Weighing and Mixing System

Abstract

The invention is a weigh ng and mixing system for the preparation of mixtures of components required by processing machines for the manufacture of plastic products. In particular the invention is suitable for the preparation of weighed mixtures comprised of at least two different masterbatches in order to obtain the color shade desired for a specific plastic product.

1 . A weighing and mixing system for the preparation of a mixture of granular components required by a processing machine for the manufacture of a plastic product, the system comprising:
 a. at least one separate weighing unit for each one of the components of the mixture; each weighing unit comprising a material hopper comprising at least one first opening and at least one second opening, a weighing hopper, a load cell and at least one feeding system; and   b. a chamber configured to receive the weighed components from all of the weighing units and to produce a homogeneous blend that can be delivered to the processing machine.   
     
     
         2 . The weighing and mixing system of  claim 1 , wherein, each weighing unit is configured to deliver a predetermined weight of the component to the chamber using a two stage weighing process; wherein, in a first weighing stage, a controlled amount of material equal to a little less than the weight required for the final batch is allowed to fall by gravity from the material hopper through the at least one first opening into the weighing station and onto the load cell and, in a second weighing stage, the at least one feeding system is activated to cause a small amount of material, which fails by gravity into the feeding system through the at least one second opening, to fall into the weighing hopper until the total weight of material weighed by the load cell is equal to the required weight, whereupon the activation of the at least one feeding system is halted and the weighed component is allowed to flow by gravity into the chamber. 
     
     
         3 . The weighing and mixing system of  claim 2 , wherein each feeding system comprises: (a) one of: an auger, a screw, a dosing cylinder, a feed tube, a vibratory mechanism or a conveyer belt and (b) a motor that rotates the auger, screw, dosing cylinder or feed tube or drives the conveyor belt or vibratory mechanism. 
     
     
         4 . The weighing and mixing system of  claim 3  wherein, the feed tube comprises a hollow interior section having a tightly fitted compression spring inserted into its front end and an opening to allow granules of material that fall from the material hopper through the second opening to enter the hollow interior section. 
     
     
         5 . The weighing and mixing system of  claim 4  wherein the diameter of the wire of which the spring is made and the diameter of the interior of the spring are chosen such that when the motor is activated causing the feed tube to rotate about its longitudinal axis, granules of material in the hollow interior section of the feed tube travel in single file in a spiral path through the interior of the spring until they reach the end of the spring and drop off one at a time into the weighing hopper. 
     
     
         6 . The weighing and mixing system of  claim 5  wherein the feed tube is surrounded by a cylindrical sleeve and a threaded section is created on the outer wall of the feed tube, wherein the threads in the threaded section are created in the opposite direction to that in which the feed tube is rotated in order to push any granules that attempt to enter the space between the feed tube and the sleeve back towards the opening of the feed tube. 
     
     
         7 . The weighing and mixing system of  claim 5 , wherein the weighing unit is configured to achieve the desired weight with an accuracy of less than 0.03 g. 
     
     
         8 . The weighing and mixing system of  claim 1  wherein the components of the mixture are chosen from: resins, masterbatches, and additives. 
     
     
         9 . The weighing and mixing system of  claim 8  wherein the components of the mixture comprise at least two masterbatches of different color shades that are combined by the system to produce a mixture that a processing machine will utilize to manufacture a plastic product having a single desired color shade. 
     
     
         10 . A masterbatch having a desired color shade, said masterbatch comprised of at least two masterbatches, each having a different color shade, wherein the at least two masterbatches are combined by the weighing and mixing system of claim I and then passed through an extruder and pelletizing machine to form new pellets with the desired color shade.