How to Guides & Technical FAQ's
What are epoxy adhesives?
Epoxy Adhesives offer excellent adhesive and mechanical strength, low shrinkage and have excellent chemical resistance. They cure to a tough, hard product.
What is the different between 1-part and 2-part epoxy adhesives?
1 part epoxies contain both the curing agent and main resin within one liquid, which cures when heated. 2 part epoxies start to cure when the 2 parts are mixed together.
How long do epoxy adhesives take to cure?
The length of time for 1 part epoxies to cure is dependent on the grade in question and the heat used. Can be anywhere between 1 to 60 minutes. 2 part epoxies cures at room temperature, fast setting grades can achieve handling strength within just 30 minutes, whereas general purpose grades can set within 24 hours.
Can epoxy adhesives be used for electrical potting and sealing?
Yes, epoxy resins can be used for a wide range of applications, including bonding, potting and sealing.
What is a Silicone?
A silicone is a polymeric product with a molecular backbone made up from alternating silicone and oxygen atoms, which has pendant hydrocarbon groups attached to the silicone atoms.
What does RTV stand for?
Room temperature vulcanizing - this means that an RTV silicone rubber will vulcanize (or cure) at room temperature, from a liquid or a paste state to a solid flexible rubber. Despite the low-temperaute connotations conveyed by this name, RTV silicones do consist of both room temperature cure and grades which the cure can be excellerated with heat.
Can RTV Silicone be removed?
Yes, use a solvent such a toluene or xylene. These solvents will soften or weaken cured silicones after soaking overnight. Silstrip is recommended; a silicone remover available in either a liquid or a gel form. Please note, this will not work on removing silicone from clothes and may damage plastic.
Can RTV Silicone be thinned down/diluted?
Silicone can be thinned using a solvent in which the silicone is miscible, generally an aromatic solvent such as a toluene or xylene. The shrinkage and the cure time of the silicone will increase with the addition of solvent.
TSF 50 is a recommended grade for the thinning of silicone. However, the more TSF 50 that is added, the softer and weaker the cured RTV will be. No more than a maximum of 10% addition by weight is recommended.
How can I tell if the RTV Silicone is still useable?
If the product still yields normal hardness after a normal cure schedule, then you may consider the material still useable. Refer to the products Technical Data Sheet for information on the cure characteristics to look for.
What is a condensation cure?
A condensation cures refers to an RTV which is cured off by adding a curing agent to the base material. DBT is the most popular curing agent for most RTV silicones. Alcohol is a by-product of a condensation cure. Condensation cure products won’t cure above 12mm thick.
How long does a condensation cure take?
A condensation cure normally takes around 24 hours at room temperature. It can be speeded up by using different catalysts or by gentle heating (do not exceed 85c).
What is the depth (bead thickness) limit for a condensation cure grade?
For 1-part, condensation cure products, the depth limitation is approximately 6mm (1/4"). For 2-part condensation cure products, the depth limitation is approximately 25mm (1").
What is an addition cure?
Addition cure refers to a two-component RTV which cures with no by-product and has low shrinkage. The cure takes place when one part is added to the other - moisture is not required for an addition cure. Typically speaking a higher heat grealty accelerates the cure time required.
How long does an addition cure take?
An addition cure time depends wholly on temperature, elevated temperatures reduce the cure time required. At room temperature, cure can take anything between 1 - 7 days depending on the product, however at 150c; it can take as little as 15 minutes.
What is an inhibition of cure?
An inhibition of cure is when the cure of the rubber is inhibited by the presence of other compounds. It is characterised by a gummy of sticky appearance of the silicone and offending substrates. Care must be taken when handling and mixing all addition cured silicone elastomers to ensure that all of the mixing tools are clean and constructed in materials which do not interfere with the curing mechanism. Inhibition can be prevented by application of a barrier coat.
What does PSA stand for?
Pressure Sensitive Adhesives - these are applied generally like paint, and are used for bonding.
How do you bond a silicone to silicone?
The only thing that will bond silicone to silicone is a silicone. RTV10533 is recommended.
How can I remove cured silicone?
Cured silicone can be removed using a digester - Silstrip Liquid and Silstrip Gel are recommended depending on the application. For applications where the silicone can be fully submerged, Silstrip liquid is recommended, however where you are unable to isolate an application easily, the Silstrip Gel is reccomended. Silstrip will need to be left for roughly 24 hours to work, after which the digested silicone can be wiped or rinsed away.
What are anaerobic adhesives?
Anaerobic adhesives cure in the absence of air - they are perfect for bonding and sealing close fitting metal parts such as threads and fits.
How long do anaerobic adhesives take to cure?
It takes about 30 minutes for anaerobic adhesives to cure to fixture strength (15% full cure) and then anywhere up to 24 hours for full cure.
What do the different colours of anaerobics signify?
