First, understand the structure of the non-metal compensator before painting-it is not metal, so don't copy the ripple painting method
To be honest, I've seen too many people paint non-metallic compensators the same way they paint metal bellows. And the result? The drawing resembles a stiff pile of iron, completely ignoring the flexible nature of the fabric skin. The core structure of non-metallic compensator (that is, we often call fabric fiber expansion joint) is three layers: the outer layer is temperature-resistant fiber fabric (such as silicone cloth and fluororubber cloth), the middle is heat insulation layer (ceramic fiber blanket or rock wool), and the inner layer has an anti-corrosion lining. The frame is metal — usually a rectangular or circular flanged frame welded from Q235 or 304 angle steel, channel steel. The skin is fastened to the frame by beading and bolting, creating a soft connection segment that can be twisted. To put it bluntly, this thing is a "rigid and soft mix" structure: the rigid one is the upper and lower flanges, and the soft one is the middle section of fabric. When you paint CAD, you would be wrong to still paint the skin corrugated-the non-metallic compensator has no corrugations, it relies on the elastic deformation of the fabric itself to absorb displacement.
2. Confirmation of key parameters: pipe size, compensation amount, skin material and flange connection form
Before you start drawing, set these numbers to death. Otherwise, if you find out that the flange bolt hole is wrong in the middle of the drawing, it will be called a collapse.
Take-over size: OD or ID of pipe? Is it a circular duct or a rectangular air duct? For example, the power station industry commonly uses round shapes, while the cement industry has more rectangular shapes. Our site hasRectangular non-metallic expansion jointAndNon-metallic expansion joint (fabric fiber expansion joint)The two products have different dimensioning habits: circles are directly marked with DN, and rectangles are marked with length × width.
Compensation amount: What are the axial, transverse and angular displacements? The compensation capacity of non-metallic compensators is much greater than that of metals, and the axial energy can reach ±50mm or even greater, but you can't blindly paint too thick. There is a standard for the number of skin layers. Referring to the JB/T 12235-2015 standard mentioned in the FAQ of this site, the number of skin layers is generally 3~5, and the thickness of each layer is 0.5~1.5mm.
Skin material: Silica gel cloth + glass fiber for high temperature working condition, polytetrafluoroethylene coating cloth for corrosion working condition. Don't confuse material labeling-for example, this site hasRubber PTFE compensator, that is, rubber and PTFE compound, can't be written as pure fluorine tape.
Flange connection form: Angle steel flange or flat flange? Is the number of bolt holes a multiple of 4 or is it divided equally according to the air duct size? These data must be extracted from the form factor chart provided by the customer, or from the ready-made data on this siteModel and size of expansion jointLook for references in Q&A.
3. Drawing of two-dimensional engineering drawings: from the main view to the cross-sectional view, emphasizing the overlap between the frame and the skin
Two-dimensional drawings are the basis of production drawings. Open CAD, and set the layers: the structure line, the marking line and the section line are separated. Draw the main view first-usually the outer contour of the flange, draw a rectangle for a rectangle, and a circle for a circle. Then the cross-sectional view is the point: you have to cut at least A-A to express the skin lap structure clearly.
How to paint skin? Don't draw it as a continuous arc! The skin of the non-metallic compensator is not corrugated, it is composed of layers of fabric superimposed and pressed against the flange surface by beading and bolting. Therefore, in the cross-sectional view, the skin part should be drawn as several parallel lines (representing different layers of fabric), and both ends should be represented by a schematic diagram of pressing. The press bar is generally flat steel, with a thickness of 4~6mm and a width of 25~40mm. The bolt spacing is usually 150~200mm. This parameter should be confirmed with the customer, and then marked next to the cross-sectional view.
Also, don't forget to markguide tube。 If you are drawing a non-metallic compensator with a deflector (such as one used in a flue gas desulfurization system), the deflector direction must be clearly marked-the arrow points to the direction of the medium flow. There are special topics in the FAQ of this siteSpecific Function of Expansion Joint Guide TubeIf the guide tube is not installed in the right direction, the consequence will be to wear the fabric skin, and the life span will be directly cut in half.
