Extrusion Blow Molding: Part Quality and Problem Solving

Extrusion blow molder face many problems daily during the production. If  problems are not solve immediately and efficiently then there is decrease in profitand efficiency. To overcome these problems and to run smooth productionanalytical method of problem solving method is used.

Analytical Method of Problem solving

In actual analytical method, one compares all the actual control settings at that timewith setup sheet and check for every setting if there is any change in any settingscorrect it. If all the settings are according to setup sheet then determine where theactual problem is and either problem is continuous are discontinuous. If notcontinuous, determine when the problem is occurs.Problem can be solved by changing in following:

Problem can be solved by changing in following:

• Variables of Plastic Processing
• Machine Control Changes
• Plastic Processing Conditions
• Molded Part Properties

Variables in plastic processing

For solving problem these four variables are changed

• Plastic Temperature
• Plastic pressure
• Plastic Flow Rate
• Plastic Cooling Rate

So to solve the problem changes can be made in any one of these four or combination for example temperature of resin may be different batch to batch. Plastic flow from hopper to barrel or from auto loader may vary. If cram feeder is being used rpm or feeder may vary.

Machine control changes

Machine control that can be changes to end problem are

• Barrel Temperature
• Parison rate
• Accumulator Temperature
• Die head temperature
• Cooling time
• Mold temperatures
• Air pressure
• Air flow rate

These 8 changes can be made in machine controls to remove problems like increase the barrel temperature if machine load is increasing and lower the barrel temperature if plastic starts degrading. Change in any above parameters may take 20 to 40 mints depends on the size of machine. So wait till that change. Change in any parameter may results in change more than one parameter so be careful while changing any parameter.

Plastic processing conditions

Plastic processing conditions that can effect production and product quality are

• Temperature
• Pressure
• Cooling
• Flow rate

These four changes effect such as high temperature outside requires high rate of coolant in the mold reverse is the case in winter.

Extrusion Blow molding Steps

Extrusion blow molding can be divided into three simple steps

• Parison, a tube like shape forming
• Reshaping the parison into a blown part that meet customers specification
• Cooling the part in the mold

Variables controlling the flow of plastic through die head

Gap thickness between mandrel and bushing

Plastic pressure

Land length of die

Viscosity of molten plastic.