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2 min read

Q&A – Do You Have Any Tips for Annealing Cast Acrylic?

By Dave Biering on August 15, 2018

Do You Have Any Tips for Annealing Cast Acrylic?

We recently had a customer ask us for some tips on annealing cast acrylic. There are definitely some potential pitfalls when working with acrylic in both sheet and finished part form, but following the guidelines outlined below should yield excellent results.

First… What is Annealing?

Annealing is the process of relieving stresses in molded or formed plastics by heating to a predetermined temperature, maintaining this temperature for a set period, and slowly cooling the parts. Sometimes, formed parts are placed in jigs to prevent distortion as internal stresses are relieved during annealing.

Tips for Annealing Acrylic Sheet

To anneal cast acrylic sheet, heat it to 180°F (80°C), just below the deflection temperature, and cool slowly. Heat one hour per millimeter of thickness – for thin sheet, at least two hours total.

Cooling times are generally shorter than heating times – see the chart below. For sheet thickness above 8mm, cooling time in hours should equal thickness in millimeters divided by four. Cool slowly to avoid thermal stresses; the thicker the part, the slower the cooling rate.

Wait until oven temperature falls below 140°F (60°C) before removing items. Removing a part too soon can offset annealing’s positive effects.

Tips for Annealing Parts Made from Acrylic Sheet

While annealing acrylic sheet parts, support them to avoid stress. For example, a part’s raised center section will need independent support – it can’t be supported from the ends. Lack of support may inhibit relaxation or cause warpage. Be sure parts are clean and dry before annealing. Remove paper masking to avoid baking it onto the material. Remove any spray masking, protective tape, or similar material. Plastic masking may remain in place.

For post machined acrylic parts - Heat to 180°F over a 2 hour period, hold for 30 minutes per each ¼” of thickness, cool at 50°F per hour until room temperature. This must be done in a nitrogen oven.

If the only fabrication you have done is surface machining and you do not need to anneal cemented joints, heating time can be reduced. This reflects the fact that machining forms stresses only at and slightly below the surface – the entire sheet thickness needn’t be annealed. Heat at least two hours; cool the same amount of time. If holes have been drilled entirely through the sheet, position the part so heated air flows through the holes.

What are your Material Fabrication, Machining, and Processing Challenges?

This post focused on a specific process for one material, but any product you work with is going to bring it's own challenges – and have a corresponding “cheat sheet’ that experienced engineers pull out to make it all go smoothly. Our engineering team has decades of combined experience and can provide this information. In fact, we’ve just launched an entirely new Enhanced Materials Division (EMD) to help people with just this sort of thing! We have a full suite of services and products to help you find the best, most cost-effective way forward.

Custom Plastic Fabrication: Get the Guide!

Topics: Q&A
1 min read

Turcite Materials – Common Applications

By Dave Biering on August 7, 2012

Q&A  Can you tell me about the acetal Turcite for industrial use?  What are some common applications?

Turcite™ is a family of materials made from both Acetal resins and PTFE.  The acetal-based Turcite products are known for exhibiting good strength and stiffness, dimensional stability, resistant to abrasion with very low stick-slip in dynamic applications.

Turcite A and X are the most popular of the acetal-based versions where copolymer resins are blended with low friction and wear additives.

Turcite A and X are common to many industrial applications since they are chemically inert to most solvents.  They are a good choice for enhanced extrusion resistance in dynamic load applications. 

The other side of the Turcite family are modified PTFE materials used for both bearing and seal applications. Turcite B is a popular linear bearing material for the machine tool industry and there are many Turcite grades used in industrial seals, wipers and wear rings for hydraulic and pneumatic cylinders, valves and other control devices.

 Ask Our Experts for more information on Turcite, or consult our Materials Database.

            ™ - Turcite is a registered trademark material from Trelleborg.

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Topics: Material Selection Q&A

Q&A: Which material do you recommend for small construction equipment? Our cast nylon bearings are not lasting as long as we’d like.

