TECHNICAL FIELD

The present invention relates to stretch blow molding systems, and more particularly, to a proportional stretch blow molding system.

BACKGROUND OF THE INVENTION

Blow molding is a generally known process for molding a preform part into a desired product. The preform is in the general shape of a tube with an opening at one end for the introduction of pressurized gas, typically air; however, other gases may be used. One specific type of blow molding is stretch blow molding (SBM). In typical SBM applications, a valve block provides both low and high-pressure gas to expand the preform into a mold cavity. The mold cavity comprises the outer shape of the desired product. SBM can be used in a wide variety of applications; however, one of the most widely used applications is in the production of Polyethylene terephthalate (PET) products, such as drinking bottles. Typically, the SBM process uses a low-pressure fluid supply along with a stretch rod that is inserted into the preform to stretch the preform in a longitudinal direction and radially outward and then uses a high-pressure fluid supply to expand the preform into the mold cavity. The low-pressure and high- pressure fluid supplies can be controlled using blow-mold valves. The resulting product is generally hollow with an exterior shape conforming to the shape of the mold cavity. The gas in the preform is then exhausted through one or more exhaust valves. This process is repeated during each blow molding cycle.

FIG. 1 shows a prior art blow molding valve block assembly 100. The prior art blow molding valve block assembly 100 includes a valve block 102, a stretch rod 104, control chambers 106a-106d, operating chamber rings 108a-108d, valve pistons 110a- HOd and pilot valves 112. The stretch rod 104 extends vertically through the center of the central chamber 101 and out through the bottom of the valve block 102. The valve block 102 includes four sets of valves that are vertically stacked in the central chamber 101 and around the stretch rod 104. As can be appreciated, a pilot air supply is provided by the pilot valves 112 in order to control the position of each valve piston HOa-l lOd. As can be seen, the valve pistons 110a and 110b are shown in the open position with the valve pistons 110c and l lOd in the closed position. The valve block 102 also includes a number of inlet and outlet ports 114, 116, and 118. In use, the valve pistons are controlled using the various pilot valves 112 in order to direct the flow of pressurized gas through the valve block 102. In addition to the four valves shown, at least one additional valve is required to control the position of the stretch rod 104. The use of five valves can result in substantial energy losses as well as pressure losses during a typical molding cycle.

As can be appreciated, with the high speed of the molding cycle that is currently achievable, even small losses in energy during each molding cycle can result in substantial increases in operating costs. One of the major costs associated with stretch blow molding systems is the compressed gas used to expand the preform. The amount of gas required and the amount of energy required to pressurize the gas can be significant. Therefore, decreasing the amount of gas required during each molding cycle can substantially reduce the cost required to expand the preform.

Prior art systems, such as the prior art system in FIG. 1, have attempted to limit the loss of pressurized gas by forming valve blocks around the stretch rod. These prior art systems attempt to position the valves closer to the stretch rod and thus, the preform, in order to minimize the distance the pressurized gas is required to travel. While these prior art attempts of minimizing the pressurized gas required for the system have made some improvements, the prior art systems require separate valves for delivering low and high-pressure gas to the mold cavity and to control the longitudinal movement of the stretch rod. Further, the prior art systems are relatively inefficient because of the two discontinuous stages that take place. During the pre-blowing stage, the stretch rod is moved in the longitudinal direction while pressurizing the mold cavity using a low- pressure gas source. The low-pressure gas is supplied through a low-pressure blow- mold valve. At the end of the pre-blowing stage, the low-pressure valve and the stretch rod control valve for the stretch rod are closed. With the low-pressure valve and the stretch rod control valve closed, the high-pressure blow-mold valve can open, thereby supplying the mold cavity with a high-pressure gas supply. The low-pressure gas is generally provided at around 7 bar (102 psi) and the high-pressure gas is generally provided at around 40 bar (580 psi). Therefore, because of the large difference in pressures, it is important that the remaining valves of the system be closed prior to opening the high-pressure valve in order to avoid damaging the lower pressure equipment. As a result, a period of time is required between the pre-blowing stage and the blowing stage to ensure that the low-pressure valve is fully closed before opening the high-pressure valve. The transition from low-pressure to high-pressure may also cause a shock to the system due to the sudden increase in pressure, which may result in a higher percentage of defective products.

