PET PREFORM

PET PREFORM

After a long time, when I want to start again writing something on Plastics, It took a while to think what should I write, which can helpful for peoples, So decided to share my Practical Experience which I gain working with different organization and different location and while handling different type of machines & molds.

So with this article, I am starting a chain of Plastic molding information which had been gain during my working, The first topic I selected is PET Preform Manufacturing, it is a wide topic involve different different type of Molding technique based on wide rage of Technology available across the world.

PET preform are present in various type, size, shape and Grammage based on End use application.

PET Preform being produced by using different type of PET material, Again Selection of right PET Material is very important, what going to be produce and what is end use of Preform.

So I will cover PET Preform manufacturing based on End use Application start from right PET material selection, Mold, Molding machine and Processing methods.

Thanks to All my friends who likes my post, You All people who are engaged in Plastic Molding manufacturing also can suggest me, What topic can be selected, or if you need more information about.

Thanks.

The 5 M’s of Molding—Part 5: Method

Once a molding problem has been identified, use “method” to determine whether the issue is with Man, Mold, Machine or Material.

The final M in the 5M equation refers to “Method”. Method is a very broad category that directly applies to man, mold, machine and material. Method also considers all internal and external contributors that affect the key measurable of a lean production operation.

Key measurables in plastic injection consist of production efficiency, scrap and downtime. The primary goal of lean manufacturing is 100% efficiency, 0% scrap and down time that is planned, not unplanned. These goals can sometimes seem to be challenging to achieve, but with proper analysis and approach the end result can be successful and profitable.

As measurables are recorded, a part history is developed. It is this historical data that we use to identify repeating and/or poorly performing variables. It also helps us to scrutinize what areas of production need improvement.

Once clear identification of a problem has been accomplished, it is then time to ask the question, “is this problem directly associated with Man, Mold, Machine or Material?” In some situations, only one of these will require change. In others, it could be all four that need correction. By establishing which of these categories need to be addressed, it becomes easier to develop solutions that will improve our “method”.

Here is an example of the 5 M method in use:

A Japanese headlight manufacturer determined through scrap data that a significant amount of scratches was appearing on parts already assembled. The cost of this sort of rework is quite costly… parts already assembled would need to be tore down, replacement lenses molded and then a second assembly performed to refurbish the part to an acceptable quality level.

man, mold, machine and material were all considered to determine when and how the scratches were occurring. After review of the entire production process from in-mold to assembly, the cause of the scratches was tracked to two separate problems, both of which were directly related to “man”. The problems were:

Parts produced were packed into cardboard for storage. Some scratches were due to operator handling as they were packed. The boxes were stacked on skids and then transported into warehouse racking.

When parts were needed, they were pulled from warehouse and then transported to the assembly area. Some scratches resulted directly from parts jostling as they were handled by warehouse personnel.

To eliminate the problem, special carts were developed made of a soft cloth that allowed for the parts to be packed, stored and transported to assembly without the threat of scratched product from packing and transport. What had been a very large problem became non-existent through proper analysis and methodical approach.

The 5M approach to molding is an excellent way to clearly identify problems, which is the foundation to any problem solving event. Full understanding of any problem helps to develop the most credible solution to the problems presented. Develop, maintain and regularly review recordable data for measuring production, scrap and downtime efficiencies. As the level of historical data increases, factors that improve production are discovered and implemented. That same data also offers insight into what problems exist. Clearly define the problem, and then review whether it is directly related to man, mold, machine or material. Remember that it could be one, several or all four contributing to the situation.

Develop a solid list of all areas contributing to the problem, and then systematically define solutions to those issues. Effective solutions require a complete understanding of the problems being addressed. Utilize all personnel directly related to the problem to best develop understanding and methods for correction. Effectively defining problems and solutions is dependent upon the complete knowledge base of your entire team. As their ability to create and adapt to change is refined, continuous improvement becomes more enjoyable. Clearly defined solutions add to the strength of your organization, bringing it one step closer to world-class manufacturing.

The 5 M’s of Molding—Part 4: Machine

Machinery/Auxiliary Equipment: The molding standard you set is highly dependent upon the machinery and auxiliary equipment you have available to you. Failure to properly assess the capabilities of your equipment will result in a poorly functioning production system. The following components strongly affect a facility’s scrap, downtime and productivity:

1.     Press: Molding machine capabilities are crucial to the design of any manufacturing system. Press tonnage and screw design (such as general purpose vs. nylon) are key factors in process consistency. Match your mold and material to the press to assure that your process control is not limited due to poorly functioning machinery. Also utilize your process data to further assess process control and machine problems.