By Dave Biering on April 3, 2012

This question was posed to us from a manufacturer of small excavators, the kind you often see in the consumer rental market.  Cast nylon is a good material for farming and construction, but with some drawbacks when it comes to moisture absorption and UV stability.  Depending on where you use them, nylon is good for cable sheaves, but for pivot points, we recommend these materials for top performance.

Topics: Construction Q&A CJ Bearings Ultracomp
1 min read

Q&A: Treating Acrylic with Plasma

By Kevin Smith on February 28, 2012

Question:

We are attempting to bond two machined pieces of acrylic together to form a microfluidic device. I know that direct plasma bonding of acrylic won't work, but that plasma treatment of the acrylic can lead to a much better seal/bond when using an adhesive (e.g., epoxy).

Can you recommend a good starting place for a plasma surface treatment of acrylic, such as gases, ballpark power value, time, etc.?

Answer:

It is true that acrylic bonding is easily achieved via solvent and/or heat welding, but if the material is be bonded by applying a conventional cyanoacrylate or epoxy, a quick pretreatment with vacuum plasma can – as you mentioned – significantly improve the strength of the bond.  In the case of treating acrylic, the preferred treatment gas is oxygen. The power required is minimal as is the processing “plasma on” time.  It can be easy to “over process” some materials; this is true with acrylic.  The amount of time that the devices are processed in the chamber can depend on the type of system used, the amount of gas flow, and the load size.  For a full load of devices in a medium-sized chamber, a treatment time of 5 minutes should be fine; however, you should test random samples with a goniometer (or Dyne pens) to make sure that the treatment is uniform and effective.

Slight adjustments to power and time will help you optimize the process for your parts and volumes.

TriStar can assist in the plasma recipe development process; just contact us to discuss your application and production requirements.  As a side note, since you will be using pure oxygen as a process gas, it is important (from a safety standpoint) that your plasma system is equipped with a vacuum pump that is either a dry (scroll) or is lubricated with PFPE (Fomblin or Krytox) oil.  Vacuum pumps used for plasma systems should not be lubricated with conventional hydrocarbon oils if oxygen is used as a processing gas.

Do you have a question about bonding your application?  Our surface modification team can help find a solution!

Topics: Surface Modification Q&A
1 min read

Q&A: Is there a seal material that will operate at 600° continuously?

By Dave Biering on February 7, 2012

This question was posed to us from an aerospace client.   Temperature is always a big issue in aerospace, particularly in military aircraft and vehicles.  And continuously maintaining 600° can be a challenge, given that the materials that resist such high temperatures are usually more rigid.

TriStar has a range of high-pressure, high temperature seals available.   More details, including the key considerations to help you improve performance in seal material, are available in our video.  Or let us review your design specs, and we’ll help you match the right polymer to the right hardware.

Topics: Material Selection Q&A

Q&A: How do I identify which Rulon material I have?

By Dave Biering on January 24, 2012

With over 300 different types of Rulon available, this is a question that we hear quite often.  TriStar is the official North American distributor of Rulon, so we have the in-house experts to help you identify and source the right material for your application.

View our video to learn about identifying the three most commonly-used Rulon materials, or download our Rulon white paper now for more information.  At TriStar, we realize the best performance begins with the right material selection.

Topics: Rulon Materials Rulon Plane Bearings Q&A
1 min read

Which Plastics are Biocompatible?

By Dave Biering on December 21, 2009

Which plastics are biocompatible?

The growth of plastics in medical devices is growing exponentially around the world. Plastics are regulated like any other materials that may come in contact with human tissue or fluids and that usually falls under testing procedures issued under USP or ISO10993.

There are three time scales for biocompatible devices:

  1. Limited - Less than 24 hour exposure
  2. Prolonged - 24 hours to 30 day exposure
  3. Permanent -  30 days and longer.

When determining biocompatibility, devices are categorized as follows:

  1. Surface Devices - Items such as electrodes for monitoring, contact lenses, catheters, endotracheal tubes, sigmoidoscopes and similar devices.
  2. Externally Communicating Devices - such as laprascopes, blood administration devices, pacemakers, oxygenators and the like.
  3. Implant Devices - such as orthopedic pins or plates, heart valves, grafts, stents and similar devices.

