Skiving Tubing / Pipe

Edge treatment of coil strip before it enters a tube and pipe mill, called skiving, is a rapidly advancing technology. Improving the coil edge before it is welded helps increase the quality of the seam join and helps prevent rejected tube or pipe.
Skiving Tubing
Edge treatment of coil strip before it enters a tube and pipe mill, called skiving, is a rapidly advancing technology. Improving the coil edge before it is welded helps increase the quality of the seam join and helps prevent rejected tube or pipe.


Edge skiving to obtain smooth abutting edges for seam welding has been a viable process for many years. Most traditional skivers use triangular high-speed steel cutting knives held in bolted, clamped holders.
The toolholders are rigidly mounted on movable screwjack slides and are manually engaged with the strip to attain the desired depth of cut. Each tool is manually set, with the individual screwjack settings determining the depth of cut with each tool and, therefore, the tool load sharing.
Traditional skiving units are most successful at speeds above effective planing speeds, or about 40 feet per minute (FPM). Below this speed, the metal tends to tear instead of being smoothly cut, resulting in jagged edges that can be worse than the "as slit" edge.
Cambered material can jam between the rigid tools used with this equipment, causing tool blunting and changed depth of cut.
When tools wear and become blunt, they have a tendency to chatter, which can cause a rough finish and poor welds. In addition, blunt tools cannot easily be changed on-stream. They must be retracted by hand and another tool station advanced to replace the cutting action of the defective tool.
The load sharing and depth of cut of each tool depends on the individual tool settings. Uneven tool wear upsets the selected load sharing.Traditional skiving equipment has been generally satisfactory, but modern mills are now demanding higher quality, a wider operating range, and less operator dependency.
For instance, since most tungsten inert gas (TIG) welding mills using stainless steel, high-alloy steels, titanium, or aluminum must run slower than 40 FPM, these materials must be used "as slit."
Untreated or imperfectly treated edges cause pinholes in completed welds. The product is often 100 percent inspected for defective welds using ultrasound, and defective lengths are scrapped. As much as 2 percent can be routinely rejected in some mills.
Conventional edging equipment performs well with high-speed mills when properly set up with sharp tools and when the material is of uniform width and free of camber.


Recent research and development has resulted in a range of new skiving equipment being developed.
A four-station edger suited to skiving at down to near-zero strip speed is available to the market. This patented edger uses electrically vibrated tools that impart relative movement between the tools and strip at all times. The vibration amplitude is fully adjustable, and so is the cutting pressure and depth of cut on each module.
These machines have a skiving speed range of 0 to 600 FPM. Each mini tool carriage is oscillated in the direction of material travel. The frequency can be varied. The higher the frequency, the less the depth of cut and the better the finish. Because vibratory action is in the direction of material travel, vibration perpendicular to direction of travel (or chatter) is suppressed.


The skiving process is still in need of improvement. Higher-frequency oscillation of vibratory tools is being developed to give better finishes at low cutting speeds. Also, new methods of reducing the effects of tool wear are being developed.
Edge sensing rolls fitted with sonic detectors are being designed to enable edge quality monitoring on-stream. These can be used to initiate automatic tool changing. The process is slowly evolving into self-checking smart technology.

The Difference between Polyurethane and Nylon Tubing

Trying to decide whether to purchase nylon tubing or polyurethane hoses for your pneumatic application? Understanding the differences in materials will enable you to make the right choice and significantly improve system performance.
Polyurethane Tubing


Flexibility: While polyurethane is naturally flexible, nylon tubing can withstand repeated flexing better and longer.
Application: Polyurethane hoses are better suited to tight bending in and through equipment, such as in robotics and pneumatic control machinery. They are also commonly used in medium pressure applications such as solid, liquid and gaseous dispensing and fuel line and wire abrasion protection. Nylon, on the other hand, is recommended for hydraulic lines and refrigeration, air conditioning systems, fuel and oil transfer and chemical transport.
Durability: Although both materials have excellent resistance to abrasion from fuels, oils and abrasion, nylon tubing offers better heat and chemical resistance as well as supports higher working pressure.
Resistance: Nylon tubing has superior crack resistance and is an industrial standard for applications requiring greater resistance to chemicals, heat and working pressure.


