Standard Purge

Standard purging is the most common form of mechanical purging. It is used to ensure the health and cleanliness of the Filament Maker. This article features the purging material, preparations, and step by step guide to a regular Standard purge.

Article Overview

DevoClean MT

Preparation

Step by step

---

DevoClean MT

(Mid-Temperature, or MidTemp, or MT)

DevoClean MT is the purging material used for Standard purging. It can generally be used for any situation and material as long as it stays within its temperature range of 190-320°C. It is also perfectly fine to leave in the machine after shutting down. 

Samples from a Standard Purge, chronologically from left to right

The good

DevoClean Mid-Temperature is based on HDPE. In addition, DevoClean MT has certain materials “grafted” on the existing polymer, which basically means that the HDPE gets synthesized and enhanced by adding specific chemicals. This blend of HDPE for example has a very favorable melt viscosity for purging all the way up to its decomposition (burning) point of 320°C. This is in contrast to pure HDPE which has a decrease in melt viscosity above 280°C. 

The bad

The disadvantage of this is that it is also harder to extrude out of the machine when starting with a new material. With DevoClean MT, the transition to a new material often takes quite long and a lot of new material needs to be extruded before the DevoClean MT is fully removed from the machine.

The solution

To speed up the transition to a new material, it is recommended to purge out the DevoClean MT with HDPE. The transition to a new material is way faster when starting with HDPE in the extruder, because the melt viscosity is much lower. This is especially the case when going back to PLA.

Here's an example of what that would look with a Standard Purge after extruding PLA.

Figure 1. 

To sum up

Advantages of Standard purging using DevoClean MT	Disadvantages of Standard purging using DevoClean MT
performs very well purging out additive-filled materials, especially colorants	not suitable for high temperature materials such as PEEK
can be used for any material within the temperature range of 190-320 °C	slow transition to the next material
leaving it in the extruder for a long time after the machine is shut down has a great cleaning effect and enhances the screw’s life span	can produce a lot of smoke when extruded at a high temperature and high RPM

Preparation

Before purging your extruder, there are a few preparation steps that should be taken for safety.

1. Gathering
   The first step is gathering all the necessary tools, materials and information for the purging process. These are:
   • at least 350 grams of DevoClean MidTemp, however this will depend on:
     
     • the type of material that needs to be purged out of the machine
     • the machine’s state
   • a piece of cardboard, or protective silicon bib

1. • multitool (or a side cutter and pincers)
   • heatproof gloves (when handling hot output)
2. Ventilation
   Make sure that the area is properly ventilated. A fume hood is also highly recommended to guarantee your safety. Wearing a gas mask is also a good option.
3. Sensors
   Turn off the hopper sensor in the "Settings" menu, so the hopper can be run completely empty before putting in the purging material. Do this by setting "off" under "Hopper empty check".
4. Fans
   Turn off the filament fans by setting the "Filament fan speed" to 0% in the "Settings" menu, and point them as in the picture on the right below.
5. Protective bib or cardboard
   Cover the filament sensor with an extrusion bib or a cardboard. 

Set up during filament making, then set up for a purge.

Step by Step

After preparations are complete, the purging process can begin.

If you're familiar with Disco Purging, go ahead and introduce it to your regular practice of purging. We recommend you perfect the process below first, before adding that method. 

Step 1: Almost empty hopper

Let the hopper run empty, until there is few to no granulate of the previous material inside the hopper. The image below shows 3devo PLA with blue colorant. Hopper running low on the processing polymer:
3devo PLA is oval, round, smooth and white with a yellowish hue.
Added to this is the blue masterbatch colorant. 

This is an important step that can often be tricky. Read more about how to properly transition here.

Alternatively you can vacuum out whatever material is left in the hopper. 

Almost empty hopper: the moment to put in DevoClean MidTemp.

Step 2: Small amount of MidTemp

Put in a small portion around 60 grams of MidTemp, so more of the previous material can be flushed out of the hopper and the feeding section of the screw.

Temperature settings don’t need to be changed as long as it is within the range of your purging material’s extruding temperature.

First (small) portion of DevoClean MidTemp.

Step 3: Purging

Wait for the small portion of MidTemp to be flushed away by the extruder. This might take around 15 minutes, but can be more or less. 

Step 4: Large amount of MidTemp

Again, when few to no granulates are left, put in the next portion of purging material, around 200 grams.

Second, larger, portion of DevoClean MidTemp.
MT is white, oval, and slightly flat. 

Step 5: Evidence of purging

Remember, the point of purging is to get rid of the material that was previously used. This can be visibly seen in the extrusion.

When MidTemp is coming out of the extruder, usually mixed with the previous material, proceed to the next step. This is usually clearly visible as the structure, color, and surface smoothness of the filament changes.

First signs of MidTemp mixed with the blue PLA. 
When heated up, MidTemp expands and becomes foamy. Notice the difference between the pile of smooth, blue PLA, and the topmost extruded material. This is MT mixing and pushing out the PLA.

After a few minutes, the transition between the smooth PLA and foamy MT is much more visible.

Adjustments:

• if the change in the extrusion is still not visible after 15-20 minutes (from the moment the first small portion was put in the hopper) increase the temperatures of all heaters with 20°C.
• If this still doesn’t work, increase the screw speed to 10 RPM to give the flow a boost. As soon as the flow is back, decrease to the original RPM.

DevoClean MidTemp is an abrasive material, meaning it can remove burnt or degraded particles that have built up in the machine over hours of use. 

MidTemp pushing out degraded black specs. 

Step 6: Finish purging

After 10 minutes, see if the extruded still contains old material or other contamination.

Here the MidTemp still has a light blue hue meaning that the purging process is not yet complete. 

Here the MidTemp is fully white, and foamy.
There is no evidence of: PLA (yellowish and smoother), colorant (blue hues), or degradation (black or dark brown burnt particles). 

If we visually confirm that the output ONLY contains DevoClean MidTemp, the purging is finished. Below is an overview of the input and output material as well as samples of the purging process. 

Top left: 3devo PLA pellets with blue colorant
Top right: DevoClean MidTemp pellets
Bottom row from left to right: blue PLA filament purge out by DevoClean MidTemp

---

 

Optional extra step

Transitioning to a new material with DevoClean MT can take a long time. To speed this up, DevoClean MT can be purged out using HDPE.

Doing this is highly recommended if you are planning to do another test soon.

 

 

Step 7: Purge DevoClean MT with HDPE and Finish purging

If you wish to extrude new filament again, and Step 6 has been completed, and the extruder is clean, then the machine can be purged with HDPE to speed up the transitioning process.

To do this:

1. set all heaters to 240°C
2. wait until the hopper is completely empty just as in Step 1
3. follow the steps of the purging process again starting at Step 2

Below is an example of this process near its finish. A few spots of old DevoClean MT are still visible, so the HDPE purge can continue for a few more minutes. Usually the total transition from DevoClean MT to pure HDPE takes around 25 minutes and 250-500 grams of HDPE granulate.

Almost pure HDPE, with a few spots of old DevoClean MT

Once there is clear HDPE coming out of the nozzle, without white spots/flakes of the DevoClean MT, then the machine is clean enough and ready for the next material.

---

To understand how Disco Purge fits into all this, head to its dedicated article. 

Know the practice, but not the theory? Have a look at What is Purging? .