Testing of these devices includes mechanical, thermal, chemical tests as well as systemic injection, intracutaneous and implantation. All of these must be done before a plastic component can be approved.

Typical materials for biocompatible applications include medical grades of PVC and Polyethylene, PEEK, Polycarbonate, Ultem PEI, Polysulfone, Polypropylene and Polyurethane.

For more specific information on biocompatible materials as well as special plasma preparation treatments of all of these materials, contact TriStar Plastics at www.tstar.com and visit our Video Learning Center.

Have a question about surface  modification? Ask our experts!

Topics: Surface Modification Q&A Medical
1 min read

Q & A: Can I use gamma radiation to sterilize a Teflon part?

By Dave Biering on December 7, 2009

The first part of the answer is we need to know what kind of Teflon. DuPont's family of Teflon products includes a number of different materials. PTFE is the best know of this family and the answer to your question for this material would be NO! PTFE does not hold up well at all in gamma radiation. As an example, 4Mrads of exposure reduces the tensile strength of the PTFE to 2% of it's original value.

A better fluoropolymer for gamma irradiation would be DuPon'ts Tefzel product which is known by the chemical moniker of ETFE. In vacuum or air irradiation, Tefzel maintains a high level of physical integrity after long exposures.

Another fluoropolymer that does well in gamma is PCTFE, formerly known as Kel-F. PCTFE has minimal property loss even after doses of 16-18Mrads of exposure. Rates of property loss in all main categories are less than 30% which is quite good for fluoropolymers.

TriStar Plastics has more information on different methods of sterilization and how it affects most medical grade polymers. Ask The Experts - you'll still like them when they're angry (but they won't be)!

 

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Topics: Surface Modification Q&A
2 min read

Q & A about Rubber Overmolding

By Frank Hild on August 3, 2009

Q: I have a question for you. We are anodizing some aluminum parts per Mil A 8625F, Type 2, Class I and it appears to be getting somewhat poor results. I wanted to get your take on this surface chemistry that we are trying to bond to. Here are some brief notes. Hopefully this is enough info for you to comment on.

Mil A 8625F, Type 2, Class 1Type II: Sulfuric Acid anodizing Class 1: This means that the anodize is not dyed or pigmented.

There is also a secondary operation of sealing:

per Mil A 8625F, Type 2, class 1, Section 3.8.1:

"When class 1 is specified, sealing shall be accomplished by immersion in a sealing medium such as a 5 percent aqueous solution of sodium or potassium dichromate (ph of 5.0 to 6.0) for 15 minutes a 90C to 100C, in boiling deionized water, cobalt or nickel acetate, or other suitable chemical solutions..."

We are trying to bond a peroxide cured silicone to this treated aluminum surface. I am not familiar with the sealing process as described above. Can you give me some insight on this?

A: Sulfuric anodize, commonly referred to as Type II anodizing, is formed by using an electrolytic solution of sulfuric acid at room temperature and a current density of 15 to 22 Amps per square foot. The process will run for 30 to 60 minutes depending on the alloy used. This will produce a generally clear coating, depending on sealing, a minimum of 8µm thick. One third of the coating thickness will build up per surface and 2/3 will be penetration. Sulfuric anodize coatings are often sealed to enhance corrosion resistance, lock in dyes, or both. Hot water seals produce the clearest sulfuric anodize while sodium dichromate yields a yellow-green appearance but is generally a better seal. Sulfuric anodizing is rather tolerant of aluminum alloys for anodizing with the exception of high-silicon die-cast alloys such as 380. The less alloying elements there are the higher the clarity and depth of color of the anodize coating.

The best adhesion is reached when each bonding aluminum atom carries a single reactive group. Even at room temperature, acetic acid or fatty acids can easily pass through a coating infiltrating chemical bonds by advanced attack and leading to adhesion failure. The aluminum atom progressive binds with reactive groups which then leave and the bond fails.

Hope that helps! If you want your questions answer - Ask The Experts!

Topics: Surface Modification Q&A