What is drawdown ratio in blown films?
What is drawdown ratio in blown films?
The drawdown ratio (DR) is the velocity of the film at the nip rolls divided by the average melt velocity at the die exit. The properties of the film produced depend on the polymer used and the processing conditions. It is well established that product properties are strongly influenced by morphology.
What is the principle of extrusion process and with a neat sketch explain about blown film die?
Blown film extrusion is a technology that is the most common method to make plasticW films, especially for the packaging industry. The process involves extruding a tube of molten polymerW through a die and inflating to several times its initial diameter to form a thin film bubble.
Which roll is used in film blowing process?
The tube of the film continues its movement upwards (constantly colling) till is is passed via nip rolls. Here, the tube is flattened for the creation of “lay-flat” tube of film. Also known as collapsed tube, this lay-flat tube goes back to the extrusion tower via rollers.
What does a blown film operator do?
The Blown Film Operator is responsible for the overall operation of the blown film line to manufacture quality (customer standards) products as determined by the production schedule, and to gain and …
What is the function of breaker plate?
Breaker plates are common in the extrusion industry and serve two main purposes: to help mix molten polymer as it exits the extruder (eliminating rotational memory and creating longitudinal memory); and to support the filtration media.
What is the difference between blown and cast film?
Cast film is minimally pre-stretched compared with blown film giving it improved depth of drawing for thermoforming operations. The cooling process can be used to produce different characteristics in the final product. Cast film can be thinned by winding the film out of the roller faster than it is extruded.
What is extrusion ratio?
The extrusion ratio is the ratio of the area of the work billets cross section (Ao) to that of the extrusion’s cross section (Af). The extrusion ratio, or reduction ratio, can be expressed as (Ao/Af). There is a general rule that if an alloy has higher mechanical properties the extrusion rate needs to be lower.
How do you calculate extrusion ratio?
The extrusion ratio of a shape is a clear indication of the amount of mechanical working that will occur as the shape is extruded. Extrusion Ratio = area of billet/area of shape.
What is the difference between draw down ratio and blow ratio?
The final thickness reduction in the melt after blowing is indicated by a draw down ratio. A third ratio, called the blow ratio (BR), is the increase of lay flat width over die diameter. BR is used less frequently, but can easily be confused in conversation with the more common BUR.
What is the bur and drawdown ratio?
The formula to obtain the BUR and drawdown ratios and their meanings are as follows: Drawdown Ratio (DDR) = Width of Die Gap Film Thickness x BUR BUR indicates the increase in the bubble diameter over the die diameter. The die gap divided by the BUR indicates the theoretical thickness of the melt after reduction by blowing.
What is the draw down ratio of a melt?
Drawdown Ratio (DDR) = Width of Die Gap/Film Thickness x BUR The final thickness reduction in the melt after blowing is indicated by a draw down ratio. A third ratio, called the blow ratio (BR), is the increase of lay flat width over die diameter. BR is used less frequently, but can easily be confused in conversation with the more common BUR.
Does practice always follow theory when making blown film?
Even though practice does not always follow theory, theory can help explain many of the problems encountered in extruding polyethylene into blown film. For example, blow-up ratio (BUR) used alone as a film-making parameter is meaning- less. BUR must be related to draw-down ratio and die gap.
