Structural Foam Injection Molding Process

Posted: April 12th, 2010

The Structural Foam Process is a low pressure injection molding process where an inert gas is introduced into melted polymer for the purpose of reducing density and hence weight of the finished product.

Structural foam molded products have cellular cores surrounded by rigid, integral skins. Foaming agent (NI, CO2   or CBA) is introduced into the polymer melt stream, creating a homogenous mixture of polymer and gas.
The mixture is short-shot injected through nozzles into the mold in a volume that is less than the amount required to mold a solid part. Injection pressure and expansion of the polymer/gas mixture fills the mold.

A porous skin is formed when the melt contacts the cold surface of the mold. The expanding polymer/gas mixture forms the cellular core.

The expanding gas provides the final pack and hold pressure. Once the plastic gas mixture enters the mold cavity, the gas expands (i.e. foams), filling the cavity and forming cellular structures within the part. The finished part is typically 10 – 30% less weight than an equivalent solid part.

Advantages over alternative methods

  • Part weight reduced 10% to 30%
  • Density Reduction, hence resin savings
  • Low cost N2 or CO2 – much less expensive than chemical blowing agents (CBA’s)
  • Large part molding with low clamp force requirements
  • Mold Cavity Pressure; typically 200 – 600 psi ( 14 -41 Bar )
  • Lower energy costs vs. other IM processes
  • Lower cost aluminum molds vs. high pressure IM machines
  • Faster cycles due to better heat transfer of aluminum
  • Thick wall parts from 0.125″ – 0.500″ ( 3 – 12 mm )
  • Stiffer parts at the same weight as IM as a result of cellular foam structure
  • Complex parts without sink marks
  • Higher impact strength than thinner wall IM
  • Parts can be sawn, screwed, nailed or stapled like wood
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Is Custom Machinery Right for You?

Posted: April 8th, 2010

It is difficult to compete in manufacturing today in this challenging global economy. The days of buying the same equipment to make the same product at the same speed as your competitor are disappearing. Everyone’s looking for a competitive edge. You can gain this competitive edge by having your own proprietary technology that only you have access to. For this to happen, you will need to build from the ground up with new concepts, technology and process controls with your industry’s latest safety measures and long-term machinery support.

The process of arriving at this proprietary machinery can be difficult and expensive, so many companies turn to a machinery manufacturer to assist and guide them through the complicated process. Contrary to what you might initially think, however, there are precautions and procedures which a buyer can apply when working with a custom machinery builder. Because we at Wilmington Machinery have a perspective from the machinery builder’s position, the following tips may be of value to those in the process of acquiring proprietary high-output processing systems.

Many problems between buyers and suppliers of proprietary machinery begin with the very first meeting, when expectations are not properly defined in writing. Let me repeat: expectations must be written so they can be considered, discussed, clarified, and understood by all. No one can read minds, and making assumptions has been the basis for many long, costly arguments. Expectations should encompass overall objectives and goals, detailed specifications, performance criteria, testing parameters, and budgetary constraints. Because custom projects are by nature highly individualized, nothing should be left to subjective interpretation. Written documentation protects all parties. This includes developing an “exit strategy” prior to beginning that can be used by either party.

The Process of Designing a Proprietary Machine

The process of designing a machine from the ground up can be overwhelming to those who have not gone through the process. In reality, the sequence must be thought of in terms of distinct steps. Wilmington Machinery has broken these out into distinct Phases that should be followed.

The Exploratory Phase. In most cases the customer has an idea to start the process. This is the learning Phase during which the customer explains the process their ideas for the future machinery. This is also a learning period for the machinery manufacturer to understand the critical elements of the particular production process and variable and interfaces necessary to deliver a successful production machine. This typically takes place in 1-2 meetings.

The Concept Phase. During this phase, the machinery builder’s engineering and production-oriented staff formulates several possible solutions and assesses each concept with its Strength, Weakness and Risk Analysis. These are reviewed in detail with the customer for their input and suggestions based upon their understanding of machinery and process requirements. This would include for the first time an estimated cost of the first and subsequent production machines along tentative timelines. This Phase can take 4-8 weeks depending upon the complexity of the project.

The Development Phase. All general arrangement drawings, detail drawings, schematics and bills of materials are created on CAD. A firm price of the machinery and firm timeline are agreed upon, along with a very detailed set of deliverables. This Phase can take 6-12 weeks, again depending upon the complexity of the project.

The Production Phase. The machine is physically manufactured and assembled. This is typically a 3-6 month project depending upon the material delivery time and amount of assembly hours required.

