The Basics Of Ceramic Ferrules For Stud Welding

Ceramic ferrules, often called arc shields, are often used in the drawn-arc stud welding process. They are, typically, a round shape that fit around the base of the weld stud. There are different ferrules for each diameter of weld stud. Often the ferrule configuration varies by application. They are critical in the drawn-arc stud weld process. They serve several key functions.

This article will review the makeup and function of ceramic ferrules.

What Are Ceramic Ferrules Made From?

As the ceramic ferrule is a single use item, the goal is to make it as inexpensive as possible. The ceramic is a mixture of earth compounds that results in a material called cordiorite. The moisture content in the raw material is critical as it controls how well the material holds together during processing and it also has a significant impact on shrink.

The compound it the pressed into dies putting it into what is known as the “green” state. The green ceramic is then baked at high temperature for 12-24 hours. Once cooled, you have a ceramic ferrule. Hundreds of thousands of parts are made at a time to maximize the economies of scale and produce the lowest cost part.

Understanding the configurations of ferrules

Shape

Ferrules fit around the base of the weld stud. Therefore, the shape of the ferrule follows the shape of the weld stud. Typically round, ferrules are also available in elliptical, square, rectangular and even ell shapes to stud weld angle iron.

Size

As weld studs vary in size, e.g. different diameters, the ferrule must also vary in diameter. The same applies to all shapes of weld studs.

Application

Ferrules can further be designed to perform a specific function. Often, studs are welded on to a flat, horizontal surface. A flat ferrule is used in this application. Sometimes an application requires a stud to be welded onto a vertical wall. In this application the vents are only on one side of the ceramic ferrule to prevent molten steel from succumbing to gravity and running out the bottom.

There are ferrules with curves on the bottom to weld to tubing. There are ferrules to weld to the inside of angles. There are many different applications which require custom ferrules. New ferrules designs are always being explored. Here are a variety of commonly used ferrules that are used across a range of drawn-arc stud welding applications.

How Are Ferrules Installed/Used?

First a weld stud is loaded into the chuck in a stud gun. Second, the ferrule is pressed into a ferrule grip that holds the ferrule in the proper position relative to the weld stud.

Ferrules are formed with a neck, specifically designed to be held by a grip. There is a unique grip for each ferrule.

The grip holds the ferrule around the base of the drawn-arc stud during the arcing processes. Once this process is complete, the ferrule is brittle and is easily broken away and discarded.

Why are ferrules single use? Why is there not a permanent ferrule?

During the welding process, oils and other contaminants on the weld surface, on the weld stud and in the air are burned. These burned contaminants form hydrocarbons which are deposited on the inside surface on the ferrule. If the ferrule were re-used those contaminants would be introduced into the next weld. Good welds have few contaminants so as a practice we don’t want to introduce more contaminants into each weld.

Do customers need to specify the type and size ferrule when ordering weld studs?

Typically, the answer is no. Image Industries has done all the leg work and matched up the proper ferrule with each stud. If no ferrule is called out, Image ships the usual ferrule with each stud (right in the same box so there is no confusion).

Sometimes, customers have special needs or a unique stud design which calls for a non-standard ferrule match. In these cases, the customer has already worked with the Image sales engineer to determine the best ferrule for the special application. Once the customer orders this ferrule with the stud, the Image ERP system will always match them up for you.

Proper ferrule alignment is key!

During the welding process, the stud gun automatically strikes the arc on the end of the weld stud. To strike the arc, the gun “lifts” the stud off of the work piece. After a predetermined amount of time, the arc gun plunges the weld stud into the molten pool of metal. The lifting and plunging action occur inside of the ceramic ferrule. If the ceramic ferrule is off center then the stud may bind, or hang-up on the ferrule and not properly complete the lifting and plunging actions resulting in a bad weld.

Functions Of Ferrules: Why Are Ferrules Used In Drawn-Arc Stud Welding?

