Patent Publication Number: US-9889581-B2

Title: Tool temperature control

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a 35 U.S.C. § 371 US National Phase application of International Patent Application PCT/GB2012/052776 having an International Filing Date of Nov. 8, 2012, which claims priority to GB application GB1119425.5 filed on Nov. 10, 2011, which applications are incorporated herein by reference in their entireties and from which priority is hereby claimed under 35 U.S.C. § 120. 
     BACKGROUND 
     The present invention is concerned with a tool element. More specifically, the present invention is concerned with a moulding tool or an element for a moulding tool having temperature control for moulding large, slow-to-cure workpieces. 
     As discussed in the applicant&#39;s prior published international patent application, WO2011/048365, it is known to provide a tool having a plurality of zones which are independently controlled in order to achieve the desired properties of the resulting moulded workpiece. 
     Known mould tools having temperature control are required to be dynamic—that is to increase and decrease the temperature of the tool as quickly as possible to respond to the tool control system (which may monitor the properties of the workpiece material). Being dynamic means that the tools can more accurately control the curing process. 
     Such systems require a source of pressurised fluid either from a pressurised tank or a compressor. Provision of a pressurised fluid allows an increased amount of energy to be transferred to and from the tool (depending on whether the user is heating or cooling the tool surface). In addition, the increased fluid velocity that compressed or pressurised cooling air provides increases the heat transfer coefficient between the fluid and the tool control surface. In certain applications, responsiveness is not a key factor in moulding. For example, when large thick structures such as wind turbine blades are moulded, curing occurs over a long period of time and is generally predictable. Tools for moulding articles of this nature do not need to be dynamic as the overall curing time is far longer than the heating or cooling time. Under these circumstances, efficiency is more important. 
     A further problem with the prior art is that compressed air lines need to be router throughout the mould tool. This is costly and complex. It is an object of the present invention to provide a tool element temperature control system which is better suited to large, slow curing workpieces. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An example tool element assembly in accordance with the present invention will now be described with reference to the accompanying figures in which:— 
         FIG. 1 a    is a side section schematic view of a first tool element assembly in accordance with the present invention; 
         FIG. 1 b    is a side section schematic view of the tool element assembly of  FIG. 1 a   ;  FIG. 2 a    is a side section schematic view of a second tool element assembly in accordance with the present invention; 
         FIG. 2 b    is a side section schematic view of a third tool element assembly in accordance with the present invention; 
         FIG. 3  is a side section schematic view of a fourth tool element assembly in accordance with the present invention; 
         FIG. 4  is a side section schematic view of a fifth schematic view of a fourth tool element assembly in accordance with the present invention; 
         FIG. 5  is a side section schematic view of a sixth tool element assembly in accordance with the present invention; and, 
         FIG. 6  is a side section schematic view of a seventh tool element assembly in accordance with the present invention 
     
    
    
     DETAILED DESCRIPTION 
     According to a first aspect of the present invention, there is provided a tool element assembly comprising a tool element having a tool surface, and a control surface opposite the tool surface, a thermal control structure defining a fluid chamber partially bounded by the control surface, the thermal control structure having a fluid inlet and a fluid heater, in which the fluid inlet is open to atmosphere in use to admit ambient pressure air into the fluid chamber to be selectively heated by the fluid heater. 
     By using ambient pressure air, a slower increase and decrease in temperature results (depending on whether used as heating or cooling) and, as such, the system is made less dynamic. Efficiency is increased as a result, because of the lack of air compression. Because the air within the chamber is near atmospheric pressure, the pressure difference between the inside and outside of the chamber is not significant, and therefore less warm gas is exhausted (reducing the energy loss, and the need to route excess exhaust gas away for safety reasons). 
     The fluid chamber tends to hold a set volume of air at a fixed temperature. As thermal energy is conducted to the mould tool, more energy is gradually added via the heating element. The fluid chamber is thermostatically controlled in order to provide a consistent temperature across the tool element. This means that less energy is used in heating any pressurised air fed into the chamber, as with the prior art. Preferably, the air heater is positioned proximate the fluid inlet and inside the fluid chamber. More preferably, the inlet may be positioned below the control surface in use such that the fluid heated by the air heater is thermally convected to the control surface. Under these circumstances, a compressed air source or indeed any kind of fluid pump is not required as the more buoyant hot air will rise towards the control surface (the air “self-pumps”). As heat is transferred to the tool, the cool layer proximate the surface will then fall to be reheated by the heating element. In this way a convection cell is build up within the fluid chamber. Optionally, an air pump may be positioned proximate the inlet. This pump may draw ambient air into the chamber thus increasing the pressure and velocity of the air therein. This helps to provide an increased level of heating to the control surface should it be required. 
     The air pump may be reversible to exhaust air from the outlet to the fluid chamber, for example if cooling is required. 
     According to a second aspect of the invention there is provided a tool element assembly comprising: 
     a tool element having a tool surface, and a control surface opposite the tool surface, 
     a thermal control structure defining a fluid chamber partially bounded by the control surface, the thermal control structure having a fluid heater having an inlet region, a heating region and an outlet region, 
     in which the fluid heater is positioned within the fluid chamber to form a convection cell such that fluid:
         enters the fluid heater at the inlet region,   is heated at the heating region,   is convected to the control surface from the outlet region, and,   is recirculated to the inlet region from the control surface.       

