Specialized in manufacturing compensators, expansion joints, baffle doors

First, find out which four kinds "four kinds" refer to?

"What are the four kinds of metal expansion joints?" In fact, strictly speaking, according to the structural form and compensation function, there are four mainstream categories:Axial, transverse, angular and pressure balanced。 But this is not random-each type corresponds to a specific pipe displacement scenario. Such asUniversal corrugated expansion jointMainly absorbs axial displacement,The transverse expansion joint of the compound hinge is specialized in treating the transverse displacement,Curved tube pressure balance type expansion energy saving balance internal pressure thrust,Sleeve-type pipe expansion joint is good at absorbing large axial displacement and resisting high pressure. To put it bluntly, if you choose the wrong type, the pipeline will go wrong sooner or later.

2. Disassembly one by one: the core characteristics of these four types of products

1. Universal corrugated expansion joint-the "old scalper" of linear pipeline

The structure is the simplest, and it absorbs axial displacement by elastic deformation of bellows. Straight line pipes suitable for power stations and cement industries. Inside our stationUniversal corrugated expansion jointAndHigh temperature axial type expansion joints all belong to this category. Note: It is only axial, don't expect it to handle lateral or angular displacements.

2. Compound hinge transverse expansion joint-specialized in treating "non-straight line" pipelines

The lateral displacement compensation is realized by two sets of bellows and hinge structures, and the key is that no blind plate force is generated. Inside our stationThe lateral expansion joint of double hinge is a typical representative. A steam pipe that turns 90 degrees? Large lateral displacement? It would be right to go.

3. Curved tube pressure balance expansion joint-the "pressure reducing valve" of pump and valve equipment

There is a pressure balancing element inside, which can eliminate the thrust of the medium pressure on the fixed bracket. Pump, valve, compressor inlet and outlet sensitive equipment, must use this. Inside our stationCurved tube pressure balance type expansion joint specializes in this. If the ordinary axial type is used, the thrust of the bracket is too large, and the equipment interface will crack sooner or later.

4. Sleeve-type pipe expansion joint-the "tough guy" of high temperature and high pressure

The displacement is absorbed by the relative sliding of the inner and outer sleeves, and the pressure resistance is extremely strong, but the sealing requirements are high. Inside our stationSleeve type pipe expansion joints are suitable for high temperature and high pressure steam pipes, such as main steam pipes. The disadvantage is that it cannot absorb lateral displacement and can only slide axially.

3. Pits that are easy to step on when selecting models: don't confuse types

Two days ago, I met a customer, and the expansion joint should be selected for the steam pipeline, which should be universal-as a result, the pipeline on site turned 90 degrees, and the lateral displacement was very large. Universal type can't solve it at all, and it is necessary to upper double hinge transverse type or angular type. Do you think this pit is injustice or not?

① Displacement direction of pipeline(axial, transverse, or angular);② Operating pressure and temperature(Decide whether to choose bellows or sleeve type);③ Whether it is necessary to balance the pressure(Pressure balanced type is preferred when pump and valve equipment is available).

In addition, don't forget to look at the media-choose corrosive mediaPTFE-lined hoses orPolytetrafluoroethylene compensator, do not use common metal expansion joints. Otherwise, the bellows will be corroded through in a few months.

4. Practical application scenarios: from power stations to cement plants, each shows its magical abilities

Power station industry

The main steam pipeline has high temperature and high pressure, which is usually usedSleeve type pipe expansion joint orExternal pressure single type axial type expansion joint. Inside our stationThe corrugated expansion joint used in the power station industry is specially designed for this kind of working condition. In addition, the air-cooled island vacuum pipe has to be usedAir-cooled island vacuum pipe double hinge expansion joint, this thing can absorb multi-dimensional displacement.

Cement industry

The axial displacement and vibration of the high-temperature flue gas pipeline and the inlet and outlet of the fan are large,Universal corrugated expansion joints andHigh temperature axial type expansion joints are used the most. Inside our stationMetal corrugated expansion joints in cement industry have served many production lines, and some have not been changed for 8 years.

