Three Preparation Steps For Part Design

So, you have a part you want made out of plastic (or rubber). You have a drawing, maybe a CAD file. You know what the part needs to do.

What now?

This is the stage where you need to make the leap from idea to practical. To get the part finalized, material specified, and actually get the part into production. What information do you need to have to finalize everything?

1.) Know Your Operational Environment

This is absolutely critical and something we often need to work through with customers before we make a recommendation. You need to know the complete operational environment for your part. This includes:

  • Min/Max operating temperature
  • Chemical exposure (and how much exposure to each chemical – it matters!)
  • UV-exposure
  • Pressure applied on the part (in PSI)

Depending on the part there may be other critical factors but you should know at least those four.

2.) Know Your Required Tolerances

This is perhaps the most important thing that keeps getting overlooked in part design. Often we’re handed a drawing with metal tolerances (+/- 0.001″) and told to make it (hint: not possible to hold those tolerances). Or, in many cases, customers simply tell us to hold “best” tolerances. Did you know there’s a premium to that? When we work out a quote internally, required tolerances are part of that because of the time and risk involved in hitting our tightest (+/- 0.005″) tolerance. Often a (+/-) 0.03″ is suitable for many applications and since it will save you money, it’s worth it to know the demands of your application.

3.) Know Your Quantities – Buy In Bulk

Quantity usually means price break when it comes to parts. Customers will often send us a drawing and ask that we quote a couple pieces, ostensibly as samples. The issue is that the cost for prototypes will be inflated compared to the prototypes…And sometimes customers just think the price would remain constant. So know an accurate number of how many parts you will need once in production and get both prototypes and production runs quoted at once for a clear picture of your costs.

For more information on how to buy your parts in the most economical way possible, please contact us today.

 

 

 

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Plastic Angle

Out of the many parts and plastic profiles requested of Redwood Plastics and Rubber, plastic angle keeps coming up. This is typically plastic bent at a 90 degree angle halfway. This is primarily used for protection of a surface or object if machined out of UHMW or nylon plastic. However, much stronger (more rigid) fiberglass reinforced plastic (FRP) angle is available and stocked by our supplier. A common example of a FRP angle application would be to bolt it in on the edge of a platform at a train station. FRP angle is available in a variety of widths and thicknesses with 1/4″ and 3/8″ thick being the most common. It is available in all three primary EXTREN resin types (general purpose polyester, fire-retardant polyester, and vinyl ester). These angle profiles are more expensive than steel or aluminum angle; however, for certain applications such as those that demand electric or radio non-conductivity, plastic angle may be your only choice.

To get a quote on an angle profile is easy. Firstly, we need to know the width of each side of the angle, they are not always the same! We then need to know both the thickness and the material required. If you need assistance selecting a material, just ask, but me sure to be ready to answer questions about your application such as what the angle is doing, if there is any chemical or high heat exposure, etc. Angle profiles of all plastic types are typically sold by the 10 foot length; however, there are cases where we can supply shorter or longer profiles.

For a quote on your plastic angle needs, please contact us today.

 

Space Shuttle Challenger and Rubber: A Cautionary Case Study

The space shuttle “Challenger” explosion in 1986 was a seminal moment for many Americans. The launch was shown on live TV and there was a high amount of interest in teacher Christa McAullife being on the flight. The shuttle exploded 73 seconds into the flight resulting in the deaths of the entire crew. An immediate investigation was launched and it was determined that a failed rubber o-ring system used as seals on the solid rocket boosters led to the explosion. The launch was on an unusually cold day – the o-ring seals were qualified for use at no less than 40 degrees Fahrenheit but the temperature got as low as 18 degrees Fahrenheit the night before.

Prior to launch several engineers attempted to warn against launching due to this reason. The engineers believed that the cold temperatures would weaken the rubber and also lead to a poor seal, which would allow hot exhaust gases to potentially escape the boosters and cause catastrophic damage. It had already been determined that the o-rings were being damaged even on successful flights. The engineers were forced by NASA management to try to prove that the application would fail at low temperature, something the engineers could not do because of a lack of testing data.

Your application with rubber will likely not be as critical as the space shuttle o-ring seals; however, even with our applications there is much to learn.

Firstly, is you need to pick a rubber that will work within the parameters of your application. You need to know what chemical exposure and temperature range the part will need to operate in.

Secondly, once you get the parts you need to use them within the parameters that you have specified because if you introduce, for example, new chemicals or operate the part outside of the prescribed temperature range, it may fail!

The third and final thing we can learn is to listen to the product experts who helped recommend a rubber solution to you. If they strongly believe a certain material is required and can give you concrete reasons, you should consider this thoroughly before going in another direction. This is particularly a concern where a desired price may be a determining factor for a purchasing decision, rather than if the rubber is actually suitable or not.

Redwood Plastics and Rubber has rubber experts standing by to help recommend the best product for your application so contact us today.

