The circular knitting machine is the backbone of the global knit fabric manufacturing industry, especially in the high-speed segment. The success of this process depends on the synchronous operation of thousands of components, among which the circular knitting machine needle plays a central role.
At modern production speeds, where machines can operate at 35–40 revolutions per minute (RPM) or more, each needle must complete its knitting cycle in less than a second. This imposes extremely strict technical requirements, transforming the needle from a mere consumable part into a high-tech engineering component.
Understanding and adhering to the mandatory technical standards for circular knitting machine needles is not only key to maintaining maximum productivity but also a strategy to prevent costly breakdowns and ensure fabric quality, free from defects like needle lines or recurring knitting faults.
This article delves into 9 core technical aspects, from base material and surface treatment technology to the complex interaction mechanism between the needle and other components in a high-speed circular knitting machine, providing a comprehensive view for technicians and production managers.
1. Requirements for Material and Enhanced Mechanical Strength
The circular knitting machine needle operating at high speed must be manufactured from materials with superior fatigue strength and wear resistance. The choice of steel must not be based solely on cost but must consider cyclic stress and operating temperature.
1.1. Selection of Specialized Tool Steel Alloys
Not all steel types are suitable. Modern circular knitting machine needle components often use special alloy steels (e.g., Chromium-Vanadium tool steel or high-carbon steel variants) designed to optimize three critical properties:
- Surface Hardness: Typically reaches 60-65 HRC (Rockwell Hardness C-Scale). This hardness helps the needle surface resist wear caused by friction with the yarn and cams.
- Core Toughness: The needle core needs to be ductile enough to absorb sudden shocks and bending forces without brittle fracture. An imbalance between hardness and toughness is the leading cause of premature needle breakage.
- Fatigue Strength: The circular knitting machine needle cycles through repeated movements millions of times. The material must withstand high cyclic stress without developing fatigue cracks, which often start from microscopic surface defects.
1.2. Heat Treatment and Vacuum Hardening Process
To achieve the optimal balance between surface hardness and core toughness, manufacturers of high-end circular knitting machine needle parts employ complex heat treatment processes, often Vacuum Hardening. This process allows for precise control of temperature and environment, minimizing surface oxidation and geometrical distortion during hardening.
Additionally, induction hardening may be locally applied to high-stress areas like the needle butt to increase hardness without compromising the body’s toughness.
1.3. Testing for Fatigue Strength and Breaking Force
The circular knitting machine needle must be regularly tested in the laboratory using:
- Cyclic Fatigue Testing: The needle is placed in a testing machine to simulate knitting movement under high load until failure. This determines the expected lifespan.
- Micro-hardness Testing: Using methods like Vickers (HV) or Knoop to precisely measure hardness at critical points such as the hook and latch.
2. Requirements for Geometric Precision and Minimal Tolerance
The geometric precision of the circular knitting machine needle determines the uniformity of the stitch loop and the quality of the fabric. For machines with high Gauge indices (e.g., E32, E36), the tolerance of the needle must be extremely small.
2.1. Relationship between Gauge and Needle Tolerance
Gauge (E) is the number of needles per cylinder inch. The higher the Gauge (the denser the needle count), the greater the requirement for precision.
At Gauge E28, the thickness of the circular knitting machine needle shank must be uniform enough to allow the needle to move freely in the cylinder slot, but not so loose as to cause vibration.
At Gauge E36 or higher, a deviation in shank thickness of only about 1–2 microns is enough to cause needle jamming or damage the cylinder slot due to excessive friction.
2.2. Control of Hook Geometry
The hook of the circular knitting machine needle is the most crucial part. The shape and angle of the hook determine:
- Lace-up Process: The hook must be sharp enough (but not overly sharp to cut the yarn) and optimally shaped to easily catch the new yarn.
- Cast-off Process: The hook angle must ensure the old stitch loop is released smoothly without snagging or breaking.
Manufacturers use optical measuring machines and profile projectors with high magnification to precisely inspect the hook profile of the circular knitting machine needle.
2.3. Latch Flatness
The Latch is the moving component responsible for opening and closing to secure the old stitch loop. The latch of the circular knitting machine needle must ensure:
- Flatness and Smoothness: The inner surface of the latch must be extremely flat and smooth to prevent friction or yarn damage.
- Dynamic Balance: The latch is designed to open/close under inertial force at high speed. The weight and balance of the latch must be controlled to ensure accurate movement in every cycle.