Desulfurization system

The flue gas contains sulfur and is corrosive, and it needs to be isolated. At this time, it is often matchedFlue gas baffle doors andDouble-sealed single-axis circular baffle door, expansion joint is selectedNon-metallic expansion joints orPTFE-lined hose. Don't use metal, it won't withstand corrosion.

5. Installation and maintenance: Details determine life

Many customers bought expansion joints, but they failed early because of improper installation. For example, the direction of the arrow of the expansion joint refers to the flow direction of the medium. If the bellows is installed backwards, it will be squeezed. There is also the adjustment of the tie rod nut-the tie rod and nut for transportation should be loosened to the designated position after installation, otherwise the expansion joint will not be able to displace normally. For specific adjustment methods, please refer to the "How to adjust the tie rod nut of expansion joint"and"Correct installation method of expansion joint of large tie rod》。

In addition,expansion joint guide tubeNor can it be ignored-it protects the bellows from being washed by high-speed media, especially must be retained under high-flow conditions. And guess what? Some customers disassembled the deflector in order to save money, and as a result, the bellows wore out in half a year.

In short, if you choose the right type, install it correctly, and check it regularly, the metal expansion joint will last for 10 years without any problem. If you are really unsure, go directly to the product information in our station:Universal corrugated expansion joint、Compound hinge transverse expansion joint、Curved tube pressure balance expansion joint、Sleeve type pipe expansion jointEach model has detailed parameters. Don't pat your head and choose, look at the working conditions more.

Start with a pipe: the core structure and working principle of metal bellows expansion joint

What is a metal bellows expansion joint? To put it bluntly, it is an "elastic joint" in the pipeline system. The core component is a section of corrugated, thin-walled metal pipe-corrugated pipe. These ripples are like the folds of an accordion, allowing the pipe to stretch, contract and bend, absorbing the thermal expansion and contraction of the pipe due to temperature changes, or offsetting the displacement caused by the vibration of the equipment.

When the pipe is elongated by heat, the corrugations are compressed; As cooling shrinks, the ripples are stretched. At the same time, transverse displacement and angular displacement can be absorbed by multi-wave or special structure. To put it bluntly, it is to exchange its own deformation for the safety of the pipeline. A few days ago, a power station customer asked me, "Is this thing the same as a spring?" Yes, it's essentially a spring, except that the spring is spiral and the bellows is annular.

But don't underestimate this design. The wall thickness, wave height, wave pitch and the number of layers of bellows directly determine the compensation amount and pressure bearing capacity. For example, we commonly useUniversal corrugated expansion joint304 or 316L stainless steel is generally used, with a single layer wall thickness of 1-1.5mm, andHigh temperature axial expansion jointHeat-resistant alloys or even multi-layer composite structures will be used to balance temperature resistance and flexibility.

What is the difference between it and ordinary metal hoses and compensators? Don't get confused

Many people take metal bellows expansion joints and metal hoses as the same thing – it's not even close. Metal hoses (like oursMetal hoseAndSpecial hose for vacuum) is mainly used for flexible connections when conveying media, allowing a small amount of displacement, but the main purpose is vibration reduction and easy installation. The bellows expansion joint is specially designed to absorb large thermal displacement, and the structure usually comes with attachments such as end tube, flange, tie rod or guide tube.

What about expansion joints and compensators? These two words are basically generic. We also explained in the question and answer: expansion joints and compensators are different names for the same thing. However, it is customary in the industry to include non-metallic products (such asNon-metallic expansion joint、Rectangular non-metallic expansion joint) is called compensator, and the metal bellows is called expansion joint. But in fact, rubber compensator is also a kind of compensator, and its materials are different. Have you figured it out?

Several common metal bellows expansion joints on the market: axial type, pressure balance type, double hinge type... How to choose?