The discontinuous two-stage system results in longer production times and higher production costs. Not only do the prior art systems require numerous blow-mold valves, but the prior art systems also require numerous pressurized fluid supplies. The use of multiple pressurized fluid supplies results in a costly and time-consuming system. Further, the use of multiple pressurized fluid supplies results in an increased wall thickness of the molded device. Therefore, the prior art systems increase production costs because of the increased material demand.

The present invention overcomes these and other problems and an advance in the art is achieved. The present invention provides a proportional stretch blow molding system that utilizes a proportional valve to pressurize the mold cavity with pressurized gas. Further, in some embodiments, the present invention provides a proportional control valve for positioning the stretch rod. Advantageously, the present invention provides a proportional stretch blow molding system with the advantages of a pre- blowing and a blowing stage that operates with a continuous, generally uninterrupted profile. Further, the present invention can operate using a single pressurized fluid source for the mold cavity.

SUMMARY OF THE INVENTION

A proportional stretch blow molding system is provided according to an embodiment of the invention. The stretch blow molding system can include a cylinder and a piston movable within the cylinder that separates the cylinder into a first chamber and a second chamber. According to an embodiment of the invention, the proportional stretch blow molding system also includes a stretch rod coupled to the piston and extending from the cylinder. According to an embodiment of the invention, the proportional stretch blow molding system also includes a proportional blow-mold valve. The proportional blow-mold valve can include a first port adapted to receive a pressurized gas and a second port in fluid communication with the cylinder and selectively in fluid communication with the first port.

A method for stretch blow molding a preform in a mold cavity coupled to a proportional stretch blow molding system including a cylinder, a piston movable within the cylinder, and a stretch rod coupled to the cylinder is provided according to an embodiment of the invention. The method comprises steps of opening a proportional blow-mold valve to a first position, wherein the proportional blow-mold valve is in fluid communication with a pressurized gas supply and pressurizing the preform to a first pressure using pressurized gas supplied from the pressurized gas supply using the proportional blow-mold valve. According to an embodiment of the invention, the method also comprises steps of moving the stretch rod out of the cylinder to stretch the preform in a longitudinal direction and opening the proportional blow-mold valve to a second position, thereby pressurizing the preform to a second pressure using pressurized gas supplied from the pressurized gas supply using the proportional blow-mold valve, wherein the second pressure is greater than the first pressure.

ASPECTS

According to an aspect of the invention, a proportional stretch blow molding system comprises:

a cylinder;

a piston movable within the cylinder and separating the cylinder into a first

chamber and a second chamber;

a stretch rod coupled to the piston and extending from the cylinder;

a proportional blow-mold valve including:

a first port adapted to receive a pressurized gas; and

a second port in fluid communication with the cylinder and selectively in fluid communication with the first port.

Preferably, the proportional blow-mold valve further comprises a third port in fluid communication with an exhaust and selectively in fluid communication with the second port.

Preferably, the proportional stretch blow molding system further comprises a proportional stretch rod control valve including: a first port adapted to receive a pressurized fluid;

a second port in fluid communication with the first chamber of the cylinder and selectively in fluid communication with the first port; and a third port in fluid communication with the second chamber of the cylinder and selectively in fluid communication with the first port.

Preferably, the proportional stretch rod control valve further comprises:

a fourth port in fluid communication with an exhaust and selectively in fluid communication with the third port; and

a fifth port in fluid communication with an exhaust and selectively in fluid

communication with the second port.

Preferably, the proportional stretch blow molding system further comprises a position sensor including a first sensor portion coupled to the cylinder and a second sensor portion coupled to the piston.

Preferably, the proportional stretch blow molding system further comprises an electrical communication cable coupled to the position sensor and to a stretch rod control valve.

According to another aspect of the invention, a method for stretch blow molding a preform in a mold cavity coupled to a proportional stretch blow molding system including a cylinder, a piston movable within the cylinder, and a stretch rod coupled to the cylinder comprises steps of:

opening a proportional blow-mold valve to a first position, wherein the

proportional blow-mold valve is in fluid communication with a pressurized gas supply;

pressurizing the preform to a first pressure using pressurized gas supplied from the pressurized gas supply through the proportional blow-mold valve; moving the stretch rod out of the cylinder to stretch the preform in a longitudinal direction; and

opening the proportional blow-mold valve to a second position, thereby

pressurizing the preform to a second pressure using pressurized gas supplied from the pressurized gas supply through the proportional blow- mold valve, wherein the second pressure is greater than the first pressure. Preferably, the step of moving the stretch rod is performed substantially simultaneously with the step of pressurizing the preform to the first pressure.

