R&B Plastics Machinery Blog

Call For More Info: 734-429-9421
plastics machinery removal
Field Service Support

We have a dedicated service team with over 450-years combined experience. They include mechanical, electrical, and hydraulics/pneumatics specialists. Call us for assistance with any make or model of blow molding or extrusion equipment.
R&B Field Service Support >>

Preventive Maintenance & Tech Tips

Vent Bleed

February 25th, 2015

There are several extrusion applications where vented extruders are used. The main purpose of a vent extruder is for devolitizing the polymer of any volatiles, air, and moisture. There are two main reasons that the vent port on the extruder will “bleed” or allow polymer to be expelled out through the vent hole. The first reason can be a poor screw design and the other is a poorly designed vent diverter.

The typical resins that are vented are HIPS and ABS, so that resin dryer do not have to use in the process. Also, certain processes such as in-line sheet thermoforming of PP and light bulk density feedstock re-pelletizing applications where the main purpose is to remove air entrapment.
Read the rest of this entry »

The Extruder Screw isn’t Always the Problem!

January 30th, 2015

For several months now I have written articles which are bits of advice that I hope can be used to improve a process issue, but this month I want to pass on an experience that happened to me several years ago.

Read the rest of this entry »

Stainless Steel Extrusion, Blow Molding and Injection Screws

January 2nd, 2015

The most common base material that extrusion, blow molding and injection screws are manufactured out of is 4140 HT Steel at a 28-32 Rc condition. This grade of 4140 has a yield strength of 95-100 kPSI. The next most common base material used is 4340 HT Steel at a 28-32 Rc, which is approximately 10% stronger than 4140 and it is highly recommended to be used for high torque applications where fraction melt HDPE, PP and other viscous resins are being processed.
Read the rest of this entry »

Feed Section – Solids Conveying ( C = Consistently)

December 4th, 2014

“First you must feed the polymer Consistently”

Material Handling
The material handling of the feedstock is a very critical part of the extrusion process. If the feedstock is not introduced to the feedsection of screw in a smooth and uniform matter, then the likelihood of a stable and consistent output is unlikely. This is the reason why it is very important that if regrind is added to the virgin feedstock, it must be done very consistently and uniformly. It should also be mentioned here that a very important part of the extrusion equipment is the hopper and feedthroat section. If the hopper and feedthroat sections are not designed properly, inconsistent material flow to the screw can take place. For example, if the conical section of the hopper (see figure) does not have the proper transition, the resin will not flow smoothly into the feedthroat of the extruder.
Read the rest of this entry »

Extruder Screw Rebuilding

November 6th, 2014

Many people don’t realize the importance of making sure that the screw flight diameter clearance has a significant effect on the performance of their screws. There are some companies that do pull their screws, measure the flight diameter, and record the information. By doing this regular maintenance routine will help production to predict when they may need their next shut down to have a screw repaired or the purchase of a new screw. Read the rest of this entry »

Extruder Screw Cooling

October 8th, 2014

coefficient of frictionThere are basically three Coefficients of Friction (Figure 1) that take place in the feed section of the screw, (1) between the barrel and the pellet, (2) between pellet to pellet, and (3) between the root of the screw and the plastic pellet.

Screw cooling on the feed section core of the screw should always be installed. In most cases, screw cooling will be a benefit to the process. It will give the operator another “zone” of control of the extruder. The main theory of “solids conveying” is that the resin must “stick to the barrel” and “slip on the screw”. By cooling the root of the screw it will reduce the Coefficient of Friction between the steel of the screw and the plastic pellet.
Read the rest of this entry »

Screw and Barrel Wear

September 11th, 2014

Screw and Barrel WearScrew and barrel wear is critical in all plasticating applications whether it is extrusion, injection molding, and blow molding, plus twin screw extrusion.

Excessive screw and barrel wear can cause instable throughput or recovery on reciprocating screws, increased melt temperature and reduced plasticating rates.
Read the rest of this entry »

Regrind Particle Size

August 14th, 2014

Almost all processes, extrusion, injection and blow molding require that regrind be used in the process. Depending on the process greatly determines the amount of regrind that is generated. Some processes produce very minimal amounts of regrind, such as an injection molding process using a hot runner system versus a flat sheet extrusion process producing thermoformed sheet and the entire skeleton has to be fed back into the process or a blow molding process which always generates large amounts of regrind.
Read the rest of this entry »

Oversize Screw and Barrel

July 17th, 2014

I have written in the past about screw/barrel wear and also screw rebuilding, but there are some screw and barrel shops that offer an alternative for excessive barrel wear and that is honing the barrel oversize and then rebuilding the screw oversize also to fit.
Read the rest of this entry »

Over-hung Loads

June 19th, 2014

Recently a processor installed a new screw into their 6” x 32:1 L/D extruder. Within a few weeks the hard facing that had been welded on the flight OD started to pop off. The flight failure was in an isolated area, so it was then assumed that the failure was due to a poor weld bond. The screw was ultra-sonically inspected and the remaining flights showed good bore, but the entire screw was rebuilt and returned to the customer.

Read the rest of this entry »