Ferrules serve four important functions in the stud welding process:

1. Venting of weld gasses
2. Providing a limited atmosphere for shielding by the flux
3. Containing the molten weld material
4. Reducing operator exposure to UV light.

The venting of gasses is important. During the stud welding process various oxides and hydrocarbons are formed. These compounds are not helpful in the welding process and the vents in the ferrules allow them to escape.

As with many welding processes oxygen is detrimental to a high-quality weld. The flux load servers to deoxidize the atmosphere to generate an oxygen free weld environment. The ferrule serves to “limit” the amount of atmosphere that needs to be deoxidized.

A ferrule acts as a mold to contain the molten pool of weld metal until it solidifies. This causes the weld puddle to be contained (imagine welding on a tube: the molten material would run down the curve of the tube). The formed fillet also provides a pleasing aesthetic to the completed weld.

Finally, a weld arc produces intense UV light which can literally be blinding. Stud welding which uses even larger electrodes and higher currents than most welding produces even more intense UV light. The ferrule masks and reduces the UV light emitted from the weld zone. Note: Proper safety gear should still be worn.

Are ferrules stock?

As ferrules are an integral part of the drawn-arc process, Image stocks all the common ferrules (sizes and applications) shown on our website. If there is a specialized ferrule, once we know you need that ferrule Image will stock that as well.

Ferrules from different manufacturers

While there are some standards for drawn-arc weld studs there are not specific U.S. standards called out for weld studs. That being said, most manufacturers’ ferrules are very similar and can often be used interchangeably. There is uniformity across neck sizes so that ferrules fit into standard grips. The largest variance occurs in two dimensions: Outside diameter and Overall height. Usually, differences in the outside diameter are immaterial.

However, some customers choose to fixture off the outside diameter of the ferrules. While this is not a recommended practice as the tolerance on ferrule OD is large some customers choose to do it. When this path is chosen variances in the OD can cause problems.

The larger issue is any difference in overall height from one manufacturer to another. When the stud weld process is set up, the tool is adjusted such that the ferrule is in the proper position relative to the end of the weld stud. If the overall height varies between manufacturers, then the set-up position will be different for each manufacturer.

While each ferrule, when set up correctly, will achieve good results, if they different ferrules are used alternatively then weld results may be mixed as the stud gun is not set-up properly for one of the ferrules. Mixing ferrules is not a recommended practice.

Other stud welding processes

Besides the drawn-arc stud welding process there is Capacitive Discharge (CD), Gas Arc and Short-cycle stud welding processes. None of the other processes require a ferrule. Why is this? Relatively speaking, the drawn-arc process has a long arcing time. A 3/8 fastener would have an arc time of .38 seconds.

Compare this to CD welding where a 3/8 fastener would have an arcing time of .012 seconds or just 1.5% of the drawn-arc time. Because of the speed of weld, the opportunity for the formation of contaminants is limited. The trade-off is that these other processes do not achieve deep weld penetration. A 3/8 drawn-arc weld will typically penetrate into the work piece .125 inches while the same size CD weld will only penetrate .004 into the work piece.

Where To Get Ceramic Ferrules

In most instances (Hydraulic Ports being the primary exception) ferrules are shipped WITH the ordered stud at no extra cost. Image always has a large stock of a wide variety of ferrules. Sometimes a customer needs additional ferrules when the provided ferrules are lost or damaged. Image Industries also sells ferrules individually, as needed, to customer request.

Can my organization receive custom ferrule designs?

If you have a special application that may require a custom ferrule, talk with your Image Industries engineering partner. We partner with customers all the time to solve manufacturing and design issues. If a custom ferrule is needed, we are your go-to team to make it happen.

Who should I contact if I have more questions about ceramic ferrules?

Image Industries has knowledgeable customer service representatives who can help you with most of your ferrule needs and questions. If you have more technical questions, Image has experts who can provide you the assistance you need. If you need custom ferrule work, our engineering team can work with you to understand your application’s need and design and develop new ferrules to solve your most challenging problems.