Biaxially Oriented HDPE Pipe Drawing Without Necking
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for producing biaxially oriented pipes often result in poor resistance to crack propagation due to the requirement for high axial draw ratios, which can lead to necking issues and make the production process challenging, especially for pipes with specific dimensions.
Innovation Solution
The use of bimodal or multimodal HDPE compositions allows for biaxial drawing at low axial draw ratios, preventing necking and enabling the production of pipes with improved resistance to crack propagation through a stable, neck-free process, where the axial draw ratio is selectively adjusted based on desired pipe dimensions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If high axial draw ratio is used for biaxial drawing, then pipe dimensions can be achieved, but resistance to crack propagation deteriorates and necking issues occur
Solution Approach 1:
The patent changes the material parameter from unimodal to bimodal or multimodal HDPE composition, which has different molecular weight distributions. This parameter change allows the material to be drawn at low axial draw ratios (1.03-2.0) without necking, while maintaining good resistance to crack propagation, thus resolving the contradiction between achieving pipe dimensions and maintaining reliability
Solution Approach 2:
The patent uses bimodal or multimodal HDPE which can be considered as a composite of polymer chains with different molecular weights and structures. This composite structure provides both the ductility needed for low draw ratio processing and the strength needed for crack propagation resistance, resolving the contradiction between manufacturing precision and reliability
2Manufacturing precision
If high axial draw ratio is used for biaxial drawing, then pipe dimensions can be achieved, but the production process becomes difficult due to necking
Solution Approach 1:
The patent changes the material parameter to bimodal or multimodal HDPE composition, which enables stable drawing at low axial draw ratios without necking. This parameter change simplifies the production process while maintaining the ability to achieve precise pipe dimensions, resolving the contradiction between manufacturing precision and ease of manufacture
3Reliability
If pipe wall thickness is increased to resist outside damage, then reliability improves, but production complexity increases
Solution Approach 1:
The patent changes the material parameter to bimodal or multimodal HDPE, which allows production of pipes with various wall thicknesses through simple adjustment of drawing parameters rather than complex process changes. This enables producing reliable thick-walled pipes while keeping the production process simple and manageable
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach results in pipes with enhanced time-to-failure properties and easier production, particularly for pipes with larger diameters or thicker walls, by allowing for a more manageable and efficient drawing process.
Implementation Method 1
Upon solid-state drawing, semi-crystalline polymers such as polyethylene form a neck. This neck has to be drawn out until a product with a uniform thickness is obtained.
Implementation Method 2
Upon solid-state drawing, semi-crystalline polymers such as polyethylene form a neck. This neck has to be drawn out until a product with a uniform thickness is obtained.
Data Source
AI summary
The invention relates to a process for producing a biaxially oriented pipe, comprising the steps of: a) forming a polyethylene composition into a tube, wherein the polyethylene composition comprises a bimodal or a multimodal high-density polyethylene (HDPE) and b) stretching the tube of step a) in the axial direction and in the peripheral direction to obtain the biaxially oriented pipe, wherein step b) is performed at an axial draw ratio of 1.1 to 3.2 and an average hoop draw ratio of 1.1 to 2.0 and the obtained biaxially oriented pipe has an outer diameter of at least 60 mm and a wall thickness of at least 5.5 mm or step b) is performed at an axial draw ratio of 1.1 to 1.9 and an average hoop draw ratio of 1.1 to 2.0 and the obtained biaxially oriented pipe has an outer diameter of less than 60 mm, and wherein step b) is performed at a drawing temperature which is 1 to 30 ºC lower than the melting point of the polyethylene composition.