Lesson video

Hello there, my name is Mrs. Dhami.

Thank you for joining me for your design and technology lesson today.

Now the big question for today is how are polymers joined? So what we're going to do is explore a variety of examples, but you might be surprised a couple that you know, but perhaps you hadn't put them into the category of polymer joining processes.

So hard hats on, let's get cracking.

Our outcome for today is we will be able to explain various mechanical and chemical methods to join different materials.

We have three keywords today, mechanical fixings, which is a part that holds materials together using force.

Chemical joining, which is when you use adhesives or heat to bomb materials through a chemical reaction.

And lastly, component.

A component is a ready made part used across different products to make manufacturing easier.

We have two learning cycles today, mechanical fixings and then moving on to chemical joining.

So let's get started with mechanical fixings.

Mechanical fixings are a way of holding materials together using physical means like fasteners or shaped joints.

Now they commonly use force or shape to hold materials in place.

They are common in polymer construction and product assembly.

They can be permanent or removable and they can be components.

Now, components, as we know, is one of our keywords today.

A component is a ready-made part used across different products to make manufacturing easier.

Quick check-in, which of the following is a mechanical fixing? A, PVA adhesive, B, epoxy resin, C, screw, or D, super glue.

Have a think and come back to me when you've got an idea.

Well done if you've got C which is screw.

A screw is a type of mechanical fixing.

Screws are mechanical fixings that grip the polymer and you can see two in the pictures on the right hand side.

Now polymers usually use what we call self-tapping screws.

Now this means that they have very sharp threads which cut into the material as it's directly driven in.

And if you look at that screw on the bottom right, that's a self-tapping thread and if you look very carefully, you can see it's a lot sharper than the normal screw above.

So where do we use screws? We tend to use them in polymer casings because they give us a stronghold but they're also removable so we can take them out.

A limitation though is that they usually require a pre-drilled hole, which we have to call a pilot hole and I'll explain a bit more about that on our next slide.

Screws used in polymers require a pilot hole as I've just said.

This is a small hole that is pre-drilled, which acts not only as a guide, but it also prevents the polymer from cracking.

And you can see that in the little picture on our right.

Depending on the type of screw, a countersunk hole may be needed.

This is a conical recess drilled into a material to let a screw head sit flush.

This means the head of the screw does not stick out the material but lies flush with the top of that material.

And hopefully you can see that in picture number three.

Understanding the parts of a screw make differentiating the different types easier.

So let's take a little look at a common screw.

First of all, we start from the top.

We have the head of the screw.

We then have the main body of the screw which we actually call the shank.

Next we have the thread which wraps around the shank And then finally, we have the tip.

Countersunk heads sit flush with a surface like we've just said on the previous slide.

And you can see that in that middle picture there while round head screws sit above the surface.

And sometimes you have round head screws for decoration too.

So it depends on what you are making and what you want the aesthetics to look like.

Do you wanna hide it or do you want to make a feature of it? There are different drive types, IE the shape of the slot in the screws head which will of course depend on what type of screwdriver you need.

So we have Phillips which is like the cross.

We have slotted which is that slot across.

We have the pozi, which is almost a little bit like a star.

And then we have the hex which is obviously like a hexagon shape.

Thread types and shank diameters can differ depending on the material type and the thickness.

Nuts and bolts are mechanical fixings used to securely joint polymer parts such as flat pack polymer furniture or polymer machine guards.

So next time you go onto a pillar drill, have a little look at the machine guard.

They are removable and allow for strong reusable connections.

Nuts and bolts, sorry, are often used with rubber washers on polymers to prevent damage or cracking and can be tightened and removed easily.

And we can see that on the diagram.

We have the bolt at the top.

We have the washer that would normally be rubber if it's with a polymer, and then we have the nut at the bottom.

So where do we tend to use them? We tend to use them with flat pack polymer furniture.

The benefits being they create a stronghold, but they are removable.

Limitation is they require access to both sides.

I'm sure you probably recognize these toy bricks in the gif on the right.

You can see them being assembled and disassembled really, really easily.

