Seal Selection and Thermal Expansion

Thermal Expansion
Thermal Expansion

Doug Sharpe
President of Elasto Proxy

In my last blog entry, I recommended grabbing a cup of coffee before diving into this week’s discussion about the coefficient of thermal expansion. Yes, the caffeine will help if you prefer explanations over calculations. But our topic this week is less about math and more about the physical properties of elastomers. Let me explain.

To choose the right compound for your sealing application, you need to know how that material will perform at specific temperatures. Physical properties such as modulus of elasticity are important, too, but let’s stick to temperature while you’ve got last week’s blog entry in mind and a hot cup of coffee in hand.

Elastomers and Changes in Temperature

All elastomers have a coefficient of thermal expansion. Simply put, this value describes how the material changes in length, area, or volume with changes in temperature. In the case of rubber door and window seals, linear expansion is important because it helps to predict how a change in temperature will literally lengthen or shorten the seal.

Let’s consider two examples, both involving a rubber door seal and a metal door frame. At high temperatures, the rubber seal expands more than the metal frame. At low temperatures, the seal contracts more than the surrounding metal material. So what happens if you choose the wrong rubber? The door may not shut if it’s hot, or may admit wind and weather if it’s cold.

Now think back to last week’s blog entry, in which we learned about tractor trailers that make northbound runs from Miami to Montreal. For drivers and vehicles alike, the temperature changes can be extreme – especially during winter. If a rubber door seal is made of a compound that can’t handle these changes, the seal may fail and jeopardize the load.

Temperature Range and Temperature Change

Seal performance isn’t just about temperature range then. To select the right compound, you must also consider temperature change – how the rubber reacts when the temperature rises and falls.

Take a look at the chart below. The data required some conversions – and some may quibble with the math – but our takeaway here is simpler than the calculations. As you can see by looking at the right-hand column, all rubber is not the same when it comes to temperature changes!

Thermal Expansion

Material Thermal Stability X10-6mm/°C
EPDM 150° C 160
NBR 120° C 230
SBR Ambient 220
Silicone Ambient 2.5
Urethane 100° – 150° 180
Neoprene 130 – 150
Teflon 230 50 – 80

Table 1: Some Common Elastomers and Their Coefficients of Thermal Expansion

For more information, including the coefficient of thermal expansion calculation itself, please visit the National Physical Laboratory. Another good on-line technical resource is Rubber as an Engineering Material: Guidelines for Users.

Feeling Stressed Out?

Don’t spill your coffee, but the relationship between elongation and temperature isn’t always so straightforward. For starters, elastomer elongation increases over a specific temperature range and then decreases at still higher temperatures.

Then there’s something called the Joule effect, which occurs only when an elastomer is under tensile stress. The easiest way to explain this is to imagine a rubber band suspending your coffee cup. If you warm the elongated rubber band with an infrared lamp (your desk lamp, perhaps), the rubber band doesn’t expand. In fact, it retracts to support the load.

Choose a Partner – Not Just a Provider

Experimenting with rubber bands and coffee cups makes for a fun science project (and perhaps a coffee-stained desk), but our job at Elasto Proxy is to help you choose the right sealing solution for your specific application. By analyzing all of your application requirements and listening to all of your needs, we can offer answers to your sealing questions – and not just explanations of coefficients and calculations.

For over 25 years, Elasto Proxy has provided sealing solutions to partners in a variety of industries. How can we help you? Please comment below, or contact us at our website today.

Seal Selection and Service Temperatures

Service Temperatures
Service Temperatures

Doug Sharpe
President of Elasto Proxy

Did you have a cup of coffee this morning? How about a glass of orange juice. If you enjoyed either of these beverages, thank a trucker. Each day, the commercial trucking industry moves billions of dollars’ worth of commodities between the United States, Canada, and Mexico. For long-haul truckers who drive from places like Miami, Florida to Montreal, Canada, the trip lasts days and involves extreme changes in temperature – especially during the winter months.