  • High compressive strength
  • Rigidity, abrasion resistance 
  • Can withstand higher temperatures
  • Good friction coefficient
  • Great resiliency
  • Inherent wear resistance
  • And low cos

Hot Extruding Steel

During hot extrusion a round steel billet is pre-heated and, after leaving the furnace, is pushed through a forming die into a profile bar using a ram with an extrusion force of 2,200 t. Hot extruding offers substantial advantages in comparison with hot rolling, forging or machining. Hot extrusion can be used to make complex steel profile shapes even using metals which are difficult to form. In addition, small lot sizes can be produced economically.
Hot Extruding Steel
Hot extruded steel profiles offer the benefit of :
* different material thicknesses within one profile cross-section
* the possibility to use in highly sensitive areas, where the special profiles must with stand specific demands of temperature, pressure, aggressive media or hygienic requirements
* seamless structure of solid and hollow sections
Technical Possibilities
Max. Circumscribed Circle Dia. for Solid and Hollow Profiles [mm] 240
Min. Diagonals Dia. for Hollow Profiles [mm] 20
Max. Diagonals Dia. for Hollow Profiles [mm] 160
Min. Wall Thickness [mm] 4
Max. Length [mm] 16800
Length c. 3,000 up to e. 16,800 mm (depending on profile cross-section); with sawn ends, (fixed lengths by agreement)
Min. Weight [kg/m] 1.5
Max. Weight [kg/m] 100
Cross-Sectional Tolerances/ Straightness Tolerances By agreement, depending on the profile cross- section and material grade; reductions possible, e.g. for functional areas, by agreement
Surface As extruded; descaled or picked on request
Materials / Treatments Nearly all quality and stainless steels in the iron and steel list, special steels, non-ferrous heavy metal alloys
All required heat treatments are available

Polymer Extrusion & Injection Molding Process Comparison

Extrusion is widely used in various industries.
The screw in the extruder rotates and develops sufficient pressure to force material to go through a die and produce products with desired geometry. 
Injection molding is the most commonly used manufacturing process for the fabrication of plastic parts. A wide variety of products are manufactured using injection molding, which vary greatly in their size, complexity, and application. The injection molding process requires the use of an injection molding machine, raw plastic material, and a mold. The plastic is melted in the injection molding machine and then injected into the mold, where it cools and solidifies into the final part.
Polymer Extrusion
Property Name   Polymer Extrusion   Injection Molding
Shapes Flat, Thin-walled: Cylindrical, Thin-walled: Cubic, Solid: Cylindrical, Solid: Cubic Thin-walled: Cylindrical, Thin-walled: Cubic, Thin-walled: Complex
Part size Diameter: 0.04 - 6.0 in Envelope: 0.01 in³ - 80 ft³
Weight: 0.5 oz - 55 lb
Materials Thermoplastics
(Elastomer, Thermosets)
(Composites, Elastomer, Thermosets)
Surface finish - Ra (μin) 16 - 63
(8 - 75)
4 - 16
(1 - 32)
Tolerance (in.) ± 0.04
(± 0.01)
± 0.008
(± 0.002)
Max wall thickness 0.016 - 6.0
(0.0008 - 6.0)
0.03 - 0.25
(0.015 - 0.5)
Quantity 10000 - 1000000 10000 - 1000000
(1000 - 1000000)
Lead time Weeks Months
Advantages Good surface finish, High production rate, Low labor cost, Little scrap generated Can form complex shapes and fine details, Excellent surrface finish, Good dimensional accuracy, High production rate, Low labor cost, Scrap can be recycled
Disadvantages Limited to uniform cross sections, High equipment cost, Long lead time possible Limited to thin walled parts, High tooling and equipment cost, Long lead time possible
Applications Rods, bars, tubing, sheet, cable, frames Housings, containers, caps, fittings

