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Frequently Asked Questions

Frequently asked questions from the world of engineering plastics can be found here.

 

Q: Why Plastic?

A: Low density
Low weight
Good noise and vibration damping
Electrically insulating or adjustable conductivity
High freedom of design
Highly efficient mass production
Permeability for electro-magnetic waves
Very good corrosion resistance
Thermal insulation
Application specific modification possible

 

Stock Shapes

Q: What is meant by short-term service temperature?

A: The short-term service temperatures are the short-term peak temperature values that the plastic can withstand for a period of minutes or sometimes even hours without the plastic being damaged, taking into account the load and its duration.

 

Q: Which plastics are resistant to UV light?

A; Fluoropolymers such as PVDF and PTFE provide good to very good UV protection. Black plastics (with carbon black, MoS2, graphite, carbon fibres) provide relatively good protection.
In colours other than black and for plastics with particularly high requirements, protection is achieved through the use of additional UV stabilizers. We can supply these products as special productions with minimum order requirements.

Recommendation:
For most applications reliable protection is achieved with PVDF or black plastic. For critical applications please consult us regarding increased effective protection.

 

Q: Can UV light damage plastics?

A: The majority of plastics in their natural state are damaged by the different wavelengths of UV light (UV-A, -B, -C). The damage depends on the duration and intensity.

 

Q: Which plastics are stable in hot water and suitable for frequent and repeated sterilisation?

A: The following plastics are suitable for hot steam sterilisation with different behaviours

DIN- Abbreviation

Resistance to stress cracking

PVDF

++

PTFE

+++

PSU

( - )

PEI

( + )

PES

-

PPSU

+

PPS

+++

PEEK

+++

+++ = very good (no danger of stress cracking)

++ = good

+ = average

(+) = sufficiently good (danger of stress cracking)

 

From +++ to (+) the material sensitivity to sterilisation and the number of cycles decreases because of the increased possibility of stress cracking.

 

Caution with sterilising.

 

Please avoid internal stress and critical chemicals.

 

 

Q: Which plastics are most wear resistant and suited for sliding applications?

A: In general the semi-crystalline materials offer good wear resistance and are therefore suitable for moving parts such as wear strips, bushes etc.

These include: -

Standard / Engineering materials

Polyolefines. PP and PE HD and, in particular, UHMW PE offers excellent abrasion resistance particularly to slurry.

Extruded PA (Nylon) and cast nylon have good wear and abrasion resistance and also good impact resistance. It is necessary to allow for water absorption. MoS2 is used as an additive to improve the crystallinity which gives a harder surface and improved wear resistance. Most nylons will run dry but life is considerably improved by initial lubrication on assembly.

POM (acetal) offers good wear, low water absorption and excellent fatigue resistance.

PET (Polyester) has wear and abrasion resistance comparable to nylon. More dimensionally stable with negligible water absorption. Has good electrical insulating properties.

High performance materials

If high sliding speeds, surface pressure and temperatures occur singularly or together then high performance materials are necessary

PPS is an optimised bearing grade. Competitive transition to high temperature materials.

PEEK offers good all round properties. PEEK bearing grade has optimised tribological properties. Wear, friction, abrasion resistance.

PAIbearing grade. Good wear resistance. For low friction and high compressive strength.

Vespel SP21 etc. A very high performance bearing material. Exceptional wear resistance and compressive strength.

 

Q: Can the values for the coefficient of friction and abrasion serve as design fundamentals?

A: Friction and abrasion values serve as orientation for the comparison of materials in a tribological system. The values have been determined under laboratory conditions with the defined test parameters of a plastic friction element in a dry condition moving against a sliding steel disc. As soon as one or several of the test parameters change, the results change to a different value and an unforeseeable direction. They will usually deviate from the corresponding specific application. Please contact us if you would like to discuss your specific applications.

 

Q: What is the difference between PET and PET-P?

A: The standards abbreviation for Polyester Terephthalate is PET.
Historically, some suppliers of Polyester Terephthalate included a "P" (phthalate) in the abbreviation.
Thus, some suppliers refer to PET as PETP. In summary: PET = PETP

 

Q: What are the tolerances for cast nylon tubes?

A: The tolerances are selected so that there is sufficient material on outside, inside diameters and length so nominal dimensions can be achieved during machining.

 

Q: What is the difference between extruded PA 6 and cast polyamide PA 6 G?

A: The main difference lies in the manufacturing process. Cast polyamide products are manufactured by means of a chemical reaction process. This allows products with extremely large dimensions and custom cast parts to be manufactured. Water absorption and dimensional changes are lower in PA6 G. The crystallinity is greater so that wear resistance and machinability are better. Extruded PA 6 absorbs more moisture and is thus tougher and has greater impact and vibration damping properties.

 

Q: What is meant by long-term service temperature?

A: The long-term service temperature is defined as being the maximum temperature at which plastics can be kept in hot air for 10,000 and 20,000 hours without losing more than 50% of the initial values for their typical properties.

 

What materials can handle 200° C and higher for long periods of time?

DIN- Abbreviation

Long-Term Service Temperature (°C)

Short-Term Service Temperature (°C)

PPS

230

260

PTFE

260

260-280

PEEK

260

300

PI

300

350

For an explanation of the concepts of long-term service temperature and short-term-service temperature see that section.

 

Q: What effects do glass and carbon fibre additives have on plastics?

A: The initial aim is to increase values for strength and rigidity, especially at high temperatures. The plastic becomes harder and has lower elongation, i.e. it is less elastic and breaks when strained. Improved dimensional stability and tighter tolerances can be achieved. The coefficient of thermal expansion is significantly lower. In some cases there are similarities with aluminium or steel. During machining operations the fibre additives cause increased tool wear.