What you might not know is that they are an example of a snap-fit mechanical fixing.

Wow, so snap-fit mechanical fixings in polymers are designed to interlock two parts without screws or adhesives allowing easy assembly and sometimes disassembly.

With the toy bricks, it's very easy assembly and very easy disassembly.

So examples not only include toy bricks but also food containers.

So what is the benefit? The benefit is that no tools are required.

They can be done by a small child or an adult very, very easily.

However, sometimes with some the limitation can be that they can weaken after repeated use.

Snap-fit mechanical fixings can be found in a variety of common products.

These examples that I'm about to show you are easy to assemble and disassemble.

So we have food containers.

You can see one of my children's lunch boxes being easily opened and closed, and again, they can do it even though they are young, they can do that themselves.

We also have fasteners which are an example of a component and there is my daughter's chair for her baby on the back of her bike.

And you can see that that fastener allows her baby to be strapped in easily and allows her baby to be taken out easily too with the simple polymer fastener.

We've looked at a few easy to assemble and disassemble examples, but also snap-fit mechanical fixings can be purposely difficult to separate.

Take a little look at the blue image there where that part is going to snap-fit into the gap, but to take it out is pretty tricky.

Here's another example in green where those little bits, you almost have to get it at an angle to be able to get it in and once it's snapped in, it's very, very difficult to remove.

Now as I've put examples include electronic housing compartments and toys.

So have a little think, perhaps the remote controller.

That one snapped in quite easily but it's quite difficult to get it out to get to the batteries.

And the ones with toys are often a lot more difficult to take out.

So use tends to be polymer casings.

The benefit is it can prevent children opening, which is great if there are batteries inside.

Limitations are obviously it is difficult to remove if required so it's a bit of both really.

The benefit is also the limitation.

True or false, snap-fix mechanical fixings are always easy to assemble and disassemble.

Have a think, decide whether it's true or false.

Come back to me when you've got an idea.

Well done if you've got false and why is that? Some snap-fit mechanical fixings in polymers are designed to be more difficult to disassemble to protect young children from accessing parts such as batteries.

For example, the batteries inside a remote control.

You don't want to be easily accessible to young children.

Push-fit mechanical fixings join two parts by simply pushing them together such as a pen lid and they require friction to hold them together so that it does not come off.

Uses are joining tubes and lids.

Benefits are it's really simple and fast.

I'm sure you probably sat in your lesson with a pen and I'm sure you've probably taken that pen lid off really, really easily.

However, the limitation is it's not very strong and sometimes after you have used it so many times, it becomes a bit weaker and it won't push-fit quite so tightly.

Polymer rivet components are semi-permanent mechanical fixings which can be pushed, screwed, or even melted together through holes to lock parts together.

Examples include car polymer trims, signage, and electronics equipment.

And you can see in the pictures on the right at the top, we have push rivets.

Now they're really difficult to undo.

On the bottom, we have the screw rivets, which you can easily take out of course with a screwdriver.

And you can see there's three pieces of acrylic there, black, green, and red.

And they have simply been joined together by a screw rivet and we use them when we create polymer light shades at my school.

So examples, for use are lightweight polymer products.

Benefits are they are inexpensive and quick and they're also very lightweight.

The limitation is that if they are push rivets, they're very hard to remove.

However, if they're screw rivets, they're a lot easier too.

Time for a quick check-in.

What I'd like you to do is match the image of the mechanical fixing to its label.

So A, we have push-fit, B, we have rivet, C, we have snap-fit easy to disassemble, and D, we have snap-fit but difficult to disassemble.

Have a go at matching those to the correct picture.

Come back to me when you've got some lovely ideas.

Well done with your hard work on that.

Hopefully, you found that A matches with number three.

So the push-fit matches with the pen.

B, we have rivet which matches with image four, which is the polymer rivet at the bottom.

C, we have snap-fit easy to disassemble and that's that little fastening that you can use perhaps around a bike helmet fastening there.

And then lastly we have D, which is the snap-fit difficult to disassemble one which matches with number two.

