Production process of stainless steel elbow

1 Overview  

 

When the stainless steel pipe needs to change direction or use point design requirements during the construction of the project, it needs to be connected with stainless steel elbows with angles of 45 °, 90 °, etc. Pipe bending can be done in different ways: around stainless steel elbows, compression molding and compression molding.

 

 2.Stainless steel elbow production process

 

The production process of the stainless steel elbow is as follows: blank inspection of the feeding tube, forming, cleaning, forming, chamfering, carving, polishing, cleaning, drying, deburring, finished product inspection, packaging, storage

 

 3.Track elbow formation

 

(1) Core bending

 

The core pipe bending is a molding method for bending a pipe of a bending tire mold by using a mandrel on a pipe bender.

 

The working principle of the core elbow is shown in Figure 5-1. The curved tire mold 4 is fixed on the main shaft of the bending machine and rotates together with the main shaft. One end of the stainless steel tube blank 6 is pressed against the curved tire mold by the clamping block 3.

 

Near the cutting point of the stainless steel tube blank and the curved tire mold, a press block 1 is provided on the outer side of the curved portion, and a wrinkle prevention block 5 is provided on the inner side of the curved portion, and the core rod 2 is inserted into the tube blank. As the curved tire mold rotates, the stainless steel tube blank gradually bends around the curved tire mold.

 

The bending angle of the stainless steel elbow is controlled by a stopper (not shown). When the curved tire mold is turned to the desired bending angle of the stainless steel tube member, the stopper is hit to stop the bending of the tire mold.

 

The design and manufacture of the main components of tools and molds will be described below. A mandrel is an important part of a core elbow device. Its function is to support the pipe wall from the inside of the stainless steel pipe blank to prevent the stainless steel pipe from deforming and wrinkling the wall.

 

The round mandrel has a simple shape and is easy to manufacture. However, since the contact area between the mandrel and the pipe wall is small, the effect of preventing cross-section deformation is poor, and it is generally used for bending unnecessary stainless steel pipes. need.

 

The mandrel is usually made of 3Cr2W8V material, and the heat treatment hardness is 52-56HRC.

 

The flexible shaft type multi-ball core rod is formed by connecting multiple bowls to form a spherical shape formed by a flexible shaft in series, which can realize space swing in any direction. It is suitable for single-, multi-, and hollow-bent thin-walled stainless steel pipe fittings.

 

Multi-ball mandrels are used to bend the tube during the process of pulling the mandrel through the cylinder after bending.

 

The main disadvantage of a multi-ball mandrel is that it is cumbersome to manufacture, and the mandrel material and heat treatment requirements are the same as those of a single-ball mandrel.

 

Mandrel bend, shape, size and working position of mandrel have a great influence on the quality of stainless steel pipe.

 

The size of the round head mandrel and the working position of entering the pipe are shown in Figure 3-5.

 

In order to insert the mandrel smoothly into the stainless steel tube blank, the diameter d (mm) of the mandrel should generally be about 0.5-1.5 mm smaller than the inner diameter of the tube blank, that is,

 

 d = D1-

 

(0.5 -1.5)

 

The cylindrical length L of the mandrel is:

 

 L = (3-5) d

 

When the mandrel diameter d is larger, the coefficient value is smaller, and vice versa.

 

The working position of the mandrel should be the distance from the mandrel to the main bending line.

 

In general, the size of e should be determined according to the diameter of the stainless steel pipe blank, the radius of curvature and the gap between the inner diameter of the pipe and the mandrel, and then appropriately adjusted according to the actual situation. Production conditions.

 

 The value of e can be calculated as follows:

 

 e = √2 (R + D1 / 2) z a z2 (5-1)

 

Where D1--the inner diameter of the tube blank, nim;

 

 R-bending radius of the main layer, mm; ## # Z--clearance between the inner wall of the stainless steel tube blank and the mandrel, mm, z = D1-d0

 

There is also a commonly used club head site, which is difficult to use and manufacture only between the above two mandrels.

 

The components of the ball mandrel are shown in Figure 5-4.

 

 B anti-wrinkle block

 

The stainless steel tube blank curved tire model groove does not support the material near the cutting point and does not enter the bending deformation area. Even with a mandrel, the stainless steel elbow may wrinkle here, so it should be installed as

 

Anti-wrinkle block shown in Figure 5-5.

 

The front end of the anti-wrinkle block is in the shape of an arc edge, inserted between the curved tire mold and the tube blank, and the front end should be close to the tangent of the tube wall and the curved tire mold, effectively filling the curved tire mold and stainless steel tube blank bending

 

The gap between the inside is used to support the wall from the outside and prevent wrinkling.