 

Q: Are plastics affected by high-energy radiation such as X-ray and gamma radiation?

A: High-energy radiation damages plastics in a certain way. POM and some fluoroplastics such as PTFE are particularly sensitive.

 

Q: Can black plastics be used for electrical insulation?

A: Black plastics have black pigments based on carbon black, graphite, MoS2 or carbon fibres, which are electrically conductive in their basic forms.
Recommendation:
We can manufacture black, electrically insulating plastics using special black pigments in a special production process

 

Q: Which plastics are particularly resistant to solvents - alcohol, oil, grease and fuel?

A: The resistance of semi-crystalline plastics to the above-mentioned group of solvents is greater than that of amorphous plastics: PA, POM-C, PET/PBT, PBT, PPS, PEEK

Recommendation:
Please see the "Chemical resistance" table or contact us. We would be pleased to help you.

 

Q: What information is available concerning the chemical resistance of ENERGETIC plastics?

A: Chemical resistance is affected by a multitude of factors. Typical factors are the chemical (or a mixture with its major constituents), its concentration, the reaction temperature and duration, the pressure and additional factors such as stress conditions or the sliding stress.
Recommendation:
Guidance regarding room temperature information can be found in the list on chemical resistance in the ENSINGER brochure "Engineering Plastic Properties and Processing Guidelines".
On request, we would be glad to give you further information if you provide us with the above-mentioned details. Information on chemical influences and effects is merely for orientation purposes and must be verified by practical tests under real application conditions.

 

Q: Which plastics are easy to bond?

A: All amorphous plastics are easy to bond, e.g. PC, ABS, etc.
Recommendation:
When selecting an adhesive please take into account the sensitivity to stress cracking.

 

Q: What materials are USP Class VI Biocompatible?

A: We are happy to discuss suitable materials. Please contact us.

 

Q: What are the different UL 94 flammability ratings?

A: In the laboratory plastics are tested according to UL94 for flammability. They are assessed as horizontal burning (HB) or vertical burning (V) according to their fire behaviour.

 

 

Self Extinguishing

Test position

HB

V-2

V-1

V-0

Drips, melts with transfer of flame

Yes

Yes

No

No

Burning time (sec)

 

25

25

5

Burning time up to extinction (sec)

 

30

30

10

 

Q: Which materials are suitable for permanent food contact in accordance with FDA?

A: V-0 = self extinguishing, shortest burn time, highest safety
V-1 = self extinguishing, extended burn time, good safety
V-2 = self extinguishing, extended burn time, drips, melts could transfer fire, restricted safety
[HB] = non self extinguishing, good combustibility, [Burn time not defined).
Not for use with high safety requirements

 

Which is better for use in contact with hot water, POM-C or POM-H?

Permanent contact of POM-H with hot water over 60°C must be avoided.
POM-C is more resistant to hot water and chemicals.

 

Q: What is the difference between acetal homopolymer (POM-H) and acetal copolymer (POM-C)?

A: Copolymer and homopolymer acetals are very similar in many characteristics. However, there are some differences, e.g. POM-H has higher mechanical values, better wear resistance and is better for use in tribological applications (friction and wear). POM-C has better chemical resistance.

 

Machined Parts

Q: When is it necessary to anneal material during machining?

A: Most of ENERGETIC materials are annealed to remove stress. However, where large amounts of material are to be removed or tight tolerances required it may be necessary to interstage anneal material during machining operations. For details please contact us.

 

Q: What precaution should be taken when cutting or machining glass reinforced materials?

A: Fibre-reinforced materials, for example glass or carbon fibre reinforced, tend to have residual stresses which are reduced by annealing. When cutting, drilling in the centre or machining, new stresses can be introduced and these can lead to cracking.
Recommendation:
Please follow the ENERGETIC’s machining guidelines:
We suggest heating these products at 120° C for 1 hour per 3/8" of cross-section prior to cutting or drilling.

We are specialist in finished parts and would be pleased to manufacture your machined parts.

 

Q: Why do cracks form in some material when machining?

A: When machining polycarbonate, ABS, PMMA, it is possible that after a period of time cracks are present that are not detectable at the time of machining. This is due to the existence of a natural sensitivity to stress cracking in conjunction with unfavourable machining conditions.
Recommendation:
When machining these materials, use air-cooling when possible or, if desired, use a water coolant. Coolants other than pure water may cause stress cracking due to chemical attack. Also, when carrying out extensive machining, you should machine in steps and perform a stress-relieving operation after rough machining.

We are specialist in finished parts and would be pleased to manufacture your machined parts.

 

Q: Which plastics require special conditions when bonding?

A: Because of their non-polar surface, some semi-crystalline plastics e.g. PE, PP, POM, PVDF and PTFE are very difficult and expensive to bond. Their adhesive strength is very low; therefore, in general we do not recommend bonding these plastics.
Recommendation:
For these plastics we suggest alternative assembly techniques such as snap fits etc.

 

Building Profiles

Q: My profiles are 'bubbling' after painting and curing. What is causing this?

A: This is likely to be caused by a high moisture level in the profiles or an excessively high curing temperature(or a combination of both).

Please contact us for more information.

 

Q: How should the building profiles be stored?

A: Indoors, out of direct sunlight and in dry conditions.

 

(FYI) Other About Injection Moulding

Q: What is the maximum weight moulded?

A: The maximum weight is between 800 - 1,000 grams.

 
     
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