WO2014065705A2 - Device for thermoforming a polymer and/or a resin by injection molding and operating method thereof (variants) - Google Patents

Abstract

The device for thermoforming a polymer by injection molding through an opening (injection press) relates to the art of mechanical engineering, and more particularly to the thermoforming of items made from polymeric materials. Two distinct practices exist in polymer processing: firstly, the vacuum forming of polymer sheets which have been heated to softening temperature; and, secondly, the high-pressure spraying of molten liquid polymer. The proposed technical solution combines the advantages of both practices by simultaneously applying pressure to the polymer and evacuating the cavity of the injection mold using vacuum-generating means and devices. This technical solution makes it possible to dispense with the need to place the polymer in a cartridge, increases the accuracy of pattern transfer, prevents the release of gases from the polymer, and increases polymer density, which is particularly important in the case of items that are to be used in medicine and in direct contact with human tissues.

Description

 Device for thermal molding of polymer and / or resin by injection molding and method of its operation (options)

This technical solution relates to the field of engineering, in particular, the thermal molding of products from polymeric materials.

 There are two independent areas in polymer processing technology: vacuum forming of heated softened polymer sheets (vacuum forming) and injection molding of molten liquid polymer, see DMS Plastics Limited advertising materials, http: /www.dmsplastics.co. uk / vacform.html and http: www.drnsplastics.co.uk/injection.html. Known areas of polymer molding, including methods and devices for their implementation, differ significantly; examples of combining two types of processes in polymer molding devices at once: injection of molten polymer under pressure and vacuum molding are not found in the literature.

 The advantages of using vacuum in thermoplastic molding of polymer structures are known:

 - the absence of vapors of volatile organic compounds, in particular, emissions of styrene compounds in the workplace;

 - 100% recyclable polymer;

 - good resistance to shock loads and abrasion;

 - reduction of labor costs and overhead costs;

 - reduction of the working cycle time;

 - reducing the cost of purchasing components;

- excellent resistance to water and chemical compounds (see the article "Vacuum Molding of Thermoplastic Composite Structures)", website www.eplcompositesolutions.co.uk/composite Vacuum MoldingCompositeStructur es.asp), which ensures widespread use of this method and automated installations in production, which, in turn, are widely represented on the website russian.alibaba.com/products/automatic-vacuum-forming-mashine.html, etc. However, it is far from always that samples of the desired shape and required accuracy can be pressed from a polymer sheet.

Another area of polymer processing technology is the injection of molten polymer through a hole under pressure using a hydraulic pair: a hydraulic cylinder, inside which a piston or plunger moves (injection press). (A piston is a cylindrical part that reciprocates inside the cylinder and serves to turn the change in gas, vapor or liquid pressure into mechanical work, or vice versa, the reciprocating motion into a pressure change. A plunger is a cylindrical displacer whose length is much longer The accuracy of machining parts of modern plunger and rotor plunger hydraulic machines is so high that the gap between the inner and outer cylindrical surfaces in the plunger pairs has reached The main and most often used in the production parameter of the surface roughness of pistons, plungers and hydraulic cylinders according to GOST 2789-73 is R _a - arithmetic mean deviation of the profile. Modern surface treatment methods, such as ion beam processing, provide a roughness level individual atoms and molecules, namely 3-4 Angstroms, that is (3-4) 10 ^"10 m. (See Simakina N.V. et al., Nanoscale surface polishing of glass blanks for laser gyroscope mirrors, Vacuum technology, materials and tech logy. Materials of the IV International scientific and technical conference, OMR PRINT, 2009). In these cases, the R _a value is estimated using scanning microscopes. (V.L. Mironov Basics of scanning probe microscopy. Moscow, Technosphere; A.V. Bolshakova, I.V. Yaminsky Scanning probe microscopy of block copolymers, Study Guide, description, tasks of a laboratory workshop, Moscow, Center for Advanced Technologies, 2008).

The prior art device is known for thermoforming products from polymers, including a rod with a piston, which under the action of a mechanical moving device, they are moved inside the cylindrical molding chamber heated by the heating device to the melting temperature of the polymer, and molten polymer is squeezed through the outlet into the mold volume, patent US5302104. The disadvantages of this technical solution: low surface quality of polymer products and the presence of voids due to the insufficiently tight fit of the polymer to the walls of the mold, the presence of gas inclusions in the polymer.