3. Requirements for Surface Treatment and Anti-Friction Coating Technology
Surface treatment is a key factor in increasing the lifespan of the circular knitting machine needle, especially in high-speed, lint-heavy operating environments. The surface coating not only reduces friction but also protects the needle from chemical corrosion from knitting oil and moisture.
3.1. Advanced Coating Technologies
Instead of conventional Chromium plating, high-end circular knitting machine needle components utilize PVD (Physical Vapor Deposition) or CVD (Chemical Vapor Deposition) coatings for superior performance:
- Hard Chrome Plating: The traditional coating, providing good smoothness and corrosion resistance. However, performance gradually decreases with use.
- TiN (Titanium Nitride) Coating: A golden-yellow PVD coating with higher hardness than Chrome and a lower coefficient of friction. It significantly increases wear resistance and needle lifespan.
- DLC (Diamond-Like Carbon) Coating: The most modern technology. The DLC coating creates a surface with a structure close to diamond, possessing an extremely Low Coefficient of Friction and near-absolute hardness. Benefits of the DLC-coated circular knitting machine needle include:
- Increased Needle Lifespan: Extends needle life by 2–3 times compared to conventional needles.
- Reduced Heat Generation: Low friction significantly reduces the temperature in the knitting area, protecting the yarn and the machine oil.
- Increased Machine Speed: Excellent gliding capability allows the knitting machine to operate at higher speeds without increasing the risk of needle breakage or knitting faults.
3.2. Effect of Coating on Machine Oil
The surface coating must be fully compatible with the knitting oil used. A poor-quality coating can react with additives in the oil, leading to the coating’s decomposition or the formation of sludge buildup on the circular knitting machine needle. High-quality needles ensure the coating does not peel, keeping the lubricating oil working most effectively.
4. Requirements for Butt Design and Motion Reliability
The butt is the part that receives and transmits force from the cam, translating the cylinder’s rotary motion into the precise reciprocating motion of the circular knitting machine needle. Faults in the needle butt can destroy the cam.
4.1. Force Distribution and Contact Design
The design of the circular knitting machine needle butt must strictly adhere to mandated geometric profiles to optimize contact with the cam:
- Radius: The curve angle of the needle butt must perfectly match the cam groove profile to distribute the contact force over a larger area, reducing local pressure and wear.
- Butt Height: In circular knitting machines, needles with different butt heights (e.g., High Butt, Low Butt) are used to create complex knit structures (like Jacquard, needle transfer) or participate in different knitting cycles (basic knit, tuck only, etc.). The precision of this height must be absolute to ensure each circular knitting machine needle is activated by the cam at the correct time.
4.2. Hardness of the Butt Area
The butt area must undergo special heat treatment to achieve maximum surface hardness, helping it resist mechanical wear due to sliding friction and impact with the cam. If the butt wears prematurely, it will alter the timing of the needle movement, leading to knitting faults in the fabric.
5. Requirements for Heat Dissipation and Temperature Stability
Friction at high speeds generates significant heat. If the temperature at the circular knitting machine needle exceeds the allowed threshold, it negatively affects the needle, the yarn, and the machine oil.
5.1. The Role of Lubricating Oil as a Coolant
In a circular knitting machine, knitting oil not only reduces friction but also acts as the primary coolant. The circular knitting machine needle must have a material structure and surface coating that facilitates rapid heat transfer to the machine oil. If the needle overheats, the lubricating oil’s chemical properties will be destroyed, leading to the formation of sludge on the needle and cylinder slots.
5.2. Consequences of Overheating for Yarn
- Synthetic Yarns: When knitting synthetic yarns like Polyester, high temperatures from the circular knitting machine needle can cause localized melting, creating hard plastic deposits that cling to the needle hook. This increases roughness, further increasing friction and causing yarn breakage.
- Natural Yarns: For cotton yarns, high temperature makes the yarn drier and more brittle, while also increasing lint in the knitting area.
Controlling the operating temperature of the circular knitting machine needle is a fundamental requirement for ensuring yarn and fabric quality.
6. Complex Interaction: The Knitting Triangle (Needle, Sinker, and Cylinder)
The process of forming a stitch loop requires the harmonious coordination of three main components: the needle, the sinker, and the cylinder. Any slight deviation in timing will cause a knitting fault.
6.1. The Critical Role of the Sinker
The Sinker is located in the needle slots and is responsible for:
- Holding the Fabric: Securing the old stitch loop and pulling the fabric down to maintain necessary tension.
- Shaping the New Loop: Assisting the circular knitting machine needle in the process of drawing the new yarn.
