This informative blog allows plastics professionals to discuss plastics training and technology. Brought to you by Routsis Training: the plastic industry's premiere training provider.

Stop Wasting Material: Learn the Right Way to Purge Your Barrel

FACT: A purging compound will help you purge better than no purging compound. Furthermore, there are some simple concepts and techniques that will ensure excellent results from your purging compound — better results than can be achieved by just following the manufacturer’s recommended procedures.

Unfortunately, bad purging habits and poor purging procedures are pervasive in the plastics industry — which is why we produced our Scientific Purging courses. In this post, we will discuss a few of the important topics introduced in Purging Techniques, the first program in our Intermediate Purging course.

Safety First: Acetal and PVC Don’t Mix

First off, there is absolutely no safe way to purge between Acetal and PVC. Unless you pull and clean the nozzle, hopper, hopper loader, grinder, blender, drier, end-cap, screw, screw tip, and check ring you risk a potentially deadly combination of PVC and POM. Every plant that processes these two materials must have procedures in place to prevent them from being used in the same machine, drier, grinder, or material blender.

Barrel Capacity ≠ Max. Shot Size

It’s a common misconception that Barrel Capacity and Maximum Shot Size are equivalent. Note that the barrel capacity indicates the amount of material contained in the screw flights. This varies with screw design and is not provided to you by your machine manufacturer. In reality, barrel capacity is typically between 2x and 2.5x the maximum shot size.

With this in mind, a quantity of purging compound equal to one half of barrel capacity is roughly equivalent to the maximum shot size. If you need a barrel full of purging compound, you will need to use a quantity that is at least 2x the maximum shot shot size.

Barrel Capacity is not the maximum shot size, it is the amount of material contained in the flights of the screw. Although this number is not provided to you by your machine manufacturer, it is typically between 2 & 2.5 times your maximum shot size.

Small Shot Purging is Most Effective

Small Shot Purging involves using 10% to 20% of your machine’s maximum shot size in each purge shot. This technique is preferred over using fewer large shots, as it keeps material moving in the feed zone, cycles the check ring more times, and increases agitation within the screw flights.

Take It Easy with Back Pressure

Minimum back pressure should be used when purging. In fact, it is usually best use no back pressure at all. Remember that the purpose of purging is positive conveyance. Back pressure creates back flow in the screw channels, which is counterproductive to purging.

Back pressure can be used to purge-out a hot runner system (like an extruder). But this is only done after the barrel itself has been thoroughly purged.

Wet Purging is Best: Always Keep Material in the Barrel

You should never empty the barrel: Always keep the barrel full of material. This is called ‘wet purging’ — and it is far more effective than ‘dry purging’.

Even when “empty”, there is material still stuck to the screw and barrel. This material will burn and degrade, risking contamination when it eventually breaks off and finds its way into the plastic melt.

Keep the barrel full of material maintain positive conveyance during purging. This eliminates the risk of ‘baking‘ the material. To ensure a full barrel, use a telescoping mirror over the feedthroat so you can stop purging when the screw flights become visible.

Take Care When Processing Unstable Materials

When processing unstable materials, it is necessary to replace them with heat stable materials such as a polyolefin or a purging compound any time the machine is stopped or shut down. Keeping in mind what we mentioned above, you will need at least 2x the maximum shot size to fill the barrel with heat stable material.

Be sure to check out Routsis’s Intermediate and Advanced Purging courses for Scientific Molders. These courses teach injection molders about proper material purging concepts, procedures, materials, methods, and cost analysis.

Looking to kickstart your company’s training initiative? Follow these 5 easy steps.

At first glance, launching a new in-house training system can appear to be a daunting task. But it’s often simpler than it seems. In short, the key to a successful training initiative is getting your employees involved in the process — keeping them excited and engaged.

Remember that most employees want to do a good job. They just need the knowledge, skills, and tools to do their jobs better. These 5 easy steps will help you build and maintain the momentum of your training initiative.