     Advantageously, providing recirculation using fluid convection makes the system inherently more efficient. Although this generally decreases response time, this type of system is ideal for large, slow to cure workpieces as discussed above. 
     Preferably the fluid chamber comprises a fluid inlet open to atmosphere in use to admit ambient pressure air into the fluid chamber to be selectively heated by the fluid heater. 
     The inlet may be below the control surface in use such that fluid heated by the fluid heater is thermally convected to the control surface. An air pump may be provided proximate the fluid chamber in order to encourage recirculation within the convection cell, which air pump may be arranged to entrain ambient pressure air into the fluid chamber to increase chamber pressure if required. Preferably, the air pump is reversible to exhaust air from the fluid chamber, such that the fluid inlet can become a fluid outlet. 
     The air heater may be positioned between the inlet and the pump, which means the pump (which may be a fan) draws air through the heater. 
     Preferably, the fluid chamber tapers outwardly towards the control surface. This not only means that a small inlet can be used to serve a large surface area, but it also means that the outward tapering prevents the side of adjacent fluid chambers from contacting each other and influencing each others temperature. It also means that thermal energy is easily conducted from the chamber walls, which is advantageous should the tool be in the cooling cycle. 
     According to a third aspect of the invention there is provided a method of manufacturing a moulded workpiece comprising the steps of: 
     providing a tool element having a tool surface and a control surface opposite the tool surface, 
     providing a thermal control structure defining a fluid chamber partially bounded by the control surface, the thermal control structure having a fluid inlet open to ambient air, 
     providing a fluid heater, and, 
     heating the control surface by drawing ambient air into the fluid chamber and heating the ambient air with the air heater. 
     The method of manufacturing according to the third aspect may include the steps of: providing an air pump proximate the fluid chamber, and, 
     pumping ambient air into the chamber. According to a fourth aspect of the invention there is provided a method of manufacturing a moulded workpiece comprising the steps of: 
     providing a tool element having a tool surface and a control surface opposite the tool surface, 
     providing a thermal control structure defining a fluid chamber partially bounded by the control surface, 
     providing a fluid heater, and, 
     establishing, a convection cell within the fluid chamber to heat air with the fluid heater, convect the heated air to the control surface, and return the convected air to the heater for re-heating. 
     The method of manufacturing according to the fourth aspect may include the steps of: providing an air pump proximate the fluid chamber, and, 
     driving the convection cell with the pump. 
     Turning to  FIGS. 1 a  and 1 b   , there is provided a tool element assembly  10  comprising a tool element  12  defining a tool surface  14  on a first side thereof, and a control surface  16  on a second side thereof. The tool surface  14  is shaped to the profile of the workpiece (not shown). The tool element  12  is square in profile so as to be tessellated with similar elements. A support beam  18  extends from the centre of each side of the tool element  12 , the beams extending towards an inlet region  20 . A side panel  22  is connected to each of the support beams  18  such as to form a fluid chamber  24 , bordered at its top surface by the control surface  16 . The side panels  22  converge at the inlet region  20  in order to form an inlet orifice  26 . 
     A heating element  28  is provided, above the inlet orifice  26  within the fluid chamber  24 . The heating element  28  is powered by an electricity supply  30  which is selectively controlled by a thermal control system. 
     Within the inlet orifice  26  an air pump  32  is provided having an impeller  34  driven by a shaft  36 . The impeller  34  is configured to draw air into the fluid chamber  24  when rotated in a first direction as shown by arrow D1. In use, a plurality of the tool elements  12  are tessellated to form a continuous tool surface. In order to heat the control surface  16  and therefore the tool surface  14  and the workpiece the element  28  is powered by the electricity supply  30 . The impeller  34  is driven by the shaft  36  in direction D1 in order to draw ambient air surrounding the tool element assembly  10  into the chamber  24  past the heating element  28 . The heated air, as shown by arrows A1, is driven towards the control surface  16  and impinges thereon, thereby heating it. As the air cools, and is pushed radially outwardly by the incoming air, it falls back towards the element  28  along arrows A2 where it is heated and rises again. In this manner, a convection cell is formed which may require little input from the pump  32  because the heated air will naturally rise. 
     Turning to  FIG. 1 b   , if the user wishes to cool the element  12 , then the shaft  36  can be rotated in the opposite direction D2. At the same time, the electricity supply  30  is interrupted such that the heating element  28  does not heat the air. Under these circumstances, the air is drawn in the direction of arrows B out of the chamber  24 . Naturally, ambient air will also be drawn into the chamber due to a negative pressure and this circulation of ambient temperature air against the control surface  16  will act to cool down the tool element  12 . 
     An alternative arrangement is shown in  FIG. 2  in which similar components have reference numerals 100 greater. 
