Effect of Tube Ovality on the Drawing Process of ERW Round
Tubes for Size Reduction
1. Introduction
Electric Resistance Welded (ERW) round tubes are extensively utilized across various
industrial sectors due to their cost-effectiveness and suitability for a wide range of
applications. A common manufacturing process to achieve specific dimensional
requirements for these tubes is cold drawing, a method that reduces the tube's
diameter and/or wall thickness by pulling it through a die. The initial geometric
characteristics of the ERW tube, particularly its roundness, play a crucial role in the
success and final quality of the drawn product. Ovality, or the deviation from a
perfectly circular cross-section, is a common geometric imperfection in tubes. The
presence and degree of ovality in the initial ERW tube can significantly influence the
subsequent drawing process, affecting stress distribution, the potential for defects,
the final dimensional accuracy, and the required processing parameters. This report
aims to provide a detailed analysis of the effects of initial ovality on the drawing
process of ERW round tubes for size reduction, encompassing the definition and
measurement of ovality, the specifics of the drawing process, the impact of ovality on
stress and defect formation, its influence on final tube dimensions, relevant industry
standards, the relationship between ovality and drawing forces, and the techniques
available to minimize its adverse effects.
2. Defining Tube Ovality in Round Tubes
Tube ovality, in the context of round tubes, refers to the extent to which the tube's
cross-section deviates from a perfect circle.1 It essentially quantifies the out-ofroundness of the tube. This deviation arises from variations in the outer diameter
measured across different axes of the tube's cross-section. Ovality is commonly
assessed by comparing the tube's major diameter, which represents the widest point,
to its minor diameter, representing the narrowest point.2
Several methods are employed to calculate and express tube ovality. One prevalent
approach is to express it as a percentage, often calculated using the formula: ((Major
Diameter - Minor Diameter) / Nominal Diameter) * 100%.2 Alternatively, some sources
might use the average diameter in the denominator: ((Major Diameter - Minor
Diameter) / Average Diameter) * 100%.5 The choice of denominator can lead to
slightly different reported ovality percentages for the same tube, highlighting the
importance of specifying the calculation method. Another way to define ovality is
through the absolute dimensional difference between the maximum and minimum
outer diameters.3 For instance, if a tube has a maximum outer diameter of 2.010
inches and a minimum outer diameter of 1.990 inches, the ovality could be expressed
as a difference of 0.020 inches. It is also noteworthy that certain industry standards
offer specific definitions. API 5L, for example, defines out-of-roundness as the
difference between the maximum (or minimum) diameter and the nominal diameter,
expressed as a percentage of the nominal diameter.4 This definition focuses on the
deviation from the intended size rather than the difference between the extremes of
the actual shape. In contrast, ISO 3162 defines out-of-roundness as the difference
between the maximum and minimum diameters, expressed as a percentage of the
nominal diameter.4 Assuming symmetric ovality, the ISO 3162 definition yields twice
the percentage ovality compared to the API 5L definition. The IADC Lexicon provides
another definition, stating that ovality is the ratio of the difference between the
maximum and minimum diameter to the sum of the maximum and minimum diameter
of the pipe.8 These variations underscore the need for clear communication and
adherence to specific standards when defining and measuring ovality.
Accurate measurement and definition of ovality are crucial for effective quality
control throughout the tube manufacturing process and for optimizing downstream
processes like drawing.2 Understanding the degree of initial ovality allows
manufacturers to predict potential challenges during drawing and to implement
necessary adjustments or corrective actions. Furthermore, acceptable levels of
ovality are often dictated by industry standards and the specific requirements of the
application for which the tube is intended.4 These tolerances can vary significantly
depending on factors such as the industry (e.g., aerospace vs. refrigeration), the
specific application (e.g., tight bends vs. fluid transport), and the governing standards
(e.g., ASTM, EN, API).
Table 1: Summary of Ovality Definitions and Formulas from Different Sources
Source
Definition
Formula
Sharpe Products
Deviation from a perfect circle
in a tube's cross-section.
Percentage = (Major Diameter
- Minor Diameter) / Nominal
Diameter) * 100%
HU-Steel
Degree of deviation between
the major axis and the minor
axis.
Percentage = (Max OD - Min
OD) / Nominal OD * 100%
HU-Steel
Difference between the
maximum and minimum
diameters divided by the
average of the inner or outer
diameter.
Δ = (D_max - D_min) / (D_max
+ D_min) * 100%
API 5L
Difference between the
maximum (or minimum)
diameter and the nominal
diameter.