Before choosing a model, you must first understand the common types. We divide into several categories by structure and compensation direction:

• Axial type: likeUniversal corrugated expansion joint、External pressure single axial expansion joint、Direct buried (fully buried) type expansion joint。 The axial type is the extension or contraction of the main absorption tube in the axial direction. Simple structure, low cost, suitable for straight line pipeline.
• Pressure balance type: likeStraight pipe pressure balanced expansion joint、Curved tube pressure balance expansion joint、Compound straight pipe bypass pressure balanced expansion joint。 These products have built-in pressure balancing elements, which can offset the thrust generated by the medium pressure on the fixed support, and are suitable for large diameter or high pressure pipelines.
• Complex hinge type：Compound hinge transverse expansion joint、Double hinge expansion joint for air-cooled island vacuum pipeline。 Direction is restricted by hinges and tie rods, allowing only lateral or angular displacements, commonly used for L-or Z-shaped pipe sections.
• Other special types：Large diameter thick wall expansion joint(for large flue),Sleeve type pipe expansion joint(mechanical compensation),Rotary compensator(for steam pipes, etc.).

How to choose? Look at the pipeline direction and displacement amount on site. If there is only axial displacement, use the axial type; If there are both axial and transverse directions, or if there is a need to reduce the thrust on the support, the pressure balanced type is preferred.

Power station, cement, desulfurization... What role does it play in different industries?

Different industries, working conditions are very different. TakeCorrugated expansion joint for power station industrySpeaking, the temperature of the main steam pipe can reach five to six hundred degrees, and the pressure is more than ten MPa. It must be usedHigh temperature axial expansion joint。 Moreover, the pipeline of the power station has a large diameter and many welds, so the expansion joint should be able to absorb the displacement in multiple directions. A system like an air-cooled island would useDouble hinge expansion joint for air-cooled island vacuum pipelineSpecially dealing with vacuum conditions and large displacements.

What about the cement industry? High temperature and dust. For flue gas pipeline at outlet of rotary kilnMetal Corrugated Expansion Joints in Cement IndustryIt is usually equipped with heat-resistant lining and guide tube to prevent dust accumulation and high-temperature ablation. AndFlue gas baffle door、Desulfurization flue gas baffle doorUse together to achieve isolation and switching.

Desulfurization systemMore troublesome-the flue gas after wet desulfurization contains acidic condensate, which is extremely corrosive. At this timePTFE-lined hose、PTFE compensatorIt is more suitable, but the metal bellows expansion joint will also choose corrosion-resistant alloy (such as C276) or lined with PTFE. At the same time, the air duct section of the desulfurization system is large, so it is often necessary to useMetal rectangular expansion jointOrRectangular non-metallic expansion joints to absorb thermal displacement.

Are non-metallic expansion joints belonging to raw materials? I was stunned. You might think that with "non-metal" in the name, it should be some kind of material, right? Actually, it's not. Non-metallic expansion joints, such as "non-metallic expansion joints (fabric fiber expansion joints)" and "rectangular non-metallic expansion joints" in our station, are all finished compensators that have been processed, which are used to absorb the thermal displacement and vibration reduction of pipelines. Raw materials refer to unassembled things such as steel plates, rubber and fibers, and expansion joints are a functional component made by combining them. These two are completely different from the same concept. If you get mixed up, you will not get the right purchase.

What is the core material? Don't be biased by the name

The main materials of non-metallic expansion joints are non-metallic composite materials such as fabric fibers, rubber and polytetrafluoroethylene. For example, "rubber compensator" and "rubber PTFE compensator" use rubber and PTFE layers. These materials themselves are raw materials, but after a series of processes such as cutting, vulcanization, molding and flange connection, they become an independent equipment. Think about it, the band part of "non-metallic expansion joint (fabric fiber expansion joint)" is made of multiple layers of fiber cloth and rubber. Can this be called raw material? No, this is the finished product made by a set of crafts. To say that it counts as raw material is as outrageous as saying that a car is iron ore.

Where is the boundary between raw materials and finished products?

Break up the difference again. For example, you buy a bundle of carbon steel pipes, which are raw materials, and use it to bend, weld, add bellows, and finally get a "universal corrugated expansion joint", which is the product. Similarly, although the name of non-metallic expansion joint sounds like a material, it already has the parameters of complete interface size, compensation amount and temperature resistance grade. When you purchase, what you need is to select the type, not take a piece of cloth and cut it yourself. So, don't be taken off by the word "non-metallic" in the name. If you buy the non-metallic expansion joint as a raw material and let the construction team cut it on the spot and then stick it to the pipeline, there will definitely be a big problem-the pressure level and compensation amount are completely wrong, leakage is still a trivial matter, and if the pipeline stress is cracked, it will be a safety accident.