For driver and vehicle alike, temperature changes can be challenging. Tractor trailers contain plenty of rubber and plastic parts – not just the tires. If a door or window seal is made of a compound that can’t handle hot or cold temperatures, the seal may fail.  Farmers, road crews, and construction workers face this problem, too, even though their vehicles travel much shorter distances. Outdoor temperatures can rise and fall rapidly, so makers of mobile specialty vehicles also need dependable sealing solutions.

Service Temperature of Elastomers

Rubber softens at high temperatures and becomes hard as a hockey puck at low temperatures. Many different elastomers are available, so how do you choose the right rubber for your sealing application?

With outdoor products such as door and window seals, you need to consider the service temperature for starters. This chart from our website lists temperature range for various types of rubber.

Material Compound Minimum Temperature Maximum Temperature
SBR -85° F +158° F
Natural Rubber -85° F +158° F
EPDM -80° F +300° F
Neoprene -65° F +225° F
Nitrile -55° F +275° F
Urethane -70° F +250° F
Silicone -180° F +525° F
Viton -40° F +500° F

Service temperature isn’t the only factor to consider, of course, but let’s start with the basics.

Rubber Seals at Low and High Temperatures

At low temperatures, elastomers do more than harden. They become less flexible. If they reach their brittle point, they may even crack. That’s what happened to the rubber O-rings on the Space Shuttle Challenger in a 1986 tragedy that claimed the lives of seven astronauts. NASA officials believed the seals were suitable for cold weather, but the O-rings were unable to withstand sub-freezing temperatures.

The weather at Cape Canaveral, Florida was unusual on that day, more like Montreal than Miami. But high temperatures can also cause seals to fail.  When the temperature of an elastomer approaches its upper service limit, the rubber may undergo chemical changes that are irreversible.

With each 10° C (18 °F) increase in temperature, the rate of some chemical reactions doubles. Again, consider the case of a trucker who is northbound bound from Miami to Montreal in the middle of a (typical) winter. If extreme cold will reduce the life of a door seal that’s helping to protect a valuable shipment, isn’t the cost of a compound with a wider temperature range a sound investment?

Elastomer Performance and Predictability

Even if a seal doesn’t fail, elastomer performance becomes less predictable when rubber reaches the limits of its service temperature range. So does that mean that we can predict how a compound will expand, contract, and recover with changes in temperature? Yes, but this is why there’s more than just temperature range alone to consider. Each material handles these changes differently.

In my next blog entry, I’ll discuss a concept called the coefficient of linear thermal expansion. So drink your orange juice – and grab a cup of coffee – before trucking over next week. In the meantime, do you have any questions about seal selection and service temperature? Please let me know by commenting below, or connect with me on LinkedIn.

One-Stop Sourcing Means More Than Supply Chain Strengths

Clyde Sharpe
President of International Sales, Elasto Proxy

Supply Chain Strengths
Supply Chain Strengths

Does your company have too many suppliers? How well do you understand the capabilities of each of your vendors? These questions seem separate, but they’re interrelated. Your answers can benefit your own buyers and managers, as well as the suppliers who serve them.

Traditionally, manufacturers divided purchases among many different vendors. Buyers focused on supplier prices, but without understanding the internal costs of maintaining a large vendor base. Tracking a multitude of purchase orders, invoices, and deliveries wasn’t the only challenge, however. Quality and reliability suffered if buyers didn’t fully understand what suppliers could and couldn’t do.

When buyers reduce their supply base, they strengthen their supply chain. At the same time, suppliers who offer one-stop sourcing can also increase business. This is good for them – and good for you, too.

Reducing the Vendor Base

Reducing the vendor base is a principle of lean manufacturing, a set of production practices that seeks to eliminate waste and deliver quality products on-time, at the lowest production costs, and according to customer needs. Companies that apply lean principles to their purchasing practices buy from fewer and more dependable suppliers, developing partnerships and building trust.