 

The shallow circular groove on the anti-wrinkle block is in contact with the outer surface of the tube blank, and sliding friction occurs during operation. Therefore, the working surface of the anti-wrinkle block requires a certain hardness and low surface roughness.

 

Wrinkle-resistant blocks are usually made of tool steel or chrome-molybdenum steel with a hardness of 50-55HRC after quenching.

 

 C bending tire mold \\ n

 

The curved tire mold is another important part of the core bending device, and its radius depends on the bending radius of the stainless steel elbow.

 

However, considering that the bending force will cause a certain amount of springback during cold bending, the designed bending die radius should be slightly smaller than the bending radius required for stainless steel pipes. Generally, it can be determined based on the following empirical data.

 

When R / D = 3-4: R1 = (0.96-0.98) R \\ n

 

#N ## where R1-the radius of the curved tire mold, mm;

 

 R-bending radius of the main layer of the elbow, mm;

 

 D-outer diameter of the tube blank, mm.

 

When R / D is large, take a small value; when R / D is small, take a large value, and then correct it by trial mode.

 

Except for the wheel type, the curved tire mold has a mold pillar type, and the positions of the mold pillars of the parts are shown in Figure 5-6.

 

Coreless elbows are basically not used in the production of pipe joints. ## # (2) Push and bend

 

Push bending is a commonly used bending method in pipe bending, mainly used for bending elbows.

 

According to the characteristics of the bending process, it can be divided into two types: cold-formed pipe and mandrel hot-formed pipe.

 

The cold push tube is a method of pushing and bending the tube blank through a tube bending device on an ordinary hydraulic press or a crank press, and pressing a stainless steel straight tube into a mold having a normal temperature curved cavity to form stainless steel.

 

 elbow.

 

As shown in Figure 5-8, the cold bending device is mainly composed of a press 1, a guide sleeve 2 and a bending die 4. ## Bending mold is composed of two main parts for easy cavity processing.

 

When the pipe is bent, after putting the pipe blank 3 into the guide sleeve, the pressure column is lowered, and an axial thrust is applied to the pipe blank, forcing the pipe blank into the bending cavity, thereby causing bending deformation.

 

Cold push tube is suitable for stainless steel elbow with small bending radius. Small relative bending radius R / D≈1.3 can bend; elbow ellipse is small (≤3% -5%); outer wall

 

The thinning amount is small (≤9%); the elbow device has a simple structure, does not require special equipment, and has high production efficiency.

 

However, the relative thickness of the pipe is usually required to be t / D ≥ 0.06. Otherwise, the tube blank will lose stability due to poor rigidity, resulting in wrinkling or distortion inside the elbow.

 

Stainless steel pipe fittings should pay attention to the following points: Cold-pressed pipe process:

 

(A) In order to reduce the frictional resistance, extend the service life of the bending mold, and improve the surface quality of the stainless steel elbow, the tube blank needs to be lubricated.

 

Practice has proved that coating 40-50 oil on the surface of stainless steel tube blank, and then coating a layer of graphite powder, can ensure a good lubrication effect in the bending process.

 

(B) During the bending process, the end of the tube blank is easily collapsed under axial thrust. To this end, the core shown in Figure 5.9 can be placed in a tube blank that will follow the elbow during the bending process.

 

Emitted by the column.

 

(C) For stainless steel thin-wall elbows, in order to prevent wrinkling during bending and bending, the filler should be placed in the tube blank, which is not only easy to operate, but also has good anti-wrinkle effect.

 

(3) Bending

 

The use of a mold to press a straight stainless steel tube has the advantages of high production efficiency and simple mold adjustment.

 

In order to prevent wrinkling and flattening of the pipe wall, thin-walled pipes with an outer diameter of 10 mm or more need to be filled with a filler or put into the core from both ends before bending.

 

There are also some disadvantages to the mold bending method. For example, when the tube blank is in contact with the concave-convex mold, there will always be some deformation in the tube part, which makes the quality of the bent tube unsatisfactory.

 

In addition, bending radii, angles, and bending shapes are also limited, so they are used less in production.

 

Figure 5-10 shows a V-bend mold. U-shaped elbow mold is shown in Figure 5-1-1. The working surface of the punch conforms to the shape of the blank and is placed in the middle of the left and right swinging die.

 

The pressed stainless steel elbow is the process of pressing the tube to make it blank by pressing the tire on a hydraulic press.

 

This method is divided into hot pressing and cold pressing, which can suppress carbon steel elbow, alloy steel elbow, stainless steel elbow, copper and aluminum elbow.

 

The pressure elbow has a diameter of 25-406 mm and a wall thickness of 2.5-40 mm.

 

Bending radius R≥D, generally R = 1.5D.