Method and means for molding plastic parts
AssigneeNicholas Plastics, Inc.
InventorClifford D. Swanson
Life of this patent
Estimating the term…
Abstract
A system for molding elongated ribbon-like products from thermoplastic materials utilizing a plurality of molds which are moved in tandem along a production line. As the molds are moved along the line at successive stations they are, while open, thermally adjusted to a temperature suitable for forming the product to be molded and then a ribbon of plastic is deposited in them. They are then closed and cooled and reopened and the molded product removed. The system utilizes only enough molding pressure to assure distribution of the plastic to all parts of the mold cavity and shaping of the molded product to the geometric design of the mold. The system includes a transfer means for the molds which returns the emptied molds for recycling through the molding process.
Claims39
The method for forming an extruded product of thermoplastic material by low pressure molding including the steps of providing a plurality of molds each having a base and a cover which when closed form a closed internal cavity shaped to form the top, sides and ends of the product, continuously transporting the molds in sequence around a closed circuit, preparing each mold to receive a charge of moldable thermoplastic material, sequentially moving each mold beneath a source of plastic material, while the mold is open flowing a charge of extruded thermoplastic material into each mold, removing each mold from the source of the plastic material, by means of the cover simultaneously closing and sealing the cavity in the mold while applying at least sufficient pressure to distribute the plastic material throughout the mold cavity whereby all areas of the mold are filled with plastic and the plastic will accuratedly reproduce the configuration of the cavity, cooling the mold sufficiently that the molded product can be removed without distortion of its molded configuration;
- as the mold and plastic are being cooled further closing the mold data rate to progressively compensate for thermal shrinkage of the plastic;
- precisely measuring the volume of plastic material discharged into the mold such that the mold cavity when initially sealed will hold the entire change of plastic delivered into the mold and such amount will be equal to the volume of the mold cavity when the plastic material has cooled to a temperature at which the molded product can be removed from the mold.
In a method of forming extruded parts from a thermoplastic material the steps which include providing a mold of a material having a thermal conductivity at least that of aluminum, the mold having a base and cover which when closed forms an internal mold cavity, moving the mold along a closed endless path and while the mold is so moving opening the mold to expose the cavity and heating the mold to receive a charge of thermoplastic material, moving the mold beneath a source of plastic material, extruding a ribbon of moldable thermoplastic material and releasing it by gravity into the open mold while measuring the quantity of material deposited to provide a volume thereof which will be equal to the volume of the mold cavity when the mold is fully closed and cooled to a temperature at which the molded part can be removed, covering the plastic material with the cover and simultaneously closing and sealing the mold cavity, applying a closing pressure to the cover of an amount only sufficient to cause the plastic material to migrate to and entirely fill all portions of the cavity, cooling the mold to cause the plastic material to set, as the plastic is cooled progressively further reducing the volume of the cavity by mold closure sufficiently only to compensate for shrinkage of the plastic as it cools and, when the plastic has been cooled sufficiently that the extruded-molded part can be removed without permanent distortion opening the mold and reoving the molded part, returning the mold for reuse.
The method of forming an elongated ribbon-like product of the type which may be used as body side moldings or bumper rub strips for automobiles and having shaped molded ends integral with the main body of the strip by molding a ribbon of plastic material, including the steps of providing a mold having a base portion and a cover portion at least one of which portion has a recess therein, the mold when closed having an internal cavity shaped to form the top, bottom, sides and ends of the product, heating the mold, while the mold is open depositing a ribbon of moldable thermoplastic material on the base portion, measuring the quantity of material deposited on the base portion to provide a volume thereof which will be equal to the volume of the space within the mold cavity when the mold is fully closed and the plastic has been cooled to a temperature at which the molded part will maintain the integrity of its molded shape when removed from the mold, simultaneously closing the mold and sealing the mold cavity with the cover portion, and after sealing by means of the cover portion exerting pressure on the plastic material just sufficient to distribute the plastic material uniformly throughout the mold and entirely fill the mold cavity and cooling the mold to set the plastic material until it can be removed from the mold without loss of shape, during the cooling of the plastic further closing the mold at a rate to both compensate for volume shrinkage, maintain total occupancy of the mold cavity and prevent the formation of sinks in the molded product, opening the mold and removing the molded part and returning the mold for reuse.
