Four kinds of flanges
The production process of flanges is generally divided into four main types.
Relatively speaking, forged flanges are the best quality and highest price flanges with different production processes. The second is cast flanges, as well as cut flanges and coiled flanges.
From the production process, the difference between cast flange and forged flange is different. For example, centrifugal flange is a kind of cast flange.
Centrifugal flanges belong to the casting method to produce flanges. Compared with ordinary sand casting, the structure of this type of casting is much finer, and the quality is improved a lot. It is not easy to have problems such as loose structure, pores, and trachoma.
How to make a cast flange
First of all, we need to understand how centrifugal flanges are produced, the process method and products of centrifugal casting to make flat welded flanges, which are characterized in that the product is processed through the following process steps:
- Put the selected raw material steel into an intermediate frequency electric furnace for smelting, so that the molten steel temperature reaches 1600-1700°C;
- Preheat the metal mold to 800-900℃ to maintain a constant temperature;
- Start the centrifuge, and pour the molten steel in step ① into the preheated metal mold in step ②;
- The casting is naturally cooled to 800-900℃ and kept for 1-10 minutes;
- Cool with water to near normal temperature, demould and take out the casting
Let us understand the production process of forged flanges:
The forging process generally consists of the following procedures, namely, selecting the blank, heating, forming, and cooling after forging.
The forging process methods include free forging, die forging and membrane forging.
During production, choose different forging methods according to the quality of forgings and the number of production batches.
Free forging has low productivity and large machining allowance, but the tools are simple and versatile, so it is widely used for forging single-piece and small-batch forgings with simpler shapes.
Free forging equipment includes air hammer, steam-air hammer and hydraulic press, etc., which are respectively suitable for the production of small, medium and large forgings.
Die forging has high productivity, simple operation, and easy realization of mechanization and automation.
The die forgings have high dimensional accuracy, small machining allowances, and more reasonable fiber structure distribution of the forgings, which can further improve the service life of the parts.
The basic process of free forging: In free forging, the shape of the forging is gradually forged from the blank through some basic deformation processes.
The basic processes of free forging include upsetting, drawing, punching, bending and cutting.
Upsetting is the process of forging the original blank in the axial direction to reduce its height and increase its cross-section. This process is often used for forging gear blanks and other disc-shaped forgings. Upsetting is divided into two types: total upsetting and partial upsetting.
Pulling is a forging process that increases the length of the blank and reduces the cross-section. It is usually used to produce blanks for shafts, such as lathe spindles and connecting rods.
A forging process in which through holes or non-through holes are punched out on the blank with a punch.
A forging process in which a blank is bent into a certain angle or shape.
A forging process in which one part of the blank is rotated by a certain angle relative to the other part.
The forging process of splitting the blank or cutting off the material head.
The full name of die forging is model forging, which is formed by placing the heated blank in a forging die fixed on the die forging equipment.
The basic process of die forging: die forging process: blanking, heating, pre-forging, final forging, punching and connecting, trimming, quenching and tempering, shot peening. Commonly used processes include upsetting, drawing, bending, punching, and forming.
Commonly used die forging equipment Commonly used die forging equipment includes die forging hammers, hot die forging presses, flat forging machines and friction presses.
In layman’s terms, forged flanges are of better quality and are generally produced by die forging, with fine crystal structure and high strength, and of course the price is more expensive.
Both cast flanges and forged flanges are commonly used manufacturing methods for flanges, depending on the strength requirements of the parts to be used. If the requirements are not high, you can also use turned flanges.
Forged flange VS cast flange
- The cast flange has accurate shape and size, small processing volume and low cost, but has casting defects (pores, cracks, inclusions); the internal structure of the casting is poor in streamline (if it is a cutting part, the streamline is worse);
- Forged flanges generally have lower carbon content than cast flanges and are not easy to rust. Forgings are streamlined, have a denser structure, and have better mechanical properties than cast flanges;
- Improper forging process will also cause large or uneven crystal grains, hardening cracks, and forging costs higher than cast flanges.
- Forgings can withstand higher shear and tensile forces than castings.
- The advantage of castings is that they can produce more complex shapes and lower costs;
- The advantage of forgings is that the internal structure is uniform, and there are no harmful defects such as pores and inclusions in the casting;
Directly cut the flange with the inner and outer diameter and thickness of the flange on the middle plate, and then process the bolt holes and waterline. The flange produced in this way is called a cut flange, and the large diameter of this type of flange is limited by the width of the middle plate.
Rolled flanges are all rolled large-diameter flanges.
The process of dividing the middle plate and then rolling it into a circle is called rolling, which is mostly used in the production of some large flanges. After the rolling is successful, welding is performed, then flattened, and then horizontal lines and bolt holes are processed.
(The flange rolled by the BIT profile bending machine is very flat and hardly needs to be flattened)
Manufacturing method of rolled flange
- Rolled flanges are cut from medium-sized steel plates into steel strips, then rolled into circular welded joints and then processed by flattening. There are cold rolling and hot rolling.
- After processing into a circle, the water line, bolt hole, spigot and other processes are processed.
- This is generally a large flange, which can be up to 7 meters in one molding.
