Plastic blank heating method and apparatus

Abstract

A method of heating plastic blanks for molding, comprising, for each blank in a sequence of blanks of different types, determining a heating requirement corresponding to a property of the blank for a molding process to be performed, and heating each blank in accordance with its heating requirement. A microwave field having a defined heating rate is generated, and the blank is placed in the microwave field for a period of time equal to a heating duration, such that the heating duration and the heating rate correspond to the heating requirement.

Description

Technical Field

[0001] This relates to plastic molding, and more specifically, to the heating of blanks used in molding operations. Background Technology

[0002] Many plastic products are manufactured using processes with multiple molding steps. For example, many containers, such as beverage containers, are produced in two molding stages. In the initial molding stage, molten molding material is injection molded into a preform, often called a preform. In the second molding stage, the preform is blow molded into the final container shape.

[0003] Based on material properties, draw ratio, required surface finish and other parameters, blow molding processes are typically designed to be performed at specific high temperatures.

[0004] A typical system is designed to process large quantities of identical billets into identical containers. Unfortunately, such a system offers very little flexibility. Summary of the Invention

[0005] An exemplary method for heating a plastic molding preform includes: a) receiving a plurality of preforms in sequence, the plurality of preforms including preforms of different types, each type for molding in an associated molding process; b) for each preform in the sequence: i) determining heating requirements corresponding to the characteristics of the preform and the associated molding process; ii) generating a microwave field having an intensity that defines a heating rate; iii) determining a heating duration based on the heating requirements; iv) advancing the preform through the microwave field at a certain speed such that the preform remains within the microwave field for a period of time equal to the heating duration, wherein the heating duration and heating rate correspond to the heating requirements.

[0006] In some embodiments, the method includes, for each billet in the sequence, measuring the input temperature of the billet before heating, and wherein determining the heating requirements includes adjusting the basic heating requirements based on the input temperature.

[0007] In some embodiments, adjusting basic heating requirements based on input temperature includes comparing the input temperature with a nominal temperature.

[0008] In some embodiments, the input temperature includes the axial temperature distribution.

[0009] In some embodiments, the method includes adjusting the heating rate based on the input temperature for each billet in the sequence.

[0010] In some embodiments, adjusting the heating rate includes adjusting the output power of the microwave generator.

[0011] In some embodiments, adjusting the heating rate includes positioning the attenuation device within a microwave field.

[0012] In some embodiments, the method includes selecting a speed based on an input temperature for each billet in the sequence.

[0013] In some embodiments, the method includes, for a sequence of billets, holding the billet in a position such that a portion of the billet receives heat from a microwave field to heat the portion relative to the rest of the billet.

[0014] In some embodiments, the method includes generating a circumferential temperature gradient around the circumference of a billet in a sequence using a microwave field.

[0015] In some embodiments, generating a circumferential temperature gradient includes moving a microwave reflector to position a region of peak microwave intensity relative to the billet.

[0016] An exemplary preform heating device for plastic molding includes: a) a heating chamber; b) a microwave generator for emitting microwaves into the heating chamber via a waveguide; c) a preform conveying device for moving the preform into and out of the heating chamber along a heating axis; and d) a controller operable to control the speed of the conveying device to limit the heating duration based on the heating requirements of the preform.

[0017] In some embodiments, the billet heating apparatus includes a microwave attenuation device that extends into a waveguide to control the microwave heating rate within the heating chamber.

[0018] In some embodiments, the billet heating apparatus includes a microwave reflector that is movable relative to the chamber to control the position of the peak microwave intensity within the chamber.

[0019] In some embodiments, the billet heating apparatus includes a temperature measuring device near the heating chamber for measuring the temperature of the billet before it enters the heating chamber.

[0020] In some embodiments, the temperature measuring device includes a plurality of pyrometers.

[0021] In some embodiments, the controller is operable to control the heating of the billet based on the input temperature of the billet.

[0022] In some embodiments, the controller is operable to control the heating of the billet by setting the speed of the conveying device.

[0023] In some embodiments, the controller is operable to control the heating of the billet by adjusting the output power of the microwave generator.

[0024] In some embodiments, the controller is operable to control the heating of the billet by adjusting the position of the microwave attenuation device.

