Steel Manufacturing Blog: Keeping it Steel

Slide Bearing Fabrication

Posted on Fri, Jul 06, 2018 @ 09:43 AM

In many of the requests we receive for Fluorogold® or Teflon® Slide Bearing Assemblies the fabricator is under the impression the specific dimensions they require will cut to size, then bonded together and finished. This can be done, but only starts to make economic sense when the requirements call for a large quantity of the same dimensions.

Frequently the need to have the Slide Bearing made to order is due to the dimensions of the steel backing plate. Whether bonded to Fluorogold® or Teflon®, which often shows on the call out as PTFE, the steel backing plate frequently calls varying thicknesses, up to as much as 1”. We can bond the Teflon® to just about any steel surface, and will do if the engineer or designer requires, but often the call out was written without an understanding of how the Slide Bearing will be produced.

Most of the Slide Bearing Assemblies produced by The Steel Supply Company are made from stock sheets that have been pre-bonded. Stock is kept in plain finish carbon steel, Hot Dip Galvanized carbon steel and stainless steel. When the issue of thickness of the steel backing plate arises our first suggestion will be to contact the Engineer of Record and suggest using stock slide bearings and making up the difference with steel or stainless backing plates.

For example;

We recently had a request for 1/4” thick Teflon® bonded to 3/4” thick carbon steel backing plates. Again, we’ll do whatever is required, but this case called for a quick discussion with the EOR. The plan as shown had the bearing at 1” thick with a pure PTFE bearing surface.

teflon slide bearing

We suggested that we supply a standard FC-1010-CS, which is 10 gauge plate steel with 3/32” thick Fluorogold® bonded to it.  Fluorogold® is a PTFE based product with glass fibers infused for maximum durability. 10 gauge steel is 9/64” thick, so together with the Fluorogold® this piece would be 15/64” thick. The fabricator could tack weld our piece to a cut to size piece of 3/4” thick carbon steel. Total thickness 63/64”.

fluorogold slide

Initially the EOR questioned the effect of welding an item that relied on a glue bold to hold the Fluorogold® and steel together. We reviewed the alternatives of a Stitch Weld and a Recessed Lip. To review drawings and information on these processes;

                                                                Stitch Weld

                                                                Recessed Lip 

The engineer in the conversation explained that he had written the call out to suit the situation assuming that all slide bearings were made to order. His desire for 1/4” Teflon® was not a requirement and 3/32” Fluorogold® would more than cover the application, especially considering its increased durability. He was very willing to sign off on the adjustment.

The result for our customer, the steel fabricator was significant. He was able to plasma cut the 3/4” thick plate from drop material available from a previous job, so the cost of material was pretty much zero, plus minimal cutting time. The Steel Supply Company was able to fabricate the actual slide bearing from stock sheets. Turnaround time went from 10 to 15 days to 2 days. Cost to the fabricator was approximately 75% lower than if the original call out had been produced.

Click here for more detailed information regarding Slide Bearings

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Tags: Slide Bearing, Slide Bearings, Teflon Slide Bearing

Bonding Teflon® or Fluorogold® To Rubber

Posted on Tue, Jan 24, 2017 @ 12:49 PM

In the field of Steel Fabrication Teflon®, PTFE and Fluorogold® are most often bonded to steel backing plates to form Slide Bearings. This type of assembly works very well when the anticipated movement will only be horizontal, such as expansion or contraction. Occasionally the application requires the bearing to also allow for some movement or cushioning vertically. In cases like these, the bearing design can have a standard thickness, sliding surface bonded to a commercial rubber cushion.

What is commonly referred to as deflection in Slide Bearing construction, is actually called “Rotation.” It is the action created when any member of the assembly moves or flexes vertically. See drawing below:

image 1.jpg

In this configuration, the Slide Bearing is constructed with a sizable thickness rubber pad bonded to the lower element. This provides for the rotation, while the mated Teflon® or Fluorogold® surfaces can still allow for horizontal expansion and contraction. It is important to note that, at moments of rotation, the two sliding surfaces always remain parallel to one another and the load of the structure remains evenly distributed.

image2.jpgAs mentioned above the commercial grade neoprene can be any thickness desired. It can also be bonded to itself for added thickness and cushioning options. The photos below show 70 Durometer Neoprene layers, each 1” thick bonded together to form a 4” thick Neoprene bearing.


What should be considered in these cases is that typical Commercial Grade Neoprene has a maximum load capacity of 800 psi. Beyond this, it will begin to lose its shape by bulging out at the sides. As well, it will be prone to premature failure. An option for if greater maximum loads are anticipated is to use Viblon® material in place of the Neoprene.  