The application scenario is the most telling

Non-metallic expansion joints are especially common in electric power, cement and chemical industries. For example, although the name of the "metal corrugated expansion joint in cement industry" in our station is metal, the "rectangular non-metallic expansion joint" is the main force in the air duct and flue of cement plant-because it is corrosion resistant, light in weight and can absorb multi-dimensional displacement. The desulfurization system of power plants is also inseparable from it, such as the "desulfurization flue gas baffle door" used with non-metallic expansion joints. Think about it, if it is used as a raw material, the construction team will paste fiber cloth directly on the pipe? That leaked in less than three days. In actual projects, non-metallic expansion joints are purchased as finished products, with standard flange connection sizes, and they can be bolted on directly on the spot.

How to avoid pits in purchasing? Three main points

First, get the drawings or parameters, and first make it clear whether you want "non-metallic compensator" or "non-metallic ring belt". The ring belt belongs to a spare part and can be replaced separately, which is regarded as a semi-finished product, but the whole expansion joint body is still a product. Don't purchase spare parts as whole machines, and don't treat whole machines as spare parts. Second, pay attention to the implementation standard-a common question and answer in our station mentioned that the national standard for non-metallic expansion joints is JB/T 12235-2015, which stipulates that it must be a finished product after type test. So next time the supplier tells you that "non-metallic expansion joints are the raw materials made of fiber cloth", you can directly say back: Is JB/T 12235 written as a product standard or a material standard? Third, look at the product label. Regular non-metallic expansion joints will be marked with the model, compensation amount, pressure grade and factory date when they leave the factory, but raw materials do not have these.

One more long-winded word

The non-metallic expansion joint is not a raw material, it is a professional pipe compensation device. Understand this positioning, and selection, quotation and acceptance will not be chaotic. If you still want to know the detailed comparison between it and metal expansion joint, or the specific installation method, you can look through the information of "rubber compensator" and "high-temperature axial expansion joint" in our station-those are real industry cases.

What is the amount of expansion and contraction of flange plus metal expansion joint? Don't be fooled by the parameter table, look at these three points

Two days ago, I met a customer and asked me with the product parameter table: The expansion and contraction amount marked in this model is ±50mm, and the thermal elongation of our steam pipeline is only 30mm. Should it be no problem? When I looked at the diameter and pressure of the pipe, I told him directly: Brother, if you install it according to this number, it will leak in less than a quarter.

The scaling amount written on the parameter table is only laboratory data under ideal working conditions. In practical application, how much the expansion and contraction of flange plus metal expansion joint can reach depends on the real situation of your pipeline-temperature, pressure and installation posture. If one is wrong, the nominal value will be directly discounted by 50%.

What exactly is the amount of expansion? Why It Matters More Than Caliber

The amount of expansion and contraction, simply put, is the maximum distance that the expansion joint bellows can safely compress or stretch in the axial direction (along the direction of the tube). For example, marked ±25mm means that it can absorb a total thermal displacement of 50mm-25mm compression in the forward direction and 25mm stretching in the reverse direction. However, note that this value is measured at normal temperature, no pressure, and the bellows is free.

Many people only stare at the caliber (how much DN) when choosing a model, and choose a large size if they think the tube is thick and under high pressure. In fact, the amount of expansion and contraction is the vital gate. The thermal elongation of the pipe is calculated according to the formula Δ L = α ·L · Δ T. No matter how thick the pipe diameter is, once the temperature rises, the length change has nothing to do with the diameter, but only with the medium temperature and the length of the pipe. A DN200 steam pipe, with a length of 50 meters, rises from normal temperature to 300℃, and has a thermal elongation of close to 180mm. If you choose an expansion joint with a telescopic amount of only 100mm, it will be hard to carry it when installed, and the fatigue life of the bellows will directly return to zero.