2.     Robot: Robotics systems are a valuable asset for establishing production and quality systems. When evaluating the production system, always review potential fixes through robot improvements, end of arm tooling or programming changes.

3.     Automation: Other sources of automation should also be reviewed. For instance, if a quality concern keeps repeating itself, look for solutions through automation development. Involve everyone on your production team to fully assess what failures exist within the production system and utilize your engineers to develop working solutions. Better equip your operators and personnel to remove problematic conditions from the production equation.

Preventative maintenance is a key measurable in the Machinery/Equipment category. Unscheduled downtime seriously impedes production efficiencies due to the nature of unexpected system failures and the resulting unprepared approach towards resolution. Scheduled maintenance events are by far the best way to prevent poor performance. Here are some of the areas where preventative maintenance can prevent unscheduled break downs. Each of these components should have their own maintenance log to help establish what concerns are and what frequency of inspection needs to be:

1.     Molding machine: Press breakdowns can be avoided with a regular inspection system in place. Here are some of the primary inspections and a recommended frequency for performing them:

§  Hydraulic Fluid- Quarterly: Fluid samples should be taken and sent to a screener to evaluate metal content and viscosity break down.

§  Hoses- Weekly: Inspect hoses for signs of wear, rubbing or blistering.

§  Screw- Bi-Annually: Remove screw for inspection. Measure flights and shank to determine whether wear is becoming an issue. Also measure the metering zone of the barrel to verify condition.

§  Electrical-Weekly: Look for unsafe conditions and integrity of connectors.

§  Heater Bands- Monthly: Verify that all bands are in working condition

2.     Tooling- It is important to note that a simple 10-minute inspection of every mold per shift can identify problems and prevent hours of down time due to dry slides, pins, etc. Keep detailed records of mold repairs and use them to develop preventative maintenance events and timing. In a short-run shop, simple teardown and cleaning should occur after every run. In cases where molds run for extended periods of time, regular inspection should occur and molds should be torn down and cleaned bi-weekly. In all cases, cleaning frequencies should be developed based on mold history to prevent breakage through intervention and care.

The 5 M’s of Molding—Part 3: Material

You’ve accounted for variability in two other “Ms”—mold and man—but materials in their lot-to-lot differences and handling challenges pose a distinct threat to repeatability.

Material:  One of the fundamental considerations in processing is the material being used. Processing relies heavily upon the consistency and quality of the plastic that has been chosen for the part’s aesthetic and dimensional make up. Here are some of the primary variables that need to be reviewed during the stages of process development and in some cases continuous improvement.

Properties: Every material has its own unique set of molding properties that must be considered as a molding operation is developed. Here is a list of some of these properties as they relate to part aesthetics and dimensions:

Temperature- Mold and barrel temperatures are a huge part of the molding equation. Some examples of potential heat-related deficiencies would be long cycles, warping, burn at end of fill, gassing, etc.

 Shrinkage- Every material has its own rate of shrinkage and this is one key measurable that should be considered as material choice is being decided.

Melt Flow: Material viscosity is a key component during process development and improvement review. For instance, a heavily ribbed part might be better suited with a material with a low viscosity to assure that the flowfront moves quickly across the ribs preventing an overpack condition.

Aesthetics & Dimension: There are many variations on engineered materials that either benefit or detract from the overall performance and functionality of part production. Utilize the knowledge and resources of your material manufacturer whenever possible to find the appropriate material solutions.

Additives: There are many situations where material additives can create problems or provide solutions. For instance, the use of color mixing may seem cost effective, yet generate scrap due to poor diffusion leading to faulty parts via color swirls. Or from a different perspective, adding a lubricant to polypropylene might eliminate parts sticking in a mold where draft cannot be added. Work with your material supplier to develop and/or improve a part’s molding capabilities.

Drying: Drying is always a major factor in process consistency. Verify that your dryer throughput is sufficient enough to allow adequate time to properly dry the material being used. It is also important to verify that the material is truly dry through moisture analysis.