Make a Formal Announcement

A department or shift meeting is a great place to give employees an overview of your training plan and its goals. Let them know the results you are expecting and why it’s important to the company. It’s also important that they see the personal benefits of training: better job security, a safer workplace, more opportunities for promotion, etc.

Post the Training Plan

Use your company bulletin board to keep your employees informed of the training plan — as well as updates on the progress of each aspect of the plan. Although you cannot post specific information about individual employees, you can announce weekly updates and important milestones, such as ‘Congratulations tor all 1st shift setups for successfully completing the certification exam!’

Help Each Employee Develop a Professional Evidence Portfolio

Each employee should have a 3-ring binder or similar organizer to retain all their training records, certificates, and other accomplishments. The first item in their binder should be a letter from their manager — thanking them for participating in the training initiative and explaining the company’s investment in their professional development.

Post Company Metrics

It’s not enough to simply tell employees what the company expects to improve as a result of continuous improvement initiatives. There should be weekly or monthly updates to company metrics — so employees can see the results of their efforts and how this affects the company’s bottom line.

Celebrate Their Accomplishments

If your employees are truly working together to make things better, it is good to acknowledge these improvements. Milestones should be celebrated with something special such as a pizza party, coffee hour, or a cookout. Such activities help your employees feel like part of a team.

These are just five simple ways to help jump-start your in-house training initiative. Please contact us for more information — and be sure to check out our free template and instructional video for developing a Professional Evidence Portfolio.

Real Skills vs. Learned Behavior: What’s the Difference?

The truth is that there is a huge difference between a skill and a behavior — a difference too frequently ignored by plastics manufacturers, to the company’s detriment. Skills are what make effective engineers, technicians, and operators in your production floor — while learned behavior involves mimicking what a fellow employee is doing.

Are your employees developing skills or just learning behaviors from their fellow employees? That’s a big question that’s critical to your company’s success.

Real Skills

The Merriam-Webster dictionary defines skill as ‘a learned power of doing something competently.’ Applicable skills contain many components — such as an understanding of how a task is to be properly performed, how things work, and why the task is done in that manner. Beyond the mere how-and-why, turning a task into a skill also requires practice.

Skills involve knowing…

  • Who is responsible for performing the task
  • How the equipment or system works
  • Why the task is done in the required manner
  • What is expected when it is done correctly
  • Where to turn if things go differently than expected

Skilled employees are the ones who can improve a procedure, identify an incorrect procedure, notice inconsistencies, and correct an issue. Furthermore, a skilled employee will recognize a problem they are not trained to handle — and they’ll inform the right person in order to resolve the issue.

Learned Behavior

Learned behavior is merely a compilation of responses to stimuli: an employee watches a fellow employee respond to a situation in a certain way and learns a response. The more times they see fellow employees do something, the more likely they are to respond in the same manner. Such a response does not involve much thinking as much as reacting with similar responses as their co-workers. The biggest downside to this process is that bad work habits are often transferred from one employee. This why shadowing should never be the primary method of instruction.

Learned behavior involves…

  • Shadowing others to learn their habits
  • Mimicking their behavior when possible
  • Relying on memory when things go wrong

Learned behavior is often the fastest way to get an employee on the production floor — doing something simple like sorting parts or moving material. Over time, plastics companies need to expand the knowledge and capability of their workforce. No company can expect to production improvements with learned behavior alone. Furthermore, employees training in this manner are incapable of quickly adapting to future changes in product, materials, equipment, or procedures.

Developing real skills is the only way your employees can quickly and confidently adapt to new equipment, products, materials, procedures, or processes. Routsis Training proudly delivers skills-based learning. Click here for more information about our company-wide training products and services.

The simplest way to review your employees’ knowledge, skills, and professional development

Employees who are developed and promoted from within tend to be more capable, contribute more, and stick around longer than those poached from other companies.