Shown in the photo below, Viblon® is made of many layers of cotton-polyester fabric which are completely infused with nitrile rubber. This construction allows for flexibility and rotation, while developing a maximum load of 1,500 psi, almost double that of Commercial Grade Neoprene.

 image 3.jpgViblon® is manufactured in sheets 48” wide, similar to neoprene. Standard thicknesses are 1/8”, 5/64”, 11/32”, 1/2”, 3/4”, and 1”. These can also be bonded to form thicker pads or layers of steel backing plates can be added. In each of these cases, the horizontal stability is greatly increased over standard neoprene.

 

Learn More About Slide Bearings

Tags: Slide Bearing

Slide Bearing Welds

Posted on Thu, Aug 06, 2015 @ 11:56 AM

An often overlooked issue with Slide Bearings is the system of welds. Before beginning the process the steel fabricator should understand what effect the weld will have on the Slide Bearing.

Whether Virgin Teflon®, generic PTFE or the more durable Fluorogold®, the bonding process is the same. For the purposes of this discussion we will use the most common configuration, FC-1010-CS. This is a 10 gauge (1/8” thick) carbon steel backing plate with 3/32” thick Fluorogold® Teflon® bonded to it. It is essential to assure the steel and Teflon® are bonded securely and most importantly so the bond will not decay over time. To achieve this a special 2-part epoxy is used and the steel and Teflon® are clamped together. For more on the manufacture of slide bearings, click here.

The clamped assembly is then put in an oven, heated to 450°F and held at that temperature for 4 hours. It is important to understand the role the heating process plays in the manufacture of Slide Bearings because the only real short term enemy of that bond is heat. Done improperly the welding process can create enough heat to cause the epoxy bond to melt, or “delaminate.”

Fig. 1 Slide Bearing Edge View
Slide Bearing Edge View

 

The drawing to the left (fig. 1) shows the edge of a typical Slide Bearing. Any welding will heat the steel backing plate so it is important to weld in a way that limits heat buildup.

The welding system used for Slide Bearings is sometimes left to the fabricator or called out as a “Stitch Weld” or “Seal Weld.”

Fig. 2 Slide Bearing Stitch Weld


Slide Bearing Stitch Weld

 

Figure 2 shows the benefit of a stitch weld which is sometimes referred to as a tack weld. By spacing out the welds heat does not build up to the point where the epoxy bond is compromised. The welder should take care to keep the length of each weld short enough to minimize heat buildup.

For most Slide Bearing applications the stitch weld is sufficient. It actually has the advantage of making the assembly easier to replace after the service life of the assembly has elapsed. As an example some pipeline work calls for a minimal stitch weld on the slide bearings. The harsh environments these pipelines pass through will cause the Teflon® or Fluorogold® surfaces to wear faster and be replaced more often. Removing a widely spaced stitch weld is far easier and less costly than a seal weld.

Fig.3 Slide Bearing Skip and Fill Weld

 

Slide Bearing Welds

 

Figure 3 shows a seal weld in progress. When complete it will seal all the edges. In order to do this and not delaminate the Slide Bearing a Skip and Fill technique is used. The drawing shows the initial 4 welds in black, spaced so the heat does not build up in any area. The dark gray welds are done second followed by the light gray. Continuing with this Skip and Fill pattern will eventually produce a weld bead around the entire perimeter.

View Stock Side Bearings

Tags: Slide Bearing, Stitch Weld

Understanding the Differences Between PTFE or Teflon® Slide Bearings

Posted on Wed, Jan 21, 2015 @ 01:21 PM

Slide bearings are a very important aspect of the construction process, but the jargon involved can often be very confusing.  There are some basic terms that need to be understood when discussing the methods of constructing a Slide Bearing or Teflon® Bearing Pad.  The many different terms associated with slide bearing surface are listed below, while next week’s article will cover backing plate options.

The actual material of slide bearings can be:

Teflon® - Pure Teflon® is typically a white solid material. Its coefficient of friction is 0.05 – 0.10. This is the third lowest coefficient of any known solid material.  Teflon® is the brand name for PTFE that is manufactured by the DuPont Corporation.

PTFE (Polytetrafluoroethylene)Pure PTFE is the same material as Teflon®, except it is produced by a generic chemical manufacturer and not subject to a registered trademark. The color of PFTE is also white.

Fluorogold®- A product that is a combination of PFTE, either Teflon® or generic, and glass fiber aggregates. The result is a material with significant compressive strength and a coefficient of friction of 0.06.  It is also more durable than standard Teflon® or PTFE.  The color of Fluorogold® is gold, as shown in the last photo below.

Slide Bearing

PTFE or Teflon® Bearing Pads

While the most common material is Fluorogold, slide bearings can be made using white PTFE or Teflon®.  When this is required, the slide bearing assembly should be made with the PTFE or Teflon® Bearing Pad on the lower member only, and the upper member should be polished stainless steel. This is a very important designation.

