Abstract:
A wide throat internal mixer and method of mixing a batch of petrochemical material wherein bales are fed by a corresponding large size ram weight from a large size hopper into a mixing chamber through a corresponding large size throat opening having wear plates.

Description:
TECHNICAL FIELD 
     This invention relates to high intensity mixing machines for elastomeric materials. A batch of ingredients including carbon black is fed into a hopper which has a ram weight connected to a piston rod for controlling movement of the materials into the mixer. The hopper is closed except when the ingredients are being loaded. 
     BACKGROUND ART 
     Internal mixers of a 8.36 cubic feet (237 liter) size such as a that shown in U.S. Pat. No. 5,492,403 have been made and operated in rubber plants for many years. The mixer body has had a rectangular throat opening of 11.5 inches (29.21 cm) by 32 inches (81.28 cm), a piston-cylinder with an 11 inch diameter (27.94 cm) for operation on 100 psi, (7.03 kg/sq cm), factory supplied air pressure providing an effective stock pressure of 27.2 psi (1.91 kg/sq cm). Mixing time, that is the time required to raise the temperature of the rubber mixture from ambient (room temperature) of 80° F.-90° F. (27° C.-32° C.) to a discharge temperature of 350° F., (662° C.) has been 3.5 to four minutes. Loading time has taken from one to several minutes. 
     The mixer body has been replaced approximately every seven years because of wear in the throat area and inside the mixer body. Complete replacement of these 237 liter mixers with new larger mixers has not been feasible in older rubber plants because of the increased weight of the new mixers which would require extensive changes to the rubber plant. Also the cost of new mixers and other equipment for the larger size mixer is substantial. [$2,200,000 for a new 8.36 cubic foot (270 liter) mixer assembly]. 
     DISCLOSURE OF INVENTION 
     The present invention is directed to a modification of the present 8.36 cubic feet (237 liter) size internal mixer which does not require enlarging the size of the mixer body. By increasing the size of the throat of the mixer body, adding a new size ram weight and hopper and a new size piston-cylinder apparatus, substantial improvements in production and quality have been achieved. Also, by adding wear plates at the throat area, the time between replacements of the mixer body has been increased. 
     In accordance with one aspect of the invention there is provided: an internal mixer for mixing petrochemical materials and other ingredients to be vulcanized comprising a mixer body, a mixing chamber in the body, a throat opening for charging the mixer, a discharge opening for discharging the mixer, a ram weight, a hopper and a piston-cylinder assembly for urging the ram weight into the throat opening and applying pressure to the petrochemical materials and other ingredients in the mixing chamber characterized by the mixing chamber having a volume not over 8.36 cubic feet (237 liters), the throat opening having an area of at least 576 square inches (3,715 cm 2 ), the hopper having a cross sectional area of at least 576 square inches and the ram having an area of at least 576 square inches (3,715 cm 2 ). 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a fragmentary sectional view of a prior art internal mixer assembly. 
     FIG. 2 is a fragmentary sectional view of the internal mixer having the same size mixer body as the mixer of FIG.  1  and the wide throat and other improvements embodying the present invention. 
     FIG. 3 is an enlarged fragmentary plan view of the mixer body taken along line  3 — 3  in FIG. 2 showing the wide throat and wear plates. 
     FIG. 4 is a sectional view of the mixer body showing the throat and wear plates taken along line  4 — 4  in FIG.  3 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, a prior art internal mixer assembly  10  is shown having a mixer body  12  with a mixing chamber  14  having a capacity of 8.36 cubic feet (237 liters). A door  16  (shown in the closed condition) is provided to close a discharge opening  18  in the mixer body  12 . A throat  20  is provided in an upper wall  22  of the mixer body for receiving the ingredients to be mixed from a hopper  24  mounted on the upper wall  22  of the mixer body  12 . A piston-cylinder assembly  26  is mounted on the hopper  24  with a piston  28  fastened to a piston rod  30  connected to a ram weight  32  located in the hopper  24 . 
     In this prior art internal mixer assembly  10  the throat  20  in the mixer body  12  has an opening having a width of 11½ inches (29.21 cm) and a length of 32 inches (81.28 cm) or a total area of 368 square inches (2,373.65 sq cm). The ram weight  32  and the hopper  24  are of substantially the same size for movement of the ram weight into the throat  20  during operation of this internal mixer assembly  10 . 
     The piston-cylinder assembly  26  has an air inlet pipe  34  in communication with a supply of air pressure from the factory which may be 100 psi (7.03 kg/sq cm). The diameter of the piston  28  is 11 inches (27.94 cm) and is slidably mounted in a cylinder  36  of the piston-cylinder assembly  26 . The cylinder  36  also has a diameter of 11 inches (27.94 cm). A loading door  38  is hinged in the hopper  24  and is movable to an open position not shown for adding ingredients to the hopper. 