Characteristics: When choosing a material, it is important to understand what the typical characteristics are regarding a material’s performance and drawbacks. For instance, nylon has a tendency to shrink; polypropylene tends to have sink issues over large or deep ribs. Look for materials that match the functionality of the part being molded while avoiding potential problems associated with material choice.

The Five “Ms” of Molding—Part II: The Mold

A bad mold can cripple a process; learn what areas should be considered as a tool is evaluated and reviewed.

 

Tooling is a key foundation block when developing a work program. A poorly designed or improperly functioning mold can become the root cause for systematic failures. In addition, as continuous improvement projects are outlined, the mold should be reviewed for potential improvements through modification. The next section outlines major areas that should be considered as the tool is evaluated and reviewed:

 

Design: The very first step of successful molding is how well the mold has been designed to fit a particular application. Molds that do not perform well because of poor processing capabilities, frequent breakage or fluctuating molding conditions are crippling to a company’s productivity and efficiencies. Molding simulation software is a great tool for mold development. The ability to analyze mold temperature, pressure fluctuation and how the flowfront will likely perform greatly improves the designer’s ability to make adjustments to the tooling to counteract potential molding problems before they happen.

 

Qualification-Tooling: There are many different aspects to mold qualification. The primary goal of qualifying a mold is to develop tooling that consistently produces quality parts at an optimal cycle time. Here is a list of some of the primary areas that are important to mold qualification.

 

Balancing the runner system: The need to verify that the cavitation is balanced is paramount to a molder’s ability to control his process. Part weights should be consistent and equal. Parts that weigh more or less than the mean should be adjusted by making changes to the gates. Sprue, runners and gates should allow for adequate filling based on material properties.

 

Mold Temperature:  The ability to heat or cool the mold consistently is a vital part of building a consistent process. The mold faces should be checked in multiple areas to verify that temperatures are equal and consistent. Hot or cold spots can cause major inconsistencies. Adding or removing circuits might be needed to accomplish this. In addition, the mold circuitry should be clearly marked to prevent irregular set ups and assure turbulent flow and consistent direction. It is important to measure mold temperature variability in a running state to assure that mold temperature is consistent and not affecting process via hot or cold spots in the mold during molding.

 

Venting: Verify that the mold has adequate venting to meet the needs of the molding application.

 

Validation-Process: Process validation assures that once a process has been developed, the set-up of that process will be repeatable and consistent. Here is a list of some of the primary process controls that should be reviewed to assure that an established process is true and dependable:

 

Melt Temperature: Melt temperature should be verified to be within the recommended temperature window supplied within MSDS data by the material manufacturer.

 

Barrel Temperature: While the process is in a running state, compare actual temperatures to set points. Conditions that allow heats to ride above what the set points dictate create inconsistency in the process.

 

Velocity vs. Fill time: Injection speed should allow room for adjustment as determined by the fill time of a process. If increasing velocity set points does not decrease the fill time, injection speed is maxed out and the potential for process variance increases.

 

Cushion: Cushion should remain consistent to assure that the process is stable.

 

Peak Pressure: Pressure at cut-off should be verified as consistent, and must not be pressure limited by the maximum pressure limit setting. The pressure limit set point should generally be about 200 PSI higher than the peak pressure achieved.

 

Mold & Area Set up: There are a variety of situations where slight or even major set up variations can affect the ability to repeat a process. Here is a list of factors to consider when developing your mold set up plan:

 

Water: It is important to repeat your water set up consistently. Once process has been established, clearly identify supply and return lines to prevent circulation from changing one set to the next. Identify hoses using color and mark circuits

 

Hot Runner: Whenever possible, use the same hot runner box every time you run a mold.

 

Clamp Force: Record and verify that tonnage used stays consistent. Variability in tonnage setpoints can lead to poor venting or flash.

The 5 M’s of Molding—Part I: Man (labor)

The 5 M’s of Molding—Part I: Man (labour)

There are many areas in which personnel affect consistency and repeatability within a plastics operation.

As a plastics operation evolves there are numerous factors affect productivity, and these detractors can be small or large…consistent or sporadic…obvious or hidden. In any continuous improvement-minded facility, there is always a need for repeated analysis of each job being run. The overall success or failure of each individual operation hinges upon effective review of inconsistencies and system failures. The company then develops and implements improvements, approaches and/or corrections to address shortcomings that could potentially include the purchase of specialized tools or equipment to better equip personnel.

