The Optimization of a Polymer Extruder

OVERVIEW

Viscous molten polymer extrusion is an industrial process used to produce polymers for a variety of applications, including medical devices, packaging, construction materials, and others. Crucial to the quality of these polymers is filtration of the molten polymer to remove any contamination, mainly small metal particles.

Filtration is done by forcing the polymer through a wire mesh screen. The mesh size is selected based on polymer property requirements but typically ranges from 20 to 100 mesh (0.60 to 0.04 mm sized particles passing). The screen is supported by a breaker plate. Collectively, the screen mesh and the breaker plate form the screen pack.

The screen pack experiences a pressure drop, which is the difference in pressure between the inlet and outlet of the screen pack. The pressure drop is important because it determines the amount of force required to extrude the polymer. The higher the pressure drop, the more force is required, which leads to increased energy consumption and wear on the extruder.

The pressure drop is affected by several factors, primarily by the viscosity of the polymer. However, the design of the screen pack used in the process is also vitally important.

This Challenge is looking to optimize the design of an extruder screen pack the Seeker uses to extrude a basic, commodity grade polypropylene. The specific goal of this Challenge is to decrease the pressure drop of the process by at least 25% and, ideally, by 50%.

This is a Prize Challenge which requires a written proposal to be submitted. Awards will be contingent upon the theoretical evaluation of the proposals by the Seeker, followed by experimental validation of a few, most promising, proposals. There will be a guaranteed award for at least one submitted solution. The total payout will be $15,000, with at least one award being no smaller than $5,000 and no award being smaller than $2,500. By submitting a proposal, the Solver grants the Seeker a right to use any information included in their proposal.

Submissions to this Challenge must be received by 11:59 PM (US Eastern Time) on December 3, 2023.

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THE CHALLENGE

An extruder is a key part of a continuous polymer manufacturing process.  The raw material is fed into the process section of the extruder, where it melts, disperses, and homogenizes (Figure 1). This is accomplished by the mechanical shearing action of the rotating screws in the processing section. Power is provided by the electric drive system, an electric motor coupled with a speed-reducing and timing gearbox to drive the screws.

                                                           Figure 1. A schematic design of an extruder

The screening section of the extruder filters the molten polymer to trap solid particles and remove them from the melt stream. (The solid particles are typically metal contamination in the feed or wear particles from the extruder; their concentration is very low but non-zero. Most of the particles are ferro-magnetic but non-magnetic material is present too.) The cleaned polymer is then forced through the form-giving die. 

While most of the drive system power is used to melt the polymer, the pressure drop through the screen pack is significant.  (Some extruder systems use a melt pump, an independently, driven gear pump, to build pressure for screening and the die).

The screening section of the extruder contains the screen pack, which has two components (Figures 2 and 3):

• Woven wire mesh screens. The standard US mesh size is selected based on product requirements.
• Breaker plate, which provides mechanical support for the screens and has 266 of 3mm capillary holes to allow product flow.

                                                          Figure 2. Wowen screen and breaker plate.                                                                                                    

                                  Figure 3. Major dimensions of the breaker plate

The open area of a screen pack is the total area of breaker plate capillaries.  For this screen pack, the open area is 266 x π x (3mm x ½)² = 1,880 mm²; the total area of wire mesh screen is π x (90mm x ½) ² = 6,362 mm², so that % open area is 29.6% (1,880/6,362).

Screen pack pressure drop is a strong function of the open area, not the total area of the wire mesh screen.

The extruder design allows easy access to the screen pack. The screen pack is changed periodically for a variety of reasons including high pressure drop due to the contamination load. 

While most of the drive system power is used to melt the polymer, the pressure drop through the screen pack is also significant, which increases the energy consumption and wear on the extruder.

The initial pressure drop is affected by several factors:

• Viscosity of the polymer
• Extruder mass flow rate
• Screen mesh size
• Breaker plate design

The goal of this Challenge is to optimize the design of an extruder screen pack to decrease the pressure drop by at least 25% and, ideally, by 50%, while extruding a basic, commodity grade polypropylene.

The Seeker envisions that this objective can be achieved by several approaches:

1. Changing the shape or diameter of the wire in or the weave of the mesh screen.
2. Changing the design of the breaker plate including open area, thickness, and material of construction (currently stainless steel).
3. Proposing a design that would remove solid particles from the molten polymer by means other than physically passing it through a ridged opening.