[0025] Implementation examples may include any combination of the features described above. Attached Figure Description

[0026] The accompanying drawings depict exemplary embodiments:

[0027] Figure 1 This is a schematic diagram of the molding system;

[0028] Figure 2 yes Figure 1 A top view of the molding system;

[0029] Figure 3 yes Figure 1 Isometric view of the system's regulating station;

[0030] Figure 4 yes Figure 3 Enlarged cross-sectional view of the heating chamber and waveguide of the regulating station;

[0031] Figure 5 It shows Figure 4 A schematic diagram of the heating chamber and waveguide, which has a fixed microwave pattern;

[0032] Figures 6A-6B They are Figure 5 The side and top views of the heating chamber show the temperature measuring equipment;

[0033] Figure 7 This is a schematic diagram showing the blank and the final molded product formed from the blank;

[0034] Figure 8A and 8B These are representative feed and discharge temperature distribution diagrams for the billet;

[0035] Figure 9 This is a block diagram showing the components of the control device;

[0036] Figure 10 It is shown Figure 9 A block diagram of the data storage of the control device;

[0037] Figure 11 This is a flowchart illustrating the billet heating process;

[0038] Figure 12 It is shown Figure 11 A flowchart detailing the initial main heating stage of the process;

[0039] Figure 13 It is shown Figure 11 A flowchart detailing the shoulder heating stage of the process;

[0040] Figure 14 It is shown Figure 11 A detailed flowchart of the temperature smoothing phase of the process; and

[0041] Figures 15A-15D It is shown in Figure 11 A graph showing the axial temperature distribution of the billet at each stage of the process. Detailed Implementation

[0042] Figure 1 An example plastic molding system 100 for producing plastic molded objects is schematically depicted. As described in further detail below, the plastic molding system 100 is capable of molding objects through a series of processing operations.

[0043] In particular, system 100 provides the flexibility to produce various types of articles. For example, system 100 can produce articles of different shapes, sizes, colors, and materials.

[0044] The plastic molding system 100 includes multiple processing stations. Each station comprises a group of stations, each operable to perform the same type of processing operation. Specifically, the illustrated embodiment includes multiple distribution stations 102, multiple forming stations 104, multiple secondary forming stations 106, and multiple adjustment stations 108.

[0045] Each dispensing station 102 is operable to perform a dispensing operation, i.e., to produce an output of molding material for subsequent operations. Each molding station 104 is operable to perform a primary molding operation. For example, each station 104 may include an injection mold for performing an injection molding operation. Each molding station 106 is operable to perform a secondary molding operation. For example, each molding station 106 includes a blow mold for reshaping the injection-molded article into its final shape.

[0046] In the example, the dispensing station 102 includes an extruder for producing a stream of molten plastic molding material (e.g., PET) from a solid (e.g., granular) raw material; the forming station 104 is an injection molding station for producing preforms known as preforms, which are then reshaped into containers, such as beverage containers; and the forming station 106 is a blow molding station for reshaping the preforms.

[0047] Blow molding operations typically require the preform to be at a relatively high temperature (e.g., well above room temperature) for reshaping. Therefore, the preform can be processed at conditioning station 108 to heat it before forming at station 106.

[0048] In some embodiments, the dispensing station 102 is operable to dispense a range of possible molding materials. For example, the dispensing station may output molding materials with different colors, compositions, or other properties. The dispensing station 102 may be configured to output discrete amounts of molding material, which may be referred to as dosage. Similarly, different molding stations 104 and different molding stations 106 may include molds of different sizes or shapes. In general, the system 100 is capable of simultaneously producing multiple different types of molded articles, wherein each particular type of article corresponds to a combination of the type and amount of molding material from the dispensing station 102, the shape and size of the injection-molded article from the molding station 104, and the shape and size of the finished article from the molding station 106.

[0049] The optimal temperature for blow molding at station 106 can vary based on many factors, such as the type of material, the quality of the material to be molded, the amount of material stretching and the desired final shape, the required wall thickness, and the shape and design of the preform. Furthermore, the amount of heat required to bring the preform to the desired thermal state and the heat distribution depend on factors such as the material type, billet size, and mass distribution within the billet.

[0050] In the depicted embodiment, the conditioning station 108 can be controlled based on parameters associated with individual input billets to produce output billets with specific desired thermal conditions.

[0051] Figure 2 A top view depicting the molding system 100 is shown. The stations of system 100 are located near the transport system, i.e., the central track 101. In-process and finished items can move between stations along track 101. Each item produced using system 100 is processed at a combination of a specific distribution station 102, a specific forming station 104, a specific forming station 106, and a specific adjustment station 108. Each unique combination may correspond to a unique type of molded object, and the type may differ from each other in characteristics such as shape, size, color, and material type.

[0052] To adapt to this change, the conditioning station 108 can perform customized heat treatment on different billets, adjusting according to the material and process characteristics of the billet and the actual conditions.

[0053] Figure 3 An example conditioning station 108 is depicted. Conditioning station 108 includes a mandrel 110 operably clamping a workpiece 112. The mandrel 110 is coupled to a drive unit 118 operable to move the mandrel 110 along a heating axis 114 and to rotate the mandrel 110 about the heating axis 114. The heating axis 114 passes through a feed tube 115 leading to a heating chamber 116.

