1. Why are non-metallic expansion joints old and bad? — — Aging, scratching and delamination of fabric layer, first find out the type of damage before talking about repair
Non-metallic expansion joints (also called fabric fiber expansion joints) are widely used in flue gas, air duct and desulfurization systems. They do not rely on the deformation of metal corrugations to absorb displacement like metal corrugated expansion joints, but rely on multi-layer flexible fabrics and thermal insulation cotton to compensate. Bad methods are also different-there are only three common ones: aging and brittleness of the fabric layer, external scratches or wear, and delamination and bulging between layers. There is also a hidden one, which is that the internal insulation cotton has been blown out and hollowed out. On the surface, it looks unbroken, but in fact it has collapsed.
So before looking for a restoration unit, you should open it yourself and have a look. Even if it's just a hole, cut a small piece to see if the surface silicone coating is cracked or the fiberglass cloth underneath has been powdered. The type of damage determines the repair method: surface scratches can be repaired locally, but if the delamination range is large and the cotton layer collapses, it is not a question of whether to repair it or not, but the whole circle has to be replaced.
2. Repair or replace? — — Calculate material costs, downtime losses and residual life, and don't spend money with a slap on your head
Many users hear that it costs 20,000 yuan to replace it and 8,000 yuan to repair it, and they immediately make a decision to repair it. But have you calculated downtime costs? The shutdown loss of a kiln may be several thousand dollars an hour. It takes two or three days to repair a non-metallic expansion joint, dismantle the old, clean the dust, polish, lay up and heat close. If there are spare parts on site, it can be done in one day. Compare the two sides, which is cost-effective is not just the material cost.
Besides, the residual life has a good foundation. If this expansion joint has been used for five years, and the fabric layer is powdered in a large area, you spend 8,000 to finish it and last another year? Then it's better to just replace it with a new one. On the other hand, if only a small piece is rubbed on the outside and the inner layer is intact, then you spend some money to repair it, and it will last for another three to five years. This account should be settled clearly before deciding.
Third, what to look for in a restoration unit? — — It is not possible to do it with a sewing machine, it depends on the standard of non-metallic expansion joints, interlayer structure and field process
The non-metallic expansion joint looks like a cloth bag with flanges, but experts know that the interlayer structure is the lifeblood. Temperature-resistant layer, heat insulation layer, airtight layer and reinforcement layer, the material, thickness and overlap direction of each layer are particular. The national standard JB/T 12235-2015 clearly states that after repair, at least the displacement, pressure resistance and temperature resistance should be guaranteed not lower than the original design. But some restoration units have never even heard of this standard. Isn't it a blind delay to take an industrial sewing machine to fill the outer layer of cloth for you?
Therefore, when choosing a repair unit, the first thing is to see if he understands the standard. Another, ask him if he can provide the interlayer structure diagram. If he can't say it, he will block it as soon as possible. Also, you have to ask about the process-is the site cold glued or heat bonded? Is there any vulcanization equipment? What material is used for coating? These key points are cut corners and you can't tell at all.
4. Is on-site repair reliable? — — The complete process from demolition to heat-sealing and vulcanization, as well as common corner-cutting techniques
On-site repair is not impossible, but it depends on how to do it. The serious process should be: first set up a shelf (if it is a high-altitude pipeline), completely remove the old failure layer, and expose the metal flange surface; Then remove rust, clean up, and apply adhesive; Then lay layer by layer according to the original structure-first lay insulating cotton, then lay airtight layer, then lay reinforcing cloth, and finally lay surface weather-resistant layer; Each layer should be compacted and bubble removed, and the corners should be fixed with pressing strips and bolts; Finally do heat sealing or vulcanization treatment. It takes a day and a half for a skilled team to finish the whole process.
But how do some people cut corners? The most outrageous thing I have ever seen is to wrap the outside of the old non-metal expansion joint directly with a layer of silicone cloth, and not tear down the old one or clean it up. Just a rub of putty is done. There is also a work team, and the insulation cotton is not laid, so two layers of cloth are sewn on it. On the third day of starting the machine, the air leaks and whines. You ask why they don't come by the standards? Answer: Party A urged tightly. Squeezing? Then don't quote the price for the repair.
5. How to accept after repair? — — Dimensional tolerance, airtightness test and warranty period agreement, all of which must be missed
After the repair, you don't just sign and leave. You have to check and accept it. Prerequisite the size-the length of the expansion joint, the flange spacing and the parallelism of the flange surface. If these tolerances are exceeded, it will be stiff when installed, and the life will be directly reduced in half. Measure the airtightness again, use compressed air or smoke cakes, and focus on whether there is any air leakage at the corner strips.
The warranty period must be stated in the contract. The warranty period of non-metallic expansion joint repair is generally one year in the industry, and better units dare to write two years. If the other party says "warranty? We don't engage in warranty", then you don't even look at it, just change to the next one. In addition, in the maintenance report taken back, the name, thickness, overlap amount and batch number of each layer of materials must be clearly listed, so that future problems can be traced back.
Non-metallic expansion joint repair unit? Easy to find, more to make do with. You first clear out the above five things, and then ask the other person with questions. Only those who can answer and come up with a plan can talk about the next step. If you dare to quote without watching the scene, most likely you want to sign it first. Equipment maintenance, the most afraid thing is the three words "said yes", written clearly in black and white, is responsible for your own equipment.