What is the focus on Pultrusion dies?

A pultrusion die should give a processor confidence that it will perform without fail to produce a quality finished product. Our goal is to optimize production line speeds, visual appearance and reduce scrap. We recognize that flow surface integrity is the single most important attribute a pultrusion die has to offer. Therefore, all aspects of manufacturing are tightly controlled including application of plating & polishing. We also continue to research and develop new coatings and materials that will benefit the process.

Why is surface finish important?

On a microscopic scale, the surface topography is a mountain range of peaks and valleys. The surface roughness average, Ra, is the average distance between these two points. Polishing reduces this distance and provides a truer molding surface with less resistance to flow. This results in faster pulling speeds with less force, without sacrificing finished product surface quality.

What materials are used?

The current proven design is a tough low carbon steel with a hard chrome surface. Both have advantages and disadvantages but this combination provides the most cost effective approach. Our most popular request is chrome plated 4140 prehard material. It is economical and has similar characteristics to P-20 but is not as inclusion free. We have also made dies from hardened and polished D-2, A-2, H-13 & 440C SS with and without flash chrome (.0005″ < .001″ thick). The harder materials have chrome in them at small percentages. When they are heat treated this chrome converts to carbides providing the hardness and some corrosion protection. Still, hardness ranges from 55 to 62 Rc (chrome is about 72 Rc) and corrosion protection is limited by the extent of the chromium carbide matrix. There are also surface treatments such as, ion nitriding, that provide some protection. There are several combinations of materials, treatments and coatings which when put together provide the processor with the best match.

Why are pultrusion dies hard chrome plated?

The internal surfaces of a pultrusion die are exposed to a highly abrasive and corrosive environment. Hard chrome plating provides a super hard, non-corrosive, non-reactive, low inclusion coating on the base metal. A generous coating thickness greatly increases finished product appearance and die wear life.

Why is chrome plating applied to the parting surfaces?

The parting line splits are the most vulnerable part of the die. Rough, chipped or otherwise damaged parting edges not only hampers performance and finished product visual appearance, but accelerates wear propagation resulting in premature die failure. Plating over the edge onto the parting surfaces strengthens the integrity of the edge to protect them during the process and handling under routine maintenance.

Do all chrome plated surfaces need to be ground?

Chrome does not plate evenly on the component without specially constructed anodes. However, when the component is suitably long or complexed or the thickness demands are at or over .001″ the thickness variance becomes more and more exaggerated. Since a bottleneck on components such as pultrusion or extrusion dies or sprues greatly reduces performance, the plating is ground to ensure dimensional integrity. Thicknesses about .0005″ plate much more evenly are are not subject to this scrutiny. The parting surface between pieces are always ground prior to assembly and the parting line edge is sharp and chip free.

Why use P-20 prehard mold steel?

Hard chrome plating quality benefits greatly by the choice of material it is applied. P-20 mold steel is engineered for inclusion free properties which improves the ability for chrome to adequately coat and thus protect the surface. Its middle range hardness (32- 34 Rc) give good machineable qualities but is tough enough to resist damage and absorb shock for incidental impacts. It is also easily repairable with weld and regrind.

Why is ground alignment preferred over dowel pins?

Die opening straightness and parallelism are important dimensional specifications. Without them it would be very difficult to maintain overall dimensional integrity. Ground features ensure extremely accurate, long lasting alignment throughout the length of the die. They also significantly ease assembly and disassembly for servicing without the risk of damage. Dowel pins are installed intermittently along the length. In most cases they can only be removed by hammering them out after the die has been in process for a period of time. Over time, the locating holes become damaged and their accuracy compromised. However, when dowels are used, we size the locating holes accordingly to allow for a smooth running fit to locate without hammers.

How long do our pultrusion die last?

We our commited to providing the lowest die cost per foot of output over its useful life. A good bench mark is a penny per foot based on a million feet. As of yet, we have not had a die that we built new returned to us for wearout repair.

Can Pultool provide resin injection features?

We have design and built high pressure resin injection as well as the more popular low pressure enclosed wet out sections. The success of resin injection is strongly influenced by profile configuration and the raw material used. Thicker cross-sectional areas and/or tighter packed reinforcing materials become more difficult for high pressure systems without special considerations.

What are our lead times?

Times will vary with complexity, however, we can typically ship 2 – 4 piece dies within 3 – 4 weeks upon receipt of order. In most cases, 6 week delivery is guaranteed.