Narrator:
the deck of a railway bridge
Is typically built of
wood-timbers called bridge ties.
They're bolted
to steel support beams
Located on concrete piers
over the water or gully below.
The rails
on which the train travels
Are bolted to the wooden ties.
Wood absorbs the noise
and vibration
Of the passing train.
The load
the railway bridge will carry
Determines the size of its ties.
To calculate the load,
Engineers factor in
the number of tracks,
Volume of traffic,
weight of the transported cargo,
And whether the bridge
is straight or curved.
A curve will put additional
stress on the structure.
The wood of choice is oak
because it's hard and strong.
When the logs
arrive at the sawmill,
They come face-to-face
with a menacing-looking device
Called a debarker.
A conveyor moves the shipment
toward the debarker,
Then drops a single log in front
of it onto spinning rollers.
The rollers rotate the log,
While the debarker makes its way
from one end to the other.
It chews off the bark
with its sharp-toothed blades.
What the debarker shaves
off is put to good use.
The bark gets processed
into gardening mulch
And they burn the sawdust
in the wood-fired boiler
That runs another part
of the plant.
Next, one log at a time
drops into a mobile carriage
That runs it
through a circular saw.
The carriage has sensors
Which detect
the log's extremities
And report its dimensions
To a console located
in the operator's cab.
The operator
interprets the data.
Using a joystick controller,
He flips the log
into whichever position
Maximizes the yield.
The first few runs
Trim off the rough surface
and square the shape.
The next runs cut boards,
Which the sawmill
sells to flooring plants.
This continues until the log
is the exact dimensions
Of the bridge tie.
Again, nothing is wasted.
The sawmill processes
the cutoffs into wood chips,
Which it then sells to companies
that make particle board,
Strand board, and similar
construction materials.
The sawmill stacks the ties
For transfer
to the bridge mill next door.
The role of the bridge mill
is to frame the bridge,
Also known as dapping.
That's the process
of making the specific holes
And notches in each tie
For attaching it to the steel
beam on which it will sit.
At the bridge mill,
The bridge layout supervisor
processes one tie at a time.
He carefully reviews
the engineer's blueprints,
Which assign a number
to each and every tie.
These numbers specify precisely
where the saw has to cut notches
And where the drill
has to bore holes.
The locations of these notches
and holes vary,
Depending on the tie's position
on the bridge.
So, he must follow
the blueprints meticulously.
After measuring
and marking it all out,
He sends the tie to the dap saw.
The operator sets up each cut,
Lining up the mark
with laser-lights,
Which indicate the location
and the cutting depth
Of the blade.
The notches are just the right
size to fit over the steel beam
On which the tie will lie.
Next,
a worker using a drill press
Bores holes for hook bolts,
which go through the tie
To secure it
onto the steel beams.
Each tie receives a metal
identification tag,
Which includes the bridge
and tie numbers.
On each end,
workers nail on a mesh plate,
Made of rust-proof
galvanized steel.
The plate has teeth designed
to grasp and hold together
The wood fiber to prevent
the end from splitting.
After nailing the id tag
to one of the end plates,
Workers force in both plates
with a press.
The tie's last stop
is the adjacent treatment plant.
They spend 24 hours
inside a high-temperature,
High-pressure chamber
Which penetrates them
with a creosote-borate solution.
This protects the wood
from rot and insect damage
And extends the tie's life-span
From about a decade
to at least 25 years.
Narrator:
when filtering liquids,
It's all about thinking small.
Membrane filters can separate
the tiniest solids from fluids,
Which purifies the liquids
and recovers the solids.
Once separated,
the two substances
May then be reused
so that nothing goes to waste.
Membrane filters can turn murky
water clear, almost magically.
To demonstrate, a technician
installs a spiral-wound membrane
In the housing
of a pumping system,
Which is a small-scale version
Of what you would see
in a factory.
She turns on the tap,
and water flows into a tank.
She adds latex paint
to purposely sully the water.
The system pumps
the contaminated water
Through a strainer
And then the membrane filter
while meters measure the flow.
Within minutes, the paint
has been filtered out,
And the water is clear.
The making of a membrane filter
begins with polypropylene mesh.
An automated system unwinds
the mesh and cuts it to length.
These mesh sheets
will be used as spacers.
They'll create gaps
for the liquid
To flow through the filter
and over the membrane.
Next, the system
cuts sheets of polyester fabric.
These will form channels
Through which the filtered
material will travel.
These sheets are known
as permeate spacers.
