1. What material is used in the non-metallic compensator "non-metallic"?
To put it bluntly, the core of a non-metallic compensator is layer after layer of "cloth" and "membrane". Although it is called non-metal, there is no iron sheet in it, but silicone cloth, fluororubber, glass fiber and other materials have their own temper. If you use it in the wrong place, you will throw money in vain.
Silicone cloth is resistant to high temperature, can run for a long time below 200℃, and has good softness, so it is suitable for flue gas pipeline. Fluorororubber is amazing, with first-class corrosion resistance. It is not afraid of strong acids and alkalis and organic solvents, but it is expensive and laborious to process. Glass fiber has high strength and higher temperature resistance, and can carry it above 550℃, but it is brittle and breaks when folded, so it is usually used together with silicone cloth.
There is also a PTFE membrane, which we call PTFE compensator-that is, the "PTFE compensator" in the product list of this site. This thing hardly sticks to anything, and it has a top corrosion resistance, but its thermal expansion and contraction coefficient is large, so pre-stretching has to be specifically considered in the process. When it comes to material selection, there are no universal materials, only materials that are most suitable for working conditions.
2. Cutting and sewing: Do you think it's just patchwork?
Don't many people think it's just cutting and sewing several layers of cloth? Wrong. It is one millimeter worse, and it leaks when installed. Customers scold their mothers and lose money after sales.
The outer layer is silicone cloth or fluororubber as a protective layer, and the middle is reinforced by glass fiber cloth. The inner layer may be lined with a layer of polytetrafluoroethylene film. The overlap direction of each layer must be consistent, and the overlap width must not be less than 50mm. The material of sewing thread can't be used casually-ordinary cotton thread will rot after one or two months of high temperature or corrosive media, so you have to use aramid thread or PTFE thread. When sewing, the needle length is controlled at 3~5mm. If it is too dense, it will easily tear the fabric, while if it is too sparse, the strength will not be enough.
When cutting, you must avoid the warp and weft deviation of the fabric. If the fiberglass cloth is cut obliquely, the force is uneven, and it won't take long to build up layers at the seams. The master will draw the positioning line on the fabric first, and then cut it with a hot knife, so that the incision will not be loose and the burrs will be less.
3. Skeleton and flange: the invisible support structure is the life gate
The ring belt of the non-metallic compensator itself, no matter how awesome, has no skeleton or flange to support it, like a boneless mollusk. The skeleton is usually welded with carbon steel or stainless steel square tubes, and anti-corrosion treatment must be done after welding-carbon steel parts are brushed with epoxy zinc-rich primer after sandblasting and rust removal, and stainless steel parts are also passivated by pickling. A customer had a cheap picture and didn't do anti-corrosion. As a result, half a year later, the skeleton was rusty and the whole compensator collapsed.
The flange seal is another gateway to hell. When pressing the sealing surface, the flatness must be controlled within 0.5mm/m. If it is large, the bolts will warp when they are screwed. The position tolerance of the bolt hole on the flange must also be strict, otherwise the on-site installation will not match the hole, and the worker can only expand the hole, and the sealing performance will be directly discounted. Our commonly used flange forms are angle steel flange and channel steel flange. Angle steel flange is light and suitable for small and medium caliber, and channel steel flange has high strength and is suitable for large diameter rectangular non-metallic expansion joint.
4. Overall assembly and sealing test: success or failure depends on this
With all the components in place, there is a detail that many people overlook when assembling it-the amount of pre-compression. The non-metallic loop belt is loose in the free state, and must be pre-compressed by a certain amount before being installed on the flange, such as compressing by 10% ~15%, so that the loop belt will not be pulled too tightly during operation. How to tune it? Control by the pre-tightening force of the flange bolt, and check the gap with a gauge after compaction.
Then there is the pressure test leak. According to JB/T 12235-2015 standard, the test pressure is 1.5 times of the design pressure, and the pressure is held for 30 minutes with a pressure drop of no more than 5%. There is a rule in our workshop: brush all welds and joints with soapy water during the pressure holding period. If it bubbles, it will be the leakage point, and it must be repaired or re-sewn. There was a new worker who was lazy. He only measured the pressure and didn't brush soapy water. As a result, he leaked when he left the factory and arrived at the site, and the freight plus labor lost 20,000 yuan-this pit can't be stepped on.
V. Process adjustment under different working conditions
It is also a non-metallic compensator, which is used in desulfurization flue gas and high-temperature drying pipelines, and the process difference is big.
The desulfurization flue gas pipeline contains a large amount of sulfur dioxide and water vapor, and the temperature is 60~80℃, but the humidity is high and the corrosiveness is strong. At this time, a rubber PTFE compensator must be used-the inner layer is polytetrafluoroethylene, the outer layer is fluororubber or neoprene, and all sewing areas should be sealed to prevent smoke from penetrating through the needle eye. However, the temperature of high-temperature drying pipelines (such as kiln tail in cement industry) can reach above 350℃, so only pure glass fiber cloth and silica gel cloth can be selected, and the skeleton has to be made of heat-resistant stainless steel. We have a "non-metallic expansion joint (fabric fiber expansion joint)" that is specially designed to deal with this kind of working condition.
Acid and alkali corrosion environment is more troublesome. For example, pipelines in chemical plants are exposed to strong acids and alkalis, and ordinary silicone cloth will be brittle in a few months. At this time, polytetrafluoroethylene compensator has to be used, the whole lining with PTFE, and the flange surface has to be processed into concave and convex grooves to prevent the medium from leaking along the bolt hole.
VI. Common process defects and pit avoidance guidelines
After ten years in this business, I have seen more pits than I have eaten. Layering, bulging and warping of flange surface are three common problems.
The temperature should be controlled uniformly during hot pressing, and a special adhesive should be applied between the silicone gel cloth and the glass fiber cloth, and then it should be rolled by hot roller. Bulging is when the gas is trapped between the layers, usually without an exhaust hole when cutting, or when sewing, the pressure of the presser foot is not enough. We will reserve 2mm diameter exhaust holes between each layer of cloth, one 300mm apart. What about the flange face warping? Nine times out of ten, the welding deformation has not been eliminated. After welding the skeleton, the sealing surface must be machined on a milling machine, or shaped with flame correction and jack.
Excessively folded when packaged for shipping. When the non-metal compensator ring belt leaves the factory, it should be rolled into a cylindrical shape and cannot be folded in half, otherwise the fiber at the crease will be broken, and it will be a hidden danger when installed. Be sure to be secured with a wooden box and lined with foam before shipping.
Okay, every step from the material to the finished product is hard work. To put it bluntly, the manufacturing process of non-metallic compensator is a work of conscience-saving money and technology, and finally saving its own reputation.