Patterson & Rothwell

INJECTION MOULDING SPECIALISTS

In Pursuit Of The Perfect Injection Moulded Part – Jetting

Jetting

Jetting refers to a kind of deformation in a moulded component that can occur when there’s an initial ‘jet’ of molten material injected into the mould cavity that starts to solidify before the cavity is filled. Jetting often appears as a squiggly line in the surface of the finished component, typically leading from the initial gate of injection. This visible flow pattern can result in part weakness.

Causes and remedies of jetting in moulded parts

The chief cause for jetting is excessive injection pressure.  When molten polymer or other material is injected through a small gate at high pressure it often squirts rapidly through the gate, rather than filling the mould cavity gradually. As this initial line of material cools against the mould walls and starts to harden, the remaining mould material pushes it, leaving impressions in the surface of the finished part. Avoid jetting in moulded parts by:

  • Reducing injection pressure to prevent rapid squirting of the material into the mould cavity
  • Increasing material and mould temperature to keep the initial jet of material from solidifying early
  • Designing the mould with the injection gate located such that the material is directed across the mould, rather than lengthwise

Defects typically related to material use or storage

Injection moulding defects can often originate from the material itself or how the manufacturer stores and handles the material prior to the production process. These defects can range from minor aesthetic issues to compromised strength of the finished component. Serious safety concerns may also result, depending on the intended application of the product affected.

Patterson & Rothwell are a Plastic Injection Moulding Company based in the North West of England, UK producing goods for many business sectors. Our ethos is to offer our customers a professional yet flexible approach and of course provide attention to detail at every stage. Please contact us if you wish to discuss any Plastic Injection Moulding Project.

In Pursuit Of The Perfect Injection Moulded Part – Weld Lines

Weld Lines

Weld lines can appear on the surface of a moulded part where the molten material has converged after splitting off into two or more directions in a mould. The hair-like weld line is the result of weak material bonding, which lowers the strength of the part.

Common causes of weld lines and how to prevent them

Two or more fronts of polymer or other molten material need to maintain a certain temperature when colliding.  Otherwise, they become partially solidified and won’t sufficiently bond where they meet, resulting in weld lines. Common remedies for weld lines in moulded parts include:

  • Increase material temperature to prevent partial solidification
  • Raise injection speed and pressure to limit cooling before the material has filled the mould
  • Redesign the mould to eliminate partitions
  • Switch to a material with a lower melting temperature or viscosity to allow faster flow and prevent early cooling

Patterson & Rothwell are a Plastic Injection Moulding Company based in the North West of England, UK producing goods for many business sectors. Our ethos is to offer our customers a professional yet flexible approach and of course provide attention to detail at every stage. Please contact us if you wish to discuss any Plastic Injection Moulding Project.

In Pursuit Of The Perfect Injection Moulded Part – Sink Marks

Sink marks

Sink marks are small recesses or depressions in an otherwise flat and consistent surface of a moulded part. These can occur when the inner part of a moulded component shrinks, pulling material from the outside inward.

Causes and prevention of sink marks

Sink marks are similar to vacuum voids but are reversed in cause and effect.  Rather than the material cooling too rapidly near the exterior of the part, the material cools too slowly. The resulting shrinkage pulls the outside material inward before it’s had a chance to adequately cool, leading to a depression. As with voids, sink marks are more likely to occur in thicker parts of a component. Here are some steps you can take to prevent this defect:

  • Increase holding pressure and time to allow the material near the part’s surface to cool
  • Increase cooling time to limit shrinkage
  • Design your mould with thinner component walls to allow for faster cooling near the surface

Patterson & Rothwell are a Plastic Injection Moulding Company based in the North West of England, UK producing goods for many business sectors. Our ethos is to offer our customers a professional yet flexible approach and of course provide attention to detail at every stage. Please contact us if you wish to discuss any Plastic Injection Moulding Project.

In Pursuit Of The Perfect Injection Moulded Part – Vacuum Voids

It is very easy to make expensive errors when it comes to injection moulding. Quality issues in injection-moulded products can range from minor surface defects to more serious problems that can affect the safety, performance and function of the product. They can be caused by problems related to the moulding process, material use, tooling design or a combination of all three.

This is the fourth on our series of posts where we look at a number of issues that can affect the quality of the end product and some of the common remedies. This post is about vacuum voids.

Vacuum voids / air pockets

Vacuum voids, or air pockets, are trapped air bubbles that appear in a finished moulded component. Quality control professionals typically consider voids to be a ‘minor’ defect.  But larger or more numerous voids can weaken the moulded part in some cases, as there’s air below the surface of the part where there should be moulded material.

Common causes of and steps to prevent vacuum voids in moulded parts

One of the chief causes of voids is inadequate moulding pressure to force trapped air out of the mould cavity. Other times, the material closest to the mould wall cools too quickly, causing the material to harden and pull the material toward the outside, creating an abscess. The material itself may be especially vulnerable to voids if its density changes significantly from the molten to hardened state. Voids are more difficult to avoid in moulded parts which are thicker than 6 mm. Common ways to prevent voids include:

  • Raise the injection pressure to force out trapped air pockets
  • Choose a grade of material with lower viscosity to limit the risk of air bubbles forming

Place gates close to the thickest parts of the mould to prevent premature cooling where the material is most vulnerable to voids.

Patterson & Rothwell are a Plastic Injection Moulding Company based in the North West of England, UK producing goods for many business sectors. Our ethos is to offer our customers a professional yet flexible approach and of course provide attention to detail at every stage. Please contact us if you wish to discuss any Plastic Injection Moulding Project.

