Fasteners and Tape

3M DP270 Potting Compound

2011-03-09T05:19:00.000-08:00

Potting compounds are used to fill an electronic assembly to make it more secure. These compounds help it resist moisture, corrosion and vibration damage.
3M DP270 is an epoxy compound which a very good temperature resistance and working life of 60-70 minutes, becoming tack free in 3 hours, and 100% cured in 48 hours. It is also UL 94HB rated and stable (resists expansion/contraction) once fully cured.

As with all adhesives, as you see me repeat constantly, make sure the substrates are clear of any dirt, oils, films of anything that will get in-between the adhesive and the substance you wish to adhere to.
The "DP" in DP270 refers to Duo-Pack. Since this is a 2 part epoxy adhesive, that becomes activated when the 2 parts are mixed, they need to be kept separate until it is time to use them. Thus, you have 2 tubes that are sold, side by side. (there is a high volume version, with pneumatic applicators, but that is not something most people are going to be using).
These Duo-packs require a 3M™ Scotch-Weld™ EPX™ Plus II Applicator (which comes with the 1:1 Plunger needed) and nozzles. There are 2 types of nozzles available, but the Gold Nozzles are far superior based on ease of application, that the small difference in price is worth it. You do need to use 3M's nozzles, because they are specifically designed to mix the 2 components.

I understand adhesives, anyone that has help on better explaining "potting" please add comments or links and I will try and put together a post to help with that.

3M VHB Technology/history

2011-02-15T18:12:00.000-08:00

This is the un-official version of VHB. If you have specific technical questions, you'll have to find someone at 3M willing to talk!

VHB, or Very High Bond (creative huh? :P) tape was, as many great inventions are, a lab mistake. They were working on a double coated foam tape when VHB was invented. To understand the difference you need to think and understand the difference between double coated/double sided" foam tape, and VHB.

Double coated foam tape is a foam, with a layer of adhesive on either side. A foam can be helpful for example, when a little cushioning is needed. The other thing you can create with a doubled coated foam, is a tape differential. Say you needed to stick one side to wood, and one side to plastic, or you needed one side removable, you can coat the foam with a different adhesive and get the desired result.

The weak point in a double coated foam, is almost always the foam. Often, maybe after time, or enough strain, the item held by a foam, falls. You notice that the foam will actually split, rather than a the good 3M adhesive failing.

You have to understand this to understand the advantage of the VHB. In a lab, over 25 years ago, 3M was cooking, coating, doing something to a double coated foam and they found they could get the adhesive to flow, for lack of a better word, into the foam. Would this did is create think "foam" adhesive, with all of the spacing and cushioning benefits, while greatly improving the strength of the foam.

Now I will admit, there is something call VHB "transfer tapes," which creates a bunch of confusion based on what I just told you. 3M's marketing people don't always make it easy, and I will try and explain that one in another post.

Buy Cut Pieces of SJ3560 Dual Lock

2010-11-24T12:23:00.000-08:00

0.5" x 1.5" - 3M SJ3560 Mated Cut Pieces
Quantity:

BasicsWhen two sides (sold separately) of Dual Lock are pressed together, hundreds of mushroom-shaped stems interlock. "Snap" announces that the fastener is engaged. Compared to Hook & Loop the tensile strength is greater with 5x more holding power
3M™ Dual Lock™ Low Profile has similar features, but in a thinner version

3M Dual Lock Reclosable Fasteners SJ3560 offer advanced closure alternatives to zippers, screws, snaps, hooks, bolts and more. They offer greater design flexibility, faster product assembly, smoother and cleaner exterior surfaces and improved product performance in many applications. The fasteners consist of continuous polyolefin strips with polyolefin stems having a mushroom shaped top. The mushroom heads allow the fasteners to easily slide over each other allowing positioning of parts before they are snapped together creating a firm fastening attachment. Simply peel the pieces apart by hand to disengage. The clear acrylic adhesive combined with the clear backing allows for the substrate color to show through the fastener. The acrylic adhesive is well suited for applications exposed to high temperatures, humidity or for high surface energy materials. This product construction is especially suited for outdoor applications, where elevated temperatures are experienced or the potential for direct exposure to sunlight or ultraviolet light may occur.

VELCRO(R) and 3M Dual Lock Coins

2010-09-10T04:48:00.000-07:00

Coins is industry jargon for 3M Dual Lock or VELCRO(R) cut into a circle. This is helpful for making a uniform size, with no need for scissors to apply you fastener. There are consumer packs with very small quantities, and you can also buy 1,000s or 10s of thousands for such things as point of purchase displays, packaging or arts and crafts.
3M Dual lock will be much more expensive, but has an extremely strong hold. VELCRO) brand fasteners are more cost efficient, but will have less holding power.

Cycle Life

2010-08-15T17:46:00.000-07:00

One of the terms to understand when talking about recloseable fasteners is "cycle life"

Simply it is the number of times you can fasten, and unfasten the fastener and it still had 50% of it's originally strength.

Typically Hook 88 and Loop 1000 has a cycle life of about 1000

TEXACRO(R) has a cycle life of around 500

3M Dual Lock 250 to 250 (or 170 to 400) is typically around 100. Other combinations can vary

Low Profile Dual lock 250 times

Loop to Dual Lock of Hook 511 has a cycle life of around 5

Stem Count On Dual Lock

2010-08-09T18:33:00.000-07:00

For nearly everyone, you want to use 250 to 250. Originally Dual Lock was 170 to 400. 250 count was later developed to make Dual Lock more convenient, so that there is no need to have 2 parts like in hook and loop fasteners.

To identify use the last number in a part number
ending in 0= 250stems/inch
ending in 1= 400stems/inch
ending in 2= 170stems/inch

for example: SJ3540, SJ3541, and SJ3542

Here is a handy little chart to for the different combinations of dual lock counts:

170 to 250	Easy opening for multiple closures. Low engagement force, low tensile strength.
250 to 250 or 170 to 400	*Most Common:*Medium engagement force balanced with moderate tensile strength.
250 to 400	Higher engagement force balances with high tensile strength.
Dual Lock to Loop fastener	Quick grab engagement, high peel force,very short cycle life

"3M Velcro" does not exisit - 3M Dual Lock

2010-08-08T16:48:00.000-07:00

Have you ever heard anyone referring to "3M velcro" for thier ezpass strips, pedal board tape?

Well that is an impossible product! 3M(TM) and VELCRO(R) USA are companies. VELCRO(R) makes hook and loop fasteners (commonly called "velcro" like facial tissue is call Klenex).

When people are referring to is 3M Dual Lock(TM). Dual Lock is a recloseable fastener that is an alternative to hook & loop fasteners. It is much stronger, molded plastic fastener. Mushroom shaped heads, snap together to to form a tight bond.