The Validation Phase. During this phase, all machines are tested under agreed-upon production conditions and validated prior to shipping. This would also be the time when extensive operator/maintenance training would be completed, as well as a thorough review of the complete documentation set that includes BOM, detailed assembly drawings, maintenance and the operator manuals.

The Installation/Commissioning Phase.
The machine is installed in customer’s facility, and start-up and full production are validated for a second time.

It is vital that buyers treat each of these phases as separate parts of the whole process and build into the arrangement an agreed-upon series of milestones with sign-offs when the written specifications for each phase have been successfully fulfilled. Again, it is also important that each phase features an exit strategy in the unlikely event that mutual objectives have not been met.

Buyers should be cautious of assuming that a turnkey system is more costly than a pieces and parts approach to custom machinery development. In fact, a turnkey approach is usually much less expensive in the long run. The reason is rooted in the reality that a turnkey supplier provides everything to produce the finished product. Moreover, if there is a component failure, the responsibility is clearly that of a single supplier and there can be no finger-pointing between dual or multiple vendors. Conversely, a system that has multiple suppliers integrating different components is ripe for the “blame game.” Once an initial turnkey system is successful, subsequent systems may be pieced together with much less chance of failure.

Some buyers have been hurt by assuming that the technology represented by the custom machinery they are buying will become their legal property. Before you sign on the dotted line, be sure that you have a binding assurance that the completed machine you receive will, in fact, be proprietary. If you don’t, you may wake up to find your competitors enjoying the technological benefits you paid for!

Because proprietary machinery is frequently required to meet unique processing criteria, a buyer can use the quotation, order and written job specifications to help ensure a comprehensive proving-out sequence of the process. Most successful projects stipulate a production run at the machinery manufacturer’s facility before shipping then a repeating, using identical processing guidelines, once the equipment is in place with the customer.

Summary

In summary, the common thread that runs through all “good practices” of customized equipment buying is the absolute need to spell out all expectations, to specify all criteria for performance, and to provide a clear, mutually acceptable method for evaluating progress at each phase of the customizing process.

For more than three decades, Wilmington Machinery has been designing and building cost-effective, highly specialized, quality custom processing machinery.

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Barrier Blow Molding is Growing at a Fast Pace! Could Your Products Benefit?

Posted: April 8th, 2010

The demands for improving extrusion blow molded containers are rapidly increasing. A recently published forecast by Mastio & Company, a consulting firm in St. Joseph, MO, estimates 6.2% growth per year in plastic containers for blow molded food and beverage. Comparable or even slightly higher expansion is predicted for segments of consumer packaging that include pharmaceutical, health care, and cosmetics. The demand for EVOH is growing at a rate of at least 10% a year with 70% of that growth being in food packaging. 2003 year-end statistical summaries from the Society of the Plastics Industry indicate that of all plastics-related equipment categories: “Blow Molding showed the most promise, realizing increases in units shipped and dollar value of shipments of 19.4 percent and 10.5 percent respectively.”

Growth of that magnitude is fueled by diverse dynamics. Consumers demand that products must be convenient to use. Retailers want great shelf appeal and containers that are easy to stock and handle. Manufacturers want lower costs combined with improved performance in the filling line and shipping chain. Product formulators want longer shelf life from containers, frequently requiring barrier properties for moisture, gas, oxygen, chemicals and other elements. Converters want faster production rates, designs that lend themselves to higher speed production and more repeatable, high quality capabilities. This trend is especially strong in food, diary and beverage packaging. “Recently we have seen more interest in multi-serving packages versus the smaller single serve containers,” says Jeff Newman, VP of Wilmington Machinery.

Solving such packaging challenges may seem overwhelming. To meet diverse and many times conflicting specifications, companies are exploring multi-layer and barrier alternatives. In that regard, working together with material suppliers and machinery manufacturers often leads to the best and fastest solutions. For instance, Wilmington Machinery, barrier specialist in high speed blow molding machinery, has identified numerous multi-layer options to help its customers solve packaging problems such as improving shelf appeal, reducing costs, and creating better barrier protections.

Barrier protection for longer shelf life and improved product formulations is easily achieved by today’s improved materials using multi-layer configurations. Some packaging can be improved by adding a layer of the new highly effective moisture barrier material to the inside. A thin layer of flavor barrier material can be added and matched to a specific product need. A chemical solvent barrier can be achieved easily by adding a thin layer of specialized material. Oxygen barriers to extend shelf life and protect products are routinely accomplished through multi-layering methods as evident by the recent success of the plastic coffee canister in North America.