[0054] The mandrel 110 serves as a conveying device for moving the billet 112 in and out of the heating chamber. Specifically, using the mandrel 110, the billet 112 can advance along the heating axis 114 into the heating chamber 116 and can retract along the heating axis 114 from the heating chamber 116. The mandrel can also rotate the billet 112 within the chamber 116 at a desired rate or angle. In the depicted embodiment, the mandrel 110 can move the billet 112 along the heating axis 114 at a rate up to 300 mm / s and can rotate the billet 112 about the heating axis at a rate up to 300 rpm.

[0055] The conditioning station 108 also includes a heating device 120. The heating device 120 is operable to apply heat to the billet 112 within the heating chamber 116. The heat can be applied at a variable rate. Furthermore, heat can be concentrated within the heating chamber 116, such that one or more locations within the heating chamber 116 experience a greater heating intensity than other locations.

[0056] In the illustrated embodiment, the heating device 120 is a microwave heating device. That is, the heating device is operable to apply heat to the blank 112 within the heating chamber 116 by generating a microwave field inside the chamber.

[0057] The heating device 120 includes a microwave generator unit 122, a waveguide 124, a heating chamber 116, and multiple adjustment pins 128-1, 128-2, 128-3 (individually and collectively, adjustment pin 128). In the illustrated embodiment, the waveguide 124 includes a manual three-stub adjuster. However, the adjuster may be omitted.

[0058] The microwave generator unit 122 includes one or more magnetron heads operable to generate microwave emissions. In the illustrated embodiment, the magnetron generator is capable of generating microwaves at a frequency of 2450 MHz and a power of 3 kW.

[0059] The microwave generator unit 122 is interconnected with the heating chamber 116 via a waveguide 124. Figure 4 This is a cross-sectional view showing the interior of the waveguide 124 and the heating chamber 116.

[0060] Waveguide 124 defines an internal channel, and heating chamber 116 defines an inner cavity 130. Microwave radiation from microwave generator unit 122 enters the internal channel 128 of waveguide 124 and the inner cavity 130 of heating chamber 116, forming a standing wave pattern 132. The standing wave pattern is partially defined by the size and shape of waveguide 124, the size and shape of inner cavity 130 of heating chamber 116, and the material, temperature, and design of the blank within the heating chamber.

[0061] Figure 5An example standing wave pattern is shown. As shown, standing wave pattern 132 produces regions of high and low microwave intensity within cavity 130. The high-intensity region 134 typically corresponds to the region of constructive interference between microwaves. The low-intensity region 136 typically corresponds to the region of destructive interference between microwaves.

[0062] like Figure 5 As shown, the high-intensity region 134 is located near one side of the wall of the billet 112. The portion of the billet 112 within the high-intensity region 134 is subjected to high-speed microwave heat input. Conversely, the opposite side of the billet 112 is located in a region with relatively low microwave intensity and is subjected to a relatively low microwave heat input rate.

[0063] Therefore, variations in microwave intensity at different locations within the cavity 130 can produce different heating rates for different portions of the billet 112. That is, portions of the billet 112 in the high-intensity region tend to heat faster than portions in the low-intensity region. Thus, this variation can be used to create a temperature gradient within the billet 112. For example, Figure 5 The configuration shown will tend to produce a decreasing temperature gradient around the circumference of the billet 112, from the portion of the billet 112 in the high-strength region 134 to the relative portion of the billet 112 in the lower-strength region.

[0064] In some cases, such a circumferential temperature gradient may be desirable. However, in other cases, it may be desirable to generate a uniform temperature around the circumference of the billet 112. In this case, the billet 112 can be rotated about its longitudinal axis using a mandrel 110, so that the average heat input is substantially uniform around the circumference of the billet 112.

[0065] like Figure 5 As shown, only a small longitudinal portion of the billet 112 is located within the inner cavity 130 of the heating chamber 116. Therefore, only the small longitudinal portion of the billet 112 is subjected to microwave heating. Thus, the mandrel 110 can be used to advance the billet 112 through the inner cavity 130 along the longitudinal axis of the billet, so that heat can be applied along the entire longitudinal range of the billet 112, or the standing wave pattern can be adjusted to position the high-intensity region 134 at the center of the cavity 130, or to generate multiple high-intensity regions 134 uniformly distributed throughout the cavity 130.

[0066] The heat applied to the billet 112 is controlled by the intensity of the microwave radiation exposed to the billet and the rate at which the billet moves through the heating chamber 116. If the billet 112 moves slowly through the heating chamber 116, the duration of its exposure to microwave heating is relatively long. Conversely, if it moves quickly through the heating chamber 116, the duration of its exposure to microwave heating is relatively short, corresponding to a relatively small total heat input.