Green is generally high strength; red is generally medium strength and blue is generally low strength.
Why are anaerobic bottles only half full?
As anaerobic products cure in the absence of air, the bottles are only half filled to ensure that the material doesn't cure inside.
Are anaerobic adhesives suitable for use on metals?
Yes, although the cure rate and bond strength achieved is relational to the activity of the metal. Active metals, such as mild steel and copper, will produce a fast cure and higher bond strength. Semi-active metals, such as stainless steel, brass and aluminium will incur a medium fast cure and bond strength. Inactive metals, such as zinc chromate will have a slower cure rate and lower bond strength.
Where are anaerobic adhesives best used?
Anaerobic adhesives are recommended for use any where there is a lot of vibration and pressure.
What are cyanoacrylate adhesives?
Cyanoacrylates are instant adhesives that cure off when they come into contact moisture - generally in the air. Monomer is the main component of cyanoacrylates, this reacts when moisture hits the surface by quickly polymerising and cures.
How can I prevent cyanoacrylates whitening plastics?
There are 2 ways to reduce this - first, choose a low odour cyanoacrylate. This will help prevent the whitening. Alternatively choose a rapidly setting cyanoacrylate with a hardening accelerator.
Techsil's new Low Odour/Low Bloom Cyanoacrylate solves both whitening and odour problems.
Can I remove cyanoacrylate?
Yes, it can be removed by applying an acetone based cleaner. However, several applications maybe required on hardened cyanoacrylate.
What is a UV adhesive?
UV adhesives are resins cured in a short time by exposure to the energy radiated from an ultraviolet lamp. Can be used for sealing, bonding and coating.
How long do UV adhesives take to cure?
UV adhesives can take just a few seconds to cure; the time required is dependent on the power of the ultraviolet lamp used.
Can UV adhesives be used for electrical potting and sealing?
Yes, UV adhesives are well suited to electrical applications.
How do I ensure I get the Best Performance from my Hotmelt Glue Gun?
- ALWAYS allow the gun to warm up to operating temperature and do not apply force to the trigger before it is ready. Most guns are ready in 5-7 minutes, spray guns need at least 10 minutes. A new gun should be loaded with glue BEFORE switch-on and the glue gradually pushed through the gun, using light pressure on the trigger, as it heats. This expresses air from the chamber and avoids cold glue melting immediately on contact with the heater housing.
- ALWAYS use the gun stand supplied, an optional stand or suspension hook if available because the gun heater housing contains molten glue. The gun should NEVER be laid on its side as this could cause the glue to “puddle” and cause melt back into the cooler part of the gun. If this happens, the gun could suffer internal damage.
- ALWAYS unplug the gun if it is not going to be used for 40 minutes or more. To cool the gun more quickly and aid easier start-up the next time it is used, disconnect from the power supply when work is complete and while the gun is cooling use the trigger to extrude about half a cartridge / stick of molten glue through it.
- ALWAYS wipe any excess molten glue from around the nozzle at the end of each work session with a cloth as this will prevent build up of glue deposits which can char. This should be done while the gun is still hot. Always wear protective gloves.
- NEVER withdraw a part melted glue cartridge / stick from the back of the gun.
- NEVER remove the nozzle from a cold gun as thread damage could result. Warm the gun first and always wear protective gloves. Most integral gun stands incorporate a nozzle remover.
How much Hot Melt Adhesive will I need?
The amount of hotmelt adhesive you will need depends on how you would like to apply the hotmelt, for example either a bead or a dot and also how thick or thin the bead of dot is.
See our handy scale below which can help you work out your overall usage based on either dots or length of beads.
How does mositure affect Polyurethane?
From BJB: The ambient air around us contains varying degrees of moisture/humidity and certain times of the year can be worse than others. It's this moisture that often gets absorbed into the liquid material and can negatively affect the cured properties and/or shorten the shelf life of the material. The best way to minimize exposure to moisture is to keep container lids closed until you need to dispense material and immediately put the cap back on. You should avoid paper cups and wood stir sticks because they tend to absorb moisture as well. Also, avoid leaving dispensed material in the cups for too long; meaning, don't pre-pour a batch of measured amounts into exposed containers sitting on the bench and go to lunch!
To help preserve polyurethane materials in storage, dry nitrogen gas is often dispensed into the container before resealing. Nitrogen in a non-flammable gas that will settle on top of the material (displacing oxygen) and form a protective barrier/blanket preventing contamination from humid, ambient air. Dry nitrogen can be purchased from many welding supply sources.