     The tool element assembly  110  is identical to the tool element  10  with the exception that no fluid pump  32  is provided. Should the user wish to heat the tool element  112 , then the electricity supply  130  is activated such that the heating element  128  heats the immediately surrounding air within the inlet orifice  126  to the extent that its buoyancy raises it towards the control surface  116  of the element  112 . As the air rises in the direction of arrow C, it transfers some of its thermal energy to the cooler control surface  116 . As the air cools and further hot air rises in the direction of arrows C, the cooling air will pass back down the sides of the side panels  122  to be reheated as it contacts the heating element  128 . In this manner a convection cell is established within the fluid chamber  124  to heat the tool element  112 . It will be noted that in order to cool the tool element, the heating element  128  is simply deactivated. Under these circumstances, cooling may take longer than the embodiment of  FIGS. 1 a  and 1 b    as the air will may tend to sit within the chamber  124  and cool by conduction through the chamber walls. For this reason, it is envisaged that the chamber walls may be constructed from a thin plate material, such as mica, preferably less than 5 mm thick, more preferably 1 mm thick. 
     An embodiment similar to that of  FIG. 2 a    is shown in  FIG. 2 b   , and in intended for use on the same tool, only to heat the upper tool part (and therefore heat the upper horizontal surface). Like components with  FIG. 2 a    are numbered 50 greater. 
     A tool element assembly  160  is provided, similar to the tool element  110  but inverted. Should the user wish to heat the tool element  162 , then the electricity supply  180  is activated such that the heating element  178  heats the immediately surrounding air. A difference to the tool element assembly  110  is that the tool element assembly  160  comprises a heater shroud  150 . The heater shroud  150  defines a conduit around the heating element  178 . As the air within the shroud is heated, it expands and is pushed from the ends of the shroud  150  in both upward and downward directions. The momentum of the downward travelling air (towards the tool element  162  in direction C) allows the air to travel to it and consequently heat it 
     When cooling of the tool element  162  is desired, the heater  178  is deactivated. As heat is conducted from the tool element  162  to the adjacent air, the air then rises and escapes through the orifice  176 . In variations of the embodiment of  FIG. 2 b   , the shroud may be shaped to encourage downward propagation of the warm air, for example by providing a constriction. Alternatively, or in addition, the heater element  178  may be pulsed to set up a resonant effect within the shroud to assist the propagation of the hot air towards the tool element. 
     A further embodiment is shown in  FIG. 3  and like components are numbered 200 greater than the embodiment of  FIGS. 1 a  and 1 b   . A tool element assembly  210  is provided having the same components as the tool element assembly  10 , however, in addition a number of orifices  238  are provided in the wall of each side panel  222 . A flap valve  240  is positioned over each of these orifices. 
     As shown in  FIG. 3 , the assembly  210  is in the cooling cycle such that the impeller  234  is being rotated in direction D2 to draw air in direction D out of the fluid chamber  224 . Under these circumstances, the flap valves  240  open such that cool air can be drawn in the direction of arrows E into the chamber  224  thus providing a cool air stream in order to cool the tool element  212 . 
     It will be noted that should the impeller  234  be reversed in order to draw air into the chamber  224  (and heat it via the element  228 ), then the slight positive pressure will close the flap valves  240  such that the hot air cannot escape. 
     Turning to  FIG. 4 , an assembly  310  is shown having reference numerals 200 greater than the assembly  10 . The assembly  310  is identical to the assembly  10  with the exception that a series of flat plate-like baffles  342  are provided parallel to and offset from side panels  322 . The baffles  342  are oriented such that an air channel  346  is formed between the centre of the fluid chamber  324  and the side panels  322  in order that exhaust air is passed in direction F back down towards the heater  328 . The precise construction of the baffles is considered to be within the remit of the notional skilled addressee. 
     Turning to  FIG. 5 , the assembly  410  is an example of an assembly similar to  310  having reference numerals of like components 100 greater. In this shown, the side panels  322  form a square or cubic fluid chamber  424 . On the left hand side of the assembly  410 , a baffle  448  is diagonal and directed towards the inlet orifice  426  below the pump  432 . On the right hand side of the assembly  410 , a straight baffle  450  is shown by comparison. Turning to  FIG. 6 , the assembly  510  is similar to the assembly  10  (with reference numerals 500 greater) with the exception that the impeller  534  is positioned between the heater  528  and the control surface  516 , within the chamber  524 . Advantageously, this arrangement tends to recirculate the air within the chamber  524  rather than drawing in new air through the inlet  526 . This makes the system more efficient. 
     In each of the above examples, a thermocouple or similar temperature sensing arrangement may be provided within the tool element, or the workpiece, to monitor temperature. In addition, it is envisaged that a thermocouple or temperature sensing means would be provided within the fluid chamber such that the temperature of the fluid therein can be measured. 
     A control system is provided which can control both the air pump (if provided) and the heater element such that the correct temperature at the tool element  12  can be maintained. This control system will also be programmed to take the tool element assembly through a work cycle depending on the required properties of the workpiece and other such factors, such as ambient air temperature and pressure and the curing rate of the workpiece material.