Ultrasonically Assisted Draw-Peeling of Wire Rods (UADP)
What Is Draw-Peeling?
Superior surface quality of very low surface roughness is the main objective of the draw-peeling process. After the draw-peeling, the wire rod has a more homogeneous material structure and a higher material purity. Draw-peeling removes surface defects, such as oxidation, chatter marks, roll scores, scale scars, double skins, overlaps, inclusions and decarburized margin layers from ferrous metals like steel or iron materials. A prominent application of draw-peeling is the removal of scale and surface rust from ferrous wire rod. Non-ferrous metals, such as copper, may make draw-peeling necessary to remove hardened surface layers after rolling or drawing. The draw-peeling process can remove between 0.01mm and 0.25mm of material from the wire rod surface in one step. Draw-peeling is also known as shaving, scalping or back-die shaving.
Draw-Peeling Vs. Rotary-Peeling
For wire rods, profiles or tubes of less than 25mm diameter, draw-peeling has big advantages over rotary-peeling. The rotary-peeling of wire rods limits production speed and may result in wave or spiral structured surfaces on small wire rods. The draw-peeling cutting tool shaves parallel to the feeding direction. This leads to superior surface topography along the wire rod and to a higher durability of the draw-peeling tool. Generally, the costs for draw-peeling tools are lower than rotary-peeling systems.
What Is The Benefit of Ultrasonically Assisted Draw-Peeling (UADP)?
The draw-peeling of wire rods requires power to overcome friction and to cut the material. In a conventional draw-peeling setup, this power comes from the rotating capstan, only. The tensile force on the wire rod rises with faster line speed, wire diameter and peeling layer thickness. Tensile strength and yield strength are critical factors in particular for smaller wire rods, as the ratio of the circumference to cross-section is higher for smaller diameters. This limits the line speed of draw-peeling or it makes a conventional draw-peeling impossible due to the high risk of fractures.
Ultrasonically assisted draw-peeling uses a high frequency longitudinal vibration of the sharp edged cutting tool. The typical vibration frequency is 20kHz, the peeling edge displacement can be up to 100 micron (pk-pk). The higher the ratio between the peeling tool vibrational velocity and the wire rod speed is, the lower can be the tensile force on the wire. Therefore ultrasonically powered draw-peeling allows faster draw-peeling line speeds or more material removal in one peeling step for any give tensile strength limit. The reduction in tensile force makes ultrasonically powered draw-peeling most favorable for small material diameters and for hollow strands, such as tubes.
Wire rods are prone to chatter marks and fractions when starting and stopping the capstan drive. This is more problematic for soft or very elastic materials and small cross-sections. The ultrasonically vibrated peeling tool moves back and forth 20,000 times per second. This continuous movement of the shaving die reduces the tensile stress and it avoids chatter marks and ripples along the wire rod surface.
The more the ultrasonic vibration pushes the cutting tool edge into the material, the lower can be the wire rod tension. This leads to significant tension reductions of up to 50% depending on the material and the dimensions. In general, the reduction in tension opens the opportunity to increase the line speed. Yet, the wire rod speed should be at least 20% below the vibrational velocity of the tool.
What Is Required For Ultrasonically Assisted Draw-Peeling?
UADP uses your standard peeling/shaving tool. An ultrasonic resonator – also known as sonotrode – replaces the conventional tool holder. This sonotrode is a special innovation of Hielscher Ultrasonics. It transmits the ultrasonic longitudinal vibrations efficiently onto the peeling tool. In order to save installation space, the ultrasonic driver – also known as transducer – agitates the sonotrode from the top. A typical UADP setup requires less than 250mm in longitudinal direction.
The ultrasonic vibrations are generated by our standard ultrasonic devices, such as: UIP1000hdT (1.0kW), UIP1500hdT (1.5kW), UIP2000hdT (2.0kW) or UIP4000 (4.0kW). These units drive various processes in 24h/7d operations around the world. The actual power requirement depends on the line speed, material and the dimensions. The ultrasonic devices are interchangeable, should developments in line speed make more power necessary. For high power applications, we can drive a peeling tool with two ultrasonic devices simultaneously (up to 2 x 4kW).
You can retrofit any existing draw-peeling machines with an ultrasonic system easily. Many machine manufacturers, such as Kieselstein (Germany) are well familiar with the installation or the retrofit using our system. Some of the newer machines have space allocated for the ultrasonic system retrofit.
There Are More Wire Rod Processes
- Other applications of ultrasonically assisted wire processing include:
- Ultrasonically Assisted Drawing of Wires, Pipes and Profiles (UAD)
- Ultrasonically Assisted Draw-Cleaning (UADC)
- Ultrasonic Cleaning of Wires, Pipes and Profiles
- Ultrasonic Cleaning of Wire Dies and Extrusion Guides
- Ultrasonic Processing of Metal Melts
Surface Roughness Parameters: Ra, Rz, Rt
Ra is a parameter of surface roughness. It is the arithmetic mean of deviations of the profile from the mean line. It is calculated as the mean result of several consecutive sampling lengths. Rz is an ISO 10-point height parameter for surface roughness. It is measured over a sampling length. It is the calculated average height difference between the 5 highest peaks and the five lowest valleys within a sample length. Rt is the maximum peak-to-valley height along the sample length. It is usually determined as the average Rtm of five consecutive sampling lengths.