Percentage = (Max OD –
Nominal OD) / Nominal OD *
100% (or Min OD)
ISO 3162
Difference between the
maximum and minimum
diameters.
Percentage = (Max OD – Min
OD) / Nominal OD * 100%
IADC Lexicon (API)
Ratio of the difference
between the maximum and
minimum diameter to the sum
of the maximum and minimum
diameter.
(Max Diameter - Min
Diameter) / (Max Diameter +
Min Diameter)
3. The Typical Drawing Process for Size Reduction of ERW Round Tubes
The drawing process is a metal forming technique employed to reduce the diameter
and/or wall thickness of tubes through cold working.10 For ERW round tubes, which
are initially manufactured by cold-forming a flat sheet of steel into a cylindrical shape
followed by electric resistance welding of the longitudinal seam 12, the drawing
process is often utilized to achieve tighter tolerances, improved surface finish, and
enhanced mechanical properties.13 A common method for this is the Drawn Over
Mandrel (DOM) process.13
The DOM process typically begins with an ERW tube where the internal weld flash has
been removed.13 This initial tube then undergoes cold drawing, where it is pulled
through a die while being supported internally by a mandrel or plug.13 The die's
internal geometry dictates the final outer diameter of the drawn tube, while the
mandrel, positioned inside the tube, controls the inner diameter.14 The precise angle
and dimensions of both the die and the mandrel are critical in achieving the desired
final size and wall thickness.14 Depending on the initial dimensions of the ERW tube
and the target specifications, multiple drawing passes might be necessary to
incrementally reduce the size and refine the material's properties.14
While DOM drawing is prevalent for achieving high-precision ERW tubes, other
drawing methods can also be used for size reduction:
Tube Sinking: This is the simplest form of tube drawing, where the tube is pulled
through a die to reduce both its outer and inner diameters without any internal
support.17 While cost-effective, the lack of internal support in sinking can make it
less controlled in terms of maintaining roundness, potentially amplifying the
impact of initial ovality.17
● Plug Drawing: These methods utilize a plug or mandrel positioned inside the
tube during drawing to control the inner diameter and wall thickness.17 Different
variations exist, including:
○ Fixed Plug Drawing: The mandrel is held stationary at the die exit, offering
excellent control over the inner surface finish but limiting the length of tubes
that can be drawn.18
○ Floating Plug Drawing: The mandrel is not anchored and its position is
maintained by friction forces between the tube and the mandrel, allowing for
the production of very long tubes.18 However, it requires precise design for
optimal results.
○ Tethered Plug Drawing: This method combines features of fixed and
floating plug drawing, where the mandrel can float but is also anchored,
resulting in straight tubes with a good inner surface finish.18
● Rod (Mandrel) Drawing: In this process, a hardened steel rod or mandrel is
inserted into the tube's bore and drawn along with the tube through the die,
defining the inner diameter.17 This method can achieve significant area reductions
but might require a secondary reeling operation to remove the mandrel.18
●
The general sequence of steps involved in the drawing process for ERW tubes
typically includes:
1. Raw Material Procurement and Preparation: This involves selecting ERW tubes
with appropriate initial dimensions and quality, followed by cleaning to remove
scale, rust, and contaminants.28 Lubrication is then applied to the tube's surface
2.
3.
4.
5.