The geometry and precision of the sinker must perfectly match the needle. If the sinker is worn or uneven, it will locally change the stitch loop length, creating horizontal stripes (Barre) or vertical stripes (Needle Lines) on the fabric.
6.2. Cylinder Slot Precision
The cylinder slot is where the circular knitting machine needle slides up and down.
- Surface Smoothness: The cylinder slot surface must be extremely smooth to minimize friction with the needle shank. Dirt or oil residue can accumulate in the slots, increasing resistance and causing needle jamming.
- Straightness and Concentricity: The circular knitting machine cylinder must be a perfect cylinder block. Any deformation (due to temperature or impact) will affect the trajectory of the circular knitting machine needle, causing knitting faults.
High-quality circular knitting machine needle components are designed to tolerate minor vibrations in the slot while maintaining stability.
7. Mandatory Quality Control (QC) Procedures for Needles
Quality control is the factor that ensures the circular knitting machine needle meets high technical requirements. Reputable needle manufacturers adhere to strict inspection processes.
7.1. 100% Geometric Inspection
Each circular knitting machine needle must be automatically inspected by high-resolution optical systems to confirm:
- Butt Height: Checked to the micron level.
- Shank Thickness: Ensuring absolute uniformity.
- Hook Angle and Latch Opening: Matching specifications.
7.2. Surface Coating Adhesion Test
The surface coating must not peel off. Tests include:
- Adhesion Test: Pull testing or friction testing to ensure the PVD/CVD coating does not separate from the steel substrate.
- Surface Roughness Test: Using a Profilometer to ensure the surface of the circular knitting machine needle meets the necessary smoothness (typically below Ra 0.2 µm) to reduce friction with the yarn.
7.3. Batch Fatigue Assessment
Every production batch of circular knitting machine needle components must undergo destructive testing to ensure the entire batch meets the lifespan standard. This test simulates the most extreme conditions the needle must endure during high-speed operation.
8. Economic and Operational Impact of Using Poor-Quality Needles
Using cheap, poor-quality circular knitting machine needle components may save initial costs but leads to much greater losses in the long run, especially in high-speed manufacturing facilities.
8.1. Higher Maintenance Cost Damage
- Cam and Cylinder Damage: Poor-quality circular knitting machine needle parts, especially butt defects due to overly soft material or inaccurate dimensions, will rapidly wear down the much more expensive cam grooves. Replacing a cam set can cost 10–20 times the cost of a batch of needles.
- Increased Downtime: The frequency of needle breakage increases sharply, leading to prolonged downtime to find and replace the broken needle and repair the knitting fault. Downtime is the greatest economic loss.
8.2. Reduced Quality of Finished Fabric
A geometrically inaccurate circular knitting machine needle will produce non-uniform stitch loops.
- Needle Lines: Vertical stripes appearing on the fabric, caused by one or a group of needles being unevenly worn or out of phase with the others.
- Stitch Length Irregularity: Affects the fabric’s gram per square meter (GSM) and hand feel, leading to the necessity of rejecting or downgrading the batch quality.
8.3. Increased Energy Consumption
A worn, rough, or slightly bent circular knitting machine needle will increase friction in the cylinder slots, forcing the knitting machine motor to operate at a higher capacity, leading to unnecessary electricity consumption.
9. Strategy for Proactive Needle Management and Preventive Maintenance
To optimize the performance of the circular knitting machine, a proactive circular knitting machine needle management strategy is needed, which goes beyond simply replacing a broken needle.
9.1. Proactive Needle Replacement Schedule
Instead of waiting for the circular knitting machine needle to break, a replacement schedule should be established based on operating hours (e.g., after 2500–3000 hours) or the fabric output produced. Replacing needles simultaneously according to a schedule helps maintain the uniformity of all stitch loops, prevents needle line faults, and reduces the risk of sudden breakage.
9.2. Needle Inventory Management
- Proper Storage: Circular knitting machine needle parts need to be stored in a dry, temperature and humidity-controlled environment to prevent rust. Needles should be kept in original packaging with an anti-moisture layer.
- Batch Control: Needles should be stored by production batch and machine model to ensure that when replacing, all circular knitting machine needle components in a machine have the same specifications and degree of wear (when replacing individual needles).
9.3. Regular Cleaning and Inspection
- Compressed Air Cleaning: Periodically clean the knitting area with compressed air to remove lint and oil residue clinging to the circular knitting machine needle.
- Needle Tension Check: Use specialized measuring devices to check the tension of the needle in the cylinder slot, ensuring the circular knitting machine needle is neither too loose nor too tight.
