The Simple Way to Minimize Angle Hairs in Plastic Pellet Conveying
Updated: Aug 28, 2020
Angel hairs are long, thin, plastic strings that are created in the pneumatic convey lines in a plastics plant. Also known as streamers or snakeskins, angel hairs are at a minimum a point of frustration and at most can be cause for rejection when a consumer receives a shipment. In this article we will go in depth on angel hairs and what you can do about them.
Causes of Angel Hairs
Preventing Angel Hairs
Types of Pneumatic Convey Lines
SPIRA/FLO - Name Brand Grooved Piping
How It's Made
What Causes Angel Hairs in Your Plastic Pellets?
Material degradation is a serious concern for everyone conveying plastic pellets. Some common problems that arise from an excess of streamers are plugged filters, higher maintenance cost, and inefficiencies in conveying. All of which lead to loss in profits.
When conveying plastic pellets in a pneumatic line, friction is the primary culprit of your angel hairs. As plastic pellets move through a pneumatic convey line, some pellets are dragged along the smooth walls of non-treated pipe. This dragging causes the pellets to heat up and melt into streamers, AKA angel hairs.
Another important note is that angel hairs cause other angel hairs. The smearing along the walls and elbows of convey lines gives other incoming pellets more to rub against and can rapidly compound your problem. It is import for your process to prevent and much angel hair formation as possible.
What Can You Do to Prevent Angel Hairs?
There are several ways to minimize angel hairs in plastic pellets conveying.
Grooved Piping – Using convey lines that are specially designed for reducing angel hairs can stop upwards of 80% of streamers from ever forming. The objective of using grooved piping is to create turbulent flow and minimize the time pellets are in contact with the walls. This should be the first step in preventing your plastic pellet streamers from forming.
Inline Coolers – Cooling down the air by installing inline coolers will help keep your plastic pellets below melting point, especially if you are already in a hot environment like Texas.
Slower Convey Speeds – Air velocity in a pneumatic convey line needs to be optimized to a 'goldilocks zone'. Too slow and you get saltation. Too fast and you get too hot.
Proper Pipe Layout– Minimizing elbows and keeping paths short will help prevent plastic pellet streamers and angel hairs by reducing impact and sliding zones.
Remove It – Avoiding all angel hairs is not possible and thus you will need an angel hair trap somewhere in your process to catch what is not prevented.
Different Types of Pneumatic Convey Lines
The simplest and most effective way to minimize angel hair production in the pneumatic line is to choose the right piping to begin with. There are several options when looking for the best tubing for plastic pellets, ranging from off-the-shelve, smooth piping to specially crafted, patented tubing design specifically for plastic pellets.
The cheapest and least effective type of tubing for pneumatic conveying is smooth, off-the-shelve piping. This tubing will give you the most headaches and requires the most human intervention for removing streamers from your angel hair trap downstream in the process.
Smooth Piping (credit: harrisonplastic.com)
The simplest and most effective way of preventing angel hairs is SPIRA/FLO piping. Available in a multitude of sizes and materials of construction, SPIRA/FLO is a pressed grove tubing for pneumatic conveying of plastic pellets. Pressed grove piping differs from cut grove piping in that the groves are pressed into the aluminum or steel displacing the metal instead of removing it.
Cut Groove Piping
Similar in principal to pressed groove tubing, cut groove tubing creates turbulence in the air stream to prevent sliding along the walls of the convey lines. The two downsides of cut grooves are short life span and more fines production. Cutting material out of the tubing creates sharp edges resulting in more fines to be removed later in your process. In addition, cutting material out of the aluminum or steel creates thinner walls where the cuts were made, shortening its lifespan.
Cut Groove Piping (credit: ptonline.com)
Dimpled/Shot Peened Piping
To avoid sharp edges in the tubing created by cut grooves, some manufactures have turned to dimpled piping. This is created by sand blasting the inside of the tubing creating small craters with the intention of creating turbulence. Dimpled piping is often preferred to cut grooves because it will have less product degradation. It is important to keep in mind dimpled needs resurfacing roughly every 12 months resulting in downtime and extra maintenance costs.
Shot Peened Piping (credit: iac-intl.com)
SPIRA/FLO Pipe – Name Brand Grooved Piping
Delta Ducon created a propriety technology in 1970 to minimize the amount of angel hairs forming in plastics conveying. With a goal of reducing streamers without generating more fines, the research team at Delta Ducon found that pressed groove piping is the most effective way of accomplishing this goal. The difference in quality over the competition is substantial. By displacing metal instead of cutting grooves out of the piping, SPIRA/FLO piping reduces production of angel hairs without increasing fines and without wearing out rapidly.
Some common reasons customers choose SPIRA/FLO:
Most effective method of preventing angel hairs in plastics conveying
Roughly same price as less-effective options
5-year guarantee (see link at bottom for details)
Does not increase fines production
Eliminates labor cost and downtime required for re-treatment
Other pipe treatment wears out and loses effectiveness
How It’s Made
The process to create SPIRA/FLO piping is applied to standard tubing specifically chosen by the customer to suit their exact process.
For example, a customer may need a schedule 10, 6” aluminum tubing for their convey lines. Delta Ducon will purchase the required amount of pipe from a qualified US supplier. Delta Ducon accepts only the highest quality US manufactured piping to ensure they can stand behind the 5 year guarantee they offer.
After receiving and inspecting the tubing, Delta Ducon will apply their patented SPIRA/FLO process to the straight tubing to displace the metal inside the aluminum creating smooth grooves. It is important to note that the metal is not cut out. Cutting out the grooves inside the pipe creates sharp edges and thinner tubing walls resulting in more fines and shorter life cycle.
After the grooves have been pressed into the aluminum, Delta Ducon will bend the pipes in locations specified by the customer and ship the end product to the customer.
For more information about SPIRA/FLO piping and information about guarantee see: http://www.deltaducon.com/spiraflo-pipe