to minimize friction during drawing.14 The end of the tube might also undergo a
pointing or tagging process to reduce its diameter over a short length, allowing it
to be fed through the drawing die and gripped by the drawing mechanism. 14
Drawing: The prepared tube is fed through the drawing die. If mandrel or plug
drawing is employed, the mandrel is inserted into the tube's bore before or
during this stage.14 A significant tensile force is applied to the tube, pulling it
through the die, resulting in a reduction in its outer diameter and potentially its
wall thickness.10
Multiple Passes and Annealing: Depending on the desired final dimensions and
the amount of reduction required, the tube might undergo multiple drawing
passes. Intermediate annealing heat treatments might be necessary between
passes to restore the material's ductility, which is reduced by the cold working
process.14
Mandrel Removal: If a mandrel was used, it needs to be removed from the
drawn tube. This can be achieved through various methods, such as applying
pressure over rollers to expand the tube slightly.14
Finishing Operations: After drawing, the tube typically undergoes finishing
operations, including straightening to correct any bending or curvature 12, cutting
to the required lengths 12, and final inspection to ensure that the tube meets the
specified dimensional tolerances, surface finish requirements, and mechanical
properties.12
4. Effect of Initial Ovality on Stress Distribution During Drawing
The presence of initial ovality in an ERW tube significantly influences the stress
distribution during the drawing process for size reduction. When an oval tube is
forced through a circular die, it undergoes non-uniform deformation, leading to a
complex stress state within the material. It can be anticipated that the portions of the
tube corresponding to the major diameter will experience higher compressive
stresses as they are the first to come into contact with the die and are subjected to
the greatest degree of radial reduction to conform to the die's circular opening.14 This
compression can lead to localized yielding if the stress exceeds the material's yield
strength. Conversely, the regions of the tube aligned with the minor diameter might
experience tensile stresses as the material is stretched circumferentially to fill the
circular die profile.14
The non-uniform deformation inherent in drawing an oval tube through a circular die
can lead to stress concentrations at the locations corresponding to the initial major
and minor diameters. These stress concentrations increase the risk of localized
yielding or even fracture if the applied drawing forces are sufficiently high or if the
material possesses inherent weaknesses.14 The magnitude and distribution of these
stresses are also influenced by the specific drawing method employed. In tube
sinking, where there is no internal support, the initial ovality might lead to a more
pronounced non-uniform stress distribution across the tube wall. The lack of a
mandrel allows for greater freedom of deformation, and the oval shape might
exacerbate tendencies for buckling or uneven thinning.17
In contrast, drawing with a mandrel or plug provides internal support that can help to
mitigate some of the effects of initial ovality on stress distribution.14 The internal tool
helps to control the inner diameter and can promote a more uniform flow of material
as the tube is drawn through the die. However, even with internal support, a
significant initial ovality will still result in variations in the contact pressure between
the tube and both the die and the mandrel, leading to a non-uniform stress state.
Simulation software, particularly those utilizing the Finite Element Method (FEM), are
valuable tools for analyzing the complex stress and deformation patterns that arise
during tube drawing, including the effects of initial ovality.14 These simulations can
provide detailed insights into the magnitude and distribution of stresses, allowing
manufacturers to optimize the drawing process and minimize the risk of failure.
5. Potential for Defects During Drawing of Oval Tubes
The presence of ovality in the initial ERW tube significantly increases the potential for
various defects to occur during the drawing process. As highlighted in the context of
tube bending, high ovality can make tubes more prone to wrinkling, flattening, or
cracking.2 Similar risks exist during the drawing process. A tube with a high degree of
initial ovality might be more susceptible to flattening or buckling (a form of wrinkling)
as it is compressed by the die to conform to a circular shape.14 The already flattened
or elongated sections of an oval tube might resist further deformation unevenly,
leading to instability and the formation of wrinkles or buckles.
Significant initial ovality can also result in uneven wall thickness in the drawn tube.14
The material at the major diameter, being subjected to greater compression and
stretching to fit the circular die, might experience more thinning compared to the
material at the minor diameter. This variation in wall thickness can compromise the
structural integrity and performance of the final drawn tube. Effective lubrication
plays a crucial role in mitigating the formation of defects during the drawing of oval
tubes.14 By reducing friction between the tube and the die, lubrication can help to
ensure a smoother flow of material and minimize the development of surface defects
such as scratches or galling, particularly in areas of high contact pressure caused by
the ovality.
Furthermore, excessive initial ovality can lead to a substantial increase in the required
drawing forces.14 The increased resistance to deformation encountered when forcing
an out-of-round tube into a round die necessitates higher pulling forces. If these
forces exceed the tensile strength of the tube material, it can result in fracture during
the drawing process.14 In tube sinking, where the tube wall might thicken due to the
drawing process, excessive sinking of an oval tube can lead to an adverse effect on
surface quality, potentially resulting in 'sunburst cracking' on the inner surface. 18 This
is an indirect consequence of how ovality can affect material flow and deformation
patterns during drawing.
6. Impact of Tube Ovality on Final Dimensional Accuracy and Roundness
The initial ovality of an ERW tube has a direct impact on the final dimensional
accuracy and roundness achieved after the drawing process. Even if the outer
diameter of the drawn tube falls within the specified tolerance, a higher initial ovality
will likely result in a final product that is less perfectly round.14 While the drawing
process aims to impose a round shape, the material might retain some "memory" of
its initial oval form, particularly if the reduction in size is not substantial or if only a few
drawing passes are performed. This residual ovality can be detrimental for
applications requiring a high degree of roundness for proper fit or function.