Preferably, the step of moving the stretch rod comprises steps of:

actuating a stretch rod control valve to a first actuated position;

pressurizing a first chamber of the cylinder; and

exhausting a second chamber of the cylinder.

Preferably, the step of opening the proportional blow-mold valve to the second position is performed based on a stretch rod position.

Preferably, the step of opening the proportional blow-mold valve to the second position is performed based on a predetermined amount of time.

Preferably, the method further comprises steps of:

actuating the proportional blow-mold valve to a third position; and

exhausting the preform through the proportional blow-mold valve.

Preferably, the method further comprises steps of:

actuating a stretch rod control valve to a second actuated position;

exhausting a first chamber of the cylinder; and

pressurizing a second chamber of the cylinder.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a prior art stretch blow molding valve block.

FIG. 2 shows a stretch blow molding system according to an embodiment of the invention.

FIG. 3 shows a cross-sectional view of the stretch blow molding system according to an embodiment of the invention.

FIG. 4a shows a graph of stretch rod position versus time according to an embodiment of the invention.

FIG. 4b shows a graph of pressure versus time according to an embodiment of the invention. DETAILED DESCRIPTION OF THE INVENTION

FIGS. 2 - 4b and the following description depict specific examples to teach those skilled in the art how to make and use the best mode of the invention. For the purpose of teaching inventive principles, some conventional aspects have been simplified or omitted. Those skilled in the art will appreciate variations from these examples that fall within the scope of the invention. Those skilled in the art will appreciate that the features described below can be combined in various ways to form multiple variations of the invention. As a result, the invention is not limited to the specific examples described below, but only by the claims and their equivalents.

FIG. 2 shows a proportional stretch blow molding system 200 according to an embodiment of the invention. The proportional stretch blow molding system 200 can include a cylinder 201, a stretch rod 202, a stretch rod control valve 203, and a blow- mold valve 204. While the stretch rod control valve 203 and the blow-mold valve 204 are shown as being coupled to the cylinder 201, in other embodiments, the valves 203, 204 may be separated from the cylinder 201. According to an embodiment of the invention, the cylinder 201 is adapted to form a substantially fluid-tight seal with a mold cavity 205. According to another embodiment of the invention, the cylinder 201 is adapted to form a substantially fluid-tight seal with the preform 211, which is positioned partially in the mold cavity 205 and in fluid communication with the blow-mold valve

204 in FIG. 2. A portion of the preform 211 is shown outside of the mold cavity 205 and coupled to the cylinder 201. In other embodiments, the cylinder 201 may couple to the mold cavity 205 and the entire preform 211 may be positioned within the mold cavity 205. It should be appreciated that the mold cavity 205 may be provided as a separate component provided by an end user, for example and may not form part of the proportional stretch blow molding system 200. Therefore, the proportional stretch blow molding system 200 may be adapted to couple numerous different types of mold cavities

205 and performs 211.

According to an embodiment of the invention, the stretch rod control valve 203 comprises a proportional valve. According to an embodiment of the invention, the blow-mold valve 204 comprises a proportional valve. Proportional valves are generally known in the art and can operate to open a port of the valve at virtually any point between fully open and fully closed. Therefore, rather than simple on/off operation as in traditional valves, proportional valves are capable of maintaining an actuation state between fully on and fully off. Because of the simple on/off operation of traditional valves, prior art stretch blow molding systems required two or more pressurized fluid sources and associated blow-mold valves. In contrast, the proportional stretch blow molding system 200 of the present invention can operate with a single blow-mold valve 204 and a single pressurized gas source to pressurize the preform 211 and mold cavity 205. This is because a valve port in a proportional valve may be partially opened, for example. This can be advantageous in situations where the valve is provided with a high input pressure and the desired output pressure is a pressure less than the input pressure. In such situations, the proportional valve can be partially opened, thereby restricting the fluid flow through the proportional valve. An example of a proportional valve is provided in PCT Publication WO/2009/018843, which is assigned to the present applicant, and provides a proportional spool valve. Another example of a suitable proportional valve is the proportional valve sold by the present applicant under the name "VP60 PROPORTIONAL VALVE." The VP60 PROPORTIONAL VALVE provides a high speed, 5/3 valve with low friction and little overlap around the mid-position thereby requiring little movement. It should be appreciated that the present invention is not limited to proportional spool valves and other proportional valves may be utilized without departing from the scope of the present invention. The proportional valves used for the stretch rod control valve 203 and the blow-mold valve 204 may comprise fluid actuated valves or electrically actuated valves. According to an embodiment of the invention, when the valves 203, 204 comprise electrically actuated valves, the size of a fluid communication path created by the valve can be determined by assigning an electrical set point signal by an external processing system or PLC as described below, which then generates a proportional flow through the blow-mold valve 204. Therefore, different electrical set point signals can be assigned for various desired fluid communication path openings corresponding to a desired output pressure for a specific input pressure. The position of the valve spool (when a proportional spool valve is used) can be adjusted based on a position sensor coupled to the cylinder 201 (described below), which can comprise a feedback loop to a valve controller (not shown) as is generally known in the art.

