sequence in the transport direction to form a heating section formed by the heating channels of the heating boxes.
4. The method according to claim 3 , wherein each of the heating boxes comprises its own cooling device and/or its own control device.
5. The method according to claim 1 , including using at least a portion of the cooling output supplied by the cooling device to cool a neck area of the preforms.
6. The method according to claim 1 , wherein the cooling device comprises at least one blower with a speed-controlled motor.
7. The method according to claim 2 , wherein the cooling device comprises at least one throttle valve that influences the conveyed air quantity.
8. The method according to claim 2 , wherein the control device adjusts the conveyed air quantity according to a preset characteristic curve as a function of the heating output of the heating elements of the heating channel.
9. The method according to claim 8 , wherein several separately controllable heating boxes form a heating section, and the control device adjusts the conveyed air quality according to a preset family of characteristics as a function of the associated heating outputs of the individual heating boxes.
10. The method according to claim 1 , wherein the control device increases the conveyed air-quantity when the temperatures of the reflective walls and/or of the neck areas of the preforms reach predetermined critical temperatures.
11. A device for tempering preforms in a blow-molding machine, the device comprising: a heating box having reflective walls that form a heating channel through which the preforms are guidable; heating elements arranged in the heating box for heating the preforms in the heating channel; at least one cooling device including a blower for cooling the reflective walls of the heating channel, wherein the cooling of the reflective walls is achieved by a quantity of air flowing along the reflective walls outside the heating channel, wherein heating output of the heating elements is adjustable; a control device configured for open-loop or closed-loop control of the cooling of the reflective walls by adjusting cooling output of the cooling device as a function of an associated heating output of the heating elements; and, temperature sensors connected to the control device to monitor a temperature of the reflective walls and/or neck areas of the preforms.
12. A blow-molding machine, comprising at least one device according to claim 11 .
13. The method according to claim 1 , including monitoring the temperature of the reflective walls and of neck areas of the preforms with the temperature sensors.