CA2132844A1 - System for feeding and mixing multi-component molding compositions - Google Patents

Abstract

2132844 9318899 PCTABS00025 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

~o 93/18899i~ 3 ~ ~ Pcr/US92/02 T~E
SYSTEM FOR ~EEDING AND MIXING MULTI-COMPONENT
MOLDING COMPOSmONS

FIELDQF l~lNVENTIO~
This invention relates to a system for supplying a plurali~ of different components in controlled amounts and component conditions to a molding machine. More particularly, the invention relates to a system for drying a plurali~r of different particulate molding composition ~omponents, lO m~untaining tbe state of d~yness of the components ~roughout the system, blending the particulate components and ~ng the components ~nth a reinforcing component to obtain a uniform mixture of all components and feeding the mixture to a molding machine.
; ~ BACKGROIII~QF ~E ~NTION
5Supplying a p urali~r 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.

2 o The use of thermoplastic pclymers which are re~yclable 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 mold~hg machine in a dry state.
Fiberglass which is used to reinforce the molded parts is delivered ~om the manufactltrer in the form of chopped bundles. DuIing handling, in particular mixing and feeding the fiberglass to a molding machine, the bundles tend to be broken apart forming "fuzzballs" whicb cause system pluggages and over-rich areas of fiberglass which detract from the ntolded article properties. The fine fibers from the bundle brealc up, blocking air filters and transport lines.
The ~ em of the present invention perm~ts combining multiple components in precise rados while at the samc dme dlying and maintaini~g the d~yness of the ingredients throughout the propordoDing, ~; ` transpor~ mixing and feeding operadons. Handling of the chopped fiber~pass 35 is conducted in such a way as to keep fibrillation and nPuz~ ball" formation of the fiberglass to a minimum.

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WO 93/18899 PCI'/US92/0214.
2~3'Z~ ~ ~ 2 SUMMARY OF l~E INVENTION
The system of the present invention comprises a plurality of holding bins for the particulate moldi~g material components. Each component requires its appropriate dr ying condition. Separate dryer hoppers 5 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 10 provided by a dehumidif~ring dryert filter and compressor. The drying hopper for each component is equipped with a special discharge valve to allow pickup of the discharged contents witb 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 15 from the respective bins to a weigh hopper which is suspended from a precision weighing strain cell. The weigh hoppers are filled to tbeir pre~ise 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 2 o components which have widely different physical properties and handling characteristics. Typically, the hopper is ellipto-conical in shape and will havea ve~tical forward wall and a steep ~70) sloping rearward wall arranged in a frustro-elliptical pattern~ -The preweighed components are then transported vîa a 2 5 pneumatic conveying ~venturi) system using conditioned air to a holdinghopper 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

3 o 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 "fu~balls"~ The cbopped fiberglass is received from the supplier in a bulk container, preferably in large bulk bags which typically 3 5 weigh 1000 to 2000 lbs. Fiberglass is fed to a weigh hopper until tbe correct weight is achieved in accordance with a control set point and in accordance ,~ ~) 93/18899 PCr/US92/02141 ~13~(~4~

with a set ratio and other set ratios for other ingredients. Upon command from a central control station, the discharge gate of th_ ~Iberglass weigh hopper is opened. Simultaneously or nearly simultaneously, a purge air sealed gate valve is opened momentarily allowing flow of the measured 5 fiberglass charge into the mixer.
Reinforcing components în addition to or in lieu of fiberglass may be used in the system.
The components are m~xed proximately above the molding machine. A horizontal shaft t~pe mixer with internal lifting and directional 10 elcments causes all thc components within the mixer to be gently tumbled together so as to create a homogenous m~xture 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 - 15 fiberglass bundles thereby reducing fibrillation to a m~nimum. Once the requi~ed number of mixer revolutions has occurred to obtain a uni~or n ~ 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 tbe molding 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 ~he components. Thus the mixture's homogeneity is preserved, via plug flow, to i`~i entry into the molding machine. Glass breakage and nfuzzball" format~on is held to a minimum thus enhancing the 2 5 molded part pr~rties.
BRIEF I)E~CRIl~ION OF l'HE DRA~INGS
The FIGURE is a schematic diagram showing a preferred embodiment of a component supply system according to the invention.
DETAII~ED D13SCRIPTION OF THE I~VENTION
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 2Q 22, 24 and 26 to dryer hoppcrs 30, 32, 34 and 36 which are eacll equipped with individually controlled heatcrs. Transport air is supplied to the dryer hoppers from - ~ 35 master dryer unit 28 through line 18. Conditioned ~dly) air is supplied to the '~

WO 93/1~899 P(:~/US~2/021~.

