Skip links

Choosing the right screw and barrel

Choosing the right screw and barrel combination for your plastics application is a critical component of any machine cell’s success or failure. However, most people may not realize how often this very selection process is performed incorrectly or incompletely.

It happens more often than you might think. Since most companies do not track this metric, hard numbers are probably elusive. Most experienced salespeople can recall five stories that corroborate this theory off the top of their heads. While it may not be as bad as it once was in the industry, barrels and screws are sometimes a secondary conversation when purchasing a machine.

Why is that so?

Typically, manufacturers focus more on the performance of the machine, the controls, the clamp speed, the dry cycle speed, and a whole slew of other features and benefits when purchasing a new machine. While it is true that they focus on clamp speed and performance, which is highly important since time is money, there is a question as to whether screw and barrel selection have been an afterthought for a number of years in the industry.

Throughout the past decade, plastics and resins used in products have continued to evolve.ressure to be more productive and eliminate scrap has caused said companies to extend their focus to the options and selection of the screw and barrel. That pressure to be more productive has been compounded over the past 10 years as the industry has continued to see an ever evolving makeup of the plastics/resins used in products. 

If the clamp end of the machine is perfectly tuned but you aren’t delivering a quality melt and mix material to the mold, then a fast clamp will only help you make bad parts faster.

So what goes into the selection of the right barrel and screw?

Most sales conversations on technical matters, including the choice of a screw and barrel, begin with the phrase “it depends”. There are a myriad of differences and varieties between industries, materials, and even general applications. The size of the machine, the potential for screw wear, heat, cycle time, melt temperature, color mix, recovery time and so many more variables can complicate the equation.

The first step is to understand the challenges of the application. Apart from providing a shameless plug for Plativo Extrusions decades of experience on “understanding the challenges of practically all plastics applications”, it is also worth noting that having a strategic manufacturing partner to guide you through that process can be extremely beneficial. The design of the screw would be the next step.

Did You Know? As the diameter of a screw increases, the design, not the metallurgy, becomes more important. In some cases, they exert a greater influence on melting than heater bands. Thus, the design of smaller screws involves more wear-related material decisions, which are then metallurgy or coating related.

The screw and non-return design/selection and metallurgy should be considered more important in the selection between the screw and barrel.

If you are keeping score, selecting the right screw and barrel is critical for any application. The question is when should this critical component be clarified in commercial discussions? As a result, it is not discussed as early as it should be when building a new machine. It is unlikely that you will find it at the top of a new machine conversation, but it should follow very closely behind.

It’s more likely than not that screw and barrel topics are discussed in an aftermarket setting. After a machine has run for a long time, many molders forget to check on newer or improved screw and barrel technology. In comparison to possible cost and changes to the clamp end, continuous improvements in screw and barrel sizing, coatings, and metallurgy have shown to improve efficiency, performance, and general material handling.

When upgrading old machines with new ones, or even retrofitting some existing machines, make sure you look at your screw and barrel for some much needed performance and productivity.