Rotational Lining Solutions - PTFE Lining Machine

To protect unconventionally sized or shaped parts,rotational lining is the best solution. Using specialized materials and technology, we can bond a uniform,seamless polymer layer to the interior of virtually any metallic structure, regardless of shape or complexity.
PTFE Lining Machine
Rotational Lining Process:
Granular polymer resin is placed inside the structure to be lined and all openings are covered. The structure is heated while simultaneously being rotated about two axes. The resin melts and flows evenly over the entire inner surface of the structure, bonding to the metal substrate. Once cooled, the result is a monolithic, corrosion- and chemical resistant lining that conforms to complex shapes and is virtually free of stresses. Wall thickness can range from 0.090” to 0.400”. Typical linings range from 0.100” to 0.250”, depending on part size and service requirements.
Standard and Custom Sizes:
We line a wide range of equipment, including some of the largest pipes and vessels in the industry. Our manufacturing capabilities can accommodate most size requirements.
Maximum dimensions for lined structures:
· 8’ diameter × 20’ length
· 10’ diameter × 12’ length
Typical lined structures include
· Tanks, pressure vessels, scrubbers, pipe spool and fittings
· Caissons and other equipment used underwater
· Pumps, valves, flowmeters, heat exchangers, filter housings and other process equipment.
Lining Materials:
Polymer selection and liner thickness are based on the chemical resistance properties the final structure requires. We work with technically engineered fluoropolymers (PTFE,PFA, ETFE, PVDF, and ECTFE), nylons (nylon 12) and olefins (HDPE) to meet the specific requirements of each application.
Our Products adheres to a rigorous quality assurance program for its rotational lining solutions. We carry the following certifications:
· AS9100 Revision C
· ISO 9001:2008
· ASME U stamp
· NBBI R stamp

Types of Plastic Extrusion Process

The plastic extrusion process is broadly classified into seven different types depending upon the specific applications.


In this extrusion process, the molten plastic material is extruded through a flat die. The cooling rolls are used to determine the thickness of sheet/film and its surface texture. The thickness of sheet can be obtained in the range of 0.2 to 15 mm. The thin flat sheet or film of plastic material can be made. Generally, polystyrene plastic is used as a raw material in the sheet extrusion process.


In the blown film process, the die is like a vertical cylinder with a circular profile. The molten plastic is pulled upwards from the die by a pair of nip rollers. The compressed air is used to inflating the tube. Around the die, an air-ring is fitted. The purpose of an air-ring is to cool the film as it travel upwards. In the center of the die, there is an air inlet from which compressed air can be forced into the centre of the circular profile, and creating a bubble. The extruded circular cross section may be increased 2-3 times of the die diameter. The bubbles are collapsed with the help of collapsing plate. The nip rolls flatten the bubble into double layer of film which is called layflat. The wall thickness of the film can be controlled by changing the speed of the nip rollers. The layflat can be spooled in the form of roll or cut into desired shapes. Bottom side of the layflat is sealed with the application of heat, and cut across further up to form opening; hence it can be used to make a plastic bag. The die diameter may vary from 1 to 300 centimeters. Generally, polyurethane plastic is used in this process.
Plastic Extrusion Process


This is also called wire coating process. In this process, a bare wire is pulled through the center of a die. There are two different types of extrusion tooling used for coating over a wire i.e. pressure or jacketing tooling. If intimate contact or adhesion is required between the wire and coating, pressure tooling is used. If adhesion is not desired, jacketing tooling is used. For pressure tooling, the wire is retracted inside the die, where it comes in contact with the molten plastic at a much higher pressure. For jacketing tooling, the wire will extend and molten plastic will make a cover on the wire after die. The bare wire is fed through the die and it does not come in direct contact with the molten plastic until it leaves the die. The main difference between the jacketing and pressure tooling is the position of the wire with respect to the die.
Plastic Extrusion Process


In this process, the molten plastic is extruded through a die and hollow cross sections are formed by placing a mandrel inside the die. Tube with multiple holes can also be made for specific applications, by placing a number of mandrels in the center of the die.


Coextrusion is the extrusion process of making multiple layers of material simultaneously. It is used to apply one or more layers on top of base material to obtain specific properties such as ultraviolet absorption, grip, matte surface, and energy reflection, while base material is more suitable for other applications, e.g. impact resistance and structural performance. It may be used on any of the processes such as blown film, over jacketing, tubing, sheet/film extrusion. In this process, two or more extruders are used to deliver materials which are combined into a single die that extrudes the materials in the desired shape. The layer thickness is controlled by the speed and size of the individual extruders delivering the materials.


