SYSTEM FOR FEEDING AND MIXING MULTI-COMPONENT MOLDING COMPOSITIONS

Abstract: A system is provided for supplying a plurality of different components in controlled amounts and component conditions to a molding machine which comprises a plurality of holding bins (10, 12, 14, 16) for particulate molding composition components, means (110, 112, 114, 116, 118) for drying said components and maintaining the dried condition of the components throughout the system, a separate source (80) for a reinforcing component, means (40, 42, 44, 46) associated with each bin for feeding the components to weighing stations (58, 58', 60, 60') under controlled drying conditions, feeding means (70) for supplying said components and feeding means (84, 85, 86) for supplying controlled amounts of reinforcing component to a mixer (90) and means (92) for releasing a uniform blend of a mixture of particulate components and reinforcing component into a molding machine (96).

Description: TITLE SYSTEM FOR FEEDING AND MIXING MULΗ-COMPONENT MOLDING COMPOSITIONS 5 FIELD OF THE INVENTION This invention relates to a system for supplying a plurality of different components in controlled amounts and component conditions to a molding machine. More particularly, the invention relates to a system for drying a plurality of different particulate molding composition components, 0 maintaining the state of dryness of the components throughout the system, blending the particulate components and mixing the components with a reinforcing component to obtain a uniform mixture of all components and feeding the mixture to a molding machine. BACKGROUND OF THE INVENTION 5 Supplying a plurality of different components to a molding machine in precise amounts and in the desired condition has been a problem. This problem is aggravated in molding operations involving large parts which are being used in increasing numbers in automotive applications, and in particular in molding such parts which are reinforced with fiberglass. o The use of thermoplastic polymers which are recyclable is becoming more important in large part molding applications. Many of these polymers are subject to hydrolytic degradation at molding temperatures and must be delivered to a molding machine in a dry state. Fiberglass which is used to reinforce the molded parts is 5 delivered from the manufacturer in the form of chopped bundles. During handling, in particular mixing and feeding the fiberglass to a molding machine, the bundles tend to be broken apart foraiing "fuzzballs" which cause system pluggages and over-rich areas of fiberglass which detract from the molded article properties. The fine fibers from the bundle break up, o blocking air filters and transport lines. The system of the present invention permits combining multiple components in precise ratios while at the same time drying and maintaining the dryness of the ingredients throughout the proportioning, transport, mixing and feeding operations. Handling of the chopped fiberglass 5 is conducted in such a way as to keep fibrillation and "fuzz ball" formation of the fiberglass to a minimum. SUMMARY OF THE INVENTION The system of the present invention comprises a plurality of holding bins for the particulate molding material components. Each component requires its appropriate drying condition. Separate dryer hoppers are provided for each component. Each hopper has its own heater control which adjusts the temperature of the conditioned air, i.e., dehumidified air, prior to its entry into the individual drying hopper. The transport system from the drying hoppers to the molding machine is supplied with conditioned air. An air transport loop is included which utilizes dehumidified air provided by a dehumidifying dryer, filter and compressor. The drying hopper for each component is equipped with a special discharge valve to allow pickup of the discharged contents with dry air for transport to smaller inventory supply bins which are a part of a compact gravimetric weigh unit. These bins empty by gravity to vibratory pan feeders which deliver the feed from the respective bins to a weigh hopper which is suspended from a precision weighing strain cell. The weigh hoppers are filled to their precise weights through automatic feedback control between weigh cells and amplitude and timing controls to vibratory pan feeders. A transport hopper is designed with steep sides to handle the components which have widely different physical properties and handling characteristics. Typically, the hopper is ellipto-conical in shape and will have a vertical forward wall and a steep (70°) sloping rearward wall arranged in a fπistro-elliptical pattern. The preweighed components are then transported via a pneumatic conveying (venturi) system using conditioned air to a holding hopper located adjacent a molding machine. The particulate components which have been preweighed and held in the holding hopper are released to a mixer. It is important to release the particulates into the mixer prior to introducing fiberglass to eliminate excess tumbling which could produce fiberglass "fuzzballs". The fiberglass component is handled in a very special and careful way to avoid fibrillation of the fiberglass bundles and to prevent the formation of "fuzzballs". The chopped fiberglass is received from the supplier in a bulk container, preferably in large bulk bags which typically weigh 1000 to 2000 lbs. Fiberglass is fed to a weigh hopper until the correct weight is achieved in accordance with a control set point and in accordance with a set ratio and other set ratios for other ingredients. Upon command from a central control station, the discharge gate of the fiberglass weigh hopper is opened. Simultaneously or nearly simultaneously, a purge air sealed gate valve is opened