And examples of that were things like electronics casings or remote controls where batteries are hidden behind and we don't want them to be easy to access.

Well done, folks.

Onto Task A.

Part one, I'd like you to describe the difference between a screw and a nut and bolt when joining polymers.

Part two, I'd like you to give an example of a snap-fit polymer and explain its purpose.

Part three, I'd like you to explain why a polymer rivet component might be appropriate for a polymer fixing.

And lastly, I would like you to choose one type of mechanical fixing for polymers and give one benefit and one limitation.

Good luck, I look forward to hearing lots of wonderful answers.

Part one, I asked you to describe the difference between a screw and a nut and bolt when joining polymers.

You might have said that a screw twists into the polymer to hold the parts together, whereas for a nut and bolt, they pass through both parts tightened with a nut for a stronger removable joint.

Part two, I asked you to give an example of a snap-fit polymer and explain its purpose.

You might have said toy bricks are an example of snap-fit polymers designed to interlock without screws or adhesives, allowing easy assembly and disassembly so that different ideas can be built time and time again.

Part three, I asked you to explain why a polymer rivet component might be appropriate for a polymer fixing.

You might have said polymer rivets are lightweight, corrosion resistant, and work well with polymers without damaging them.

Part four, I asked you to choose one type of mechanical fixing for polymers and give one benefit and one limitation.

You might have said push-fit polymer mechanical fixings join two parts together by simply pushing them together such as a pen lid.

They use friction to hold together and are quick and easy to use.

However, they do not provide a strong and secure fixing so are limited to what they can be used with.

Onto learning cycle two and chemical joining.

Chemical joining is the process of bonding materials using substances sometimes known as adhesives that create a chemical reaction to hold parts together.

Chemical joining is often invisible and used for clean finishes, not all the time though.

It can also be dependent on material compatibility and it's not easily reversible.

Quick check in, what makes chemical joining different from mechanical fixings? A, it's always weaker.

B, it uses force.

C, it requires bolts, or D, it involves a chemical reaction to bond materials.

Have a think.

Come back to me when you've got an idea.

Well done if you got D.

What makes chemical joining different from mechanical fixings is that it involves a chemical reaction to bond the materials.

Polymer welding chemically joins two polymer parts by heating and fusing them together with an added thermopolymer.

This creates a strong permanent bond often used in pipes, car parts, and polymer containers.

Let's take a closer look.

Have a little look at the diagram.

You can see that there is a heat gun there and the joining thermopolymer.

Now if we zoom into that, you will see that that joining thermopolymer is going all around the joint between that one pipe and the connector.

And that is basically what's going to create that strong permanent bond.

So, uses, pipes and large polymer parts.

The benefit is it is very strong.

The limitation though is it requires heat but also skill to get that really precise and leak-proof.

Solvent welding is a chemically joining process used mainly for thermopolymers.

The solvent softens or slightly dissolves the surface of the polymers allowing the polymer chains to merge as the solvent evaporates the materials fused together creating a really strong bond.

Now you might have had a go at chemically joining using solvent welding without knowing.

You are likely to have used tensile cement in your schools because we often use it for joining acrylic by the process of solvent welding.

And you'll recognize it because it's that bottle where your teacher will have said, "Make sure you put the lid back on" because as I've just said, the solvent evaporates and it will evaporate out of the bottle.

So it's really important to keep that lid on.

So where do we use it? We use it with plumbing and with joining rigid polymers.

The benefits are that it is permanent and watertight.

However, as you will know, the limitation is dangerous fumes.

That's why we encourage you to use it in a well-ventilated area with a mask.

And it can sometimes leave a white stain.

So if you've got a part of your product which is going to be seen and you want the aesthetics to be fantastic, you need to be careful about the use of solvent welding.

Epoxy resin chemically joins by mixing two parts, a resin and a hardener, which chemically reactor form a very strong and rigid bond.

Epoxy resin has a long curing time in comparison to other adhesives.

That means it takes a long time to set.

However, it is waterproof and chemically resistant and can be used with both thermopolymers and thermosetting polymers.