Lean buyers take the time to fully understand each supplier’s capabilities. Lean managers understand that “value” means more than low prices, and seek suppliers who can help improve quality, enhance functionality, and reduce costs.  So how lean is your company’s procurement process?

Strengthen the Supply Chain

Businesses that reduce their vendor base strengthen their supply chain, as a case study of one our specialty vehicle customers proves. When Volvo of Ontario asked Elasto Proxy what more we could do for them, my colleague John Rye described our technical design and custom fabrication capabilities.

Volvo’s Ontario division reduced its vendor base repeatedly, but Elasto Proxy made each cut and even landed larger contracts. The specialty vehicle manufacturer has moved these operations to the United States, but Elasto Proxy continues to provide high-quality rubber and plastic parts on-time and according to specification.

Increase Business

Like many multinational corporations, Volvo maintains production facilities beyond just Europe and North America. So when Volvo of Brazil needed a supplier that could strengthen their supply chain, they approached Elasto Proxy because of our work for Volvo in Canada and the U.S. As Elasto Proxy seeks new partners in international markets, we’re proud to showcase Volvo of Brazil as an example of how we’re meeting sealing challenges in South America.

One-stop sourcing means more than just supply chain strength. By helping Volvo of Brazil to reduce its vendor base, Elasto Proxy is learning lessons that can benefit other partners in the many industries we serve. Does your company have too many suppliers? Do you fully understand the capabilities of each of your vendors? Our advice is to choose a partner – not just a provider. How may we help you?

How to Manage Price Fluctuations for Raw Materials

Price Fluctuations and the Supply Chain
Price Fluctuations and the Supply Chain

Paulo Arruda
Purchasing and Logistics, Elasto Proxy

How well do you handle risk? For businesses that source raw materials internationally, risk management is a key to supply chain strength. By identifying all of their risks and applying resources efficiently, global companies can minimize the probability and impact of price fluctuations for raw materials.

Too many buyers are lured by low unit prices that skyrocket when global prices rise sharply. You can control your agreements with vendors, but your business cannot control the weather, political unrest, strikes, and transportation issues in a supplier’s country. So what should buyers and managers do?

The answer is to build partnerships, understand demand, and buy the right amounts.

Building Partnerships

Here at Elasto Proxy’s headquarters in Boisbriand, Quebec, Canada, it’s my job to manage and optimize our material procurement, logistics, and inventory strategies. Before we partner with a vendor, we visit the company’s facilities and evaluate their business operations. Our supply chain strength benefits our customers, for whom we custom-fabricate rubber and plastic components such seals and gaskets.

Price is important, but it’s not the only factor that Elasto Proxy considers. Innovation, quality, honesty, and dependability are values that our company looks for and expects partners to share. For the suppliers that we select, regular on-site visits help us to identify risks and strengthen business relationships.

Understanding Demand

As a custom fabricator of high-value, low-volume rubber and plastic parts, Elasto Proxy needs few long-term contracts. Rubber prices fluctuate throughout the year, so we manage most vendor agreements on a monthly or quarterly basis, depending on the material compound. There is more price variability with synthetic rubber than silicones, and our agreements reflect this.

During the agreed-upon period, prices are fixed. Some vendors can hold their prices for longer than others, but the global chemical market varies. Industrial usage such as seals, belts, and hoses accounts for only 20% to 25% of worldwide rubber demand. Because the tire industry consumes most of the rest of the world’s rubber, an increased demand for automobiles drives up raw material prices in our own market.

Buying the Right Amounts

Strengthening your supply chain involves building partnerships, understanding demand, and knowing how much to buy. Here at Elasto Proxy, our supply chain is strong enough that we can purchase just enough materials to maintain our service-level agreements with customers. By analyzing customer sales forecasts and annual estimated usage, we minimize risks such buying too much or too little material.

Logistics provides value to your company’s customers. By building partnerships, understanding demand, and buying the right amounts, buyers and managers can strengthen their supply chain to account for price fluctuations in raw materials.