momentarily allowing flow of the measured fiberglass charge into the mixer. Reinforcing components in addition to or in lieu of fiberglass may be used in the system. The components are mixed proximately above the molding machine. A horizontal shaft type mixer with internal lifting and directional 0 elements causes all the components within the mixer to be gently tumbled together so as to create a homogenous mixture with limited rotations and controlled speed of the apparatus. The separate handling of the fiberglass using only gravity (except for the vibratory feeder) to unload and direct the fiberglass down into the mixer is important to preserve the integrity of the 5 fiberglass bundles thereby reducing fibrillation to a minimum. Once the required number of mixer revolutions has occurred to obtain a uniform mixture, a full bottom, close-fitting, contoured discharge slide-gate is opened on command from a central control station. This allows the charge of well mixed components to enter the holdup hopper and the throat of the molding 0 machine. By locating the mixer proximately above the extruder, segregation of the components is not allowed to occur because of differences in solids flow characteristics of the components. Thus the mixture's homogeneity is preserved, via plug flow, to its entry into the molding machine. Glass breakage and "fuzzball" formation is held to a minimum thus enhancing the 5 molded part properties. BRIEF DESCRIPTION OF THE DRAWINGS The FIGURE is a schematic diagram showing a preferred embodiment of a component supply system according to the invention. DETAILED DESCRIPTION OF THE INVENTION o Referring now to the drawings, a plurality of particulate molding composition components are stored in holding bins 10, 12, 14, and 16. The components are delivered through feed lines 20, 22, 24 and 26 to dryer hoppers 30, 32, 34 and 36 which are each equipped with individually controlled heaters. Transport air is supplied to the dryer hoppers from 5 master dryer unit 28 through line 18. Conditioned (dry) air is supplied to the dryer hoppers from dryer 110 through heaters 112, 114, 116 and 118 which are located in conditioned air supply lines 120, 122, 124 and 126. The particulate components may include thermoplastic polymers among which are polyesters and polyamides, toughening agents, various additives such as viscosity reduction agents, colorants, mold release agents, antioxidants, UV light stabilizers and flame retardants. Recycled thermoplastic polymer such as recycled bottle resin from postconsumer polyethylene terephthalate soft drink bottles may also be used. When the components have reached the desired level of dryness, they are transported through feed lines 40, 42, 44 and 46 by conditioned air to inventory supply bins 50, 52, 54, and 56. Each bin employs one vertical wall and steep angled side walls to promote the evacuative flow of its particular contents. Each feeder's receiving port is loosely connected through a coated flexible sock to its individual feed bin and similarly at its exit to weigh hoppers 60 and 60' to prevent ingress of room air, excess loss of purge air, and the escape of any particulate material. On command from a central controller, predetermined amounts of the components as determined by gravimetric weigh units 48 and 48' are fed to weigh hoppers 60 and 60'. Each hopper is suspended from a weigh cell 58 and 58' controlled to yield an accurate weight for those components designated to pass through it. For example, a total charge could be 50 lbs (22.7 kg) composed of components, respectively, of 35%, 35%, 25% and 5% from inventory bins 50, 52, 54 and 56. Separate weigh hoppers 60 and 60' provide for simultaneous weigh-up and an increase in cycle speed. The feeders of the weighing units are preferably covered pan high frequency vibrating units although auger feeders could be used. The pan feeders have the general advantage of delivering very uniformly under precise control at the lip whereas auger feeders have the disadvantage of slugging slightly as material from each thread pitch is delivered. Consequently, the range of precision of each auger is limited more so than a vibrating pan feeder. Weigh hoppers 60 and 60' are filled to their precise weights through automatic feedback control between weigh cells and amplitude and timing controls to vibratory pan feeders. The two or more components designated for each weigh hopper are fed in sequence. Both weigh hoppers can be operated in sequence or at the same time. When the designated weight charges have been reached in the weigh hoppers, the charges are automatically dropped into a scale collection hopper 64 by the opening of flapper valves 62 and 62' on the bottom of the respective weigh hoppers. The combination of weigh hoppers, flapper valves and collection hopper is referred to herein as a confluencing means. Dry air is supplied to the confluencing means to prevent ingress of atmospheric air. Hopper 64 is designed with steep sides to appropriately handle the components fed thereto which have widely different physical properties and handling characteristics. Typically, this hopper is ellipto-conical in shape and will have a vertical forward wall and steep (70°) sloping rearward wall arranged in a frustro-elliptical pattern. The preweighed components are transported via a pneumatic conveying (venturi) system 66 and feed line 68 using dry air to a dry air purged holding hopper 70 located proximately above an injection molding machine 96. A fiberglass source, bulk bag 80, is suspended from a holding rack which is supported by superstructure 72 and travelling crane 74. Using long-armed glove entry ports 82, drawstrings on bag 80 can be untied and the bag's downspout placed inside a funnel to discharge apparatus 84. The