[0067] In some cases, the billet 112 can advance through the heating chamber 116 at a constant rate to apply a constant amount of heat along the length of the billet. In other cases, it may be desirable to create a temperature gradient along the length of the billet 112. This gradient can be created by varying the microwave intensity as the billet 112 advances through the heating chamber 116, such that different portions of the billet 112 are exposed to microwave heating of different intensities. Additionally or alternatively, the rate at which the billet 112 advances through the chamber 116 can be varied. For example, to generate a relatively higher temperature in the first region compared to the second region, the advance rate can be reduced when the first region is in the chamber 116.

[0068] The output power of the microwave generator unit 122 can be increased or decreased to increase or decrease the average microwave intensity within the heating chamber 116.

[0069] Additionally or optionally, the microwave heating characteristics within the heating chamber 116 can be controlled by moving the adjusting pin 128.

[0070] The adjustment pin 128 is formed of a material that attenuates microwaves. For example, the adjustment pin 128 can be made of materials such as CuZn. 39 Nonferrous metal formation of Pb3.

[0071] The average microwave intensity within the heating chamber 116 can be reduced using adjusting pins 128-1 and 128-2. Specifically, adjusting pins 128-1 and 128-2 can be advanced into the waveguide 124 to partially attenuate the microwaves emitted by the microwave generator unit 122, thereby reducing the single-mode microwave field strength within the heating chamber 116. The amount of attenuation depends on the distance the adjusting pins 128-1 and 128-2 travel into the waveguide 124. In this example, each adjusting pin 128 can be extended or retracted by a stroke of 14 mm. However, the length of the adjusting pin stroke can depend on the resonator design. The adjustment made by moving the pins 128 allows impedance matching of the blank in the heating chamber 116. That is, the characteristics of the microwave field in the heating chamber 116, as adjusted using the pins 128 and the blank in the chamber, produce an impedance between 0 and 1, reflecting the proportion of microwave energy delivered to the blank. By moving the pins 128, the impedance can be moved closer to the theoretical maximum value of 1.

[0072] Adjusting pin 128-3 reflects incident microwaves. Therefore, during operation of the microwave generator unit 122, the standing wave pattern within the heating chamber 116 can be controlled by moving the adjusting pin 128-3. Retraction of the adjusting pin 128-3 away from the microwave generator unit 122 typically moves the high-intensity region in a direction away from the microwave generator unit 122. Extension of the adjusting pin 128-3 typically moves the high-intensity region towards the microwave generator unit 122. Therefore, the adjusting pin 128-3 can be used to position the high-intensity region only on a portion of the billet 112, such that different portions of the billet are heated at different rates, or to position the high-intensity region at, for example, the center of the heating chamber 116, such that the billet 112 is heated uniformly. In this example, pin 128-3 is formed of the same material as pins 128-1 and 128-2.

[0073] The amount of heat required to bring the billet 112 to the desired thermal state depends on the thermal state of the billet before heating. A temperature sensor can be provided to measure the thermal state of the billet 112 before heating. Figure 6A and 6B These are side and top views, respectively, illustrating the structure of the temperature sensor.

[0074] In the described embodiment, the temperature sensor includes a pyrometer 140 positioned around the heating axis 114 near the entrance of the heating chamber 116. As shown, four pyrometers 140-1, 140-2, 140-3, and 140-4 are present. However, in other embodiments, more or fewer pyrometers may be used. In some instances, a suitable pyrometer may have high accuracy (e.g., an error of less than 1 degree Celsius). The pyrometer may also be selected for a fast response time, such as 9 ms or less. An example of a suitable pyrometer is the Micro Epsilon model CTF-SF25-C3.

[0075] As the billet 112 advances past the pyrometer 140, the pyrometer acquires temperature measurements. These measurements can be performed continuously or at discrete time intervals. Each measurement corresponds to a specific location along the axis of the billet 112. Thus, a set of measurements from a particular pyrometer 140 describes the longitudinal temperature distribution of the billet 112.

[0076] Each measurement also corresponds to a specific location on the surface of the billet 112. That is, in the case of the billet with a generally cylindrical cross-section, each pyrometer obtains a measurement at a specific circumferential location.

[0077] Measurements from a single pyrometer 140 can be considered representative of the entire billet 112. Alternatively, multiple pyrometers can be used to obtain measurements at each location of interest on the surface of the billet 112.

[0078] In the depicted embodiment, four pyrometers are positioned at equal intervals around the circumference of the billet. That is, pyrometers 140-1, 140-2, 140-3, and 140-4 are positioned approximately 90 degrees apart from each other.

[0079] The number and location of the pyrometers 140 can vary depending on the characteristics of the billet 112 or its processing. For example, if the billet 112 has a non-uniform or asymmetrical cross-section, the temperature at certain specific locations may be of particular interest.

[0080] Based on the temperature measured by each of the multiple pyrometers 140, the circumferential temperature distribution can be obtained. That is, the relatively hot or relatively cold parts around the circumference of the billet 112 can be identified.

