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Practical tips for welding: contact tips

Posted by Markus Preis on Aug 11, 2020 5:34:31 AM
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What you need to know for the use of power contact tube, contact nozzle, contact tube & Co.

The contact tip – also known as contact nozzle or power contact tube – is the smallest but most important wear part on a MIG/MAG torch, and it makes no difference whether it is a hand-held torch, an automatic torch or a robotic welding torch. The contact tip has a very considerable influence on the quality of the MIG/MAG welding process and the service life or machine availability in the welding process.Header_Stromduesen_800x300px

Hardly any wear part is subject to deterioration and is as close to the welding process as the contact tip. For this reason, we dedicate our own blog to this relatively small part.

Task of the contact tip

The task of the contact tip is to transfer the welding current to the wire electrode and to ensure a stable, directional arc. To ensure this, the welding wire runs through the contact tip. Several kilometers of wire run through the welding torch during one working day. The wire in the cable assembly and in the torch neck must overcome the frictional resistance.

What problems can arise with the contact tip?

Depending on the wire, spiral material and torch neck structure, abrasion occurs during the wire feed. These particles are sometimes brought up to the contact tip and cause clogging. Especially with hard wires, there is sometimes an opposite effect in the contact tip, namely that it is ground out by the wire. This is also supported by the process heat, which is partially dissipated via the contact tip. The contact tip loses its hardness from a certain temperature and thus wears out more easily.

Especially with straight torch necks – often used with machine or robot torches – there are contacting problems in the contact tip because the contact surface and contact time are too short. This leads to so-called micro arcs in the contact tip, which also causes faster wear. Depending on the process and quality of the wire and the contact tip material, the contact tip loses its process-relevant properties more or less quickly and needs to be replaced accordingly before the welding process becomes unstable.

With unstable processes, the wire burns back to the contact tip. Then the so-called freezing happens, which leads to an immediate failure of the contact tip.

What types of contact tips are there?

Depending on the type of torch, the welding torch manufacturers recommend a selection of suitable contact tips in the catalog or other documentation for an optimal welding process that is tailored to the torch. The basic features here are the overall geometry including the threaded connection (standard: M6, M8, M10 or larger), the central hole for the corresponding wire diameter and the material used. Basically, as in welding technology in general, the dimensions of the contact tip increase with the amount of welding power. So up to a current of approx. 180 amperes, you can still cope with relatively short geometries with an M6 thread; at over 400 amperes, it must be a longer version with an M8 or M10 thread. For a proper power transmission and because more heat is absorbed by the process, you simply need these larger dimensions. More material also means the contact tip is more heat-resistant and wear-resistant.

What are the differences between cheap and expensive contact tips?

If you compare the different suppliers of contact tips, you sometimes notice relatively high price differences from the brand provider, especially with third-party providers. In most cases, cheaper recycled copper is used here, which can lead to increased wear due to its low hardness as well as reduced thermal and electrical conductivity. Only brand manufacturers have a certified, internally QA-monitored manufacturing process that only allows high-quality material for processing. One such provider is ABICOR BINZEL, who always delivers consistently high quality through the corresponding manufacturing processes – such as the high-speed deep drilling process – and an internal company standard.

What is the difference in the material of the contact tips?

There are three different basic contact tip materials for welding: E-Cu, CuCrZr and HDS. Each has its own individual characteristics, properties and advantages, which we will now show in detail.

E-Cu contact tip

This contact tip is made of very pure electrolytic copper (E-Cu). The Vickers hardness of this contact tip is approx. 110 to 115 HV. 140_0242-Contact_tip-M_2The purity of the copper ensures very good power transmission and good heat and electrical conductivity. Their softening temperature is around 260 °C and is therefore more suitable for the low-amperage area and a not very long service life. For a harder version with a higher softening temperature, a contact tip made of CuCrZr is recommended.

Conclusion: A contact tip with very good process properties, but less wear-resistant.

CuCrZr contact tip

The component of this contact tip is copper-chrome-zirconium (CuCrZr). The alloy elements chrome and zirconium are very hard and ensure high thermal resistance. 140_0245-Contact_tip-MThe current transfer is a little less good, but this is not a noticeable problem for most processes. With a Vickers hardness of approx. 168 HV and a temperature resistance of approx. 500 °C, this contact tip material type is practically the standard. A high hardness combined with a high thermal load capacity means a low degree of wear with a correspondingly high process load.

