How the right pelletizer can help you make the most of your materials | Plastic Technology

2021-11-16 19:44:54 By : Mr. zhi jiang

Not all pelletizers have the same design, so which one is right for your application? What you have today may be purchased for a completely different application, and may not be the best fit for your needs. Here are some things to consider that can help you decide what is best for you. #Best Practices

Good granulation materials have uniform particle size, no dust and fine particles. 

The size and shape of inferior granular materials are irregular (excessive dust and fine powder).

The "super tangential" cutting chamber with a three-blade open rotor is the best choice for large items such as bottles and containers. It is also suitable for a large number of runners and small parts, as well as thin films.

The "tangential" cutting chamber with a five-blade open rotor is optimized for thin plates and thicker wall parts. It is also effective for large quantities of pre-shredded materials and higher capacity films.

The modern granulator design provides a safe and convenient passage for cleaning and maintenance.

When planning to invest in pelletizing equipment, choosing the right equipment for your application allows you to start with simple tasks at the beginning, and once you start asking questions, you will become overwhelmed. When you hear buzzwords such as low speed and high speed, you start to wonder what you really need. They are all the same, right? From the big picture, they all cut things into small pieces.

But what are you really buying? Think of the pelletizer as a tool, like a drill. When buying a drill, your goal is to choose a drill that allows you to drill a good hole of the required size in a specific type of material. With a pelletizer, the ultimate goal is to transform your materials from their current state into high-quality pellets, thereby maximizing the reuse of these materials.

Therefore, where things start to get more complicated is that the pelletizer is not a one-size-fits-all solution. To better understand this, let us define what high-quality granular materials are.

The quality of the particles boils down to three main issues:

 • Cleanliness: it must be free of dust and fine powder, if it separates from the particles during the air conveying process, they represent the loss of material. Or, if it is not filtered out, it will have a negative impact on processing when it is reintroduced into the extruder or molding machine. The type of material needs to be considered, because brittle materials may be more likely to break during the granulation process and produce fine powder and dust.

 • Uniformity: Consistent particle size results in a consistent bulk density and a more consistent feed and mixing with the original particles-and a more consistent melting in the barrel.

 • Size: Choosing the appropriate size of the granulator screen helps to balance the required throughput and the final particle size that is compatible with the original feed size.

No matter what plastics processor you are in, there will always be materials that can be recycled. Whether it is the runner in the injection molding process, the corner trimming of sheet or film extrusion lines, or the burrs of blow molding, this form of material has value. This does not include substandard parts or starting materials.  

When you consider rising raw material costs, increased demand for price reductions, and end-user market hopes to include recycled materials, the use of granular materials should be viewed as marketing opportunities and cost control. 

If this material is improperly handled or simply discarded, it will have a significant and direct impact on the bottom line. Taking the time to assign a dollar value to this material can bring a very fast return on investment (ROI). This material is already on hand-if it contains color, the value will increase because the color masterbatch may be more expensive than the resin itself. More importantly, if the colors do not match, the non-compliance will again have a negative impact on your bottom line. In addition to saving costs, recycling waste is also a responsible approach.

Now that we have defined what we are going to do, what do you need to know to choose the right tool for the job? 

With the advancement of cutting technology and machine design, the reduction of energy consumption, and the increase in the degree of automation that can be used in size reduction systems, there are many cost-effective solutions that can be used to provide high-quality regrinds for the manufacturing process without compromising Productivity, part quality, or plant environment. Many years ago, it was common for processors to specify a certain size of pelletizer motor or cutting chamber opening. Nowadays, suppliers of downsizing equipment like to ask specific questions in order to provide processors with the best solutions.

The following are important key questions to help select the best pelletizer for the application:

 • What is your application? The most common is that we handle blow molding, injection molding, extrusion, thermoforming and recycling, and distinguish between post-industrial and post-consumer varieties.

 • What kind of material do you want to process? The type of material affects the recommendation. The types of common resins and the presence of fillers or reinforcing materials must be considered.

 • How will you introduce the material into the pelletizer? Common methods are manual feeding, feeding with conveyors, pull rollers or robots, and blowing materials through an air conveying system.

 • What will you feed? This will be the physical description of the material to be fed-that is, the bottle, sheet, film, tube, or gate/runner.

 • What is the size of the food you wish to feed? Understanding the maximum to minimum size range and wall thickness will help guide the selection of the best pelletizer.

 • How much throughput do you need? It is important to understand this, and it is usually expressed as lb/hr or kg/hr.

 • What size particles do you want? This is the final output size, usually ⅛ inch (4 mm) to 1 inch (25 mm), of which 5/16 inch (8 mm) to ⅜ inch (10 mm) is very common.