- Plate-type flat welding flanges are mostly used, and the connection method is welding.
- If the production process of segmented production is used, the specifications of 12 meters to 15 meters or larger can be achieved.
- This kind of flange has good quality assurance because the raw material is medium-sized steel plate with good density.
Points to note for rolled flanges
- The welding process at the interface of the rolled flange is the most important thing, and X-ray or ultrasonic film inspection should be done. After the interface is completed, the material of the entire flange is no problem.
- Relatively speaking, the price of processed products with thin thickness, light weight, narrow one side of the product, and some sealing grooves is higher, while the price of some thick, heavy, and no very cumbersome processing technology rolled flanges. It should be lower.
- When processing the bolt holes, it is not allowed to drill the bolt holes to the place where there are welds. The materials of this kind of flanges are carbon steel, stainless steel, alloy steel and so on.
Photos of flange bending machine
WHAT ARE PIPE FLANGES AND HOW DO THEY WORK?
Offering a reliable way to connect pipe systems with the various equipment, valves, and other components of virtually any processing system, flanges are the second most used joining method after welding.
Using flanges adds flexibility when maintaining piping systems by allowing for easier disassembly and improved access to system components.
A typical flanged connection is comprised of three parts:
- Pipe Flanges
In most cases, there are specific gasket and bolting materials made from the same, or approved materials as the piping components you wish to connect. Stainless Steel flanges are some of the most common. However, flanges are available in a wide range of materials so matching them with your needs is essential.
Other common flange materials include Monel, Inconel, Chrome Moly, and many others depending on the application.
The best option for your needs will depend on both the system in which you intend to use the flange and your specific requirements.
COMMON FLANGE TYPES AND CHARACTERISTICS
Flanges are not a one-type-fits-all sort of solution. Sizing aside, matching the ideal flange design to your piping system and intended usage will help to ensure reliable operation, a long service life, and optimal pricing.
Here’s a look at the most common flange types available.
MAKING THE CONNECTION: FLANGE FACING TYPES
Flange design is only the start when considering the ideal flange for your piping system. Face types are another characteristic that will have a major impact on the final performance and service life of your flanges.
Facing types determine both the gaskets needed to install the flange and characteristics related to the seal created.
Common face types include:
- Flat Face (FF): As the name suggests, flat face flanges feature a flat, even surface combined with a full face gasket that contacts most of the flange surface.
- Raised Face (RF): These flanges feature a small raised section around the bore with an inside bore circle gasket.
- Ring Joint Face (RTJ): Used in high-pressure and high-temperature processes, this face type features a groove in which a metal gasket sits to maintain the seal.
- Tongue and Groove (T&G): These flanges feature matching grooves and raised sections. This aids in installation as the design helps the flanges to self-align and provides a reservoir for gasket adhesive.
- Male & Female (M&F): Similar to tongue and groove flanges, these flanges use a matching pair of grooves and raised sections to secure the gasket. However, unlike tongue and groove flanges, these retain the gasket on the female face, providing more accurate placement and increased gasket material options.
Many face types also offer one of two finishes: serrated or smooth.
Choosing between the options is important as they will determine the optimal gasket for a reliable seal.
In general, smooth faces work best with metallic gaskets while serrated faces help to create stronger seals with soft material gaskets.
THE PROPER FIT: A LOOK AT FLANGE DIMENSIONS
Apart from the functional design of a flange, flange dimensions are the most likely factor to impact flange choices when designing, maintaining, or updating a piping system.
However, you must consider how the flange interfaces with the pipe and the gaskets in use to ensure proper sizing.
Common considerations include:
- Outside diameter: The distance between two opposing edges of the flange face
- Thickness: A measure of the thickness of the outer attaching rim
- Bolt circle diameter: The distance between opposing bolt holes when measured from centre to centre
- Pipe size: A designation of the pipe size with which the flange corresponds
- Nominal bore size: A measurement of the flange connectors inner diameter
FLANGE CLASSIFICATION & SERVICE RATINGS
Each of the above characteristics will have an influence on how the flange performs across a range of processes and environments.
So how can you tell which flanges are up to the task and which are not?
Flanges are often classified based on their ability to withstand temperatures and pressures.
This is designated using a number and either the “#”, “lb”, or “class” suffix. These suffixes are interchangeable but will differ based on the region or vendor.
Common classifications include:
Exact pressure and temperature tolerances will vary by materials used, flange design, and flange size. The only constant is that in all cases, pressure ratings decrease as temperatures rise.
FLANGE STANDARDS AND MARKINGS
To help make comparison easier, flanges fall under global standards established by the American Society of Mechanical Engineers (ASME) — ASME B16.5 & B16.47.
If you’re attempting to replace or verify existing parts, all flanges must include markers — typically on their outer perimeter — to aid in the process.
These markers also follow a strict order:
- Manufacturer logo or code
- ASTM material code
- Material Grade
- Service rating (Pressure-temperature Class)
- Thickness (Schedule)
- Heat Number
- Special designations, if any — for example, QT for Quenched and tempered or W for repair by welding
:: READ MORE : COLD BENDING AND HOT BENDING IN PIPE BENDING