     With reference to FIG. 2, an internal mixer assembly  40  is shown embodying the invention wherein the mixer body  12 ′ is the same as the mixer body  12  of the prior art internal mixer assembly  10 , except a new throat opening  42  has a width w of 18 inches (45.72 cm) and a length of 32 inches (81.28 cm). This provides an area of 576 square inches (3,715 sq cm) in contrast to the area of the throat  20  of the prior art assembly  10 , which is 368 square inches (2,378.60 sq cm). The new throat opening  42  also has wear plates  44  and  46  covering the side surfaces of the opening. 
     Mounted on the mixer body  12 ′ is a hopper  48  containing a ram weight  50 . The ram weight  50  is sized to fit in the new throat opening  42  and has a width of 17.625 inches (44.76 cm) and a length of 31.625 inches (80.32 cm), providing enough clearance to slide into the new throat opening. Mounted on the hopper  48  is a piston-cylinder assembly  52  having a piston  54  slidably in mounted in a cylinder  56  with a piston rod  58  connected to the ram weight  50 . A pipe  60  in communication with the cylinder  56  and a source of factory air is also provided at the top of the cylinder  56 . The piston and cylinder have a diameter of 22 inches (55.88 cm) and the factory supply of air pressure may be around 79 psi (5.55 kg/sq cm). A loading door  62  may be hinged in the side of the hopper  48  and is movable to an open position not shown for adding ingredients to the hopper. 
     The wear plates  44  and  46  of the new throat opening  42  are of a material such as heat tempered steel plate having a 55-60 Rockwell hardness which is of greater hardness than the cast steel material of the ram weight  50 . This results in the ram weight  50  wearing out sooner than the wear plates  44  and  46  at the throat  42  of the mixer body  12 ′. With this construction there is a savings in the replacement of worn parts since it is less costly to replace the ram weight  50  than the mixer body  12 ′. 
     In operation it has been found that substantial improvements in production and quality of the mixing have been achieved with the new internal mixer assembly  40 . In loading the mixer  40 , bales of petrochemicals, such as natural rubber, are fed into the throat openings  20  and  42 . These bales have one side of 11.5 inches by 32 inches (29.21 cm by 81.28 cm) and it has been found that because of the wider throat opening of the new internal mixer assembly  40  there is an improvement in loading which can be done automatically in 45 seconds for each charge. Other ingredients which are mixed in with the petrochemicals are paraffins, carbon black in powder or granule form and process oils which may be heated in liquid form. With the new internal mixer assembly  40  it has been found that the dispersion of the carbon black and heated oils in the mixed product over the dispersion in the mixture produced by the prior art mixer assembly  10  is much improved. This has been determined by examining the product for dispersion under magnification. 
     The new internal mixer assembly  40  provides mixing under an effective stock pressure of 54 psi (3.94 kg/sq cm). This is compared with an effective stock pressure of 27.2 psi (1.91 kg/sq cm) for the prior art internal mixer assembly  10 . Effective stock pressure is the product of the pressure in the cylinder  26  and the face area of the piston  54  divided by the ram weight  50 . The mixing time has also been reduced to 1.5 minutes from 3.5 to 4 minutes necessary with the prior art internal mixing assembly  10 . The mixing time is determined by the time required to increase the temperature from the feeding temperature, or ambient (room) temperature of 80° to 90° Fahrenheit (270 to 32° C.) to a discharge temperature of 350° F. (177° C.). It is believed the rapid increase in temperature is due to the increased size of the ram weight  50  and the pressure exerted by the ram weight on the batch of rubber in the mixer chamber  14 ′. After the batch of rubber is mixed, the door  16 ′ is opened to discharge the batch from the mixing chamber  14 ′. With the new internal mixer assembly  40  the loading time has been reduced to 45 seconds from the 1 to several minutes with the prior art mixer assembly  10 . This is a substantial savings in a 24 hour period of continuous operation. 
     From these test results it has been demonstrated that without any substantial change to the mixer body  12  substantial improvements in production and quality can be obtained. This has resulted in large savings in not having to buy new and larger equipment and redesigning factory space for the larger equipment. Before this invention, larger internal mixers were designed and made with 9.53 cubic feet (270 liter) volumes, whereas the new internal mixer assembly  40  makes this economically unnecessary at this time. 
     While certain representative embodiments and details have been shown for the purpose of illustrating the invention, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention. Having thus described the invention, it is now claimed: