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TECHNICAL DETAILS

 STAPP molding capabilities:

  Material Properties

Durable and Abrasion-Resistant
High Strength
Wide Range of Densities
Easy to alter with tools
Insulative
Waterproof
Solvent Resistant
UL Rateable
NSF Approvable
X-Ray Transparency

 Mechanical Features

Threaded Inserts and Studs
Cast Threads, Internal and External
Pilot holes & specialty pockets/sockets
Reinforcing Inserts
Encapsulation
Bosses
Thick and thin-walled sections
Zero draft and undercuts
Close Dimensional tolerances
Precision mating parts

 Cosmetics

Coloration
Decoration
Surface detail
Logos/signage

 

STAPP molding limitations:

Large, simple parts
Wheels and rollers
High performance physicals
High temperature
Clear, translucent
Weld, thermal or solvent

 


 

MATERIAL PROPERTIES

Polyurethane can be hard or soft, flexible or rigid, light or heavy, all depending on its chemical formulation. There are many specific off-the-shelf systems on the market. But by custom formulating in-house, we are able to think in terms of a spectrum of properties, infinitely variable within certain boundaries. Here are some of the things you can do or have, depending on how we formulate your material:

DURABLE & ABRASION-RESISTANT

HIGH STRENGTH
Even though polyurethane doesn't have as much tensile strength as a high-performance thermoplastic, like nylon, it can usually be made to accommodate harsh physical demands because of its extreme versatility. Strategic design utilizing sound structural geometry, thicker sections, and/or ribbing can produce dramatic results. Plus, there's a whole realm of encapsulated reinforcing inserts, including metal forms and fiberglass.

WIDE RANGE OF DENSITIES
Parts can be molded as light as 2 pcf, as heavy as 70 pcf, or anywhere between, just by controlling blow. But we can go quite a bit heavier yet. By adding high density fillers we can mold parts in excess of 150 pcf. And, of course, there's always the option of embedding a chunk of metal for even greater weight.

EASY TO ALTER WITH TOOLS
Cut with ordinary saws
Grind / sand
Drill
Tap threads
Machine with mill or lathe
Screw, nail, staple into

INSULATIVE
Polyurethane foam has more R value per inch than almost any other substance. This property is commonly put to use in the construction industry, with sprayed-on foam and cast sheets. But it can also be advantageous in certain molded parts.
(Polyurethane is also electrically insulative, as are most other polymers. But that usually goes without saying. What is worth saying is that, for some applications, it can be made mildly conductive.)

WATERPROOF
Won't rot or rust (good replacement for wood or metal)
Won't get waterlogged

SOLVENT RESISTANT
Some polymers dissolve in common solvents (like lacquer thinner, gasoline, acetone, etc.), some don't. Polyurethane is extremely resistant to most solvents, so applications involving exposure to, containment of, or immersion in a volatile solvent are no problem.

UL RATEABLE

NSF APPROVABLE

X-RAY TRANSPARENCY


 

MECHANICAL FEATURES

Polyurethane is a design engineer's dream-come-true. No matter how creative, artistic, exotic, or downright bizarre the thing you're trying to do is, our answer is almost always, "Can do!" Here are some of the basics:

THREADED INSERTS & STUDS
Threaded inserts and studs can be applied as a post-molding operation (which is pretty good when you consider that urethane is not a thermoplastic). But these things can also be molded right into the part, providing the ultimate in strength, and many, many more choices of fasteners.

CAST THREADS, INTERNAL & EXTERNAL

PILOT HOLES & SPECIALTY POCKETS/SOCKETS

REINFORCING INSERTS
Metal forms, stampings, weldments
Fiberglass and other fibrous materials
Custom cast parts

ENCAPSULATION
Since STAPP molding is done at relatively low temperatures and pressures, there is almost no limit on what can be safely encapsulated. And parts can be fully encapsulated, or stick out in one or more places. Seal and protect delicate electronic & mechanical equipment and components while simultaneously molding finished surface features. Make another product, fitting, or material integral with your molded part.

