The following article references the many different ways to fabricate tube and pipe product.
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There are many ways to cut. The methods described in this manual are generally accepted as the primary methods used to cut steel tubing.
Die-cutting is the fastest way to cut tubing. The term “die-cut” refers to a die block, with appropriate inserts, to cut a particular size (OD) tubing. Additional equipment from a manual press to a mechanical/hydraulic press to a dedicated system is necessary to complete the process. The die block is designed for a specific OD range and gauge combination. The inserts in the die block can be used with one tube diameter. If several different tube sizes are being cut, a separate set of inserts will be needed for each tube OD. Die blocks are interchangeable in ten minutes to accommodate various tube sizes, wall thickness, and shapes.
The die-cut process lends itself to a clean, burr-free end condition. If a two blade cutoff is used (one blade scarfs the top of the tube and the second vertical blade comes down and cuts the tube) a burr-free, dimple-free end cut will result.
Saw cutting is the slowest method of cutting tubing. The advantages of this method proportionately increase with: size of tube being cut (OD), the wall thickness (gauge), the carbon content of the steel. There are two common methods of saw cutting, cold saw and band saw.
Cold saw cutting equipment can be the most economical dedicated cutting system available. A cold saw is a self-contained system requiring a minimum of set-up and operator expertise, utilizing a spinning blade to cut a clamped tube. The quality of a cold saw cut is dimple-free and usually burr-free. The length of the cut can be controlled to ± .010″.
Band saw cutting utilizes a continuous ribbon blade in either a horizontal or vertical plane to cut a clamped tube or tubes. This method of cutting provides the ability to cut multiple pieces of tubing of the same or different diameters to the same length at the same time. For example, a bundle of tubing can be cut to a pre-determined length without breaking the bundle and cutting each piece individually. This is a self-contained dedicated cutting system requiring minimum operator skill. Length tolerances are dependent on the number of tubes being cut simultaneously. Generally, band saws can meet a length tolerance of ± 1/16″.
Lathe cutting is slower than die cutting but faster than saw cutting. The lathe method utilizes a stationary blade (tool bit) while spinning the tube to perform the cutting process. Only round tubing can be cut on a lathe. As a self-contained, dedicated system, the initial investment for lathe cutting equipment is high. A fairly skilled operator is required for optimum set-up and maintenance. The lathe cut is very clean and square. Cut ends can be chamfered on both the OD and the ID of the tube, and tolerances of ±.010″ can easily be held.
Piercing a tube is the fastest conventional method to perforate (put a hole in) a tube. There are four different types of perforations: Single Dimple, Double Dimple, Clean hole one end and Clean hole two walls.
Different shapes and sizes of perforations can be punched into a tube depending on the design of the perforator. Some examples are elongated holes, square, diamond, rectangular, and star-shaped. Punching units can be used in an arbor press, punch press, press brake, air or hydraulic press, or in a self-contained system.
Tube End Forming & End Finishing
The terms end forming and end finishing can mean many different things, depending of the point of view of the interpreter. It is safe to assume that these terms are often overlapping and easily misinterpreted. In this guide, we will consider swaging, expanding, flaring, doming (closing), and beading (external or internal) as end forming operations. All other operations will be considered end finishing.
Swaging is reducing the OD dimension at the end of a tube. The length of the swage and the final OD depends on the method used and the characteristics of the material being swaged. Swages can be round to round, round to square, round to oval, oval to round, etc. Swaging equipment is dedicated but existing presses can be utilized for short lengths.
Expanding is increasing the OD dimension at the end of a tube. Like swaging, many options are available. The length, shape, and final OD depend upon the method, capacity, tooling, and tube characteristics.
Flaring is an operation that forms the tube end at a specific angle, OD, and depth to meet application demand. This method can be achieved by band (thin wall tubing), punch press (short lengths), and primarily a dedicated end finishing machine.
Beading means to expand the tube, internally or externally, a specific radius or diameter. A punch press and die assembly is required for each OD. Short lengths can be formed on a punch press, but long lengths require a dedicated end forming machine.
Doming is simply closing the end of a tube. The tube end is rolled or pressed to the application requirements. This operation is typically performed with a dedicated end forming machine, but short lengths can be formed on a press.
