The Real Position of Metal Expansion Joint Forming Machine in the Production Line: Not Just Pressing Corrugations
Many friends who have just entered the industry call it "corrugation machine". This name can't be said wrong, but it is easy to lead people off. If the metal expansion joint forming machine only presses a few folds out of the flat plate, what is the difference between it and the stamping machine?
The real difference is in the way it is formed. When you go to those factories that make corrugated expansion joints and high-temperature axial expansion joints in power station industry, the forming process is basically hydroforming. The advantages of hydroforming are that the pressure is uniform, the material flow is controllable, and the shape and wall thickness distribution of the corrugation can achieve a relatively ideal state. If it is extruded mechanically, the wall thickness difference between the crest and the trough will be ugly. The thin ones are too thin and the thick ones are too thick, and the fatigue life behind it will simply not be able to bear it.
To be honest, the accuracy of many factory equipment is actually decent, and what really opens the gap is the understanding of the forming process. At the same station, the old master can adjust the mold gap and pressure holding time according to the material rebound amount. The new thing is to set the parameters and press the buttons. The products that come out are all the same in appearance. When the wall thickness and residual stress of corrugations are measured, the gap is exposed.
How forming process determines the performance of metal expansion joints: an account from corrugation parameters to fatigue life
How to calculate the fatigue life of bellows? There are only a few core parameters: wave height, wave distance, wave number, wall thickness, single layer or multi-layer. These parameters are all given by the forming machine.
Take an example. If the wave height of a ripple is 3% larger, the stiffness and compensation amount will change accordingly. When the stiffness changes, the force system of the pipeline changes; When the amount of compensation changes, the displacement absorption capacity of the pipe system changes. You can't feel it on the spot, but when the pipeline stress analysis calculates, the fatigue life may be discounted by 30%. In turn, when the wave pitch is pressed too densely, the metal hardened layer between the corrugations is superimposed, the plastic reserve of the material is reduced, and cracks appear first from the trough.
There is another layer of account that is easy to overlook-material utilization rate. The same roll of 316L stainless steel, the forming parameters are well adjusted, and two or three sheets of material can be reduced. For enterprises that make general-purpose corrugated expansion joints, the cost of light materials is tens of thousands a year. That's without counting the hidden costs of rework and customer complaints.
When selecting a forming machine, think about these four things first: material, wave height, caliber, and automation degree
There is no such thing as a "universal forming machine". The equipment you choose must match the product positioning.
First, the material determines the forming pressure. 304, 316L and Inconel 625, the yield strength of these three materials is obviously different, and the equipment tonnage and die material should be matched. You want to make a thin-walled piece such as a vacuum special hose, which will directly crack the corrugation if the pressure is too high; To make a large-diameter thick-walled expansion joint, the pressure is not enough, and the corrugation is not in place at all.
Second, wave height and caliber are a combination problem. If the diameter is small, you can do single-wave forming. If the diameter exceeds DN500, you have to consider multi-wave one-time forming or gradual forming, otherwise the equipment cost is ridiculously high. Manufacturers who make supporting products of metal corrugated expansion joints and desulfurization flue gas baffle doors in cement industry generally have a large caliber span, so leave a margin when selecting equipment.
Third, how to determine the degree of automation? It depends on your order structure. There are batch activities every day, and the fully automatic one with PLC control is cost-effective in efficiency and consistency. If you do non-standard, single-piece small batches, semi-automatic ones are flexible. Don't blindly pursue automation, the taste of molds such as production line shutdown is unpleasant.
Fourth, the stability of the hydraulic system, to put it bluntly, is the oil temperature control and pressure holding accuracy. Many people who choose the type don't ask this question. When the oil temperature is high in summer and the ripple size drifts, they find that trouble is behind.
The daily maintenance and common faults of forming machine, several details that only the old master in the factory knows
"Change the hydraulic oil regularly" and "check the sealing ring" written in the maintenance manual are nonsense, which are operations that everyone knows under normal working conditions. Let's talk about some actual combat details.
At the R corner of the wave crest of the mold, there are often fine metal chips embedded. You may not be able to tell if you take a flashlight. However, once periodic scratches appear on the corrugated surface, this is probably the reason. The treatment method is also simple. Use fine oil stone to gently take it a few times along the R angle direction. Don't rub it back and forth. It is easy to rub the surface of the mold.
Many faults of the pressure preservation valve of the hydraulic system are actually that the valve is stuck by oil sludge, not that the valve body is really broken. Take an Allen wrench to open the pilot valve and clean it, put it back and try again. Replace the valve directly, which costs money and wastes time. And guess what? Eighty percent can be used after washing.
There is also a link that often goes wrong-demolding. After the forming is completed, the demoulding is not smooth. Don't rush to increase the ejection force. First, see if there is a viscous substance mixed with rust-proof oil and metal powder in the mold cavity. This thing is much more stubborn than oil sludge, and it needs to be cleaned regularly with kerosene and a soft bristle brush. Hard scratch? Once the surface finish of the mold is injured, the quality of the inner surface of the corrugation is finished.
What is the difference between the expansion joints of the same drawings and different forming machines? Speak with cases
Two years ago, a customer who made an export order brought a set of drawings of the transverse expansion joint of a compound hinge. The standard is EJMA, and the materials, wave number and layer number are clearly marked. Their original equipment was broken, so they found two foundries to do it. And guess what? The products made by the two companies are all qualified in static size inspection, but the data of fatigue testing machine is nearly double.
What's the problem? By disassembling and comparing, it is found that the magnification is well controlled during forming, the thinning rate of corrugated wall thickness is around 12%, and the material streamline at the corrugated fillet remains intact; Another company increased the forming speed in order to catch up with the construction deadline, and the thinning rate rushed to 18%, and there were slight wrinkles. This fold is not visible during assembly, and once the high-temperature steam is introduced into the pipeline, it becomes a source of stress concentration, and the crack begins to crawl from there.
The quality of the expansion joint is not tested, but "given" when forming. The aging degree of the equipment, the response speed of the hydraulic system, and the maintenance status of the mold all left traces in the finished product. This is why some factories dare to guarantee the same drawings for ten years, while others only dare to guarantee them for two years.
Conversely, as an end user, when you accept metal expansion joints, don't just stare at the size report and material sheet. If you have a chance, see what forming equipment is used in the other factory and how the mold is, which can at least help you eliminate more than half of the unreliable suppliers. The same is true for equipment selection. It is more useful to ask, "How much can the corrugation thinning rate made by this equipment be controlled" than to listen to the sales saying, "Our machine has high accuracy".