Extrusion coating is used to make an additional layer onto an existing rollstock of paper, foil or film. For example, to improve the water resistant of paper polyethylene coating is used. The applications of extrusion coating are liquid packaging, photographic paper, envelopes, sacks lining for fertilizers packaging and medical packaging. Generally, polyethylene and polypropylene are used.

Types of extrusion and extrusion equipment

Extrusion is a compressive deformation process in which a block of metal is squeezed through an orifice or die opening in order to obtain a reduction in diameter and increase in length of the metal block. The resultant product will have the desired cross-section. Extrusion involves forming of axisymmetric parts. Dies of circular on non-circular cross-section are used for extrusion. Generally, extrusion involves greater forming forces. Large hydrostatic stress in extrusion helps in the process by enhancing the ductility of the material. Metals like aluminium, which are easily workable, can be extruded at room temperature.
Plastic Extrusion


Direct extrusion:Direct extrusion, also called forward extrusion, is a process in which is the billet moves along the same direction as the ram and punch do. Sliding of billet is against stationary container wall.Friction between the container and billet is high. As a result, greater forces are required. A dummy block of slightly lower diameter than the billet diameter is used in order to prevent oxidation of the billet in hot extrusion. Hollow sections like tubes can be extruded by direct method, by using hollow billet and a mandrel attached to the dummy block. 
Indirect extrusion:Indirect extrusion (backward extrusion) is a process in which punch moves opposite to that of the billet. Here there is no relative motion between container and billet. Hence, there is less friction and hence reduced forces are required for indirect extrusion. For extruding solid pieces, hollow punch is required. In hollow extrusion, the material gets forced through the annular space between the solid punch and the container. The variation of extrusion pressure in indirect extrusion is shown above. As seen, extrusion pressure for indirect extrusion is lower than that for direct extrusion. Many components are manufactured by combining direct and indirect extrusions. Indirect extrusion can not be used for extruding long extrudes.
Hydrostatic extrusion:In hydrostatic extrusion the container is filled with a fluid. Extrusion pressure is transmitted through the fluid to the billet. Friction is eliminated in this process because of there is no contact between billet and container wall. Brittle materials can be extruded by this process. Highly brittle materials can be extruded into a pressure chamber. Greater reductions are possible by this method. Pressure involved in the process may be as high as 1700 MPa. Pressure is limited by the strength of the container, punch and die materials. Vegetable oils such as castor oil are used. Normally this process is carried out at room temperature. A couple of disadvantages of the process are: leakage of pressurized oil and uncontrolled speed of extrusion at exit, due to release of stored energy by the oil. This may result in shock in the machinery. This problem is overcome by making the punch come into contact with the billet and reducing the quantity of oil through less clearance between billet and container. 
Impact extrusion: Hollow sections such as cups, toothpaste containers are made by impact extrusion. It is a variation of indirect extrusion. The punch is made to strike the slug at high speed by impact load. Tubes of small wall thickness can be produced. Usually metals like copper, aluminium, lead are impact extruded. 
Tube extrusion:Employing hollow billet and a mandrel at the end of the ram, hollow sections such as tubes can be extruded to closer tolerences. The mandrel extends upto the entrance of the die. Clearance between the mandrel and die wall decides the wall thickness of the tube. The mandrel is made to travel alongwith the ram in order to make concentric tubes by extrusion.


Cold extrusion could produce parts with good surface finish, high strength due to strain hardening, improved accuracy, high rate of production. However, the process requires higher pressure and tools are subjected to higher stresses. Proper lubrication is necessary for preventing seizure of tool and workpiece. Phosphate coated billets are lubricated with soap.
Hot extrusion can be employed for higher extrusion ratios. Inhomogeneous deformation can occur due to die wall chilling of the billet. Metal may get oxidized. The oxide layer can increase friction as well as the material flow. Glass is used as lubricant for hot extrusion. Molybdenum disulfide or graphite are the solid lubricants used in hot extrusion. Canned extrusion using thin walled cans made of copper or tin is usually used for extruding highly reactive metals and metal powders.


Hydraulic presses of vertical or horizontal type are used for extrusion. Vertical presses are of capacity ranging from 3 to 20 MN. Horizontal presses occupy less space, but the billets get nonuniformly cooled. Horizontal presses upto 50 MN capacity are being used. Tubular extrusions are mostly done in vertical presses, while horizontal presses are used for bar extrusion.