A system for molding elongated ribbon-like plastic strips from a thermoplastic material, said system comprising:
- a plurality of stations, a plurality of molds each having a base portion and a cover portion at least one of which has a mold cavity recess therein shaped to form the strip when the mold is closed, said mold being made of a non-ferrous material, transport means interconnecting all of the stations;
- at least one of the stations having means for preparing the molds to receive a charge of moldable thermoplastic material;
- another station having means under which the molds pass in tandem for flowing a ribbon of precise and predetermined volume of hot thermoplastic material into each mold as it passes through the station;
- mold controlled means for controlling the discharge of the plastic material such that the length and volume of the discharged ribbon is commensurate with the length and volume of the mold cavity;
- means or closing the mold and sealing the mold cavity, pressure exerting means for engaging the mold and solely by pressure exerted by said means on the cover pressurizing the plastic material at least to that necessary to cause the mold cavity to be entirely filled with the plastic material and be impressed with the configuration of the mold cavity said pressure exerting means including means to limit the closing pressure only to that necessary to positively fill the mold cavity with the material and to thereafter continue to progressively reduce the size of the mold cavity at a rate commensurate with the rate of shrinkage of the plastic as it cools to cause adequate material migration within the cavity to prevent sink formation or other distortion during cooling;
- and means for removing the molded strip after it has cooled until it can be removed without distortion of its physical shape.
A system for molding a plastic product from a thermoplastic material, said system comprising:
- a plurality of stations, a plurality of molds each having a base portion and cover portion at least one of which has a mold cavity therein shaped to form the product when the mold is closed, transport means interconnecting all of the stations;
- at least one of the stations having means for preparing the molds to receive a change of moldable thermoplastic material;
- another station having a nozzle for flowing into each mold while the mold is present at the station a discrete quantity of hot thermoplastic material, said quantity being of a precise and predetermined volume and means for controlling the discharge of the plastic material such that the volume of the discharged material is commensurate with the volume of such material in the product being molded at the time the molded product is removed from the mold;
- means for closing the mold and sealing the mold cavity and means acting on the cover for pressurizing the plastic material to apply to the plastic material only that force which is necessary to cause the mold cavity to be entirely filled and the plastic material be impressed with the precise configuration of the mold cavity, means to thereafter cool and the mold and plastic, control means to prgressively reduce the size of the mold cavity during cooling by closure movement of the cover at a rate commensurate with the rate of shrinkage of the plastic as it cools to cause adequate material migration within the cavity to maintain at all times total occupancy of the cavity and to prevent sink formation or other distortion during cooling;
- and means for removing the molded product after it has cooled until it can be removed without distortion of its physical shape.
A system for molding plastic product from a thermoplastic material, said system comprising:
- a plurality of staitons, a plurality of molds each having a base portion and a cover portion at least one of which has a mold cavity therein shaped to form the product when the mold is closed, transport means interconnecting all of the stations;
- at least one of the stations having means for preparing the molds to receive a charge of moldable thermoplastic material;
- a mold charging station having a nozzle for flowing into each mold while the mold is present at the station a discrete qunatity of precise and predetermined volume of hot thermoplastic material and means for controlling the discharge of the plastic material such that the volume of the discharged material is commensurate with the volume of the product to be modlded at the time it is removed from the mold;
- means for closing the mold to seal the mold cavity against escape of any of the plastic material therein and for progressively continuing the closing at a rate commensurate with the reduction in volume of the plastic therein resulting from cooling, said means including a control element to maintain at all times total occupancy of the cavity by the plastic and to prevent the formation of sinks and to limit the closing pressure only to that necessary to maintain said condition;
- means for removing the molded product after it has cooled to a temperature at which it can be removed without distortion of its physical shape.
