Troubleshooting – Operator Influence
Even in highly automated processes, machinery operators can still have a sizeable influence on the success and effectiveness of their machinery’s operation. However clear and well-written an instruction manual may be, wherever humans are involved, there is always going to be room for variation, making it important to find ways for various operators to be on the same page. The following looks at two examples where subtle variations in technique by the machinery operators caused variations in outcome, and ways that the problem was overcome.
Example 1
From one shift to another, a customer was experiencing bond strength variations with a product that utilised surface-activated acrylic adhesives. The bond strength was well within the quality control limits the manufacturer had set, but the variation was still large enough to cause concern.
Temperature Resistant Adhesives
- Temperature Resistance
- Differential Thermal Expansion
- Thermal Cycle – Thermal Shock
Temperature Resistance
Why is it that some adhesives are listed as high temperature resistant when they resist only 150 °C while others are classified as high temperature resistant and resist 300 °C or more? The classifications are based on what typical temperature resistance is for that technology. For example a standard anaerobic threadlocker resists 150 °C so a threadlocker that resists 230 °C is listed as high temperature resistant threadlocker. Standard ethyl based cyanoacrylates resist 82 °C where some specialty grades can withstand 250 °C.
Glossary of Cure Time Terms
Cure time, pot life, working life, working strength etc. What do they all mean? So many terms, so many figures, curing time information can be very confusing… Here are some explanations for the common terms used to measure adhesive cure time.
Fixture time: Normally this term is used for a very fast setting adhesive such as a cyanoacrylate, UV-curable adhesive or a very fast setting structural acrylic. It is the time taken to reach the point at which, for example two adherents being bonded together can no longer be “wiggled” (the adhesive sets firm and the parts can no longer be moved independently).
Pot-life: This is valid for 2-part mixable adhesives such as 2-part epoxies or structural acrylics. If you mix resin and hardener together in the correct ratio in a “pot”, the pot life is how long you have from the point of mixing until you need to have used all the mixed adhesive (before the viscosity increases to an unusable level). It is important to remember pot life can be shortened considerably if you are working in a high temperature environment, e.g. at 30°C, the pot life quoted on the technical datasheet is halved (so a 1 hour pot life at 21-23°C will be reduced to 30 minutes). Conversely, if you are working in a cold environment you would end up with a longer pot life allowing more time for mixing and applying adhesive product.
How long will my adhesive bond last?
This is a difficult question, engineering or structural adhesives are designed to be permanent i.e. last the useful lifetime of the bonded parts. It’s impossible to say “in seventeen year, five months and three days time your adhesive bond is scheduled to fall apart” the adhesive bond should last indefinitely.
There are some exceptions to this. Certain types of adhesive are designed to be temporary so will break down as and when they are supposed to under the correct conditions. The other exception is when a permanent adhesive is put into very stressful conditions – such as temperature extremes, exposure to harsh chemicals or a combination of the two. If the adhesive joint is unduly loaded and becomes fatigued it can also lead to long term failure. Harsh chemicals include strong acids and alkalis and polar solvents which can have a damaging effect on adhesives.
The Importance of Clamping During Adhesive Cure
There are several reasons why it is important to clamp component parts together or hold parts in a jig when using adhesives.
Firstly, and most obvious, is to prevent the components falling apart whilst the adhesive is curing. Adhesives have different cure speeds, where some products (e.g. cyanoacrylates) cure in seconds and can be easily held by hand until handling strength is achieved (i.e. the point at which the bond holds itself together firmly enough to be lightly handled), other products such as epoxies, can take several hours – it might get a bit boring and uncomfortable holding a joint by hand for this long! RTV silicones can even take days although many of these types of products have a high initial “grab” strength which tends to hold the joint fairly well without clamping, providing it is not in a load-bearing joint.
Structural Adhesives – Tough, Reliable and Multipurpose
Adhesives are classified in many different ways, usually on the basis of their chemical composition. Different classes include cyanoacrylate, epoxy, acrylic, urethane etc….
Sometimes they’re described by the way they cure, like UV curable, pressure sensitive, moisture curable, two-component or heat curable. (Note: This is actually a secondary classification for practical purposes. Curing types relate directly to assembly process issues. A UV curable adhesive is cured using UV after the adhesive is in place, etc.)
In this case the term “structural adhesive” refers to the role the adhesive plays as part of the physical structure of joined surfaces.
A more formal definition of structural adhesive is: An adhesive which forms bonds that will bear loads of considerable magnitude; a structural adhesive will not fail when a bonded joint prepared from the thickness of metal, or other material typical for that industry, is stressed to its yield point.
Bonding Agents for Packaging and Processing
We receive a lot of requests for advice in permanent bonding in one or two stages in the context of packaging and processing. The use of bonding agents in these areas is based on a range of practical considerations regarding improving procedures and problem solving. A good example is a replacement parts manufacturer which found that rubber gaskets were often not included or simply weren’t fitted during the installation process. Simply permanently bonding the gasket was the right solution.
Procedurally, bonding can add productivity and simplify many processes. In another case a glass factory discovered that bonding sheets of glass before cutting improved efficiency and productivity as well as simplifying the workload and reducing the amount of actual work required.
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Anaerobic threadlockers
Anaerobic threadlockers are anaerobic adhesives designed to lock fasteners in place. Their role is to prevent loosening due to vibration, thermal expansion or other stresses. Anaerobic threadlockers are also designed to permit safe removal of the fastener. Strange as this may seem at first glance, the most important need is to protect the fastener against damage during the removal process.
How to increase the usable life of your Super Glue
How many times have you gone to fix something, delved into the depths of your tool shed, located your superglue and then discovered it has gone solid in the tube or bottle? More often than not probably!
There are a lot of different “species” of this type of glue, which is technically called a cyanoacrylate adhesive. These very fast acting glues are sometimes a bit too good at their jobs, and that’s where the storage problems start.
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Bond it, don’t break it! The benefits of using UV-cure adhesives on glass
Drilling holes and cutting notches in glass panels is a specialist and skilled operation, often involving a third party, extra processing time, transportation and cost, without even thinking about the risk of breakage. Using UV-cure adhesives can take the headache out of fitting door handles, hinges, edging extrusions and various fixtures and fittings to glass panels.
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