 A known device for injection molding of polymer molded products, which consists of an injection machine and mold, patent RU2284913. A device for injection molding of polymer molded products consists of an injection machine and a mold. In the mold there are at least two cavity corresponding to the dimensions of the manufactured molded products. The injection machine is designed as a conventional standard injection machine. One channel is made in the mold for supplying molten polymer. To increase the production of the number of finished molded products per unit time, a channel is passed in the mold from the first plane of the connector and then to the second plane of the connector, from which additional channels extend to the cavities. The disadvantages of the technical solution: low surface quality of polymer products and the presence of voids due to the insufficiently tight fit of the polymer to the walls of the mold, the presence of gas inclusions in the polymer material.

 A known method of producing castings and a device for its implementation, see patent RU2353469. The device comprises a casting body made of a base and a lid, a molten mold, a heated container for storing the mold material, a low pressure casting furnace installed in the furnace, a gate, heating, cooling, vacuum and low pressure air supply elements. A heated container for storing mold material is placed on a casting casing located on a low pressure casting furnace. The molds are made according to a one-time model by filling with vacuum suction and crystallization of the material of the form in the cavity formed by the model in the foundry case. Mold material

s pour from the middle of the casting housing directed up and down. Metal castings are cast by low pressure casting with evacuation. The disadvantage of this technical solution: it is used only for casting metals and alloys, but not polymers.

 The closest to the claimed technical solution is an injection smelting press, see application US2007194474. US2007194474 proposes a press for molding molten polymer and / or resin by injection molding (injection press), in which there is a hydraulic cylinder and a pressure piston disposed inside the hydraulic cylinder. The pressure piston divides the hydraulic cylinder into two chambers: retraction and extrusion. The pump and the device for creating pressure along the axis are connected to the extrusion chamber. The sensor measures the pressure in the extrusion chamber. The controller receives signals from the sensor and controls the pump. The pump delivers hydraulic fluid to the extrusion chamber in order to squeeze and pour through the hole (inject) the polymer / resin into the single-cavity mold by means of a piston. The controller stops the pump when the pressure in the extrusion chamber reaches the set shutdown level. A pressure generating device along the axis creates back pressure on the liquid in the extrusion chamber after the controller stops the pump to provide excess pressure on the injected polymer. The axial pressure generating device may be a storage battery that is charged by a pump. Safe operation devices prevent the controller from turning on the pump in unsafe conditions.

 The disadvantages described in US2007194474 the closest analogue is

 - the need to use a cartridge made of easy-crushable (easily deformable) material, for example aluminum, to place the polymer / resin;

 - the presence of gas inclusions in the polymer / resin after cooling;

- insufficient filling of the mold volume with polymer / resin; - insufficient force clamping the polymer to the walls of the mold.

- the presence of residual unstable and non-copolymerized compounds;

 - the presence of toxic substances;

 - the need to use various auxiliary devices and consumables, for example, a cartridge made of easily removable / easily deformable material, in order to accommodate polymer / resin.

 In turn, the invention will allow:

 - increase the filling volume of the mold;

 - to improve the quality of the polymer after molding due to the lack of gas inclusions and an increase in the density of the material of the finished product under the influence of a larger pressure difference;

 - increase the accuracy of the transfer of the shape and surface quality of products made of polymeric materials;

 - reduce the presence of vapors of volatile organic compounds, in particular, styrene emissions;

 - provide 100% possibility of recycling of polymer residues.

 - significantly reduce the cost of equipment and technology for the consumer.

 The above advantages will be achieved by using a device for thermoforming molten polymer / resin by injection molding (injection press), consisting of

 - a cylindrical molding chamber, inside of which a piston is placed on the rod with the possibility of movement along the axis of the chamber from the inlet to the outlet

 - a piston that divides the molding chamber into two cavities: a rod cavity and a piston cavity;

- while between the piston and the outlet of the molding chamber is a disk to protect the surface of the piston from polymer / resin melt; - the outlet of the molding chamber is connected to the volume of the cavity of the injection mold into which molten polymer granules are supplied by moving the piston;

 - a pressure sensor connected to the input of the controller containing a microprocessor connected to a device for moving the piston is connected to the piston cavity of the molding chamber,

 in which, unlike known solutions

 - the piston interacts with the polymer directly or through the disk, with the possibility of extruding the polymer / resin through the outlet from the volume of the molding chamber into the cavity of the injection mold,

 the roughness of the outer surface of the piston and the inner surface of the molding chamber for its movement is in the range of values

1,0-10 ^"6 MM <R _a <1, 0MM,

where R _a is the arithmetic mean deviation,

 - the size of the gap h between the outer surface of the piston and the inner surface of the molding chamber for its movement is in the range of values

2.0-10 ^"6 mm <p <1.0 mm,

 - the injection mold for feeding the polymer into the volume of the cavity has at least one hole-channel connecting the volume of the cavity of the injection mold with a vacuum device,

 - at least one pressure sensor connected to the controller is connected to the volume of the cavity of the injection mold

 - outside the molding chamber and injection mold placed electric heaters and temperature sensors,

 wherein the temperature sensors of the molding chamber and the injection mold are connected to a controller connected to a vacuum device and devices for regulating the current value in electric heaters.

