Bimetallic Barrels


Are plasticating barrels an industrial commodity?

Hardly! As there are no specific industry-standards for barrel and screw configurations, each machine builder develops barrel configurations that suit his particular needs for fitting the barrel to his extruder or injection molding machine.

There are thousands of different barrel designs in use today; many of them have spawned further modifications at the user level to suit the needs of particular processing applications.

Keeping track of all these different designs, and providing the buyer withexactly what he/she wants is a daunting task for the barrel manufacturer that requires an extensive technical drawing library and dedicated, knowledgeable staff to research the information on behalf of the buyer.

WEXCO has built up an extensive technical library in 29 years of manufacturing nothing but plasticating barrels, and we have the knowledgeable sales staff to expertly serve our customers.

Considerations for Barrel straightness:

One of the most important aspects of a high-quality and high-performance barrel is straightness. Nothing affects barrel and screw wear as much asstraightness, or the lack thereof.

For example, to make a long and straight plasticating barrel is not an easy undertaking for any manufacturer. Starting with different interpretations by barrel makers of the requirement for straightness, some will abide by the straightness standards set by the Society for Plastics Industry.

WEXCO, in contrast, adheres to much tighter WEXCO straightnesstolerances to ensure a perfect fit of the screw in the barrel bore. Perfect fit equals long service life, which equals excellent return on investment and makes for a happy customer.

Why select a WEXCO high-performance barrel?

You cannot add better performance or wear characteristics once the barrel is mounted to your machine! You cannot straighten a crooked barrel, and you cannot readily change a bore inlay incorrectly specified foryour specific processing application.

To get good performance and long service life from a screw andbarrel, you need to do your homework up front!

Involve the barrel maker in your selection and decision process on the purchase of a barrel, whether as a replacement for a worn-out barrel or as part of a new extruder or injection press.

There is little you can do personally to kick the tires when it comes to choosing a barrel brand or type. Just like all tires look the same (they are round) but do not perform the same, plasticating barrels will vary greatly in performance characteristics and in the cost/benefit ratio for the user.

A high-performance barrel may cost a few more dollars initially, but themoney you save by not having to replace the barrel as often (consider thetime and money spent on frequent barrel replacements) and by getting much higher production yields, far outweighs any higher upfront costs.

As a processor fighting cheap foreign competition, you already know what counts in YOUR business: Performance!Performance is a combination of product quality, manufacturing efficiency, and goodcustomer service!

Surely, you will not get good product quality and good processing efficiency using a low-performance plasticating barrel! Are you really willing to gamble with your company's performance in a highly competitive global market?

The selection of the proper inlay (bore lining material) is often the most confusing aspect for the buyer when ordering a replacement barrel.

WEXCO alone offers six choices of bore protection: there are corrosion or abrasion resistant types, and those that combine both features. Then there are tool steel liners, as well as tungsten-carbide inlays with non-prorated 5-year wear warranty. Still other inlays offer protection against severely corrosive resins. Many machine builders offer nitrided barrels withtheir standard press or extruder to keep the overall cost down.

Considerations for selecting the best barrel bore protection for your application:

While several barrel makers (including Wexco) offer selection charts on theirthe buyer is well advised to pick up the telephone and talk to the barrel maker about his specific processing applications.

With considerable price differences among the various inlays, a knowledgeable sales person will not only assist the customer with the inlay selection but will also advise on cost/benefit ratios for the various inlay types suitable for thecustomers specific processing applications.

Often the customer can choose between a higher upfront cost for a particular type barrel and longer service life, or lower upfront cost with shorter service life. Dont expect to get something for nothing! Finding the right combination that benefits the customer most is the true skill of a technically trained, professional salesperson.

Nitrided vs. Bimetallic Barrels:

If straightness of the barrel tube is a prerequisite for good performance and long wear life, the selection of the bore lining material is equally as important. Clearly, the bore of an unprotected plain steel barrel will deteriorate quickly when the processor molds abrasive or corrosive plastic resins.

Nitriding the barrel is a common and cost-effective treatment of the barrelbore if the resin to be processed is only mildly abrasive and not corrosive. Not knowing the types of resins a processor may run, many machine builders select nitrided barrels as their standard for their new off-the-shelf equipment, only to exchange this type with a higher-priced bimetallic barrel for superior wear and output performance when the customer demands it or the processing application requires it.

However, high-performance barrels with superior output and long service life require more than a thin nitrided bore surface. The potential for contact between the rotating screw and the barrel bore and the effect of heat, abrasion, and possibly corrosion, make it necessary that the barrel bore is well protected. Bimetallic barrels feature a super-hard or anticorrosive protective layer in the bore that is applied there through a complex process involving high heat and centrifugal forces.

Only a handful of companies in the world have developed the skills and the capabilities to manufacture spun-cast bimetallic plasticating barrels. Among those, Wexco is one of the few that can perform all critical manufacturing processes in-house for improved quality control, including deep-hole boring, spin-casting of the bore lining materials, barrel straightening, and bore honing.

Considerations for processors on barrel maintenance and regular services:

To prolong the service life of your barrel, make sure that you are processing only those resins for which the barrel is designed. For example, if you decide to process corrosive resins in a nitrided or tool-steel lined barrel, you are asking for trouble! Your nitrided or tool-steel lined barrel will not last very long, and output performance will be affected very quickly!

Periodically, and at the first sign of performance deterioration, check for visible wear signs in the barrel bore, such as discolorations of the bore surface or better yet: using a bore gauge, measure the bore at different locations to find wear spots. Obviously, you will need to remove the screw to check the barrel bore.

While you have the screw out off the barrel, check the plasticating screw for straightness and for wear (check O.D.). Typically, a screw will wear much faster than a barrel. You may need to replace the screw three times for each time you will need to replace the barrel, especially a high-quality, high-performanceWEXCO bimetallic barrel.

Why not "bargain basement"-priced plasticating barrels?

Consider this: Plasticating barrels are pressure vessels requiring barrel makers to employ appropriate engineering and manufacturing skills, from the selection of high-grade steel bars as acking material employing certified welders and highly skilled machinists, to maintaining immaculate records on every barrel shipped. Making a pressure vessel such as a plasticating barrel is serious business!

Once you have a plasticating barrel mounted to your machine, there is little you can do to improve upon the performance of your new barrel. You cannot straighten a crooked barrel and you cannot readily change an incorrectly specified bore inlay.

Assuming that you have purchased a high-performance barrel manufactured by a reputable, experienced barrel maker, and you have it properly installed on your machine, you will, nevertheless, be faced with this fact of barrel life: The performance of your plasticating barrel and the screw will deteriorate with use and with time! However, choosing a "bargain-basement"-priced barrel or screw will virtually assure a short service life of the two most critical machine components that affect output performance.

What about repairing or re-sleeving worn barrels?

Depending on the severity of the wear or damage in the barrel bore, it may be cost-effective to have the barrel repaired or re-sleeved (i.e. removing the worn bore section and inserting a sleeve featuring the same protective bore lining material as the original barrel).

As re-sleeving will be considered primarily for injection molding barrels with their inherent high pressure operating conditions, the user is well advised to have this work done by qualified shops specializing in plasticating barrel repair.

Such reputable repair shops for plasticating barrels will advise the customer about the pros and cons of repairing or re-sleeving his damaged or worn barrel versus buying a new one.