According to an embodiment of the invention, the stretch rod control valve 203 is adapted to control movement of the stretch rod 202 using pressurized fluid provided from a pressurized fluid source 363 (See FIG. 3) via a fluid supply conduit 206. The pressurized fluid may comprise a liquid or a gas. For example, the stretch rod control valve 203 may be suitable for use as a pneumatic or a hydraulic valve. While the pressurized fluid provided to the stretch rod control valve 203 may be at any suitable pressure, according to an embodiment of the invention, the pressurized fluid source 363 is at a pressure between approximately 10 and approximately 16 bar (145 and 232 psi). However, because the stretch rod control valve 203 comprises a proportional valve in some embodiments, the pressure of the fluid delivered to the cylinder 201 may be at a pressure less than the pressurized fluid source 363. In other embodiments, the stretch rod control valve 203 may not comprise a proportional valve, but rather comprise a traditional valve, in which case, the pressure supplied to the cylinder 201 will comprise approximately the same pressure supplied to the stretch rod control valve 203.

According to an embodiment of the invention, the blow-mold valve 204 is adapted to control a pressurized gas supply to/from the mold cavity 205. While the pressurized gas is typically air, other gases may be desired depending on the particular application. In the embodiment shown in FIG. 2, the pressurized gas is received by the pressure control valve 204 from a high-pressure gas supply 364 (See FIG. 3) via a pressurized fluid supply conduit 207. According to an embodiment of the invention, the pressurized gas supplied to the blow-mold valve 204 may be at a pressure around 40 bar (580 psi), for example. However, other pressures are certainly contemplated by the present invention. Based on the blow-mold valve's position, the pressurized gas can be provided to the mold cavity 205 through an opening 208 defined between the preform 211 and the stretch rod 202. The conduits or other fluid communication paths between the valves 203, 204 and the cylinder 201 are not shown in FIG. 2 in order to minimize the complexity of the drawing; however, they are shown schematically in FIG. 3. As can be appreciated, because the blow-mold valve 204 comprises a proportional valve, the fluid communication path formed in the valve 204 for providing the pressurized gas to the mold cavity 205 may be restricted, resulting in a decreased pressure being provided to the mold cavity 205.

According to an embodiment of the invention, the stretch rod control valve 203 and the pressure control valve 204 may be in electrical communication with one another. In the embodiment shown, the two valves 203, 204 are in electrical communication via cable 209; however, the two valves 203, 204 could communicate via a wireless communication interface. Further shown in FIG. 2 is a cable 210, which provides an electrical communication interface between the stretch rod control valve 203 and a position sensor 330a-b (See FIG. 3) provided in the cylinder 201. The position sensor 330a-b may provide a signal to the stretch rod control valve 203 indicating a position of the stretch rod 202 relative to the cylinder 201, for example. Additionally shown in FIG. 2 is a cable 212. The cable 212 can provide an electrical communication interface between the valve 204 and a valve controller, such as an external processing system (not shown). According to an embodiment of the invention, the cable 212 may also provide power to the valves 203, 204 if the valves are electrically actuated, such as solenoid-controlled valves. The processing system may comprise a microprocessor, a CPU, or some other processing device. The processing system may be distributed among multiple devices. The processing system may include an internal and/or external storage system. The processing system may include various valve set points and stretch rod position set points to accommodate various blow- molding applications. The processing system may include a user interface such as a monitor, keyboard, and mouse, etc., as is well known in the art. The processing system may allow a user or operator to control the valves 203, 204. Alternatively, each of the valves 203, 204 may include a programmable logic controller (PLC) (not shown) and the cable 212 can be provided to supply power to the valves 203, 204. The PLC may be provided to control the valve's solenoid and/or provide feedback to the valve's controller. In some embodiments, the use of a PLC may reduce the response time of the valves 203, 204 thereby providing increased accuracy. The PLC may provide an output signal to a user or operator via the cable 212.