The caliber determines whether it can be installed, and the amount of expansion determines how long it will last。

Three factors influencing the amount of expansion and contraction: temperature, pressure and pipe posture

Temperature – the most hidden killer

The extension and contraction amount on the parameter table is mostly measured at 20℃. If you run 300℃ steam in your pipe, the elastic modulus of the bellows material (usually 304 or 316L stainless steel) will decrease and the fatigue strength will be discounted. In industry practice, when the temperature exceeds 350℃, the safety factor will be amplified by 1.2 times for every 100℃ increase. That is to say, the amount of stretching and contraction corresponding to the actual allowable fatigue life may be only ±35 mm in nominal ±50 mm.

Pressure-the "internal pressure thrust" of the bellows

The pressure will generate an internal pressure thrust (also called blind plate force) through the bellows, which will offset part of the elastic rebound ability of the bellows. The higher the pressure, the "harder" the bellows and the smaller the amount of expansion and contraction it can actually absorb. Take our commonly used general-purpose corrugated expansion joint as an example. When the design pressure is 1.6MPa, the effective expansion and contraction amount is about 70% of the nominal value. If the pressure is higher than 2.5MPa, it may only be 60% left.

Piping Position-Is It Straight

Many on-site pipes are not straight, with elbows and vertical sections. If the flange plus metal expansion joint is installed on a horizontal pipe, its own gravity plus the vibration of the pipe will generate additional lateral displacement and angular displacement. Although these displacements are not written in the parameter table, the axial expansion and contraction capacity of the bellows decreases with every little lateral deflection. There is the most terrible situation: vertically installed and without guide bracket, relying on the expansion joint to support gravity by itself, and the axial expansion and contraction amount is directly discounted by 40%.

How much difference does the amount of telescoping vary between models? Take our products as an example

The expansion and contraction of the expansion joints with the same caliber and different structures can be several times different. Let's talk briefly about the categories on our site:

• Universal corrugated expansion joint: Single-layer corrugation, large expansion and contraction (for example, DN100 can reach ±40mm), suitable for low-pressure normal-temperature pipelines, with the highest cost performance when the temperature is lower than 200℃ and the pressure is lower than 1.0MPa.
• High temperature axial expansion joint: Multi-layer corrugation plus outer sheath, the temperature resistance can reach 550℃, but each layer of corrugation shares the displacement, and the nominal expansion and contraction amount may only be ±20mm. The high temperature can be made up by adding pre-stretching.
• External pressure single axial expansion joint: The bellows is external, and the bellows bears external pressure under working condition, which avoids the "expansion" problem caused by internal pressure. The expansion and contraction amount under the same diameter can be 15%-20% larger than that of internal pressure type. Suitable for high pressure steam piping.
• Compound hinge transverse expansion joint: This kind of hinge absorbs lateral displacement, and the axial expansion and contraction amount is very small (within ±5mm). However, if the pipeline needs L-shaped or Z-shaped compensation, it can achieve large displacement through the combination of multiple hinges, which is different from the conventional expansion and contraction amount.

When selecting the type, you can't just look at the number, but also the "direction" of pipeline displacement-if there is more axial displacement, choose the axial type, and if there is more lateral displacement, consider the compound hinge or curved pipe pressure balance type.

What will happen if the telescoping amount is large? The role of pre-tensioning and tie rods

Some people think that it is better to choose it bigger. The nominal is 100mm, but the actual use is 30mm. Is it always safe? Wrong. If the expansion and contraction amount is too large, the bellows is "too loose" in the cold state, and the slight vibration of the pipeline during operation will cause unnecessary deformation of the bellows, which will accelerate fatigue. Moreover, the expansion joint with large expansion and contraction amount usually has a large number of corrugated layers and a longer whole, so it is easy to become unstable, so it is necessary to provide additional pull rods or guide brackets.

Then when to reverse the operation – with pre-stretch? When the temperature of your pipe medium is high and the amount of thermal elongation is large, but the nominal compression of the product is not enough, you can pre-stretch the expansion joint to half the nominal value in the cold state. For example, the hot elongation is 80mm, and the maximum compression amount of the product is 60mm, then the cold state is stretched 30mm, so that the hot state is compressed to-50mm (the medium is compressed 50mm after expansion, not more than 60mm). The function of the tie rod is to limit excessive stretching or compression and protect the bellows from exceeding the limit.

