Loctite 638 vs. 680: what’s the difference?
Loctite 638 would be preferred for faster cure time and higher strength, while Loctite 680 offers better flow properties and higher heat resistance. 680 may not be suitable for preventing metal roof screws from backing out. It is more effective for filling gaps up to 0.015 inches, making it challenging to achieve a small gap with sheet metal screws.
- Loctite 638 vs. 680: Specs & Uses
- My Hands-on Test of Loctite 638
- My Hands-on Test of Loctite 680 (Retaining Compound)
Loctite 638 vs. 680: Specs & Uses
⏰Fastest Full Cure Time
Loctite 638: 15 min
Loctite 680: 1 hr
🆚Chemical/Solvent Resistance
Loctite 638: Good resistance to oils, fuels
Loctite 680: Good resistance to oils, fuels
🛠️Common Uses
Loctite 638 can be used to secure machine parts, repair metal structures, or assemble metal components; seal gaps, joints, or connections in metal components, providing resistance against leaks, vibrations, or environmental factors.
Loctite 680 can be used to provide a secure hold for M2 taper chucks or arbors. It can prevent slippage when used in conjunction with a clean shrink fit, a heated chuck, a cooled arbor tapped together with a lead hammer.
Technical Info
My Hands-on Test of Loctite 638
✅Pros
Now, let’s get back to the performance. Loctite did exactly what it promised. It secured the bearings in my gearbox, ensuring smooth operation and minimizing any potential wobbling or shifting. I’ve had my fair share of disappointments with other products, but Loctite lived up to its reputation. It’s a reliable choice for mechanical applications, and I couldn’t be happier with the results.
I also used Loctite to keep a pinion gear on the motor shaft of my 31 lbs RC car, and it has been holding up remarkably well. It’s been through some intense off-road adventures, and the bond remains strong. So, if you’re looking for a solution to keep your gears in place, Loctite might just be the answer.
Speaking of the bottle, I lucked out because instead of the 50ml bottle I ordered, I received a generous 250ml bottle. Talk about a pleasant surprise! Initially, I was a bit skeptical since it was labeled as being from India. However, I soon realized that it was not a counterfeit product. But once I peeled away the tape, I discovered that the product was well within its shelf life. It was about 18 months old and still good for another 18. Phew!
❌Cons
Now, let’s talk about the bottle itself. When my package arrived, I was a bit alarmed to see that the bottle was only half full. Naturally, I wondered if I had received an incomplete product. However, after doing some research, I discovered that this is actually intentional. Due to the chemical nature of Loctite, the bottle is filled with air to maintain its effectiveness. So, no need to panic if you find your bottle half empty upon arrival!
FAQ of Loctite 638
Q: How much should a new bottle weigh? Mine feels kind of empty.
A: Ideally, the bottle should have a weight that indicates it is half empty. This allows for the necessary presence of air to prevent the content from hardening within the bottle.
Q: What country is Loctite 638 manufactured in?
A: The product originates from India.
Q: Can Loctite 638 be used on an O.D. rubber seal surface to metal housing, or is it only suitable for metal-to-metal applications?
A: This particular product is specifically designed for metal-to-metal applications and may not be suitable for use on an O.D. rubber seal surface to metal housing.
Q: How effective is “638” in providing sealing properties?
A: Authentic Loctite products, such as “638,” have a QR verification code on the bottle to ensure their genuineness. I personally returned a product that did not have this code.
Q: Is Loctite 638 reliable to use?
A: I suspect Loctite 638 might be counterfeit since it lacks the QR verification code found on genuine Loctite bottles.
Q: Does this formula have a quick setting time?
A: Yes, I believe it does. After approximately one minute, it becomes difficult to separate the bonded parts.
Q: Can you provide the expiration date for this bottle of Loctite 638?
A: The expiration date is indicated by a code on the bottle. To decipher the code and determine the exact expiration date, it is best to contact Loctite directly.
Q: Why does Loctite arrive empty?
A: As I said, it is empty intentionally. If you put a drip of Loctite on the table, it is never gonna dry. That said, it is going to stay in that form because Loctite takes an absence of air to create the chemical reaction to harden it. That’s also why when you buy a new bottle of Loctite it feels like it’s kind of empty. It’s actually because they put it too much. There won’t be enough air for it to stay in its liquid form. The absence of air within the bottle will cause the entire bottle to harden.
My Hands-on Test of Loctite 680 (Retaining Compound)
The high number signifies its strength, and it requires heating to over 500 degrees F to break the bond. I was excited to try it out, but it’s essential to note that there is very little time to make adjustments for close-fit applications.
I found that this retaining compound works great when used correctly. Thoroughly cleaning both parts with brake cleaner or acetone is crucial before use. Additionally, Loctite 680 works even better when used with the appropriate primer for slip-fit applications. However, it sets quickly, so it’s essential to plan on assembling immediately.
Loctite 609 vs. 680
Loctite 680 has a higher viscosity, faster cure speed, higher strength, and better temperature/chemical resistance compared to Loctite 609. Loctite 609 may be preferred where a slower cure speed is acceptable.