FIG. 3 shows a cross-sectional view of the proportional stretch blow molding system 200 according to an embodiment of the invention. In FIG. 3, the valves 203, 204 are shown schematically. Further, it should be appreciated that the electrical cabling 209, 210, 212 are not shown in FIG. 3 in order to simplify the complexity of the drawing.

According to the embodiment of the invention provided in FIG. 3, the stretch rod control valve 203 is in fluid communication with a first port 321 and a second port 322 formed in the cylinder 201. According to an embodiment of the invention, a piston 302 separates the cylinder 201 into a first chamber 331 and a second chamber 332. According to an embodiment of the invention, the piston 302 is coupled to the stretch rod 202. The piston 302 and stretch rod 202 may be movable within the cylinder 201. The piston 302 may include a sealing member 303, which can provide a substantially fluid-tight seal between the piston 302 and the cylinder 201. Further, the cylinder 201 can include additional sealing members 350, 351, 352, which form a substantially fluid- tight seal with the stretch rod 202. The sealing members 303 and 350-352 can prevent pressurized fluid from passing between chambers 331, 332 or from the second chamber 332 to the mold cavity 205. According to an embodiment of the invention, the first port 321 is in fluid communication with the first chamber 331 and the second port 322 is in fluid communication with the second chamber 332. According to an embodiment of the invention, when pressurized fluid is provided to the first port 321, the first chamber 331 is pressurized thereby actuating the piston 302 and thus, the stretch rod 202 in a first direction. Conversely, when pressurized fluid is provided to the second port 322, the second chamber 332 is pressurized, which actuates the piston 302 and thus, the stretch rod 202 in a second direction, substantially opposite the first direction.

Also provided in FIG. 3, is the position sensor 330, which comprises a first sensor portion 330a coupled to the cylinder housing 201 and a second sensor portion 330b coupled to the piston 302. Although not shown in FIG. 3, the first sensor portion 330a may be in communication with the stretch rod control valve 203 via the cable 210. According to one embodiment of the invention, the first portion of the position sensor 330 may comprise one or more magnetic sensors 330a while the second portion comprises a magnet 330b. One example of a position sensor that may be used with the present invention is disclosed in United States Patent 7,263,781, which is assigned to the applicants of the present invention. However, it should be appreciated that other position sensors may certainly be utilized with the present invention without departing from the scope of the invention.

As discussed briefly above, according to an embodiment of the invention, the stretch rod control valve 203 comprises a proportional valve. However, the stretch rod control valve 203 does not have to comprise a proportional valve and other types of valves may be used. In the embodiment provided in FIG. 3, the stretch rod control valve 203 comprises a 5/3 proportional valve. The stretch rod control valve 203 may comprise a 5/3 proportional spool valve, for example. According to an embodiment of the invention, the stretch rod control valve 203 comprises a solenoid- actuated proportional spool valve. A spring 365' or other biasing member may be provided to de-actuate the valve 203 or bring the valve 203 to a default position. In other embodiments, a second solenoid (not shown) may be provided. According to an embodiment of the invention, in a de-actuated position, the stretch rod control valve 203 is closed. According to an embodiment of the invention, in the de-actuated position, pressurized fluid is not provided to or exhausted from the first or second chambers 331, 332.

