FAQ High Performance Engineering Plastics

FAQ High Performance Engineering Plastics

What’s the difference between Nylon 6, Nylon 66 and Nylon 101?

Nylon 6 is cast nylon. Nylon 6/6 is extruded. Nylon 101 is a brand-name of Nylon 6/6 (sometimes typed Nylon 66). Nylon 6/6 has the best resistance to chemicals, like gasoline and oil, better for machining, has lower water absorption and higher melting point. Nylon 6 has high molecular weight and improved dimensional stability due to the cast process. However, tolerance in thickness and/or diameter is not as tight as the extruded product.

What adhesive can be used on polyethylene?

It is not recommended to use adhesives on polyethylene as the material is inherently resistant to glues and other adhesives. It is recommended that polyethylene be mechanically fastened or welded.

How do you machine nylon?

Carbide tooling is recommended for machining nylon. If sawing a wide tooth blade should be used. If turning on a CNC lathe use high speeds of 600 to 900 ft/min.

Can plastic be heat sterilized?

For the healthcare industry there are two heat sterilization methods used on plastic: steam autoclave and dry heat. Steam autoclave is the most common. Plastics with service temperatures above 270-degree F are required, but dry heat sterilizers can be considerable higher. There are a number of polymers suitable for steam autoclave sterilization including PEEK, PPSU PSU, some acetal copolymers, PEI, HSPP (heat stabilized polypropylene), and a few others. Service temperature is key, and it is always recommended to test the process before a final decision is made as to which plastic is most suitable.

What is Delrin?

Delrin is a trademarked name for acetal resins, which are semi-crystalline thermoplastic resins. Acetal is appropriate for high wear applications and excellent for moist or wet environments. Acetal products excel in pumps, valves, and food processing equipment.

What is Ultem?

Ultem is an amorphous thermoplastic that is characterized by its amber to transparent appearance. It exhibits excellent impact strength, heat, solvent and flame resistance, mechanical properties and machinability.

What is Teflon?

Teflon is a DuPont trade name for PTFE which stands for Polytetrafluoroethylene. PTFE is one of the best materials for applications in the electric industry. It is also a very slippery material and the reason why many frying pans have a PTFE coating.

What is Kevlar?

Kevlar is a tradename of a synthetic fiber material created by DuPont. Kevlar is a plastic product with a chemical structure of poly-para-phenylene terephthalamide.

Is there a plastic stronger than metal?

While it is difficult for plastics to achieve the strength of metals, some modified plastics actually have better strength when comparing weight ratios. The most common of these would be carbon-filled or reinforced plastics. A good example would be 60% woven carbon fiber filled PEEK, whose strength vs. its weight is greater than most metals. Many of us have seen prosthetical legs used by amputees, particularly athletes, with curve-shaped blades at the bottom to simulate the feet. These can be made of metal or a woven carbon-fiber filled polymer (PEEK or an epoxy are common). Both do very well, but because of the lightweight characteristics of the plastic, it is preferred over metal. Thin cross-sections of these reinforced polymers also exhibit great flexibility.

What is standard tolerance on cut-to-size plastic?

A standard tolerance is +/- .060. Many factors play a role in determining a true tolerance for a part including, and more importantly, the material being cut.

What’s the difference between HDPE and UHMW?

Both are in the olefin family and semi-crystalline. UHMW is an ultra-high molecular weight polyethylene and because of that it has the best coefficient of friction and wear properties of most standard plastics. HDPE can be heated and bent and heat formed and welded. UHMW can be heated and bent in some instances, but this is not standard due to the high molecular weight. UHMW has the best coefficient of friction and wear properties of most standard plastics due to its molecular weight. UHMW is a denser polyethylene and preferred for parts in sliding applications where overcoming friction is critical. UHMW is easier to machine but offers better wear and abrasion resistance and lower coefficient of friction.

What kind of material is phenolic?

Phenolics are thermoset materials, as opposed to thermoplastics, which means the only way to change its shape is to machine it. Thermoplastics shape can be changed by heat. Phenolic materials come in many different grades, like X, XX, XXX, XP, C, CE, L, LE and than all the glass filled grades G3, G5, G7, G9, G10, G11. All are thermoset and all have different properties. The green panel inside many of today’s electronics is a phenolic grade material known as G10.

Is plastic waterproof?

Yes, most plastics are waterproof. There are some porous material made, but most are waterproof due to the way the polymer chains form together.

What plastic should not be cut with a laser?

Do not cut fluorine- or chorine-based material in a laser cutter. It will damage the equipment and it will emit dangerous fumes into the air. Before cutting a material, consulted the manufacturers SDS sheet to confirm material makeup. Materials that are commonly cut with a laser cutter are acrylic, acetal, polyester and polypropylene.

What is the difference between virgin and reprocessed plastic?

Virgin plastic is the manufacture of product using direct resin that has never been used or processed before. Reprocessed (often called repro or regrind) is plastic made from either post-consumer or post-industrial recycled material and may contain higher levels of contaminants, which might yield imperfections.

Why are metal detectable plastics usually some shade of blue?

Metal detectable PEEK, Nylon, UHMW, Acetal are produced in blue to differentiate them from their standard versions. This helps to avoid using a costlier product where it isn’t needed. The color also lends another layer of protection because it makes it easier to see shards that break off in food processing applications.

What does USP Class VI material mean?

USP Class VI is a designation that determines the biocompatibility of a material for use in medical devices. In plastics, Class VI compliant materials are commonly referred to as implantable grade (long term and short term), such as PEEK.

What is the difference between amorphous and semi-crystalline plastics?

Amorphous have no patterned order. Semi-crystalline have closer patterned and tighter packed molecules. Amorphous have lower melt points and heat resistance. Most see through plastics and formable plastics are amorphous. Semi-crystalline have higher heat resistance, are more opaque and have higher dimensional stability. Most engineering plastics fall into the semi-crystalline category.

How do you identify plastics?

A common way to identify a plastic material is through a flame test. The color of flame, odor, if it continues to burn after removal of heat source and whether it drips can all be used to identify the material. For instance, Nylon 6/6 burns blue, may smell like burnt hair and will drip. Acetate burns yellow, may smell like vinegar and will not drip. Also called a burn test, there are tables available online that break down the various burn characteristics.

What is the specific gravity of PE and PP and why is this important?

Less than one and one is the specific gravity of water. PE and PP will float because they are lighter than water.

What is Tg and why is it important in plastics?

Tg stands for glass transition temperature. This is the temperature where the properties of the plastic start to degrade. For thermoplastics, the Tg is where the material starts to get soft and rubbery. When selecting a thermoplastic for a specific application it is important to consider its Tg, as well as heat deflection temperature.

What material is used for concept prototyping?

High density polyurethane board (HDU) is a closed-cell foam board available in large blocks and sheet thicknesses and used for larger-scale prototypes, models and proof-of-concept designs of vehicles, furniture, boats, appliances and other equipment. The material can be machined to close tolerances, giving a design a light-weight, real size, low cost finished part. HDU is considered easier to work with than MDF (medium density fiberboard).

Why is nylon used to make bearing and bushing?

The use of nylon as a bearing and/or bushing means part does not need external lubricant. Nylon has a low co-efficient of friction as well.

What is centerline porosity with acetal and why is it important?

Acetal homopolymer (Delrin) can have centerline porosity due to the material cooling while being manufactured. The outside cools first, creating a line or small voids in the center of the material. This can result in gas leakage in an application or creates an environment where bacteria can grow in food processing or medical applications. Acetal copolymer typically does not have centerline porosity.

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