Throughout their career, your employees acquire a great deal of experience: solving problems, achieving goals, and developing skills. A professional evidence portfolio is a great way for managers to objectively review these accomplishments.

Degrees & Certificates

Certifications and degrees imply a certain level of knowledge. Classroom training certificates should include course syllabi or class outlines to provide a clearer idea of exactly what the certification indicates.

Specific Accomplishments

Documentary evidence of participation in work projects (i.e. implementing the 5S System, installing a new machine, solving a particular production problem, etc.) are important records to maintain. Evidence such as photographs, prints, or approvals help demonstrate tangible skills and professional capabilities.


Testimony from reliable coworkers, employers, and instructors speak to the skills, knowledge, and professionalism of the employee.

Skills Exercises & Worksheets

A structured training program, such our RightStart™ system, include job-specific tasks to help establish and maintain proper daily work habits. Once completed and approved, these worksheets are valuable additions to any portfolio.

Associations & Trade Shows

Any relevant trade associations, guilds, unions, or other industry memberships should be included — along with attendance to industry-related events, such as tradeshows, seminars, and conferences.

These are just five important factors in an employee’s professional development.  This information greatly helps managers and human resources objectively evaluate an employee’s skills & capabilities — as well as highlight opportunities for improvement and development.

Please check out our Professional Evidence Portfolio page, which includes a free template and instructional video.

The Importance of Proper Mold Venting

It is important to understand that all the air in the mold cavity must escape to atmosphere in order for the plastic to properly fill the mold cavity. Inadequate venting is an extremely common cause of molded part defects. At Routsis Training, customers sometimes ask us how many vents a particular mold should have. It’s a simple question to answer:

Q: “How many vents are required?”
A: “As many as possible.”

While this information is obviously critical to mold designers and mold makers, it is also important for production personnel to understand this concept when troubleshooting molded part defects. Let’s review what is happening with the mold, plastic material, and your process with respect to venting.

Air Volume = Plastic Volume

The moment you start pushing plastic into the mold, air must escape the mold cavity. This means the more avenues the air has to escape, the faster and easier the material can enter the mold. It is important to allow the volume of air in the cavity and runners to escape the mold to atmosphere so it can be effectively displaced by the incoming plastic.

Mold designers often indicate an end-of-fill location as the best place to vent, but this just one of many vents you must cut into your mold. In fact, you should vent the runners, sprue puller, cold slug, slides, bosses, lifters, ejector pins, ejector blades, stripper plates, start of fill, middle of fill, and the end of fill.

All these vents must have a clear path out of the mold to atmosphere. When the plastic resin enters the cavity, you want an even, uninterrupted flow. Venting everywhere ensures this.

Aqueous Volatiles

Plastics have all sorts of additives, moisture, stabilizers, plasticizers, lubricants, low molecular weight chains, colorants, etc. When the plastic pellets are subjected to the heat and sheer during the molding process, they give off gas — resulting in aqueous volatiles. You often see this as a waxy buildup along the vents and the ejector pins.

Over time, these volatiles collect on mold surfaces, causing inconsistent part finish and gloss, and decreased surface texture quality.

Internal Stresses

If most of the air does not escape, the part will have internal stresses and will deform after it is ejected from the mold. This often results in cracking, crazing, and part warpage. Looks for signs of bad venting such as consecutive circles or a cloudy area at the gate, shiny spots at the parting line, as well as inconsistent gloss.

Narrow Process Window

Your process window is greatly affected by the range of pressures in which you can fill and pack the mold cavity. If a great amount of pressure is needed to push the gas out of the mold, you have a very small process window between filling the mold cavity and flashing the tool. It is not uncommon to see molds where the venting is so inadequate that the mold cavity cannot fill without flashing — because the escaping gas forces the mold open.

We hope this information has helped educate you on the important of proper mold venting. Tooling personnel can learn more from our Mold Design & Moldmaking Series. The importance of venting is also discussed in Scientific Troubleshooting for Injection Molders.