Basic Fabrication Flashcards
What are transitional fittings used for ?
Are used to change the aspect ratio and to move duct for architectural reasons.
Why is the use of transitional fittings avoided?
Time and money
What are the 3 types of joints used to join transitional fittings ?
- Slip and drive
- cp
- proprietary connection
Why must the slip and drive joint be adjusted on transitional fittings ?
Because the 1” slip cannot be at an angle to the next fitting
You must reduce the length of the net pattern by ____ for each slip and drive connection
1”
When developing the piece for a 2 side flat transition. What should determine which sloped side gets pocket allowances ?
The side that has the most amount of slope because there is less angle for transfer of angle notch.
Why would blocking be used when assembling a transitional fitting with raw edges ?
- form seams and edges
- open pittsburgh locks
Why would the throat and heel be fastened to one cheek instead of fastening both cheeks to either the throat or the heel?
The throat or heel can help support the cheek during assembly
What portion of a plan view for a rectangle to round fitting needs to be developed if the round portion is flat on top and centred in the other direction?
1/2 plan view
When is it advisable to use more then 12 element points for a square to round fitting ?
If the diameter is over 12”
When laying out a pattern for a square to round fitting that is centred you need to lay out how much of the pattern ?
1/4 pattern for the fitting
Why should construction lines be on the inside ?
Makes for a neater job
When folding the allowance for a grooved seam what should you always do?
Fold slightly less than its nominal size
What is the first step when completing a groove seam?
Dress the hooked material down to 4 metal thicknesses using a smooth hammer
What is the material removed by the plasma called ?
Kerf
What is the power source of the plasma ?
Silicon controlled rectifiers or inverters called plasma aggregates
What shade of eye protection should be used with the plasma ?
Eye protection or dark goggles that have a shade from 7-9
What is auto nesting ?
Auto nesting allows you to optimize material usage
What is a duty cycle ?
Rated as a percentage of a 10 minute period
What are the consumables on a plasma ?
The nozzle and the electrode
What is a good rule of thumb when cutting with the plasma ?
Choose a machine class that is 2 times your cutting thickness
What is needed to change the size of the plasma arc ?
Amperage, voltage, gas flow and velocity
How are nozzles sized ?
According to amperage rating
What do slow cutting speeds produce ?
Vertical lag lines that are perpendicular to the plane of the plate
What do fast cutting speeds do??
Make slanted - s shape lag lines that run parallel to the plate on the bottom edge
How should dross be removed ?
By grinding or filing mechanically to minimize the wearing out of equipment parts
What is the most important piece of PPE to wear ?
A welding helmet
why is argon dangerous in an enclosed space ?
Because it is heavier than air and can displace oxygen
What 3 procedures are required before returning an empty compressed gas cylinder ?
- close the valve completely
- install the protective cap
- replace any valve plugs or caps
What are 3 advantages of GTAW?
- ability to join most weldable metals
- most welds are high quality
- the heat source and filler can be controlled separately
What is the most common gas used for GTAW?
Argon
What color is 2% thoriated tungsten coded?
Red
What color is pure tungsten coded?
Green
What polarity is used when welding steel?
DCSP or DCEN
What may cause a lack of fusion ?
- arc length too long
- current setting too low
- incorrect joint preparation
- poor joint alignment
Why is it better to make proper round template before starting to brake form an aluminum square to round?
Shaping is easier to control which makes tracking easier
Why is it good trade practice to weld 4 piece fittings on the centre of the conical portion?
Proper fit and shaping is easier.
What is the most common method to minimize warping when welding aluminum?
Increase the distance between welds
What color is 1% thoriated tungsten coded?
Yellow
What polarity is used when welding aluminum ?
AC
What is the most common symptom of inadequate or wrong type of gas flow ?
Tungsten is immediately consumed
What tungsten would be the best to use on 1/8” thick aluminum ?
1%
What should you do when using a band saw to cut aluminum?
- use proper coolant
- listen to the saw
- keep blade tight
A shear is rated for 16ga mild steel. What is the rating for stainless steel?
20ga
When forming or cutting stainless, equipment must be de rated by how many gauges ?
4ga
Iron dust contamination can cause what to happen to stainless steel?
Rust
When bending stainless you need to compensate for _______ by over bending
Spring back
What is the best advantage of using an air bending dye over a 90 degree v-dye for bending acute angles ?
Less pressure is required
In which series do austenitic steels belong ?
300 series
What is the most common group of stainless steel used today?
Austenitic
What should be done when using a band saw to cut stainless?
Lower blade speed
What method of bending should be used when power braking ?
Air bending
Can stainless steel be soldered ?
Yes
Can stainless steel be polished to a mirror finish?
Yes
What settings must be done prior to spot welding stainless steel?
Increase pressure, decrease current
What is the best method of welding stainless ?
GTAW
What are some methods of distortion control on stainless Steel?
Copper chill plates, skip welding , step back welding
What are the 4 steps in finishing stainless steel?
Grind, sand, polish, buff