One of the key requirements for profitable continuous improvement is starting out with a solid base to build on. When a job is turned over from engineering to production, all facets of the production line need to be in stable working order. This helps to prevent costly down time and scrap directly related to poor set up, and will assure bad product does not reach the customer.

There are 5 key components that must not only be reviewed during engineering’s development of each work system, but also as the job matures through continuous improvement. The “5 M’s of Molding” make up the solid foundation upon which a company develops a successful molding operation. This article outlines these principles and suggests ways to use them for the evolution of a company’s production capabilities.

Man (Labor):
Labor is one of the most critical contributors to the success or failure of any production development. There are many areas in which personnel affect consistency and repeatability within a plastics operation as it evolves. Here are some of the primary points to consider when evaluating labor as an area for improvement:

Work area: Engineering does not end when parts have been removed from the mold. An evaluation must be made as to what steps need to be taken to provide the customer with a top quality part every time. Make sure the area is well lit and mark locations for tables, tools, scrap bin, etc. Area layout should be designed to maximize operator efficiency and great care should be taken to assure that waste-of-motion has been eliminated. Inspection, part preparation and packaging should flow smoothly allowing the operator both comfort and ample inspection time. It is important to remember that the more labor intensive a job becomes, increased quality problems directly related to human error could be the end result.

Tools: As continuous improvement efforts intensify, it is important to listen to the workers who are most involved with the production end. These are the people who day in and day out have their hands on the parts being produced. Listen to their concerns and suggestions for areas of improvement and provide them with the tools that best fits what needs to be accomplished, thoroughly and quickly.

Defects: It is important to note that quality should be molded in and not sorted. There are circumstances though where depending on operators is necessary. Be sure that they have been fully trained regarding what defects they are looking for, and whenever possible show them what area on the part a defect would normally be found. Track scrap data to identify what defects are most common and then look for solutions through mold modification, process change, etc. to eliminate or significantly reduce the defect.

Ergonomics: It is easy to overlook the importance of this category to the overall profitability of a company. Workplace injuries drive insurance costs, which inevitably reduce the overall profitability of every project on the floor. As you are developing work instructions, look for areas of the job that require frequent twisting, bending and turning. Evaluate methods and/or tools to improve the workflow of the station.

Work instructions: Operational instructions are a vitally important tool once the work pattern has been established. Great care should be put into providing all personnel responsible for the various tasks a job requires with very complete and concise directives. Pictures are a great tool that allow visual explanations of various components. Work instructions should be written in the simplest form possible with detailed explanations of all required information.

Human Error: As mistakes happen, review the fault for ways to eliminate failures from happening again. The “5 Why” system is an effective method for getting to the root cause of failures and developing solutions. Here is an example of this method:

Problem: 32 bad pieces were packed that had splay on the parts
 
Why? The operator did not catch the mistake
Why? It was a new defect that had never been seen on this part
Why? The dryer ran low on material which resulted in light splay
Why? The material handler did not check the material as frequently as he should
Why? He is new and needs retraining on the frequency of checking the hopper

Once the 5 why’s have been asked, it is now time to review the problems and establish solutions to prevent a reoccurrence. For instance, the operator missed the mistake because it had never happened before. To fix this we can implement a visual picture or defect part to be kept at the press in order to assure ourselves that the new problem has been passed along to everyone responsible for part inspection. The hopper also ran low due to an inexperienced material handler. The 5 why’s suggests that this person be retrained to prevent this situation from happening again.

Improve Pinch-off result of multi-layer blow molding

Focus on HDPE PE/EVOH based COEX bottle having drop test failure, Specially in Agrichemical / Pesticide bottles : For reference PA (Polyamide) Material from BASF taken and truly incorporated with new mold design :-

Focusing on PE-HD/Recycled/Tie/PA/ EVOH multi-layer blown molding only. Polyamide here provides good resistance to various chemicals therefore this multi-layer structure is widely used for agro-chemicals e.g. liquid pesticides which contain organic solvents.
[Determination of a “good pinch-off” or a “bad pinch-off” result]
A good pinch-off should to create a welding line which is rather smooth on the outside and forms a flat elevated line or a low bead inside, not a groove.

