{"id":1627,"date":"2021-09-16T10:36:13","date_gmt":"2021-09-16T10:36:13","guid":{"rendered":"https:\/\/www.plastikcity.co.uk\/blog\/?p=1627"},"modified":"2021-10-08T10:40:30","modified_gmt":"2021-10-08T10:40:30","slug":"two-causes-of-flash","status":"publish","type":"post","link":"https:\/\/www.plastikcity.co.uk\/blog\/two-causes-of-flash\/","title":{"rendered":"The Two Causes of Flash and How to Troubleshoot Them"},"content":{"rendered":"

Struggling with flash? In this blog, process support and training provider RJG<\/a> explains what flash is, its two causes and how to troubleshoot them.<\/strong><\/p>\n

<\/p>\n

We know what you\u2019re thinking\u2026 there are definitely more than two causes of plastic injection moulding flash, but just hear us out.<\/p>\n

First, a story\u00a0<\/span><\/h3>\n

A few years ago, we were called into a client who was dealing with a mould that he couldn\u2019t run without flashing. He said he tried every solution possible, and he wanted us to make sure he wasn\u2019t doing anything to cause the issue.<\/p>\n

When we arrived to see a brand new 16-cavity mould, we figured it was a processing problem because how could a brand new mould be flashing so badly? So we started it up, and sure enough, the mould flashed across the parting line into the other cavities.<\/p>\n

After doing everything we could within the process to fix the issue, we decided to try spraying bluing compound down the stationary side of the mould then clamping it up. Lo and behold, we only transferred about 50% of the compound \u2014 the mould was not shutting off.<\/p>\n

So back to the toolmaker it went.<\/p>\n

What is flash in injection moulding?\u00a0<\/span><\/h3>\n

Let\u2019s start at the beginning. Injection moulding flash is a common moulding defect where excess plastic flows outside of the cavity, causing a flap of excess material.<\/p>\n

\"Flash<\/p>\n

The two causes of flash in injection moulding<\/h3>\n

Yes, the above was an extreme example, but it shows that you can\u2019t rule anything out when dealing with a potential problem. Flash is quite simply caused by one of two issues:<\/p>\n

1. Mould damage (parting line damage can\u2019t be processed around, so please stop trying)<\/p>\n

2. Pressure in the cavities exceeds the tonnage<\/p>\n

There are several ways pressure in the cavities can exceed the tonnage, which are probably the causes of flash that came to your head initially: shot size is too big, transfer position is too low, hold pressure is too high, tonnage is too low, and so on.<\/p>\n

How to troubleshoot flash\u00a0<\/span><\/h3>\n

We always start troubleshooting flash with a fill-only part. When second stage is turned off, the part should come out 95-98% full. If it is too full, then the likelihood of flashing increases. Adjust the shot size as necessary to get the fill-only part back to where it needs to be.<\/p>\n

One of the critical principles of plastic injection moulding process development and troubleshooting is the fill-only part. Known by many terms like fill-only, first stage, and 95 \u2013 98% full shot, RJG has created this short video to demonstrate a procedure for developing a fill-only shot \u2013 alternatively, read the instructions here<\/a>.<\/p>\n