The high number signifies its strength, and it requires heating to over 500 degrees F to break the bond. I was excited to try it out, but it’s essential to note that there is very little time to make adjustments for close-fit applications.
One thing to keep in mind is that Loctite 680 sets up very quickly, especially if used with primer beforehand. I’ve used it with primer and found that it starts to cure within 60 seconds or less. I have yet to attempt to disassemble anything that I’ve used it on, but from what I have read online, it’s worse than trying to take apart stuff with red Loctite. I use 680 over red 271 only in situations where I never want to take two things apart, such as mounting studs that form part of an adapter or sleeves that will never need to be pressed out, etc.
It’s essential to work fast with Loctite 680, primarily when using primer before using it. This liquid sets up quickly and hard in a very short time. However, it works great when used to retain bearings. I used it for sleeving a wheel cylinder in brass, and the 680 setup instantly. The bond has never failed even once over many different repairs.
I was impressed with how Loctite 680 worked for me. I used it to replace a loose pusher button on my Chronograph watch, and it worked great. It also helped me attach a sling swivel and front sight barrel band to a Ruger No.1-A barrel. However, it’s important to note that it can be pricey, but it’s worth it, considering the money it saves you in repairs.
💬 FAQ of Loctite 680 (Retaining Compound)
Q: Can this be used to secure M2 taper chucks or arbors in place?
A: I have seen it used for that purpose, but for a more secure hold, I recommend using a clean shrink fit with a heated chuck and cooled arbor tapped together with a lead hammer. I have never had issues with slippage using this method.
Q: Is there a specific primer to use with this retaining compound for non-ferrous metal?
A: I have used this retaining compound successfully on plastic, aluminum, and all types of steel without a primer. It works well on these surfaces without one.
Q: Will this retaining compound provide a strong enough bond between a steel electric motor shaft and a bronze press-fit gear?
A: This retaining compound is quite strong, but I cannot confirm its suitability for this specific application. I have only used it for a small mounted micrometer that is moved manually.
Q: Does this retaining compound produce foam?
A: No, it does not foam.
Q: Is the bottle completely filled or partially filled?
A: The bottle is only partially filled, leaving some air space. This is because Loctite products need to cure in the absence of air.
Q: Can this retaining compound prevent metal roof screws from backing out?
A: Unfortunately, I don’t believe this retaining compound is suitable for your needs. The lock tight, threads on the bolt/but, and pressure are what create the bond. It only fills gaps of up to 0.015 inches, and it may be difficult to achieve such a small gap with sheet metal screws.
Q: Should I use this retaining compound for an AR-15 barrel extension to mate with the upper receiver, or stick with 620?
A: I recommend sticking with 620, as this retaining compound can be difficult to remove once the object is installed.
Q: I am interested in purchasing Loctite 680 for aircraft assembly. Can you tell me the expiration date?
A: I have only used Loctite 680 and cannot speak to the differences between the two products.
Q: What is the curing time for this retaining compound?
A: This retaining compound typically sets up within 5-10 minutes but should be allowed to set overnight, around 10 hours, for a solid bond.
Q: Is this retaining compound conductive?
A: While this retaining compound is made of plastic and is not inherently conductive, it could conduct electricity if there are voids or uneven surfaces, especially if high voltage or contact is made.
Q: I am looking for a product to repair a cold solder joint on a double-barrel shotgun. Can this retaining compound be used for that?
A: Unfortunately, you cannot repair a cold solder joint. It needs to be reheated, the proper flux used, and then cooled slowly.
Q: Can this retaining compound, along with a primer, hold a 15mm bicycle lug nut permanently, even against breaker bars? I plan to use heat to remove them for theft protection.
A: I have only used this retaining compound for precision work, so I’m uncertain if it can withstand the pressure of breaker bars. It’s designed for slip-fit applications, so it may not be as strong as red or blue Loctite.
Q: Can this retaining compound handle the high temperatures of an AR-15 barrel, or will it cook off?
A: Loctite 680 is primarily used for slip connections and is very strong, but it may not be ideal for threaded connections. If you plan to use it on the flash suppressor, compensator, or sound suppressor that is threaded on the end of the barrel, or to attach the barrel to the upper receiver, I recommend using Loctite 271 instead.
Q: Can this retaining compound work as well as Loctite 638 for bushings?
A: This retaining compound actually works better than Loctite 638 for bushings.
Q: Can this retaining compound be used to glue a hand-cranked meat grinder to a surface?
A: No, this retaining compound is not an adhesive glue and is only designed to fuse metal to metal through a chemical etching process.
Q: My retainer is broken. What kind of glue can I use to fix it?
A: Without knowing the specific details of your retainer, it would be best to consult Loctite’s application guide to determine the appropriate product for your needs.
I’m Ronald Stevens, a Mechanical Engineer obsessed with adhesives, glue, and all things sticky! My passion began in childhood when I’d always be the one playing with glue during arts and crafts. And I’d spend hours researching and experimenting. Happy reading, and remember: stick with the best, and you’ll never be stuck in a mess!
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