Furthermore, non-uniform initial ovality along the length or circumference of the ERW
tube can lead to variations in the inner diameter and wall thickness of the drawn
tube.14 Different sections of the tube, having varying degrees of out-of-roundness,
might deform differently under the drawing forces, resulting in inconsistencies in the
final dimensions. The choice of drawing method also plays a significant role in the
final roundness of tubes with initial ovality. Mandrel or plug drawing, due to the
internal support they provide, are generally more effective in improving the
roundness of initially oval tubes compared to tube sinking.14 The internal tool acts as a
defined inner boundary, helping to correct the out-of-roundness as the tube is
drawn. Achieving tight dimensional tolerances and a high degree of roundness in the
final drawn tube often necessitates strict control over the initial ovality of the ERW
tube. Starting with a more round tube minimizes the amount of non-uniform
deformation required during drawing, leading to a more accurate and round final
product.
7. Industry Standards and Guidelines for Acceptable Ovality in ERW Tubes Prior
to Drawing
Several industry standards and guidelines specify acceptable levels of ovality for ERW
tubes, which can serve as a benchmark for tubes intended for subsequent drawing
processes. These standards often provide tolerances on the outer diameter, which
implicitly include allowances for ovality.
ASTM specifications are widely used in North America and internationally. ASTM A513
covers ERW mechanical tubing and includes tolerances for outside diameter and, by
extension, ovality.37 Notably, ASTM A513 indicates that ovality should generally be
within the specified OD tolerances, except in cases where the wall thickness is less
than 3% of the outside diameter.37 For such thin-wall tubes, additional ovality is
permitted, with specific allowances outlined in other ASTM standards. ASTM
A1016/A1016M-21 and ASTM B751-21, which provide general requirements for steel
and nickel alloy tubes respectively, define thin-wall tubes as those with a wall
thickness of 3% or less of the OD or 0.020 inches or less. 41 For these thin-wall ERW
tubes, the difference between the maximum and minimum outside diameter (ovality)
in any cross-section should not exceed 0.020 inches for tubes with an OD of 1 inch or
less, or 2.0% of the specified outside diameter for tubes with an OD over 1 inch. 41
ASTM A999, which covers general requirements for stainless steel pipe, specifies a
maximum allowable ovality of 1.5% of the specified OD for thin-wall pipes.41 ASTM
A554 pertains to welded stainless steel tubing for mechanical applications 43,
although the provided snippets do not detail specific ovality tolerances for ERW tubes
before drawing under this standard.
European standards, such as EN 10305-2, which applies to cold-drawn ERW tubes for
precision applications, also address dimensional tolerances.16 Under this standard,
the tolerance for the outside diameter includes ovality, without specifying a separate
tolerance solely for ovality.45 The permissible variation in the outside diameter
depends on the size range, and the ovality must remain within these overall diameter
tolerances.
API standards are crucial in the petroleum and natural gas industries. API 5L, which
covers line pipe, defines out-of-roundness and provides tolerances on diameter.47 API
5L defines out-of-roundness as the difference between the maximum (or minimum)
diameter and the nominal diameter, expressed as a percentage of the nominal
diameter.4 While the acceptable ovality is often determined by the user, a guideline of
5% is typical, and ASME defaults to 8%.4 One source indicates that API 5L allows an
out-of-roundness of 1% of the pipe diameter.54 ISO 3162 offers another perspective,
defining out-of-roundness based on the difference between the maximum and
minimum diameters.4
It is essential to recognize that the acceptable levels of ovality in ERW tubes prior to
drawing are often contingent upon the specific application and the requirements of
any subsequent processing.6 Applications demanding tight bend radii or precise fitup with other components might necessitate stricter (lower) ovality tolerances. 2
Conversely, some applications, such as certain uses in the refrigeration industry,
might tolerate higher levels of ovality if it does not significantly impede the
functionality of the final product.56 Therefore, manufacturers must carefully consider
the end-use requirements and relevant industry standards when establishing
acceptable ovality limits for ERW tubes before the drawing process.
