Method and apparatus for heating plastic preforms

Abstract

Provided is a method for heating plastic preforms, wherein the plastic parison are transported along a predetermined transport path and are heated during this transport, wherein at least one first heating section with at least one first heating element as well as at least one second heating section with at least one second heating element is arranged along the transport path, by a first temperature measuring device an actual temperature of the plastic preforms is measured in or before a start region of the transport path, and as a function of this actual temperature of the plastic preforms the at least one first heating element is controlled in such a way that the plastic preforms reach a predetermined target temperature after heating by this at least one first heating element.

Claims

1. A method for heating plastic preforms, wherein the plastic preforms are transported along a predetermined transport path and are heated during this transport, wherein at least one first heating section with at least one first heating element as well as at least one second heating section with at least one second heating element is arranged along the transport path, wherein by a first temperature measuring device an actual temperature of the plastic preforms is measured in or before a start region of the transport path, and as a function of this actual temperature of the plastic preforms the at least one first heating element is controlled in such a way that the plastic preforms reach a predetermined target temperature after heating by this at least one first heating element, wherein a material constant of the plastic preforms is determined, wherein in this determination of the material constant, which considers a mass of the plastic preforms, an absorption coefficient of the plastic preforms and a specific thermal capacity of the plastic preforms, is taken into consideration, wherein the material constant is taken into consideration during the heating of the plastic preforms.

2. The method according to claim 1, wherein the plastic preforms are first of all heated by the at least one first heating element and then are heated by the at least one second heating element.

3. The method according to claim 1, wherein the heating elements are arranged stationary and the plastic preforms are transported past these heating elements.

4. The method according to claim 1, wherein by a second temperature measuring device a second actual temperature of the plastic preforms is measured and as a function of this second actual temperature of the plastic preforms the at least one second heating element is controlled.

5. The method according to claim 1, wherein a length of the plastic preforms is determined.

Description

BRIEF DESCRIPTION

(1) Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein:

(2) FIG. 1 shows a schematic representation of an apparatus according to embodiments of the invention; and

(3) FIG. 2 shows a representation of a method according to embodiments of the invention.

DETAILED DESCRIPTION

(4) FIG. 1 shows an apparatus 1 according to embodiments of the invention for heating plastic preforms 10. This apparatus 1 has a transport device 2 which has a plurality of holding elements 22 for holding the plastic preforms 10. This transport device is designed here as a transport chain circulating in an oval configuration. The references 4 relate to a plurality of first heating elements (which are preferably components of a first heating section), such as heater boxes, and the references 14 relate to a plurality of second heating elements (which are components of a second heating section) or heater boxes. Correspondingly the reference G1 designates the first warming section (that is to say den first heating section) and the reference G2 designates the second warming section (that is to say the second heating section).

(5) The reference P designates the entire transport path of the plastic preforms which can be divided into a first path section P1 and a second path section P2. During the transport along the first transport section P1 the plastic preforms are heated by the heating elements 4 and during the transport P2 the plastic preforms are heated by the heating elements 14. A longitudinal direction (not shown) of the plastic preforms extends perpendicular here to the drawing plane, that is to say the plastic preforms are transported in a vertical orientation with their mouths upwards. However, transport of the plastic preforms with their mouths downwards would also be conceivable.

(6) The reference 6 designates a first temperature measuring device, such as a pyrometer, which contactlessly detects the temperature, more precisely the actual temperature T.sub.I of the plastic preforms at the start of heating, that is to say here in particular before they are heated by the first heating element 4. The reference sign 20 identifies a control device which serves to control the first heating elements 4. In this case, as mentioned above, the heating elements 4 are controlled using the preform temperature or temperature of the plastic preforms determined by the temperature measuring device 6. The reference T.sub.S designates the target temperature which the plastic preforms should reach after passing through the first path section.

(7) In addition, a processor device 22 is also provided which, starting from the actual temperature of the plastic preforms and taking the target temperature of the plastic preforms into consideration, calculates a heating power which is required in order to reach this target temperature. The control device is preferably also suitable and intended to take a transport speed of the plastic preforms into consideration in the determination of the heating power.

(8) This control device 20 or optionally also a further control device is suitable and intended to control the individual heating elements 4. In this case this control can take place in such a way that the plastic preforms reach the required target temperature at the outlet of the heating device.

(9) The reference 18 designates a deflection region in which the plastic preforms are transferred from the first transport section P1 into the second transport section P2. No heating of the plastic preforms takes place in this region. The reference 30 designates a transport device which transports the already heated plastic preforms to a further plant such as in particular a stretch blow moulding machine (not shown) (of which the oven is a component).

(10) The reference 16 designates a further temperature measuring device which is arranged at the end of the transport path and thus determines the starting temperature of the plastic preforms. Thus, it is possible to determine a temperature difference of the plastic preforms between the inlet and the outlet of the oven and thus in particular to calculate the material constants, as mentioned above.

(11) Thus, the plastic preforms can be brought to a uniform temperature along the first transport section P1, and an individual profiling of the individual temperatures of the plastic preforms takes place in the second transport section P2. In this case it is also possible that this profiling already takes place in the first heating section, in particular individually in an end region of this first heating section.

(12) FIG. 2 shows a further representation of a method according to embodiments of the invention. It will be recognised here that the warming device has a plurality of heating elements or heater boxes, in the example a total of 43 heating elements, which are arranged one behind the other along the transport path of the plastic parisons, and past which the individual plastic preforms are transported.

(13) In this case each of these individual heating elements has a plurality of heating zones which are arranged one above the other in the longitudinal direction of the plastic preforms. In this case these heating zones can be formed by heat radiators which are arranged one above the other in the longitudinal direction of the plastic preforms. It will be recognised here that the heating zones 6-9 or the heat radiators of these zones are deactivated in each case. In particular in this setting shorter plastic preforms should be heated, which do not extend into the region of the heating zones 6-9.

(14) In the remaining heating zones, the respective heating elements or heater boxes are partly activated and partly not activated. It will be recognised for example that in the fourth heating zone several of the heating elements are not activated. This means that the plastic preforms in a vertical position which corresponds to this heating zone are heated less than in another vertical position. In this way a changing temperature profile can also be applied in the longitudinal direction of the plastic preforms.

(15) Thus, in the example illustrated in FIG. 2 the central regions in the longitudinal direction of the plastic preforms are heated less strongly than the lower and upper regions.

(16) Furthermore, it will be recognised that in the illustrated example a profiling of the heating profile occurs from the heating elements 9+10. Thus in the start region that is to say here in the region of the heating elements 1-8 the plastic preforms are heated uniformly, wherein here in the heating zones 1-5 in each case the heating elements 1-4 are activated and the heating elements 5-8 are deactivated.

(17) Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.

(18) For the sake of clarity, it is to be understood that the use of “a” or “an” throughout this application does not exclude a plurality, and “comprising” does not exclude other steps or elements. The mention of a “unit” or a “module” does not preclude the use of more than one unit or module.

LIST OF REFERENCES

(19) 1 apparatus according to the invention

(20) 2 transport device

(21) 4 first heating elements or heater boxes

(22) 6 first temperature measuring device

(23) 10 plastic preforms

(24) 14 second heating elements or heater boxes

(25) 16 further temperature measuring device

(26) 18 deflection region

(27) 20 control device

(28) 22 holding elements

(29) 30 transport device

(30) G1 first warming section, first heating section

(31) G2 second warming section, second heating section

(32) P transport path

(33) P1 first path section

(34) P2 second path section

(35) T.sub.I actual temperature

(36) T.sub.S target temperature