10. VieTextile: Strategic Partner for Leading Circular Knitting Machine Needle Supply
VieTextile is committed to providing comprehensive solutions for high-speed circular knitting machines, starting from the most basic component: the needle. We understand that the difference in a high-quality circular knitting machine needle lies in the alloy steel material, vacuum hardening technology, and especially the anti-friction surface coating (such as DLC or TiN).
We supply a diverse range of circular knitting machine needle components, sinkers, and platines (selectors) compatible with most popular circular knitting machine models on the market. Each circular knitting machine needle product supplied by VieTextile is sourced from the world’s leading manufacturers, ensuring absolute geometric precision, long lifespan, and stable operation capability at maximum speed.
Our technical team does not just supply parts; they are strategic maintenance consultants, helping you optimize the circular knitting machine needle replacement schedule and manage operating costs effectively. With a clear warranty policy and fast technical support service, VieTextile is the reliable partner that helps your business maintain a competitive edge in quality and productivity.
11. Frequently Asked Questions about High-Speed Circular Knitting Machine Needles (FAQ)
11.1. What is the difference between a standard circular knitting machine needle and a DLC-coated needle?
The DLC-coated circular knitting machine needle has a diamond-like hard carbon layer on the surface, which reduces the coefficient of friction by 50–70% compared to standard needles (Chrome plated). This helps the DLC-coated circular knitting machine needle resist wear better, reduce heat generation, and extend its lifespan by 2–3 times, which is essential for machines operating continuously at ultra-high speeds.
11.2. What is the acceptable tolerance level for a Gauge E32 circular knitting machine needle?
For Gauge E32, the tolerance for the shank thickness of the circular knitting machine needle must typically be within ± 0.005 mm (5 microns). Deviation exceeding this level will lead to uneven yarn tension and cause knitting faults.
11.3. Which knitting fault is directly related to poor-quality circular knitting machine needle components?
The most common fault is Needle Lines, appearing as vertical stripes on the fabric caused by one or a group of circular knitting machine needle parts being unevenly worn or having poor geometric accuracy. Additionally, Missing Stitches often occur when the latch does not open or close in phase due to high friction or a bent latch.
11.4. Is it necessary to replace the Sinker when replacing the circular knitting machine needle?
The Sinker and the circular knitting machine needle operate as a pair. If only the circular knitting machine needle is replaced, the worn old sinker will continue to cause friction and knitting faults. For optimal quality, it is recommended to replace both the needle and the sinker simultaneously according to the same preventive maintenance schedule.
11.5. Is visual inspection of the circular knitting machine needle sufficient?
Visual inspection only helps detect large defects like breakage, bending, or rust. For high-speed circular knitting machines, specialized magnification devices or digital microscopes are needed to inspect microscopic defects such as fatigue cracks, hook wear, and surface smoothness.
11.6. How to distinguish between genuine and counterfeit circular knitting machine needle components?
Genuine circular knitting machine needle components typically have a high surface finish, no rough grinding marks, a uniform surface coating, and are carefully packaged with a clear Part Number. Counterfeit needles often have unstable hardness, easily peeling coatings, and poor geometric tolerance. They should be purchased from reputable suppliers like VieTextile.
11.7. What is the optimal operating temperature for the circular knitting machine needle?
The optimal temperature in the knitting area should be maintained between 40°C and 55°C. Temperatures exceeding 60°C can cause some synthetic yarns to melt and accelerate the decomposition of lubricating oil.
11.8. Can the circular knitting machine needle be reused (sharpening)?
Modern circular knitting machine needle parts cannot be reused (sharpened) because the entire geometry of the needle (especially the hook and butt) is very precisely designed and heat-treated. Any change in size will cause the circular knitting machine needle to operate inaccurately and cause faults.
11.9. What is the “Breaking Strength” of the circular knitting machine needle and why is it important?
Breaking Strength is the maximum force the circular knitting machine needle can withstand before breaking. For high-speed needles, the breaking strength must be significantly higher than the normal working load to ensure the circular knitting machine needle can withstand sudden shocks due to yarn faults or local jamming without immediate failure.
11.10. What is the difference between different butt heights used for?
Different circular knitting machine needle butt heights (e.g., high butt, middle butt, low butt) are used to allow the same needle to participate in different knitting cycles (e.g., tuck stitch, transfer stitch, basic knit stitch) at different cam positions on the machine. This helps the circular knitting machine create complex fabric structures (like Jacquard) by merely controlling the cams.
Contact VieTextile today for expert consultation and the highest quality circular knitting machine needle supply for your production line!
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