BOSSES

THICK & THIN WALL SECTIONS
This is one of the really big advantages of STAPP molding over injection molding-- you never have to worry about slink marks or warping when combining thick and thin sections. Mold a big thick boss behind an 1/8th inch panel if you want. There won't be any dip in the front to give it away.

ZERO DRAFT AND UNDERCUTS
This is another major advantage. Our tooling utilizes both rigid and flexible materials, often combined within the same mold. Even severe undercuts can often be molded seamlessly in a part without special coring.

CLOSE DIMENSIONAL TOLERANCES
On critical dimensions we can typically hold +/-.001"/inch.

PRECISION MATING PARTS
Slip fits
Press fits
Snap fits
Interlocking parts
Precision alignment


COSMETICS:

COLORATION
The natural color of polyurethane varies from off-white to dark brown. A molded part can end up almost any desired color through the use of one or more of these three principle coloration techniques:
Pigmentation--coloring the urethane compound itself
In-mold coating--a film sprayed into the empty mold that becomes integral with the surface of the molded part.
Post-painting--conventional painting of the finished molded part.
Polyurethane can be pigmented with almost any color, including fluorescent (Day-Glo) colors, and even be made to glow in the dark with phosphorescent pigments.

DECORATION
Painting
Uniform color, various texture techniques
Masked patterns, designs
Hand artistic painting
Staining / antiquing
Silk screening
Decals / transfers

SURFACE DETAIL
Virtually any kind of texture can be molded in. The mold surface is cast against a pattern, so any texture we can put on a pattern can end up on a molded part. Splatter textures and leather textures are the most common, but the possibilities are only limited by creativity. Molds cast from a wood pattern can produce amazingly realistic imitation wood. Stone & masonry surfaces can be use to create interesting decorative effects. Even body contours and skin textures are reproducible.

LOGOS / SIGNAGE
Lettering and designs can be raised or recessed.


LIMITATIONS

As versatile as STAPP molding may be, there are still some things it is not well suited for:

LARGE, SIMPLE PARTS
Polyurethane raw material isn't as expensive as some plastics, but that doesn't mean it's cheap. If a large part can be made out of a less expensive material, chances are it should be. The advantage of STAPP molding is in being able to make detailed or complex shapes without all the labor that would be involved in fabricating or machining, and without a huge financial investment in tooling. Things like broomsticks, table tops, plastic 2x4's, etc. don't involve any exorbitant efforts to get them into those shapes, so there is usually no reason not to make them out of something cheaper, like wood.

WHEELS & ROLLERS
There are some types of polyurethane with special physical properties that can't be processed at low temperatures and pressures, and consequently require special machinery and handling. Wheels and rollers are usually made of such materials. Consequently, we leave that production to the manufacturers who have chosen to specialize in it.

HIGH PERFORMANCE PHYSICALS
A properly designed polyurethane part can offer outstanding performance in many high physical applications. But you can't squeeze blood from a turnip, and you can't get 12,000 psi tensile strength from a molded urethane part. If you need something as strong as nylon, and you have no room for reinforcements or geometry modifications, you're pretty much stuck with thermoplastics, and either fabrication or high tooling costs.

HIGH TEMPERATURE
How much heat a material can withstand varies depending on how the heat is applied, for how long, and what you want from the material at elevated temperature. Urethanes usually have no problem at 1200F, and are often used in applications that may intermittently see temperatures of 1500F or more. But if you need a part that has to function in an environment that is usually over 1800F, you probably shouldn't be using urethane.

CLEAR, TRANSLUCENT
It's not that clear urethanes don't exist. But they tend to be very pricey. And if the application involves UV exposure, there's an added challenge, since the methods normally used to protect urethane from UV degradation-- high pigment loading or opaque coatings--obviously defeat the purpose of letting light through. And if you want optical clarity, you're talking about highly polished mold surfaces that aren't compromised by uneven films of release agent. Everything considered, we've chosen to avoid clear urethane molding.

WELD, THERMAL OR SOLVENT
There are numerous ways to attach two or more molded urethane parts together, but welding is not one of them. Urethane isn't a thermoplastic. It doesn't melt and resolidify, so you can't thermal weld it. And it is impervious to virtually all solvents, so you can't solvent weld it. There are several good adhesive choices, though.

 

 

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