The blow molding industry is moving toward multi-layer and barrier applications. “Coextrusion blowmolded, barrier, single serve containers can be produced at a lower cost than comparable containers made using coinjection, barrier, stretch blowmolding,” says Bob Miller of Business Development Associates, a packaging consulting firm. “In addition the growing trend of using full body shrink labels eliminates any issues previously associated with gloss or clarity requirements of the container; thus, potentially favoring extrusion blowmolded polyolefin containers over PET.” Product designers, material suppliers and machinery manufacturers are now integral in the conversion process for testing, material evaluations and package performance. To meet the demand for new product development, Wilmington has equipped its laboratory with two multilayer machines for packaging and industrial applications. Additional process engineering, design engineers and a new field service manager support the overall turnkey efforts. “The focus at Wilmington Machinery is delivering the finished part. That means providing complete blow molding production lines that meet customers’ expectations, regardless of how demanding,” says Newman, a 20-year veteran of high output blow molding systems. “Innovations in multi-layer blow molding systems and materials have opened the door for cost effective conversion and package improvement opportunities that were not possible 5 years ago.”

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Blow Molding Process Comparison

Posted: April 7th, 2010

If you are new to blow molding or if you have been in the industry for 30 years, it can still be confusing as to what type of blow molding machinery or process is best for your next application. I have been fortunate in my career to design and build machinery for every type of blow molding process. For your information I consider there to be 7 primary machinery processes for packaging applications.

Shuttles (Continuous extrusion)
Wheels (Continuous extrusion)
Injection Blow
Injection Stretch Blow (1 Step)
Reheat Stretch Blow (2 Step)
Reciprocating screw (Intermittent extrusion)
Accumulator Head (Intermittent extrusion)

Some people may refer to them differently and some may argue several of these should be grouped together, but for sake of discussion, we will use this grouping. Further definition of the technologies, along with pros and cons for each process, can be found in the links above.

  Shuttle Wheel Injection Blow Injection Stretch (1-Step) Reheat Stretch (2-Step) Recip Screw Accumulater HD
HDPE Yes Yes Yes No No Yes Yes
PP Yes Yes Yes Sometimes No Yes Yes
PET No No Yes Yes Yes No No
PVC Yes Yes Yes No No No No
Styrene No No Yes No No No No
Multilayer / coinjection Yes Yes Difficult Difficult Difficult No Difficult
IML Yes Yes No No No Difficult Difficult
Handleware Yes Yes No No No Yes Yes
Injection Finish Good Fair Excellent Excellent Excellent Fair Good
In-machine Deflashing Yes No N/A N/A N/A No No
Flashless Process No No Yes Yes Yes No No
Small Bottle<100 ml

low/med vol.

Yes No Yes No No No No
Small Bottle<100 ml

high vol.

Yes Maybe Yes No No No No
Med. Bottle(1 litre)

low vol.

Yes No Yes Yes No Yes No
Med. Bottle(1 litre)

high vol.

Yes Yes No No Yes Yes No
Large Bottle(4 litre)

low vol.

Yes Yes No No No Yes No
Large Bottle(4 litre)

low vol.

No Yes No No No Yes No
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Blow Molding Process Comparison: Wheels (Continuous Extrusion)

Posted: April 7th, 2010

Rotary Wheel Blow Molding Machinery

The rotary wheel blow molding machines are the machine of choice for very high volumes of containers for markets such as liquid detergent and juice in North American markets. Wheels are typically chosen over shuttles because of processing ease (and cost) due to single parison technology and lower cost per container for high-volume applications. This is especially true for coextrusion and multilayer applications. Machines can be designed to handle a wide range of container sizes, but are typically committed to a narrow range of container variation after built. Because the containers are blow with a needle (instead of blow pin), it is not unusual to blow containers in a neck to neck configuration to increase the production output. Wheels come in various configurations including indexing, continuous motion, vertical (like a ferris wheel) and horizontal (like a merry go round). Some even now have the capability to produce calibrated neck containers, such as a reciprocating screw (Intermittent extrusion). Most, however, rely on downstream trimming equipment to trim and finish the container.

PROS:

  • Lowest cost method for high volume production requirements
  • Simple design and controls for maintenance
  • Single parison well suited for multilayer application for repeatability and cost
  • Easy to utilize IML
  • Can achieve very high production volume from a single machine

CONS:

  • Typically can not be converted to different number of cavities after being built
  • High investment requires commitment to high volume production situations
  • Requires secondary trimming and finishing equipment

Back to Blow Molding Process Comparison.

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