Proper design of Slide Bearings will always have the upper member wider than the lower.  As expansion or contraction occurs, the upper member moves and the lower member, which is stationary and should always remain fully covered.

That is done so:

A) The lower member always has consistent pressure on its entire surface, thereby providing the maximum support and wearing evenly.

B) The lower member is always covered so that debris cannot collect on it. This prevents anything from getting in between the upper and lower members, which could create an abrasive condition that would dramatically lower the expected life of the Slide Bearing.

If standard PTFE is used for both upper and lower members of this process, eventually the lower will begin to indent when it stays in one position for an extended period or as temperatures rise. Then, when movement occurs, the indent will create unnecessary pressure and premature wear.  By always using a polished stainless steel surface of the upper member, the issue of indenting is alleviated.

Hypothetical Drawing Showing Teflon® on Both Upper and Lower Surfaces

Fluorogold Slide Bearings

To see properly constructed PTFE slide bearings, click here.

Flourogold Slide Bearing

One of the greatest benefits of Fluorogold is that it can withstand the uneven pressures and still not show any impression of the edge.

Shown at the bottom is a typical FC-1010-CS Slide Bearing.  It has 3/32” thick Fluorogold bonded to a 1/8” carbon steel backing plate.

For link to the catalog of Fluorogold slide bearing and all other sliding bearing assembly configurations, click here.

Fluorogold Slide Bearing

For any additional questions about the pros and cons of using Teflon® or generic PTFE, contact Steel Supply with any of your questions or comments!  To see more slide bearing measurements and configurations, click below:

Slide Bearing Configurations

Tags: Slide Bearing, Slide Bearings, Teflon Slide Bearing

Teflon® Slide Bearings vs. Teflon® For Other Construction Uses

Posted on Tue, Oct 29, 2013 @ 04:10 PM

See below for disclaimer on the trademarks regarding Teflon® and FLUOROGOLD®.

For this discussion Teflon® shall be referred to by its industrial name PTFE.

Most frequently our Steel Fabricating customers are called on to use PTFE (Teflon®) in the basic Slide Bearing configuration. The actual product in a Slide Bearing should be a glass fiber reinforced PTFE known as FLUOROGOLD®.

As engineering and environmental standards have evolved there is also an increasing demand for PTFE in other uses in steel construction.

  • Gaskets - Typically on carbon steel to carbon steel PTFE Teflon® gasketconnections gaskets are not required. When connecting dis-similar metals a gasket will often be used to eliminate galvanic corrosion. In the photo to the right PTFE inserts were used to separate carbon steel from aluminum. (Note white pad beneath the clip angle)
  • Electrical Insulation - PTFE is an excellent electrical insulator. Standard measurements indicate PTFE can insulate 500 volts per thousandth of an inch. Note again the drawing to the right. We were unable to verify with the engineer why Teflon® was required in this application, but these beams are supporting the ground floor of a laboratory that uses a lot of radiology and medical imaging equipment. Excluding any considerations for insulation against electrical current, more common insulations would be a high durometer commercial grade neoprene or Korolath HDPE plastic, both of which are supplied by The Steel Supply Company.
  • Bearing Pads - For light loads standard white (virgin) PTFE can be used as a bearing pad. For heavier loads the design usually calls for a Teflon® Bearing made with FLUOROGOLD® which provides much greater dimension strength.PTFE Teflon® Bearing Pad / Thermal Break

  • Thermal Break - PTFE is also an excellent insulator to prevent thermal bridging. Thermal bridging is the path energy would follow to move from a heated environment into a colder environment. Uses such as these are becoming increasing more common as designers and engineers adapt to LEEDS standards and other environmentally conservative practices.

PTFE has a number of characteristics that are very attractive to engineers;

  • Very low co-efficient of friction
  • Corrosion Resistance
  • Chemically Inert ( i.e. PTFE is unaffected by almost all acids, caustics and solvents)
  • Excellent machine-ability
  • Temperature feasibility ; PTFE can have operating temperatures from - 100° F to 500° F
  • Good abrasion resistance
  • Nonporous

At times a drawing will call for the Fluorogold® or Teflon® to have a dimpled surface. This would be a case where an addition lubricant will be applied. The dimples serve to collect the lubricant and distribute it sparingly as the surfaces move. Otherwise two perfectly flat surfaces would very quickly squeeze the lubricant out. Situations like this are usually applications subject to "Stick-Slip" conditions that are produced by sudden movement. An example would be a Slide Bearing being utilized on the mounting of an electrical generator. In building construction the anticipated movements are not sudden enough that Stick-Slip will be a factor. 

Note :

To maximize the value of a Slide Bearing it is important theTeflon® Slide Bearing, FLUOPROGOLD® Slide Bearing surfaces of the upper and lower member be as parallel as possible. The drawing to the right shows in exaggerated form what occurs when the bearing surfaces are not parallel. The red arrows indicate where stress is created. The Teflon® or FLUOROGOLD® can absorb some of the deflection. As well, in steel construction there is more than enough strength to offset and overcome the stress. At the least, this condition will cause accelerated wear and most likely premature failure.

