Don't be fooled by the name, metal expansion joints are not one thing, but a whole family
"Can your molding machine press my thin-walled wavelet?" As a result, the drawing he brought wasDirect buried (fully buried) type expansion jointWith a wall thickness of 6mm, ordinary hydraulic presses can't chew at all. You see, many people think that a metal expansion joint is just a bellows and finished it. In fact, fromUniversal corrugated expansion jointToCorrugated expansion joint for power station industry, fromHigh temperature axial expansion jointToLarge diameter thick wall expansion jointEach product has different requirements for production equipment. So before talking about equipment, you have to figure out what type of expansion joint you want to produce. Otherwise, when the equipment is bought, it is too late to find that it can't do the work, and it is too late to cry.
The molding equipment is the core, and the selection depends on three parameters: caliber, wall thickness and wave height
Hydroforming and mechanical rolling.Hydroforming machineSuitable for small and medium diameter (DN50-DN600), thin wall (≤4mm) general purpose bellows, such as our commonUniversal corrugated expansion jointAnd bellows for metal hoses. Hydraulic press one-time molding, high efficiency, low mold cost, productionMetal hoseAndPTFE-lined hoseThe inner bellows also relies on it. But bumping intoLarge diameter thick wall expansion joint(above DN2000, wall thickness 8mm +), the hydraulic press is either not powerful enough or the mold cost is ridiculously high. That's when you have to use itRoll forming machineBy multiple rounds of progressive extrusion, the steel plate is "rolled" out of ripples. Mechanical rolling has another advantage: the wave pitch is controllable, suitable for demandingCorrugated expansion joint for power station industryAndDouble hinge expansion joint for air-cooled island vacuum pipeline— — Once the corrugation parameters of these products deviate, the on-site compensation amount will not match, and the whole pipe system will have to be reworked. And guess what? In order to save money, some small factories use hydraulic presses to hard press thick-walled corrugated pipes. As a result, the corrugations cracked, the welds cracked, and finally the customers claimed bankruptcy.
Pipe alone is not enough, but it has to be set up right-how to match welding equipment? Look at the working conditions
The finished metal expansion joint includes bellows, end pipe, guide tube, tie rod nut and other parts. Different materials and different working conditions, the welding scheme is completely different. The gas-shielded welding efficiency of ordinary carbon steel end pipes is high, and dozens of them can be welded a day; The welding of stainless steel corrugated pipe and end pipe is best by argon arc welding or plasma welding. The welding seam is beautiful and the heat affected zone is small, especiallySpecial hose for vacuumAndExternal pressure single axial expansion jointSo that the air tightness of the weld is extremely high. encounterPTFE-lined hoseOr products that need lining internally have to do PT (penetration detection) or RT (radiation detection) after welding-don't be too troublesome. Once the fluoroplastic lining is burned through by welding slag, media leakage is a safety accident. Oh, yeah,guide tubeThe function has been mentioned in the FAQ-to reduce media erosion. This part generally has to be accurately aligned during welding, otherwise it will affect the compensation amount. In actual production, we often encounter customers who weld the guide tube crooked. As soon as the corrugated tube is compressed, the guide tube directly resists the inner wall of the end tube, and the whole expansion joint fails. Therefore, welding tools must have positioning pins, so don't rely on naked eye estimation.
Welding is not the end, stress should be eliminated, and surface corrosion protection should not be saved
EspeciallyHigh temperature axial expansion jointAndMetal Corrugated Expansion Joints in Cement IndustryThe working temperature is always above 500℃, and the residual stress of the weld seam is not handled properly, and the upper pipeline will crack. Therefore, heat treatment equipment cannot be saved: local annealing furnace or integral vacuum heat treatment furnace, according to the product size. Some manufacturers have cheap pictures, and once baked with oxyacetylene flame, it is annealed. As a result, the grains in the heat-affected zone of the weld are coarse, and the fatigue life is directly halved. There's one more detail: the surface anti-corrosion treatment. The commonly used ones are sandblasting + anti-corrosion paint, or pickling passivation of stainless steel.Direct buried (fully buried) type expansion jointBuried in the soil, the exterior has to be wrapped with a 3PE anti-corrosion layer, which requires a special winding machine. In corrosive environments, such asDesulfurization flue gas baffle doorThe matching expansion joint, the medium contains sulfur, in addition to the stainless steel matrix, also has to be made acid-resistant coating, otherwise it will be perforated in half a year. Don't ask me how I know-we recycled a batch of expansion joints removed from a power plant, and the wall thickness was corroded as thin as paper.
Testing equipment is the watershed — here's the difference
Stiffness testing machines, hydraulic test benches, air tightness testers, fatigue testing machines-these devices determine whether you can give your customers a reliableMetal expansion joint weight tableAnd performance reports. Take the stress test, for example,Universal corrugated expansion jointAccording to the national standard, it is necessary to make 1.5 times the design pressure and water pressure, but likeDesulfurization flue gas baffle doorThe matching expansion joint, the medium contains sulfur, and additional ammonia leakage test is required. In addition,Stiffness and Calculation Formula of BellowsIt is in the FAQ, but the material deviation of each batch in actual production will affect the stiffness, so it must be measured piece by piece, otherwise the on-site tie rod nut will not be adjusted correctly. Last time, a customer reported that the expansion joint tie rod nut was still leaking after being adjusted to the end. We sent someone to have a look, and the rigidity of the bellows was 30% greater than the design value-because the steel mills were changed when the batch of stainless steel plates was purchased, and the yield strength was different. From now on, we stipulate that each batch of materials will be tested for tensile testing first, and the bellows will be put on the stiffness testing machine one by one after being formed. Is Testing Equipment Expensive? Expensive, but compared to the compensation after an accident, it is a drop in the bucket.
Don't forget those "non-standard" products-taking it all in one line is a dream
Metal rectangular expansion joint、Rectangular non-metallic expansion joint、Flue gas baffle door、Circular (rectangular) shaped flap door— These guys have completely different structures. Rectangular expansion joints should be made with special four-corner welding tires to ensure that the four fillet welds are equal in strength, otherwise the corners will crack first when the pressure comes up;Non-metallic expansion joint (fabric fiber expansion joint)It is necessary to use sewing machines and striping machines, which are incompatible with metal equipment. Have you ever seen a non-metallic compensator pressed with a hydraulic press? That's pure nonsense.Electric plug-in insulation door、Manual plug-in insulation doorThe production involves plate bending and guide rail assembly, which is completely another set of production lines. AndRotary compensator、Sleeve type pipe expansion jointThese, the seal structure is processed by turning, and a CNC lathe is required. So don't expect one line to take everything. The smart way is to configure core equipment according to the mainstream products in the market, reserve interfaces, and expand flexibly in the later stage. For example, in our workshop, three lines run in parallel: one hydraulic line doesUniversal corrugated expansion jointAnd metal hoses, a rolling line to makeLarge diameter thick wall expansion jointAnd power station products, and one specializes inRectangular expansion jointAnd an assembly welding line for the baffle door. The investment is a little big, but when customers come, any product can be accepted, which is competitiveness.