 Variants of using the device described above are proposed.

According to a first embodiment of a method for operating a device for thermally molding a molten polymer / resin channel,

b connecting the molding chamber with the volume of the cavity of the injection mold, overlap with a sealing element; the polymer / resin is melted under pressure and the molten polymer is injected due to the pressure difference in the molding chamber and the mold cavity.

 According to a second embodiment of the method for operating the device for thermally molding the molten polymer / resin, the channel connecting the molding chamber to the volume of the cavity of the injection mold is closed with a sealing element, the polymer / resin is melted under pressure, and the molten polymer is injected by moving the piston into the cavity of the mold having a negative value compared to atmospheric.

 According to a third embodiment of the method for operating the device for thermally molding the molten polymer / resin, a channel is opened connecting the molding chamber with the volume of the cavity of the injection mold, the polymer / resin is melted in vacuum, and the molten polymer is injected by the movement of the piston.

 The device diagram is presented in graphic materials.

 I - sensor for measuring vacuum;

 2 - a connecting pipeline connecting the volume of the injection mold with means and devices of evacuation;

 3 - the body of the injection mold;

 4 - mold electric heater;

 5 - inlet of the injection mold;

 6 - at least one sealing element, for example a shutter valve plug, covering the outlet of the forming chamber and the inlet of the injection mold;

 7 - the outlet of the forming chamber;

 8 - polymer / resin;

 9 - electric heater forming chamber;

 10 - molding chamber;

 I I - a protective disk;

 12 - piston / plunger;

13 - stock; 14 is a device for moving the rod with a piston / plunger along the axis of the forming chamber from the inlet to the outlet, controlled by electric signals from the controller, for example, containing an electric motor,

 as well as devices for protecting the electric motor from overload and burnout of the winding coils, in particular, with an increase in the current value above the level of safe operation;

 15 is a sensor for measuring the temperature of the housing of the forming chamber;

 16 - control device for the operation of the electric heater forming chamber;

 17 is a controller containing a microprocessor;

 18 - indicating means, for example, a liquid crystal display, as well as means for entering parameter values, for example, a button or touch keyboard;

 19 - control device sealing element;

 20 - control device for an electric heater of an injection mold;

 21 - sensor for measuring the temperature of the body of the injection mold; 22 - a shutter element that overlaps the pipeline means of evacuation, for example, a shutter valve;

 23 is a vacuum device comprising, for example, a vacuum pump.

In one embodiment, the device operates as follows. The molding chamber (10) is installed vertically with the outlet (7) up. From below, through the inlet insert the protective disk (1 1) and slide the rod (13) with the piston / plunger (12). The polymer / resin granules (8) are poured through the outlet (7). If necessary, carry out weighing and determine the weight of the filled polymer. Set parameters input means, for example, manually using the keyboard (18) to the controller (17) apply signals corresponding to the parameter values. The controller gives the command to start the execution of the process program. The control device (19) sealing element (6) hermetically closes the outlet (7) a forming chamber with an inlet of the injection mold, leaving the cavities between them open. The sealing element (6) is left open. The controller (17) sends a signal to the evacuation device. Thus, the polymer is melted with the sealing element (6) open, the injection mold channels (3) and the forming chamber (10) are connected, i.e. the polymer itself is melted in a vacuum. Volatile compounds and excess air are pumped out. In this case, the injection occurs only due to the movement of the piston (12, 13, 14).

The vacuum pump (23) is turned on and in the cavity of the injection mold (3), as well as in the volume of the forming chamber connected to it (10), air is pumped out from the initial ambient pressure p ₀ and also gas evolution from the polymer to a predetermined value pi. When the sensor (1) sends a signal to the controller that the set Pi value has been established, the signal is sent to the electric heater control devices (16,20) from the controller (17) and they give a signal to heat the electric heaters (4,9). Sensors (15,21) measure the temperature of the forming chamber (10) and the injection mold (3), respectively. The initial temperature value t ₀ corresponds to the ambient temperature, when the temperature of the forming chamber reaches the set value ti, a signal is sent from the sensor to the controller and the controller (17) together with the heater control device (16) maintain the temperature at the set value level - When the temperature of the injection press form (3) of the set value t _{3 the} sensor (21) sends a signal to the controller (17). The controller (17) together with the heater control device (20) maintain the desired mold temperature. The controller and the heater control device (16) maintain the temperature of the forming chamber at the level ti for the time required to melt all the polymer in the forming chamber. The processes of heating and maintaining the set temperature values in the mold and the forming chamber occur simultaneously and run in parallel, but ti> t ₂ .