A system for molding a plastic product from a thermoplastic material, said system comprising:
- a plurality of molds each having a base portion and cover portion at least one of which has a mold cavity therein shaped to form the product when the mold is closed, a mold charging station;
- means for delivering a mold in open condition to said charging station to receive a charge of thermoplastic material in moldable condition;
- said mold charging station having a nozzle for flowing into each mold while the mold is present at the station, a discrete quantity of precise and predetermined volume of hot thermoplastic material and means for controlling the discharge of the plastic material and such that the volume of the discharged material is commensurate with the volume of the product to be molded at the time it is removed from the mold;
- means for closing the mold to seal the mold cavity against the escape of any of the plastic material therein and means for thereafter applying sufficient pressure to the plastic material to assure total occupancy of the mold cavity by the plastic material and control means for thereafter progressively continuing the closing at a rate commensurate only with the reduction in volume of the plastic therein resulting from cooling while maintaining a total occupancy of the cavity by the plastic;
- means for removing the molded product after it has cooled until it can be removed without distortion of its physical shape.
A system for molding a plastic product from a thermoplastic material, said system comprising:
- a mold having a base portion and cover portion at least one of which has a mold cavity therein shaped to form the product when the mold is closed, a mold charging station having a nozzle for flowing into the mold hot thermoplastic material and means for controlling the discharge of the plastic material such that the volume of the discharged material is precisely commensurate with that necessary to produce a product which will entirely occupy the mold cavity at the time it is removed from the mold;
- closure means for closing the mold to seal the mold cavity against escape of any of the plastic material therein and applying a positive pressure to the plastic in the mold cavity, said pressure being only sufficient to so distribute the plastic that all portions of the mold cavity are entirely filled and pressure means for progressively continuing the closing at a rate commensurate with the reduction in volume of the plastic therein resulting from cooling to maintain total occupancy of the cavity by the plastic at all times until the charge has cooled sufficiently that the molded product can be removed without distortion of its physical shape;
- means for removing the molded product.
The method of molding a plastic product from thermoplastic material including the steps of providing a mold having a removable cover to provide access to an internal mold caivty, while the cover is removed flowing into the mold a charge of hot thermoplastic resin and simultaneously measuring the volume of the charge such that it will equal the volume of the mold cavity when the mold is fully closed and the charge has been cooled sufficiently that the molded product can be removed from the cavity without distortion of its physical shape, closing the mold contain the entire charge and to seal the mold cavity against escape of any of the plastic material and simultaneously applying pressure to the charge of a magnitude only sufficent to cause the plstic material to entirely fill the mold cavity and accurrately reproduce the configuration thereof, thereafter continuing to progressively close the mold at a rate sufficient to create only enough pressure on the plastic to maintain the established relationship between the quantity of the charge and the volumetric capacity of the mold cavity and prevent the formation of any sinks or separation of the plastic from the walls of the cavity as the volume of the charge decreases in response to cooling until the plastic has cooled to a condition permitting removal.
The method of molding a plastic product having the appearance of depth from a thermoplastic material containing a dispersion of discrete relfective particles including the steps of providing a mold having a removable cover to provide access to an internal mold cavity, preparing the plastic material in an extruder, discharging the plastic material from the extruder into an accumulator and in the accumulator permitting the material to become a homogenous mass by releasing the stresses and eliminating the flow patterns acquired during extrusion and while the cover of the mold is removed, flowing the plastic from the accumulator at a rate such that it is discharged into the mold in an unstressed condition without visual flow pattern and simultaneously measuring the volume of the charge such that it will equal the volume of the mold cavity when the mold is fully closed and the charge has been cooled sufficiently that the molded product can be removed from the cavity without distortion of its physical shape, closing the mold to seal the mold cavity against escape of any of the plastic material and thereafter applying to the charge only that amount of pressure necessary to cause the plastic material to entirely fill the mold cavity and reproduce the configuration thereof without creating visible flow patterns in the plastic, thereafter progressively further closing the mold at a rate sufficient to maintain the established relationship between the quantity of the charge and the volumetric capacity of the mold cavity as the volume of the charge decreases in response to cooling until the plastic has cooled to a condition permitting removal.
Dependencies are inferred from the claim text.