[0081] Alternatively, the circumferential temperature distribution can be obtained by rotating the billet 112 about its longitudinal axis. This rotation allows the circumferential temperature distribution to be obtained using a single pyrometer.

[0082] Longitudinal temperature distribution and circumferential temperature distribution can be used in combination to determine the heating requirements of the entire billet 112.

[0083] Heating requirements may also be affected by the material properties of the billet 112. For example, the material type, additives, color, heat capacity, and density of the billet 112 can affect the amount of heat required to achieve a given temperature rise.

[0084] The forming station 108 can sequentially process various types of blanks 112. For example, the molding system 100 can simultaneously manufacture objects such as liquid containers of various sizes, shapes, and colors. Each blank 112 for a specific container type can have an associated heat distribution for optimal processing at the forming station 106. The associated heat distribution can depend, for example, on the material type, the specific type of blank 112 and the wall thickness of the container to be formed from the blank 112, and the material draw ratio (circumferential draw ratio, axial draw ratio, and planar draw ratio) required to achieve the final shape to be formed from the blank 112.

[0085] Figure 7A representative blank 112 and finished product, container 150, are shown. The blank will be formed into container 150 at forming station 106. Container 150 typically has a base portion 152, a body portion 154, a shoulder portion 156, and a neck portion 158. The neck portion 158 may define a threaded or other retaining feature ring for connecting the closure. To be re-formed into container 150, the walls of blank 112 are stretched as indicated by arrow S. Stretching can be characterized by circumferential stretching, i.e., radial stretching; axial stretching, i.e., stretching along the axial direction; and planar stretching, i.e., a combination of circumferential and axial stretching. Clearly, the amount of stretching varies across blank 112. For example, the portion of blank stretched to form body portion 154 undergoes approximately uniform stretching. Conversely, the stretching of shoulder portion 156 and base portion 152 is non-uniform.

[0086] Furthermore, some portions of the blank 112 are stretched very little or not at all during forming at the forming station 106. For example, the neck portion 158 may not be re-formed.

[0087] Precise temperature control plays a crucial role in ensuring the quality and consistency of finished products.

[0088] Uniform temperature distribution generally promotes consistency in finished molded articles, such as consistent surface appearance and wall thickness. However, higher temperatures may be required in areas experiencing large draw ratios. Conversely, lower temperatures may be needed in areas with little or no draw, such as the threaded closure at the neck. Maintaining low temperatures in these areas limits the possibility of unwanted deformation or creep. For molding long, round articles such as bottles, a uniform circumferential temperature distribution may be particularly important. However, significant temperature variations along the longitudinal direction may be necessary to accommodate different draw ratios at different locations on the bottle.

[0089] Figures 8A-8B Example axial temperature distributions of the billet before and after heating at conditioning station 108 are depicted.

[0090] The temperature distribution prior to heating can be referred to as the feed temperature distribution. In the described example, a single feed temperature distribution is generated by averaging readings from all pyrometers 140 around the circumference of the billet 112. However, multiple feed temperature distributions can be measured at different locations on the circumference of the billet.

[0091] Figure 8AThe feed temperature distribution 160 shown is affected by heat generated during processing, for example at the distribution station 102 and the forming station 104, and by heat lost after such processing. The feed temperature distribution can be variable. For example, the heat from the distribution station 102 and the forming station 104 can vary slightly, and the amount of time elapsed between stages of processing the blank 112 (and therefore the heat lost) can also vary. Some variables are based on differences in processing between different blank types. For example, certain types of materials can be distributed at higher temperatures than other types. Other variables are based on cycle-cycle variations between a given type of blank. For example, the amount of time elapsed between processing steps can be different for each individual blank 112.

[0092] from Figure 8A It is evident that the temperature distribution along the feed axis may not be constant. That is, a temperature gradient may exist along the axis of the billet 112. In the depicted example, temperature peaks are present near the base portion 152 and shoulder portion 156 of the billet 112, and the temperature typically decreases in the axial direction from the shoulder portion 156 to the base portion 152. The precise location of any peak and the amount of the gradient can vary with the billet.

[0093] like Figure 8B As shown, the discharge axial temperature distribution 162 is higher than the feed temperature distribution 160 and is generally more uniform. In order to obtain the desired axial temperature distribution from the non-uniform feed axial temperature distribution, heat is applied non-uniformly along the length of the billet 112.

[0094] The regulating unit 108 can be operated by a control system configured to adjust the heat treatment applied to each individual billet 112 based on various characteristics such as billet size, material and additional properties, the shape to be formed of the billet and the input thermal conditions of the billet, in order to achieve the desired discharge temperature distribution.

[0095] Figure 9 An exemplary control unit for operating the adjustment unit 108 is shown. The control unit includes a control processor 170, a data storage 172, a working memory 174, and a plurality of input / output devices 176.