Extrusion blow molded parts often fail at the parison pinch-off seam of the mold parting line. Common forms of part failure at the pinch-off are cracking from impact, fatigue failure from flexing, or chemical stress cracking. Once the mode of failure is identified, the appropriate processing changes or pinch-off design modifications can be selected to optimize part performance and appearance.
Part failure along the parting line is related to material processing conditions, mold design, or a combination of these factors. Developing the optimal material shape inside the part at the pinch-off is a key to build parting-line integrity.
Selection of polymers

• Ultramid B40L and C40L/C40LX are recommended for multi-layer blow molding containers or bottles, C40L and C40LX provide better dart impact strength therefore suitable for finished product volume bigger than 500ml, while B40L is usually used for no more than 500ml bottles.
• Various tie materials are available in market, but to match low MI and high viscosity PA, strongly suggest to select low MI (no higher than 2.0) MAH-grafted LLDPE based tie material.
• Lower MI HDPE (higher molecular weight) definitely increases the impact strength but anyway its melt viscosity needs to match with polyamide under processing temperature. For example a MI-0.25 is just well matched to Ultramid C40L(X).
Parameters optimization
• Typical temperature profile for Ultramid B40L and C40L(X): 230C/250C/250C for extruder and 195-200C for the die, too low melt temperature of polyamide may cause melt fracture, poor thickness distribution and “bad” grooved pinch-up Weld line.
Mold design
Because of the comparatively high pressure and mechanical stress extered on the mold bottom when (in the closing step) it pinches one end of the parison together, the pinch-off in a nonferrous metal mold is frequently an insert made of hard, tough steel. The effect on the blown part always shows in the so-called weld line.
The pinch-off section does not cut off the excess parison tail. Its protruding edges cut nearly through, creating an airtight closure by pinching the parison along a straight line which makes it easy later to break off or otherwise remove the excess tail piece. A high quality pinch-off of a thick-walled parison is more difficult to obtain than that of a thin-walled parison. However, much depends on the construction of the pinch-off insert.




 The pinch-off should not be knife-edged, but, according to some molders, should be formed by lands about 0.1-0.5mm long. The total angle outward from the pinch-off should be acute, up to 15 degree. These two features combine to create a high quality welding line. A groove, which weakens the bottom along the seam, may be formed when these two features of the pinch-off are missing.
One method of obtaining more uniform weld lines is to build “dams” into the mold halves at the parison pin-off areas. These dams force some of the molten resin back into the mold cavities to produce strong, even weld lines.