large sacks are characterized by a bottom seal composed of an inner tubular funnel tied together with a drawstring device and with outside flaps which are also operated with a drawstring device and tied with a knot. The filled sack is lowered onto the top surface of a discharge box 88 which contains a flexible rubber seal which envelopes the discharge area of the sack. Steep sides, one vertical, on the discharge box direct the fiberglass to a sock sealed vibratory covered pan feeder 85. Through a sequence control station, the feeder directs the fiberglass into a separate weigh hopper 86. This weigh hopper is supported from the superstructure with a weigh cell. Fiberglass is allowed to enter the weigh hopper 86 until the correct weight is achieved in accordance with a control set point and in accordance with set ratios with the other ingredients. Reinforcing components in addition to or in lieu of fiberglass, such as mineral fibers, carbon fibers and aramid fibers, mica, glass or ceramic spheres and the like may be used in the system and fed to weigh hopper 86 as described above. Mixer 90 is placed proximately above the feed throat of molding machine hopper 94. Ingredients which have been fed from inventory supply hoppers 50, 52, 54 and 56 and from the fiberglass feed source 80 are gently tumbled together and after a homogenous mixture is obtained are released by a contoured-discharge slide gate valve 92 on command from a central control station to machine hopper 94. By locating the mixer proximately above molding machine 96, segregation of the components due to differences in solids flow characteristics of the components is not allowed to occur. Also, fuzzball formation and glass breakage is held to a minimum. It is critical that mixing of the particulate components and fiberglass be carefully controlled. As indicated earlier herein, the particulates should be fed into the mixer prior to feeding the fiberglass; however, with careful control the different materials may be fed simultaneously to the mixer. A high efficiency magnetic grate 95 is located at the bottom of machine hopper 94 to remove any magnetic tramp materials that might have entered the system with components or from machinery breakdown. The high efficiency magnet allows for wider spacing of bars in the grating permitting free flow of the components. The mixture of components is fed, via plug (gravity) flow into the moveable portion 98 of injection molding machine 96 where the plastic components are melted and blended with the other components after which the mixture is fed to tool 100 to form a molded part. The system can be fully automated and can be programmed to deliver the precise quantities of the various components desired for a particular product to a molding machine. An essential requirement for the successful operation of the system and obtaining quality molded parts is providing dry air for the transport of components. Air is fed to the system through supply line 102 through filter 78 to heat exchanger 104. Master dryer unit 28 includes a dew point meter 106 as well as other controls to deliver conditioned air to the system. Purge air can be supplied by a separate dryer 108 through feed line 38. The purge air dryer supplies dehumidified blanketing air to various system units thereby preventing ingress of nearly all room (ambient) air into the system. Modifications to the system can be made. For example, the air supply and drying means could be combined in a single master unit, and inventory supply bins could be eliminated with the particulate components being fed directly to associated weighing and confluencing means adjacent the fiber glass supply source. Accordingly, the invention should be understood to include embodiments which can be made without departing from the principle of the invention set out in the appended claims.

Claims: CLAIMS We claim: 1. A system for supplying a plurality of different components in controlled amounts and component conditions to a molding machine, comprising in combination a) a plurality of holding bins (10)(12)(14)(16) for particulate molding composition components, b) means for drying said components (110)(112)(114)(116)(118) and maintaining a dried condition of said components throughout the system, c) a bulk supply source (80) for storing a reinforcing component, d) means (40)(42)(44)(46)(50)(52)(54)(56) associated with said bins for feeding the components to weighing stations (58)(58'), e) confluencing means (48)(48')(62)(62')(64) including said weighing stations for establishing a predetermined mixture of said particulate components, f) feeding means (70)(85) for supplying said particulate components and controlled amounts of reinforcing component to a mixer (90) wherein a uniform blend of said components and said reinforcing component is formed, and g) means(92) for releasing said blend of said mixture of particulate components and said reinforcing component from said mixer into a hopper (94) for feeding said blend to said molding machine (96). 2. The system of Claim 1 wherein said reinforcing component is fiberglass. 3. The system of Claim 1 wherein said hopper (94) is positioned proximately above said molding machine (96). 4. The system of Claim 2 wherein said means for releasing said blend of particulate components and said fiberglass comprises means for gravity feeding said components and fiberglass from said hopper (94) to said molding machine (96).

Inventors: CROFT NEIL JAY, GAUL MILTON U JR, LATHROP JOHN FRANCIS, MAURER HEINRICH, SHIH CHI-KAI, CROFT, NEIL, JAY, GAUL, MILTON, U., JR., LATHROP, JOHN, FRANCIS, MAURER, HEINRICH, SHIH, CHI-KAI
Applicants: DU PONT, E.I. DU PONT DE NEMOURS AND COMPANY
Application year: 1992
Main classification: B29B7
IPC codes: B29B7, B29C31, B29C47