[0096] In the described embodiment, a virtualized PLC running on an industrial computer is used to implement the control components. A suitable industrial computer is the Beckhoff GmbH C6930PC, based on a multi-core Intel CPU and Microsoft Windows 10 operating system. The virtualized PLC can be implemented in the runtime of a Beckhoff TwinCAT 3 PLC. Alternatively or additionally, control can be implemented using a conventional (physical) PLC.

[0097] Input / output device 176 includes interfaces to multiple sensors and actuators. The sensors include a pyrometer 140 and one or more position sensors for determining the position of the billet 112. The position sensors can directly measure the position of the billet 112 or infer the position based on the position of the measuring mandrel 110.

[0098] The actuator includes a linear actuator for positioning the adjusting pin 128, a device for controlling the axial movement and rotation rate of the spindle 110, and a device for controlling the output power of the microwave generator unit 122.

[0099] The regulating unit can communicate with one or more other controllers via network connection 177. For example, the regulating unit can communicate with the management controller responsible for coordinating the overall operation of system 100. For example, the supervisory controller can define the sequence of blanks to be processed at the regulating unit 108.

[0100] refer to Figure 10 The data memory 172 contains instructions that are accessed by the control processor 170 during operation. These instructions include a basic heating routine definition 180 and adjustment parameters 182.

[0101] The basic heating distribution definition 180 provides the required thermal conditions for the blanks of various articles produced at the molding system 100 (referred to as SKU). That is, for each SKU, a heating distribution definition 180 is provided, which defines the thermal state of the blank 112 to be processed at the forming station 106.

[0102] For some SKUs, the basic heating distribution definition 180 can define both circumferential and axial heating distributions. For example, SKUs molded into shapes with elliptical or other non-circular cross-sections may require concentrating heat in areas subjected to maximum stretching.

[0103] In an exemplary embodiment, the heat distribution definition is characterized by the operations to be performed on the billet. For example, the heat distribution definition may define the baseline microwave output power, the position of the adjustment pins, and the linear feed rate of the billet 112 through the heating chamber 116. For SKUs requiring non-uniform circumferential heat distribution, the heat distribution definition may specify the positions of the adjustment pins 128-1, 128-2 in a specific synchronization with the rotation of the billet 112. Alternatively, such a heat distribution definition may specify the positioning of the adjustment pin 128-3 to position the peak microwave intensity as needed.

[0104] Alternatively, the heating distribution definition can be characterized based on the desired output temperature distribution, and the corresponding output power, pin position, and feed rate can be derived from this temperature output distribution.

[0105] Adjustment parameter 182 includes adjusting the basic heating distribution 180 based on operating conditions.

[0106] Adjustment parameters can include scalar adjustments corresponding to various billet characteristics. For example, for each possible color of billet, or for transparent billet, a scalar factor can be applied to increase the basic heating method by a specific amount. Such scalar adjustment can include proportionally increasing the microwave output power or decreasing the linear feed rate to increase the heat applied to the billet. Conversely, scalar adjustment can include proportionally decreasing the output power or increasing the linear feed rate to increase the heat applied to the billet.

[0107] The adjustment parameters may also include a function to correct heating based on the heat distribution of the billet 112 entering the heating chamber 116. For example, a nominal heat distribution can be stored, representing the input heat distribution corresponding to the basic heating distribution 180. The actual measured heat distribution can be compared with the nominal distribution, and the actual heating distribution can be increased or decreased to compensate for deviations from the nominal distribution. In some embodiments, the nominal profile may be different for different SKUs.

[0108] The data storage 172 may also contain a billet sequence definition 184. The billet sequence definition 184 reflects the sequence of billets 112 to be processed in the conditioning station 108, that is, the SKU sequence corresponding to the billets.

[0109] The billet 112 can be heated in multiple stages to produce the desired temperature distribution.

[0110] Figure 11-14 An exemplary multi-stage heating process 200 is shown for heating a blank 112 having a base portion 152, a body portion 154, a shoulder portion 156, and a neck portion 158.

[0111] In frame 202, mandrel 110 moves billet 112 through pyrometer 140 toward heating chamber 116. Pyrometer 140 is used to obtain the feed temperature distribution of the billet.

[0112] In box 204, a basic heating distribution is selected based on the type of billet 112 and the forming operation to be performed on the billet at forming station 106. The basic heating distribution is adjusted according to the feed temperature distribution. In this example, if the feed temperature distribution is higher than the nominal expected feed temperature distribution, the speed at which the billet 112 moves through the heating chamber 116 is increased, thereby reducing the heating duration. If the feed temperature distribution is lower than the nominal expected feed temperature distribution, the speed at which the billet 112 moves through the heating chamber 116 is reduced, thereby increasing the heating duration.