Cooling Channel Design for Mould- Design tips

Cooling Channel Design for Mould- Design tips Moulds are usually built with cooling channels. These channels are usually connected in series with one inlet and one outlet for water flow. The water flow rate may not be enough for turbulent flow because the water pump capacity itself may not be adequate. This obviously leads to random temperature variation on the mould surface. With the result, uncontrolled temperature drift, varying part dimensions and irregular warped surface appears on mouldings. The mould designer should take care of following points: • Thermal conductivity of mould steel influences the rate of heat transfer though mould steel to cooling channel. • Pure Ethylene glycol can be used as Primary fluid transfer medium in closed loop cooling system. Ethylene glycol does not produce rust and mineral deposits in cooling channels. Mixture of water and Ethylene glycol can also be used for circulation through the cooling channel. • Cooling channel diameter should be more for thicker wall thickness: • For wall thickness upto 2mm, channel diameter should be 8 - 10 mm., • For wall thickness upto 4 mm, channel diameter should be 10 - 12 mm., • For wall thickness upto 6 mm, channel diameter should be 10 - 16 mm. • Cooling channels should be as close as possible to the mould cavity / core surfaces. The distance of cooling channel from mould surface should be permissible by the strength of mould steel against possible failure under clamp and injection forces. It could be 1.2 to 2 times diameter of cooling channel. • Cooling system of the mould should have adequate number of cooling channels of suitable size at equal distance from each other and from cavity walls. The center distance between adjacent channel can be 1.7 to 2 times diameter of the channel. This is also governed by the strength of mould steel. • The difference between the inlet and outlet water temperature should be less than 2 to 5 degrees C. However, for precision moulding, it should be 1 degree C or even 0.5 degree C. • Cooling circuits should be positioned symmetrically around the cavity. There can be sufficient number of independent circuits to ensure uniform temperature along the mould surface. • The coolant flow rate should be sufficient to provide turbulent flow in the channel. • There should be no dead ends in the cooling channels. It could provide opportunity for air trap. • Many a times it is difficult to accommodate cooling channels in the smaller cores or cores with difficult geometry. In such case the core should be made of Beryllium copper which has high thermal conductivity. These core inserts should be located near the cooling channel. • The seals of coolant system should not leak inspite of application of frequent clamping force and mould expansion / contraction due to thermal cycle during moulding. The O-ring should be positioned so that there is no chance of them being damaged or improperly seated during mould assembly. Seal and O-ring grove should be machined to closely match the contour of the seal. It should ensure that seal is slightly compressed when the mould is assembled. • Mould temperature above 90 degree C normally requires oil as the heating medium. Heat transfer coefficient of oil is lower than that of water. • There is enough scope for confusion while giving water connection to mould when there are more number of cooling circuits particularly on bigger moulds. A sketch indicating cooling circuits should be available during mould set up. • Hot runner mould should be provided with compression resistant insulating plate between back plate and machine platen. This is to prevent the heat flow from mould to machine platen, which can create an unbalanced heat flow in the mould. With out insulating plate machine platen will act like a big heat sink, there by destabilising the possible balance between heat given to the mould by the hot melt, and heat taken away by circulating water through mould. • The cooling channel layout is suitable when the isothermal i.e. the equi-potential lines, are at a constant distance from surface of the mouldings. This ensures that heat flow density is same everywhere. • Provision for thermocouple fixing should be available at specific one or two places in core as well as cavity to monitor the temperature of mould. • Use efficient sealing methods and materials to eliminate cooling leaks. • Poor mould surface temperature control can cause following quality problems: Axial eccentricity, Radial eccentricity, Angular deviation, Warpage, Surface defects, Flow lines, The mould has to be heated or cooled depending on the temperature outside mould surface and that of environment. If heat loss through the mould faces is more than the heat to be removed from moulding, then mould has to be heated to compensate the excess loss of heat. This heating is only a protection for shielding the cooling area against the outside influence. The heat exchange takes place during cooling time. The design of cooling system has to depend on that section of part, which requires longest cooling time to reach demoulding temperature. Cooling Channel layout depends on : • part geometry, • number of cavities, • ejector and cam systems, • part quality, • dimensional precision, • part surface appearance, • polymer etc. The sizing of cooling channels is dependent on the rate of cooling and temperature control needed for controlling part quality. CAE software like MOLDFLOW or C-Mold can be used to determine the optimised dimension of cooling channel and distance from mould surface, distance between cooling channel, flow rate.

Understanding Mould cooling channel and Cooling system in factory

Understanding Mould cooling channel and Cooling system in factory Introduction Injection moulding process is cyclic in characteristic. Cooling time is about 50 to 75% of the total cycle time. Therefore, optimising cooling time for best performance is very important from quality and productivity point of view. Cooling time is proportional to square of wall thickness. Therefore part design should ensure more or less uniform wall thickness through out the part. Part design should also ensure that the melt flow is uniform in all direction from the gate and melt should reach the boundary of the part more or less at the same time. Cooling channel design - location and size and type - should ensure that melt freezes uniformly inside the mould. Cooling channel design can be perfected with the help of MOLDFLOW analysis. It is necessary to understand Heat Exchange and Cooling Channel design in the mould. Heat Exchange in mould During every injection moulding cycle following heat transfers take place: • from the hot melt to mould steel (heat input to the mould) and • from mould steel to coolant flowing through cooling channel of the mould. (heat removal from the mould) If heat input is more than heat removal, then the mould temperature would keep on increasing from cycle to cycle. Therefore moulding quality would not be constant from cycle to cycle. The moulding quality would be erratic- i.e. varying from cycle to cycle. Therefore, there is a need to balance between the heat input and heat removal in the mould after the desired mould surface temperature is reached. In other words, removal of heat by circulating coolant through the mould cooling channel would arrest the rise of mould temperature above the desired value. In practice, it may not be possible maintain constant mould temperature with respect to time. However, the mould temperature would fluctuate between two values around the desired value. During injection moulding cycle heat flow takes place from polymer melt to mould steel by • effective thermal difusivity of polymer melt and • conduction. This heat is to be removed by circulating cooling fluid through the cooling channels in core as well as cavity during cooling period in order to maintain the desired temperature. Uneven temperature of the mould surface results (uneven shrinkage) in parts with moulded-in stresses, warped sections, sink marks, poor surface appearance and varying part dimensions from cycle to cycle and even cavity to cavity. cont...