Gravimetric Compounders

A New Multi-Channel Gravimetric Batch Compounder is Weighing Up to be the Biggest Innovaation in Plastics Auxiliary Machinery and Raw Material Flow Management

The existing plastic manufacturing process of weighing, blending and conveying, which plastic manufacturers have accepted as “standard practice”, is fraught with waste, inefficiency and unnecessary complexity.

At stake are large capital expenditures on auxiliary machinery for plastics injection molding and extrusion manufacturers, in addition to floor space and ongoing maintenance costs.

This white paper examines a new gravimetric batch compounder that significantly improves plastics manufacturing job management, reduces capital expenditures and improves factory efficiency.

Today’s injection molding and extrusion plants convey their raw materials from silos via a dizzying maze of tubing; flowing into an array of plastic process equipment including hopper loaders installed on gravimetric blenders, from which the weighed batches are mixed and distributed to their respective processing machines.

As a case in point, consider a factory with 96 injection machines processing 1.2 tons/hour (each injection machine is processing on average 50kg/hr). The factory uses 10 different raw materials, and stores them in silos which are located 50 meters from a 3002 meter room that is filled with auxiliary plastic process equipment; in this case 50 four-bin gravimetric batch blenders and 200 hopper loaders. And to supply all of the raw materials from the silos to their respective hopper loader, the company will lay down a complex network of plastic tubing.

While the plastics industry has accepted the space requirements and kilometers of tubing as standard practice, one plastics auxiliary machinery manufacturer has recognized that the existing gravimetric batch blenders are both expensive and inefficient. To solve these challenges, the plastics auxiliary equipment manufacturer has developed a patent pending, automated multi-channel weighing and batch compounding system.

As a case in point, consider a factory with 96 injection machines processing 1.2 tons/hour (each injection machine is processing on average 50kg/hr). The factory uses 10 different raw materials, and stores them in silos which are located 50 meters from a 3002 meter room that is filled with auxiliary plastic process equipment; in this case 50 four-bin gravimetric batch blenders and 200 hopper loaders. And to supply all of the raw materials from the silos to their respective hopper loader, the company will lay down a complex network of plastic tubing.

While the plastics industry has accepted the space requirements and kilometers of tubing as standard practice, one plastics auxiliary machinery manufacturer has recognized that the existing gravimetric batch blenders are both expensive and inefficient. To solve these challenges, the plastics auxiliary equipment manufacturer has developed a patent pending, automated multi-channel weighing and batch compounding system.

By integrating the gravimetric batch compounder, our representative factory will be able to feed all 96 processing machines with only 4 gravimetric batch compounders, 40 hopper loaders, 96 mixers, and 136 vacuum pumps (96 machines and 40 hopper loaders), while taking up just 202 meters of space and spreading out a simple tube arrangement.

Yet of even greater significance, this new gravimetric batch compounder solves many of the complexities associated with switching between different jobs and job management; saving factories time and money far in excess than the reduced space requirements and elimination of unnecessary plastic process equipment.

Multi-Channel Weighing & Blending

The new gravimetric batch compounder simplifies and improves plastics raw material processing by centralizing the compounding of all plastic raw materials within a single system.

As opposed to the traditional gravimetric batch blender which is limited to the number of machines it can serve due to the multitude of formula variations (and therefore requires factories to be outfitted with a large number of gravimetric batch blenders), a single batch compounding system takes up only 52 meters of space and is capable of supplying up to 24 injection machines.

The new gravimetric batch compounder is comprised of up to 14 different weighing units which weigh in parallel all of the factory’s raw materials. Via an array of individual chutes and a common funnel, the plastics auxiliary equipment manufacturer has developed a plastics compounder that makes use of an advanced set of algorithms to weigh and distribute the different recipes via a single automatic manifold, which are then sent via tubing to the corresponding injection machine.

Should the plastics factory make use of multiple colors, the process can be further enhanced by integrating a gravimetric feeder that connects to the neck of the injection machine and is capable of adding the masterbatch with a level of precision unmatched in the industry.

Switching Jobs & Contamination Prevention

For factories producing multiple lines of high-quality products with very specific formulas, the weight and ratio of the raw materials which make up the batches are of utmost importance. A slight change to a formula can oftentimes effect the properties of the product, which may result in its being discarded.

When changing materials within the bins of traditional gravimetric batch blenders, operations come to a halt as the equipment requires sterilization. In contrast, the new gravimetric batch compounder stores all of the raw materials in different bins, with each of them connected to its own weighing chamber. With this simple but ingenious setup, the plastics auxiliary equipment manufacturer eliminates the need for batch blender sterilization, and makes the entire process of switching between jobs exceptionally easy. Furthermore, within the common funnel and distributor pipe of the automatic manifold, the new plastics compounding system uses a high-pressured air blast between each batch to sterilize the area and prepare for the next batch of raw materials.

Batch Uniformity

In typical plastics manufacturing, as the mixed batch is released from the gravimetric batch blender and conveyed via the delivery tube to the corresponding injection machine, it is assumed that the components of the batch are significantly blended when they enter the processing machine. However, this assumption doesn’t take into account that as the batch is vacuumed from the gravimetric blender, the materials will separate according to their specific weight, and the batch will no longer be sufficiently mixed.

The plastics auxiliary equipment manufacturer solves this problem, and achieves superior batch uniformity by placing a mixer within the free fall hopper connected to the inlet of each processing machine. Regardless of tube distance or vacuum pressure, the batch enters the injection machine thoroughly mixed.

Production Speed & Batch Accuracy

Gravimetric blenders weigh batch components in a serial order. Each component is dispensed separately into a single, common weighing chamber, from which they are all subsequently dropped into a mixing chamber before being vacuumed to their respective injection line. This method of serial weighing limits the speed with which a blender can release a batch. In addition, there is the down-time for bin cleaning and contamination prevention when changing components between jobs.

The new batch compounder improves production plastics job management speed by dedicating a weighing chamber for each individual bin; thereby weighing in parallel all of the batch components. In addition to the enhanced weighing speed, the new raw material processing system enables the use of significantly smaller load cells; thereby affording higher batch accuracy with a relatively high throughput.

Program Monitoring

By utilizing this advanced plastics batch compounder, factory managers now have access to continuously updated information concerning equipment and material efficiency. As all of the raw materials flow through a common system, the plastics auxiliary equipment manufacturer affords factory managers full monitoring of job status, and provides batch auditing, historic graphs and performance reports for each machine and job via an interactive PC dashboard.

Overall, the plastics compounding system allows factories to run a much leaner and efficient operation by reducing the need for capital equipment and simplifying the flow of raw materials. Man hours which used to be spent on batch preparations are dramatically reduced, while additional factory space is now used for other revenue generating activities.