In Pursuit Of The Perfect Injection Moulded Part – Warping

It is very easy to make expensive errors when it comes to injection moulding. Quality issues in injection-moulded products can range from minor surface defects to more serious problems that can affect the safety, performance and function of the product. They can be caused by problems related to the moulding process, material use, tooling design or a combination of all three.

This is the third on our series of posts where we look at a number of issues that can affect the quality of the end product and some of the common remedies. This post is about Warping.

Warping

Warping is deformation that can occur in injection moulded products when different parts of a component shrink unevenly. Just as wood can warp when it dries unevenly, plastic and other materials can warp during the cooling process when uneven shrinkage puts undue stress on different areas of the moulded part. This undue stress results in bending or twisting of the finished part as it cools. This is evident in a part that’s meant to lie flat but leaves a gap when laid on a flat surface.

Causes and prevention of warping in moulded parts

One of the main causes for warping in injection-moulded plastic and similar materials is that cooling happens too quickly. Often excessive temperature or low thermal conductivity of the molten material can worsen the problem. Other times mould design can contribute to warping when the walls of the mould are not of uniform thickness—shrinkage increases with wall thickness. Here are some common ways to prevent warping in your moulded parts:

  • Ensure the cooling process is gradual and long enough to prevent uneven stresses on the material
  • Lower the temperature of the material or mould
  • Try switching to a material that shrinks less during cooling (e.g. particle-filled thermoplastics shrink much less than semi-crystalline materials or unfilled grades)

Redesign the mould with uniform wall thickness and part symmetry to ensure greater stability in the part during cooling.

Patterson & Rothwell are a Plastic Injection Moulding Company based in the North West of England, UK producing goods for many business sectors. Our ethos is to offer our customers a professional yet flexible approach and of course provide attention to detail at every stage. Please contact us if you wish to discuss any Plastic Injection Moulding Project.

In Pursuit Of The Perfect Injection Moulded Part – Burn Marks

It is very easy to make expensive errors when it comes to injection moulding. Quality issues in injection-moulded products can range from minor surface defects to more serious problems that can affect the safety, performance and function of the product. They can be caused by problems related to the moulding process, material use, tooling design or a combination of all three.

This is the second on our series of posts where we look at a number of issues that can affect the quality of the end product and some of the common remedies. This post is about Burn Marks.

Burn marks

Burn marks typically appear as black or rust-coloured discoloration on an edge or surface of a moulded plastic part.  Burn marks generally don’t affect part integrity, unless the plastic is burned to the extent of degradation.

Causes and prevention of burn marks

The usual cause for burn marks in injection-moulded parts is trapped air, or the resin itself, overheating in the mould cavity during the injection process. Excessive injection speeds or heating of the material often lead to overheating that causes burns. Consider the following preventative measures to avoid burn marks in moulded components:

  • Lower the melt and mould temperature to prevent overheating
  • Reduce the injection speed to limit the risk of trapping air inside the mould
  • Enlarge gas vents and gates to allow trapped air to escape the mould
  • Shorten the mould cycle time so that any trapped air and resin don’t have a chance to overheat

Patterson & Rothwell are a Plastic Injection Moulding Company based in the North West of England, UK producing goods for many business sectors. Our ethos is to offer our customers a professional yet flexible approach and of course provide attention to detail at every stage. Please contact us if you wish to discuss any Plastic Injection Moulding Project.

In Pursuit Of The Perfect Injection Moulded Part – Flow Lines

It is very easy to make expensive errors when it comes to injection moulding. Quality issues in injection-moulded products can range from minor surface defects to more serious problems that can affect the safety, performance and function of the product. They can be caused by problems related to the moulding process, material use, tooling design or a combination of all three.

In this series of posts, we will look at a number of issues that can affect the quality of the end product – and some of the common remedies.

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A Plastic Stepping Stone?

A new opportunity presented itself here at Patterson & Rothwell and we were quick to see the potential for manufacturing a new product for a number of existing customers.

Surely the easiest sale a company can make is that to one of its existing customers and yet how often do we see companies spend hard earn profits on new markets and new ventures with big risks? Injection Moulding Companies are no different and should be aware of the risks of entering new markets in the belief that a pot of gold lies at the other end. We all wish, right?!
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Paul Scholes and the Patterson & Rothwell T Shirt

The Real Story about the most famous wearer of the Patterson & Rothwell T Shirt.

Ok so what does an ex Man Utd and England central midfielder have to do with Patterson & Rothwell an injection moulding company from Oldham? Early in the year of 2015 we were approached by our long term customer and part time commercial manager of Mossley AFC Stephen Porter to see if we would benefit from some kind of sponsorship of a charity football match. Mossley is a lovely village on the outskirts of Saddleworth with perhaps the best view from their Seel Park grounds of any football club. Nestled in the foothills of the Pennines the view from the pitch is the Western edge of the Saddleworth Moor, which sometimes draws the eye from the football.  As the match was in July the scene was set could not really hope for a better venue and as we are practically neighbours here at P&R how could we not get involved.

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Robotics Playing Their Part

To solve many issues with a complex moulded part the team here at P&R were able to utilise a 6 axis and a 3 axis robot to work in harmony with each other to complete 4 operations. The 6 axis robot picks and places 7 grub screws inside the tool whilst the 3-axis robot de-gates, jigs and drills the part. This procedure was completed entirely in-house.  Follow the link for a short video clip of the operation. Continue reading