According to an embodiment of the invention, a solenoid 365 may be used to open the stretch rod control valve 203 towards one or more actuated positions. Further, in embodiments where the stretch rod control valve 203 comprises a proportional valve, the solenoid 365 may be used to actuate the valve 203 to positions between a de- actuated position and a fully actuated position based on the set point signal provided to the solenoid 365. As mentioned briefly above, the set point signal may be provided by the processing system according to the desired operating parameters. According to an embodiment of the invention, when the solenoid 365 actuates the stretch rod control valve 203 to a first actuated position, pressurized fluid is provided from a first port 203a to a second port 203b. In the embodiment shown, the first port 203a is adapted to receive a pressurized fluid. For example, the first port 203a is shown in fluid communication with the pressurized fluid source 363 while the second port 203b is in fluid communication with the first port 321 formed in the cylinder 201 via fluid pathway 341. The first port 203a is selectively in fluid communication with the second port 203b when the stretch rod control valve 203 is opened towards the first actuated position. Further, pressurized fluid can be exhausted from the third port 203c to the fourth port 203d. Therefore, as the stretch rod control valve 203 is actuated towards the first actuated position, pressurized fluid is supplied from the pressurized fluid source 363 to the first chamber 331 and exhausted from the second chamber 332. It should be appreciated that when the stretch rod control valve is partially opened and between the de-actuated position and the first actuated position, the fluid communication path between the first port 203a and the second port 203b is only partially opened. Thus, less than the full pressure provided to the first port 203a of the stretch rod control valve 203 from the pressurized fluid source 363 is delivered to the second port 230b of the stretch rod control valve 203. Additionally, prior to fully reaching the first actuated position, the fluid communication path between the third port 203c and the fourth port 203d is not fully opened and therefore, the fluid exhausted from the second chamber 332 is limited. Advantageously, if only a small movement of the stretch rod 202 is desired, the stretch rod control valve 203 can be actuated to a position between the de-actuated position and the first actuated position and only partially opened.

According to an embodiment of the invention, when the stretch rod control valve

203 is actuated and opened towards a second actuated position, the first port 203a is brought into fluid communication with the third port 203c and the second port 203b is brought into fluid communication with the fifth port 203e, which comprises an exhaust. Therefore, when the stretch rod control valve is opened towards the second actuated position, the stretch rod control valve 203 provides pressurized fluid to the second chamber 332 and exhausts the first chamber 331 to move the piston 302 and thus, the stretch rod 202 in a second longitudinal direction. It should be appreciated that less than the full pressure provided to the first port 203a is delivered to the third port 203c prior to the stretch rod control valve 203 fully reaching the second actuated position.

Also shown schematically in FIG. 3 is the blow-mold valve 204. As briefly discussed above, according to an embodiment of the invention, the blow-mold valve 204 comprises a proportional valve. According to the embodiment shown, the blow-mold valve 204 comprises a solenoid-actuated proportional valve with a solenoid 366; however, in other embodiments, the blow-mold valve 204 could be fluid actuated. In the embodiment shown, a spring 366' or other biasing member is provided to bias the blow-mold valve 204 to a de-actuated or default position. However, in other embodiments, a second solenoid (not shown) could be provided. The blow-mold valve

204 may comprise a proportional spool valve, for example. According to the embodiment shown, the blow-mold valve 204 comprises a 3/3 -way proportional spool valve. In embodiments where the blow-mold valve 204 comprises a 3/3-way valve, a separate exhaust valve is not required and the blow-mold valve 204 can pressurize the mold cavity 205 as well as exhaust the mold cavity 205. However, in other embodiments, a separate exhaust valve may be provided to exhaust the mold cavity 205 at the end of a molding cycle. Further, it should be understood that the blow-mold valve 204 is not limited to a 3/3 valve, but rather other valves may be utilized such as a 3/2, a 2/2, etc. According to an embodiment of the invention, when the blow-mold valve 204 is in a de-actuated position, the valve is closed and pressurized gas is not provided to the mold cavity 205 or exhausted from the mold cavity 205. In other embodiments, such as for example, when the blow-mold valve 205 comprises a 3/2-way valve, a second port 204b may be open to exhaust when the blow-mold valve 204 is in a de-actuated position. According to an embodiment of the invention, when the blow-mold valve 204 is actuated towards a first actuated position using the solenoid 366, for example, a first port 204a is in fluid communication with the second port 204b, thereby providing pressurized gas to a third port 323 formed in the cylinder 202. The third port 323 formed in the cylinder 202 may be in fluid communication with a preform 211 or mold cavity 205 when the cylinder 201 is coupled to the preform 211 or mold cavity 205. Therefore, when the blow-mold valve 204 is in a first actuated position, the pressurized gas provided to the first port 204a from the pressurized gas source 364 is provided to the mold cavity 205. It should be appreciated that prior to the blow-mold valve 204 fully reaching the first actuated position, the pressure of the gas provided to the second port 204b and thus, the mold cavity 205 is less than the pressure supplied to the first port 204a. This is because the fluid communication path between the first port 204a and the second port 204b is only partially opened, thereby restricting flow through the valve 204 and creating a pressure drop. The amount of the pressure drop may depend on the precise position of the blow-mold valve 204 in combination with the pressure of the pressurized gas source 364. The position of the valve 204 can be determined based on the set point signal received by the solenoid 366, for example. The set point signal may be received from a controller (not shown) or a PLC (not shown) associated with the blow-mold valve 204, as discussed above.