In other embodiments of the device, the sealing element (6) may optionally overlap the connecting holes of the forming chamber and the injection mold. In this case, polymer melting comes with a closed sealing element (6), i.e. the polymer itself melts without vacuum. Volatile compounds and excess air are not pumped out, and injection occurs due to the pressure difference in the injection mold (3) and the forming chamber (10) or due to the movement of the piston (12,13,14) during the melting of light and viscous polymers . At the end of the polymer melting time, the controller (17) sends a signal to close the shutter element (22), which prevents the polymer from entering the pumping means pipeline. The controller stops the vacuum pump. The sealing element (6) opens the connecting holes of the mold and the forming chamber. The rod (13) begins to move the piston / plunger (12), pushing the polymer melt into the injection mold (3). When the polymer fills the entire cavity of the mold and the rod pressure exceeds a predetermined value, the piston movement control device will give a signal to the controller and the rod movement will stop, it will stop and hold the polymer under pressure until the polymer cools in the injection mold (3).

 When the temperature sensors (4.9) give a signal to the controller (17) that the temperatures of the mold housings and the forming chamber have dropped below 50 ° C, the piston will begin to move in the opposite direction upon the command of the controller (17) and the motion control device (14) to the inlet, freeing the forming chamber. The injection mold moves away from the forming chamber; it is possible to remove the finished product from the press and the injection mold.

 Despite the fact that some of the applied features are known, their combination and relative position of structural elements in this technical solution is new. The total effect is that the structure and composition of the polymeric material changes due to stronger compression caused by a significantly larger pressure difference and a decrease in the concentration of gas inclusions, which is of great importance primarily for materials used in medicine and for a long time in contact with human tissues, in particular denture materials.

Yu

Claims

CLAIM 1. Device for thermoforming molten polymer / resin by injection under pressure, consisting of:  - a cylindrical molding chamber, inside of which a piston is placed on the rod with the possibility of movement along the axis of the chamber from the inlet to the outlet  - the piston divides the molding chamber into two cavities: the rod cavity and the piston cavity;  - between the piston and the outlet of the molding chamber is a disk to protect the piston surface from polymer / resin melt;  - the outlet of the molding chamber is connected to the volume of the cavity of the injection mold into which molten polymer granules are supplied by moving the piston;  - a pressure sensor connected to the input of the controller containing a microprocessor connected to a device for moving the piston is connected to the piston cavity of the molding chamber,  characterized in that  - the piston interacts with the polymer directly or through the disk, with the possibility of extruding the polymer / resin through the outlet from the volume of the molding chamber into the cavity of the injection mold,  the roughness of the outer surface of the piston and the inner surface of the molding chamber for its movement is in the range of values 1,0-10 ^"6 mm <Px _a <1,0 mm, where R _a is the arithmetic mean deviation, - the size of the gap h between the outer surface of the piston and the inner surface of the molding chamber for its movement is in the range of values 2.0 ^"6 mm <p <1.0 mm,  - the injection mold for feeding the polymer into the volume of the cavity has at least one hole-channel connecting the volume of the cavity of the injection mold with a vacuum device,  - at least one pressure sensor connected to the controller is connected to the volume of the cavity of the injection mold  - outside the molding chamber and injection mold placed electric heaters and temperature sensors,  wherein the temperature sensors of the molding chamber and the injection mold are connected to a controller connected to a vacuum device and devices for regulating the current value in electric heaters.  2. The method of operation of the device for thermoforming molten polymer / resin, characterized in that in the device according to claim 1  the channel connecting the molding chamber with the volume of the cavity of the injection mold is closed with a sealing element,  perform polymer / resin melting under pressure,  and the molten polymer is injected due to the pressure difference in the molding chamber and the cavity of the injection mold.  3. The method of operation of the device for thermoforming molten polymer / resin, characterized in that in the device according to claim 1  the channel connecting the molding chamber with the volume of the cavity of the injection mold is closed with a sealing element,  perform polymer / resin melting under pressure,  and the molten polymer is injected due to the movement of the piston. 4. The method of operation of the device for thermoforming molten polymer / resin, characterized in that in the device according to claim 1 open a channel connecting the molding chamber with the volume of the cavity of the injection mold,  perform the melting of the polymer / resin in vacuum,  and the molten polymer is injected due to the movement of the piston.