Table 2: Examples of Maximum Allowable Ovality for Thin-Wall Tubes Based on
ASTM Standards
Outside Diameter (in)
Ovality Allowance (in)
Source
1 and under
0.020
ASTM A1016/A1016M-21,
ASTM B751-21
1.5
0.030
Based on 2.0% of OD (ASTM
A1016/B751)
2
0.040
Based on 2.0% of OD (ASTM
A1016/B751)
2.5
0.050
Based on 2.0% of OD (ASTM
A1016/B751)
3
0.060
Based on 2.0% of OD (ASTM
A1016/B751)
4
0.080
Based on 2.0% of OD (ASTM
A1016/B751)
6
0.120
Based on 2.0% of OD (ASTM
A1016/B751)
8
0.160
Based on 2.0% of OD (ASTM
A1016/B751)
Any
1.5% of specified OD
ASTM A999
8. Relationship Between Initial Tube Ovality and Required Drawing Force or
Power
Drawing an ERW tube with initial ovality typically requires a greater drawing force and
consequently more power compared to drawing a perfectly round tube of the same
nominal dimensions. The non-uniform geometry of an oval tube leads to increased
resistance as it is forced to conform to the circular shape of the drawing die.14 This
increased resistance manifests as higher frictional forces between the tube's outer
surface and the die's inner surface, especially at the points corresponding to the
major diameter of the oval. The greater contact area and pressure distribution
associated with an oval tube within a circular die necessitate a larger pulling force to
achieve the desired size reduction.14
The degree of initial ovality directly correlates with the increase in drawing force. A
tube with a higher percentage or greater dimensional difference between its major
and minor diameters will present a more significant deviation from the die's circular
form, thus requiring a proportionally higher force to overcome the resistance to
deformation and friction.14 This increased drawing force naturally translates to higher
power consumption during the drawing process, as power is a function of both force
and the speed at which the drawing occurs.
While specific quantitative studies directly linking the initial ovality percentage to the
exact increase in drawing force or power for ERW tubes were not explicitly found in
the provided snippets, the principle of increased resistance due to non-ideal
geometry is well-established in metal forming processes.14 Research utilizing FEM to
optimize die and plug geometry for reducing drawing force implicitly acknowledges
that the initial geometry of the workpiece, including ovality, is a critical factor
influencing the required force.29 Furthermore, the choice of drawing method can
influence how initial ovality affects the drawing force. Tube sinking, lacking internal
support, might be more susceptible to the effects of ovality, potentially leading to a
greater increase in drawing force compared to mandrel or plug drawing, where the
internal tool can help to guide the deformation more uniformly.17
9. Methods and Techniques to Minimize the Effects of Tube Ovality During the
Drawing Process
Several methods and techniques can be employed to minimize the adverse effects of
initial tube ovality during the drawing process of ERW round tubes for size reduction.
Utilizing mandrels or plugs during the drawing process is a primary technique for
mitigating the impact of ovality.2 The internal support provided by these tools helps to
maintain the roundness of the tube and control its deformation as it passes through
the die. Different types of plug drawing, such as fixed, floating, and tethered plug
drawing, offer varying degrees of control over the inner diameter and can be selected
based on the specific requirements of the drawing operation and the initial ovality of
the tube.
Optimizing lubrication is also crucial for minimizing the effects of ovality. 14 Effective
lubrication reduces friction between the tube and the die, facilitating a smoother flow
of material and preventing surface defects that might be exacerbated by the nonuniform contact pressures arising from ovality.
Careful control of drawing parameters, such as the drawing speed, die angle, and
reduction ratios, can also help to minimize the impact of initial ovality.14 Using a die
angle that promotes a more gradual deformation of the tube might be beneficial for
accommodating the initial out-of-roundness.
In cases where the initial ovality of the ERW tube exceeds acceptable limits, predrawing ovality correction techniques can be employed.4 Methods such as
mechanical expanding, where a mechanical expander is used to force the tube
outwards from the inside, or hydraulic pressing, where pressure is applied to the
major diameter to encourage the minor diameter to expand, can improve the
roundness of the tube before it enters the drawing process.
Selecting raw materials with uniform properties can also contribute to minimizing
ovality variations in the initial ERW tube.2 Additionally, pre-bending preparation
techniques like annealing or heat treatment can reduce material stresses and improve
the tube's overall roundness before drawing.2 Finally, utilizing optimized tooling,
including customized dies designed for the specific tube diameter and material, can
help to minimize the introduction or amplification of ovality during the drawing
process.2
10. Effect of Thickness Variation and Eccentricity on Tube Drawing
Thickness variation, which is closely related to eccentricity, can significantly affect
the tube drawing process. Eccentricity in a tube means that the center of the outer
diameter (OD) is not the same as the center of the inner diameter (ID), leading to
inconsistent wall thickness around the circumference.7
Here's how thickness variation and eccentricity can affect tube drawing:
●
●
●
●
●
●
Uneven Stress Distribution: When a tube with varying wall thickness is drawn,
the thinner sections will likely experience higher stresses compared to the thicker
sections. This is because the drawing force will be distributed unevenly across
the cross-section.7
Increased Risk of Defects: The uneven stress distribution can lead to localized
yielding or even fracture in the thinner areas if the drawing forces are too high.