The evaluation of the proposed designs will be done on a laboratory scale twin-screw extruder fed with Raffia grade polypropylene homopolymer (hPP) with a Melt Flow Rate (MFR) of 4.5 g/10 min as measured at 230°C and 2.16 kg of applied load according to ASTM D1238. The following baseline conditions will be applied: 

• Extruder mass flow rate: 45 kg/h
• Melting temperature: 230°C
• Wire screen: US Standard Mesh 100 (149 µm)

SOLUTION REQUIREMENTS & ACCEPTANCE CRITERIA

The Seeker is open to any innovative approach for as long as the proposed solution would meet the following Solution Requirements:

1. The proposed solution should decrease the clean screen pressure drop by at least 25% and, ideally, by 50%.
2. Particles larger than 149 µm must be separated from the polymer melt prior to reaching the die.
3. The design must either fit in the volume occupied by the incumbent screen pack or fit on the top of the breaker plate as does the current screen mesh.
4. The design must be operational under the following conditions:
   1. Operating temperature: 300^oC – 450^oC.
   2. Maximum pressure drop: 150 bar.
5. Material of construction must be a 21 CFR food contact material as does the current material (stainless steel).
6. The device (without disposable standard wire mesh screens) must be reusable after a furnace cleaning.

However, the Seeker will not accept solutions based on:

1. Modification of the extruder itself (e.g., screen pack of a larger diameter).
2. Use of pleats or other 3D designs which only increase the open screen area.

Solutions with Technology Readiness Levels (TRLs) 5-6 are invited.

This is a Prize Challenge, which has the following features:

1. The best solution in a Prize Challenge has the opportunity to win the award of $15,000 if you meet all requirements, as solely determined by the Seeker.
2. There will be a guaranteed award for at least one submitted solution. With the total payout being $15,000, at least one award will be no smaller than $5,000 and no award being smaller than $2,500.
3. Awards will be contingent upon the theoretical evaluation of the proposals by the Seeker followed by experimental validation of a few, most promising, proposals.
4. By submitting a proposal, the Solver grants the Seeker a right to use any information included in their proposal.
5. The Seeker may also issue “Honourable Mention” recognitions for notable submissions that are not selected for monetary awards.

YOUR SUBMISSION

Please complete the submission form.

The submitted proposals must be written in English and can include:

1. Participation type – you will first be asked to inform us how you are participating in this challenge, as a Solver (Individual) or Solver (Organization).
2. Solution Stage - the Technology Readiness Level (TRL) of your solution, TRL1-3 ideation stage, TRL4-6 proof of concept stage, TRL7-9 production ready stage.
3. Problem & Opportunity - highlight the innovation in your approach to the Problem, its point of difference, and the specific advantages/benefits this brings  (up to 500 words).
4. Solution Overview - detail the features of your solution and how they address the Solution Requirements (up to 500 words, there is space to add more, and to add any appropriate supporting data, diagrams, etc).
5. Experience - Expertise, use cases and skills you or your organization have in relation to your proposed solution. The Seeker may wish to partner at the conclusion of the Challenge; please include a statement indicating your interest in partnering (up to 500 words).
6. Solution Risks - any risks you see with your solution and how you would plan for this (up to 500 words).
7. Timeline, capability and costs - describe what you think is required to deliver the solution, estimated time and cost (up to 500 words).
8. References - provide links to any publications or press releases of relevance (up to 500 words).

Wazoku encourages the use by Solvers of AI approaches to help develop their submissions, though any produced solely with generative AI are not of interest.

Find out more about participation in Wazoku Crowd Challenges.

Submissions to this Challenge must be received by 11:59 PM (US Eastern Time) on on December 3, 2023.

Late submissions will not be considered.

Your submission will be evaluated by the evaluation team first reviewing the information and content you have submitted at the submission form, with attachments used as additional context to your form submission. Submissions relying solely on attachments will receive less attention from the evaluation team.

After the Challenge submission due date, [the Seeker] will complete the review process and make a decision with regards to the winning solution(s) according to the timeline in the Challenge header. All Solvers who submit a proposal will be notified about the status of their submissions.