Pex is a high-density cross-linked polyethylene material. When the degree of cross-linking is good, it is of high quality and low price, better than pert. The only good feature of pert is that it can be hot-melt connected. PEX can't, you can only rely on special connectors. PB is polybutylene material PE-X: Domestic production generally adopts the method of medium density polyethylene or high density polyethylene and silane cross-linking or peroxide cross-linking. It is chemical bonding between long linear molecular chains of polyethylene to form a three-dimensional network molecular chain structure. Compared with ordinary polyethylene, its properties such as tensile strength, heat resistance, aging resistance, stress cracking resistance and dimensional stability are improved. The entire production process is a chemical reaction process. This type of floor heating has difficulties such as the cross-linking agent being difficult to disperse evenly, the degree of cross-linking being difficult to control consistently, and the screw needing to be cleaned regularly to prevent the generation of gel particles. The quality control of the product is difficult, and it is difficult for ordinary small-scale production companies to do a good job. Qualified PE-X pipes have the advantages of good mechanical properties, high temperature resistance and low temperature resistance. However, PE-X pipes have no thermoplastic properties and cannot be connected and repaired by hot melt welding.
PB: Known as the soft gold among plastics, it has superior creep resistance and mechanical properties. It is the softest among several floor heating pipes and has the thinnest calculated wall thickness under the same design pressure. Under the same conditions of use and the same wall thickness series of pipes, this variety has the highest safety. However, the price of raw materials is the highest, more than double that of other varieties, and currently its application area in China is small.
PE-RT: The raw material for floor heating is a medium-density polyethylene with very stable mechanical properties. It is made of ethylene and octene monomers catalyzed by metallocene polymerization. Its unique ethylene main chain and octene short-chain branch structure enable it to simultaneously possess the superior toughness of ethylene, stress crack resistance, low-temperature impact resistance, outstanding long-term water pressure resistance, and the thermal creep resistance of octene. It can be connected by hot-melt connection. If it is accidentally damaged, it can also be repaired by hot-melt connection of pipe fittings. The raw material for floor heating has a creep failure curve that meets product standards. It is the only polyethylene variety at this stage that can be used in hot water pipes without cross-linking. , commonly known as the soft gold in plastics, its performance in all aspects is higher than the former. It's just a question of price. PE-RT - high temperature resistant polyethylene pipe, which is a polyethylene pipe formed by extrusion using medium density polyethylene DOWLEX*2344E produced by the American Dow Chemical Company as raw material. The improvement in raw materials and unique molecular structure make it have significant advantages in other aspects compared with PEX cross-linked polyethylene, in addition to the same high thermal conductivity, mainly in the following aspects:
1. Long service life
The damage of plastic pipes usually has the following three stages: creeping damage, brittle damage, and oxidative decomposition. These three stages are related to the molecular weight, crystallinity and the length and number of interconnected "chain segments" between the lattice of the plastic pipe. PEX cross-linked polyethylene pipe is a semi-crystalline polymer, so its cross-linking degree and cross-linking uniformity greatly affect the service life of the pipe. PERT pipes use ethylene and octene as monomers and do not need to be cross-linked. There is no need to control the degree and uniformity of cross-linking. The service life will not be affected by the degree of cross-linking, thus maintaining an excellent long-term service life.
2. Good temperature and pressure resistance
PERT is different from ordinary polyethylene in that it has a unique molecular structure, with linear ethylene as the main chain, plus controllable branches, and moderate The molecular design of the molecular weight and the control of the number and density of "chain segments" provide good temperature and pressure resistance.
After long-term certification by the German SKZ Pipe Laboratory and the Swedish Studsvik Pipe Laboratory, under the stress condition of 110℃1.9Mpa, the life of the PERT material exceeds 8760 hours. According to the extrapolation basis of ISO 9080, The life of PERT materials at 70℃ is more than 50 years.
3. Hot melt connection
As we all know, most of the heating coils of the floor radiant heating system are usually inside the concrete filling layer, so in principle no joints are allowed, but During construction, accidents often occur. For example, if the coil is damaged during decoration, it is obviously impossible to remove the filling layer and replace the coil. The conventional treatment method is to make partial repairs and add a joint.
Because they are buried in concrete, the joints not only need anti-corrosion treatment, but also need to be close to the linear expansion coefficient of the coil. Otherwise, the difference in expansion length will cause the joints to loosen, leak, or even fall off.
The biggest difference between PERT and PEX is that in addition to using special accessories to connect PERT pipes, it can also be connected by hot melt. Hot melt connection refers to using the same polymer material on both the joint and the pipe, and using a special connection equipment to heat the joint and the pipe to a certain temperature and fuse them together to form a uniform, permanent watertight connection. This avoids problems with the joints and eliminates hidden dangers in the floor radiant heating project.