How to adjust the tie rod nut specifically? We talked about it specifically in an article before, but the core principle is one:The amount of pre-stretch cannot exceed 60% of the maximum allowable stretch of the productAnd must be mated with the pipe fixing bracket.

Actual Combat Calculation: A Steam Pipeline Case, See How to Determine the Expansion and Contraction Quantity

A medium-pressure steam pipeline in a chemical plant, with a working temperature of 300℃ and a design pressure of 1.6MPa, is made of No.20 steel, with a length of 40 meters. Both ends are fixed, and a flange plus metal expansion joint needs to be installed in the middle.

Step 1: Calculate thermal elongation
The expansion coefficient α of No. 20 steel wire is 12.2×10⁻⁶/℃, and the temperature difference Δ T =300-20=280℃
Δ L =12.2×10⁻⁶ ×40×1000 (mm) ×280=136.64mm

Step 2: Consider pressure and temperature reductions
Under the working conditions of 1.6MPa and 300℃, the actual expansion and contraction amount corresponding to the allowable fatigue life of 304 stainless steel bellows shall be taken as 65% of the nominal value according to experience. Then the nominal amount of expansion and contraction required =136.64/0.65 ≈ 210mm

Step 3: Select Products
Universal corrugated expansion joints with nominal expansion and contraction of ±105mm (total 210mm), the largest in DN200 series is only ±80mm. What to do? Two scenarios:
First, the high-temperature axial expansion joint is used, which is nominal ± 60mm but is pre-stretched by 60mm (cold stretching), and the maximum compression in hot state is 120mm, which is close to the requirements. However, note that a tie rod must be set after pre-stretching.
Second, the external pressure single axial expansion joint is used instead. Under the same circumstances, the effective expansion and contraction amount can reach 80% of the nominal value. Just choose a product with a nominal ± 130mm.

The final customer adopted Scheme 2 because the external pressure bellows does not directly contact the medium, has better fatigue resistance, and does not need pre-stretching, so the installation is hassle-free.

You see, if you only look at the maximum expansion and contraction of DN200 series on the parameter table of ±80mm, and put it on directly, the thermal elongation of 136mm has long been exceeded. But after reduction and selection optimization, the problem is solved.

There is no standard answer about how much the flange plus metal expansion joint expands and contracts. Remember three points: don't believe in the nominal value, it depends on the reduction of working conditions; The direction of displacement determines the model; Pre-stretching and tie rods are remedies not conventional schemes. Next time you get the parameter sheet, ask yourself first: What's my pipe temperature? How much pressure? Is the installation position straight or curved? Do the math before placing the order.

First, I will answer you first: Non-metallic expansion joints do have glass filaments, and they are very critical

Let's get straight to the point – there are indeed glass filaments in the non-metallic expansion joints. If you take one apartNon-metallic expansion joint (fabric fiber expansion joint)The ring belt, you can feel the sticky glass fiber when you touch it with your hand. It's no secret, it's part of the design to begin with.

But many people panic when they hear "glass filament": Will this thing blow off at high temperature? Will it corrode? Is it durable?

Tsk, you're right worried.Glass filament plays the same role in non-metallic expansion joints as steel in concrete-Responsible for carrying the pull force and maintaining the shape. Without this skeleton, the soft materials of silicone cloth and polytetrafluoroethylene simply can't hold up the thermal displacement and pressure of the pipe system.

So don't just hear glass filament and think it's cheap. On the contrary,It is precisely one of the core materials that determine the life of the expansion joint。

Second, the "sandwich" structure of non-metallic expansion joint: glass filament is only one layer

Let's draw a picture for you first (think about it): The circle of non-metal expansion joints is actually a multi-layer sandwich.

• The outermost is silicone cloth or fluororubber coated cloth, which is used to resist aging, oxidation and wind and sand.
• The middle layer is glass silk cloth, and some will lay several layers of reinforcing net.
• The inner layer is usually pasted with polytetrafluoroethylene (PTFE) film to prevent corrosion and adhesion.

You see, glass filament cloth does not exist alone, it is pressed between two layers of flexible material. Take a real case: Last year, there was a cement plant project, which used the one in our stationMetal Corrugated Expansion Joints in Cement IndustryReplacement scheme, but the customer's flue gas pipe temperature fluctuates greatly, and finally selected a non-metallic expansion joint. When the manufacturer sends the sample, take the blade to cut the section of the circle belt, and the naked eye can see three layers of glass filament checkered cloth sandwiched in the middle.