Additionally, it can cause uneven material flow, potentially resulting in defects like
wrinkling or cracking during the drawing process.27 In tube sinking, significant
thickness variation might lead to an irregular inner surface and potentially
cracking.27
Dimensional Inaccuracy: Starting with a tube that has inconsistent wall
thickness makes it more challenging to achieve the desired final dimensions and
a uniform wall thickness after drawing. The thinner areas will tend to reduce in
thickness more readily than the thicker areas.39
Tooling Challenges: Eccentricity can lead to non-uniform contact between the
tube and the drawing die, as well as the mandrel or plug if one is being used. This
can result in uneven wear on the tooling and may affect the surface finish of the
drawn tube.18
Importance of Concentricity: For many applications, especially those where
one tube needs to fit inside another, good concentricity (minimal wall thickness
variation) is more critical than perfect roundness (ovality).7
Comparison with Manufacturing Methods: Cold-drawn seamless tubes often
have an inherent characteristic of eccentricity due to the manufacturing
process.39 Drawn Over Mandrel (DOM) tubing, which starts with an ERW tube,
typically offers a more uniform wall thickness and better concentricity compared
to seamless tubes at the same stage.13
Therefore, controlling the thickness variation and minimizing eccentricity in the initial
ERW tube is important for a successful and high-quality tube drawing process. Tubes
with more uniform wall thickness will generally experience more consistent
deformation, leading to better dimensional accuracy and a reduced risk of defects.
11. Conclusion and Recommendations
The initial ovality of ERW round tubes significantly affects their subsequent size
reduction through the drawing process. Ovality, representing the deviation from a
perfect circle, leads to non-uniform stress distribution during drawing, increasing the
potential for defects such as wrinkling, flattening, and cracking. It also impacts the
final dimensional accuracy and roundness of the drawn tube and necessitates higher
drawing forces and power consumption. Industry standards like ASTM, EN, and API
provide guidelines for acceptable ovality levels, which vary depending on the
application and tube dimensions. Furthermore, thickness variation and eccentricity in
the initial tube can lead to uneven stress distribution, increased risk of defects,
dimensional inaccuracies, and tooling challenges during the drawing process.
To ensure a successful and high-quality drawing process for ERW tubes,
manufacturers should implement the following recommendations:
Establish clear and measurable specifications for acceptable ovality levels and
thickness variation in ERW tubes prior to drawing, taking into account relevant
industry standards and the specific requirements of the intended application.
● Implement robust quality control measures to accurately measure and monitor
the ovality and wall thickness uniformity of incoming ERW tubes, ensuring that
they fall within the established specifications.
● Select appropriate drawing methods, such as mandrel or plug drawing, which
provide internal support and better control over the tube's shape during
deformation, especially when processing tubes with some degree of initial ovality
or thickness variation.
● Optimize drawing parameters, including drawing speed, die angle, and reduction
ratios, to minimize the stresses induced by the initial ovality and thickness
variations and promote a more uniform deformation.
●
Consider employing pre-drawing ovality and concentricity correction techniques
for ERW tubes exhibiting higher levels of out-of-roundness or thickness variation
to improve their initial geometry before drawing.
● Ensure effective lubrication is applied to the tube's surface before drawing to
reduce friction between the tube and the die, thereby minimizing the risk of
surface defects and reducing the required drawing force.
● Utilize simulation tools, such as FEM software, to analyze the effects of initial
ovality and thickness variation on stress distribution and deformation during the
drawing process, allowing for process optimization and defect prevention.
● Continuously monitor the quality of the drawn tubes, including their roundness,
dimensional accuracy, and wall thickness uniformity, to identify and address any
issues that might be attributed to the initial characteristics of the ERW tubes.
●
Further research could focus on quantifying the precise relationship between
different levels of initial ovality and thickness variation and the resulting drawing
forces and power consumption for various ERW tube sizes and drawing methods.
Additionally, studies investigating the effectiveness of different pre-drawing
correction techniques and their impact on the final properties of the drawn tubes
would be valuable for the industry.
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