According to an embodiment of the invention, when the blow-mold valve 204 is opened towards a second actuated position, the third port 323 and thus, the mold cavity 205 is exhausted through the second port 204b and the third port 204c. It should be appreciated that when the blow-mold valve 204 is between the de-actuated position and the second position, the fluid communication path between the second port 204b and the third port 204c may not be fully open. Therefore, the rate at which the mold cavity 205 can exhaust will be less than when the blow-mold valve 204 has fully reached the second actuated position. As discussed above, the present invention can advantageously replace the pre- blowing stage and the blowing stage of typical stretch blow molding systems with a substantially continuous stage. The substantially continuous stage of the present invention utilizes a single pressurized gas source 364 for pressurizing the preform 211 and mold cavity 205 at a low-pressure and at a high-pressure.

According to an embodiment of the invention, the stretch rod control valve 203 and the blow-mold valve 204 can be controlled such that the blow-mold valve 204 supplies pressurized gas to the mold cavity 205, and thus, the preform 211 based on a position of the stretch rod 202. Starting with the stretch rod 202 in a fully retracted position, the piston 302 abuts a stopper 340 that is located in the first chamber 331. The stopper 340 restricts the movement of the piston 302 and thus, the stretch rod 202. According to an embodiment of the invention, to start a mold cycle, the stretch rod control valve 203 and the blow-mold valve 204 are actuated and opened towards their first actuated positions. According to one embodiment of the invention, the stretch rod control valve 203 and the blow-mold valve 204 are actuated at substantially the same time. According to an embodiment of the invention, if the stretch rod control valve 203 comprises a proportional valve, the stretch rod control valve 203 may be partially opened and set to a position between the de-actuated position and the first actuated position. In other embodiments where the stretch rod control valve 203 comprises a traditional control valve without the capability of operating as a proportional valve, the stretch rod control valve 203 may be actuated fully to the first actuated position. As discussed above, when the stretch rod control valve 203 is actuated towards the first actuated position, the first chamber 331 is pressurized while the second chamber 332 is exhausted, thereby causing the piston 302 and the stretch rod 202 to move in the first longitudinal direction, i.e., out of the cylinder 201.

According to an embodiment of the invention, the blow-mold valve 204 may be opened to a first position and set to the first position, which is between the de-actuated position and the first fully actuated position. As a result, the fluid communication path between the first port 204a and the second port 204b partially opens. For example, the valve 204 may open a predetermined amount such that a first pressure is supplied to the preform 211 from the pressurized gas source 364. According to an embodiment of the invention, the first pressure supplied to the preform 211 is less than the pressure of the pressurized gas source 364. For example, with an input pressure of approximately 40 bar (580 psi) provided at the first port 204a by the pressurized fluid source 364, the first pressure at the second port 204b is approximately 7 bar (102 psi). The reduction in pressure may be due to a pressure drop created by the partially opened blow-mold valve 204. According to an embodiment of the invention, the blow-mold valve 204 can remain in the first position until the piston 302 and thus, the stretch rod 202 reaches a predetermined position. The predetermined position may depend on the various set points provided by the processing system or user, which may vary depending on the particular blow molding application.