Compression bending. In compression bending, the work piece is clamped to a bend die (or radius block). A wipe shoe (or slide block) is then brought into contact with the work piece. As the wipe shoe rotates around the static bend die, it forces the work piece to assume the radius of the bend die. This type of bending represents certain advantages for bending of open extrusions and shapes
Press bending. A ram die with the desired radius of bend is fitted to the press arm. The arm forces the tubing down against the opposing two wing dies. The wing dies, with resisting pressure, pivot up, forcing the tube to bend around the ram. Press bending is very fast and may bend more miles of tubing than any other method. Since the tubing cannot be internally supported, considerable distortion can occur.
Rotary draw bending. Rotary draw bending may be the most versatile, precision system of bending. It certainly produces high quality bends on the tightest radius within thin wall tubes. With a heavy walled tube on a generous radius, only a three piece family of tools is required. The work piece is locked to the bend die by the clamp die. As the bend die rotates the follower type pressure die advances with the tube. As the wall of the tube becomes thinner and/or the radius of bend is reduced, a mandrel and a wiper are required.
When you weld galvanized steel tubing, all protective coatings are vaporized, thus leaving a raw, unprotected area in the weld zone. Salt spray tests have proven that powder coating over zinc could increase the product life 4-6 times. For customers who powder coat, and are concerned about corrosion protection in the weld zone, we would like to suggest four cold galvanizing compounds that are heat resistant (up to 750° F) and act as a primer for powder coating. They are: ZRC cold galvanizing compound (battleship gray); ZRC Galvilite cold galvanizing compound (shiny); Rustolastic #24-A-120 (sales code 073258); Kalcor 75% zinc dust epoxy primer #61-2373.
Allied’s galvanized tube products are protected by a clear organic top coating which provides excellent adhesion properties to most thermo-set powder coatings, as well as to the following air dry and bake topcoats:
|Paints Generally||Compatible with Allied's||Clear Organic Top Coat|
|High-Bake thermoset acrylic||High-bake alkyd||Two-part urethane or epoxy|
|High bake Polyester||Solvent-based paints for metals||Solvent-based paints for wood|
|Solvent-based high-solids paint||Oil-based paints||Paints for car bodies or appliance|
Paints requiring individual evaluation:
- Water-based latex paints
- PVC, fluorocarbon paints, or when special primers are required
- Water-based high-solids paints
- Silicone paints and caulk
- Water colors, tempera, or artistic paint
Cleaning Flo-Coat Tubing Prior to Powder Coating
Allied’s unique in-line Flo-Coat process provides an excellent finished tube surface which can be readily post-coated with either a powder or a liquid coating application and curing process. Allied’s manufacturing process applies three layers of protection on the steel tube; zinc, conversion coating, and a clear priming polymer, resulting in a clean and ready-to-coat tube as a final product.
The cleaning of the tube surface for post painting or powder coating is required only for the removal of the surface contaminants deposited on the tube surface during storage, transit, handling, or processing. No additional pre-treatment is required for improving the coating adhesion over Allied’s products.
Benefits of using Allied’s Galvanized Products when Powder Coating
If a surface grinding process is required in your powder coating operation, it demands additional manpower and maintenance expenses. With Allied’s galvanized products, there is no need for the use of this abrasive cleaning process.
The only cleaning that is required when powder coating over Allied’s galvanized tubing is to remove the dust and dirt that builds up during storage, transportation, and handling. A light detergent or simply a warm water wash is all that is needed. If the tubing is not smeared with a greasy or oily film, a simple wiping action does the job.
The clear third coating on Allied’s products acts as a primer for powder coating and liquid coating applications, exhibiting excellent adhesion and abrasion characteristics. For those that require a high temperature baking process, it is heat-stable for the normal curing cycle (450° for 10-12 minutes).
The advantages of using Allied’s triple coated products are numerous from the processing point of view. However, the biggest benefit is from the phenomenal corrosion resistance that can be exploited from the synergism of powder coating over Allied’s galvanized surface. Recent salt spray tests showed that scribed powder coating over untreated tube peeled 1½” after only 549 hours. No significant creepage was found at 3000 hours on Allied’s Flo-Coat product.