The weaving density, yarn thickness and temperature resistance grade of glass filament directly determine how many kilograms of tensile force this loop can carry. Do you think it's not critical?

Third, what is the effect of matching glass filament with silicone cloth and polytetrafluoroethylene?

This set of combination boxing is actually very sophisticated. Glass filament is responsible for strength, silicone cloth for sealing and weather resistance, and PTFE for corrosion resistance. Each performs his duty.

The thermal expansion coefficients of glass filament and silicone gel cloth are different。 When the temperature is high, the silicone cloth expands greatly, while the glass filament expands less, and the layers are easily detached. Therefore, regular manufacturers (such as us) will do pretreatment in the process-impregnating a layer of coupling agent on the surface of the glass filament cloth, so that the glue and glass filament can "bite" tighter.

So what exactly is the matching effect? I'll tell you directly about the data:
In the flue gas pipeline below 350℃, this composite belt has been running continuously for 2 years, and the interlayer adhesion is still above 80% when it is torn apart. If the medium contains sulfur or acid, the inner layer must be replaced with PTFE film, and the glass filament should be used correctly.

Then why not just make a whole with pure PTFE? The answer is very simple: pure PTFE is too soft, and it creeps after a few pulls, which can't replace the skeleton function of glass filament at all.

4. Don't just look at whether there is glass filament when selecting the type. These three points are more critical

Many purchases ask "Is there any glass filament" as soon as they come, as if they can't do without glass filament. But I'm telling you,When choosing non-metallic expansion joints, these three points are ten times more important than whether there is glass filament：

First, the medium temperature and composition.Glass filaments are divided into two kinds: medium alkali and non-alkali. Ordinary medium-alkali glass filament is temperature resistant to 550℃, and alkali-free glass filament is temperature resistant to 650℃, but it is immediately scrapped when it encounters hydrofluoric acid. If there is fluoride in your smoke, the inner layer must be PTFE, and the glass filament must be covered with a fluorine-resistant coating. Many people ignore this detail.

Second, the displacement amount and direction.Non-metal expansion energy saving absorbs multi-directional displacement, but the number of layers of the loop band is designed ≠ thick to be durable. Large displacement on rectangular pipe, it is necessary to calculate the warp and weft strength of each layer of glass filament cloth. From our stationRectangular non-metallic expansion jointOften, an extra layer of reinforcing strips is added in the corners, because the stress of the four corners of the rectangle is concentrated.

Third, the installation environment.Open air plumbing? Coastal high salt spray? There is a dust explosion risk? These directly determine whether flame retardant coating or UV protection coating should be added to the outer layer. Glass filament itself is not UV-proof, and it will brittle when exposed to the sun for a long time. This is protected by an outer silicone cloth.

You see, model selection is a systematic project. Just staring at the glass filament is equivalent to buying tires only looking at the rubber but not the depth of the pattern.

5. Two days ago, a customer asked me: Is rectangular non-metallic expansion energy-saving glass filament used?

Two days ago, a buddy who was doing desulfurization engineering called and asked, "That guyRectangular non-metallic expansion jointIs there any glass filament in the belt?”

I said yes, the standard is three layers of alkali-free glass filament cloth and two layers of PTFE film. He immediately asked, "Then there is sulfuric acid condensate in our smoke, so the glass filament will not be broken by corrosion?"

I understand this concern. But the point is,The glass filament cloth is wrapped between that PTFE inner layer and the silicone cloth outer layerThe condensate does not contact the glass filament at all. Our salt spray experiment also proved that the strength of glass filament decreased by less than 5% when sprayed continuously for 720 hours under acid mist environment at PH =2.

After he listened, he dropped eight rectangular non-metal expansion joints on the same day. Tsk, sometimes as long as customers understand the structure, their worries will naturally disappear.

Do non-metallic expansion joints have glass filaments?The answer is yes, but it's not a weakness, it's a skeleton. What really determines whether the product is good or not is the matching process of this layer of skeleton and inner and outer materials.