Many of these issues seem to be common sense... and usually they are. Although it is difficult to find one of the most important questions, one that seems very elusive is "What is the throughput?" Really understanding this value helps machine selection and return on investment.

Buying a pelletizer that is too small or too large will have a major impact on the success of your project. It is very important to have a firm grasp of the amount of material that needs to be processed.

Compared with the intermittent rate, the connection between how much you need to deal with and the selected granulator can be directly related to the instantaneous throughput. Considering only the intermittent rate, it is easy to reduce the size of the granulator.

To explain the intermittent rate, we assume that the information provided is 600 pounds per hour, and your parts are each 10 pounds. With this in mind, only one part can be fed into the pelletizer per minute. However, if you collect 600 pounds of material before the end of an hour, and you want to process them within 15 minutes, the instantaneous rate is 2400 pounds per hour, and the choice of granulator changes radically. But be careful, because the oversized granulator is also something you want to avoid. If the large granulator is idle and the rotor runs idly, the energy efficiency ratio is greatly reduced.

In this example, if you choose a 600 lb/hr machine and feed it at an equivalent rate of 2400 lb/hr, the pelletizer that is too small will eventually be overfed and eventually lead to unplanned maintenance. The granulator works best with a stable diet at its designed rate.

Advances in the design of the cutting chamber have enabled the pelletizer to operate at an optimal level, extending tool life, reducing dust and fines generated, and reducing energy consumption.

Accepting the fact that the pelletizer is not a panacea, it is important to realize that the type or design of the cutting chamber will have a significant impact on the quality of the pelletized material.  

Taking blow molding applications as an example, modern granulator designs will adopt technologies such as "super tangential cutting chamber", in which there is an abdomen in the cutting chamber, and parts are consumed faster, thereby minimizing the cutting time. Consumed in the cutting room. This more efficient cutting procedure helps to extend tool life because materials are processed faster; reduce noise and energy consumption; and most importantly, produce the high-quality particles you are looking for. The correct cutting chamber design will be more efficient, and usually allows physically smaller machines to complete tasks that used to require larger machines.

Unplanned maintenance is costly, but improper cleaning and non-compliance with planned maintenance can be very expensive, which can lower your bottom line.

The maintenance and cleaning of pelletizers and their key components is usually the most overlooked service area in many facilities. Machines that are difficult to clean are usually directly related to poor designs that prevent people from easily entering the cutting room. Modern pelletizer design allows quick and easy access to the cutting room, reducing planned or unplanned downtime. Statistics tell us that cleaning and maintenance can account for 80% of the operating cost of the pelletizer. The newer design greatly helps to reduce the overall impact.

The modern design also extends to the cutting action inside the pelletizer. It is best to look for a machine that uses "scissors cutting" to reduce the energy required and produce the most uniform granular material, while reducing the wear of the granulator. Scissor cutting helps reduce the overall impact on the cutting system, thereby reducing power consumption, reducing noise and improving operating efficiency.

Another key feature of modern granulator design is the adjustable rotating knife. These knives are connected to the rotor, which rotates in the cutting chamber to produce the cut. The principle of the adjustable rotor knife is to make the knife tip as close as possible to the granulator screen. This eliminates areas where material can accumulate and reduces frictional heat, preventing the screen from clogging.

Many pelletizers have knives that can be sharpened, and there is approximately 10 mm (⅜ inch) of material available when sharpening the knives. Rotating tools and fixed tools gradually become shorter until the minimum length is reached.

In older pelletizer designs, these knives were fixed on the rotor, and they could not be adjusted. The bedknife could only be moved forward to compensate for the material removed during the sharpening process. The sharpening process is a variable-it is quite difficult to obtain the same tool. The result is that you can finally use tools of different lengths. If the length changes more than 0.002 inches, the bed knife can only be set to the highest knife, so only one knife completes most of the cut. When this happens, it is difficult to set all tools to the same clearance. This will also lead to increased heat and motor load, thereby increasing the hidden costs of the process.

Although there are many variables to consider, if you start with the above variables, you will easily find the best pelletizer for your application and enable you to get the most benefit from the materials you have purchased.

About the author Jim Hoffman is the vice president of sales/marketing and service for Rapid Granulator Inc. in Leedsdale, Pennsylvania. He is responsible for sales in North America and has been with Rapid for more than 28 years. Rapid Granulator, Inc. is a wholly-owned subsidiary of Rapid Granulator, AB of Sweden. Contact: jimh@rapidgranulator.com; rapid granulator

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