An employee stacks
the polyester fabric sheets.
Using high-frequency
sound waves,
She welds one sheet to the next
at just one end.
She layers and welds
a total of 15 sheets,
And then applies
double-sided tape.
The tape is for attaching
the packet to a central tube,
And it will also serve as
a guide to correctly align it.
Next, the membrane soup
flows into a long trough.
It's a mix
of melted plastics and solvents.
Paper backing unwinds
into the trough
And is coated with the soup
on one side.
The coated paper then travels
through two quench tanks,
And the plastic components
solidify
As the solvents are drawn out.
The exiting solvents
create a unique core structure
In the remaining
white plastic membrane.
The membrane now
travels by a light box,
Which illuminates
any visual defects.
An applicator also drips a
preservative onto the membrane.
A team unrolls the membrane
onto a work table.
They lay a sheet
of the polypropylene mesh,
Which we saw cut to size
earlier, on the membrane.
The employee
then cuts the membrane
To twice the length of the mesh.
They fold the membrane
over the mesh,
Creating a membrane envelope.
The mesh serves as a pathway
for fluid
To flow between the membranes.
Meanwhile, another worker
Applies epoxy
to perforated plastic tube.
He attaches
the permeate spacers to it
With the double-sided tape,
Giving the epoxy time to cure
for a permanent seal.
He and a colleague
apply more epoxy
To the perimeter
of the bottom sheet.
They transfer
the membrane envelope to it
And continue to layer,
Making a permeate fabric
and membrane sandwich.
The worker then winds
the glued layers snuggly
To a perforated plastic core,
Forming
the spiral membrane filter.
He tapes the multi-layered wad
from one end to the other.
The tape holds everything
tightly in place
As the epoxy cures overnight.
They leave the tape
on after the cure,
And a machine winds
epoxy-drenched fiberglass rope
Around the entire filter.
As the epoxy cures,
The rope will form a hard shell
around the membrane filter.
Partway through,
They apply the label
with a company name.
The operator captures the glue
runoff during the wind.
And it's a wrap,
so he cuts the rope.
From the side,
you can see the flow channels
Between the layers.
Concentrated contaminants will
travel through them and out.
The filtered liquid will seep
into the core and exit,
Clearly improved.
Narrator: the invention
of the hydraulic post driver
In the 1960s
Allowed workers to drop
their shovels and sledgehammers
And let a machine do the job
of pounding fence and sign posts
Into the ground.
When it comes
to labor-saving inventions,
This one is definitely
a striking example.
The post driver
Raises hefty fence
or sign posts into position,
And then slams them
into the ground.
Inside a vertical case,
a hydraulic system
Drops a 300-pound weight
to drive the post,
And then lifts it
for another hit.
This machine does the work
of two or more brawny humans
With just one person
at the controls.
To make it, they start with
a vertical case for the weight.
A high-precision plasma torch
Cuts steel
into a rectangular shape
And makes holes for components.
They insert the rectangle
into a break-press repeatedly
To bend it
into a three-sided part.
The profile includes flanges
For welding it
to the back wall of the case.
He fits the part
to the back wall
And welds them together,
completing the post driver case.
An employee builds
the post driver weight
Working within a weld fixture.
It's a box-shaped weight,
and he welds it at the seams.
He taps the corners
between the welds
To maintain
a tight configuration.
This 300-pound weight can later
be filled with steel shot
To make it even heavier
for greater impact.
The next worker assembles
yellow steel jaws to a hub
To produce the grapple.
This is the part
that grips the fence post
And raises it into position.
He sticks a danger label
onto the hub
To warn people to stay clear
of these powerful jaws.
He attaches
a hydraulic cylinder,
Which will make
the jaws open and close.
He connects the cylinder
to the grapple jaw.
Next,
they move on to the metal plate
That will be used to mount
the post driver to a vehicle,
Like a skid-steer loader.
It includes
a hydraulic mechanism
For tilting the fence post
left or right.
The employee installs a control
valve next to the cylinder
And links the two with hoses.
He'll also connect the grapple
And weight hydraulics
to this valve.
Back to the post driver case
now -- it's been painted,
And they're ready to install
the hydraulic motor.
The worker connects it
to the sprockets and chains
That will lift the weight.
He pins the sprockets into place
And installs tensioning rods
on either side.
Next, a cover plate
protects the sprockets.
The tensioning rods
protrude through it.
He slides springs
onto those tensioning rods
And compresses the springs
to maintain the tension.