According to an embodiment of the invention, once the piston 302 reaches a predetermined position as detected by the position sensors 330a-b, the stretch rod control valve 203 may be actuated to the de-actuated position. Alternatively, the stretch rod control valve 203 may be actuated towards the second actuated position to partially exhaust the first chamber 331 and pressurize the second chamber 332 in order to stop movement of the stretch rod 202 and maintain its position. Substantially simultaneously, the blow-mold valve 204 can open to a second position. According to an embodiment of the invention, the second position may comprise the first fully actuated position. In other embodiments, the second position may be between the first position and the first fully actuated position (fully open position). In the second position, the fluid communication path between the first port 204a and the second port 204b is opened allowing an increased fluid flow through the valve 204. According to an embodiment of the invention, once the blow-mold valve 204 reaches the second position, the second port 204b is provided with a second pressure. Therefore, when the second port 204b is in fluid communication with the mold cavity, the mold cavity 205 and thus, the preform 211 are pressurized to the second pressure. According to an embodiment of the invention, the second pressure is greater than the first pressure. For example, the first pressure may be approximately 7 bar (102 psi) while the second pressure is approximately 40 bar (580 psi). In other embodiments, if the second position of the blow-mold valve 204 is not the first fully actuated position, the second pressure may be less than 40 bar, for example. Therefore, the first and second pressures correspond to the pre-blowing and blowing stage pressures of prior art blow molding systems. According to an embodiment of the invention, the transition of the blow-mold valve 204 from the first position to the second position provides substantially continuous fluid flow to the mold cavity 205. Advantageously, the pressure profile is substantially continuous.

While the embodiment disclosed in FIG. 3 includes the position sensor 330, in other embodiments, the position sensor 330 may be omitted, and the blow-mold valve 204 may be fully actuated to the first actuated position, thereby pressurizing the preform 211 to 40 bar (580 psi) after a predetermined amount of time rather than a predetermined piston position. Therefore, the position of the piston 302 and stretch rod 202 can be determined as a function of time during an initial calibration of the blow molding system 200, for example.

According to an embodiment of the invention, when the blow-mold valve 204 is actuated to the second position, the stretch rod control valve 203 may be de-actuated such that the stretch rod 202 and piston 302 stop moving in the longitudinal direction and maintain a substantially constant position. Maintaining a constant piston position may require the stretch rod control valve 203 to be opened towards the second actuated position in order to exhaust some of the pressure in the first chamber 331 in order to obtain an equilibrium position.

According to an embodiment of the invention, after the molding cycle is complete, the stretch rod control valve 203 can be actuated to towards the second fully actuated positions. Further, the blow-mold valve 204 can be actuated to a third position, which is towards the second fully actuated position. As a result, the second chamber 332 is pressurized and the first chamber 331 is exhausted causing the stretch rod 202 and the piston 302 to move in the second direction back into the cylinder 201. Further, the mold cavity 205 and the newly molded product can be exhausted through the blow- mold valve 204 or through a separate exhaust valve (not shown).

FIGS. 4a & 4b show position and pressure profiles for the blow molding system 200 according to an embodiment of the invention. As shown in FIG. 4a, the piston 302 and stretch rod 202 start at a retracted position and increase to a maximum position. As shown in FIG. 4b, as the piston 302 and stretch rod 202 are moving towards their maximum position, the pressure provided to the preform 211 substantially simultaneously increases to approximately 7 bar (102 psi). Once the piston 302 and stretch rod 202 reach a predetermined position, the pressure supplied to the preform 211 rapidly increases to approximately 40 bar (580 psi). The pressure remains at approximately 40 bar (580 psi) for a predetermined amount of time. After a predetermined amount of time, the piston 302 and stretch rod 202 return to their original positions while the preform 211 and mold cavity 205 are exhausted.

The proportional stretch blow molding system 200 as described above can advantageously reduce the time and costs associated with stretch blow molding. The present invention can eliminate the need for two separate pressurized gas sources to pressurize the preform and mold cavity by utilizing a proportional blow-mold valve 204 that can reduce the pressure supplied to the preform and mold cavity. Further, in some embodiments, the proportional stretch blow molding system 200 comprises a proportional stretch rod control valve 203 that can control the longitudinal movement of the stretch rod 202. Advantageously, in order to adapt to various sized final products, the stretch rod position set point can simply be adjusted.

The detailed descriptions of the above embodiments are not exhaustive descriptions of all embodiments contemplated by the inventors to be within the scope of the invention. Indeed, persons skilled in the art will recognize that certain elements of the above-described embodiments may variously be combined or eliminated to create further embodiments, and such further embodiments fall within the scope and teachings of the invention. It will also be apparent to those of ordinary skill in the art that the above-described embodiments may be combined in whole or in part to create additional embodiments within the scope and teachings of the invention.

Thus, although specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize. The teachings provided herein can be applied to other blow molding systems, and not just to the embodiments described above and shown in the accompanying figures. Accordingly, the scope of the invention should be determined from the following claims.