Chill Blocks for Welding

Chill blocks for welding are additional pieces of metal that are placed onto a workpiece that absorb a significant portion of the heat that is input into the metal during welding. This helps prevent overheating of the workpiece allowing for more consistent, precise, and above all else, controlled welding. Chill blocks for welding are typically made of a highly thermally conductive metal. Most often, this is copper, but aluminum is sometimes also used. They can work passively, or they can be actively cooled using liquids.

These chill blocks come in a variety of forms. They can be simple blocks of additional materials placed on top of the workpiece serving as ersatz heat sinks. However, this is uncommon as using chill blocks is an extra step and another thing the welder needs to work around—not something most welders would use unless they absolutely had to. Using chill blocks for welding is an additional step that adds complexity. Usually, it is something that is mandated by a welding parameter to ensure the final weld meets specifications, and chill blocks for welding are carefully chosen, specially engineered, and specially machined for the task.

How Excessive Heat Affects Welds and Welded Materials

Heat is one of the most basic ways to obtain a chemical transition in a material. That is effectively what cooking is. Although, the temperatures required to affect a chemical transition in metals are quite a bit more than those for steak or vegetables. Nevertheless, overheating metal beyond parameters can change its metallurgical properties and render both the weld and the pieces it is joining unfit for purposes. The only indication that this may have occurred is potential discoloration of the weld or the surrounding materials, and it is impossible to be absolutely certain whether or not this has happened short of destructive testing of the material.

Falling short of metallurgical alterations of the metal are gross physical deformations of the metal. Materials like stainless steel are somewhat infamous for their tendency to distort under heat, with thin-walled stainless steel tubes being prone to welding heat expansion and contractions. In addition to heat distortion, there always exists the possibility for localized burn-through during welding. While burn-through isn’t a huge issue in structural welding, it can be a massive issue in high specification, high purity, or ultra-high purity applications where product control is exceptionally demanding.

Chill blocks for welding can help to prevent these issues in welding when they are most critical. They provide an effective way to dissipate heat actively and allow wider tolerances for heat minimization strategies. In other words, they allow for slower travel and deposition rates and higher amperages that enhance welding penetration in thin materials. They can also reduce the need for lengthy cooldown periods between passes while keeping interpass temperatures within the needed ranges. However, the effectiveness of chill blocks for welding depends on their implementation.

Types of Chill Blocks for Welding

Chill blocks for welding can come in various sizes, shapes, and styles. At the simplest level, they are extra mass that absorbs heat, and this can be as simple as some additional scrap metal that was clamped onto the workpiece to draw away some of the heat. These improvised chill blocks are sometimes called chill bars. However, when chill blocks are called for in a welding parameter, it will certainly be for an engineered chill block, and there are a few different varieties of these, which include:

• Interior Diameter: These chill blocks are designed to fit inside a pipe or a tube on either side of the joint to be welded. These sometimes double as a purge fitting for inert gas as well. However, these are somewhat uncommon as there are limited opportunities for heat dissipation inside a pipe or tube.
• Backing Plate: Sometimes called a chill plate, this is an additional piece of material placed directly behind the weld. This serves multiple purposes, such as diverting heat, reinforcing the weld, and preventing intrusion of molten material into the space behind the weld. Applications for this type of chill block are limited to circumstances where achieving the necessary weld penetration has a high chance of melt through. 
• Exterior Diameter: These chill blocks are for welding pipe or tube and are carefully drilled to ensure a tight fit between the block and the workpiece. These offer a large amount of cooling as their size and volume can be adjusted as needed. They can also be hooked up to an external cooling supply and actively cooled.

Exterior diameter chill blocks are the most common in orbital TIG welding. This is because they offer the most cooling potential. Other options, like backing plates in orbital welding, will probably be used for reinforcing the weld or controlling molten materials rather than their cooling potential. These exterior diameter chill blocks for welding aren’t without their disadvantages when it comes to orbital welding. The majority of orbital weld heads sit on the exterior of a pipe or tube, and chill blocks on either side of the joint can interfere with the movement of the weld head. 

Additionally, exterior diameter chill blocks also tend to be actively cooled. The presence of an additional cooling unit specifically for the chill blocks is an additional complication that adds hoses and wiring to things in the weld zone that can interfere with the free movement of the weld head. Most welders likely aren’t looking for additional hoses and wiring that they need to keep track of, as they have more than enough already. However, despite these complications and drawbacks, chill blocks for welding do offer an exceptional level of control over the heat input into a workpiece. In certain applications, that is absolutely indispensable.