He now attaches the grapple
to the post driver case.
He locks it into place
with a long pin.
He links the grapple hydraulics
to the control valve.
And it's ready to grab
big fence posts
And hold on tight.
They attach the metal mounting
plate to the post driver case.
The work table tilts back
to move the post driver
Into an upright position.
With the help of a crane,
The next worker
moves the weight into position
And lowers it into the case.
He slides a pin into the top end
To keep the weight
from falling out
When the post driver
is on an angle.
One day in the making,
This hydraulic post driver is
ready for years of heavy labor,
Taking over for humans so they
don't have to move a muscle.
Narrator: a biplane
is a vintage-style aircraft
With two pairs of wings
sitting one above the other.
The top wings are typically
raised above the fuselage
With vertical struts bracing
them to the bottom wings.
Dating back to the earliest days
of aviation,
They're still popular
for performing aerobatics.
A biplane's lower wings
have ailerons,
Which bank the airplane
to the right or left.
On the plane's tail,
Elevators pitch the plane's nose
up or down
While a rudder steers it
left or right.
A propeller
provides the propulsion.
The plane has four wings.
Each wing has two spars,
Wooden beams
at the front and rear,
Which form
the perimeter structure.
A craftsman skillfully fashions
these spars out of sitka spruce.
This wood is exceedingly light,
yet exceptionally strong,
Making it one
of only a few woods
Approved for structural use
in airplanes.
After sawing the wood
to the spar's shape,
He mounts attachment plates
made of sitka spruce
And mahogany plywood.
These are the end struts,
Steel vertical bars
which will connect the upper
And lower wings.
He finishes the spar
by refining its contour,
First with a hand plane,
then an electric plane.
Using strips of sitka spruce,
He constructs 15 structural ribs
for each wing.
He begins with long strips,
Which have been soaking in water
for a week to make them pliable.
He inserts one end
into a curved fixture
And leaves the strips to dry.
When he removes them a couple
of days later,
They have a permanent
aerodynamic curve.
He glues
two curved strips together
To form the perimeter
of one rib.
In between, he glues short
diagonal strips called trusses.
He reinforces both sides
of each intersection
With a rectangular piece
called a gusset.
An assembler mounts the 15 ribs
crosswise
On the front and rear
wing spars,
Then installs three aluminum
tubes called compression ribs.
These absorb air load
hitting the spars,
Keeping the wooden ribs
from flexing under pressure.
The craftsman
connects the compression ribs
With criss-crossing metal rods.
After applying more glue
to critical areas,
He nails an aluminum trim
Over the front spar
and nose of the ribs.
This is called the leading edge.
It's the first part of the wing
to hit the wind,
So it takes the brunt
of the air load.
Finally, he laces reinforcement
tape through the ribs
In an x pattern.
The completed structure now
moves to the covering department
Where technicians drape it
In heat shrinkable
polyester fabric.
They cut the fabric to size,
glue it to the wing perimeter,
And heat the surface
with an iron
To shrink the fabric
until it's taut.
Then, they stitch over the glued
areas with polyester cord.
They brush on a chemical
which seals the pores
Of the fabric.
This primes the surface
to receive a spray coat
Of polyurethane paint,
Which is a special formulation
designed for aircraft bodies.
Technicians construct
the fuselage frame
Out of high-strength
steel alloy tubes.
They use an electric torch to
slightly melt adjoining pieces
So they fuse to each other.
Because there's no filler metal
bonding the pieces,
The welds don't add any weight
to the structure.
After painting the frame,
Technicians install aluminum
floor panels and bulkheads.
In the tail, they add
lighter weight bulkheads
Made of mahogany plywood
and sitka spruce.
Then it's time
to bolt the engine
To the front
of the fuselage frame.
The engine drives a propeller
Made of either wood, aluminum,
or a composite material.
Painted aluminum body panels
cover the frame.
Technicians
install the fuel tank
Between the front c*ck
and the engine.
Then they bolt the wings
to the fuselage.
Vertical steel struts
connect and reinforce
The two levels of wings
Bolting to those attachment
plates on the wing spars.
Next, technicians mount
the painted aluminum ailerons,
The tail,
with its elevators and rudder
Made of painted fabric
over welded steel,
And then the engine cover.
They install a windscreen
And instrument panel
for each c*ck.
The front screen can be replaced
with a c*ck cover
To keep the pilots warm
when flying in cold weather.
If you have any comments
about the show,
Or if you'd like to suggest
topics for future shows,
Drop us a line at...
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