HDPE Shredding Technology Introduction
One of the most frequently recycled plastics is High-Density Polyethylene (HDPE) which is found in milk jugs and detergent bottles as well as industrial piping and plastic lumber. The shredding of HDPE is the initial essential process in the recycling of HDPE. Industrial shredders convert large HDPE waste into flakes or granules of the same size that can be easily washed, segregated and remodeled.
The decision to use single-shaft or double-shaft shredder is one of the most basic decisions to make when investing in an HDPE shredding system. Both designs have unique benefits based on your material, throughput and end product specifications. This guide entails a comprehensive comparison that will enable you to choose the best shredder in your HDPE recycling facility.
Single-Shaft Shredders: Strength and Accuracy
Design and Operating Principles
Single-shaft shredders have a durable rotating shaft with hardened steel cutting blades which engage with non-moving bed knives. A hydraulic ram feeder is used to exert consistent pressure on the material to feed it into the cutting chamber, providing a consistent process of bulky items. This design provides high torque at quite low rotational speeds (usually 30-60 RPM) so it is very effective with thick-walled HDPE materials.
Single-shaft shredders have a combination of shearing and tearing forces in the cutting action. The rotating blades catch and draw material into the chamber against the bed knives to produce a scissor-like cutting action as material enters the chamber. The hydraulic ram ensures that large pieces do not bridge and the feeding pressure remains constant all through the shredding process.
Important Benefits of HDPE Processing
Single-shaft shredders are particularly good in a number of important aspects of HDPE recycling:
- Thick Material Capability: These machines are able to shred HDPE to a thickness of 2 inches, which makes them well suited to industrial piping, plastic lumber and heavy containers that would be difficult to shred with other types of shredders.
- Controlled Particle Size: The accurate blade design and sizing screens allows the production of uniform output flakes of a typical size of 10-50mm, which is suitable to most washing and pelletizing systems.
- Contaminant Tolerance: The design is very strong and can tolerate materials with moderate contamination (dirt, minor metal content) in a better way compared to many other systems.
- Large Item Processing: The hydraulic ram system allows the whole HDPE pipes to be fed up to 48 inches in diameter without pre-cutting.
Typical Applications
Single-shaft shredders are especially suitable in:
- Municipal and industrial recycling of HDPE pipe
- Reduction in size of plastic pallets and containers
- Purge material processing and thick plastic sheet
- Heavy plastic vehicle and industrial recycling
Performance Specifications
Single-shaft shredders of industrial-strength are generally powered by 50-400 horsepower motors, and have a throughput capacity of 500-5,000 pounds per hour, depending on the density of the material and the desired output size. The output flakes of these machines are normally in the range of 10-50mm, and sizing can be changed by altering the screen.
Efficiency and Versatility: Double-Shaft Shredders
Design and Operating Principles
The two counter-rotating shafts of a double-shaft shredder have intermeshing cutters and produce a tearing and crushing effect. They are usually not hydraulic rams but gravity or conveyor fed as opposed to single-shaft models. The twin-shaft system has greater rotational speed (60-120 RPM) and offers self-cleaning effect, which eliminates the chance of material wrapping around the shafts.
The shearing action typical of single-shaft shredders is less aggressive than the tearing action of the cutting mechanism of the double-shaft shredders. This makes them particularly effective for mixed material streams and thinner plastic items that might otherwise slip through single-shaft cutters.
Important Benefits of HDPE Processing
There are a number of advantages of using a double-shaft shredder:
- Increased Throughput: The constant feeding and twin-shaft action normally gives 20-30 percent increased throughput over the equally powered single-shaft model.
- Energy Efficiency: The tearing operation uses a smaller amount of energy per ton processed in comparison to shearing which is dominant in single-shaft machines.
- Material Flexibility: These shredders can process mixed plastic streams (HDPE and LDPE etc.) easier than a single shaft shredder.
- Small Footprint: Depending on the design, twin-shafts may have small footprint in comparison with identical single-shaft types.
Typical Applications
The double-shaft shredders are especially useful in:
- Recycling of HDPE bottles and containers as post-consumer material
- HDPE packaging and film materials that are thin-walled
- Mixed plastic bales with HDPE constituents
- Mass recycling plants that handle a variety of plastic streams
Performance Specifications
The typical motor power of industrial double-shaft shredder is 30-300 horsepower, and the throughput is 1,500-10,000 pounds per hour. The sizes of output are usually bigger compared to single shaft machines (15-100mm), and the distribution of particle size is more varied. The increased operating speeds will increase the throughput but can cause additional heat in the processed material.
Comparative Analysis: Choosing an Appropriate Shredder
Material Considerations
What type of HDPE feedstock you have should make the decision of the shredder you use:
Single-shaft shredders have the following advantages:
- Heavy walled materials (solid blocks, pipes)
- Bulky items that have to be forced fed
- Applications that require accurate particle sizing
- Potentially-contaminated materials
The double-shaft shredders are excellent with:
- Packages and containers that are thin-walled
- Mixed plastic flows
- Mass production
- Energy efficient operations
Operational Factors
There are some major differences in the operations that should guide your choice:
- Throughput Requirements: The double-shaft models tend to provide greater throughput with equal power, whereas single-shaft gives greater controlled processing of hard materials.
- Energy Consumption: Single-shaft shredders are usually more energy consuming per ton of work processed since these machines exhibit high-torque shearing capacity.
- Maintenance Needs: The single-shaft type machines needed more frequent knock-off of the blades but boasted greater accessibility to the cutting components. The interval between servicing is longer in double-shaft models but the disassembly is more complex.
- Floor Space: Double-shaft designs tend to be smaller which is a significant fact since space is at a premium in many facilities.
Cost Considerations
There is a big variance in total costs of owning technologies:
- Capital Cost: Single-shaft shredders are generally priced at 20-30 percent premium compared to similar double-shaft shredders
- Running Cost: The double-shaft shredder usually has lower running cost on each ton processed
- Maintenance Cost: Single-shaft types are more expensive to maintain with regards to maintaining the blades but can potentially last a longer service life
High Configuration Options
A lot of contemporary recycling processes have adopted a hybrid system that combines the use of the two technologies:
- Primary/Secondary Systems: The single-shaft is used as primary size reduction and the double-shaft as final grinding.
- Parallel Processing: Sorting of various streams of material to dedicated shredders
- Integrated Systems: Making use of shredders in combination with downstream washing, separation and pelletizing machinery
There are newer technologies such as intelligent load-sensing control, automated blade gap control, and predictive maintenance capabilities that are being introduced on both types of shredders and further increasing the performance of these systems and their reliability.
The Final Decision
In choosing between single-shaft and double-shaft HDPE shredders, the following are some of the critical questions that should be put in mind:
- Which is your main HDPE material to process?
- What is your throughput requirement?
- What is the big deal with particle size consistency to your downstream processes?
- What are your space and power limitations?
- How much is your overall budget including operating costs?
Single-shaft shredders are usually the best solution to operations that only deal with thick-walled HDPE materials. The double-shaft technology is more useful in facilities that process mixed plastics or those that need maximum throughput. Most large-scale recyclers end up adopting both of them in order to manage their entire material streams in the most efficient manner.
Asking a professional shredder manufacturer can also offer good advice that is specific to your application. Most suppliers with a good reputation provide material testing so that you can test your machine with your own feedstock before you make the purchase decision.