Weathering and Exposure Concerns

There is unfortunately some misinformation in the plastics world regarding weathering, exposure, and UV-resistance. In some cases where applications go wrong, customers simply did not consider how a certain plastic might handle being exposed to certain environmental factors. One of the largest pieces of misinformation is that reprocessed-black UHMW often called “UHMW black” is UV-stable. It is not; however, and has only some limited UV-resistance due to the addition of carbon black in the resin. The following are examples of weathering and exposure concerns for some popular plastics and options to mitigate these issues.

Nylon:

-Brittle in cold temperatures (below -15 degrees C)

-Absorbs water

Solution:

-Switch to acetal or Tuffkast

UHMW/Polyethylene:

-Poor UV-resistance makes it prone to cracking with UV-exposure

Solution:

-Procure a fully UV-stable grade

Polyurethane:

-Certain varieties weaken and break down in wet environments (hydrolysis)

Solution:

-Work with a plastics expert to select a polyurethane variety not weakened by hydrolysis

Polycarbonate:

-Poor weathering resistance, will yellow and crack with exposure

-Poor scratch resistance and tends to become cloudy with small marks when used in outdoor applications

Solution:

-Request sheets with UV stable and/or scratch-resistant masking. These will be typically unstocked.

 

 

 

 

 

 

 

 

 

Dura CRIB vs. Dura STAT

The two most popular products of our cribbing and blocking line are Redco “Dura Stat” and “Dura Crib”. Customers often request quotations on both, or confuse each product, but the differences are distinct and important enough to create a write up. The “Stat” is Dura stands for “static” it is designed solely for cribbed storage of equipment that is not dynamic, IE. no movement. An example of a Dura Stat application would be lowering an engine onto the cribbing for storage. The Dura Stat set up should not be moved after the load is placed.

It is very important for Dura Stat that what is being cribbed is loaded vertically. The product is not resilient to sheer pressure and could break. Also, as a non-interlocking product, there could be slipping issues as well. Dura Crib on the other hand, is meant to be stacked and is commonly available in interlocking forms it is designed to handle applications where there may be a little dynamic movement. An example of this application would have Dura Crib providing cribbing for a railway maintenance vehicle’s outrigger feet. The stack of cribbing will endure vibration and oscillation as the load shifts on the feet while the vehicle works.

For more information on our cribbing products please check out our First Responders literature available here.

Super-Crib

New Product: Foamlite P Polypropylene

We have a new product available in our mix: Foamlite P Polypropylene. This is a lightweight plastic that offers 30% weight savings over other materials commonly used in similar applications which include everything from tank cladding, washdown areas, cargo crates among many others. Additional benefits to the product include excellent chemical resistance, UV and moisture resistance. The product is weldable and adhesives can be used (this is not the case for all plastics). One of the better rules of thumb for Foamlite is to use it as a replacement for wood, where wood’s deficiencies (rot, moisture absorption, cracking) are unacceptable.

Important to know as well is this is a European manufactured product meaning it is manufactured under metric system measurements not the imperial system like most North American made plastics. The sheet is available in thicknesses from 6mm (approximately 1/4″) to 21mm (approximately 7/8″) and in one size only that is 2000mm x 3048mm. We are not stocking this product at our locations but bringing it in from our supplier as necessary, therefore a 1-2 week delivery is typical. Lastly, Foamlite is available in three colors: black, grey, and white only.

If you’re interested in Foamlite P Polypropylene please contact us today.

 

Budgetary Expectations And Lifecycle Cost

One of the most important topics that comes up in a plastic application are issues of cost, budget, and expectations. Most commonly the request we get is to provide a better better performing plastic at less cost. In the vast majority of situations, frankly, this is unreasonable. Plastics, like any quality product, generally follow the old cliche “you get what you pay for” and a better performing, longer-lasting, plastic will almost always cost more money. There are rare exceptions, for example everything being equal, reprocessed (“repro”) UHMW will actually outperform the slightly more expensive natural grade in wear applications specifically. However, these are very rare exceptions to the rule.

It is important to know your budget up front. If there is no ability to fund a higher priced solution you may simply need to make due. However, if you have room in your budget then we have some room to work. Most commonly, a premium grade of the same material would be suggested. For example, switching from reprocessed UHMW to Redco Titanium or Tivar 88. This is generally the first step to take as the premium product provides all of the properties of the lower grade, just much improved. For example, slicker, better wear properties, and UV resistance or weathering.

At times, the application may require a jump to a new plastic. For example, if a nylon part is failing due to being brittle in cold temperatures or moisture swell, then a switch to Redco Tuffkast may be in order. Similarly, most plastics cannot hold tight tolerances; however, acetal is perhaps the best at doing so and bears a similar load to nylon. Were a nylon part to fall out or be unable to retain tolerances, acetal would be an excellent substitute in most applications.

However, the most important point of all is this: selection of the optimal material for an application will almost always result in a lower lifecycle cost and therefore cost-savings. Reduced maintenance costs, replacement, and downtime, will all save the customer money in the long run. It is this critical factor which is often overlooked in the decision to switch to a premium grade of plastic or a more expensive, but ideal, plastic for an application!

For assistance in choosing the best grade or plastic for your application please contact us.