I've put here with the example picture, epoxy resin is often sold in a double syringe so that when you push that syringe, the resin and the hardener are dispersed evenly so that you don't have to guess at trying to get the same amount of both.

So use, it bonds dissimilar materials so that's great.

Benefit is it creates a very strong bond.

It is water and chemical resistant.

However limitations, it requires precise mixing.

Got to get it perfect and then it takes a long curing time.

So a long time to set.

You often have to leave it overnight.

A hot glue gun is a tool that melts solid glue sticks and dispenses hot adhesive for chemically joining various materials such as cardboard, fabric, polymers, and timbers.

However, as I'm sure you know, it may weaken, peel, or fail over time.

So uses, we use them a lot don't we in schools for joining various materials together.

And it's great when you are prototyping.

So benefits, it's got a quick setting bond and it can provide a good amount of strength when needed.

Limitations are it's messy.

There's a chance of burns.

You have to be really careful not to get that on your skin.

And as we've just said, it can weaken or peel or fail over time.

Super glue is a liquid adhesive that cures quickly by reacting with moisture to form a chemical bond.

It can join a variety of materials including some thermopolymers and thermosetting polymers too.

So we tend to use it with small polymer repairs.

Lots of people do tend to have a bottle of that in their homes.

Benefit, it is very fast-setting, especially in comparison to epoxy resin.

Limitations, it can sometimes be brittle and weak on flexible polymers.

Time for a quick check-in.

Which chemical joining process uses heat? Is it A, polymer welding? B, super glue? C, solvent welding, or D hot glue gun? Have a think.

Come back to me when you've got an answer.

Well done if you got A and D.

See, I was trying to trick you without saying processes.

Well done if you didn't get tricked.

So chemical joining processes that use heat are both polymer welding and hot glue gun.

Different adhesives suit different applications depending on strength, setting time, and environment.

Considerations include polymer type.

Is it a thermo or thermosetting polymer? Or can you join both of them? Polymer thickness, strength required, indoor or outdoor use, and drying or curing time.

The time it takes to set.

Onto Task B.

Part one, I'd like you to compare the use of solvent welding and super glue when joining polymers.

Give one advantage of each part.

Part two, a designer is creating an outdoor polymer toy for a young child.

Explain why polymer welding may be more appropriate than hot glue gun.

And lastly, part three, explain why epoxy resin is often used in high strength polymer applications.

Good luck with your answers.

Come back to me when you've got some fabulous ones.

Part one, I asked you to compare the use of solvent welding and super glue when joining polymers and then give one advantage of each.

You might have said solvent welding softens the surface as the solvent evaporates, the materials fused together creating a strong bond, and advantage is that it is ideal for joining similar polymers securely.

Whereas super glue bonds quickly by reacting with moisture in the air.

An advantage is it is fast-setting and can join a mixture of polymer types and works on small or intricate parts.

Part two, I asked you a designer is creating an outdoor polymer toy for a young child.

Explain why polymer welding may be more appropriate than hot glue gun.

You might have said polymer welding fuses the polymer parts together, making a strong, durable, and permanent joint that can withstand outdoor use and rough play, whereas hot glue may weaken, peel, or fail over time.

Part three, I asked you to explain why epoxy resin is often used in high strength polymer applications.

You might have said epoxy resin creates a very strong, durable, and rigid bond that can withstand stress, impact, and harsh conditions making it ideal for high-strength polymer applications such as sports equipments, bikes and surfboards, aerospace and automotive components, marine products and protective coatings.

Well done with all of your hard work on your wonderful answers.

This brings us to the end of our lesson today.

Let's summarize what we have found out.

Materials can be joined using mechanical fixings or components.

Materials can be joined using substances that create chemical bonds between surfaces.

Mechanical fixings for polymers can include snap-fit, push-fit, and rivets.

Chemical joining can be a variety of adhesives including polymer welding, solvent welding, epoxy, and hot glue.

Well done with all of your hard work today.

I hope you have enjoyed learning about different joining processes for polymers.

And I hope to see you in another lesson soon.

Take good care.

Bye, bye, bye.