[0113] Additionally or optionally, if the feed temperature distribution is lower than the nominal expected distribution, the microwave output power can be increased or the adjusting pins 128-1 and 128-2 can be retracted to reduce microwave attenuation; if the feed temperature distribution is higher than the nominal expected distribution, the microwave output power can be decreased or the adjusting pins 128-1 and 128-2 can be extended to increase microwave attenuation.

[0114] For some SKUs, the adjustment pin 128 can be moved relative to the heating chamber to position the peak microwave intensity at the desired location, so that certain circumferential portions of the blank 112 are preferentially heated.

[0115] In frame 206, the entire billet 112 undergoes an initial heating stage. Figure 12 Details of the initial heating phase are shown.

[0116] In box 206-1, the microwave output power is set based on the adjusted heating distribution.

[0117] In frame 206-2, adjusting pins 128-1, 128-2, and 128-3 are positioned according to the adjusted heating distribution. Specifically, pins 128-1 and 128-2 extend into or retract from waveguide 124 to attenuate the microwaves specified by the heating distribution. Pin 128-3 extends or retracts to position the peak microwave intensity region within heating chamber 116 at the same location as the wall of blank 112.

[0118] In frame 206-3, the axial speed of the mandrel 110 moving the billet 112 is set based on an adjusted heating distribution. The axial speed determines the duration for which the billet 112 is within the heating chamber 116 and exposed to heat. The amount of heat input varies inversely with the speed and is proportional to the product of the microwave output power (attenuated by adjusting pins 128-1, 128-2) and the heating duration.

[0119] In frame 206-4, billet 112 advances through heating chamber 116.

[0120] exist Figure 15A An exemplary temperature distribution 300 of the blank 112 after initial heating is shown. The initial heating produces a generally uniform temperature distribution through the body portion 154 of the blank 112. Due to the larger mass of material in the base portion 152 and shoulder portion 156, the temperatures in the base portion 152 and shoulder portion 156 tend to be slightly lower. In the depicted example, the neck portion 158 is not heated or is heated only minimally because the neck portion 158 has threads for the container closure and is not stretched during forming at the forming station 106.

[0121] Typically, during forming at forming station 106, the shoulder portion 156 undergoes significant stretching, which requires relatively high temperatures.

[0122] Reference Figure 11 In frame 208, additional heat is applied to the shoulder portion 156. Details of the shoulder heating are in... Figure 13 As shown in the image.

[0123] In frame 208-1, mandrel 110 moves the billet to the shoulder heating position. The shoulder heating position is the location of the shoulder region 156 within the peak microwave intensity region. The shoulder heating position is defined by the geometry of the heating chamber 116 and the geometry of the billet 112, and can be defined as part of a basic heating distribution.

[0124] Set the microwave output power in frames 208-2 and 208-3 respectively, and position pins 128-1 and 128-2 to attenuate the microwaves according to the adjusted heating distribution.

[0125] In frame 208-4, heat is applied to shoulder region 156. The billet 112 remains stationary at the heated shoulder position for a period defined within an adjusted heat distribution; this time may be referred to as the homogenization period. During this period, heat is preferentially applied to shoulder region 156, causing the temperature of shoulder region 156 to rise relative to the rest of the billet 112.

[0126] Figure 15B An exemplary temperature distribution 300 of the billet 112 after shoulder heating is shown. As shown, shoulder heating tends to produce localized temperature peaks at the shoulder region 156.

[0127] like Figure 15B The abrupt temperature changes of the localized temperature peaks shown are generally undesirable because they can cause inconsistencies during subsequent forming operations, such as changes in wall thickness.

[0128] Refer again Figure 11 In box 210, additional heat is applied to smooth the temperature distribution near shoulder 156. Details of the temperature smoothing are shown in... Figure 14 As shown in the image.

[0129] In frame 210-1, the mandrel 110 moves to position the blank 112 at the shoulder heating position.

[0130] In box 210-2, the microwave output power is set based on the adjusted heating distribution.

[0131] In frame 210-3, adjusting pins 128-1, 128-2, and 128-3 are positioned according to the adjusted heating distribution to provide the desired attenuation and position the area of ​​peak microwave intensity within the heating chamber 116 at the same location as the wall of the blank 112.

[0132] In frame 210-4, the axial speed at which the mandrel 110 moves the blank 112 is based on the adjusted heating distribution setting.

[0133] In frame 210-5, billet 112 advances through heating chamber 116. Heat is applied only to the portion of billet 112 adjacent to shoulder 156.

[0134] Refer again Figure 11 In box 212, an additional heating step is applied to the entire billet 112. The heating at box 212 follows largely the same steps as those in box 206 above, except that the power and speed are set to incrementally heat the billet 112 to the desired temperature.

[0135] After the billet is heated, the mandrel 110 extracts the billet from the heating chamber 116 and transfers it to the forming station 106. Then, the mandrel 110 can pick up another billet and repeat the process 200 for subsequent billets.