If welding is carried out with a high-amperage arc or in the area of the spray arc, the contact tip is so heavily loaded that the thermal load capacity of the E-Cu contact tip is quickly reached and can exceed it. The fact that the time has come is shown by the bluish-black tarnish of the copper material. If welding continues with excessive thermal stress, the copper material softens, the wire erodes into the hole – also known as an oval washout – and can get stuck. In such a case, only the replacement of the contact tip helps. Fortunately, this is only the case with CuCrZr material under extreme process loads.

In addition to the chemical composition, especially with CuCrZr contact tips – this also applies to HDS contact tips – a good coordination of the bore diameter with the wire diameter is required. If the bore diameters in the contact tip are too narrow, the clogging will be faster. On the other hand, if the bore diameters are too wide, this will favor freezing. Quality manufacturers like ABICOR BINZEL can guarantee tolerances of a few hundredths of a millimeter thanks to special manufacturing processes.

Conclusion: Contact tips made of CuCrZr material are very suitable for welding processes in the medium to high ampere range. They offer good process properties with low wear.

HDS contact tip / heavy duty silver tip

For thermally extremely stressed processes with already high wear or even failure of contact tips made of CuCrZr material, a special variant can be considered as a problem solver: the HDS contact tip. 147_6563_10-Contact_tip-MThe inner core around the bore consists of a dispersion-hardened copper (mineral hardness is a special form of precipitation hardening in the manufacturing process). As a result, the inner core is extremely hard and at the same time extremely heat-resistant. What this contact tip loses in terms of electrical conductivity is compensated by its silver coating, so to speak.

Especially in welding processes with a high duty cycle and high power consumption, the HDS variant can utilize its power reserves compared to a CuCrZr contact tip and is a good problem solver in terms of service life and wear. This is also the reason why it is often used in air cooled welding torches with marginal duty cycles and high welding currents. HDS contact tips are available in all common standard geometries and can be used in almost all ABICOR BINZEL welding torch systems.

Conclusion: The HDS contact tip is a good alternative, especially with high welding currents and/or high duty cycles in the welding process, when the type CuCrZr reaches its limits. Frequent areas of application are air-cooled torches with a comparatively long duty cycle at high ampere loads.

Areas of application for the HDS contact tip:

  • Automated MIG/MAG welding, especially high-powered, air cooled applications
  • Welding with cored wire
  • Build-up welding and plating
  • Ship and container construction
  • Earth moving machinery

Production processes in robot and automation welding technology are continuously being optimized. It is therefore all the more important to use a contact tip that meets these requirements. For example, the HDS from ABICOR BINZEL is ideally suited for this.

Which contact tip for which wire?

Can that be answered in such a general way? Is there possibly a list where you can see which contact tip is suitable for which wire?

Basically, you can feed all three contact tip types CuCrZr, E-Cu and HDS with each wire. With E-Cu contact tips, it is easier to weld aluminum, which is due to the power transmission: an aluminum wire itself is not as conductive as, for example, a copper-plated wire. Meanwhile, aluminum can also be welded well with CuCrZr contact tips. When welding aluminum, however, contact tips with an adapted (somewhat larger) inner bore should be used due to the increased thermal expansion of the aluminum.

Wires made of copper-plated and non-copper-plated carbon steel, stainless steel in any alloy, aluminum, copper-soldering alloys (AlSi, CuSi, etc.) and cored wires are welded. Depending on the surface quality and surface cleanliness, these wires are differently abrasive. Due to their contour, cored wires or because of their rough surface, some non-coppered wires (with remnants of drawing soap) are highly abrasive. Here, harder materials are available for the contact tip, such as CuCrZr for example.

How to find the right contact tip for your application

It is best to get advice from the dealer you trust or ask the manufacturer directly. Every good supplier recommends to the welding torches – some also say »welding equipment« – also consumables in his documents, as well as the optimal contact tip. As there is also the option of using special geometries in addition to the standard versions, it is best to get professional advice.

There is much more to say about contact tips, but here we focus on the questions that come directly from the users. The next »Practical tips for welding« will deal with how you can avoid and remove welding spatter.