4. Thoughts of 3D modeling: Using lofting and curved surface tools to simulate the twist and wrinkle of fabric skin
Three-dimensional drawings are mainly used to inspect assembly interference or show them to customers. But how to draw the folds of non-metal skin? Stumped a bunch of people.
What I do is: first build two upper and lower flange boxes (stretch solid), then between the two boxes withloftingCommand to generate a connector. However, don't loft directly into a straight contour-the skin will have natural wrinkles under pressure, so add several control points to the loft path to make the surface slightly bumpy. For example, in a rectangular compensator, the central area of the side of the skin can be retracted by 5~10mm to simulate the effect of depression under negative pressure. Of course, this is just a sign, and the real fold shape is ever-changing, but CAD modeling doesn't have to be completely real, so long as customers can understand "this is the flexible section".
For circular fabric compensators, you can useRotating surfaceOrsweepCommand, but pay attention to the thickness of the skin (0.5mm fabric layer can be ignored directly in three dimensions, too thin to show). The key point is to draw the metal parts such as flanges, bolts and strips clearly, and the skin is represented by translucent materials or maps, so that you can see which parts are soft at a glance.
V. Distinguishing Occasions: Drawing Differences between Rectangular Nonmetallic Expansion Joints and Circular Fabric Compensators
Rectangular non-metallic expansion joint (refer to this siteRectangular non-metallic expansion jointProducts) are usually used in flue gas pipes, which are large in size and can reach 5 meters in side length. At this time, the graphic should focus on the arrangement of reinforcing ribs of the frame-the angle steel frame needs to add vertical ribs in the middle of the long side to prevent the skin from bulging. In the cross-sectional view, draw the cross-section of the stiffener.
Circular fabric compensators (that is, we often call non-metallic expansion joints) are mostly used in small-diameter pipes. The flange is a circular ring and the skin is a cylindrical surface. The marking method is closer to the metal compensator, but it should be noted that round products usually need to be marked with "installation length L", which includes flange thickness + skin free length + strip height, while metal compensators generally only mark the length of corrugated section, which is different.
In addition, guide tubes are rarely used for round products (the flow rate of small-diameter pipes is fast, but the guide tubes increase the resistance), but rectangular products must be added with guide tubes in the desulfurization system to prevent dust accumulation. You have to distinguish between scenes when drawing.
6. Common marking traps-don't miss the direction of the guide tube, the thickness of the heat insulation layer and the hole distance of the mounting bolts
Finally checking, these are the most error-prone places:
Direction of guide tube: As mentioned earlier, the arrow points to the flow direction of the medium, and the front end of the guide tube should extend into the inside of the pipe, leaving a gap of 10~20mm between the rear end and the inner wall of the skin. This gap is not marked, and it is easy for workers to push the skin when they install it.
Insulation thickness: The insulation layer of non-metallic compensator is generally only written "xx mm" on the design drawing, but in actual production, customers may require two layers of ceramic fiber + one layer of air. You have to write clearly in the technical description of the drawing: total thickness, material and density of the insulation layer (e.g. 128kg/m³). Otherwise, if you buy the wrong purchase, the insulation effect will be discounted.
Installation Bolt Hole Spacing: The bolt holes in the flange must be marked with center distance and distribution. Circular flanges are generally marked with PCD (pitch circle diameter) and number, while rectangular flanges are marked with adjacent hole spacing and corner hole positions. Many novices only mark the outer contour size of the flange and forget to mark the hole distance. Consequences? It can't be installed on site, and rework takes time and loses money.
In addition,Length of overlap between skin and flangeIt should also be marked-usually 20~30mm, and the width of the strip covers the overlap area. This number is clearly marked on the partial enlargement of the drawing. Don't expect workers to guess for themselves. If they guess wrong, it is a quality accident.
Alas, in the final analysis, drawing a CAD drawing of a non-metallic compensator is completely two sets of ideas than drawing a metal. The metal compensator is deformed by corrugation, and the non-metal is stretched by fabric. You have to have that "soft box" concept in your head before you write. If you just want to draw a picture of a non-metallic expansion joint at hand, you might as well compare the above points and dismantle the structure before starting. The drawn picture in this way can be directly cut by the workshop master after reading it, which is more worry-free.