[0136] Conveniently, each blank can be subjected to a unique heat treatment based on its SKU, associated material and physical properties, and feed temperature distribution. Therefore, the regulating unit 108 can provide precise heat conditioning to prepare various types of blanks for any of the possible forming operations. This unique heat treatment can be applied to blank types in any arbitrary order. The regulating unit 108 thus enables the system 108 to simultaneously produce multiple types of articles at different numerical proportions.

[0137] When describing elements of the invention or embodiments thereof, the articles “a,” “an,” “the,” and “the” are intended to indicate the presence of one or more elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that additional elements may be present besides those listed.

[0138] The term “including” includes any variations thereof, is intended to be open-ended, and means “including but not limited to” unless otherwise expressly indicated to the contrary.

[0139] When an "or" sign is used before the last item to give a list of possibilities or items, any one of the listed items or any suitable combination of two or more of the listed items can be selected and used.

[0140] The above embodiments are for illustrative purposes only. Modifications can be made, such as changes to the form, component arrangement, details, and operating sequence. The embodiments detailed herein are not intended to limit the invention. Rather, the invention is defined by the claims.

Claims

1. A method for heating a preform (112) for plastic molding, comprising: a) Receive a plurality of blanks (112) in sequence, the plurality of blanks (112) including different types of blanks, each type being used for molding in an associated molding process; b) For each blank (112) in the said sequence: i) Determine the heating requirements corresponding to the characteristics of the blank and the associated molding process; ii) Generate a microwave field having an intensity that defines a heating rate; iii) Determine the heating duration based on the heating requirements; iv) The billet (112) is moved forward through the microwave field at a certain speed, such that the billet is in the microwave field for a period of time equal to the heating duration, wherein the heating duration and the heating rate correspond to the heating requirement; In this process, for the blank (112) in the sequence, a circumferential temperature gradient is generated by moving the microwave reflector (128-3) to locate the region of peak microwave intensity relative to the blank (112) using the microwave field around the circumference of the blank (112).

2. The method according to claim 1, comprising: For each blank (112) in the sequence, the input temperature of the blank (112) is measured before heating, and the determination of the heating requirements includes adjusting the basic heating requirements based on the input temperature.

3. The method according to claim 2, wherein, The basic heating requirement based on the input temperature includes comparing the input temperature with the nominal temperature.

4. The method according to any one of claims 2 to 3, wherein, The input temperature includes the axial temperature distribution (160).

5. The method according to any one of claims 2 to 4, comprising: For each blank (112) in the sequence, the heating rate is adjusted based on the input temperature.

6. The method according to claim 5, wherein, Adjusting the heating rate includes adjusting the output power of the microwave generator (122).

7. The method according to claim 5 or 6, wherein, Adjusting the heating rate includes positioning the attenuation device (128) within the microwave field.

8. The method according to any one of claims 2 to 7, comprising: For each blank (112) in the sequence, the speed is selected based on the input temperature.

9. The method according to any one of claims 2 to 8, comprising: For the blank (112) in the sequence, the blank (112) is held in a position such that a portion of the blank (112) receives heat from the microwave field to heat the portion relative to the rest of the blank (112).

10. A preform heating device (120) for plastic molding, comprising: a) Heating chamber (116); b) A microwave generator (122) for transmitting microwaves into the heating chamber (116) via a waveguide (124); c) A billet conveying device for moving the billet (112) into and out of the heating chamber (116) along the heating axis (114). d) A controller operable to control the speed of the conveying device to limit the heating duration based on the heating requirements of the billet (112); and e) A microwave reflecting device (128-3) movable relative to the heating chamber (116) to control the position of the peak microwave intensity within the heating chamber (116).

11. The billet heating device (120) according to claim 10, comprising a microwave attenuation device (128) extendable into the waveguide (124) to control the microwave heating rate within the heating chamber (116).

12. The billet heating apparatus (120) according to claim 11, comprising a temperature measuring device (140) near the heating chamber (116) for measuring the input temperature of the billet (112) before the billet (112) enters the heating chamber (116).

13. The billet heating device (120) according to claim 12, wherein, The temperature measuring device includes multiple pyrometers.

14. The billet heating device (120) according to claim 12 or 13, wherein, The controller is operable to control the heating of the billet (112) based on the input temperature of the billet (112).

15. The billet heating device (120) according to claim 14, wherein, The controller is operable to control the heating of the billet (112) by setting the speed of the conveying device.

16. The billet heating device (120) according to claim 14 or 15, wherein, The controller is operable to control the heating of the billet (112) by adjusting the output power of the microwave generator (122).

17. The billet heating apparatus (120) according to any one of claims 14 to 16, wherein, The controller is operable to control the heating of the billet (112) by adjusting the position of the microwave attenuation device (128).

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