2~-3;~84~ 4 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, s various additives such as viscosity reduction agents, colorants, mold release agents, antioxid~nts, W light stabilizers and ~lame retardants. Recycled thermoplastic polymer such as recycled bottle resin from postconsumer polyethylene terephtbalate soft drink bottles may also be used. When the components have reached the desired level of dIyness, they are transported through feed lines 4Q 42, 44 and 46 by conditioned air to inventory supply bins 50, 52, 54, and 56. Each bin employs one vertical wall and xteep 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' tolS prevent ingress of room air, excess lQSS of purge air, and the escape of any particulate material.
0~ command from a central controller, predetermined amounts of the components as determined by gra~nmetric weigh units 48 and 48' are fed to weigh hoppers 60 and 60'. Each hopper is suspended from a ~o weigh cell 58 and 58' controlled to yield an accurate w¢ight for tliose 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~o and 5~o irom inventory bins~0, 52, S4 and 56. Separate wei~h hoppers 60 and 60' provide for simultaneous weigh-up and an inc~ease in ~ycle speed.
The feeders of the weighing units are preferably covered pan high frequen~y vibrating units although auger feeders could be used. The pan feeders have the general advantage of delivering vely uniformly under precise control at the lip whereas auger feeders have the disadvantage of slugg~ng slightly as material from each thread pitch is delivered.
3 o CoDsequently, the range of precision of each auger is limited more so than a vibrating pan feeder.
Weigb hoppers 60 and 60' are filled to their precise wdghts tbrough automatic feedback control between weigb cells and amplitude and timing controls to vibratory pan feeders. The two or more components 3 5 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 ,vo 93/18899 21 ~ 2 ~ 9 'I PCr/US92/02141 weight charges have been reached in the weigh hoppers, the charges are automatically dropped into a scale collection hopper 64 by the opening of 1apper valves 62 and 62' on the bottom of the respective weigh hoppers.
The combination of weigh hoppers, flapper valves and collection hopper is 5 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 physi~l properties and handling characteristics~ Typically, this bopper is ellipto conical in sha~,0 and will have a vertical forward wall and steep (70) sloping rearward wall ~; arranged in a f~ustro-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 injec~on molding 5 machine 96.
A iberglass source, bulk bag 80, is suspended from a holding rack which is supported by superstructure 72 a~d travelling crane 74. Using ; long-almed glove ent~y ports 82, drawstrings on bag 80 can be untied and the bag's downspout placed inside a funnel to discharge apparatus 84. The large 20 sacks are characterized by a bottom seal composed of an inner tubular funnel tied together with a dra~s~ring de ~ice and with outside flaps which are also operated with a drawstring device and tied with a knot. The ~llled sack is lowered onto the top surface-of a discharge box 88 which contains a flexible rubber seal which envelopes the disch rge area of the sack. Steep sides, one 2 5 vertical~ on the discharge box direct the fiberglass to a sock sealed vibrator,v covered pan feeder 85. Through a sequence control station, the feeder directs ~ fibergl~ss into a separate weigh hopper 86. This weigh hopper is support~ from the superstructure with a weigh cell. Fiberglass is allowed to enter the weigh hopper 86 until the correct weight is achieved in accordance 3 o with a control set point ar~d in accordance with set ratios with the other ingredients.
Reinforcing components in addition to or in lieu of fiberglass, such as mineral fibers, c~rbon fibers and aramid fibers, mica, glass or ceramic spheres and the lL~ce may be used in the system and fed to weigh hopper 86 as 35 described above.

WO 93/18899 PCT/US92/0214.
2~3~28~

MLxer 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 mLxer proximately above molding machinë 96, segregation of the components due to differences in solids flow characteristics of the components is not al~ed to occur. Also, fu~ball formation and glass breakage is held to a-~sinimum. - ~
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 mLxer.
~- 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 ~ystem with compvnents or from machine~y breakdown. The - ~ ~ high effidency magnet allows for wider spacing of bars in the grating permittingfreeflowofthecomponents~
The mixture of components is fed, via plug (gravity) flow into the moveable portion 98 of injection moiding machine 96 where the plastic components are melted andblended 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 3 o 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 tbe system. Purge air can be supplied by a separate dryer 108 througb feed line 38. The purge air dryer supplies debumidified blanketing air to various system units thereby prcvendng ingress of nearly all room (ambient~ air into the system.
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wo93/l8899 ~1 32(~ PC~/US92/0~141 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 confluenc,ing means adjacent 5 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 elaims.

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Claims (4)

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).