Of course Steel Fabricating, and especially Erecting are subject to field conditions and physical limitations. While it may be theoretically impossible to align the bearing surfaces perfectly, care should be taken to see they are as straight as possible.

 

Note: Teflon® is a registered trademark of the DuPont Corporation. In general industrial terms this product is known as PTFE. (Polytetrafluoroethylene) 

FLUOROGOLD® is the industry designation for the type of PTFE used in our slide bearings. It is a special formulation PTFE, reinforced with a glass fiber aggregate. This reinforcement is what allows for its exceptional compressive strength. Fluorogold® is a registered trademark of Saint Gobain and is used with permission through exclusive license.

 

Tags: Slide Bearing, Teflon Slide Bearing

Teflon Slide Bearings

Posted on Sat, Jul 20, 2013 @ 12:40 PM

Note: Teflon® is a registered trademark of the DuPont Corporation. The generic name for that product is Polytetrafluoroethylene, or more simply, PTFE. 

Fluorogold® is the trade name for the type of PTFE used in our slide bearings. It is a special formulation PTFE, reinforced with a glass fiber aggregate. This reinforcement is what allows for its exceptional compressive strength. Fluorogold® is a registered trademark of Saint Gobain and is used with permission through exclusive license.

Teflon® Slide Bearings can be found in many configurations, but the basic principle is true for all of them. Teflon® bonded to some kind of steel backing plate. Their function is to allow for expansion, contraction or movement in any structure, bridge, pipe support, etc.

To keep it simple, here is the most common and most basic construction.

Fluorogold Teflon Slide Bearing CS-1010

10 gauge steel is 1/8" thick (+/- 1/64"). The Teflon® material used on our slide bearings is known as Fluorogold®. It is 3/32" thick, so an upper and lower assembly combine to be 7/16". As shown in the drawing above, the upper element, as the movement element, is usually longer and wider than the lower element which is stationary. This serves two purposes;

                 - As movement occurs, the full surface of the lower slide bearing always has an even load on its entire surface.
                 - By always covering the lower element particles of debris, grit, etc. cannot settle onto the Teflon® surface. This prevents premature failure due to abrasion occurring during movement.
 

In the drawing above the PTFE extends to the edges of the 10 gauge steel plate. This will provide maximum surface area, however the heat generated while welding can cause the teflon to de-laminate. The bond is quite strong and welding with attention paid to not overheating the plate can avoid this problem. One additional step to assure de-lamination does not occur is to recess the PTFE back from the edge. In the drawing below, note the PTFE is recessed 1/4" from all edges. This is especially important if the steel plate is to be fully welded all the way around its perimeter.

Slide Bearing Line Drawing 1 4 Lip 550 red 

 

The configuration can change but the fundamental design is fairly consistent. Often we see drawings which require the Slide Bearing to be thicker. For instance 3/32" thick Fluorogold® Teflon bonded to 1/2" thick steel plate. This can be made to order, but a work around would be to use the stock Slide Bearing and weld to another 3/8" thick filler plate, thereby creating the same thickness. This controls the cost and can be done quickly. Any such alterations should be approved by the Engineer or Architect responsible for the project.

An alternative design, not seen as often employs a polished stainless steel upper member. In this case the Teflon® surface of the lower member mates with the polished stainless steel surface of the upper member. The advantage of this system is its ability to carry a heavier load. The standard Fluorogold® Teflon Slide Bearings we keep in stock have a load limit of 2,000 psi. So a bearing assembly with a lower element surface area of 8" x 6" would have a load limit of 96,000 lbs. The same assembly with a polished stainless steel upper member would have a load limit of 192,000 lbs.

Critical to the understanding of the strength and durabililty of these Slide Bearing Assemblies is the difference between Virgin PTFE and the fiberglass aggregate Fluorogold® Teflon used in both our stock and made to order bearings. Virgin Teflon® cannot support the weight a slide bearing is placed under without compressing and distorting. As mentioned above, the specially formulated Fluorogold® PTFE used in our slide bearings has a strong glass aggregate that provides far greater compressive strength and yet retain the low friction capability of virgin PTFE. As well the glass aggregate PTFE remains chemically inert, allowing it to remain in service indefinitely. 

PTFE can also be bonded to other substrates such as commercial grade neoprene. This applies to situations where cushioning is required, such as machinery mounting and loading dock ramps. Note that while PTFE bonded to commercial grade neoprene has a co-efficient of friction similar to PTFE bonded to steel, it does have a lower compressive strength.  

 

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Tags: Slide Bearing, Teflon Slide Bearing