How does Temperature affect Casting Materials
From BJB: Ambient temperature and storage temperature can have a drastic affect on materials. Working time, demould time, viscosity, and physical properties of the material are all affected by temperature. In cold winter months working with thermal set systems (urethanes, epoxies, etc.) can present challenges not seen in more moderate seasons. Materials can be much higher in viscosity making mixing, degassing, and pouring more difficult. You can also experience brittleness on demould. This is not the fault of the material; it is the nature of chemistry for these materials. Extra care should be taken to pre-warm materials prior to mixing and the same goes for moulds. Warm material poured into a cold mould can have undesired results, especially if the material has a long working time. Also, heat can work to your advantage if you need to process faster but it can also work against you. Pre-heating materials can lower viscosity making it easier to mix and pour but it will shorten your work time. Sometimes going with a longer work life and heating the material can give you the benefit of lower viscosity without sacrificing valuable work time. Elevated temperatures can also greatly increase strength of materials.
How Do I Work With Water Clear Polyurethanes?
From BJB: Aliphatic Water Clear (WC) materials are a wonderfully unique material. They have unrivalled clarity and when pigmented they are the most colour stable material we manufacture. They offer outstanding UV resistance; some of our WC systems can withstand years of outdoor exposure. Note that Water Clear refers to their clarity (also called Water White) and does not mean they are water-based or water soluble. Working with them does require a few essential steps to ensure success. First, they are not tolerant of cold casting temperatures. Clarity and physical properties can be severely affected if cast below 70 degrees F. Moulds must also be preconditioned to minimum temperature (75-85°F) or heat may be pulled from the curing material. They also require a good vacuum system to pull the trapped air out of mixed material prior to pouring into a mould. BJB Water Clears do not self release entrapped air. Without pulling a vacuum on the mixed material, a cast part may end up looking more like a glass of carbonated soft-drink than a glass of crystal clear water. Casting the part in a pressure tank/vessel can also aid in reducing bubbles in a part by compressing bubbles down to the point they are not visible anymore (see Vacuum and Pressure). Casting in thin sections may also require additional heat to make up for the lack of internal exotherm (less mass equals less self generated heat). Water Clears operate best if preconditioned to a minimum of 75-85°F range and a max of 100-110°F keeping in mind that higher temperatures will shorten work life. Refer to the technical Data Sheet or call Techsil for more assistance regarding proper temperature settings.
What is Post Curing and why should I do it?
From BJB: Post curing is a confusing subject for many people. The majority of BJB materials are designed to cure at room temperature and will continue to improve physical properties over several days. For some applications this may be sufficient but there are some instances where we need additional performance out of the same material.
A post cure at elevated temperatures increases the level of cross-linking in two-component thermosetting systems. In flexible materials this typically increases tear strength and tensile strength. For rigid polyurethane and epoxies the main improvement is an increase in the heat distortion temperature (HDT), and you will also see a reduction in cold flow/creep over time.
Don't be fooled by claims that a rigid thermosetting material does not have to be post cured; it's a half truth to say that. The truth is you don't have to post cure, but don't expect the optimum performance properties stated on the Technical Data Sheet. Even running a "mild" elevated temperature post cure can have benefits on the material. Many BJB users do not want to subject their tools to extreme temperatures (above 65c) so they run a mild post cure at 49c to achieve a certain degree of improvement over a room temperature cure.
Note that even silicone tools will improve physical properties and mould life if you run a post cure prior to putting the tool into service. However, be aware that high heat can swell silicones and may not be a suitable procedure for high tolerance tools. Post curing is best done in a properly controlled parts oven (never a household oven). Some materials can have undesired results if subjected to extreme elevated temperatures (swelling, bubbles, deformation) so always check the recommended procedure on the data sheets or consult Techsil's Technical Department.
How Do I De-Air or De-Gas Casting Materials?
From BJB: When you are hand mixing casting materials, air bubbles are inevitably going to be stirred in. Viscosity, temperature, and surface tension of the material will determine how well the air will or will not self release from the liquid. Other than a few of our low viscosity systems, the mixed material will need to be placed in a vacuum chamber to remove those air bubbles prior to pouring in the mould; also called de-airing or de-gassing. The vacuum expands the trapped air causing the bubbles to grow, rise to the surface of the material and release. After a period of time these bubbles decrease in quantity meaning that air is effectively being removed from the material. This air would otherwise cause voids and potential mechanical issues with your cast part. Cold materials will have higher viscosities and may be more difficult to de-gas. Raising temperatures lowers the viscosity which will aid in pulling air out of the material but may also reduce working time if taken to extremes. Pressure casting can be an alternative or secondary process to vacuum ‘degassing’ casting material. Pulling air out of the material ensures the material isn’t latent with bubbles as it goes into the mould, but air can be re-introduced into the material as it is poured in from splashing or mould features that trap air (e.g. sharp corners). In some applications, vacuum and pressure must be used in conjunction to produce air free parts. Typical pressure values, when material is degassed, are in the 40-50psi range. Higher pressures may be required if material is not degassed. Pressure does not remove air; it compresses air bubbles down to the point that they are not visible anymore. If pressure is released too soon (before material has had time to set) the bubble could potentially reappear.