Description
PEX (cross-linked polyethylene) pipe is a type of flexible plastic plumbing tubing used for both hot and cold water supply lines. The formation of PEX (cross-linked polyethylene) pipe involves a process called cross-linking, which enhances the polymer’s properties and makes it suitable for various applications, particularly in plumbing. There are three main methods for cross-linking PEX: peroxide (PEX-a), silane (PEX-b), and electron beam (PEX-c).
Peroxide Method (PEX-a):
- In this method, polyethylene is mixed with a peroxide catalyst.
- The mixture is then extruded through a die to form the pipe’s initial shape.
- The extruded pipe is exposed to high-temperature water or steam, causing the peroxide to decompose.
- The decomposition of peroxide generates free radicals, which initiate the cross-linking of the polymer chains.
- This method, known as the Engel method, produces PEX-a pipe with a highly uniform and flexible cross-linked structure.
Silane Method (PEX-b):
- Polyethylene is mixed with a silane compound to create a silane-grafted polyethylene.
- The silane-grafted polyethylene is then extruded into the desired pipe shape.
- The extruded pipe is exposed to moisture, which activates the silane groups, leading to a reaction that forms cross-links between the polymer chains.
- This method produces PEX-b pipe, which is known for its balance of flexibility and durability.
Electron Beam Method (PEX-c):
- In this method, the polyethylene is extruded into the desired pipe shape.
- The extruded pipe is then exposed to high-energy electron beams.
- The energy from the electron beams induces the formation of free radicals, initiating the cross-linking process.
- PEX-c pipe is characterized by its consistent and controlled cross-linking, resulting in a durable and heat-resistant product.
Each method of cross-linking has its advantages, and the choice between them often depends on factors such as the intended application, manufacturing preferences, and regional standards. PEX pipes, regardless of the cross-linking method used, exhibit improved properties such as enhanced resistance to temperature, chemicals, and stress cracking compared to non-cross-linked polyethylene.
Applications
- Water Supply Lines
- Radiant Floor Heating Systems
- Hydronic Heating Systems
- Snow and Ice Melting Systems
- Potable Water Distribution
- Fire Sprinkler Systems
- Mobile Home Plumbing
